Ultralow-Concentration (0.1M) Electrolyte for stable bulk alloy (Sn, Bi) anode in Sodium-ion battery via Regulating Anions Structure

Alloy anodes (e. g. Sn, Bi) applied in sodium-ion batteries (SIBs) have received a lot of interest due to their increased capacity and mild sodiation/desodiation potentials. However, severe capacity fading caused by high volume changes, as well as brittle SEI issues, limit the practical uses. An electrolyte engineering using ultra-low concentration electrolyte strategy containing sodium salt with super bulky BPh4- anions and 1,2-dimethoxyethane (DME) solvent is employed in this work to stabilize micron Sn and Bi anodes, where a cation solvation structure including the type and location of the anions plays a critical role. In this designed 0.1M NaBPh4-DME electrolyte system, Na+ has a faster migration rate due to substantial steric hindrance of BPh4- anions and side reactions on the electrode/electrolyte interface are decreased because it is difficult for BPh4- anions to get close to the alloy anode. This electrolyte design may expose the core cause of alloy anode failure and pave the way for a new approach to stabilizing alloy anodes in SIBs.