Rationalizing Na-ion solvation structure by weakening carbonate solvent coordination ability for high-voltage sodium metal batteries

Commercial carbonate-based electrolytes feature highly reactive activities with alkali metals, yielding low Coulombic efficiencies and poor cycle life in lithium metal batteries, which possess much higher chemical activity in the rising star sodium metal batteries. To be motivated, we have proposed that decreasing the solvent solvation ability in carbonate-based electrolytes stepwise could enable long-term stable cycling of high-voltage sodium metal batteries. As the solvation capacity reduces, more anions are enticed into the solvation sheath of Na+, resulting in the formation of the more desirable interphase layers on the surface of the anode and the cathode. The inorganic-dominated interphases allow highly efficient Na+ deposition/stripping processes with a lower rate of dead sodium generation, as well as maintain a stable structure of the high-voltage cathode material. Specifically, the assembled Na||Na3V2(PO4)2F3 battery exhibits an accelerated ion diffusion kinetics and achieves a higher capacity retention of 85.9% with during the consecutive 200 cycles under the high voltage of 4.5 V. It is anticipated that the tactics we have proposed could be applicable in other secondary metal battery systems as well.