Co-reporter:Min-Joon Lee, Eunsol Lho, Peng Bai, Sujong Chae, Ju Li, and Jaephil Cho
Nano Letters June 14, 2017 Volume 17(Issue 6) pp:3744-3744
Publication Date(Web):May 2, 2017
DOI:10.1021/acs.nanolett.7b01076
Despite their good intrinsic rate capability, nanosized spinel cathode materials cannot fulfill the requirement of high electrode density and volumetric energy density. Standard carbon coating cannot be applied on spinel materials due to the formation of oxygen defects during the high-temperature annealing process. To overcome these problems, here we present a composite material consisting of agglomerated nanosized primary particles and well-dispersed acid-treated Super P carbon black powders, processed below 300 °C. In this structure, primary particles provide fast lithium ion diffusion in solid state due to nanosized diffusion distance. Furthermore, uniformly dispersed acid-treated Super P (ASP) in secondary particle facilitates lower charge transfer resistance and better percolation of electron. The ASPLMO material shows superior rate capability, delivering 101 mAh g–1 at 300 C-rate at 24 °C, and 75 mAh g–1 at 100 C-rate at −10 °C. Even after 5000 cycles, 86 mAh g–1 can be achieved at 30 C-rate at 24 °C, demonstrating very competitive full-cell performance.Keywords: carbon composite; electrochemistry; High power density; lithium ion battery; spinel cathode material;
Co-reporter:Wei-Zhong Han, Jian Zhang, Ming-Shuai Ding, Lan Lv, Wen-Hong Wang, Guang-Heng Wu, Zhi-Wei Shan, and Ju Li
Nano Letters June 14, 2017 Volume 17(Issue 6) pp:3725-3725
Publication Date(Web):May 10, 2017
DOI:10.1021/acs.nanolett.7b01015
The intriguing phenomenon of metal superelasticity relies on stress-induced martensitic transformation (SIMT), which is well-known to be governed by developing cooperative strain accommodation at multiple length scales. It is therefore scientifically interesting to see what happens when this natural length scale hierarchy is disrupted. One method is producing pillars that confine the sample volume to micrometer length scale. Here we apply yet another intervention, helium nanobubbles injection, which produces porosity on the order of several nanometers. While the pillar confinement suppresses superelasticity, we found the dispersion of 5–10 nm helium nanobubbles do the opposite of promoting superelasticity in a Ni53.5Fe19.5Ga27 shape memory alloy. The role of helium nanobubbles in modulating the competition between ordinary dislocation slip plasticity and SIMT is discussed.Keywords: helium bubble; irradiation; phase transformation; Shape memory alloy; superelasticity;
Co-reporter:Kai Liu;Peng Bai;Martin Z. Bazant;Chang-An Wang
Journal of Materials Chemistry A 2017 vol. 5(Issue 9) pp:4300-4307
Publication Date(Web):2017/02/28
DOI:10.1039/C7TA00069C
While lithium metal anodes have the highest theoretical capacity for rechargeable batteries, they are plagued by the growth of lithium dendrites, side reactions, and a moving contact interface with the electrolyte during cycling. Here, we synthesize a non-porous, elastomeric solid–electrolyte separator, which not only blocks dendritic growth more effectively than traditional polyolefin separators at large current densities, but also accommodates the large volume change of lithium metal by elastic deformation and conformal interfacial motion. Specially designed transparent capillary cells were assembled to observe the dynamics of the lithium/rubber interface in situ. Further experiments in coin cells at a current density of 10 mA cm−2 and an areal capacity of 10 mA h cm−2 show improved cycling stability with this new rubber separator.
Co-reporter:Bu Yuan Guan;Akihiro Kushima;Le Yu;Sa Li;Xiong Wen (David) Lou
Advanced Materials 2017 Volume 29(Issue 17) pp:
Publication Date(Web):2017/05/01
DOI:10.1002/adma.201605902
Metal–organic frameworks (MOFs) or coordination polymers (CPs) have been used as precursors for synthesis of materials. Unlike crystalline MOF, amorphous CP is nonspecific to metal cation species, therefore its composition can be tuned easily. Here, it is shown that amorphous CP can be used as general synthesis precursors of highly complex mixed metal oxide shells. As a proof of concept, NiCo coordination polymer spheres are first synthesized and subsequently transformed into seven-layered NiCo oxide onions by rapid thermal oxidation. This approach is very versatile and can be applied to produce ternary and quaternary metal oxide onions with tunable size and composition. The NiCo oxide onions exhibit exceptional charge storage capability in aqueous electrolyte with high specific capacitance (≈1900 F g−1 at 2 A g−1), good rate capability, and ultrahigh cycling stability (93.6% retention over 20 000 cycles). A hybrid supercapacitor against graphene/multishelled mesoporous carbon sphere shows a high energy density of 52.6 Wh kg−1 at a power density of 1604 W kg−1 (based on active materials weight), as well as remarkable cycling stability.
Co-reporter:Yuming Chen, Xiaoyan Li, Kyusung Park, Wei Lu, ... John B. Goodenough
Chem 2017 Volume 3, Issue 1(Volume 3, Issue 1) pp:
Publication Date(Web):13 July 2017
DOI:10.1016/j.chempr.2017.05.021
•Bimetallic MOF-based nanocomposites enable self-etching and graphitization•A N-doped porous carbon tubule possesses large interlayer spacing up to 0.44 nm•The carbon tubule paper manifests ultralong cycling life for Na-ion batteriesCarbon nanofibers (CNFs) and carbon hollow tubules (CHTs) are attractive anode materials for Na-ion batteries. Here, we report a method of self-etching and graphitization of metal-organic-framework-based nanocomposites for synthesizing a series of N-doped porous nanocarbons with a large fraction of graphitic carbon with larger spacing (0.38–0.44 nm). The N-doped porous CHT paper shows an outstanding cycling life over 10,000 cycles with no clear decline in capacity. Such a strategy could provide new avenues for the rational engineering of nanostructured N-doped carbonaceous materials with large graphene interlayer spacing for better Na-ion batteries.The greater availability of sodium (Na) over lithium (Li) motivates development of a Na-ion battery that can compete with a Li-ion battery. In these batteries, both electrodes consist of hosts into which Li+ or Na+ can be inserted reversibly. Graphite has been the anode host for Li-ion batteries, but the Na+ ion is too large to be inserted easily between the flat graphene layers of common graphite. We report the synthesis and electrochemical performance of N-doped carbon nanofibers and tubules with an organic-liquid electrolyte and a large fraction of graphitic carbon and larger spacing (0.38–0.44 nm) between carbon sheets; the carbon hollow tubules yield ultrastable (10,000 cycles), high-rate capabilities of Na+ intercalation and deintercalation with reversible capacities up to 346 mAh g−1.Download high-res image (240KB)Download full-size image
Co-reporter:Sulin Zhang, Kejie Zhao, Ting Zhu, Ju Li
Progress in Materials Science 2017 Volume 89(Volume 89) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.pmatsci.2017.04.014
Enormous efforts have been undertaken to develop rechargeable batteries with new electrode materials that not only have superior energy and power densities, but also are resistant to electrochemomechanical degradation despite huge volume changes. This review surveys recent progress in the experimental and modeling studies on the electrochemomechanical phenomena in high-capacity electrode materials for lithium-ion batteries. We highlight the integration of electrochemical and mechanical characterizations, in-situ transmission electron microscopy, multiscale modeling, and other techniques in understanding the strong mechanics-electrochemistry coupling during charge-discharge cycling. While anode materials for lithium ion batteries (LIBs) are the primary focus of this review, high-capacity electrode materials for sodium ion batteries (NIBs) are also briefly reviewed for comparison. Following the mechanistic studies, design strategies including nanostructuring, nanoporosity, surface coating, and compositing for mitigation of the electrochemomechanical degradation and promotion of self-healing of high-capacity electrodes are discussed.
Co-reporter:Weijiang Xue, Qing-Bo Yan, Guiyin Xu, Liumin Suo, Yuming Chen, Chao Wang, Chang-An Wang, Ju Li
Nano Energy 2017 Volume 38(Volume 38) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.nanoen.2017.05.041
•We report an efficient sulfur host based on two oxides, yielding high sulfur loading as high as 80 wt%.•The host could effectively trap lithium polysulfides benefitting from the unique structural and compositional advantages.•Lithium-sulfur batteries using this host exhibit excellent electrochemical performance.Although lithium-sulfur batteries show fascinating potential for high-capacity energy storage, their practical applications are hindered by the fast capacity decay and low sulfur utilization at high sulfur loading. Herein we report an efficient sulfur host based on two oxides, in which SiO2 hollow spheres with radial meso-channels are covered by a thin TiO2 coating. SiO2 spheres not only yield high sulfur loading as high as 80 wt% but also possess strong lithium polysulfides (LiPS) adsorption capability. The thin TiO2 coating can effectively prevent the LiPS outward diffusion, giving rise to a long-term stability. Meanwhile, the oxide-supported carbon from the carbonization of surfactants enables good electrical conductivity to facilitate electron access and improve sulfur utilization. Experimental and theoretical studies show the strong adsorption of LiPS by SiO2. Benefitting from the unique structural and compositional advantages, we achieve a high sulfur loading up to 80 wt% with ~65.5% and 33% capacity retentions over 500 and 1000 cycles when tested at 0.5 C and 1 C, respectively.Download high-res image (275KB)Download full-size image
Co-reporter:Yang Jin;Sa Li;Akihiro Kushima;Xiaoquan Zheng;Yongming Sun;Jin Xie;Jie Sun;Weijiang Xue;Guangmin Zhou;Jiang Wu;Feifei Shi;Rufan Zhang;Zhi Zhu;Kangpyo So;Yi Cui
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 2) pp:580-592
Publication Date(Web):2017/02/15
DOI:10.1039/C6EE02685K
Despite active developments, full-cell cycling of Li-battery anodes with >50 wt% Si (a Si-majority anode, SiMA) is rare. The main challenge lies in the solid electrolyte interphase (SEI), which when formed naturally (nSEI), is fragile and cannot tolerate the large volume changes of Si during lithiation/delithiation. An artificial SEI (aSEI) with a specific set of mechanical characteristics is henceforth designed; we enclose Si within a TiO2 shell thinner than 15 nm, which may or may not be completely hermetic at the beginning. In situ TEM experiments show that the TiO2 shell exhibits 5× greater strength than an amorphous carbon shell. Void-padded compartmentalization of Si can survive the huge volume changes and electrolyte ingression, with a self-healing aSEI + nSEI. The half-cell capacity exceeds 990 mA h g−1 after 1500 cycles. To improve the volumetric capacity, we further compress SiMA 3-fold from its tap density (0.4 g cm−3) to 1.4 g cm−3, and then run the full-cell battery tests against a 3 mA h cm−2 LiCoO2 cathode. Despite some TiO2 enclosures being inevitably broken, 2× the volumetric capacity (1100 mA h cm−3) and 2× the gravimetric capacity (762 mA h g−1) of commercial graphite anode is achieved in stable full-cell battery cycling, with a stabilized areal capacity of 1.6 mA h cm−2 at the 100th cycle. The initial lithium loss, characterized by the coulombic inefficiency (CI), is carefully tallied on a logarithmic scale and compared with the actual full-cell capacity loss. It is shown that a strong, non-adherent aSEI, even if partially cracked, facilitates an adaptive self-repair mechanism that enables full-cell cycling of a SiMA, leading to a stabilized coulombic efficiency exceeding 99.9%.
