Effect of secondary particle fracture on the accumulated cycle capacity fade of LiNi1-x-yCoxMnyO2 cathode is difficult to evaluate since performance degradation of electrode material is always caused by several factors simultaneously. Herein, LiNi0.5Co0.2Mn0.3O2 single particles (Sin-P) are prepared and introduced as a reference to understand the accumulated cycle capacity fade caused by the secondary particle fracture of LiNi0.5Co0.2Mn0.3O2 secondary particles (Sec-P). Sec-P exhibited accumulated cycle capacity fade compared to Sin-P when cycled at high rate, high voltage, and high temperature. The accumulated cycle capacity fade was mainly caused by the secondary particle fracture of Sec-P, which was confirmed by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) analysis. Further, XPS and electrochemical impedance spectroscopy (EIS) analysis indicated that the surface property changes and resistance rise were responsible for the accumulated cycle capacity fade. The study provides a novel way to analyze the accumulated cycle capacity fade caused by the secondary particle fracture and is helpful for understanding the performance degradation mechanism of electrode material.

The development of fast-charging lithium-ion batteries (LIBs) is an urgent necessity. Nevertheless, it is still a huge challenge to prepare superior high-rate cathode materials for LIBs. In this work, porous Mg–Ti co-doped LiFe0.985Mg0.005Ti0.01PO4 microspheres are successfully synthesized via a carbothermic reduction reaction in combination with a spray drying process, with FePO4 as the Fe and P source. Through X-ray diffraction (XRD) combined with X-ray photoelectron spectroscopy (XPS) Ar+-sputtering technology, it confirms that Mg and Ti are in the form of doping rather than surface recombination inside LiFePO4 microspheres, and the existence of Fe3+ inside the samples is confirmed as residual FePO4. Compared to the undoped sample, the porous Mg–Ti co-doped LiFePO4 microspheres show great improvement in electronic conductivity (1.58 × 10−3 S cm−1) and diffusion coefficient (5.97 × 10−9 cm s−1 for charging and 4.30 × 10−9 cm s−1 for discharging). More importantly, the porous Mg–Ti co-doped LiFe0.985Mg0.005Ti0.01PO4 microspheres show excellent high-rate capabilities, delivering a discharge capacity of 161.5, 160.3, 156.7, 147.5, 139.8 and 131.5 mA h g−1 at 0.2C, 0.5C, 1C, 3C, 5C and 8C, respectively.

Unlike conventional carbon coating strategies which only focus on the macrodimension to enhance electrical conductivity and alleviate volume variation for high-capacity metal oxide anode materials, a hierarchically raspberry-like microstructure embedded with three-dimensional carbon-coated Fe3O4 quantum dots is built for ultrafast rechargeable sodium ion batteries. Taking advantage of using metal organic frameworks (MOFs) as templates, it realizes an in situ quantization process in which Fe3O4 quantum dots are formed and uniformly embedded in microcarbon coating protection. Due to the short diffusion length and integrated hierarchical conductive network, the electrode combines supercapacitor-like rate performance (e.g., less than 6 minutes to full charge/discharge) and battery-like capacity (e.g., maintaining >90% of theoretical capacity). An interesting surface-induced process which imitates pseudocapacitive behaviors in supercapacitors is analyzed in detail. This proof-of-concept study and insightful understanding on sodium storage in this investigation may inherently solve the widely encountered problems existing in high-capacity metal oxide anode materials and point out new directions for the future development of ultrafast rechargeable sodium ion batteries.

An in situ simple and effective synthesis method is effectively exploited to construct MOF-derived grape-like architecture anchoring on nitrogen-doped graphene, in which ultrafine Fe3O4 nanoparticles are uniformly dispersed (Fe3O4@C/NG). In this hybrid hierarchical structure, new synergistic features are accessed. The graphene oxide plane with functional groups is expected to alleviate the aggregation problem in the MOFs’ growth. Moreover, the morphology and size of iron-based MOFs and carbon content are conveniently controlled by controlling the solution concentration of precursor. Through making use of in situ carbonization of the organic ligands in MOFs, Fe3O4 subunits are effectively protected by 3D interconnected conductive carbon at microscale. Consequently, when applied as anode materials, even as high as 10 A g–1 after 1000 cycles, Fe3O4@C/NG still maintains as high as 458 mA h g–1.

•Effect of trace Al surface doping is systematically studied.•Al surface doping alters the surface property of LiNi0.5Co0.2Mn0.3O2 particle.•The lattice parameters are decreased after Al surface doping.•Lithium ion diffusion coefficients are enhanced after Al surface doping.•Al surface-doped LiNi0.5Co0.2Mn0.3O2 exhibits high rate performance at −20 °C.Effect of trace Al surface doping on the structure, surface chemistry and low temperature performance of LiNi0.5Co0.2Mn0.3O2 cathode is studied. Trace Al surface doping significantly promotes the low temperature performance of LiNi0.5Co0.2Mn0.3O2. At −20 °C, the discharge capacity of the bare LiNi0.5Co0.2Mn0.3O2 is 37.8 mAh g−1 at 5C, while it increases to 60.5 mAh g−1 after trace Al surface doping, nearly twice magnitude of the bare material. Via the X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and X-ray photoelectron spectroscopy analysis, it is confirmed that Al element has been successfully doped into the surface of LiNi0.5Co0.2Mn0.3O2. Surface-doped trace Al efficiently changes the lattice parameters, inhibits the resistance rise, accelerates lithium ion diffusion, and finally promotes the low temperature performance of LiNi0.5Co0.2Mn0.3O2.

