Temperature-dependent properties of FePO4 cathode materials

The temperature of formation and crystallinity of iron phosphate, FePO4, is critical in determining its electrochemical behavior in lithium cells. Amorphous FePO4 formed by heating amorphous iron phosphate dihydrate was found to have good capacity both in chemical and electrochemical lithiation. Initial capacities of up to 140 mAh/g were obtained at a current density of 0.2 mA/cm2. Material formed from crystalline iron phosphate dihydrate was found to be much less active, due to both the crystallinity of the product and to the iron being in tetrahedral coordination. The trigonal quartz phase of FePO4 loses almost all capacity after heating to 700°C, which might be due to glass formation on the surface.