Synthesis and electrochemical characteristics of Li₁.₂(Ni₀.₂Mn₀.₆)ₓ(Co₀.₄Mn₀.₄)y(Ni₀.₄Mn₀.₄)₁₋ₓ₋yO₂ (0 ≤ x + y ≤ 1) cathode materials for lithium ion batteries

According to the tetrahedral phase diagram of LiNiO₂–LiCoO₂–LiMnO₂–Li₂MnO₃, a series of Li₁.₂(Ni₀.₂Mn₀.₆)ₓ(Co₀.₄Mn₀.₄)y(Ni₀.₄Mn₀.₄)₁₋ₓ₋yO₂ (0 ≤ x + y ≤ 1) have been designed to explore new Li-rich solid solution cathode materials. The effects of Li₁.₂Ni₀.₂Mn₀.₆O₂, Li₁.₂Co₀.₄Mn₀.₄O₂ and Li₁.₂Ni₀.₄Mn₀.₄O₂ content in solid solutions on structure and electrochemical properties are investigated. Micro-sized spherical or ellipsoidal precursors are first prepared via a carbonate co-precipitation route. After calcination with lithium sources, all samples are indexed to a typical layered structure with an R3m space group as detected by X-ray diffraction (XRD). It is found that the introduction of Co can improve the tap density. However, these Co referred samples reveal lower discharge specific capacities and inferior cycle life. For these Co-free materials with high Ni content, for instance Li₁.₂Ni₀.₃Mn₀.₅O₂, although low capacity is observed in the initial cycle, a large capacity of above 250 mA h g⁻¹ is achieved after about 10 cycles. Importantly, the activated Li₁.₂Ni₀.₃Mn₀.₅O₂ material still delivers a high capacity of over 230 mA h g⁻¹ after 70 cycles, displaying superior cycle stability. These results may be instructive in designing and exploring high performance cathode materials for advanced LIBs.