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 reversibly 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, alpha- and beta-Ge3N4, 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 Ge3N4 with lithium may be limited thereby converting only the outermost shell of the Ge3N4 crystal. The identification of alpha-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. (C) 2003 The Electrochemical Society.