The Electrochemistry of Germanium Nitride with Lithium

Ge 3 N 4 was investigated for its electrochemical activity with Lithium as a possible negative electrode material for Li-ion batteries. Ge 3 N 4 was found to reversibly react with Li, exhibiting high capacity, 500 mAh/g, and maintaining good cycling stability. The reaction mechanism of Ge 3 N 4 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 ­ Ge 3 N 4 , of the electrode material mostly maintained their respective crystalline microstructure during cycling. A substantial integrated intensity decrease in the XRD Bragg reflections observed during the first lithiation and the concurrent emergence of diffuse rings in SAED suggest the reaction of Ge 3 N 4 with lithium may be limited thereby converting only the outermost shell of the Ge 3 N 4 crystal. The identification of α ­ Li 3 N and Ge at the end of the first delithiation using SAED supports a lithium/metal nitride conversion reaction process. The formation of the Li 3 N matrix was found to be consistent with a 50% irreversible capacity loss in the first cycle.