Regulating Solvation Shell to Fortify Anion–Cation Coordination for Enhanced Sodium Metal Battery Stability

The use of sodium metal as an anode presents a promising avenue for high energy density sodium rechargeable batteries given its high specific capacity and low redox potential. However, sodium metal batteries (SMBs) encounter significant challenges, including interfacial parasitic reactions and dendrite growth. Developing a robust solid electrolyte interphase (SEI) is crucial for SMB engineering. This study introduces hydrofluoroether as a diluent in high-concentration electrolytes, effectively modifying the solvation structure to enhance ion-pair coordination, which leads to an inorganic-rich SEI, mitigating sodium depletion and dendrite formation. Consequently, localized high concentration electrolytes achieve a 98.3% Coulombic efficiency in Na||Cu batteries, while the Na||NaFe1/3Ni1/3Mn1/3O2 battery retains 86.4% capacity after 750 cycles at 1C. Additionally, the Na||Na3V2(PO4)3 battery achieves an exceptional average Coulombic efficiency of 99.97% at 1C, with a capacity retention of 95.4% after 517 days. This study provides a framework for enhancing efficiency and longevity in SMBs that can be applied to other battery systems.