Thermodynamic Control of Oxygen Vacancies for Li‐Rich Cathode Materials

Oxygen vacancies (OVs) play a critical role in tuning the properties of oxides, yet their rational control remains challenging. We present a meticulous engineering approach to modulate OVs in lithium-rich layered oxides (LRLOs), a promising cathode material for next-generation lithium-ion batteries. Guided by a Mn-O₂ binary phase diagram, our method achieves accurate and broad tuning of the oxygen partial pressure (PO₂) during calcination using a pyrometallurgical CO/CO₂ gas pair. Using an ultra-high-Mn LRLO model, we quantify a thermodynamic equilibrium between OV concentration and a wide PO₂ range (10^-0.7-10^-10.0 atm). Structural characterizations reveal progressive lattice expansion and an unprecedented enhancement of Li@Mn₆ superstructures. An optimized LRLO with 3.8 mol % OVs shows a sixfold improvement in initial discharge capacity (175.9 mAh g^-1) over a reference sample (28.5 mAh g^-1) at 0.1C, achieving a maximum capacity of 287.9 mAh g^-1. Theoretical calculations clarify the role of OVs in modifying the electronic structure of LRLOs, which enables ideal conditioning for facile and reversible anion redox. This study provides a generalizable and facile strategy for OV engineering, which accelerates the commercial viability of LRLOs and offers a new framework for the rational design of other modern materials.