Controlling the lattice oxygen content regulates cycling stability and rate capability of Co-free ultrahigh-Ni cathodes

Co-free and Ni-rich layered cathode materials for lithium-ion batteries have attracted significant attention due to their high capacity and low cost. Existing research has mainly focused on the impact of lattice oxygen (Oo) and oxygen vacancies (Ov) during the charging and discharging processes on the electrochemical performance. However, the influence of intrinsic Oo and Ov on the electrochemical performance of Co-free and Ni-rich cathodes remains to be investigated. In this work, LiNi_0.95Mn_0.05O₂ (NM95) cathodes with different Oo contents were prepared, and their effect on electrochemical performance was studied. The results demonstrate that an optimal Oo content enhances the structural ordering of NM95 and improves Li⁺ diffusion kinetics. This dual optimization reduces parasitic capacitance effects, ultimately boosting the practical capacity of NM95. At the optimum Oo content, high capacity and rate performance are achieved, with discharge capacities of 208.6 mA h g⁻¹ (2.7–4.3 V) and 222.5 mA h g⁻¹ (2.7–4.5 V) at 1 C. At 5 C and 10 C (2.7–4.3 V), the capacities are 171.6 mA h g⁻¹ and 129.4 mA h g⁻¹, respectively. The Ov content influences the TM-O bonds, Li⁺ diffusion channels, Oo content at high voltage, and cycling stability of the NM95 cathode. At the optimum Ov content, NM95 exhibits excellent cycle stability, with retention rates of 87.1% and 84.3% after 100 cycles at 2.7–4.3 V and 2.7–4.5 V, respectively. Therefore, controlling the Oo content is an effective and feasible approach to enhancing the capacity and cycle stability of Co-free and Ni-rich cathodes.