The Preparation And Investigation Of Electrolyte For Supercapacitor Applications

As the key materials of supercapacitors, Gel polymer electrolyte has attract more attentions recently in this area. However, with the development of supercapacitor, more affort should be focused on improving the Gel polymer electrolyte performance such as, ionic conductivity, thermal stability, and electrochemical stabilities as high performance electrolyte for supercapacitor applications. This paper focuses on the preparation and performance of the polyvinylidene fluoride-hexafluoropropylrne(PVDF-HFP)-based gel polymer electrolyte, and a inorganic material doping method is utilized to improve the electrolyte performance. The main works in this paper are as follows:1. A solution casting method was used to prepare PVDF-HFP-based gel polymer electrolyte. This composite electrolyte showed highest 3.76 m S/cm conductivity at room temperature and a stable 3.2 V electrochemical voltage window was achieved. A Doping treatment with the addition of nano Al2O3 into PVDF-HFP is utilized to improve the polymer electrolyte performance. It has been found that, at a mass ratio of nano Al2O3 to PVDF-HFP polymer matrix about 8%, the PVDF-HFP/Al2O3 composite electrolyte showed a 4.12 m S/cm ionic conductiviey and a 3.4 V electrochemical voltage window. The relationship of conductivity and the temperature in these two electrolytes can be explained by a Arrhenius theory. Furthermore, these two eletrolytes are assembled into supercapacitr as electrolyte films. The testing results of devices indicate that the double electrode capacitance of PVDF-HFP and PVDF-HFP/Al2O3 polymer electrolytes based devices are 10.36 m F/cm2 and 18.36 m F/cm2 respectively, which showed excellent capacitive behavior.2. A PMMA polymer was added into PVDF-HFP electrolyte to prepare composite electrolyte. It has been found that, at a mass ratio of PMMA to PVDF-HFP about 20%, the composite electrolyte exhibited a 4.12 m S/cm conductivity at room temperature and a stable electrochemical voltage window up to 3.6 V is achieved. As a doping treatment, a nano Al2O3 as doping materials was added into PVDF-HFP/PMMA composite electrolyte for better electrolytic performance. The testing results reveal that a 8% mass ratio of nano-Al2O3 in composite result in a highest 4.31 m S/cm conductivity of this composite electrolyte at room temperature and showed stable electrochemical voltage window at 3.9 V. The relationship between the conductivity and temperature in this Al2O3 doping PVDF-HFP/PMMA composite electrolyte can also explained by a Arrhenius theory. The furether electerochemical testing indicate that, after modifying and doping treatment, the double electrode capacitance of PVDF-HFP/PMMA electrolyte based supercapacitor increase to 13.6 m F/cm2, and Al2O3 doping PVDF-HFP/PMMA composite based supercapacitor had highest double electrode capacitance about 21.36 m F/cm2, which are attributed to the addition of PMMA and doping of nano Al2O3 into PVDF-HFP.3. The scanning electron microscopy(SEM), fourier transform infrared(FTIR) spectroscopy, thermal gravity analysis(TGA) and differential scanning calorimetry(DSC) are used to characterize the PVDF-HFP based gel polymer electrolyte. The characterization results confirm that the uniform distribution of different contents in composite electrolyte is achieved and no distinct phase separation was observed. The PVDF-HFP/PMMA exhibited good thermal stability, and the addition of PMMA into PVDF-HFP decreased the decomposition temperature of electrolyte. It has been found that composition of PMMA reduced the crystallinity of PVDF-HFP, which leads to the decrease of decomposition temperature. The further investigation show that the nano Al2O3 dispersed well into polymer matrix, and the higher decomposition temperature of composite electrolyte was achieved. The addition of Al2O3 into PVDF-HFP/PMMA improved the thermal stability of composite electrolyte, which results from the crystallinity reducement of composites after the doping of Al2O3. The change of crystallinity in composite is also attributed to the conductivitiy enhancement of polymer electrolyte.