Electrochemical Characteristics of Li4Ti5O12 - Coated MCMB as an Anode Material for Hybrid Capacitor

Abstract

In recent years, the over consumption of fossil fuels leads to critical environmental problems and increasing attentions are being paid on energy security issues. The green energy sources, such as solar and wind, are typically periodic or intermittent and therefore requires an electrical energy storage for utilization purposes. Great research effort has been focused on the energy storage systems of capacitors and batteries. The hybrid capacitor incorporates a faradaic lithium ion battery system in combination with a non faradaic electric double layer capacitor system in a unit cell. This combination called hybrid capacitors can be used to obtain better performance in power/energy demands. In this research, we coated Li4Ti5O12 onto meso - carbon micro beads (MCMB) to form a core - shell structure by a sol–gel process followed by calcinations. This MCMB-Li4Ti5O12 of core-shell structure was prepared to improve low electric conductivity of Li4Ti5O12 and cycling behavior. Prepared MCMB-Li4Ti5O12 composite was analyzed by XRD and SEM. The electrochemical performances of hybrid capacitor were investigated using MCMB-Li4Ti5O12 as the negative electrode and LiMn2O4, Active Carbon Fiber (ACF) as the positive electrode. The anodes were prepared by coating slurries containing the active materials (76wt%), Super P (17wt%), and polytetrafluroethylene (PTFE, 7wt%) on Al foil. The cathodes were made by dispersing 85wt% LiMn2O4, 10wt% Super P and 5wt% PTFE binder. The electrolyte consisted of 1M LiPF6in a mixture of ethylene carbonate(EC) / dimethyl carbonate(DMC) / ethyl-methyl carbonate(EMC) with a volume ratio of 1:1:1. The electrochemical behaviors of hybrid capacitor using organic electrolytes were characterized by charge/discharge, cyclic voltammetry, impedence and cycle tests. The hybrid capacitor using MCMB-Li4Ti5O12/LiMn2O4 electrodes had better capacitance than MCMB hybrid systems and was able to deliver a specific energy as high as 67 Wh/kg at a specific power of 781 W/kg. Also, it was found that MCMB-Li4Ti5O12 composite exhibited very good cycle life performance.