A Dynamic Structural Stabilization Strategy for Li-Doped Sodium-Ion Battery Cathodes.

Unfavorable phase transformations and limited practical capacity remain significant challenges to the widespread application of layered oxides in sodium-ion batteries. Lithium doping has emerged as an effective strategy to suppress phase transformations and activate oxygen redox reactions. However, solid-state NMR reveals that Li gradually deintercalates from the bulk of the cathode during repeated cycles, ultimately compromising the efficacy of Li-doping. To address this, we introduce a straightforward yet effective approach involving the introduction of exogenous Li into the electrolyte, dynamically compensating for and mitigating undesired Li loss. Complementary solid-state NMR and XRD characterizations confirm that the exogenous Li preserves the bulk lithium content within the cathode, preventing structural degradation at both the long-range crystal structure and the local atomic environment. Additionally, interfacial characterization and electrochemical analysis demonstrate that exogenous Li optimizes the cathode-electrolyte interface and reduces interfacial impedance. As a result, the capacity retention of NaLiNiMnO improved significantly from 73.5% to 90.7% after 200 cycles. This study underscores the pivotal role of electrolytes in preserving the long-term effectiveness of structural modifications in the cathode, providing an approach to extending the cycling lifespan of high-performance sodium-ion batteries.