Lithium nitrate/Lithium bis(oxalate)borate dual-salt in sulfolane as nonflammable electrolyte for stable lithium-metal batteries

Lithium metal batteries have shown great potential in energy storage applications, and the development of novel electrolytes provide new opportunities to enhance their performance. This study proposes an innovative dual-lithium-salt electrolyte composed of lithium nitrate (LiNO 3 ) and lithium bis(oxalato)borate (LiBOB) in sulfolane solvent. The electrolyte exhibits high Li plating/stripping reversibility and stability, effectively improving electrode interfacial compatibility. The introduction of LiBOB regulates the solvation structure, optimizes lithium-ion transport, and promotes the formation of a robust solid electrolyte interphase, which is crucial for interfacial stability and prolonged battery life. NMR spectra reveal that oxygen-rich groups in bis(oxalato)borate anion (BOB - ) participate in Li + solvation, increasing electron cloud density. This structural reorganization facilitates Li + dissociation and further improves ionic conductivity. The electrolyte maintains stable Li plating/stripping voltage profiles with significantly lower polarization over long-term cycling in Li//Li cells, demonstrating smooth Li + transport and stable interfaces that suppress dendrite growth and impedance rise. In Li//Cu cell, the electrolyte achieves an average coulombic efficiency of 97.85 %, showing high reversibility and stable interfacial behavior. Furthermore, in the Li//LiMn 2 O 4 half-cell tests, the electrolyte demonstrated outstanding performance under various operating conditions. It achieved stable cycling for 680 cycles at 100 mA g −1 while maintaining an average coulombic efficiency of 99.2 % and a capacity retention of 84.54 %. Even at a high current rate of 500 mA g −1 , the cell continued to operate stably for more than 260 cycles with a coulombic efficiency of approximately 99.2 %. Under elevated-temperature conditions of 60 °C, the electrolyte also exhibited excellent cycling stability and thermal tolerance. Overall, the novel electrolyte combines high ionic conductivity, superior thermal and electrochemical stability, and long cycling life, confirming its potential as a safe and high-performance electrolyte candidate for lithium metal batteries.