•In situ anchoring of lithium iodide in carbon/sulfur electrode was achieved.•The good rate capability results from the improvement of ionic and electronic conductivity.•The synthesis strategy is beneficial to industrialization of Li-S batteries.Lithium sulfur battery is one of the most cost-effective alternatives to meet the requirement of high energy density for power sources due to its high energy density and low cost. However, lithium sulfur battery still suffers from a rapid capacity fading and poor rate performance, which are mainly related to the shuttle effect of polysulfides during cycling and the insulating nature of sulfur as well as the reduced product of Li2S or Li2S2. Here, we proposed an iodine-incorporated carbon/sulfur electrode to improve the rate performance of Li-S batteries. The resultant composite electrode exhibits good high-rate charge-discharge capability with a high discharge capacity of 479 mAh/g at 3C after 100 cycles. The excellent rate capability is mainly correlated to the iodine-doped carbon host with improved electronic conductivity, formation of lithium iodide (LiI) served as solid-state electrolyte in electrode during the first discharge process and the dissolution of iodine species into the electrolyte as additive for improving the ionic conductivity. This work offers an innovative, effective and facile method to ameliorate the electrochemical performance of lithium sulfur batteries.Download high-res image (86KB)Download full-size image

NaAlO2-coated LiCoO2 materials have been synthesized as cathode materials for lithium-ion batteries. The NaAlO2 layer is coated on the LiCoO2 particles successfully. NaAlO2-coated LiCoO2 materials exhibit the improved cycling stability and rate capability at a high cutoff voltage of 4.5 V vs Li+/Li. The LiCoO2 sample coated by 2 wt.% NaAlO2 demonstrates the excellent cyclability with a capacity retention of 95.7 % after 50 cycles at 100 mA g−1. In the meantime, the sample shows superior rate performance, delivering a quite high capacity of over 135 mA h g−1 at a current density of 1600 mA g−1, corresponding to 73.4 % of the capacity at 20 mA g−1. NaAlO2-coating layer acts as a physical barrier that separates the LCO electrode and electrolyte, which will suppress the oxidation of solvents, dissolution of cobalt ions, and the evolution of oxygen at high cutoff voltage. Moreover, the NaAlO2 layer can provide two-dimensional ion diffusion channel for lithium ions, resulting in improvement of electrochemical performance for LiCoO2.

•Micro-sized spherical Si@C@RGO was synthesized by spray drying process.•The Si@C@RGO composite exhibits excellent electrochemical performance.•The unique structure significantly enhances the conductivity of silicon.The micro-sized silicon@carbon@graphene spherical composite (Si@C@RGO) has been prepared by an industrially scalable spray drying approach and a subsequent calcination process. The obtained Si@C@RGO anode exhibits a high initial reversible specific capacity of 1599 mAh g−1 at a current density of 100 mA g−1 with a good capacity retention of 94.9% of the original charge capacity at a higher current density of 200 mA g−1. Moreover, the Si@C@RGO anode shows a high reversible specific capacity of 951 mAh g−1 even at a high current density of 2000 mA g−1. The excellent cycling stability and superior rate capability are attributed to the unique structural design of carbon coating and wrapped by highly conductive graphene. The combination of carbon shells and flexible graphene can effectively enhance the electrical conductivity of the composite and accommodate significant volume changes of silicon during cycling. The presented spray drying strategy is adaptable for large-scale industrial production of Si-based composite, and it can be extended to the design of other promising micro-sized electrode materials.Download high-res image (345KB)Download full-size image

LiCoO2 (LCO) has been functionally modified with electronic conductive Al-doped ZnO (AZO) via a sol-gel method. The physicochemical characterization results demonstrate that the AZO layer is coated onto the surface of LiCoO2 particles successfully, and the AZO-coated LCO material shows a higher electronic conductivity than pristine sample. The LCO sample coated by 2 wt.% AZO shows the excellent cyclability with a capacity retention of 98.2% after 50 cycles in the voltage range of 2.75–4.5 V under room temperature. More importantly, this material exhibits outstanding rate capability and delivers a quite high capacity of 156 mA h g−1 at the rate of 8 C (1600 mA g−1), corresponding to 86.6% of the capacity at the rate of 0.1 C. Such superior electrochemical performance results from the effective coating of AZO layer which not only acts as a physical protection layer to stabilize the surface structure, but also supplies the conductive networks to decrease charge transfer impedance. The conducting functionalized AZO coating is a facile and efficient approach to improve the electrochemical performance of LCO at a high cut-off voltage of 4.5 V vs. Li+/Li for large-scale application of high energy density lithium ion batteries.

