Microstructural Characterization of Damage Mechanisms of Graphite Electrodes in Li-ion Cells

摘要

Understanding microstructural aspects of graphite electrode damage mechanisms is essential to control capacity loss and enhance energy efficiency of Li-ion batteries. By applying novel material characterization techniques including in-situ digital microscopy and focused ion-beam methods for high resolution TEM, the micromechanisms of graphite surface and subsurface damage were identified. Deposition of Li-C compounds at the tips of cracks generated predominantly during the first de-lithiation cycle, and bridging of crack faces by interconnecting lithiated graphite fibers, were observed to delay crack growth. During the solid electrolyte interphase(SEI)formation process, the Li-ion diffusion coefficient(D_(Li)~+)at the electrode/electrolyte interface was controlled by the voltage scan rate(dV/dt); for dV/dt＜3.00 mVs~(-1), and at low D_(Li)~+(0.57×10~(-8)c㎡s~(-1))a uniform and continuous SEI layer was formed that reduced graphite particle loss.