Performance of solid-state hybrid supercapacitor with LiFePO4/AC composite cathode and Li4Ti5O12 as anode

We report the studies on quasi-solid battery-supercapacitor (BatCap) systems fabricated using sol-gel-prepared LiFePO4 and its composites (LACs) with activated charcoal (AC) as hybrid cathode and Li4Ti5O12 powder as anode separator by flexible gel polymer electrolyte (GPE) film. The GPE film comprises 1.0 M lithium trifluoromethane sulfonate (LiTf) solution in ethylene carbonate (EC)-propylene carbonate (PC) mixture, immobilized poly(vinylidene fluoride-co-hexafluoro-propylene) (PVdF-HFP), which is of high ionic conductivity (similar to 3.8 x 10(-3) S cm(-1) at 25 degrees C) and electrochemical stability window (similar to 3 V). The effect of the addition of AC in composite electrode LACs has been analyzed using various techniques such as X-ray diffraction, porosity analysis, and electrochemical methods. The interfaces of composite LACs and GPE film not only offer high rate performance but also show high specific energy (> 27.8 Wh kg(-1)) as compared to the symmetric supercapacitors and pristine lithium iron phosphate (LiFePO4)-based lithium ion batteries. The full BatCap systems have been characterized by cyclic voltammetry and galvanostatic charge-discharge tests. The BatCap systems with composite electrodes (LACs) offer better cyclic performance as compared to that of pristine LiFePO4-based BatCap or LIB LiFePO4/Li4Ti5O12.