A Trifluoroacetate-based Concentrated Electrolyte for Symmetrical Aqueous Sodium-ion Battery with NASICON-type Na₂VTi(PO₄)₃ Electrodes

Abstract

A safe and low-cost aqueous electrolyte, in which maximum amount of sodium trifluoroacetate (NaTFA) is dissolved (26 mol kg⁻¹), showed high ionic conductivity of 23 mS cm⁻¹ and provided wide electrochemical stability window of 3.1 V. These attractive features may originate from so-called “water-in-salt” effect of the highly concentrated electrolyte in addition to a robust fluoride layer formed on anode thereof. This novel electrolyte enabled reversible operation of NASICON-type Na₂VTi(PO₄)₃ as symmetrical operation based on V^3+/4+ at cathode and Ti^3+/4+ and V^2+/3+ at anode, respectively.