Ni-induced stepwise capacity increase in Ni-poor Li-rich cathode materials for high performance lithium ion batteries

Li-rich cathode materials have been considered as promising candidates for high-energy lithium ion batteries (LIBs). In this study, we report a new series of Li-rich materials (Li[Li_1/3-2x/3Mn_2/3-x/3Ni_x]O₂ (0.09 ≤ x ≤ 0.2)) doped with small amounts of Ni as cathode materials in LIBs, which exhibited unusual phenomenon of capacity increase up to tens of cycles due to the continuous activation of the Li₂MnO₃ phase. Both experimental and computational results indicate that unlike commonly studied Ni-doped Li-rich cathode materials, smaller amounts of Ni doping can promote the stepwise Li₂MnO₃ activation to obtain increased specific capacity and better cycling capability. In contrast, excessive Ni will over-activate the Li₂MnO₃ and result in a large capacity loss in the first cycle. The Li_1.25Mn_0.625Ni_0.125O₂ material with an optimized content of Ni delivered a superior high capacity of ~280 mAh·g^-1 and good cycling stability at room temperature.