Ionic-Diluent-Engineered Ether Electrolyte for Rechargeable Sodium Batteries

Rechargeable sodium batteries (RSBs) are pivotal for fulfilling the energy requirements of large-scale grid storage. Organic-ether-based electrolytes still suffer from poor antioxidation stability against the cathode materials. Here we introduce an “ionic diluent”, N-butyl-N-methyl-piperidinium bis(trifluoromethyl)imide (PP14TFSI), into the ether-based electrolyte to stimulate the formation of an “anion-enriched” Na+ solvation sheath via creating an anion-rich (canion/cNa+ > 1) environment. The tailored solvation structure endows the modified electrolyte with an improved oxidation potential (>4.8 V vs Na+/Na) while maintaining an ionic conductivity of 4.12 mS cm–1 at 30 °C. Both Na3V2(PO4)2F3(NVPF)-based and NaNi1/3Fe1/3Mn1/3O2(NFM)-based RSBs demonstrate enhanced interfacial stability, achieving 94.4% capacity retention after 1000 cycles (4.3 V) and 83.5 mAh g–1 after 250 cycles at 1C (4.2 V), respectively. The impressive performances of NVPF||Hard carbon full cell further indicate the practical applicability of the designed electrolyte and provides insights into the rational design of RSBs via electrolyte engineering.