Electric Field-Driven Competitive Ionic–Molecular Coordination in the Helmholtz Plane Enables High-Voltage and High-Temperature Sodium-Ion Batteries

Enhancing the interfacial stability between layered oxide cathodes (LOCs) and the electrolyte is considered to be pivotal for sodium-ion batteries (SIBs). However, the critical challenges of electrolyte oxidation and cathode degradation driven by the interfacial electric field remain unsolved, particularly under high-voltage and high-temperature conditions. Herein, we harness the interfacial electric field to precisely steer the species adsorption and solvation structure configuration of the Helmholtz plane (HP) through the steric exclusion effects of cations and the competitive coordination of multiple anions, thereby tailoring the interfacial chemistry of LOCs. Under electric field activation, the synergistic effect of ionic-molecular adsorption and coordination facilitates the formation of a robust inorganic-rich cathode electrolyte interphase, equipped with a uniform thickness and low energy barrier for smooth Na⁺ diffusion. These endow the O3-NaNi_1/3Fe_1/3Mn_1/3O₂ cathode with an enhanced capacity retention of 73.5% after 250 cycles under extreme operating conditions of 4.5 V and 60 °C. Furthermore, the viability of HP engineering is proven in practical Ah-level pouch cells, showcasing 79.5% capacity retention after 80 cycles at 4.3 V and 60 °C. This work underscores the relevance of HP regulation and interfacial chemistry manipulated by the electric field, providing valuable insights into electrolyte engineering for SIBs.