The electrochemistry of germanium nitride with lithium

Ge₃N₄ was investigated for its electrochemical activity with Lithium as a possible negative electrode material for Li-ion batteries. Ge₃N₄ was found to reversible react with Li, exhibiting high capacity, 500 mAh/g, and maintaining good cycling stability. The reaction mechanism of Ge₃N₄ with lithium was investigated in detail using in situ and ex situ X-ray diffraction (XRD) in reflection, in situ XRD in transmission, ex situ transmission electron microscopy, and selected-area electron diffraction (SAED). The two-phases, α- and β-Ge₃N₄, of the electrode material mostly maintained their respective crystalline microstructure during cycling. A substantial integrated intensity in the XRD Bragg reflections observed during the first lithiation and the concurrent emergence of diffuse rings in SAED suggest the reaction of Ge₃N₄ with lithium may be limited thereby converting only the outermost shell of the Ge₃N₄ crystal. The identification of α-Li₃N and Ge at the end of the first delithiation using SAED supports a lithium/metal nitride conversion reaction process. The formation of the Li₃N matrix was found to be consistent with a 50% irreversible capacity loss in the first cycle.