Secondary LiFePO4/C microspheres (LFP) are synthesized with different carbon sources by the spray drying process. The carbon sources effect on the structures, morphologies, and 3D conductivity of the secondary structure are systematically investigated. LFP samples prepared with polyethylene glycol (PEG) and beta-cyclodextrin (β-CD) as mixing carbon sources possesses the loose structure with higher specific surface area, showing the best rate capability, cycling stability and low-temperature discharge characteristic. Additionally, the differences of 3.3 V plateau performance at room temperature and 2.85 V plateau performance at −20 °C are investigated. It could be observed that the electronic and ionic conductivities are reduced gradually with the decrease of the discharge cut-off voltage, while the electronic conductivities are greater than ionic conductivities for the four LFP samples, indicating that the ionic transport is more difficult and the electrochemical reaction is more and more difficult with the increase of Li-ion intercalation. Li-ion diffusion coefficients at the cut-off voltage of 3.30 V under room temperature and at the cut-off voltage of 2.85 V under −20 °C are both the highest for the LFP sample synthesized with PEG and β-CD, further indicating that PEG and β-CD as mixing carbon sources can decrease the charge transfer resistance and promote the 3D electronic/ionic conductivities and Li-ion diffusion coefficients in the secondary structure, thus greatly improve the rate capability, cycling stability and low-temperature capacity of LFP cathode.

Self-supported α-Fe2O3 nanorod arrays consisting of mesocrystalline nanorod bundles with tunable interstices were prepared by solution-phase growth coupled with chemical etching. The existence of acetic acid and sulfate ions in the hydrothermal system promoted the direct growth of α-Fe2O3 nanorod bundles with a mesocrystalline structure on a Ti substrate. The robust α-Fe2O3 nanorod arrays with optimized interstices are able to offer reduced lengths for electron transport and ion diffusion, and enough spaces to accommodate lithiation-induced volume expansion, leading to novel three-dimensional (3D) anodes with significantly improved rate capability and cyclability. When used as binder-free anodes for lithium ion batteries (LIBs), the α-Fe2O3 nanorod arrays retained a reversible capacity of 801 mA h g−1 after 500 cycles at 5 C (namely, 5 A g−1), and achieved practically valuable capacities of 499 mA h g−1 and 350 mA h g−1 at high rates of 20 C and 30 C, respectively. Furthermore, a flexible full battery with high capacity and fast charging capability was assembled using the α-Fe2O3 nanorod arrays as the anode, demonstrating their potential applications in flexible electronic devices.

A one step in situ synthesis approach is developed to construct 3D nitrogen-doped reduced graphene oxides, in which olive-like multi-component metal oxides are homogeneously dispersed. The novel hybrid nanoarchitecture shows some particular properties derived from synergistic effects. The size of Fe/Co/O oxides is reduced and better controlled compared to that of individual oxides due to mutual dispersant interactions. Furthermore, the positive synergistic interaction between heterogeneous oxides and graphene nanosheets has effective control on the particle size and dispersion of nanoparticles. Taking advantage of the flexibility and the cohesiveness of graphene nanosheets, the obtained composite can be directly processed into a binder-free electrode through a unique time-saving “squeezing” process. The obtained electrode possesses a reprocessable feature, which provides possibilities for convenient storage and quick fabrication at any time and presents attractive electrochemical performance of robust long-term capability retention (562 mA h g−1 after 300 cycles at 10 A g−1) and superior rate performances (1162 mA h g−1 at 0.5 A g−1, 737 mA h g−1 at 5 A g−1, and 585 mA h g−1 at 10 A g−1).

A novel organic solvent-assisted freeze-drying pathway, which can effectively protect and uniformly distribute active particles, is developed to fabricate a free-standing Li2MnO3·LiNi1/3Co1/3Mn1/3O2 (LR)/rGO electrode on a large scale. Thus, very high energy density and power density are realized for LR materials with robust long-term cyclability.

•The effect of surface property on the low temperature performance is studied.•Ti surface doping alters the surface property of LiNi1/3Co1/3Mn1/3O2 particle.•The lattice parameters are increased after Ti surface doping.•Ti surface-doped LiNi1/3Co1/3Mn1/3O2 exhibits high rate performance at −20 °C.The effect of surface property of LiNi1/3Co1/3Mn1/3O2 on the low temperature performance is seldom studied. Herein, the trace Ti surface-doped LiNi1/3Co1/3Mn1/3O2 exhibits enhanced discharge capacity under low temperature. After doping, the discharge capacity of LiNi1/3Co1/3Mn1/3O2 at −20 °C is 51.3 mAh g−1 at 5C, which is near twice as much as the bare material (30.1 mAh g−1). Via the X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and X-ray photoelectron spectroscopy analysis, it is confirmed that Ti doping on the surface significantly alters the surface property of LiNi1/3Co1/3Mn1/3O2 particle. The surface-doped Ti efficiently changes the lattice parameters, reduces the electrochemical reaction resistance and finally enhances the discharge capacity. The study clarifies the nature of trace Ti surface doping and is helpful for understanding the enhancement mechanism of the low temperature performance of LiNi1/3Co1/3Mn1/3O2.

