Effect of particle size on lithium intercalation rates in natural graphite

The intercalation rate of Li+-ions in flake natural graphite with particle size that ranged from 2 to 40 mum was investigated. The amount of Li+-ions that intercalate at different rates was determined from measurement of the reversible capacity during deintercalation in 1 M LiClO4/1:1 (volume ratio) ethylene carbonate-dimethyl carbonate. The key issues in this study are th e role of particle size and fraction of edge sites on the rate of intercala tion and deintercalation of Li+-ions. At low specific current (15.5 mA/g ca rbon), the composition of lithiated graphite approaches the theoretical val ue, x = 1 in LixC6, except for the natural graphite with the largest partic le size. However, x decreases with an increase in specific current for all particle sizes. This trend suggests that slow solid-state diffusion of Li+- ions limits the intercalation capacity in graphite. The flake natural graph ite with a particle size of 12 mum may provide the optimum combination of r eversible capacity and irreversible capacity loss in the electrolyte and di scharge rates used in this study. (C) 2001 Elsevier Science B.V. All rights reserved.