Preparation And Performance Of PVDF-LLZO/ALF₃ Composite Nanofiber Separator

With the rapid development of energy storage devices, lithium ion battery has been widely concerned due to its high energy density and long cycle life. In lithium ion battery, the separator plays a crucial role that isolates anode and cathode to prevent short circuit, while permitting Li+ to pass through. It`s property directly affects the charge-discharge and safty performance. Therefore, the development of separator which has excellent performance is positive to improve the performance of lithium ion battery.First of all, the garnet type LLZO was prepared by solvent-thermal method. Then, three PVDF-LLZO composite separators?2%, 4% and 6% LLZO separators? were constructed by doping LLZO powders with different proportion into PVDF solutions using electrospinning. The micro morphology, thermal and mechanical properties, the affinity of the electrolyte and electrochemical performances of three kinds of composite separators were studied, used Celgard 2400 and PVDF separator as reference separator. The results showed that the thermal properties, mechanical properties and affinity of the electrolyte were improved. The electrolyte uptake of 6% LLZO composite separators reached 407% which was 2.9 times of Celgard 2400?140%?, and the ionic conductivity of 6% LLZO composite separators was 1.453 m S·cm^-1, increased 4.6 times of Celgard 2400(0.260 m S·cm^-1).Then, AlF₃ nanoparticles were deposited on both sides of the aboved 6% LLZO separator by magnetron sputtering deposition technology and the effect of AlF₃ nanoparticles on the performances of separator via changing depositing time?10min, 15 min, 20min? was studied. The micro morphology, porosity, the affinity of the electrolyte and electrochemical performances of three kinds of composite separators were researched, used Celgard 2400 and 6% LLZO separator as reference separator. The results of the cycling performance after 100 cycles showed that the capacity of composite separators deposited AlF₃ nanoparticles after 20 min retained 93.84% which was 34.8% higher than Celgard 2400?69.61%? and 1.2 times of 6% LLZO separator?79.31%?.At the same time, the composite separators deposited AlF₃ nanoparticles after 20 min was chose as experimental subject and the founctions of suppressing electrolyte decomposition and Li dendrites were carried out, used Celgard 2400 and 6% LLZO separator as reference separator. The analysis of HF contents and XPS spectra illustrated that the composite separator modified by AlF₃ is effective in suppressing electrolyte decomposition. The HF content of PVDF-LLZO/AlF₃ composite separator was 90 ppm only after storing at 55? for three days while the HF content of Celgard 2400 was as high as 200 ppm. The SEM of separators after 200 charge-discharge cycles showed that PVDF-LLZO/AlF₃ still retained the integrated morphology of fiber membrane, while there had amount of debris appeared on the surface of Celgard 2400 and PVDF-LLZO and some pores had been blocked already. This meant that PVDF-LLZO/AlF₃ could restrain the growth of Li dendrites in some extent.