High energy density Na-metal batteries enabled by a tailored carbonate-based electrolyte

High-voltage sodium metal batteries (SMBs) offer a viable way toward high energy densities. However, they synchronously place severe demands on the electrolyte for the notorious reactivity of Na-metal and the catalytic nature of aggressive high-voltage chemistries. Here, we fabricate a tailored carbonate-based electrolyte involving lithium difluorobis(oxalato) phosphate (LiDFBOP) as a multifunctional additive, where DFBOP- anions can generate stable and robust interphases on both the anode and cathode. Meanwhile, Li+-ions can take part in the solvation structure to regulate the electrolyte stability as well as resist dendritic deposition via electrostatic shielding. Such optimization effectively realizes high coulombic efficiency (98.6%) and prolonged life (2600 h) of Na plating/stripping together with the upgraded reversibility of the Na3V2(PO4)(2)F-3 cathode. Moreover, the assembled 4.5 V Na||Na3V2(PO4)(2)F-3 SMB achieves impressive cycling stability with 90% capacity retention after 220 cycles and a high energy density of 295 W h kg(-1) with limited Na. The proposed electrolyte strategy can shed light on further optimization for high-energy sodium metal chemistries.

Automated summary

Electrolyte plays a critical role in high-energy sodium metal batteries. In this study, a tailored carbonate-based electrolyte with lithium difluorobis(oxalato) phosphate (LiDFBOP) as an additive was fabricated to achieve stable electrode reactions and control electrolyte stability. The optimized electrolyte demonstrated improved coulombic efficiency, prolonged battery life, high energy density, and cycling stability for high-energy sodium metal chemistries.