Study On Improving The Performance Of All-solid-state Battery By Modified Nano-Al₂O₃ With Silane Coupling Agent

Polymer electrolytes have the advantages of high mechanical strength,suppression of lithium dendrites,non-flammability,and high safety,and have gradually become a hot spot in the research of all-solid-state batteries.In this paper,aiming at the high crystallinity,low conductivity and low thermal stability of PEO at room temperature,the polymer composite solid electrolyte membrane was explored and prepared to improve the conductivity,voltage window and thermal stability of the polymer electrolyte membrane.However,due to the high Gibbs free energy of the selected filler nano-Al₂O₃,the hydroxyl groups adsorbed on the surface can easily form hydrogen bonds,causing Al₂O₃to agglomerate into large particles,so the surface needs to be activated.The silane coupling agent has a hydrophilic group and a hydrophobic group.The hydrophilic group can bond with the hydroxyl group on the surface of Al₂O₃,and the hydrophobic group can interact with PEO.Through the"bridging"function,the effect of PEO and Al₂O₃is enhanced,which can improve the dispersibility of Al₂O₃in the PEO polymer electrolyte membrane,and improve the uniformity of the polymer composite electrolyte membrane.In this paper,the solution casting method combined with hot pressing technology is used to prepare the polymer composite electrolyte membrane PEO₁₈LiTFSI-x%Al₂O₃,and the influence of different Al₂O₃filler ratios on the performance of the polymer composite electrolyte membrane is explored.The results show that the optimal proportion of Al₂O₃filler is 10%.Al₂O₃is evenly distributed in PEO₁₈LiTFSI-10%Al₂O₃in the SEM image,with the highest ionic conductivity of1.58×10^-5S/cm,the best mechanical strength,and the tensile stress is 4.285 MPa,strain is 746.08%,the stability and thermal stability of lithium metal are improved compared with PEO₁₈LiTFSI.When assembled with the positive electrode material LFP to form a battery LFP/SPE/Li,at the 55th cycle of discharge,the discharge capacity of LFP/PEO₁₈LiTFSI/Li drops to 134.09 m Ah/g,and the capacity retention rate is 92.49%,while the battery LFP/PEO₁₈LiTFSI-10%Al₂O₃/Li has a discharge capacity of 136.58m Ah/g and a capacity retention rate of 96.34%.When matched with the cathode material LCO,the discharge capacity of LCO/PEO₁₈LiTFSI/Li is basically reduced to 0m Ah/g at the 40th cycle,while the battery LCO/PEO₁₈LiTFSI-10%Al₂O₃/Li still has51.74 m Ah/g at the 40th cycle.Besides,when discharged to the 80th cycle,the discharge capacity is still 24.88 m Ah/g.The cycle performance has been greatly improved.In this paper,nano-Al₂O₃was modified by silane coupling agent KH-560.When the concentration of silane coupling agent KH-560 is 2.5%and the water bath time is 3h,the surface grafting effect of Al₂O₃is the best.The particle size of the modified M-Al₂O₃decreased from D₅₀=6.17?m to D₅₀=705 nm,and the lipophilic and hydrophobic properties of M-Al₂O₃were also improved.The best ratio of M-Al₂O₃in PEO₁₈LiTFSI-x%M-Al₂O₃is 20%,and the highest conductivity of PEO₁₈LiTFSI-20%M-Al₂O₃is 2.78×10^-5S/cm,which has the best mechanical strength,and the tensile stress is 5.979 MPa,and the tensile deformation is 840.32%.After matching with the cathode material LFP,the discharge capacity is 136.58 m Ah/g and the capacity retention rate is 96.34%at the 55th circle of discharge;,after matching with the LCO,the battery LCO/PEO₁₈LiTFSI-20%M-Al₂O₃/Li discharges at the 80th circle The capacity is 24.25m Ah/g,and the cycle performance of the battery is significantly improved compared with the optimal group LCO/PEO₁₈LiTFSI-10%Al₂O₃/Li before modification.