Toward High Temperature Sodium Metal Batteries via Regulating the Electrolyte/Electrode Interfacial Chemistries

Rechargeable batteries based on sodium metal anodes (SMAs) are endowed with much higher energy density than traditional sodium-ion batteries. However, the use of SMAs brings intrinsic challenges of dendrite growth and unstable solid/electrolyte interphase (SEI) formation. This situation can be further exacerbated at high temperature (>55 °C, HT). Here, we resolve such "HT-challenge" by formulating a thermally stable sulfolane (SL)-based electrolyte that regulates the electrode/electrolyte interfacial chemistries. Besides rapid Na anode passivation enabled by fluoroethylene carbonate (FEC) molecules, a nitrile-based 1,3,6-hexanetricarbonitrile (HTCN) cosolvent is simultaneously introduced, whose three electron-rich -C≡ N groups interact with the electropositive metal ions of Na3V2(PO4)2O2F, shielding away solvent attacks occurring at the cathode interface. As a result, we realize a high capacity retention (91.7% after 500 cycles at 1 C) for the Na/Na3V2(PO4)2O2F cell at 60 °C, with a high average carbon equivalent (CE) of ∼99.6%. Even at 80 °C, the cell still delivers ∼89.1% of its initial capacity after 100 cycles, whereas the control sample fails rapidly within 30 cycles.