The insertion mechanism of lithium into Mg2Si anode material for Li-ion batteries

The reaction mechanism of lithium insertion into Mg2Si was studied using va rious analytic techniques including electrochemical measurements, X-ray dif fraction (XRD), and Auger electron spectroscopy (AES). Electrochemical test s demonstrated that 1 mol Mg2Si reacted with 3.9 mol Li from which the init ial capacity obtained was approximately 1370 mAh/g. Ex situ XRD and AES dat a showed that lithium intercalated into the Mg2Si lattice first followed by alloying with Si and Mg. The degradation mechanism of Mg2Si during cycling was investigated because the Mg2Si materials degraded rapidly within ten c ycles. The electrode material disintegrated and Li remained within the acti ve material after ten cycles. The XRD and scanning electron microscope data suggested that the degradation mechanism of Mg2Si was due to the volume ch ange during the alloying/dealloying reaction, and the volume expansion/cont raction made the Mg2Si electrode materials electrically isolated. (C) 1999 The Electrochemical Society. S0013-4651(99)05-068-5. All rights reserved.