Lithium-sulfur (Li-S) batteries are considered one of the most promising energy storage systems because of their high energy density and natural abundance of sulfur. However, the inferior cycle stability and low Coulombic efficiency mainly due to the dissolution of ploysulfides impede the practical application of Li-S batteries. Herein, a novel three-dimensional clew-like N-doped multiwalled carbon nanotube (MWCNT) structure is obtained by carbonizing a kind of Ni-based metal-organic complex. When developed as conductive sulfur-loading hosts for Li-S batteries, the interconnected open-ended MWCNT materials show outstanding properties on encapsulating sulfur and immobilizing polysulfide intermediates. Moreover, the porous graphitic carbon as a conductive matrix facilitates the electron transport and the reversible electrochemical reaction of active materials during cycling. Therefore, a good cycling stability for 1000 cycles with a low capacity decay rate of 0.053% per cycle and a high Coulombic efficiency up to nearly 100% at 0.2C are achieved for the three-dimensional clew-like N-doped MWCNT/sulfur cathode material for Li-S batteries.Download high-res image (389KB)Download full-size image

Although physical confinement and chemical adsorption have been adopted for trapping sulfur species within cathodes, there still exist some drawbacks, including low charge/discharge coulombic efficiency and unsatisfied cycleability in terms of the slow kinetic process of polysulfide conversion. Herein, we propose a KB@Ir-modified separator with a catalytic layer to facilitate the redox reaction of polysulfide intermediates and to achieve improved electrochemical performance in lithium sulfur batteries. The iridium nanoparticles not only exhibit strong chemical interaction with the polysulfides, but also efficiently accelerate the kinetic process for polysulfide conversion, especially for the reduction of soluble polysulfides towards insoluble Li2S2/Li2S. A high initial capacity of 1508 mA h g−1 along with 90.0% utilization of sulfur could be achieved under a charge/discharge rate of 0.2C. Also the cell showed a low capacity decay rate of 0.105% per cycle over 500 cycles at 1.0C. This strategy from the point of view of electrocatalysis is expected to be effective for achieving high-energy lithium–sulfur batteries with excellent electrochemical performance.

•A binder-free RGO/Si composite anode was fabricated by a straight-forward coating method.•The composite anode possesses a unique multi-layered architecture.•The composite anode exhibits a high reversible capacity and excellent cycle performance.A novel binder-free reduced graphene oxide/silicon (RGO/Si) composite anode has been fabricated by a facile doctor-blade coating method. The relatively low C/O ratio plays an important role for the fabrication of the bind-free multilayered RGO/Si electrode with silicon nanoparticles encapsulating among the RGO sheet layers. The RGO provides the electron transport pathway and prevents the electrode fracture caused by the volume changes of active silicon particles during cycling. The RGO/Si composite anode with a silicon content of 66.7% delivers a reversible capacity of 1931 mAh g−1 at 0.2 A g−1 and still remains 92% of the initial capacity after 50 cycles.

Here, we prepared LiMn0.8Fe0.2PO4 microspheres with an open three-dimensional nanoporous structure by a facile ion-exchange solvothermal method. The micro/nano-structured material exhibits an ultralong cycle life, and retains a reversible capacity of 105 mA h g−1 after 1000 cycles at 5 C, corresponding to the capacity retention of 94.0% and only 0.0068 mA h g−1 loss per cycle.

Nano-sized LiMn1−xFexPO4 (x = 0 and 0.1) was prepared by a solvothermal method in a mixed solvent of water and ethanol. LiMn0.9Fe0.1PO4–polyacene (PAS) composite exhibits a high conductivity (0.15 S cm−1), resulting in an excellent rate performance and good cycle life. The LiMn0.9Fe0.1PO4–PAS composite delivers a discharge capacity of 161, 141, and 107 mA h g−1 at 0.1 C, 1 C and 10 C, respectively. The well-distributed conductive polyacene surrounding the LiMn0.9Fe0.1PO4 nanoplates enhances the electronic contact of the nanosized crystalline particles and suppresses the manganese dissolution related to the structure evolution during cycling. Specifically, the manganese dissolution, electrolyte decomposition and the antisite defects are the most significant factors that impact the capacity degradation of olivine iron-doped lithium manganese phosphate cathode materials.

