Mixtures of TiO2•0.2H2O and LiFePO4 as Li-ion Battery Cathode Materials

Mixtures of TiO2 center dot 0.2H(2)O (HTO) and LiFePO4 were prepared via three main composite methods: 2-2 series model, 2-2 parallel model and 3-3 model. HTO has been reported to exhibit high specific capacity (similar to 200 mAh/g at 1 C) as well as excellent cycle property, whereas its plateau voltage is too low (about 1.7 V vs. Li) as a cathode material. LiFePO4 is a promising cathode material for its high voltage plateau (about 3.4 V vs. Li), low cost and high specific capacity (similar to 150 mAh/g at 1 C). However, because of its low conductivity, the rate property as well as cycle property is limited. The mixtures of HTO and LiFePO4 were considered to combine the advantages of both materials. By comparison, the 2-2 parallel model excelled in both rate property and cycle property than two other models. Its specific capacity can reach as high as 220 mAh/g with a high specific energy of 450 Wh/Kg at 0.1 C. Even after cycled 200 times at 2 C, the capacity can still be higher than 100 mAh/g. CV measurements and a combined constant current and constant voltage tests supported a two plateaus process for 2-2 parallel model. The charge-discharge voltage gap increased for the 2-2 parallel composite, which was supposed to be related to the interface effect. In general, the specific energy of the 2-2 parallel composite was much higher than HTO while the specific capacity as well as cycle property of the 2-2 parallel composite was much better than LiFePO4 as cathode material.