•Performance of LiFePO4/C under extreme conditions is improved by trace Mn doping.•Large-radius Mn doping enhances the Li+ diffusion coefficient in LiFePO4/C.•Poor intrinsic kinetics of Mn retards the charge transfer process of LiFePO4/C.Uniform minor Mn-doped LiFePO4/C cathode materials are synthesized and their electrochemical performances are investigated systematically. Via tuning the doping amount of Mn, it is found that the well crystallized LiFePO4/C doped with 11000 ppm Mn gives the highest discharge capacity of 165 mAh g−1 at 0.1 C at room temperature. Remarkably, it holds a quite stable cycling performance at 45 °C, with capacity retention of 97.4% after 200 cycles using a high rate of 3.0 C, and its low-temperature (−20 °C) specific capacity maintains at high up to 131.4 mAh g−1 at 0.1 C, higher than that of the majority reports. The higher or lower Mn-doping amount than 11000 ppm is found to have less positive impact on the performance of LiFePO4/C. Such phenomenon may be attributed to the negative cooperative effect of Mn doping, which enlarges the crystal space for improving the Li+ transfer under low dose due to the large radius of Mn, but increases the charge transfer resistance and declines the performance under high dose owing to its poor intrinsic kinetics.

•Cross-linked PAN coating was prepared without damaging the surface of LiCoO2.•The coating layer owns good electronic conductivity and mechanical strength.•The cross-linked PAN coating layer is more sufficient than Al2O3 coating.•It shows much improved cyclability than that of bare and Al2O3 coated LiCoO2.LiCoO2 has been widely used in lithium ion batteries for digital electronic products. However, the limited cycling performance under high cut-off voltage hinders its commercial application. Many metal oxides and/or phosphorus coating have been reported to improve the cycling performance of LiCoO2. In this paper, we report on cross-linked PAN coated LiCoO2 composite as a cathode material for lithium ion batteries. The coating layer was obtained by intermolecular crosslinking of PAN polymer chain by heat treatment at high temperature in air. The air heating process avoids the possible damage arising from the carbon thermal reduction to the surface structure of LiCoO2. Electrochemical test indicates that the LiCoO2 with the cross-linked PAN coating layer shows much improved cycle performance compared with that of bare and Al2O3 coated LiCoO2. These findings might also open new avenues to explore polymer coating for other cathode materials of lithium ion batteries.

Facile fabrication of well-aligned Li4Ti5O12 (LTO) nanosheet arrays grown directly on conductive Ti foil was achieved by hydrothermal growth in LiOH solution. The reaction between Ti foil and LiOH led to the growth of vertically aligned, rectangular lithium titanate oxide hydrate (H-LTO) nanosheet arrays, which could be converted into LTO nanosheet arrays through topotactic transformation via thermal decomposition. An appropriate LiOH concentration was essential for the formation of densely aligned H-LTO nanosheet arrays on the substrate. It was proposed that the formation of the H-LTO nanosheet arrays was through kinetics-controlled growth during the hydrothermal metal corrosion process. When used as a binder-free anode for LIBs, the self-supported LTO nanosheet arrays standing on Ti foil exhibited an excellent rate capability (a reversible capacity of 163 mA h g−1 and 78 mA h g−1 at 20 C and 200 C, respectively) and an outstanding cycling performance (a capacity retention of 124 mA h g−1 after 3000 cycles at 50 C). Furthermore, a flexible lithium ion battery, which could be fully recharged within 30 s and was able to light an LED, was assembled by using the LTO nanosheet arrays as the anode.

Doping, incorporating a conductive phase and reducing the particle size are three strategies for improving the rate capability of Li4Ti5O12 (LTO). Thus, the synergistic employment of these three strategies is expected to more efficiently improve the rate capability. To achieve this goal, Fe2+ doped LTO/multiwall carbon nanotube (MWCNT) composites were prepared by post-mixing MWCNTs with Fe2+ doped LTO particles from a solid-state reaction, while Cr3+ doped LTO/MWCNT composites were fabricated by a facile one-step solid-reaction using MWCNT premixing. Fe2+/Cr3+ doping not only remarkably improves the electronic conductivity and Li+ ion diffusion coefficient in LTO but also lowers its working potential. The carbon existed in the material fabrication processes leads to the reduction of the particle size. The introduction of MWCNTs in the Fe2+/Cr3+ doped LTO/MWCNT composite significantly enhances the electrical conduction between Fe2+/Cr3+ doped LTO particles. As a result of this novel synergistic strategy, performances of Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites are comprehensively improved. The Li3.8Fe0.3Ti4.9O12/MWCNT composite shows a working potential of 8.9 mV lower than that of pristine LTO. At 10 C, its capacity is up to 106 mA h g−1 with an unexpected capacity retention of 117% after 200 cycles in a potential window of 1.0–2.5 V (vs. Li/Li+). The corresponding values for LiCrTiO4/MWCNT composites are 46.2 mV, 120 mA h g−1 and 95.9%. In sharp contrast, the pristine counterpart shows a very disappointing capacity of only 11 mA h g−1 at 10 C. Therefore, the novel Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites possess great potential for applications in high-power lithium-ion batteries.

