Unlocking the Potential of Cobalt-Free Lithium-Ion Cathodes via Lithium-Rich Disorder Domains.

High-voltage, low-nickel, cobalt-free layered oxides are promising candidates for high-energy-density lithium-ion batteries. However, their practical application is hindered by intrinsic cation disorder and structural degradation at high voltages, leading to a poor electrochemical performance. Here, we report a slightly lithium-enriched, cobalt-free layered oxide, Li1.05Ni0.43Mn0.52O2, featuring lithium-rich disorder domains achieved through chemical composition optimization. Advanced structural characterization demonstrates that nickel ions not only reside within the TM layers but also occupy the Li layers, acting as pinned ions. Theoretical calculations indicate that this in-plane and out-of-plane disorder enables reversible oxygen redox activity without oxygen release at high voltages. Moreover, this local structural framework preserves integrity even after extended cycling, ensuring chemical and structural stability during battery operation. Consequently, the cathode delivers an impressive discharge capacity of 202.2 mAh g-1 at C/10 and exceptional cycling stability, retaining 96.3% of its capacity after 200 cycles at C/3 within a voltage range of 2.5-4.55 V. Our findings provide valuable insights into the design of high-energy-density, cobalt-free layered cathodes.