Fine-tuning Li+ solvation structure enabled by steric effect and solvating chemistry of the anion for practical electrolyte engineering

Electrolytes capable of stably functioning in high-voltage lithium metal batteries are forwardly pursued to exceed the energy storage limits of current devices. Practical electrolyte engineering is required to promote anode and cathode compatibility without sacrificing bulk transfer capability and cost-effectiveness. Herein, based on the steric effect and solvating chemistry of anions, we propose a fine-tuning of carbonate-based electrolytes with high anodic stability to derive an optimal solvation structure for better interfacial behaviors of Li+. This strategy enhances the Li plating/stripping Coulombic efficiency in the Li||Cu cell to an ultra-high value of 99.61% without increasing the cost and lowering the ionic conductivity of the electrolytes. Besides, when the design is applied to practical Li||NMC811 full cells, a capacity retention of 88.5% and an average Coulombic efficiency of 99.74% after 200 cycles are obtained at a current density of 1 C. This work provides insights into the functions of anions in electrolytes and demonstrates a novel designing perspective for high-voltage lithium metal battery electrolytes.