HIGH PERFORMANCE ENERGY STORAGE SYSTEM BASED ON Li-ION BATTERY AND - SUPERCAPACITOR HYBRID

Abstract

Nowadays the demand of electrochemical energy sources for various devices viz from portable electronic devices to hybrid electric vehicles (HEVs) has become extremely high. However, achieving high energy density as well as high power density from a single energy source is not easy. A hybrid system involving Li-ion battery (for high energy density) and supercapacitor (for high power density) may be the possible solution for future energy source especially for hybrid electric vehicles. Present dissertation work deals with the features of lithium titanate (Li4Ti5012 abbreviated as LTO), method for the synthesis of Li4Ti5012. Pure lithium titanate (Li4Ti5Oi2) has been prepared by solid state reaction. Safety of Li-ion batteries depend on purity of electrodes materials because the undesired phases may react with the anode and cathode materials or electrolytes, which decrease the life of battery. Phase verification of the heat-treated Li4Ti5012 powders have been done by X-Ray diffraction. Morphology and particles size of heat treated Li4Ti5Oj2 powders have been determined by field emission scanning electron microscopy (FE-SEM). Weight loss during the calcinations has been determined by Thermogravimetric analysis (TGA). Electrochemical performance of (i) Li-ion battery half cells, (ii) Comparison of supercapacitor, battery and hybrid half cells and, (iii) Comparison of supercapacitor and hybrid supercapacitor full cells, has been performed by charging-discharging, capacity retention and CV tests. Pure and smaller particles size material has advantage in all electrochemical tests over the impure and larger particle size material in case Li-ion battery half cell test. More over hybrid half cell has high capacity as compare to supercapacitor half cell and, better stability at high current rate from Li-ion battery cell. Hybrid supercapacitor has higher capacities as compare to normal supercapacitor. Hybrid supercapacitor also shows the better stability, high capacity retention and low internal resistance at high current rate.