Performance decline in Li-excess cathodes is generally attributed to structural degradation at the electrode-electrolyte interphase, including transition metal migration into the lithium layer and oxygen evolution into the electrolyte. Reactions between these new surface structures and/or reactive oxygen species in the electrolyte can lead to the formation of a cathode electrolyte interphase (CEI) on the surface of the electrode, though the link between CEI composition and the performance of Li-excess materials is not well understood. To bridge this gap in understanding, we use solid-state nuclear magnetic resonance (SSNMR) spectroscopy, dynamic nuclear polarization (DNP) NMR, and electrochemical impedance spectroscopy (EIS) to assess the chemical composition and impedance of the CEI on Li₂RuO₃ as a function of state of charge and cycle number. We show that the CEI that forms on Li₂RuO₃ when cycled in carbonate-containing electrolytes is similar to the solid electrolyte interphase (SEI) that has been observed on anode materials, containing components such as PEO, Li acetate, carbonates, and LiF. The CEI composition deposited on the cathode surface on charge is chemically distinct from that observed upon discharge, supporting the notion of crosstalk between the SEI and the CEI, with Li⁺-coordinating species leaving the CEI during delithiation. Migration of the outer CEI combined with the accumulation of poor ionic conducting components on the static inner CEI may contribute to the loss of performance over time in Li-excess cathode materials.

锂过量阴极的性能下降通常归因于电极-电解质界面的结构退化，包括过渡金属迁移到锂层中以及氧气向电解质中释放。这些新的表面结构和/或电解质中的活性氧之间的反应可能导致在电极表面上形成阴极电解质中间相（CEI），尽管CEI成分与过量锂材料的性能之间的联系是不太了解。为了弥合这种认识上的差距，我们使用固态核磁共振（SSNMR）光谱，动态核极化（DNP）NMR和电化学阻抗谱（EIS）来评估Li ₂ RuO ₃上CEI的化学组成和阻抗作为充电状态和循环次数的函数。我们显示，当在含碳酸盐的电解质中循环时，在Li ₂ RuO ₃上形成的CEI与在阳极材料上观察到的固体电解质中间相（SEI）相似，其中包含PEO，乙酸锂，碳酸盐和LiF等组分。电荷沉积在阴极表面上的CEI成分在化学上与放电时观察到的化学成分不同，这支持了SEI与CEI之间的串扰概念，其中Li ^+-配位物质在脱锂过程中离开CEI。外部CEI的迁移以及不良的离子导电组分在静态内部CEI上的积累可能会导致锂过量的正极材料随着时间的流逝而导致性能下降。