Co-reporter:Guiyin Xu;Akihiro Kushima;Jiaren Yuan;Hui Dou;Weijiang Xue;Xiaogang Zhang;Xiaohong Yan
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 12) pp:2544-2551
Publication Date(Web):2017/12/06
DOI:10.1039/C7EE01898C
The performance of lithium–sulfur (Li–S) batteries is greatly improved by using acidized carbon nanotube paper (ACNTP) to induce in situ polymerization of ether-based DOL/DME liquid to grow an ion-selective solid barrier, to seal in soluble polysulfides on the cathode side. The Li–S battery with the in situ barrier showed an initial specific capacity of 683 mA h g−1 at a high current density of 1675 mA g−1, and maintained a discharge capacity of 454 mA h g−1 after 400 cycles. The capacity decay rate was 0.1% per cycle and a high Coulombic efficiency of 99% was achieved. Experimental characterizations and theoretical models demonstrate the in situ polymerized solid barrier stops sulfur transport while still allowing bidirectional Li+ transport, alleviating the shuttle effect and increasing the cycling performance. The soft and sticky nature of the solid electrolyte barrier makes it a good sealant, forming an enclosed catholyte chamber on the sulfur side.
Co-reporter:Wenbin Li;Lei Sun;Jingshan Qi;Pablo Jarillo-Herrero;Mircea Dincă
Chemical Science (2010-Present) 2017 vol. 8(Issue 4) pp:2859-2867
Publication Date(Web):2017/03/28
DOI:10.1039/C6SC05080H
We use first-principles calculations to show that the square symmetry of two-dimensional (2D) metal–organic frameworks (MOFs) made from octaamino-substituted phthalocyanines and square planar Ni2+ ions, which enable strong conjugation of π electrons, has a critical impact on the magnetic properties of the lattice. In particular, we predict the unexpected emergence of a rare high-temperature ferromagnetic half-metallic ground state in one case. Among charge neutral MOFs made from (2,3,9,10,16,17,23,24)-octaiminophthalocyanine (OIPc) metallated with divalent first-row transition metal ions (M-OIPc; M = Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and connected through square planar Ni-bisphenylenediimine moieties, NiMn-OIPc exhibits a half-metallic and ferromagnetic ground state with a large exchange energy resulting from the unique strong hybridization between the d/π orbitals of Mn, the Pc ring, and the Ni-bisphenylenediimine nodes. Notably, we show that for NiMn-OIPc there is a considerable difference between the ferromagnetic ordering temperature (Tc) predicted by a 2D Ising model, which exceeds 600 K, and a Tc of 170 K predicted by our more realistic Monte Carlo simulation that includes magnetic anisotropy. Critically, our simulations adopt two spin models that incorporate magnetic anisotropy in the form of exchange anisotropy and single-ion anisotropy. We further show that in the bulk, 2D layers of NiMn-OIPc adopt a slipped-parallel stacking configuration, and exhibit interlayer magnetic coupling that is sensitive to the relative in-plane displacement between adjacent layers. These results highlight the critical role of magnetic anisotropy in modeling the properties of 2D magnetic systems. More generally, it demonstrates that strong hybridization between open-shell ions and delocalized aromatic π systems with appropriate symmetry, combined with large magnetic anisotropy, will be an effective design strategy to realize ferromagnetic 2D MOFs with high Tc.
Co-reporter:Guiyin Xu;Qing-bo Yan;Shitong Wang;Akihiro Kushima;Peng Bai;Kai Liu;Xiaogang Zhang;Zilong Tang
Chemical Science (2010-Present) 2017 vol. 8(Issue 9) pp:6619-6625
Publication Date(Web):2017/08/21
DOI:10.1039/C7SC01961K
Lithium–sulfur batteries are one of the most promising next-generation batteries due to their high theoretical specific capacity, but are impeded by the low utilization of insulating sulfur, unstable morphology of the lithium metal anode, and transport of soluble polysulfides. Here, by coating a layer of nano titanium dioxide and carbon black onto a commercial polypropylene separator, we demonstrate a new composite separator that can confine the polysulfides on the cathode side, forming a catholyte chamber, and at the same time block the dendritic lithium on the anode side. Lithium–sulfur batteries using this separator show a high initial capacity of 1206 mA h g−1 and a low capacity decay rate of 0.1% per cycle at 0.5C. Analyses reveal the electrocatalytic effect and the excellent dendrite-blocking capability of the ∼7 µm thick coating.
Co-reporter:Guiyin Xu, Qing-bo Yan, Akihiro Kushima, Xiaogang Zhang, Jin Pan, Ju Li
Nano Energy 2017 Volume 31() pp:568-574
Publication Date(Web):January 2017
DOI:10.1016/j.nanoen.2016.12.002
•A conductive composite binder with high electric conductivity and strong adhesion was obtained by a simple solution process.•The conductive composite binder could trap lithium polysulfides by a chemical absorption.•Lithium-sulfur batteries using the conductive composite binder exhibit excellent electrochemical performance.Lithium-sulfur batteries have high cathode theoretical energy density, but the poor conductivity of sulfur and polysulfide shuttling result in serious polarization and low sulfur utilization. Moreover, the addition of insulating binder in the electrode increases the internal resistance, reducing specific capacity and rate performance. Herein, we develop a composite binder with higher electronic conductivity, superior mechanical property and strong adsorption of polysulfides that imparts it some electrocatalytic activity. The reduced graphene oxide- polyacrylic acid (GOPAA) binder is prepared via a simple solution process. At constant loading fraction of 10 wt%, using GOPAA binder induces a 30% enhancement in the cathode capacity, better cycle life and rate capability compared to using PAA binder, reducing both the local charge-transfer resistance and the global electronic resistance before and after cycling. These are attributed to the enhanced binding strength and synergistic effect of reduced graphene oxide and PAA forming well-dispersed conductive bridges to promote rapid electron transfer. Additionally, GOPAA provides active sites for adsorption of lithium polysulfides and electrocatalytic activity, shifting redox peaks in cyclic voltammetry and improving roundtrip efficiency.
Co-reporter:Weijiang Xue, Lixiao Miao, Long Qie, Chao Wang, ... Ju Li
Current Opinion in Electrochemistry 2017 Volume 6, Issue 1(Volume 6, Issue 1) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.coelec.2017.10.007
•A realistic and balanced perspective is provided on the gravimetric and volumetric energy density of Li-S batteries.•A model is established based on a commercial pouch cell configuration and the effects of various cell parameters are discussed.•Higher volumetric energy density for Li-S batteries could be expected by further balancing the sulfur loadings and sulfur utilization while reducing the electrode porosity as well as the amount of inactive additives in cathode.Lithium-sulfur (Li-S) batteries receive considerable attention as a potential alternative to lithium-ion batteries (LIBs) due to their high theoretical gravimetric energy density (Eg). However, their volumetric energy density (Ev), which is also very important for practical applications is often neglected to emphasize their superior gravimetric energy density. In this review, we will try to provide a realistic and balanced perspective on the Ev of Li-S batteries. To calculate Ev, we establish a model based on a commercial pouch cell configuration, which allows one to evaluate the effect of various cell parameters. The requirements for Li-S batteries to be competitive against commercial LIBs in terms of Ev are proposed. Higher Ev for Li-S batteries could be expected by further balancing the sulfur loadings and sulfur utilization while reducing the electrode porosity as well as the amount of inactive additives in cathode. In particular, based on the calculated Ev values of recent works, we highlight the recent progress in both coin and pouch cells.
Co-reporter:Ming-Shuai Ding, Jun-Ping Du, Liang Wan, Shigenobu Ogata, Lin Tian, Evan Ma, Wei-Zhong Han, Ju Li, and Zhi-Wei Shan
Nano Letters 2016 Volume 16(Issue 7) pp:4118-4124
Publication Date(Web):June 1, 2016
DOI:10.1021/acs.nanolett.6b00864
The workability and ductility of metals usually degrade with exposure to irradiation, hence the phrase “radiation damage”. Here, we found that helium (He) radiation can actually enhance the room-temperature deformability of submicron-sized copper. In particular, Cu single crystals with diameter of 100–300 nm and containing numerous pressurized sub-10 nm He bubbles become stronger, more stable in plastic flow and ductile in tension, compared to fully dense samples of the same dimensions that tend to display plastic instability (strain bursts). The sub-10 nm He bubbles are seen to be dislocation sources as well as shearable obstacles, which promote dislocation storage and reduce dislocation mean free path, thus contributing to more homogeneous and stable plasticity. Failure happens abruptly only after significant bubble coalescence. The current findings can be explained in light of Weibull statistics of failure and the beneficial effects of bubbles on plasticity. These results shed light on plasticity and damage developments in metals and could open new avenues for making mechanically robust nano- and microstructures by ion beam processing and He bubble engineering.
