UV-induced Solid Polymer Electrolyte For Lithium-ion Batteries

Lithium-ion batteries insufficient securitysafe due to the flammable volatile liquid electrolytes.Developing solid electrolytes is the best solution for the problem.Polymer material is the first choice for preparation of solid electrolyte because of easy processing and flexible.PEO-based polymer electrolyte is the most widely studied,but PEO has the disadvantages of low ionic conductivity at room temperature and poor mechanical properties.Added the oligomer of PEGDA to polymer electrolyte can maintain flexibility and have high mechanical strength when PEGDA used as a crosslinking agent.Ionic liquids were used as additives in polymer electrolytes due to their high ionic conductivity and stable thermodynamic properties.In this paper,PEGDA was used as a cross-linking agent,PEO-based polymer solid electrolyte membranes with different mass ratios of PEGDA was prepared by UV-polymerization.The ionic liquid of BVIm-TFSI was added to 30%PEGDA/PEO polymer electrolyte to improve the ionic conductivity.Physical characterization（XRD,FTIR,tensile stress-strain,SEM,TG）and electrochemical characterization（EIS,LSV,CV）.Solid-state batteries of Li/SPE/LiFePO₄ were assembled.The cycle performance and rate performance of solid-state batteries were tested at 65°C.The conclusions as follows:（1）The PEGDA/PEO/LiTFSI polymer electrolyte membrane was prepared by UV-crosslinking.PEGDA was successfully cross-linked and the semi-interpenetrating polymer electrolyte membrane was successfully prepared by FTIR.The mechanical properties of the modified PEO-based SPE were improved by tensile strain-stress analysis.（2）The ionic conductivity of SPE was calculated by AC impedance test.The conductivity was improved at room temperature of the crosslinked polymer film.The SPE membrane containing 20 wt.%of PEGDA has the ionic conductivity of 1.59×10^-4 Scm^-1 and is electrochemically stable under potential of 4.2 V.The thus-assembled lithium ion battery using lithium iron phosphate as cathode and lithium metal as anode exhibits a first discharging capacity of 148 mAh/g with coulombic efficiency of 98%at 0.1 C and the discharge capacity remains 145 mAh/g with coulombic efficiency of94.8%after 40 charge-discharge cycles.The discharge specific capacities were 148mAh/g,150 mAh/g,and 150 mAh/g at 0.1 C,0.2 C,and 0.3 C respectively.（3）The ionic liquid BVIm-TFSI and BVIm-TFSI/30%PEGADA/PEO SPE membrance were synthesized by FTIR.Tensile stress results show that the successful doping of Added BVIm-TFSI to 30%PEGADA/PEO SPE membrance has reduced the tensile stress but increased the tensile stress of the SPE membrance.（4）The ionic conductivity of BVIm-TFSI/30%PEGADA/PEO SPE membrance is8.7×10^-5 S/cm at 30°C which improved relative to 30%PEGADA/PEO SPE membrance,Li/SPE/LiFePO₄ solid-state battery was assembled exhibits the first discharge specific capacity of 153 mAh/g with the coulombic efficiency of 97%at 0.1C.After 35 cycles,the discharge specific capacity was 130 mAh/g.The discharge specific capacities were 160 mAh/g,162 mAh/g,and 160 mAh/g,at 0.1 C,0.2 C,and0.3 C respectively.