Electrochemical performance degeneration of LiCoO2 electrodes under high state of charge (SOC) during long-term cycling was studied using LiCoO2/MCMB batteries. The batteries were charged/discharged at 0.6C with 30% depth of discharge (DOD) for 100, 400, 800, 1600, 2000 and 2400 cycles, respectively, and then disassembled to analyze the evolution of morphology, element content, microstructure and electrochemical performance. Through energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) characterization, it was confirmed that the formation of discontinuous solid electrolyte interface (SEI) layer consisting of Li2CO3, RCOOLi and LiF led to the increase of electrochemical charge transfer resistance (Rct). Although the X-ray diffraction (XRD) refined results showed that there was no new phases were formed during the long-term cycling, the actually increased Li/Co exchange ratio of LiCoO2 from 1.6% at 800th to 2.1% at 2400th resulted in the decrease of lithium ion diffusion coefficient and deterioration of the rate performance.

•LMFP/C powders were prepared by an ascorbic acid-assisted solvothermal process.•The LMFP/C sample exhibits an excellent discharge capacity of 145 mA h g−1.•The LMFP/C holds highly uniform distribution of particle size and better conductivity.Morphology-controlled LiMn0.9Fe0.1PO4 nanoplatelets as high performance cathode material for lithium ion batteries have been synthesized via a simple ascorbic acid-assisted solvothermal process in water-ethanol solvent. The phase structure and morphology of the products were characterized by XRD, SEM and TEM. The results reveal that decreasing the crystallite size along b-axis direction and increasing the surface area of (010) plane can shorten Li+ diffusion path and increase the electrode reaction activity. The LiMn0.9Fe0.1PO4 nanoplatelet holds the high capacity of 145 mA h g−1, 134 mA h g−1, 119 mA h g−1, 97 mA h g−1 and 68 mA h g−1 at 0.1 C, 0.5 C, 1 C, 5 C and 10 C respectively, and it can retain 75% of the initial reversible capacity even after 100 cycles at 10 C rate.

Li2FeSiO4/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li2FeSiO4/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li2FeSiO4 nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li2FeSiO4/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA h g−1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li2FeSiO4/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.

A Li2FeSiO4/C composite cathode material was prepared by a solid-state method with sucrose as a carbon source. The effect of carbon on the structure and electrochemical performance of Li2FeSiO4/C cathode materials for lithium-ion batteries was investigated. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). SEM images show that the obtained Li2FeSiO4/C materials consist of partially agglomerated nanoparticles with an average particle size of 100 nm. TEM images confirm that the carbon layer formed on the surface of Li2FeSiO4/C particles enhances the electronic conductivity and inhibits the agglomeration of the active particles during the annealing process. The electrochemical measurement results reveal that the Li2FeSiO4/C composite with 7.5 wt% carbon shows a good electrochemical performance with an initial discharge capacity of 141 mA h g−1 at 0.1 C. After 50 cycles, the discharge capacity of the Li2FeSiO4/C composite remains 94.2% of the initial capacity at a discharge rate of 0.5 C.

The silicon/carbon (Si/C) composite material was prepared, and the electrochemical performance was investigated as a promising anode material for lithium ion batteries. The results show that the binder in the electrode acts as an important role for improving the reversible capacity of the Si/C materials during cycling. The Si/C electrode with CMC/SBR binder possesses a better cycle performance than that with PVDF binder. The Si/C composite material shows an initial reversible capacity of more than 700 mAh∙g−1 and remains a reversible capacity of 597 mAh g−1 after 40 cycles.

The silicon/carbon composite was prepared by mixing the silicon, graphite and pitch in the tetra-hydrofuran solution followed by pyrolyzing the blends after the evaporation of solvent. The electrochemical performance of the silicon/carbon anode for lithium ion batteries was improved by the treatment of composite powders with KCl aqueous solutions. Scanning electron microscope (SEM) observation and electrochemical impedance spectroscopy (EIS) results showed that the morphology stability of the composite electrodes can be kept during the electrochemical charge/discharge process. The composite electrode of silicon/carbon composite showed an initial reversible capacity of 575 mAh g−1 and still maintained a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of ∼0.3% per cycle.

Silicon-graphite composites were prepared by mechanical ball milling for 20 h under argon protection. The microstructure and electrochemical performance of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical experiments. XRD showed that the materials prepared by ball milling were composites consisting of Si and graphite powders. The composite electrode showed the best performance, especially when annealed at 200 °C for 2 h, which had a reversible capacity of 595 mAh g−1 and an initial coulombic efficiency of 66%, and still retained 469 mAh g−1 after 40 cycles with about 0.6% capacity loss per cycle.