Co-reporter:Junhang Luo, Jiangwei Wang, Erik Bitzek, Jian Yu Huang, He Zheng, Limin Tong, Qing Yang, Ju Li, and Scott X. Mao
Nano Letters 2016 Volume 16(Issue 1) pp:105-113
Publication Date(Web):November 16, 2015
DOI:10.1021/acs.nanolett.5b03070
Silica (SiO2) glass, an essential material in human civilization, possesses excellent formability near its glass-transition temperature (Tg > 1100 °C). However, bulk SiO2 glass is very brittle at room temperature. Here we show a surprising brittle-to-ductile transition of SiO2 glass nanofibers at room temperature as its diameter reduces below 18 nm, accompanied by ultrahigh fracture strength. Large tensile plastic elongation up to 18% can be achieved at low strain rate. The unexpected ductility is due to a free surface affected zone in the nanofibers, with enhanced ionic mobility compared to the bulk that improves ductility by producing more bond-switching events per irreversible bond loss under tensile stress. Our discovery is fundamentally important for understanding the damage tolerance of small-scale amorphous structures.
Co-reporter:Xiaohui Liu, Jianfeng Gu, Yao Shen and Ju Li
NPG Asia Materials 2016 8(10) pp:e320
Publication Date(Web):2016-10-01
DOI:10.1038/am.2016.154
At 0 K, phonon instability controls the ideal strength and the ultrafast dynamics of defect nucleation in perfect crystals under high stress. However, how a soft phonon evolves into a lattice defect is still unclear. Here, we develop a full-Brillouin zone soft-phonon-searching algorithm that shows outstanding accuracy and efficiency for pinpointing general phonon instability within the joint material-reciprocal (x–k) spaces. By combining finite-element modeling with embedded phonon algorithm and atomistic simulation, we show how a zone-boundary soft phonon is first triggered in a simple metal (aluminum) under nanoindentation, subsequently leading to a transient new crystal phase and ensuing nucleation of a deformation twin with only one-half of the transformation strain of the conventional twin. We propose a two-stage mechanism governing the transformation of unstable short-wave phonons into lattice defects, which is fundamentally different from that initially triggered by soft long-wavelength phonons. The uncovered material dynamics at stress extremes reveal deep connections between delocalized phonons and localized defects trapped by the full nonlinear potential energy landscape and add to the rich repertoire of nonlinear dynamics found in nature.
Co-reporter:Junyan Zhang, Yunwei Mao, Dong Wang, Ju Li and Yunzhi Wang
NPG Asia Materials 2016 8(10) pp:e319
Publication Date(Web):2016-10-01
DOI:10.1038/am.2016.152
Once a structural glass is formed, its relaxation time will increase exponentially with decreasing temperature. Thus, the glass has little chance of transforming into a crystal upon further cooling to zero Kelvin. However, a spontaneous transition upon cooling from amorphous to long-range ordered ferroic states has been observed experimentally in ferroelastic, ferroelectric and ferromagnetic materials. The origin for this obvious discrepancy is discussed here conceptually. We present a combined theoretical and numerical study of this phenomenon and show that the diffusive and displacive atomic processes that take place in structural glass and amorphous ferroics, respectively, lead to markedly different temperature-dependent relaxation behaviors, one being ‘colder is slower’ and the other being ‘colder is faster’.
Co-reporter:Chao Wu, Hua Wang, Jiajia Zhang, Gaoyang Gou, Bicai Pan, and Ju Li
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 4) pp:2526
Publication Date(Web):January 6, 2016
DOI:10.1021/acsami.5b09949
Recent works demonstrated that the superconductivity at two-dimensional (2-D) can be achieved in Li-decorated graphene (Nature Phys. 2012, 8, 131 and Proc. Natl. Acad. Sci. 2015, 112, 11795). Inspired by the progress made in graphene, we predict by using the first-principles calculations that Li-incorporated B monolayers (Li–B monolayers) can be alternative 2-D superconductors. First-principles cluster expansion approach was used to evaluate the structural diversity and energetic stability of the 2-D Li–B monolayers by treating them as ternary Lix⬡yB1–x–y pseudoalloys (⬡ refers to B hexagonal hole). After thoroughly exploring the Li–B configuration space, several well-ordered and stable Li–B monolayers were identified. Detailed analyses regarding the electronic structures and lattice dynamics properties of the predicted Li–B monolayers were performed. Compared with the non-superconducting pure B-sheet, some predicted Li–B monolayers can exhibit the phonon-mediated superconducting properties above the liquid helium temperature.Keywords: boron monolayers; cluster-expansion approach; first-principles calculations; phonon-mediated superconductivity; two-dimensional materials
Co-reporter:Shijie Hao, Lishan Cui, Hua Wang, Daqiang Jiang, Yinong Liu, Jiaqiang Yan, Yang Ren, Xiaodong Han, Dennis E. Brown, and Ju Li
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 5) pp:2917
Publication Date(Web):January 8, 2016
DOI:10.1021/acsami.5b10840
Individual metallic nanowires can sustain ultralarge elastic strains of 4–7%. However, achieving and retaining elastic strains of such magnitude in kilogram-scale nanowires are challenging. Here, we find that under active load, ∼ 5.6% elastic strain can be achieved in Nb nanowires embedded in a metallic matrix deforming by detwinning. Moreover, large tensile (2.8%) and compressive (−2.4%) elastic strains can be retained in kilogram-scale Nb nanowires when the external load was fully removed, and adjustable in magnitude by processing control. It is then demonstrated that the retained tensile elastic strains of Nb nanowires can increase their superconducting transition temperature and critical magnetic field, in comparison with the unstrained original material. This study opens new avenues for retaining large and tunable elastic strains in great quantities of nanowires and elastic-strain-engineering at industrial scale.Keywords: elastic strain; elastic strain engineering; high-energy X-ray diffraction; nanowires; shape memory alloy
Co-reporter:Qing-Jie Li, Ju Li, Zhi-Wei Shan, Evan Ma
Acta Materialia 2016 Volume 119() pp:229-241
Publication Date(Web):15 October 2016
DOI:10.1016/j.actamat.2016.07.053
Abstract
Under very high stresses, dislocations can be accelerated to approach the speed of shear wave over a distance as short as 101 nm. Our atomistic simulations demonstrate that dislocations with such high speeds often react in counter-intuitive manners that are beyond textbook descriptions of conventional dislocation behavior. A high-speed dislocation can “rebound” when hitting a free surface rather than simply annihilate. When two high-speed dislocations collide, they can “penetrate” through each other. An individual dislocation can even spontaneously generate multiple dislocations via self-dissociation. These anomalous mechanisms lead to rapid proliferation of dislocations that are strongly correlated both spatially and temporally, and as such may play a role in high-stress and high-strain-rate plastic deformation; a potentially related case is nanoscale pristine single crystals, which often yield via a large strain burst at ultrahigh stresses.
Co-reporter:Nai-qiang Zhang, Zhong-liang Zhu, Hong Xu, Xue-ping Mao, Ju Li
Corrosion Science 2016 Volume 103() pp:124-131
Publication Date(Web):February 2016
DOI:10.1016/j.corsci.2015.10.017
•The thickness ratio of the outer to inner oxide layer is related to Cr concentration of alloys.•Flowing or static SCW environment have an effect on oxidation time exponent.•Hydrogen and oxygen partial pressure influence oxide scale internal structure and oxidation rate.•The formation of hematite is associated with flow state, dissolved oxygen and oxidation rate constant.The oxidation of ferritic steel and ferritic–martensitic steel was investigated by exposure to flowing and static supercritical water (SCW) at 550–600 °C. The oxidation kinetic curves follow parabolic and near-cubic rate equations for the samples exposed to flowing and static SCW, respectively. The phase analysis shows the presence of hematite, magnetite and spinel in flowing SCW while only the magnetite and spinel phases are identified in static SCW. The mechanism of the formation of hematite and the effect of the flow state of SCW on the time exponent of oxidation kinetics are discussed.
Co-reporter:Kang Pyo So, Xiaohui Liu, Hideki Mori, Akihiro Kushima, Jong Gil Park, Hyoung Seop Kim, Shigenobu Ogata, Young Hee Lee, Ju Li
Extreme Mechanics Letters 2016 Volume 8() pp:245-250
Publication Date(Web):September 2016
DOI:10.1016/j.eml.2016.04.002
One-dimensional carbon nanotubes (CNT), which are mechanically strong and flexible, enhance strength of the host metal matrix. However, the reduction of ductility is often a serious drawback. Here, we report significantly enhanced plastic flow strength, while preventing tensile ductility reduction, by uniformly dispersing CNTs in Al matrix. Nanoscale plasticity and rupturing processes near CNTs were observed by in-situ mechanical tests inside Transmission Electron Microscope (TEM). CNTs act like forest dislocations and have comparable density (∼1014/m2), and such 1D nano-dispersion hardening is studied in detail by in situ TEM and molecular dynamics simulations. Rupture-front blunting and branching are seen with in situ TEM, which corroborates the result from macro-scale tension tests that our Al+CNT nanocomposite is quite damage- and fault-tolerant. We propose a modified shear-lag model called “Taylor-dispersion” hardening model to highlight the dual roles of CNTs as load-bearing fillers and “forest dislocations” equivalent that harden the metal matrix, for the plastic strength of metal+CNT nanocomposite.
Co-reporter:Zongyou Yin;Casandra Cox;Michel Bosman;Xiaofeng Qian;Zhengqing Liu;Na Li;Hongyang Zhao;Yaping Du;Daniel G. Nocera
Science Advances 2016 Volume 2(Issue 9) pp:
Publication Date(Web):
DOI:10.1126/sciadv.1501425
A novel facile strategy was developed to synthesize MgO nanocrystals for producing H2 through photodecomposing methanol.
Co-reporter:Ju Li;Le Yu;Xiong Wen (David) Lou;Bu Yuan Guan
Science Advances 2016 Volume 2(Issue 3) pp:e1501554
Publication Date(Web):04 Mar 2016
DOI:10.1126/sciadv.1501554
A universal cooperative assembly method is developed for growing mesostructured TiO2 shells on diverse functional particles.
