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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 Rm 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.