Inhibition of sodium dendrites by solvent structural reorganization for non-flammable high-performance sodium-metal batteries

Abstract

NaPF₆ is a common electrolyte for sodium-metal batteries (SMBs) due to its high ionic conductivity and stability. However, SMBs using NaPF₆ electrolyte face the risk of electrolyte hydrolysis and disordered growth of sodium dendrites. Herein, N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was introduced into triethyl phosphate solvent for stabilizing the electrolyte and inhibiting the growth of dendrites in SMBs. Self-extinguishing experiments show the non-flammability of the electrolyte to realize high cycling safety of the cell. Simulations explored the solvent structure of the electrolyte with the addition of BSTFA. Experimental and Gibbs free energy calculations demonstrate the spontaneous reaction of BSTFA with trace amounts of water, thereby protecting NaPF₆. By in situ optical microscopy, it was found that the stable SEI layer generated by the reduction of the BSTFA additive at the sodium anode inhibited the growth of sodium dendrites, and the excellent cycling performance of the Na₃V₂(PO₄)₃/Na full cell further proved the effect of the addition of BSTFA.