Co-reporter:Hua Wang, Gaoyang Gou, Ju Li
Nano Energy 2016 Volume 22() pp:507-513
Publication Date(Web):April 2016
DOI:10.1016/j.nanoen.2016.02.036
Highlights•Demonstrate the ferroelectricity in perovskite sulfides for the first time.•Propose a new strategy for designing the stoichiometric ferroelectric–photovoltaic materials.•Ferroelectric Ca3Zr2S7 is predicted to have large visible-light absorption coefficients exceeding that of Si.Perovskite ferroelectric materials exhibit the novel ferroelectric photovoltaic effect, where photon-excited electron–hole pairs can be separated by ferroelectric polarization. Especially, semiconducting ferroelectric materials with small band gaps (Eg)(Eg) have been extensively studied for applications in solar energy conversion. Traditional route for creating semiconducting ferroelectrics requires cation doping, where Eg of the insulating perovskite ferroelectric oxides are reduced via substitution of certain cations. But cation doping tends to reduce the carrier mobility due to the scattering, and usually lead to poor photovoltaic efficiency. In the present work, based on first-principles calculations, we propose and demonstrate a new strategy for designing stoichiometric semiconducting perovskite ferroelectric materials. Specifically, we choose the parent non-polar semiconducting perovskite sulfides AB S3S3 with Pnma symmetry, and turn them into ferroelectric Ruddlesden–Popper A3B2A3B2S7S7 perovskites with spontaneous polarizations. Our predicted Ruddlesden–Popper Ca3Ca3Zr2Zr2S7S7 and other derived compounds exhibit the room-temperature stable ferroelectricity, small band gaps (Eg<2.2eV) suitable for the absorption of visible light, and large visible-light absorption exceeding that of Si.Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Kang Pyo So, Di Chen, Akihiro Kushima, Mingda Li, Sangtae Kim, Yang Yang, Ziqiang Wang, Jong Gil Park, Young Hee Lee, Rafael I. Gonzalez, Miguel Kiwi, Eduardo M. Bringa, Lin Shao, Ju Li
Nano Energy 2016 Volume 22() pp:319-327
Publication Date(Web):April 2016
DOI:10.1016/j.nanoen.2016.01.019
•Dispersion of CNTs showed improved tensile strength without reduction of ductility.•CNTs in Al reduced void/pore generation and radiation embrittlement at high DPA.•Under He ion irradiation, 1D CNTs survive, while sp2 bond transform to sp3 carbon.•Formation of metastable 1D Al4C3 from CNTs still recombine radiation defects.•This nanocomposite can help improve bulk properties for nuclear applications.We can mass-produce metal/carbon nanotube (CNT) composites that show improved radiation tolerance. The 0.5 wt% Al+CNT composite showed improved tensile strength without reduction of tensile ductility before radiation, and reduced void/pore generation and radiation embrittlement at high displacements per atom (DPA). Under helium ion irradiation up to 72 DPA, the 1D carbon nanostructures survive, while sp2 bonded graphene transforms to sp3 tetrahedral amorphous carbon. Self-ion (Al) irradiation converts CNTs to a metastable form of Al4C3, but still as slender 1D nanorods with prolific internal interfaces that catalyze recombination of radiation defects, reducing radiation hardening and porosity generation. The 1D fillers may also form percolating paths of “nano-chimneys” that outgas the accumulated helium and other fission gases, providing an essential solution to the gas accumulation problem.
Co-reporter:Xuli Ding, XiaoXiao Liu, Yangyang Huang, Xuefu Zhang, Qianjin Zhao, Xinghua Xiang, Guolong Li, Pengfei He, Zhaoyin Wen, Ju Li, Yunhui Huang
Nano Energy 2016 Volume 27() pp:647-657
Publication Date(Web):September 2016
DOI:10.1016/j.nanoen.2016.07.031
•In-situ metal melt-assembly is employed to encapsulate nano-Si by chemical vapor deposition.•Cu is used as the sacrificial layer and catalyst to controllably synthesize monolayer graphene to wrap the nano-Si.•Si@void@mGra composite anode shows excellent electrochemical performance.•The effects of different graphene layer number on electrochemical performance are compared for the Si-based anodes.The high specific capacity battery electrode materials have stimulated great research interest. Silicon (Si) as a low-cost abundant material with a theoretical specific capacity of 4200 mA h g−1, offers an attractive option for the low-cost next-generation high capacity Li-ion batteries anode. However, successful applications of silicon anode have been impeded by several limitations such as large volume expansion (400%) with lithiation, poor conductivity and unstable solid electrolyte interphase (SEI) with cycles. To address these challenges, we engineered Si nanoparticles by encapsulating them with monolayer graphene (mGra) with empty space generated by melt-self-assembly Cu layer. Here, a new method is introduced to uniform encapsulate the nano-silicon particles. The synthesis process used low-cost Si nanoparticles and Cu foils via chemical vapor deposition methods. The mGra and void space around the Si nanoparticles guaranteed to overcome mentioned problems. The flexibility nature and high conductivity of mGra effectively accommodate the Si volume expansion associated with the lithiation, and function as charges fast channels that allow for ions and electrons transport in fast kinetics. Most important, the crystalized mGra layer served as a flexible protective layer avoiding the SNPs direct exposed to electrolyte, which boosted the formation of stable and thin SEI interface. Our anode demonstrated a high initial coulomb efficiency (CE) 85% with gravimetric capacity ~1450 mA h g−1 (based on the total mass) and long cycle life (500 cycles with 89% capacity retention). Such SNP@void@mGra structure orienting excellent cycle life and high charge capacity provide a promising prospect for the next-generation high specific energy battery.
Co-reporter:Hongti Zhang;Jerry Tersoff;Shang Xu;Huixin Chen;Qiaobao Zhang;Kaili Zhang;Yong Yang;Chun-Sing Lee;King-Ning Tu;Yang Lu
Science Advances 2016 Vol 2(8) pp:e1501382
Publication Date(Web):17 Aug 2016
DOI:10.1126/sciadv.1501382
Single-crystalline silicon nanowires can be reversibly stretched above 10% elastic strain at room temperature.
Co-reporter:Akihiro Kushima, Tetsuya Koido, Yoshiya Fujiwara, Nariaki Kuriyama, Nobuhiro Kusumi, and Ju Li
Nano Letters 2015 Volume 15(Issue 12) pp:8260-8265
Publication Date(Web):November 4, 2015
DOI:10.1021/acs.nanolett.5b03812
Liquid-cell in situ transmission electron microscopy (TEM) observations of the charge/discharge reactions of nonaqueous Li–oxygen battery cathode were performed with ∼5 nm spatial resolution. The discharging reaction occurred at the interface between the electrolyte and the reaction product, whereas in charging, the reactant was decomposed at the contact with the gold current collector, indicating that the lithium ion diffusivity/electronic conductivity is the limiting factor in discharging/charging, respectively, which is a root cause for the asymmetry in discharging/charging overpotential. Detachments of lithium oxide particles from the current collector into the liquid electrolyte are frequently seen when the cell was discharged at high overpotentials, with loss of active materials into liquid electrolyte (“flotsam”) under minute liquid flow agitation, as the lithium peroxide dendritic trees are shown to be fragile mechanically and electrically. Our result implies that enhancing the binding force between the reaction products and the current collector to maintain robust electronic conduction is a key for improving the battery performance. This work demonstrated for the first time the in situ TEM observation of a three-phase-reaction involving gold electrode, lithium oxides, DMSO electrolyte and lithium salt, and O2 gas. The technique described in this work is not limited to Li–oxygen battery but also can be potentially used in other applications involving gas/liquid/solid electrochemical reactions.
Co-reporter:Chao Wang, Xusheng Wang, Yuan Yang, Akihiro Kushima, Jitao Chen, Yunhui Huang, and Ju Li
Nano Letters 2015 Volume 15(Issue 3) pp:1796-1802
Publication Date(Web):January 29, 2015
DOI:10.1021/acs.nanolett.5b00112
Lithium sulfide (Li2S) is a promising cathode material for Li–S batteries with high capacity (theoretically 1166 mAh g–1) and can be paired with nonlithium–metal anodes to avoid potential safety issues. However, the cycle life of coarse Li2S particles suffers from poor electronic conductivity and polysulfide shuttling. Here, we develop a flexible slurryless nano-Li2S/reduced graphene oxide cathode paper (nano-Li2S/rGO paper) by simple drop-coating. The Li2S/rGO paper can be directly used as a free-standing and binder-free cathode without metal substrate, which leads to significant weight savings. It shows excellent rate capability (up to 7 C) and cycle life in coin cell tests due to the high electron conductivity, flexibility, and strong solvent absorbency of rGO paper. The Li2S particles that precipitate out of the solvent on rGO have diameters 25–50 nm, which is in contrast to the 3–5 μm coarse Li2S particles without rGO.
Co-reporter:Kai He, Huolin L. Xin, Kejie Zhao, Xiqian Yu, Dennis Nordlund, Tsu-Chien Weng, Jing Li, Yi Jiang, Christopher A. Cadigan, Ryan M. Richards, Marca M. Doeff, Xiao-Qing Yang, Eric A. Stach, Ju Li, Feng Lin, and Dong Su
Nano Letters 2015 Volume 15(Issue 2) pp:1437-1444
Publication Date(Web):January 29, 2015
DOI:10.1021/nl5049884
Nanoparticle electrodes in lithium-ion batteries have both near-surface and interior contributions to their redox capacity, each with distinct rate capabilities. Using combined electron microscopy, synchrotron X-ray methods and ab initio calculations, we have investigated the lithiation pathways that occur in NiO electrodes. We find that the near-surface electroactive (Ni2+ → Ni0) sites saturated very quickly, and then encounter unexpected difficulty in propagating the phase transition into the electrode (referred to as a “shrinking-core” mode). However, the interior capacity for Ni2+ → Ni0 can be accessed efficiently following the nucleation of lithiation “fingers” that propagate into the sample bulk, but only after a certain incubation time. Our microstructural observations of the transition from a slow shrinking-core mode to a faster lithiation finger mode corroborate with synchrotron characterization of large-format batteries and can be rationalized by stress effects on transport at high-rate discharge. The finite incubation time of the lithiation fingers sets the intrinsic limitation for the rate capability (and thus the power) of NiO for electrochemical energy storage devices. The present work unravels the link between the nanoscale reaction pathways and the C-rate-dependent capacity loss and provides guidance for the further design of battery materials that favors high C-rate charging.
