A free-sealed high-voltage aqueous polymeric sodium battery enabling operation at −25°C

Abstract

An increasing demand for electric vehicles and flexible electronics focuses attention on developing a safe, high-energy, and sustainable battery that can work under severe conditions. Emerging high-voltage aqueous batteries based on highly concentrated salts and molecular crowding electrolytes are likely to be hampered by their poor low-temperature performance because of a high freezing point and salting out at low temperature. Inspired by the antifreezing ionogel electrolyte for transport measurements at subzero temperatures, we design a water-in-ionogel electrolyte with a low salt-concentration (2m NaTFSI) and high operational voltage (3.0 V) by changing the hydrogen bonding and introducing fluoride additives for low-temperature operation. A full cell with a P2-type Na 2/3 Mn 2/3 Co 1/3 O 1.98 F 0.02 cathode and hard-carbon anode could deliver high energy densities of 109 and 23.4 Wh kg −1 at room temperature and −25°C. This eco-friendly aqueous polymeric battery could be free sealed and perform in water. This work opens an avenue for designing high-energy, free-sealed aqueous batteries for low-cost, sustainable energy storage, enabling subzero temperature operation. • F-containing water-in-ionogel electrolyte enables high-voltage, low-temperature operation • F doping endows Mn-based P2-type cathodes with enhanced hydrophilicity and rate performance • The fabricated aqueous polymeric sodium-ion battery enables subzero temperature operation • The free-sealed battery can work under severe condition with advantage in weight Rong et al. demonstrate that a water-in-ionogel (WIG) electrolyte with low salt concentration (2m NaTFSI) and high operational voltage (3.0 V) can rival the high voltage of typical “water-in-salt” and “molecular crowding” electrolytes. The WIG electrolyte, exhibiting superior antifreezing properties without salting out at low temperature and high stability against sodium metal, is a promising candidate for aqueous polymeric batteries.