Electrolyte Salts for Sodium-Ion Batteries: NaPF₆ or NaClO₄?

Abstract

NaClO₄ and NaPF₆, the most universally adopted electrolyte salts in commercial sodium-ion batteries (SIBs), have a decisive influence on the interfacial chemistry, which is closely related to electrochemical performance. The complicated and ambiguous interior mechanism of microscopic interfacial chemistry has prevented reaching a consensus regarding the most suitable sodium salt for high-performance SIB electrolytes. Herein, we reveal that the solvation structure induced by different sodium salt anions determines the Na⁺ desolvation kinetics and interfacial film evolution process. Specifically, the weak interaction between Na⁺ and PF₆^- promoted sodium desolvation and storage kinetics. The solvation structure involving PF₆^- induced the anion's preferential decomposition, generating a thin, inorganic compound-rich cathode-electrolyte interphase that ensured interface stability and inhibited solvent decomposition, thereby guaranteeing electrode stability and promoting the charge transfer kinetics. This study provides clear evidence that NaPF₆ is not only more compatible with industrial processes but also more conducive to battery performance. Commercial electrolyte design employing NaPF₆ will undoubtedly promote the industrialization of SIBs.