Nafion-212 Membrane Solvated by Ethylene and Propylene Carbonates as Electrolyte for Lithium Metal Batteries

The use of cation-exchange membranes as electrolytes for lithium metal batteries can prevent the formation of lithium dendrites during extended cycling and guarantee safe battery operation. In our study, the Nafion-212 membrane in lithium form solvated by a mixture of ethylene carbonate and propylene carbonate (EC-PC) was used as an electrolyte in a lithium metal battery with the LiFePO₄ cathode. The Nafion-212-EC-PC electrolyte is electrochemically stable up to 6 V, indicating its suitability for high-energy density batteries. It has an ionic conductivity of 1.9 × 10^-4 S/cm at 25 °C and a high lithium transference number. The symmetric Li|Nafion-212-EC-PC|Li cell shows a very low overvoltage of ~0.3 V at a current density of ±0.1 mA/cm². At 25 °C, the LiFePO₄|Nafion-212-EC-PC|Li battery exhibits a capacity of 141, 136, 125, and 100 mAh/g at 0.1, 0.2, 0.5, and 1C rates, respectively. It maintains a capacity of 120 mAh/g at 0 °C and 0.1C with stable performance for 50 charge/discharge cycles. The mechanism of conductivity and capacity retention at low temperatures is discussed.