Solid-Solution Reactions in Layer-Structured Oxide Cathodes Driven by Local Disorder and Electron Delocalization.

Layer-structured transition metal oxides show great potential in alkali metal ion batteries, their structural phase transitions, however, lead to mechanical disintegration, resulting in capacity decay and severely limiting the lifespan. Traditional modification strategies struggle to suppress phase transitions at their thermodynamic root cause, while the ideal solid-solution reaction paradigm faces the challenge of difficult-to-control electronic structures. A novel physical paradigm was proposed that drives the solid-solution-dominated reaction by reshaping the electronic state through a quenching process herein. A locally disordered layered oxide, K0.5(Mn0.85Fe0.1Ti0.05)0.99(VTMBi)0.01O2 (KMFTB), was constructed through a quenching-assisted vacancy-mediated boron (B) incorporation process, in which TM vacancies (VTM) capture Bi and reconstruct the local coordination into stable [BO4] units. Experiments and theoretical calculations confirm that the synergistic interaction between the locally disordered structure and strong B─O bonds not only stabilizes the transition metal framework through the pinning effect, but also induces a significant band broadening and electronic delocalization. This electronic structure restructuring enables KMFTB to suppress destructive phase transitions and achieve a highly reversible solid-solution-dominated reaction pathway, providing profound theoretical insights for the rational design of high-performance cathode materials.