Co-reporter:Akihiro Kushima, Xiaofeng Qian, Peng Zhao, Sulin Zhang, and Ju Li
Nano Letters 2015 Volume 15(Issue 2) pp:1302-1308
Publication Date(Web):January 6, 2015
DOI:10.1021/nl5045082
Dislocations are topological line defects in three-dimensional crystals. Same-sign dislocations repel according to Frank’s rule |b1 + b2|2 > |b1|2 + |b2|2. This rule is broken for dislocations in van der Waals (vdW) layers, which possess crystallographic Burgers vector as ordinary dislocations but feature “surface ripples” due to the ease of bending and weak vdW adhesion of the atomic layers. We term these line defects “ripplocations” in accordance to their dual “surface ripple” and “crystallographic dislocation” characters. Unlike conventional ripples on noncrystalline (vacuum, amorphous, or fluid) substrates, ripplocations tend to be very straight, narrow, and crystallographically oriented. The self-energy of surface ripplocations scales sublinearly with |b|, indicating that same-sign ripplocations attract and tend to merge, opposite to conventional dislocations. Using in situ transmission electron microscopy, we directly observed ripplocation generation and motion when few-layer MoS2 films were lithiated or mechanically processed. Being a new subclass of elementary defects, ripplocations are expected to be important in the processing and defect engineering of vdW layers.
Co-reporter:Wei Guo, Zhao Wang, and Ju Li
Nano Letters 2015 Volume 15(Issue 10) pp:6582-6585
Publication Date(Web):August 31, 2015
DOI:10.1021/acs.nanolett.5b02306
We predict a strongest size for the contact strength when asperity radii of curvature decrease below 10 nm. The reason for such strongest size is found to be correlated with the competition between the dislocation plasticity and surface diffusional plasticity. The essential role of temperature is calculated and illustrated in a comprehensive asperity size-strength-temperature map taking into account the effect of contact velocity. Such a map should be essential for various phenomena related to nanoscale contacts such as nanowire cold welding, self-assembly of nanoparticles and adhesive nanopillar arrays, as well as the electrical, thermal, and mechanical properties of macroscopic interfaces.
Co-reporter:Xiao Lei Wang, Feng Jiang, Horst Hahn, Ju Li, Herbert Gleiter, Jun Sun, Ji Xiang Fang
Scripta Materialia 2015 Volume 98() pp:40-43
Publication Date(Web):15 March 2015
DOI:10.1016/j.scriptamat.2014.11.010
The mechanical properties of a Sc75Fe25 nanoglass and monolithic metallic glass (MG) with identical chemical composition were investigated by means of nanoindentation tests and quantitative in situ compression tests and tensile tests in a transmission electron microscope. The nanoglass exhibits excellent plastic deformation ability relative to the monolithic MG. It is particularly interesting to find that the 400 nm Sc75Fe25 nanoglass exhibits a 15% plastic strain under uniaxial tension. Such a nearly uniform tensile plasticity is unprecedented among MGs of similar sample sizes. The enhanced plasticity of the nanoglass can be attributed to its unique microstructure.
Co-reporter:Xiaofeng Qian, Mitsumoto Kawai, Hajime Goto, Ju Li
Computational Materials Science 2015 Volume 108(Part A) pp:258-263
Publication Date(Web):October 2015
DOI:10.1016/j.commatsci.2015.06.011
As-grown GaAs nanowires often possess high density of twin boundaries and stacking faults, which serve as scattering planes for electrons. Here, using density functional theory and Green’s function method, we demonstrate that the planar faults can significantly alter the transport properties depending on different planar defects and in-plane wavevector of the electronic state. Conductance eigenchannel analysis was applied to reveal the microscopic mechanism of electron scattering. A formalism is developed to estimate the reduction of the electron and hole mobilities due to planar faults and structural polytypes, based on quantum transmission coefficients computed in phase-coherent transport calculations. For twin spacing of 2.4 nm, electron mobility and hole mobility were predicted to be 3000 cm2/V/s and 500 cm2/V/s, respectively. The findings highlight the necessity of removing twins for high-performance nanowire solar cells.
Co-reporter:Wenbin Li
Nano Research 2015 Volume 8( Issue 12) pp:3796-3802
Publication Date(Web):2015 December
DOI:10.1007/s12274-015-0878-8
It is found that several layer-phase group-III monochalcogenides, including GaS, GaSe, and InSe, are piezoelectric in their monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe, and InSe (2.06, 2.30, and 1.46 pm·V™1) are of the same order of magnitude as previously discovered two-dimensional (2D) piezoelectric materials such as boron nitride (BN) and MoS2 monolayers. This study therefore indicates that a strong piezoelectric response can be obtained in a wide range of two-dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these monochalcogenide monolayer semiconductors means they have the potential to allow for the integration of electromechanical and optical sensors on the same material platform.
Co-reporter:Cheng-Cai Wang;Qing-Jie Li;Liang Chen;Yong-Hong Cheng;Jun Sun
Nano Research 2015 Volume 8( Issue 7) pp:2143-2151
Publication Date(Web):2015 July
DOI:10.1007/s12274-014-0685-7
Using nanoscale electrical-discharge-induced rapid Joule heating, we developed a method for ultrafast shape change and joining of small-volume materials. Shape change is dominated by surface-tension-driven convection in the transient liquid melt, giving an extremely high strain rate of ~106 s–1. In addition, the heat can be dissipated in small volumes within a few microseconds through thermal conduction, quenching the melt back to the solid state with cooling rates up to 108 K·s-1. We demonstrate that this approach can be utilized for the ultrafast welding of small-volume crystalline Mo (a refractory metal) and amorphous Cu49Zr51 without introducing obvious microstructural changes, distinguishing the process from bulk welding.
Co-reporter:Xuewen Fu;Cong Su;Qiang Fu;Xinli Zhu;Rui Zhu;Chuanpu Liu;Zhimin Liao;Jun Xu;Wanlin Guo;Ji Feng;Dapeng Yu
Advanced Materials 2014 Volume 26( Issue 16) pp:2572-2579
Publication Date(Web):
DOI:10.1002/adma.201305058
Co-reporter:Menghao Wu, Xiaofeng Qian, and Ju Li
Nano Letters 2014 Volume 14(Issue 9) pp:5350-5357
Publication Date(Web):August 11, 2014
DOI:10.1021/nl502414t
A spatially varying bandgap drives exciton motion and can be used to funnel energy within a solid ( Nat. Photonics 2012, 6, 866−872). This bandgap modulation can be created by composition variation (traditional heterojunction), elastic strain, or in the work shown next, by a small twist between two identical semiconducting atomic sheets, creating an internal stacking translation u(r) that varies gently with position r and controls the local bandgap Eg(u(r)). Recently synthesized carbon/boron nitride ( Nat. Nanotechnol. 2013, 8, 119) and phosphorene ( Nat. Nanotechnol. 2014, 9, 372) may be used to construct this twisted semiconductor bilayer that may be regarded as an in-plane crystal but an out-of-plane molecule, which could be useful in solar energy harvesting and electroluminescence. Here, by first-principles methods, we compute the bandgap map and delineate its material and geometric sensitivities. Eg(u(r)) is predicted to have multiple local minima (“funnel centers”) due to secondary or even tertiary periodic structures in-plane, leading to a hitherto unreported pattern of multiple “exciton flow basins”. A compressive strain or electric field will further enhance Eg-contrast in different regions of the pseudoheterostructure so as to absorb or emit even broader spectrum of light.
Co-reporter:Wenbin Li, Hongyou Fan, and Ju Li
Nano Letters 2014 Volume 14(Issue 9) pp:4951-4958
Publication Date(Web):July 30, 2014
DOI:10.1021/nl5011977
We model the mechanical response of alkanethiol-passivated gold nanoparticle superlattice (supercrystal) at ambient and elevated pressures using large-scale molecular dynamics simulation. Because of the important roles of soft organic ligands in mechanical response, the supercrystals exhibit entropic viscoelasticity during compression at ambient pressure. Applying a hydrostatic pressure of several hundred megapascals on the superlattice, combined with a critical deviatoric stress of the same order along the [110] direction of the face-centered-cubic supercrystal, can drive the room-temperature sintering (“fusion”) of gold nanoparticles into ordered gold nanowire arrays. We discuss the molecular-level mechanism of such phenomena and map out a nonequilibrium stress-driven processing diagram, which reveals a region in stress space where fusion of nanoparticles can occur, instead of other competing plasticity or phase transformation processes in the supercrystal. We further demonstrate that, for silver–gold (Ag–Au) binary nanoparticle superlattices in sodium chloride-type superstructure, stress-driven fusion along the [100] direction leads to the ordered formation of Ag–Au multijunction nanowire arrays.
Co-reporter:Junjie Niu, Akihiro Kushima, Xiaofeng Qian, Liang Qi, Kai Xiang, Yet-Ming Chiang, and Ju Li
Nano Letters 2014 Volume 14(Issue 7) pp:4005-4010
Publication Date(Web):May 13, 2014
DOI:10.1021/nl501415b
Nanostructured LiFePO4 (LFP) electrodes have attracted great interest in the Li-ion battery field. Recently there have been debates on the presence and role of metastable phases during lithiation/delithiation, originating from the apparent high rate capability of LFP batteries despite poor electronic/ionic conductivities of bulk LFP and FePO4 (FP) phases. Here we report a potentiostatic in situ transmission electron microscopy (TEM) study of LFP electrode kinetics during delithiation. Using in situ high-resolution TEM, a Li-sublattice disordered solid solution zone (SSZ) is observed to form quickly and reach 10–25 nm × 20–40 nm in size, different from the sharp LFP|FP interface observed under other conditions. This 20 nm scale SSZ is quite stable and persists for hundreds of seconds at room temperature during our experiments. In contrast to the nanoscopically sharp LFP|FP interface, the wider SSZ seen here contains no dislocations, so reduced fatigue and enhanced cycle life can be expected along with enhanced rate capability. Our findings suggest that the disordered SSZ could dominate phase transformation behavior at nonequilibrium condition when high current/voltage is applied; for larger particles, the SSZ could still be important as it provides out-of-equilibrium but atomically wide avenues for Li+/e– transport.
