NaNO₃ Solubilization in Ester Electrolyte by CuCl₂ Additives to Enhance the Stability of Hard Carbon Anode

Cost-effective NaNO₃ additive in the electrolyte shows an outstanding stabilizing effect on hard carbon anodes by forming a Na₃N-rich solid electrolyte interface (SEI) film. However, the low solubility in solvent limits the effectiveness. In this study, a Cu²⁺ promoting NaNO₃ cluster dissociation strategy is developed based on the strong coordination effect of Cu²⁺ on NO₃^-. With the addition of 0.0078 M CuCl₂ in 1,2-dimethoxyethane (DME), the solubility of NaNO₃ increases from 0.0137 to 0.0224 M. The electrolyte system with NaNO₃ solubilization helps in the construction of a more NaF, Na₃N, and NaCl-rich SEI film. Results show that these inorganics significantly enhance the ionic conductivity, electronic insulation, and mechanical properties of the SEI film and ensure that the SEI film on the hard carbon electrode surface remains structurally intact after long cycling, extending the battery life. As a result, after 300 cycles, the capacity retention of cells increases from 85.75% to 91.52%. This study develops a strategy to achieve nitrate solubilization and enhances the effectiveness of electrolyte interface engineering in improving battery performance.