Bulk bismuth anodes for wide-temperature sodium-ion batteries enabled by electrolyte chemistry modulation

Sodium ion batteries (SIBs) are considered reliable supplies for next-generation energy devices. However, there is a limited understanding of strategies to prevent the performance deterioration of SIBs under extreme temperature conditions. This study aimed to address this challenge by developing modified electrolyte chemistry to achieve stable wide-temperature SIBs. Weakly Na⁺-solvating solvent 2-methyltetrahydrofuran (MeTHF) was used to promote the kinetics of Na⁺ de-solvation. Moreover, 1,2-dimethoxyethane (DME) was introduced as a co-solvent because of the high solubility for Na salts and the coupling reaction mechanism with the Bi electrode. The formulated electrolyte not only endows an anion-dominated NaF-rich solid electrolyte interface (SEI) layer, but also reduces the energy required for the Na⁺ across the SEI layer (from 291.2 to 89.6 meV). Consequently, Na||Bi half batteries achieve stable cycles at 400 mA g^-1 at -20, 20 and 60 °C, respectively. Meanwhile, the extreme operating temperature of the batteries can be extended to -40 and 80 °C, which exceeds those of most current lithium/sodium-based batteries. Furthermore, full batteries employing Na₃V₂(PO₄)₃ as the cathode material exhibit stable operation over a wide temperature range of -20 to 60 °C. This electrolyte design strategy presented in this study shows significant promise for enabling wide-temperature SIBs with improved performance.