Freestanding Mo3N2 nanotubes for long-term stabilized 2e- intermediate-based high energy efficiency Li-CO2 batteries

Li-CO2 batteries are considered one of the promising power sources owing to ultrahigh energy density and carbon fixation. Nevertheless, the sluggish reaction kinetics of 4e(-) discharged process (Li2CO3) impede its potential application. One of the efficient strategies for developing cathode catalysts is to stabilize 2e(-) intermediate Li2C2O4 and improve reaction reversibility. However, long-term catalysts of stabilized Li2C2O4 are barely achieved, whereas cycle stability is far from satisfactory level. Herein, non-noble metal-based Mo3N2 is synthesized and employed as freestanding cathodes for Li-CO2 batteries. Owing to rich delocalized electrons of Mo2+ and reversible electron localization structure, freestanding Mo3N2 cathodes exhibit a low charge potential (3.28 V) with an ultralow potential gap (0.64 V), high energy efficiency of up to 80.46%, fast rate capability, and outstanding cycle stability (>910 h). In situ experiments and theoretical calculation verify that Mo3N2 stabilizes 2e(-) Li2C2O4 intermediate by the interaction of Mo2+ as active sites where Mo2+ promotes the transfer of outer electrons to O, prevents its disproportionation to Li2CO3, and promotes reaction kinetics, contributing to high energy efficiency and outstanding cycle reversibility. In addition, the pouch-cells deliver ultrahigh energy density of up to 6350.7 W h kg(-1) based on the mass of cathode materials.