Solvation Chemistry‐Driven Interfacial Engineering Enables Reversible Anionic Redox in Sodium‐Layered Oxide Cathodes

ABSTRACT Layered oxide cathodes with activated anionic redox reaction (ARR) have been considered as promising candidates for high‐energy‐density sodium‐ion batteries (SIBs) due to their high reversible capacity. Unfortunately, they suffer from irreversible oxygen release, successive electrolyte decomposition, severe transition metal dissolution, and crystal structure degradation, resulting in unsatisfactory sodium storage performance. Herein, the highly reversible ARR in Na 0.67 Li 0.24 Mn 0.66 Zn 0.05 Ti 0.05 O 2 (NLMZTO) is realized through the incorporation of multifunctional electrolyte additive (ethoxy (pentafluoro) cyclotriphosphazene, PFPN) into a traditional ester‐based electrolyte. The PFPN additive regulates the anion‐reinforced solvation structure, promotes the formation of a robust N/P‐rich cathode‐electrolyte interphase, and scavenges highly reactive oxygen species, which facilitates the formation of robust interfacial chemistry, suppresses continuous side reactions, and accelerates the desolvation kinetics. These combined effects effectively solve the key challenge for layered oxide cathodes with activated ARR. Consequently, the capacity retention of NLMZTO is significantly increased from 25.0% to 81.6% after 600 cycles at a high cut‐off voltage of 4.5 V. More importantly, the hard carbon||NLMZTO full cell delivers a high energy density of 472.6 Wh kg −1 and superior cycling performance, demonstrating the feasibility of PFPN in SIBs. This work provides valuable guidance in interfacial chemistry engineering employing multifunctional electrolyte additives for highly reversible ARR in layered oxide cathodes for high‐energy‐density SIBs.