Tuning the solvation structure with salts for stable sodium-metal batteries

摘要

Sodium-metal batteries are an appealing, sustainable, low-cost alternativeto lithium metal batteries due to the high abundance and theoretical specificcapacity (1,165 mA h g~(?1)) of sodium. However, the poor compatibility ofthe electrolyte with the cathode and anode leads to unstable electrode–electrolyte interphases. Here we introduce the concept of using a saltas a diluent, which enables the use of a single non-flammable solvent,such as trimethyl phosphate. By using sodium nitrate (NaNO_3) salt asa model diluent, we report a 1.1 M NaFSI–NaNO_3–trimethyl phosphateelectrolyte that forms a stable interface with sodium-metal anode. Inaddition, the formation of robust cathode–electrolyte interphases onNa(Ni_(0.3)Fe_(0.4)Mn_(0.3))O_2 cathode facilitates smooth phase transitions, thusleading to stable cycle life with a capacity retention of 80 over 500 cyclesat C/5 rate in NaNa(Ni_(0.3)Fe_(0.4)Mn_(0.3))O_2 cells. The work demonstrates apromising approach towards the development of safe, low-cost, sustainablehigh-performance sodium-metal batteries.