Stabilizing the cathode–electrolyte interphase and promoting Na+ desolvation by a tris(trimethylsiloxy)borate additive for sodium-ion batteries

Abstract

Layered metal oxide NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) is a promising cathode for high energy density sodium-ion batteries. However, it suffers from issues such as poor interfacial stability and dissolution of transition metal ions, which result in unsatisfactory cycle and rate performance. Herein, tris(trimethylsiloxy)borate (TMSB) is introduced into the electrolyte to improve the interfacial stability and facilitate the Na⁺ transfer. First, TMSB can preferentially form a stable and uniform interface layer on the NFM cathode surface, enhancing the stability of the electrode–electrolyte interface and reducing the dissolution of transition metal ions. In addition, TMSB can weaken the interaction between Na⁺ and solvent molecules, facilitating Na⁺ desolvation, which improves Na⁺ diffusion and deposition. Therefore, the addition of 2% TMSB improves the cycle and rate performance of NFM||Na cells. After 200 cycles at 1C, the capacity retention of the NFM||Na battery with 2% TMSB electrolyte was 86.38%, compared to only 72.03% for the baseline electrolyte. Additionally, TMSB extends the cycle life of Na||Na symmetric cells (from 180 hours to 280 hours). This work provides a reference for improving the interface stability and Na⁺ dynamics of sodium-ion batteries through a single electrolyte additive.