Preparation,Characterization Of High Performance Polymer Electrolytes And Their Applications In All Solid State Lithium Batteries

Conventional lithium ion secondary batteries generally suffer from leakage and explosion due to the use of liquid organic electrolytes.The new solid polymer electrolyte can effectively solve the safety problem caused by the use of liquid electrolyte and becomes a research hot spot.At present,the solid polymer electrolyte suffers from the problem of low lithium ion conductivity and narrow electrochemical window.In order to improve the low temperature ionic conductivity of solid polymer electrolyte and further promote the development of solid polymer lithium ion battery,we design and use many methods such as physical blending,inorganic doping and in-situ polymerization to modify the polyethylene oxide（PEO）-based polymer electrolyte in this thesis.Two types of polymer electrolytes with high safety and stable electrochemical performance are prepared.The preparation process is as follows:1.The amorphous polypropylene carbonate（PPC）material was physically blended with PEO in different proportion;then change the molecular weight of PEO in a certain proportion;finally,the inorganic solid electrolyte Li_1.5Al_0.5Ge_1.5（PO₄）₃（LAGP）is introduced into the polymer matrix.The composite solid polymer electrolyte PPC-PEO 10W[5:5]-1%wt LAGP with high ionic conductivity is successfully prepared,its ionic conductivity reaches8.79×10^-5 S cm^-1 at 30°C,and presents good electrochemical performance.At60°C,the assembled LiFePO₄/Li solid lithium-ion batteries are assembled and the initial discharge specific capacities of the batteries are 152.9,135.1,114.9,and 99.1 mAh g^-1 at 0.1,0.2,0.5,and 1 C at 60°C,respectively.At 0.5 C,the capacity retention retaintion rate still reached 88.2%(103.1 mAh g^-1)after 700cycles,and the capacity retention rate was still 73.4%after 500 cycles at 1 C.2.A novel solid polymer electrolyte with comb-like structure is prepared by mixing poly（ethylene glycol）methyl ether methacrylate（PEGMEM）with lithium bis（trifluoromethane）sulfonimide（LTFSI）via a solvent-free UV-cured method.At 30°C,the ionic conductivity of the poly-PEGMEM 950 polymer solid electrolyte reached to 1.44×10^-4 S cm^-1,and presents a wider electrochemical window（>5V）.Furthermore,the LiFePO₄/Li coin cells show initial discharge specific capacities of 163.2,147.7,137.3 and 108.7 mAh g^-1 at0.1,0.2,0.5 and 1 C under 60 ^oC.The coin cells can work well at 30 ^oC,and the initial discharge specific capacities at 0.05,0.1,0.2 and 0.5 C are 140.5,133.5,107.7 and 55.6 mAh g^-1.Most importantly,a 3.5×7 cm solid-state battery is fabricated and cycling at 30 ^oC.The first discharge capacity reaches to 137.5mAh g^-1 and the capacity retention reach to 84.4%after 100 cycles at 0.2 C and remain 95.5%after 100 cycles at 0.5 C.