Preparation Of Solid Polymer Composite Electrolytes And Its Performance Study

Solid-state electrolytes are expected to fundamentally replace liquid electrolytes due to their high safety and high energy density.However,solid electrolytes still suffer from poor solid-solid contact interface performance,difficulty in inhibiting lithium dendrite growth,and low ionic conductivity at room temperature in practical applications.In this thesis,the composite electrolytes were prepared by combining the advantages of high mechanical strength of inorganic electrolytes and excellent interfacial compatibility of polymer electrolytes,and their components and structures were optimized.The physical properties,electrochemical properties,interfacial stability and battery performance of the composite electrolyte were studied as follows:1 Acrylate polymers with long carbon chains（trimethylolpropane trimethacrylate（TMPTMA）and 1,6-hexanediol diacrylate（HDDA））were selected to construct a monomer cross-linked network structure,and dimethyl carbonate（DMC）,lithium bis（trifluoromethanesulfonyl）imide（Li TFSI）and imidazole-based ionic liquids(N_1,4,4,4TFSI)were added to prepare the polymer electrolytes.The composite electrolytes were prepared by in situ polymerization method by adding 5wt%,10wt%,15wt%,20wt%ceramic fillers（LLZTO）to the polymer electrolytes,and the electrochemical properties of the composite electrolytes with different proportions of ceramic fillers were investigated,and the optimal incorporation ratio of ceramic fillers was determined.The results showed that the ionic conductivity of the composite electrolyte with 15wt%ceramic filler（THCE-15%LLZTO）could reach 1.1×10^-3 S·cm^-1 at room temperature（25℃）.The battery assembled with Li Fe PO₄（LFP）cathode material has an initial discharge capacity of138.8/128.2 m Ah·g^-1 at 50°C and 1 C/2 C multiplier,and the capacity retention rate is81.34%/75.48%after 150 cycles,which has excellent stability and cycling performance.2 On this basis,the composite electrolyte with asymmetric structure（As-THCE-XLLZTO）was prepared based on the characteristics of selective adsorption of glass fiber septum.Firstly,the ratio of monomers in the gel polymer electrolyte was adjusted（5wt%,7.5wt%,10wt%,12.5wt%,15wt%）to investigate whether the asymmetric structure has an effect on the state of the polymer chain segments.Next,the proportions of ceramic fillers（LLZTO）in the composite electrolytes（5wt%,10wt%,15wt%,20wt%）were adjusted to investigate the optimal incorporation of ceramic fillers in the asymmetric structure.The results show that the electrolyte with 10wt%LLZTO（As-THCE-10%LLZTO）incorporated has the best electrochemical performance.To further optimize the anode interface of the electrolyte,Fluoroethylene carbonate（FEC）-modified lithium sheets were selected as the anode,and the assembled Li-FEC||As-THCE-10%LLZTO||Li-FEC cell could be stably cycled for 200 h at a current density of 50°C,0.5 m A·cm^-2,with a stable polarization voltage of about 0.1 V.The battery assembled with the matched Li Fe PO₄（LFP）cathode material has an initial discharge capacity of 111.6 m Ah·g^-1 at room temperature（25°C）and 2 C multiplicity,and the capacity retention rate is 84.73%after500 cycles of stabilization.The asymmetric structure of the composite electrolyte further improved the cycle life and capacity retention of the battery.