Efficient Decomposition of Electrolyte Salt Reconstructing Helmholtz Plane for Long Life Sodium-Ion Batteries

The properties of the solid electrolyte interphase (SEI) film determine the performance of batteries. This film is proven to be mainly formed by the solid products of the electrolyte salt in the inner Helmholtz plane. However, the SEI derived by the limited decomposition of salt has an imperceptible dissolution tendency and sluggish Na+ diffusion kinetics, resulting in the restriction of the further increase of battery cycle stability. This study employed the strategy of repeatedly charging and discharging within a certain voltage range to realize the efficient decomposition of NaBF4 and lead to producing more NaF to reconstruct the configuration of the Helmholtz plane. In addition, the dissolved NaF in electrolytes is further utilized to build a double electric layer with a high electric field at the electrode–electrolyte interface, facilitating the simultaneous reduction of NaBF4 and solvents. Consequently, a significant number of boron-containing compounds were produced, leading to the improved stability of the SEI film and enhanced battery cycling performance. By employing this approach, Na||HC half-cells showed a significant improvement in the capacity retention rate, increasing from 71.5 to 91.1% after 500 cycles at 1C. Additionally, the remaining capacity also improved from 256 to 270 mAh g–1. This method opens up an avenue for enhancing the stability of battery cycling without altering the composition of electrolytes.