Suppressing Oxygen-Loss-Driven Lattice Expansion Cascades in Disordered Rock-Salt Li-Ion Cathodes via Electrolyte Engineering

Disordered rock-salt (DRX) cathodes have emerged as promising candidates for low-cost, high-energy lithium-ion batteries that are free of nickel and cobalt. However, their practical use is hindered by rapid capacity and voltage degradation during cycling. This degradation has largely been attributed to chemical instability at high charge states, where unstable oxygen oxidation leads to oxygen loss, electrolyte decomposition, and transition metal dissolution. Recently, mechanical instability has been recognized as a key issue, driven by large volume changes in DRX particles that induce composite electrode-level cracks and pores. Here, through combined in situ and ex situ characterization with density functional theory calculations and machine learning applied to a model DRX compound, Li 1.2 Mn 0.6 Nb 0.2 O 2, we demonstrate that irreversible oxygen loss triggers cascading lattice expansion in DRX, establishing strong coupling between chemical and mechanical instabilities that leads to composite electrode damage and accelerated performance degradation. Notably, we show that this coupled degradation pathway can be significantly mitigated by employing a highly concentrated electrolyte, which suppresses oxygen loss and stabilizes the DRX structure. These findings provide a more complete understanding of DRX degradation and highlight electrolyte engineering as a key strategy to improve the durability of high-energy DRX cathodes across material, composite electrode, and cell levels.