To comprehensively improve the performance of Li4Ti5O12 (LTO), a synergistic method combining compositing, crystal structure modification and hierarchical particle structuring is employed in this work. Monodispersed/multidispersed mesoporous Li4Ti5O12−x/C submicrospheres were fabricated using monodispersed/multidispersed TiO2 submicrospheres, lithium hydroxide and sucrose as precursors. The Li4Ti5O12−x/C submicrospheres have a well-crystallized spinel structure, no blockages of Li+ ion transport pathways, 2.69–3.03% O2− vacancy contents (vs. all 32e sites in the spinel structure), and 12.9–14.6% Ti3+ ion contents (vs. all titanium ions). Thus, the electronic conductivity and Li+ ion diffusion coefficient of particles can be significantly improved, and the working potential is 4.4–4.7 mV lower than that of LTO. Furthermore, these submicrospheres contain 1.06–1.44 wt% carbon as carbon coatings (2–3 nm in thickness) and carbon nanoparticles (∼20 nm in size), resulting in smaller primary particle sizes (<100 nm), large specific surface areas (12–15 m2 g−1), proper pore sizes (∼4 nm) and enhanced electrical conduction between particles. In addition, the submicrospherical morphology allows large tap densities (1.41–1.71 g cm−3). As a result of this desirable structure, these mesoporous Li4Ti5O12−x/C submicrospheres exhibit comprehensively improved electrochemical performances. The optimized sample, with an ideally graded sphere-size distribution ranging from 100 nm to 600 nm, shows the largest tap density of 1.71 g cm−3, high first cycle Coulombic efficiency of 95.0% and 4.5 mV lower working potential. At 10 C, its capacity is as high as 119 mA h g−1 with capacity retention of 95.9% over 100 cycles.

The effects on electrochemical performance of C14H8O2 organic cathode materials with and without SO3Na– functional groups for lithium ion batteries were investigated. The Na2C14H6O8S2 with two SO3Na– shows the best cycle performance and highest lithium storage voltage, while an outstanding rate performance is also achieved after combination with graphene paper.

Although disordered spinel Li4Ti5O12 with Fd3̅m space group is an attracting anode material for lithium ion batteries, it suffers from its poor rate performance. Moreover, there are very limited studies of ordered spinel anode materials with P4332 space group. Here, spinel Li4–2xCo3xTi5–xO12 materials with Fd3̅m (0 ≤ x ≤ 0.2) or P4332 (0.25 ≤ x ≤ 0.5) space group have been synthesized. The lattice parameter and occupancy of Co2+ ions in tetrahedral 8a/8c sites quasi-linearly increase with the amount of Co2+ substitutes. Due to the increased lattice parameter and free 3d electrons in Co2+ ions, Co2+-substituted samples exhibit improved Li+ ion diffusion coefficients and electronic conductivities. The optimized sample, Li3.5Co0.75Ti4.75O12 with P4332 space group, shows the highest Li+ ion diffusion coefficient of 9.07 × 10–11 cm2 s–1 and electronic conductivity of 1.49 × 10–7 S cm–1. Consequently, Li3.5Co0.75Ti4.75O12 has the best rate performance with a large capacity of 158 mAh g–1 at a current density of 1000 mA g–1, while Li4Ti5O12 only possesses 70 mAh g–1. Furthermore, the considerable occupancy of Co2+ ions in the tetrahedral sites tailors the shape of discharge profiles. Li3.5Co0.75Ti4.75O12 exhibits a much smaller plateau hysteresis than the previously developed spinel anode materials with the same space group.

Spherical LiFe0.6Mn0.4PO4/C particles with high tap density were successfully synthesized by sintering spherical precursor powders prepared by a modified spray drying method with a double carbon coating process. The obtained secondary spheres were made of carbon-coated nanocrystallines (∼100 nm), exhibiting a high tap density of 1.4 g cm−3. The LiFe0.6Mn0.4PO4/C microspheres had a reversible capacity of 160.2 mAh g−1 at 0.1C, and a volume energy density of 801.5 Wh L−1 which is nearly 1.4 times that of their nano-sized counterparts. This spherical material showed remarkable rate capability by maintaining 106.3 mAh g−1 at 20C, as well as excellent cycleablity with 98.9% capacity retention after 100 cycles at 2C and 200 cycles at 5C. The excellent electrochemical performance and processability of the LiFe0.6Mn0.4PO4/C microspheres make them very attractive as cathode materials for use in high rate battery application.

