HIGH-CAPACITY LITHIUM-ION CELLS USING GRAPHITIZED MESOPHASE-PITCH-BASED CARBON-FIBER ANODES

We have developed high-capacity lithium-ion cells using graphitized me sophase-pitch-based carbon fiber (MCF) as an anode material, The graph itized MCF is a highly graphitized carbon fiber with a radial-like tex ture in the cross section. This structure contributes to the rapid dif fusion of lithium ions inside the carbon fiber. The diffusion coeffici ent of lithium ions in the graphitized MCF was one order of magnitude larger than those for graphite, resulting in an excellent high-rate pe rformance of the carbon electrode. The graphitized MCF anode showed la rger capacity, a higher rate capability, and better reversibility than the graphite anode. The 863448 size (8.6 mm x 34 mm x 48 mm) prismati c cell with the graphitized MCF anode exhibited a large capacity of > 1000 mAh. At 3 A discharge, the prismatic cell had 95% of its capacity at 0.5 A discharge with a mid-discharge voltage of 3.35 V, The cell m aintained > 85% of its initial capacity after 500 cycles and showed hi gh capacity at -20 degrees C. It has thus been demonstrated that the p rismatic cell using the graphitized MCF anode has excellent performanc e, and is an attractive choice for the power sources of cellular phone s and other appliances. (C) 1997 Elsevier Science S.A.