Revealing the Effect of High Ni Content in Li-Rich Cathode Materials: Mitigating Voltage Decay or Increasing Intrinsic Reactivity

Li-rich cathode materials are considered as one of the most promising cathode materials for secondary lithium batteries due to their high specific capacities, but suffer from continuous voltage decay during cycling hindering their market entry. Increasing the Ni content in Li-rich cathode materials is assumed to be an effective way to address this issue and attracts recent research interests. However, a high Ni content may induce increased intrinsic reactivity of materials, resulting in severe side reactions with the electrolyte. Thus, a comprehensive study to differentiate between the two effects of the Ni content on cell performance of Li-rich cathodes is carried out in this work. Herein, we demonstrate that a properly dosed amount of Ni can effectively suppress the voltage decay in Li-rich cathodes, while over-loading of Ni, on the contrary, can cause structural instability, Ni dissolution, and non-uniform Li deposition during cycling as well as severe oxygen loss. This work facilitates a deep understanding on the impacts of Ni content in Li-rich materials, which can be a good guidance for the future design of such cathodes for high energy density lithium batteries.