Monodisperse spherical Mn0.75Ni0.25(OH)2 precursors built up from plate-like primary particles have been successfully synthesized by the control of pH values during a co-precipitation reaction. The size of spherical particles, namely the secondary particles, is observed to decrease with increasing pH value from 9.0 to 11.0, and is accompanied by a series of shape changes of the primary particles from close-packed plates to well-exposed nanoplates, and then to nanoparticles. Further lithiation of these hydroxide precursors produces the final lithium-rich layered Li1.2Mn0.6Ni0.2O2 cathode materials without destroying the morphology of the precursors. Electrochemical measurements show that the spherical cathode material assembled from well-exposed nanoplates exhibits superior rate capability and good cyclability compared to other electrode materials, which can be attributed to its uniform particle size and the favorable shape which facilitates the diffusion of lithium ions. Through the control of the sample morphologies, we provide a simple and effective way to enhance the lithium storage capability of lithium-rich layered oxide cathode materials for high-performance lithium-ion batteries.

Li4−2xNi3xTi5−xO12 (0 ≤ x   ≤ 0.25) has been synthesized via solid-state reaction. X-ray diffractions (XRD) demonstrate that all doped samples have a spinel structure with Fd3¯m space group without any impurities. Through further Rietveld refinements, it is shown that both lattice parameter and occupancy of non-Li+ ions in the 8a sites negligibly change with the amount of Ni2+ dopants. Scanning electron microscope reveals that Ni2+ doping does not change the morphology of Li4Ti5O12. The best electronic conductivity of Ni2+ doped Li4Ti5O12 is at least one order of magnitude higher than that of the pristine one, while all samples have similar Li+ ion diffusion coefficients. The electrochemical performance of Ni2+ doped Li4Ti5O12 shows good rate capability. The specific capacity of Li3.9Ni0.15Ti4.95O12 at 5 C is as high as 72 mAh g−1, while that of the pristine one can only achieve 33 mAh g−1. This improved rate performance can be ascribed to its enhanced electronic conductivity.Graphical abstractHighlights► Li4−2xNi3xTi5−xO12 (0 ≤ x ≤ 0.25) from solid-state reaction is systematically studied. ► The effects of material structure on electrochemical properties are investigated. ► The electronic conductivity is largely improved through Ni2+ doping. ► Li3.9Ni0.15Ti4.95O12 anode exhibits high rate performance.

•LiAlO2-surface modified LiMn1.58Ni0.42O4was prepared from Al2O3-coated Mn0.79Ni0.21CO3 precursor.•LiAlO2 modification enhances the rate capability and cyclability of LiMn1.58Ni0.42O4.•LiAlO2 modification stabilizes the electrode/electrolyte interface.LiAlO2-surface modified LiMn1.58Ni0.42O4 spinel cathode materials have been prepared by coating Al2O3 on Mn0.79Ni0.21CO3 precursors, followed by post-sintering with Li2CO3 at 900 °C. X-ray diffraction and FT-IR analyses indicate that during the calcination process aluminum ions not only react with Li2CO3 to form a strengthened LiAlO2 coating layer but also migrate from the surface into the spherical particles. The LiAlO2-surface modified LiMn1.58Ni0.42O4 samples exhibit excellent electrochemical performance compared to that of the bare one in terms of rate capability and cyclability. In particular, the 1 mol.% LiAlO2-surface modified sample can deliver a discharge capacity of 100.6 m Ah g−1 even at a high current density of 4 C-rate, while the bare one only has a discharge capacity of 49.5 m Ah g−1. At 55 °C, the 1 mol.% LiAlO2-surface modified LiMn1.58Ni0.42O4 sample shows outstanding cyclability with less than 5% capacity fade after 150 cycles. Based on these results, coating on the precursors to prepare a strengthened LiAlO2 coating layer would be a promising method to enhance the electrochemical performance of 5 V spinel cathode materials.

Silicon is a promising anode material for lithium ion batteries because of its low discharge potential and high theoretical charge capacity (4200 mA h g−1). However, the poor cycle performance, which arises from the large volume change upon the insertion and extraction of lithium ions, has limited its application. Here, we introduce a composite structure of coaxial carbon–silicon–carbon nanotube arrays in a porous anodic aluminium oxide membrane as a high-capacity and long-life anode. The carbon layer can not only protect silicon from generating a solid electrolyte interphase, but can also function as the current collector. These anode materials have a high first Coulombic efficiency of 90% and high specific capacities (∼4000 mA h g−1 for silicon and more than 600 mA h g−1 for the whole anode). Significantly, using these composite structures we have obtained an area capacity of ∼6 mA h cm−2, which is larger than commercial graphite anode values.

