Water plays a key role in the nitrogen conversion pathway in lithium-nitrogen batteries

Lithium-nitrogen batteries can deliver high energy densities using environmentally friendly and abundant nitrogen as a resource. According to previous studies, the nitrogen conversion pathway is expected to consist of formation and decomposition of lithium nitride. However, the reaction deserves more attention prior to forming a consensus. The thermodynamic equilibrium reaction potential for lithium nitride is low, 0.44 V, versus Li/Li+, which is far from the higher operational experimental potentials. In this work, with a series of characterizations from macro- to microscale in initial and subsequent cycles, we reveal that trace water in the electrolyte would promote the nitrogen reduction reaction at a higher working potential in the discharge process. We invoke a reaction in the water-containing battery where formation of lithium amide and lithium hydroxide is key. This finding suggests a new nitrogen conversion pathway in lithium-nitrogen batteries and will provide insight for further studies on metal-nitrogen batteries.