Co-reporter:Junjie Niu, Akihiro Kushima, Mingda Li, Ziqiang Wang, Wenbin Li, Chao Wang and Ju Li
Journal of Materials Chemistry A 2014 vol. 2(Issue 46) pp:19788-19796
Publication Date(Web):03 Oct 2014
DOI:10.1039/C4TA04759A
Although lithium–sulfur batteries exhibit a high initial capacity, production costs and lack of cyclability are major limitations. Here we report a liquid-based, low-cost and reliable synthesis method of a lithium–sulfur composite cathode with improved cyclability. An open network of Conductive Carbon Black nanoparticles (Cnet) is infused with a sulfur network (Snet) to form sponge-like networks (Cnet + Snet). Initially, Snet is open to the outside, allowing liquid electrolyte to infiltrate and impart Snet Li+ conductivity. During lithiation, Cnet could accommodate the volume expansion of Snet largely without losing electrical contact. During delithiation, the carbon nanoparticles would preferably flocculate on the outer surface due to polysulfide dissolution and depletion of sulfur, to form a passivation layer that still allows Li+ exchange, but prevents more polysulfides from escaping, thus slowing the leaching of polysulfides into the bulk electrolyte liquid. The plausibility of a carbonaceous passivation layer was checked using an extra carbon deposition layer to achieve an improved performance of ∼400 mA h g−1 after 250 cycles under a high rate 2.0 C. A 763 mA h g−1 discharge specific capacity of this sulfur nanosponge cathode (abbreviated as “SULFUN”) was obtained after 100 cycles under a rate of 0.2 C. Discharge capacities of 520 mA h g−1 and 290 mA h g−1 were attained after 300 and 500 cycles, respectively, making this cathode material attractive for rechargeable battery applications.
Co-reporter:Pengyang Zhao, Ju Li, Yunzhi Wang
Acta Materialia 2014 Volume 73() pp:149-166
Publication Date(Web):July 2014
DOI:10.1016/j.actamat.2014.03.068
Abstract
Initial condition dependence is the key to understanding the difference between ideal strength and actual strength of both crystalline and amorphous materials. Besides intrinsic structural heterogeneities in metallic glasses (MGs), a class of “extended defects” based on the “connected atomistic free volume” (CAFV) is proposed to define the microstructure (initial condition), which is crucial to understanding the strength. To explore these concepts and theories, deformation of finite-sized MG samples with different populations of pre-existing extended defects (damages) are simulated using a nanometer-scale shear transformation zone (STZ) model based on microelasticity and the kinetic Monte Carlo method. A “smaller is stronger” effect on the peak stress of simulated true stress–strain curves is seen in samples with pre-existing damage introduced as post-activated STZ clusters. Samples with “chemically contaminated” surface STZs also exhibit a size effect on the peak stress, and depending on whether the surface STZs are softer or harder than the bulk STZs, smaller can be either weaker or stronger.
Co-reporter:Hongyi Li;Jinshu Wang;Man Liu;Hong Wang;Penglei Su;Junshu Wu
Nano Research 2014 Volume 7( Issue 7) pp:1007-1017
Publication Date(Web):2014 July
DOI:10.1007/s12274-014-0464-5
To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity (3×) and stability (60×) for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3× and 60× improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.
Co-reporter:ZhangJie Wang;ZhiWei Shan;Jun Sun;Evan Ma
Science China Technological Sciences 2014 Volume 57( Issue 4) pp:663-670
Publication Date(Web):2014 April
DOI:10.1007/s11431-014-5498-0
Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility, the controllability of deformation would be crucial for the purpose of precise plastic shaping. In our present work, a “mechanical controllability index” (MCI) has been proposed to assess the controllability of mechanical deformation quantitatively. The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain. MCI=0 means completely uncontrollable plastic deformation, MCI=∞ means perfectly controllable plastic shaping. The application of the index is demonstrated here by comparing two example cases: 0.273 to 0.429 for single crystal Al nanopillars that exhibit obvious strain bursts, versus 3.17 to 4.2 for polycrystalline Al nanopillars of similar size for which the stress-strain curve is smoother.
Co-reporter:Xiaofeng Qian;Junwei Liu;Liang Fu
Science 2014 Volume 346(Issue 6215) pp:1344-1347
Publication Date(Web):12 Dec 2014
DOI:10.1126/science.1256815
Abstract
Quantum spin Hall (QSH) effect materials feature edge states that are topologically protected from backscattering. However, the small band gap in materials that have been identified as QSH insulators limits applications. We use first-principles calculations to predict a class of large-gap QSH insulators in two-dimensional transition metal dichalcogenides with 1T′ structure, namely, 1T′-MX2 with M = (tungsten or molybdenum) and X = (tellurium, selenium, or sulfur). A structural distortion causes an intrinsic band inversion between chalcogenide-p and metal-d bands. Additionally, spin-orbit coupling opens a gap that is tunable by vertical electric field and strain. We propose a topological field effect transistor made of van der Waals heterostructures of 1T′-MX2 and two-dimensional dielectric layers that can be rapidly switched off by electric field through a topological phase transition instead of carrier depletion.
Co-reporter:Yujie Zhu;Jiang Wei Wang;Yang Liu;Xiaohua Liu;Akihiro Kushima;Yihang Liu;Yunhua Xu;Scott X. Mao;Chunsheng Wang;Jian Yu Huang
Advanced Materials 2013 Volume 25( Issue 38) pp:5461-5466
Publication Date(Web):
DOI:10.1002/adma.201301374
Co-reporter:Meng Gu, Akihiro Kushima, Yuyan Shao, Ji-Guang Zhang, Jun Liu, Nigel D. Browning, Ju Li, and Chongmin Wang
Nano Letters 2013 Volume 13(Issue 11) pp:5203-5211
Publication Date(Web):September 30, 2013
DOI:10.1021/nl402633n
Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with density functional theory calculations, we probed the structural and chemical evolution of SnO2 nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries (Huang, J. Y.; et al. Science 2010, 330, 1515−1520). Upon Na insertion into SnO2, a displacement reaction occurs, leading to the formation of amorphous NaxSn nanoparticles dispersed in Na2O matrix. With further Na insertion, the NaxSn crystallized into Na15Sn4 (x = 3.75). Upon extraction of Na (desodiation), the NaxSn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na2O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO2. DFT calculations indicate that Na+ diffuses 30 times slower than Li+ in SnO2, in agreement with in situ TEM measurement. Insertion of Na can chemomechanically soften the reaction product to a greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO2 significantly less dislocation plasticity was seen ahead of the sodiation front. This direct comparison of the results from Na and Li highlights the critical role of ionic size and electronic structure of different ionic species on the charge/discharge rate and failure mechanisms in these batteries.
Co-reporter:Jianping Lin, Xudong Li, Guanjun Qiao, Zhao Wang, Jesús Carrete, Yang Ren, Lingzhi Ma, Youjian Fei, Baifeng Yang, Lei Lei, and Ju Li
Journal of the American Chemical Society 2013 Volume 136(Issue 4) pp:1497-1504
Publication Date(Web):December 23, 2013
DOI:10.1021/ja410605f
β-Zn4Sb3 has one of the highest ZT reported for binary compounds, but its practical applications have been hindered by a reported poor stability. Here we report the fabrication of nearly dense single-phase β-Zn4Sb3 and a study of its thermoelectric transport coefficients across a wide temperature range. Around 425 K we find an abrupt decrease of its thermal conductivity. Past this point, Zn atoms can migrate from crystalline sites to interstitial positions; β-Zn4Sb3 becomes metastable and gradually decomposes into Zn(hcp) and ZnSb. However, above 565 K it recovers its stability; in fact, the damage caused by decomposition can be repaired completely. This is key to its excellent thermoelectric performance at high temperature: the maximum ZT reaches 1.4. Molecular dynamics simulations are used to shed light on the microscopic behavior of the material.
Co-reporter:Jingshan Qi, Xiaofeng Qian, Liang Qi, Ji Feng, Daning Shi, and Ju Li
Nano Letters 2012 Volume 12(Issue 3) pp:1224-1228
Publication Date(Web):February 24, 2012
DOI:10.1021/nl2035749
Two-dimensional atomic sheets such as graphene and boron nitride monolayers represent a new class of nanostructured materials for a variety of applications. However, the intrinsic electronic structure of graphene and h-BN atomic sheets limits their direct application in electronic devices. By first-principles density functional theory calculations we demonstrate that band gap of zigzag BN nanoribbons can be significantly tuned under uniaxial tensile strain. The unexpected sensitivity of band gap results from reduced orbital hybridization upon elastic strain. Furthermore, sizable dipole moment and piezoelectric effect are found in these ribbons owing to structural asymmetry and hydrogen passivation. This will offer new opportunities to optimize two-dimensional nanoribbons for applications such as electronic, piezoelectric, photovoltaic, and opto-electronic devices.
Co-reporter:Hui Yang, Shan Huang, Xu Huang, Feifei Fan, Wentao Liang, Xiao Hua Liu, Long-Qing Chen, Jian Yu Huang, Ju Li, Ting Zhu, and Sulin Zhang
Nano Letters 2012 Volume 12(Issue 4) pp:1953-1958
Publication Date(Web):March 22, 2012
DOI:10.1021/nl204437t
Recent independent experiments demonstrated that the lithiation-induced volume expansion in silicon nanowires, nanopillars, and microslabs is highly anisotropic, with predominant expansion along the ⟨110⟩ direction but negligibly small expansion along the ⟨111⟩ direction. The origin of such anisotropic behavior remains elusive. Here, we develop a chemomechanical model to study the phase evolution and morphological changes in lithiated silicon nanowires. The model couples the diffusive reaction of lithium with the lithiation-induced elasto-plastic deformation. We show that the apparent anisotropic swelling is critically controlled by the orientation-dependent mobility of the core–shell interface, i.e., the lithiation reaction rate at the atomically sharp phase boundary between the crystalline core and the amorphous shell. Our results also underscore the importance of structural relaxation by plastic flow behind the moving phase boundary, which is essential to quantitative prediction of the experimentally observed morphologies of lithiated silicon nanowires. The study sheds light on the lithiation-mediated failure in nanowire-based electrodes, and the modeling framework provides a basis for simulating the morphological evolution, stress generation, and fracture in high-capacity electrodes for the next-generation lithium-ion batteries.
