Soluble lithium polysulfide intermediates dissolve and shuttle during the process of charge/discharge, leading to the rapid capacity decline of a Li–S battery. Density functional theory (DFT) computation is used to research the thermodynamic behavior of the polysulfides. The computation indicates that the stable molecular structures tend to be in a ring shape. This is helpful for cathode modification at a molecular level to fix the polysulfides.

•The electrochemical properties of the LiNi0.6Co0.2Mn0.2O2 cathode are investigated at high voltage of 4.6 V.•The Li2SiO3 suppresses the decomposition of LiPF6 and carbonate solvents.•Li2SiO3 helpfully retards the transition metal dissolution by consuming HF.•The enhanced electrochemical properties of the LiNi0.6Co0.2Mn0.2O2 cathode mixed with Li2SiO3.Developing high-voltage Li ion batteries (LIBs) is an important trend to meet the requirement of high energy density battery. However, high voltage will cause a series of problems harming the cycle performance of LIBs at the same time. This work is to investigate the effect of inorganic substance Li2SiO3 on the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode at high cutoff voltage of 4.6 V. XRD result shows that the structure of NCM622 cathode material is not affected by mixing Li2SiO3. However, XPS and EIS tests indicate that Li2SiO3 has an evident influence on suppressing the decomposition of LiPF6 and carbonate solvents at high voltage, reducing interfacial solid film impedance and modifying electrode/electrolyte interface. In addition, Li2SiO3 retards the transition metal dissolution by consuming HF. Therefore, it enhances the electrochemical properties of the NCM622 cathode significantly. The highest discharge capacity increases to 191.7 mA h g-1 by mixing Li2SiO3, compared with the value of 180 mA h g-1 in the case of NCM622 cathode. The NCM622 electrode mixed with Li2SiO3 also exhibits a better capacity retention of 73.4% after 200 cycles and a high rate capability at 20C with the value of 89 mA h g-1, in contrast with 62.2% and 31 mA h g-1 attained in the NCM622 cathode.

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.

•A single-crystal LiNi0.6Co0.2Mn0.2O2 is prepared by a hydrothermal method.•A high discharge capacity of 183.7 mA h·g−1 at 0.2 C and good cycling stability.•It yields an initial discharge capacity of 153.6 mA h·g−1 at 10 C-rate under 2.8 V–4.3 V.•Superior electrochemical performance may be obtained attributed to the single-crystal structure.Single-crystal nickel-high materials (ST-LNCMO) LiNi0.6Co0.2Mn0.2O2 have been synthesized using a versatile hydrothermal method. The as-prepared samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and selected area electron diffraction (SAED). The results show that the sample annealed at an optimized temperature of 850 °C reveals uniform fine well-crystallized single-particles with diameters of ～800 nm. Electrochemical data demonstrate that the cell using this nickel-high material as the cathode exhibits excellent performance. The sample displays a high capacity of 183.7 mA h·g−1 at 36 mA·g−1 (0.2 C) and excellent cycling stability at different rates. It yields an initial discharge capacity of 153.6 mA h·g−1 at a rate of 10C-rate and a voltage of 2.8 V – 4.3 V. The sample also has an outstanding rate capacity at a high cut-off voltage (4.6 V). This superior performance is attributed to the merits of the single-crystal structure, which may be beneficial to the transportation of the Li+ ion along the grain.

•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.

•A novel sand-like electrolyte is prepared.•The anodic stability of sand-like electrolyte is superior in the presence of Li2SiO3.•Cycling stability of 5 V LiNi0.5Mn1.5O4 is enhanced.•Intensive electrolyte oxidation is supressed during cycling under high potential.•Li2SiO3 can consume the PF5 and HF in electrolyte.The electrochemical performance of LiNi0.5Mn1.5O4 is investigated in a sand-like carbonate electrolyte containing 4 wt.% lithium metasilicate (Li2SiO3). The capacity fading rate of the LiNi0.5Mn1.5O4 electrode working in the sand-like electrolyte (2-5 V) is reduced to 0.171 mAh g−1 per cycle, quite smaller than the value of 0.613 mAh g−1 per cycle in the electrolyte without Li2SiO3. The capacity of 159.5 mAh g−1 is delivered at 0.5 C after 118 cycles while it is only 99.4 mAh g−1 for the Li2SiO3-free counterpart. Cyclic voltammetry, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopic measurements are conducted to explore the modification mechanism. It is found that the anodic stability of the sand-like electrolyte is improved compared to the base electrolyte. The Li2SiO3 precipitates on the electrode surface make contribution to the performance enhancement of the cathode at high potential.

•Advances on layered LiNixCoyMn1−x−yO2 (x ≥ 0.5) positive electrode materials.•Detailed discussion on the preparation, microstructure, modification, etc.•Structure stability, interface compatibility of the positive electrode materials.•The challenges and prospects of nickel-rich layered oxide materials.High energy density lithium-ion batteries are eagerly required to electric vehicles more competitive. In a variety of circumstances closely associated with the energy density of the battery, positive electrode material is known as a crucial one to be tackled. Among all kinds of materials for lithium-ion batteries, nickel-rich layered oxides have the merit of high specific capacity compared to LiCoO2, LiMn2O4 and LiFePO4. They have already become one of the most attractive candidates for the mainstream batteries in industries. In this work, the recent advances on three commonly concerned nickel-rich layered oxides are presented. The preparation, microstructure, electrochemical performances are focused, the modification including coating design as well as dopant selection is specially discussed in details, which is essential to enhance the durability and energy density of lithium-ion batteries. Additionally, the prospects and challenges are also systematically discussed, as well as the potential applications in the field of energy storage technologies.