RATE EFFECT ON LITHIUM-ION GRAPHITE ELECTRODE PERFORMANCE

The electrochemical performance of lithium-ion graphite electrodes wit h particle diameter in the range of 6-44 mu m was evaluated at differe nt discharge (intercalation)/charge (deintercalation) rates (C to C/60 ). The electrode capacity depends on both the average particle size an d rate. With a simple rate programme, the electrode performance is dep endent on the cycling rate, The capacity of small graphite particles ( 6 mu m) at C/2 rate was 80% of that achieved at C/24 rate (similar to 372 mAh g(-1)). The capacity of large graphite particles (44 mu m) obt ained at fast rates (C/2) was only 25% of that obtained under near-equ ilibrium conditions (C/24). The electrode capacity, however, is nearly independent of the charge rate when the electrode is fully intercalat ed using a modified rate programme containing a constant-voltage hold at 0.005 V (vs Li+/Li) for several hours. The electrochemical behaviou r is related to the physicochemical properties of the graphite particl es.