Co-Doping of Al3+ and Ti4+ and Electrochemical Properties of LiNiO2 Cathode Materials for Lithium-Ion Batteries.

LiNiO2 cathode material for lithium-ion batteries has the advantages of high specific capacity, abundant resources, and low cost, but it suffers from difficulties in preparation, structural instability, and serious capacity decay. In this work, highly pure and layered structural LiNi0.95 Ala Ti0.05-a O2 (a=0, 0.025, 0.05) cathode materials were synthesized by a simply sol-gel method. The cation mixing of Ni2+ and Li+ , structural deterioration, irreversible conversion between H2 and H3 phases and unstable surface and CEI (Cathode-electrolyte interface) film can be effectively suppressed by co-doping with Al3+ and Ti4+ . A preferred LiNi0.95 Al0.025 Ti0.025 O2 sample provides a discharge specific capacity of 223 mAh g-1 at 0.1 C and 148.32 mAh g-1 at 5 C, a capacity retention of 72.7 % after 300 cycles at 1 C and a Li+ diffusion coefficient of about 2.0×10-9 cm2 s-1 .

Outstanding Electrochemical Performance of Ni-Rich Concentration-Gradient Cathode Material LiNi0.9Co0.083Mn0.017O2 for Lithium-Ion Batteries.

The full-concentrationgradient LiNi0.9Co0.083Mn0.017O2 (CG-LNCM), consisting of core Ni-rich LiNi0.93Co0.07O2, transition zone LiNi1-x-yCoxMnyO2, and outmost shell LiNi1/3Co1/3Mn1/3O2 was prepared by a facile co-precipitation method and high-temperature calcination. CG-LNCM was then investigated with an X-ray diffractometer, ascanning electron microscope, a transmission electron microscope, and electrochemical measurements. The results demonstrate that CG-LNCM has a lower cation mixing of Li+ and Ni2+ and larger Li+ diffusion coefficients than concentration-constant LiNi0.9Co0.083Mn0.017O2 (CC-LNCM). CG-LNCM presents a higher capacity and a better rate of capability and cyclability than CC-LNCM. CG-LNCM and CC-LNCM show initial discharge capacities of 221.2 and 212.5 mAh g-1 at 0.2C (40 mA g-1) with corresponding residual discharge capacities of 177.3 and 156.1 mAh g-1 after 80 cycles, respectively. Even at high current rates of 2C and 5C, CG-LNCM exhibits high discharge capacities of 165.1 and 149.1 mAh g-1 after 100 cycles, respectively, while the residual discharge capacities of CC-LNCM are as low as 148.8 and 117.9 mAh g-1 at 2C and 5C after 100 cycles, respectively. The significantly improved electrochemical performance of CG-LNCM is attributed to its concentration-gradient microstructure and the composition distribution of concentration-gradient LiNi0.9Co0.083Mn0.017O2. The special concentration-gradient design and the facile synthesis are favorable for massive manufacturing of high-performance Ni-rich ternary cathode materials for lithium-ion batteries.

Electrochemical Performance and Behavior Mechanism for Zn/LiFePO4 Battery in a Slightly Acidic Aqueous Electrolyte.

The electrochemical performances and process mechanisms of Zn/LiFePO4 cells in a slightly acidic 1.9 m Li2 SO4 -0.5 m ZnSO4 aqueous solution were investigated. The results showed that the hydrogen depletion side reaction on the surface of the zinc sheet led to an increase in pH of the electrolyte and fluctuations in specific capacity of the cells, and that the dissolution of Fe2+ ions and the lamination of LiFePO4 particles resulted in a decrease in the specific capacity of the cells. At pH 5.0, the initial discharge specific capacity of the Zn/LiFePO4 cell was about 120.0 mAh g-1 at 0.25 C, about 64.4 mAh g-1 at 3 C, with about 60.9 % capacity retention rate after 200 cycles at 1 C, and the Li+ ions diffusion coefficient was about 7.75×10-12  cm2 s-1 .