Cooperative structure of Li/Ni mixing and stacking faults for achieving high-capacity Co-free Li-rich oxides

Co-free Li-rich layered oxides (LLOs) are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity. However, they commonly face severe structural instability and poor electrochemical activity, leading to diminished capacity and voltage performance. Herein, we introduce a Co-free LLO, Li1.167Ni0.222Mn0.611O2 (Cf-L1), which features a cooperative structure of Li/Ni mixing and stacking faults. This structure regulates the crystal and electronic structures, resulting in a higher discharge capacity of 300.6 mA h g−1 and enhanced rate capability compared to the typical Co-free LLO, Li1.2Ni0.2Mn0.6O2 (Cf-Ls). Density functional theory (DFT) indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities, while stacking faults further optimize the electronic interactions of transition metal (TM) 3d and non-bonding O 2p orbitals. Moreover, stacking faults accommodate lattice strain, improving electrochemical reversibility during charge/discharge cycles, as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls. This study offers a structured approach to developing Co-free LLOs with enhanced capacity, voltage, rate capability, and cyclability, significantly impacting the advancement of the next-generation Li-ion batteries.