Co-reporter:Ji Feng, Wenbin Li, Xiaofeng Qian, Jingshan Qi, Liang Qi and Ju Li
Nanoscale 2012 vol. 4(Issue 16) pp:4883-4899
Publication Date(Web):06 Jun 2012
DOI:10.1039/C2NR30790A
Two-dimensional atomic sheets of carbon (graphene, graphane, etc.) are amenable to unique patterning schemes such as cutting, bending, folding and fusion that are predicted to lead to interesting properties. In this review, we present theoretical understanding and processing routes for patterning graphene and highlight potential applications. With more precise and scalable patterning, the prospects of integrating flat carbon (graphene) with curved carbon (nanotubes and half nanotubes) and programmable graphene folding are envisioned.
Co-reporter:Liang Qi, Yunwei Mao and Ju Li
Nanoscale 2012 vol. 4(Issue 19) pp:5989-5997
Publication Date(Web):17 Jul 2012
DOI:10.1039/C2NR31405C
The electronic and magnetic properties of bilayer graphene (BLG) depend on the stacking order between the two layers. We introduce a new conceptual structure of “slip corona” on BLG, which is a transition region between A–A stacking close to a nanopore composed of bilayer edges (BLEs) and A–B stacking far away. For an extremely small nanopore (diameter Dpore < ∼5 nm), both atomistic simulations and a continuum model reach consistent descriptions on the shape and size of this “corona” (diameter ∼50 nm), which is much larger than the width of the typical dislocation core (∼1 nm) in 3D metals or the nanopore itself, due to the weak van der Waals interactions and low interlayer shear resistance between two adjacent layers of graphene. The continuum model also suggests that the width of this “corona” from the BLE to the A–B stacking area would increase as Dpore increases and converge to ∼40 nm when Dpore is more than ∼80 nm. This large stacking transition region provides a new avenue for tailoring BLG properties.
Co-reporter:C.-C. Wang, J. Ding, Y.-Q. Cheng, J.-C. Wan, L. Tian, J. Sun, Z.-W. Shan, Ju Li, E. Ma
Acta Materialia 2012 Volume 60(13–14) pp:5370-5379
Publication Date(Web):August 2012
DOI:10.1016/j.actamat.2012.06.019
Abstract
For metallic single crystals with dimensions in the micrometer and sub-micrometer regime, systematic studies have established that sample size has an obvious influence on the apparent strength, following a “smaller is stronger” trend. For amorphous metals, several metallic glasses (MG) appear to exhibit a similar trend, while a few others do not. Here, another MG is examined, Al88Fe7Gd5, using quantitative in situ tensile and compression tests inside electron microscopes, with sample effective diameter covering a wide range (100 nm to 3 μm). A clearly elevated strength is observed, as high as about twice the value of bulk samples, for samples with diameters approaching 100 nm. A size regime is proposed, where the strength is controlled by the nucleation of the shear band, starting from its embryonic stage: the smaller the sample size, the more difficult this nucleation becomes. The size dependence is also discussed from an energy balance perspective: the resulting simple power law fits the data as well as other published strength data for a number of MG systems.
Co-reporter:Zhang-Jie Wang, Zhi-Wei Shan, Ju Li, Jun Sun, Evan Ma
Acta Materialia 2012 Volume 60(Issue 3) pp:1368-1377
Publication Date(Web):February 2012
DOI:10.1016/j.actamat.2011.10.035
Abstract
Pristine single crystalline gold particles with sizes ranging from 300 to 700 nm have been fabricated through high-temperature (1150 °C) liquid de-wetting of gold thin films atop a specially designed SiO2/Si substrate for in situ transmission electron microscopy testing. Quantitative compression tests showed that these particles display cataclysmic structural collapse immediately following elastic loading to very high stresses (over 1 GPa), resulting in a nearly pristine postmortem microstructure despite the large plastic deformation experienced by the particle. This distinct class of dislocation plasticity behavior is attributed to the very high degree of structural perfection of the initial sample, resulting from high-temperature formation or annealing around the melting point. Temporally correlated dislocation nucleation from the contact interface together with the inability to form stable junctions inside is proposed to explain the pristine-to-pristine structural collapse. Upon further compression, once the contact diameter d increases to above a critical value (∼250 nm), continuous plastic deformation begins to set in under relatively low flow stress with the postmortem microstructure containing a high density of tangled dislocations, suggesting that a critical dislocation tangling volume under multiple slip is needed for the onset of dislocation storage (robust dislocation jamming) and more conventional plasticity.
Co-reporter:Akihiro Kushima, Jian Yu Huang, and Ju Li
ACS Nano 2012 Volume 6(Issue 11) pp:9425
Publication Date(Web):October 1, 2012
DOI:10.1021/nn3037623
We report in situ tensile strength measurement of fully lithiated Si (Li–Si alloy) nanowires inside a transmission electron microscope. A specially designed dual probe with an atomic force microscopy cantilever and a scanning tunneling microscopy electrode was used to conduct lithiation of Si nanowires and then perform in situ tension of the lithiated nanowires. The axial tensile strength decreased from the initial value of 3.6 GPa for the pristine unlithiated Si nanowires to 0.72 GPa for the lithiated Li–Si alloy. We observed large fracture strain ranging from 8% to 16% for Li–Si alloy, 70% of which remained permanent after fracture. This indicates a certain degree of tensile plasticity in the lithiated silicon before fracture, important for constitutive modeling of the lithium-ion battery cyclability. We also compare the ab initio computed ideal strengths with our measured strengths and attribute the differences to the morphology and flaws in the lithiated nanowires.Keywords: apparent strain vs true strain; battery cyclability; bending; constitutive law; ideal strength
Co-reporter:Suzhi Li, Yonggang Li, Yu-Chieh Lo, Thirumalai Neeraj, Rajagopalan Srinivasan, Xiangdong Ding, Jun Sun, Liang Qi, Peter Gumbsch, Ju Li
International Journal of Plasticity (November 2015) Volume 74() pp:175-191
Publication Date(Web):1 November 2015
DOI:10.1016/j.ijplas.2015.05.017
•By using multi-scale simulation techniques, we probed the role of hydrogen-vacancy complexes on proto nano-voids formation due to dislocation plasticity in α-Fe during hydrogen embrittlement.•Our atomistic and coarse-grained cluster dynamics simulations show that the concentration of hydrogen-vacancy complexes can reach extremely high levels during dislocation plasticity in the presence of hydrogen, and these hydrogen-vacancy complexes prefer to aggregate by absorbing additional vacancies and act as nuclei for nano-voids.•The current work provides the link between hydrogen-vacancy complexes at the atomic scale to macroscopic failure by nano-void coalescence in hydrogen embrittlement.By using molecular dynamics and cluster dynamics simulations, we probed the role of hydrogen-vacancy complexes on nucleation and growth of proto nano-voids upon dislocation plasticity in α-Fe. Our atomistic simulations reveal that, unlike a lattice vacancy, a hydrogen-vacancy complex is not absorbed by dislocations sweeping through the lattice. Additionally, this complex has lower lattice diffusivity; therefore, it has a lower probability of encountering and being absorbed by various lattice sinks. Hence, it can exist metastably for a rather long time. Our large-scale molecular dynamics simulations show that when metals undergo plastic deformation in the presence of hydrogen at low homologous temperatures, the mechanically driven out-of-equilibrium dislocation processes can produce extremely high concentrations of hydrogen-vacancy complex (10−5 ∼ 10−3). Under such high concentrations, these complexes prefer to grow by absorbing additional vacancies and act as the embryos for the formation of proto nano-voids. The current work provides one possible route for the experimentally observed nano-void formation in hydrogen embrittlement of steels and bridges atomic-scale events and damage with macroscopic failure.
Co-reporter:Liang Qi, Ju Li
Journal of Catalysis (November 2012) Volume 295() pp:59-69
Publication Date(Web):1 November 2012
DOI:10.1016/j.jcat.2012.07.019
Ab initio electronic-structure calculations of surface catalysis often give changes ⩾0.1 eV for activation energies of intermediate steps when the surface structure or composition is varied, yet ⩾50-fold change in activity according to naive interpretation of the Arrhenius formula is usually not seen in corresponding experiments. To quantitatively analyze this sensitivity inconsistency between simulations and experiments, we propose a mean-field microkinetic model of electrochemical oxygen reduction reaction on Pt (1 1 1) and (1 0 0) surfaces, which outputs similar steady-state reaction rates despite of large differences in adsorption energies of reaction intermediates and activation energies. Sensitivity analyses indicate lateral repulsions between surface adsorbates (“enthalpic effect”) and site competition (“entropic effect”) flatten the catalytic activity vs. adsorption strength volcano plot and reduce sensitivity to material elementary energetics, in agreement with the observed experimental sensitivity behavior. Our analyses provide a systematic method to quantitatively investigate sensitivities of surface reactions when the mean-field approximation is reasonable.Graphical abstract(a) Interactions between adsorbates flatten the volcano plot of catalytic activity vs. adsorption strength and reduce sensitivity to material energetics from Arrhenius-law expectation; the interactions of different adsorbates may also shift volcano peak position. (b) Considering these interactions, a microkinetic model of oxygen reduction reaction based on first-principle calculations can show flattened volcano plot, in agreement with experimental sensitivity behavior. Out model and analyses provide a systematic method to quantitatively investigate sensitivities of surface reactions when mean-field approximation is reasonable.Download high-res image (246KB)Download full-size imageHighlights► We propose a microkinetic model of oxygen reduction with adsorbate interactions. ► It outputs similar steady-state reaction rates on Pt (1 1 1) and (1 0 0) surfaces. ► It explains why surfaces with different adsorption strengths have similar activities. ► Adsorbate interactions reduce sensitivities of activities to material energetics. ► It provides a systematic method to quantitatively investigate sensitivities of surface reactions when mean-field approximation is reasonable.
