Effect of Electrode Parameters on LiFePO[sub 4] Cathodes

electrodes with thicknesses from were coated on Al current collectors. The electrochemical characteristics of these electrodes depend strongly on film thickness, with the largest rate capability for the thinnest film—a electrode can be discharged at a current rate of and still give a capacity of . This shows great promise for high-power applications such as hybrid electrical vehicles. Increasing the amount of carbon in the electrode, decreasing the packing density, or using an electrolyte with lower viscosity and higher ionic conductivity improved the rate performance. This suggests that the thickness effect is caused by a larger electrode resistance and a slower Li-ion conduction through the electrolyte for thicker films. Electrode thickness in turn affects the energy density of a battery, because the percentage of inactive materials increases with decreasing film thickness. An energy density prospect for a 18650-type battery with these electrodes gives a maximum capacity of at rate for a electrode. This corresponds to a volumetric and gravimetric energy density of and , respectively. The effective Li diffusivity in the active material is estimated to be of the order of .