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

Abstract

According to the tetrahedral phase diagram of LiNiO₂–LiCoO₂–LiMnO₂–Li₂MnO₃, a series of Li_1.2(Ni_0.2Mn_0.6)_x(Co_0.4Mn_0.4)_y(Ni_0.4Mn_0.4)_1−x−yO₂ (0 ≤ x + y ≤ 1) have been designed to explore new Li-rich solid solution cathode materials. The effects of Li_1.2Ni_0.2Mn_0.6O₂, Li_1.2Co_0.4Mn_0.4O₂ and Li_1.2Ni_0.4Mn_0.4O₂ 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 Li_1.2Ni_0.3Mn_0.5O₂, 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 Li_1.2Ni_0.3Mn_0.5O₂ 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.