Study On Li₄TI₅O₁₂/C Composites For Supercapacitors

We need to develop pseudocapacitive system to improve the specific energy of supercapacitors. Since Li4Ti5O12has small volume change during lithium insertion and has long charge-discharge cycle life because of the stable the unique spinel structure. So we chose Li4Ti5O12as the pseudocapacitive material to compound with carbon materials to prepare electrode materials with excellent performance. On the one hand, the carbon can improve the conductivity of the composite through the conductive network; on the other hand, the Li4Ti5O12can improve the capacity of the composites. So we can prepare the supercapacitor materials by the combination of Li4Ti5O12and carbon materials such as carbon nanotubes or mesoporous carbon.For the first time, we used the solvothermal method with a earlier sol-gel process to prepare MWNTS/Li4Ti5O12composites. The composites had high surface area because of the three-dimensional conductive carbon nanotube network structure. Among the samples with different condition of heat treatment, the sample which is sintered at600℃for2h had the best electrochemical perfonnance. The specific capacity of Lithium titanate among the MWNTS/Li4Ti5O12composites is170mAh.g-1at0.2C, and115mAh.g-1at 30C.We prepared composites of lithium titanate and mesoporous carbon which had more excellent electrochemical performance. The sample prepared by solvothermal method with the addition of benzyl alcohol had excellent rate properties The discharge specific capacity of the sample is175mA.g-1at0.2C,144mAh.g-1at5C and144mAh.g-1at20C. The rate capability of the sample prepared by solvothermal method with no addition of benzyl alcohol has a little decrease. But it has better cycling performance. The initial specific capacity at1C is144mAh.g-1, but it retains128mAh.g-1after500cycles.When we reduced the content of lithium titanate in the composites, we found that the overall performance of the composites is even better. The sample treated at600℃for2h which the content of lithium titanate is33%has the best comprehensive performance. The capacity is58mAh.g-1,46mAh.g-1,38mAh.g-1mAh.g-1,23mAh.g-1at the current density of0.05A.g-1,1A.g-1,20A.g-1,30A.g-1.The capacity retains84%after5000cycles at the current density of0.4A.g-1(based on the total weight of the electrodes).In the end, the AC/Li4Ti5O12/C) hybrid capacitor which used commercial activated carbon as cathode and AC/(Li4Ti50]2/C) as anode was assembled.The energy density of the hybrid capacitor is29Wh.Kg-1when the power density is59W.Kg"’and the energy density of the hybrid capacitor is still24Wh.Kg-1when the power density increases to W.Kg-1. The performance of the hybrid capacitor is better than AC/AC capacitor under the same conditions.