Preparation And Performance Of PVDF-HFP/2D Nanosheets Gel Polymer Electrolytes

Lithium-ion batteries dominate the current rechargeable battery market because of their high volumetric specific energy and mass specific energy,no memory effect and pollution.However,the safety hazard and energy density of batteries are limited by using of liquid electrolyte at the same time.Gel polymer electrolyte can replace the liquid electrolyte because of the advantages of high safety and excellent shape plasticity,which has received a lot of attention from scholars all over the world.But the room temperature ionic conductivity and the stability between the gel polymer electrolyte and lithium metal still need to be further improved.In this paper,PVDF-HFP is selected as the polymer matrix for modifying the safety and electrochemical performance by doping with different structure of layered two-dimensional materials.（1）The h-BN nanosheets were used as additives to improve the comprehensive performance of PVDF-HFP-based gel polymer electrolytes.It was found that when the doping amount of h-BN is 0.3 wt%,the ionic conductivity increases from 0.09×10^-3S/cm to0.4×10^-3S/cm,the electrochemical window reaches 4.78V,the LiFePO₄/GPE-0.3 wt%BN//Li battery discharge specific capacity reaches up to 120m Ah/g at 0.2C,and the charge/discharge efficiency reaches 98.4%.And the capacity basis can reach 116 m Ah/g,the capacity retention rate attains 96.7%,the charge/discharge efficiency reaches 91.2%after100 cycles,reflecting a good cycle stability.The charging capacity of the battery is 150m Ah/g,120 m Ah/g and 90 m Ah/g at 0.1C,0.2C and 0.5C rate,respectively,and it reaches140 m Ah/g when the rate returns to 0.1C.（2）With BP nanosheets as additives and PVDF-HFP as gel polymer electrolyte matrix,the experimental results show that the ionic conductivity rises from 0.09×10^-3S/cm to 1.34×10^-3S/cm,the electrochemical window reaches 5V,the first discharge specific capacity reaches 139m Ah/g at 0.2C when the doping amount of BP is 0.3 wt%.And the capacity can reach 120 m Ah/g,the capacity retention rate reaches 86.3%,and the charging/discharging efficiency reaches 97.8%after 100 cycles,reflecting a good stability of charging/discharging cycles.And the charging specific capacity can reach 150 m Ah/g,139 m Ah/g,98 m Ah/g at 0.1C,0.2C,and 0.5C rate,respectively.（3）Mg-Al-LDHs nanosheets as ion migration carriers are introduced into the PVDF-HFP-based gel polymer electrolyte,the test results show that the ionic conductivity increases from 0.09×10^-3S/cm to 1.36×10^-3S/cm,the electrochemical window reaches4.85V at room temperature when the doping amount of Mg-Al-LDHs is 0.4 wt%.The first discharge specific capacity at 0.2C reaches 131 m Ah/g,and the capacity can reach 121m Ah/g,the capacity retention rate reaches 92.4%,the charge/discharge efficiency reaches98.8%,reflecting a better charge/discharge cycle stability based on 100 cycles.And the charging capacity of 150 m Ah/g,131 m Ah/g,103 m Ah/g at 0.1C,0.2C and 0.5C reveals superior rate properties.