Cycling performance improvement of polypropylene supported poly(vinylidene fluoride-co-hexafluoropropylene)/maleic anhydride-grated-polyvinylidene fluoride based gel electrolyte by incorporating nano-Al2O3 for full batteries

Abstract

To improve the electrochemical performance of traditional poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)] based gel polymer electrolyte (GPE), maleic anhydride-grated-polyvinylidene fluoride (MA-PVdF) was introduced to form polypropylene (PP) supported MA-PVdF/P(VdF-HFP) based GPE. Nano-Al2O3 was also incorporated into MA-PVdF/P(VdF-HFP) blend in order to further enhance the comprehensive performance of GPE. The corresponding membranes and GPEs were characterized by porosity, electrolyte uptake, scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, mechanical test, thermogravimetric analyzer, charge/discharge test and nail penetrates experiment. It is found that the performances of GPEs are significantly improved when the mass ratio of MA-PVdF to P(VdF-HFP) is 1:6. Doping 10wt% nano-Al2O3 further influences the characterization of selected membranes and GPE, in which the electrolyte uptake is enhanced from 128 to 192%, the ionic conductivity of corresponding GPE is improved from 2.39×10−3Scm−1 to 3.84×10−3Scm−1, the mechanical strength increases from 6.34 to 6.98N, the thermal decomposition temperature from 260°C to 420°C. Thus, the full battery LiCoO2|GPE|Artificial graphite exhibits good rate and cycling performances. After 100 cycles, the discharge capacity of the cell retains 97.2% of original one for the Al2O3 doped GPE, while 95.6% for the GPE without nano-Al2O3 and 93.2% for P(VdF-HFP) based GPE. Additionally, the safety performance of full charged battery is enhanced, in which the highest temperature is rapidly declined from 250°C for the polypropylene (PP) membrane to 104°C for PP supported MA-PVdF/P(VdF-HFP)/Al2O3 membrane in the nail penetrates experiment.