Solvation-enhanced electrolyte on layered oxide cathode tailoring even and stable CEI for durable sodium storage

Abstract

Layered transition-metal oxide materials are ideal cathode candidates for sodium-ion batteries due to high specific energy, yet suffer severe interfacial instability and capacity fading owing to strongly nucleophilic surface. In this work, the interfacial stability of layered NaNi_1/3Fe_1/3Mn_1/3O₂ cathode was effectively enhanced by electrolyte optimization. And the interfacial chemistry between the cathode and four widely used electrolytes (EC/DMC, EC/EMC, EC/DEC and EC/PC) was elucidated through experiments and theoretical calculations. The Na⁺ solvation structures at cathode-electrolyte interface in all four electrolytes exhibited enhanced coordination due to high electron density and strong nucleophilicity of oxide surface, which promoted the electrolytes’ decomposition with decreased oxidation stability. Among them, the EC/DMC electrolyte showed the tightest solvation structure due to smaller molecular chains and stable electrochemistry, which derived an even and robust cathode electrolyte interphase. It effectively protected the cathode and facilitated the reversible Na⁺ transport during long cycles, enabling the batteries with a high capacity retention of 83.3% after 300 cycles. This work provides new insights into the role of electrode surface characteristics in interface chemistry that can guide the design of advanced electrode and electrolyte materials for rechargeable batteries.