Ultra-long cycle sodium ion batteries enabled by the glutaric anhydride additive.

For sodium-ion batteries, solving the issue of short cycle life is key to their large-scale adoption in the industry, and the electrolyte plays an important role on this. Herein, this work aims to design a practical sodium ion battery electrolyte with industrial application value and introduces anhydride compounds as additives for the first time. Meanwhile, by adjusting the solvent composition and using a combination of ether and ester solvents, the optimal electrolyte formulation of 1 M NaPF (sodium hexafluorophosphate) + DME (glycol dimethyl ether)/VC (vinylidene carbonate) (1 : 1, v/v) + 2 wt% GA (glutaric anhydride) is designed. Na-VC, which has the highest occupied molecular orbital in this electrolyte, is preferentially oxidized to form a cathode electrolyte interface on the cathode. And synchronously, Na-GA with the lowest unoccupied molecular orbital is preferentially reduced to form a surface electrolyte interface on the anode. This electrolyte can achieve simultaneous film formation on both sides of the electrode, thus greatly increasing the cycle life of the sodium-ion battery. For example, the Na‖NVP (sodium vanadium phosphate) battery still maintains a specific capacity of 91.16 mA h g with a capacity retention rate of 85.06% after 2500 cycles. And the NVP‖HC (hard carbon) full battery also maintains a capacity retention rate of 66.50% after 800 cycles. This work will provide important ideas and strong evidence for the industrial application of sodium ion battery electrolytes with long cycle life.