Co-reporter:Akio Ishii, Ju Li, Shigenobu Ogata
International Journal of Plasticity (July 2016) Volume 82() pp:32-43
Publication Date(Web):1 July 2016
DOI:10.1016/j.ijplas.2016.01.019
•General mathematical definition of solid–solid transformation is given.•Gibbs energy landscape of Mg{101¯2}〈101¯1¯〉 twinning nucleation was computed based on DFT.•Minimum Gibbs energy paths of the twinning nucleation processes were computed based on DFT.•HCP Mg{101¯2}〈101¯1¯〉 deformation twinning is local atomic shuffling-controlled in particular at the twin nucleation stage.The atomistic pathways of deformation twinning can be computed ab initio, and quantified by two variables: strain which describes shape change of a periodic supercell, and shuffling which describes non-affine displacements of the internal degrees of freedom. The minimum energy path involves juxta-position of both. But if one can obtain the same saddle point by continuously increasing the strain and relaxing the internal degrees of freedom by steepest descent, we call the path strain-controlled, and vice versa. Surprisingly, we find the {101¯2}〈101¯1¯〉 twinning of Mg is shuffling-controlled at the smallest lengthscale of the irreducible lattice correspondence pattern, that is, the reaction coordinate at the level of 4 atoms is dominated by non-affine displacements, instead of strain. Shuffling-controlled deformation twinning is expected to have different temperature and strain-rate sensitivities from strain-controlled deformation twinning due to relatively weaker strength of long-range elastic interactions, in particular at the twin nucleation stage. As the twin grows large enough, however, elastic interactions and displacive character of the transformation should always turn dominant.
Co-reporter:Pengyang Zhao, Ju Li, Yunzhi Wang
International Journal of Plasticity (January 2013) Volume 40() pp:1-22
Publication Date(Web):1 January 2013
DOI:10.1016/j.ijplas.2012.06.007
A nanoscale kinetic Monte Carlo (kMC) model is developed to study the deformation behavior of metallic glasses (MGs). The shear transformation zone (STZ) is adopted as our fundamental deformation unit and each nanoscale volume element (∼1 nm voxel) in the MG is considered as a potential STZ that may undergo inelastic rearrangements sampled from a randomized catalog that varies from element to element, with stress-dependent activation energies. The inelastic transformation sampled out of spatially randomized catalogs (a key characteristic of glass) is then treated as an Eshelby’s inclusion and the induced elastic field is solved in the Fourier space using the spectral method. The distinct features of our model, compared to previous work, are the introduction of randomized event catalogs for different nanoscale volume elements, repeated operations within the same element, and a “generation-dependent” softening term to reflect the internal structural change after each deformation. Simulations of uniaxial tension show the important effect of softening on the formation of shear bands, with a size-independent thickness of 18 nm. Statistical analysis of the accumulated strain at the ∼1 nm voxel level is carried out and sample size effect on the extreme value statistics is discussed.Highlights► A new mesoscale model is developed to study the deformation of metallic glasses. ► Structural softening is key in strain localization and the formation of shear band. ► A size-independent shear band thickness of ∼20 nm is revealed. ► Extreme value statistics reveals size effect and determines onset of final failure. ► Temperature rise in the center of shear bands is estimated to exceed hundreds of K.
Co-reporter:Shitong Wang, Yong Yang, Wei Quan, Ye Hong, Zhongtai Zhang, Zilong Tang, Ju Li
Nano Energy (February 2017) Volume 32() pp:
Publication Date(Web):February 2017
DOI:10.1016/j.nanoen.2016.12.052
•Ti-based nanoplates with abundant phase boundaries have been synthesized.•A combined hybrid pseudocapacitive and battery style electrode kinetics has been discovered.•Ti3+ defects or excessively large surface area may not be the only approaches for the conductivity enhancement.Ti-based nanoplates with abundant phase boundaries have been synthesized via partial lithiation reaction and optimized heat treatment. Using phase boundaries (rather than free surfaces) to keep the crystalline domains small might have significant advantages, such as improved tap density (therefore volumetric energy density) and reduced loss of live Lithium to the solid electrolyte interphase (SEI) which only coats the free surfaces. As lithium ion battery anode, the obtained Li4Ti5O12/TiO2(Anatase)/TiO2(Rutile) three-phase mixture shows a capacity of about 170 mA h g−1 at 4000 mA g−1 (fully charged in ~150 s), and undergoes more than one thousand cycles with capacity fade of only 0.02% per cycle. It also demonstrates excellent cycling stability even after 4000 cycles at 500 mA g−1 in a Li-matched full cell vs. LiFePO4 cathode in large pouch cell format, with tolerable gassing behavior. Rather than relying on Ti3+ defects or excessively large surface area, the present material is prepared in fully oxidizing environment, with abundant phase boundaries as the main capacity enhancement mechanism, which simplify its industrial production.Figure optionsDownload full-size imageDownload high-quality image (209 K)Download as PowerPoint slide
Co-reporter:Akihiro Kushima, Kang Pyo So, Cong Su, Peng Bai, Nariaki Kuriyama, Takanori Maebashi, Yoshiya Fujiwara, Martin Z. Bazant, Ju Li
Nano Energy (February 2017) Volume 32() pp:
Publication Date(Web):February 2017
DOI:10.1016/j.nanoen.2016.12.001
•Electrodeposition of lithium was observed by in-situ liquid cell TEM.•The root growth and tip growth mechanisms were characterized at nanoscale.•The ultrathin SEI layer was found to be critical for lithium surface instability.We present in situ environmental transmission electron microscopy (ETEM) observation of metallic lithium nucleation, growth and shrinkage in a liquid confining cell, where protrusions are seen to grow from their roots or surfaces, depending on the overpotential. The rate of solid-electrolyte interface (SEI) formation affects root vs. surface growth mode, with the former akin to intermittent volcanic eruptions, giving kinked segments of nearly constant diameter. Upon delithiation, root-grown whiskers are highly unstable, because the segmental shrinkage rate depends on Li+ transport across SEI, which is the greatest around the latest grown segment with the thinnest SEI, and therefore the near-root segment often dissolves first and the rest of the whisker then loses electrical contact. These electrically isolated dead lithium branches are also easily swept away into the bulk electrolyte to become “nano-lithium flotsam” because the hollowed-out SEI tube is very brittle. Our observations are consistent with SEI-obstructed growth by two competing mechanisms; surface growth of dense Eden-like clusters and root growth of whiskers, resulting from the voltage-dependent competition between lithium electrodeposition and SEI formation reactions. Similar phenomena could occur whenever chemical deposition/dissolution competes with irreversible side reactions that form a passivating layer on the evolving surface.
Co-reporter:Dan Feng, Zhen-Hua Ge, Di Wu, Yue-Xing Chen, Tingting Wu, Ju Li and Jiaqing He
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 46) pp:NaN31827-31827
Publication Date(Web):2016/10/26
DOI:10.1039/C6CP06466C
We present in this manuscript that enhanced thermoelectric performance can be achieved in polycrystalline SnSe prepared by hydrothermal reaction and spark plasma sintering (SPS). X-ray diffraction (XRD) patterns revealed strong orientation along the [l 0 0] direction in bulk samples, which was further confirmed by microstructural observation through transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). It was noticed that the texturing degree of bulk samples could be controlled by sintering temperature during the SPS process. The best electrical transport properties were found in the sample which sintered at 450 °C in the direction vertical to the pressing direction, where the highest texturing degree and mass density were achieved. Coupled with the relatively low thermal conductivity, an average ZT of ∼ 0.38, the highest ever reported in pristine polycrystalline SnSe was obtained. This work set up a forceful example that a texture-control approach can be utilized to enhance the thermoelectric performance effectively.
Co-reporter:Wenbin Li, Lei Sun, Jingshan Qi, Pablo Jarillo-Herrero, Mircea Dincă and Ju Li
Chemical Science (2010-Present) 2017 - vol. 8(Issue 4) pp:
Publication Date(Web):
DOI:10.1039/C6SC05080H
Co-reporter:Kai Liu, Peng Bai, Martin Z. Bazant, Chang-An Wang and Ju Li
Journal of Materials Chemistry A 2017 - vol. 5(Issue 9) pp:NaN4307-4307
Publication Date(Web):2017/01/24
DOI:10.1039/C7TA00069C
While lithium metal anodes have the highest theoretical capacity for rechargeable batteries, they are plagued by the growth of lithium dendrites, side reactions, and a moving contact interface with the electrolyte during cycling. Here, we synthesize a non-porous, elastomeric solid–electrolyte separator, which not only blocks dendritic growth more effectively than traditional polyolefin separators at large current densities, but also accommodates the large volume change of lithium metal by elastic deformation and conformal interfacial motion. Specially designed transparent capillary cells were assembled to observe the dynamics of the lithium/rubber interface in situ. Further experiments in coin cells at a current density of 10 mA cm−2 and an areal capacity of 10 mA h cm−2 show improved cycling stability with this new rubber separator.
Co-reporter:Junjie Niu, Akihiro Kushima, Mingda Li, Ziqiang Wang, Wenbin Li, Chao Wang and Ju Li
Journal of Materials Chemistry A 2014 - vol. 2(Issue 46) pp:NaN19796-19796
Publication Date(Web):2014/10/03
DOI:10.1039/C4TA04759A
Although lithium–sulfur batteries exhibit a high initial capacity, production costs and lack of cyclability are major limitations. Here we report a liquid-based, low-cost and reliable synthesis method of a lithium–sulfur composite cathode with improved cyclability. An open network of Conductive Carbon Black nanoparticles (Cnet) is infused with a sulfur network (Snet) to form sponge-like networks (Cnet + Snet). Initially, Snet is open to the outside, allowing liquid electrolyte to infiltrate and impart Snet Li+ conductivity. During lithiation, Cnet could accommodate the volume expansion of Snet largely without losing electrical contact. During delithiation, the carbon nanoparticles would preferably flocculate on the outer surface due to polysulfide dissolution and depletion of sulfur, to form a passivation layer that still allows Li+ exchange, but prevents more polysulfides from escaping, thus slowing the leaching of polysulfides into the bulk electrolyte liquid. The plausibility of a carbonaceous passivation layer was checked using an extra carbon deposition layer to achieve an improved performance of ∼400 mA h g−1 after 250 cycles under a high rate 2.0 C. A 763 mA h g−1 discharge specific capacity of this sulfur nanosponge cathode (abbreviated as “SULFUN”) was obtained after 100 cycles under a rate of 0.2 C. Discharge capacities of 520 mA h g−1 and 290 mA h g−1 were attained after 300 and 500 cycles, respectively, making this cathode material attractive for rechargeable battery applications.
.jpg)