The high-temperature cycling stability at a high cutoff voltage of LiNi0.5Co0.2Mn0.3O2 was improved by TiO2 coating. The mechanism of enhancement was elucidated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. TiO2 coating formed a uniform layer on the surface of LiNi0.5Co0.2Mn0.3O2 particles without changing the crystal structure. Electrochemical tests indicated that TiO2 coating can improve the lithium ion intercalation stability at 328 K and at a high cutoff voltage of 4.4 V. The 1.0% TiO2-coated LiNi0.5Co0.2Mn0.3O2 discharged 149.2 mAh g−1 after 100 cycles at 0.5C, and maintained 92.1% of the initial discharge capacity. By contrast, the bare sample discharged only 87.7 mAh g−1 with 48.2% capacity retention. ICP-AES results proved that the TiO2 coating layer can reduce the dissolution of transition metal ions from LiNi0.5Co0.2Mn0.3O2. EIS and XPS confirmed that the improved cycling stability can be attributed to the suppression of the reaction between cathode and electrolyte in lithium-ion batteries.Highlights► TiO2 coating improves cycling stability of LiNi0.5Co0.2Mn0.3O2 at 328 K and 4.4 V. ► TiO2 coating can prevent the increase of charge-transfer resistance (Rct). ► LiF/MFx species deposited on the electrode lead to capacity deterioration. ► The deposition of LiF/MFx species can be suppressed by TiO2 coating. ► TiO2 coating reduces metal dissolution at a highly delithiated state.

We first report a facile hydrothermal route for preparing TiO2(B) nanowires with ultrahigh surface area, up to 210 m2 g−1. Due to the 1D structure, high BET surface area and shorter b-and c-axis channel across the nanowires, the obtained TiO2(B) nanowire was shown to be a good anode material for lithium-ion batteries, especially on the fast charging and discharging performance.

A nano-LiFePO4/C composite has been directly synthesized from micrometer-sized Li2CO3, NH4H2PO4, and FeC2O4·2H2O by the lauric acid-assisted solid-state reaction method. The SEM and TEM observations demonstrate that the synthesized nano-LiFePO4/C composite has well-dispersed particles with a size of about 100–200 nm and an in situ carbon layer with thickness of about 2 nm. The prepared nano-LiFePO4/C composite has superior rate capability, delivering a discharge capacity of 141.2 mAh g−1 at 5 °C, 130.9 mAh g−1 at 10 C, 121.7 mAh g−1 at 20 °C, and 112.4 mAh g−1 at 30 °C. At −20 °C, this cathode material still exhibits good rate capability with a discharge capacity of 91.9 mAh g−1 at 1 °C. The nano-LiFePO4/C composite also shows excellent cycling ability with good capacity retention, up to 100 cycles at a high current density of 30 °C. Furthermore, the effect of lauric acid in the preparation of nano-LiFePO4/C composite was investigated by comparing it with that of citric acid. The SEM images reveal that the morphology of the LiFePO4/C composite transformed from the porous structure to fine particles as the molar ratio of lauric acid/citric acid increased.

Al2O3-modified Li(Ni1/3Co1/3Mn1/3)O2 is synthesized by a modified Al2O3 coating process. The Al2O3 coating is carried out on an intermediate, (Ni1/3Co1/3Mn1/3)(OH)2, rather than on Li(Ni1/3Co1/3Mn1/3)O2. As a comparison, Al2O3-coated Li(Ni1/3Co1/3Mn1/3)O2 also is prepared by traditional Al2O3 coating process. The effects of Al2O3 coating and Al2O3 modification on structure and electrochemical performance are investigated and compared. Electrochemical tests indicate that cycle performance and rate capability of Li(Ni1/3Co1/3Mn1/3)O2 are enhanced by Al2O3 modification without capacity loss. Al2O3 coating can also enhance the cycle performance but cause evident capacity loss and decline of rate capability. The effect of Al2O3 coating and Al2O3 modification on kinetics of lithium-ion transfer reaction at the interface of electrode/electrolyte is investigated via electrochemical impedance spectra (EIS). The result support that the Al2O3 modification increase Li+ diffused coefficient and decrease the activation energy of Li+ transfer reaction but the traditional Al2O3 coating lead to depression of Li+ diffused coefficient and increase of activation energy.

A modified Zr-coating process was introduced to improve the electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2. The ZrO2-coating was carried out on an intermediate, (Ni1/3Co1/3Mn1/3)(OH)2, rather than on Li(Ni1/3Co1/3Mn1/3)O2. After a heat treatment process, one part of the Zr covered the surface of Li(Ni1/3Co1/3Mn1/3)O2 in the form of a Li2ZrO3 coating layer, and the other part diffused into the crystal lattice of Li(Ni1/3Co1/3Mn1/3)O2. A decreasing gradient distribution in the concentration of Zr was detected from the surface to the bulk of Li(Ni1/3Co1/3Mn1/3)O2 by X-ray photoelectron spectra (XPS). Electrochemical tests indicated that the 1% (Zr/Ni + Co + Mn) ZrO2-modified Li(Ni1/3Co1/3Mn1/3)O2 prepared by this process showed better cyclability and rate capability than bare Li(Ni1/3Co1/3Mn1/3)O2. The result can be ascribed to the special effect of Zr in ZrO2-modified Li(Ni1/3Co1/3Mn1/3)O2. The surface coating layer of Li2ZrO3 improved the cycle performance, while the incorporation of Zr in the crystal lattice of Li(Ni1/3Co1/3Mn1/3)O2 modified the rate capability by increasing the lattice parameters. Electrochemical impedance spectra (EIS) results showed that the increase of charge transfer resistance during cycling was suppressed significantly by ZrO2 modification.

