An acetamide additive stabilizing ultra-low concentration electrolyte for long-cycling and high-rate sodium metal battery

Due to the abundant reserves and low cost of sodium resources, sodium metal batteries (SMBs) can be used as a promising energy storage technology with high energy density. Recently, ultralow-concentration electrolytes (ULCEs) with 0.3 mol/L (M) NaPF6 are greatly attractive because of their low cost and high permeability. However, the cycle life and rate performance of SMBs in ULCEs are limited by the high reactivity of sodium metal anodes. Here, an acetamide additive, N, O-bis(trimethylsilyl) trifluoroacetamide (BSTFA), is introduced into an ULCE (0.3 M NaPF6 in EC/PC, 1:1 vol %) for stabilizing the electrolyte and fabricating a highly conductive interface in SMBs. Theoretical and experimental results prove that BSTFA can scavenge HF and H2O in the NaPF6-based electrolyte spontaneously and inhibit the hydrolysis reaction of NaPF6. Owing to protective interface layers on sodium metal anode and Na3V2(PO4)3 (NVP) cathode, the Na||NVP battery in 2% BSTFA-containing ULCE shows a high-capacity retention rate of 92.63% after 1955 cycles at 2 C and a superior rate capability of exceeding 105 mAh g−1 at 40 C.