•The phase transformation mechanism for NaNiO2 during cycling was elucidated.•The in situ TXM-XANES results confirm the “core-shell” reaction process.•The irreversible phase transformation during charging was unraveled by in situ HEXRD.•The correlation of capacity evolution with reaction kinetics was revealed.Layered transition metal compounds have attracted much attention due to their high theoretical capacity and energy density for sodium ion batteries. However, this kind of material suffers from serious irreversible capacity decay during the charge and discharge process. Here, using synchrotron-based operando transmission X-ray microscopy and high-energy X-ray diffraction combined with electrochemical measurements, the visualization of the dissymmetric phase transformation and structure evolution mechanism of layered NaNiO2 material during initial charge and discharge cycles are clarified. Phase transformation and deformation of NaNiO2 during the voltage range of below 3.0 V and over 4.0 V are responsible for the irreversible capacity loss during the first cycling, which is also confirmed by the evolution of reaction kinetics behavior obtained by the galvanostatic intermittent titration technique. These findings reveal the origin of the irreversibility of NaNiO2 and offer valuable insight into the phase transformation mechanism, which will provide underlying guidance for further development of high-performance sodium ion batteries.The dissymmetric phase transformation and structure evolution mechanism of layered NaNiO2 material during initial charge and discharge cycling were comprehensive understood with transmission X-ray microscopy and synchrotron-based X-ray diffraction. We directly observed the structural evolution of the NaNiO2 cathode in sodium-ion batteries and elucidated the irreversible phase transformation mechanism during the initial electrochemical cycling.

•Micro-sized SiO-based composite anode is prepared by a facile approach.•The composite maintains an excellent cycling stability after prelithiation by SLMP.•The degree of prelithiation can be controlled by adjusting the SLMP amount.•Prelithiation counteracts the capacity loss corresponding to the SEI formation.The micro-sized SiO-based composite anode material (d-SiO/G/C) for lithium-ion batteries (LIBs) is achieved via the disproportionation reaction of SiO followed by a pitch pyrolysis reaction. The d-SiO/G/C composite exhibits an initial reversible capacity of 905 mAh g−1 and excellent cycling stability. The initial Coulombic efficiency of the d-SiO/G/C composite can be significantly improved from 68.1% to 98.5% by the prelithiation of the composite anode using stabilized lithium metal powders (SLMP), which counteracts the irreversible capacity loss caused by the solid electrolyte interphase (SEI) formation and irreversible conversion reaction during the first lithiation. The micro-sized d-SiO/G/C composite anode with SLMP prelithiation maintains an excellent cycling stability, suggesting its great potential in practical application for high specific energy lithium ion batteries.Download high-res image (223KB)Download full-size image

Nano-sized LiMn1−xFexPO4 (x = 0 and 0.1) was prepared by a solvothermal method in a mixed solvent of water and ethanol. LiMn0.9Fe0.1PO4–polyacene (PAS) composite exhibits a high conductivity (0.15 S cm−1), resulting in an excellent rate performance and good cycle life. The LiMn0.9Fe0.1PO4–PAS composite delivers a discharge capacity of 161, 141, and 107 mA h g−1 at 0.1 C, 1 C and 10 C, respectively. The well-distributed conductive polyacene surrounding the LiMn0.9Fe0.1PO4 nanoplates enhances the electronic contact of the nanosized crystalline particles and suppresses the manganese dissolution related to the structure evolution during cycling. Specifically, the manganese dissolution, electrolyte decomposition and the antisite defects are the most significant factors that impact the capacity degradation of olivine iron-doped lithium manganese phosphate cathode materials.

Although physical confinement and chemical adsorption have been adopted for trapping sulfur species within cathodes, there still exist some drawbacks, including low charge/discharge coulombic efficiency and unsatisfied cycleability in terms of the slow kinetic process of polysulfide conversion. Herein, we propose a KB@Ir-modified separator with a catalytic layer to facilitate the redox reaction of polysulfide intermediates and to achieve improved electrochemical performance in lithium sulfur batteries. The iridium nanoparticles not only exhibit strong chemical interaction with the polysulfides, but also efficiently accelerate the kinetic process for polysulfide conversion, especially for the reduction of soluble polysulfides towards insoluble Li2S2/Li2S. A high initial capacity of 1508 mA h g−1 along with 90.0% utilization of sulfur could be achieved under a charge/discharge rate of 0.2C. Also the cell showed a low capacity decay rate of 0.105% per cycle over 500 cycles at 1.0C. This strategy from the point of view of electrocatalysis is expected to be effective for achieving high-energy lithium–sulfur batteries with excellent electrochemical performance.