Electrochemical Conversion of Nitrogen Trifluoride as a Gas-to-Solid Cathode in Li Batteries.

Nonaqueous metal-gas batteries have emerged as a growing family of primary and rechargeable batteries with high capacities and energy densities. We herein report a high-capacity primary Li-gas battery that uses a perfluorinated gas, nitrogen trifluoride (NF3), as the cathode reactant. Gravimetric capacities of ∼1100 and 4000 mAh/gC are achieved at 25 and 55 °C, respectively (at 20 mA/gC), with discharge voltages up to 2.6 V vs Li/Li+. NF3 reduction occurs by a 3e-/NF3 process, yielding polycrystalline lithium fluoride (LiF) on a carbon cathode. The detailed electrochemical NF3 conversion mechanism is proposed and supported by solid- and liquid-phase characterization and theoretical computation, revealing the origin of observed discharge overpotentials and elucidating the significant contribution of N-F bond cleavage. These findings indicate the value of exploring fluorinated gas cathodes for primary batteries; moreover, they open new avenues for future targeted electrocatalyst design and cathode materials synthesis applications benefiting from conformal coatings of LiF.