A poly(vinylidene difluoride) (PVDF) membrane was grafted with styrene (St) and maleic anhydride (MAn) using an electron-beam-induced pre-irradiation grafting technique. The grafted membrane (PVDF-g-PS-co-PMAn) was then sulfonated and hydrolyzed to give an ion exchange membrane (denoted as PVDF-g-PSSA-co-PMAc) for vanadium redox flow batteries (VRB) use. Micro-FTIR analysis indicated that PVDF was successfully grafted and sulfonated at the above condition, and the membrane with a high grafting yield (GY) can be easily prepared in a St/MAn binary system at low dose due to a synergistic effect. The water uptake and ion exchange capacity (IEC) of the PVDF-g-PSSA-co-PMAc membrane increased with GY, so too did the conductivity. At a GY of 33.6%, the resulting PVDF-g-PSSA-co-PMAc membrane showed a much higher IEC and conductivity than a conventional Nafion117 membrane, and a much lower permeability of vanadium ions: ca. 1/11 to 1/16 of that through Nafion117. Open circuit voltage measurements showed that the VRB assembled with the PVDF-g-PSSA-co-PMAc membrane maintained values above 1.3 V after a period of 33 h, which was much longer than that with the Nafion117 membrane. It is expected that this work provides a new approach for the fabrication of ion exchange membranes for VRB.

LiCo0.2Ni0.4Mn0.4O2, as the cathode material for lithium ion batteries, was modified by TiO2-coating. The effect of TiO2-coating on the structure and electrochemical performance of LiCo0.2Ni0.4Mn0.4O2 was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic charge-discharge tests. The results suggest that a small amount of TiO2-coating does not change the crystalline structure, but considerably improves the electrochemical performance of LiCo0.2Ni0.4Mn0.4O2 in terms of capacity delivery and cyclability. XPS measurements confirm that the improved electrochemical performance is most possibly attributed to a decrease in interaction between the layered material and non-aqueous electrolyte during the charge-discharge processes.

Olivine-type LiFePO4 has been a promising electrode material for lithium ion battery, but the poor conductivity limits its practical application. In order to improve the electronic conductivity, a small amount of ion (Mg2+, Cu2+ and Zn2+) was added by the route of co-precipitation. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS), and their electrochemical properties were investigated by cyclic voltammetry (CV) and galvanostatic charge and discharge tests. The results indicate that these ion dopants do not affect the structure of the material but considerably improves its capacity delivery and cycle performance, which is ascribed to the enhancement of the electronic inductivity by ion doping. Co-precipitation doping is an effective method to improve the ion doping results.

Unlike conventional carbon coating strategies which only focus on the macrodimension to enhance electrical conductivity and alleviate volume variation for high-capacity metal oxide anode materials, a hierarchically raspberry-like microstructure embedded with three-dimensional carbon-coated Fe3O4 quantum dots is built for ultrafast rechargeable sodium ion batteries. Taking advantage of using metal organic frameworks (MOFs) as templates, it realizes an in situ quantization process in which Fe3O4 quantum dots are formed and uniformly embedded in microcarbon coating protection. Due to the short diffusion length and integrated hierarchical conductive network, the electrode combines supercapacitor-like rate performance (e.g., less than 6 minutes to full charge/discharge) and battery-like capacity (e.g., maintaining >90% of theoretical capacity). An interesting surface-induced process which imitates pseudocapacitive behaviors in supercapacitors is analyzed in detail. This proof-of-concept study and insightful understanding on sodium storage in this investigation may inherently solve the widely encountered problems existing in high-capacity metal oxide anode materials and point out new directions for the future development of ultrafast rechargeable sodium ion batteries.

A novel organic solvent-assisted freeze-drying pathway, which can effectively protect and uniformly distribute active particles, is developed to fabricate a free-standing Li2MnO3·LiNi1/3Co1/3Mn1/3O2 (LR)/rGO electrode on a large scale. Thus, very high energy density and power density are realized for LR materials with robust long-term cyclability.

Monodisperse spherical Mn0.75Ni0.25(OH)2 precursors built up from plate-like primary particles have been successfully synthesized by the control of pH values during a co-precipitation reaction. The size of spherical particles, namely the secondary particles, is observed to decrease with increasing pH value from 9.0 to 11.0, and is accompanied by a series of shape changes of the primary particles from close-packed plates to well-exposed nanoplates, and then to nanoparticles. Further lithiation of these hydroxide precursors produces the final lithium-rich layered Li1.2Mn0.6Ni0.2O2 cathode materials without destroying the morphology of the precursors. Electrochemical measurements show that the spherical cathode material assembled from well-exposed nanoplates exhibits superior rate capability and good cyclability compared to other electrode materials, which can be attributed to its uniform particle size and the favorable shape which facilitates the diffusion of lithium ions. Through the control of the sample morphologies, we provide a simple and effective way to enhance the lithium storage capability of lithium-rich layered oxide cathode materials for high-performance lithium-ion batteries.

