Energy Dispersive X-ray Diffraction (EDXRD) of Li 1.1 V 3 O 8 Electrochemical Cell
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Energy Dispersive X-ray Diffraction (EDXRD) of Li1.1V3O8 Electrochemical Cell Qing Zhang1, Andrea M. Bruck2, David C. Bock3, Jing Li1, Eric A. Stach4, Esther S. Takeuchi1,2,3*, Kenneth J. Takeuchi1,2*, Amy C. Marschilok1,2* 1
Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794 2 Department of Chemistry, Stony Brook University, Stony Brook, NY 11794 3 Energy Sciences Directorate, Brookhaven National Laboratory, Upton, NY 11973 4 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973 *corresponding authors: (EST) [email protected], (KJT) [email protected], (ACM) [email protected] ABSTRACT In this study, we conducted the first energy dispersive x-ray diffraction (EDXRD) experiments on Li/Li1.1V3O8 coin cells discharged to different lithiation levels in order to investigate the phase transitions upon electrochemical reduction. The phase transformation from layered Li-poor α to Li-rich α to defect rock-salt β phase was confirmed with cells of different lithiation stages. No spatial localization of phase formation was observed throughout the cathodes under the conditions of this measurement. INTRODUCTION The layered material Li1+nV3O8 (n=0-0.2) is recognized as an interesting cathode material for lithium based batteries, due to its high theoretical capacity (362 mAh·g-1) and power capability.(1, 2) The Li1+nV3O8 structure can be viewed as a stack of V3O8 layers with Li+ ions in the interlayer space. Each V3O8 consists of alternating edge-sharing VO5 trigonal bi-pyramids and edge-sharing VO6 octahedrons.(3) Upon lithiation to Li~2.5V3O8, the parent layered phase (Li-poor α) undergoes distortion to form the less crystalline Li-rich α while maintaining the same V3O8 layer structure. Upon further lithiation to Li~4V3O8, the layered α phase transforms to a defect-rock salt phase β. Further lithiation beyond Li4V3O8 takes place in the β phase.(3, 4) The transition from the α to the β phase has only been evaluated on bulk electrodes as a function of depth of discharge. To get full utilization of an active material in the electrode, homogeneous discharge is critical where the phase transition occurs evenly throughout the entire electrode. If phase transition is localized, it could prevent full utilization of the active material and result in lower delivered capacity. Therefore, a composite electrode must have a full percolation network to allow for good electron conduction, while the active material retains good intrinsic Li+ conductivity. Energy dispersive x-ray diffraction (EDXRD) uses high energy X-rays that can penetrate the steel casing of a coin cell and record XRD patterns as a function of spatial location in the cell. Recent studies by Kirshenbaum et al. have shown a rate dependence on the homogeneity of discharge of the Ag2VP2O8 material, a bimetallic, layered cathode material.(5) The reduction of Ag+ to Ag0 was an indicator of discharge homogeneity with more localized Ag0 formation taking place at
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