High-Safety Symmetric Sodium-Ion Batteries Based on Nonflammable Phosphate Electrolyte and Double NaV(PO) Electrodes

Sodium-ion batteries (SIBs) have been viewed as a promising candidate for grid-scale energy storage systems owing to their low cost and abundant Na resources. However, insufficient safety and poor cycling performance of current SIBs are hampering their implementation. Herein, we develop a symmetric SIB by employing NaV(PO) as both cathode and anode along with the nonflammable triethyl phosphate dissolving 0.9 M NaClO as the electrolyte. The symmetric SIB demonstrates a superior rate capability (35.1 mA h g at 32 C) and excellent cycling performance with a capacity retention of 88.9% after 500 cycles at 2 C. This work demonstrates a new avenue to construct safe and long-cycle-life SIBs with a simple electrode manufacturing process.