Investigation of the chemical stability of Li7MnN4 in air

The chemical reactivity in air of the promising metallic nitride Li7MnN4 as negative electrode for Li-ion batteries has been studied. The evolution of the ageing process with exposure time has been examined by XRD and the degradation kinetics has been determined. This cubic metallic nitride is found to be much less sensitive to the air atmosphere than that exhibited by the lamellar nitridocobaltates Li3−2xCoxN (0.1 ⩽ x ⩽ 0.44). A fast oxidation step in air leads to the delithiated Li6.2MnN4 phase after a few hours and is thereafter progressively destroyed by reaction with moisture leading to the formation of LiOH⋅H2O and Li2CO3. Electrochemical experiments on various aged samples support these results. The demonstration of Li7MnN4 storage in dry air is showed to constitute a relevant solution to preserve the integrity of the nitride host lattice and then its excellent electrochemical properties.