Doping, incorporating a conductive phase and reducing the particle size are three strategies for improving the rate capability of Li4Ti5O12 (LTO). Thus, the synergistic employment of these three strategies is expected to more efficiently improve the rate capability. To achieve this goal, Fe2+ doped LTO/multiwall carbon nanotube (MWCNT) composites were prepared by post-mixing MWCNTs with Fe2+ doped LTO particles from a solid-state reaction, while Cr3+ doped LTO/MWCNT composites were fabricated by a facile one-step solid-reaction using MWCNT premixing. Fe2+/Cr3+ doping not only remarkably improves the electronic conductivity and Li+ ion diffusion coefficient in LTO but also lowers its working potential. The carbon existed in the material fabrication processes leads to the reduction of the particle size. The introduction of MWCNTs in the Fe2+/Cr3+ doped LTO/MWCNT composite significantly enhances the electrical conduction between Fe2+/Cr3+ doped LTO particles. As a result of this novel synergistic strategy, performances of Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites are comprehensively improved. The Li3.8Fe0.3Ti4.9O12/MWCNT composite shows a working potential of 8.9 mV lower than that of pristine LTO. At 10 C, its capacity is up to 106 mA h g−1 with an unexpected capacity retention of 117% after 200 cycles in a potential window of 1.0–2.5 V (vs. Li/Li+). The corresponding values for LiCrTiO4/MWCNT composites are 46.2 mV, 120 mA h g−1 and 95.9%. In sharp contrast, the pristine counterpart shows a very disappointing capacity of only 11 mA h g−1 at 10 C. Therefore, the novel Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites possess great potential for applications in high-power lithium-ion batteries.

Silicon is a promising anode material for lithium ion batteries because of its low discharge potential and high theoretical charge capacity (4200 mA h g−1). However, the poor cycle performance, which arises from the large volume change upon the insertion and extraction of lithium ions, has limited its application. Here, we introduce a composite structure of coaxial carbon–silicon–carbon nanotube arrays in a porous anodic aluminium oxide membrane as a high-capacity and long-life anode. The carbon layer can not only protect silicon from generating a solid electrolyte interphase, but can also function as the current collector. These anode materials have a high first Coulombic efficiency of 90% and high specific capacities (∼4000 mA h g−1 for silicon and more than 600 mA h g−1 for the whole anode). Significantly, using these composite structures we have obtained an area capacity of ∼6 mA h cm−2, which is larger than commercial graphite anode values.

Self-supported α-Fe2O3 nanorod arrays consisting of mesocrystalline nanorod bundles with tunable interstices were prepared by solution-phase growth coupled with chemical etching. The existence of acetic acid and sulfate ions in the hydrothermal system promoted the direct growth of α-Fe2O3 nanorod bundles with a mesocrystalline structure on a Ti substrate. The robust α-Fe2O3 nanorod arrays with optimized interstices are able to offer reduced lengths for electron transport and ion diffusion, and enough spaces to accommodate lithiation-induced volume expansion, leading to novel three-dimensional (3D) anodes with significantly improved rate capability and cyclability. When used as binder-free anodes for lithium ion batteries (LIBs), the α-Fe2O3 nanorod arrays retained a reversible capacity of 801 mA h g−1 after 500 cycles at 5 C (namely, 5 A g−1), and achieved practically valuable capacities of 499 mA h g−1 and 350 mA h g−1 at high rates of 20 C and 30 C, respectively. Furthermore, a flexible full battery with high capacity and fast charging capability was assembled using the α-Fe2O3 nanorod arrays as the anode, demonstrating their potential applications in flexible electronic devices.

We first report a facile hydrothermal route for preparing TiO2(B) nanowires with ultrahigh surface area, up to 210 m2 g−1. Due to the 1D structure, high BET surface area and shorter b-and c-axis channel across the nanowires, the obtained TiO2(B) nanowire was shown to be a good anode material for lithium-ion batteries, especially on the fast charging and discharging performance.

Spherical LiFe0.6Mn0.4PO4/C particles with high tap density were successfully synthesized by sintering spherical precursor powders prepared by a modified spray drying method with a double carbon coating process. The obtained secondary spheres were made of carbon-coated nanocrystallines (∼100 nm), exhibiting a high tap density of 1.4 g cm−3. The LiFe0.6Mn0.4PO4/C microspheres had a reversible capacity of 160.2 mAh g−1 at 0.1C, and a volume energy density of 801.5 Wh L−1 which is nearly 1.4 times that of their nano-sized counterparts. This spherical material showed remarkable rate capability by maintaining 106.3 mAh g−1 at 20C, as well as excellent cycleablity with 98.9% capacity retention after 100 cycles at 2C and 200 cycles at 5C. The excellent electrochemical performance and processability of the LiFe0.6Mn0.4PO4/C microspheres make them very attractive as cathode materials for use in high rate battery application.