Understanding Voltage Decay and Hysteresis in Li‐Rich Layered Oxide Cathodes

Abstract

Li‐rich layered oxide cathodes (LLOs) with anionic redox are promising to boost the energy density of lithium batteries beyond 500 Wh kg−1. However, their commercialization has long been hampered by inherent drawbacks, particularly voltage decay and hysteresis, which reduce energy density and efficiency, shorten battery life, and challenge battery management. To address these issues, a prerequisite is establishing a comprehensive understanding of voltage‐related phenomena correlated with anionic redox reactions (ARR), which remains elusive despite extensive research. Therefore, in this review, the proposed mechanisms are systematically summarized and the fundamental origins of voltage decay and hysteresis are identified, together with elucidating their relationship with ARR. Voltage decay is mainly attributed to irreversible TM migration and phase transition, whose driving force involves factors like lattice strain accumulation and oxygen loss. A relatively unified theory, the asymmetric non‐equilibrium reaction path during ARR, is identified as the fundamental origin of voltage hysteresis. This path includes sequential electrochemical reactions and chemical processes (sluggish electronic and atomic structural rearrangements, such as TM migration and ligand‐to‐metal charge transfer). Recent achievements and effective solutions for these voltage issues are also elaborated. After deeply understanding voltage decay and hysteresis, inspiring insights for mitigation strategies and forward‐looking remarks are provided.