Synthesis And Electrochemical Performance Analysis Of Polyethylene Glycol-Based Composite Electrolytes

All-solid-state lithium battery is considered as one of the best candidates to solve the thermodynamic stability and safety issues of the lithium anode in conventional liquid electrolytes.polyethylene glycol（PEG）-based solid polymer electrolytes attracted widespread attention due to their high lithium-ion conductivity,low interfacial impedance and flexibility,while problems such as poor mechanical properties and instability between lithium anode and electrolyte need to be solved.Basing on this,this thesis uses inorganic fillers and construct new structures,successfully prepared an ultra-thin,electrochemically stable and high-safety solid-state composite flexible electrolyte membranes,using in-situ polymerization method to solve above problems.It provides a feasible idea for realizing a"rigid and flexible"all-solid-state lithium metal battery.The specific research work is described as follows:1.Using the Polyethylene terephthalate-Al₂O₃（PET-Al₂O₃）composite film with three-dimensional structure as the main body and the mixture of Poly（glycol）methyl ether methacrylate（PEGMEM）,Lithium Bis（trifluoromethane）sulfonimide lithium salt（Li TFSI）and 2,2-Bis（hydroxymethyl）propionic acid（DMPA）as the polymer matrix,the ultrathin PEG@PET-Al₂O₃（～25μm）was prepared by solution casting and UV-induced in-situ curing method.The obtained PEG@PET-Al₂O₃flexible electrolyte membrane has not only excellent mechanical properties（16.75 MPa）but also wide electrochemical window（4.9 V）.In addition,PEG@PET-Al₂O₃ can effectively control the deposition of lithium metal,enabling Li/PEG@PET-Al₂O₃/Li cycled stably for at least 1600 h at a current density of 0.1 m A cm^-2.And the assembled all-solid-state lithium metal battery LiFePO₄/PEG@PET-Al₂O₃/Li can be cycled at 1 C for 2000cycles with a capacity retention rate of 75.8%,demonstrating excellent cycling stability.2.The Li_1.5Al_0.5Ge_1.5（PO₄）₃（LAGP）inorganic framework with three-dimensional structure is prepared by the template calcination method.By pouring PEGMEM-Li TFSI-Benzoyl peroxide（BPO）-mixture precursor into the LAGP framework,the electrolyte will be layered due to the gravitational force,and as a result,an unique flexible composite polymer electrolyte（PEG@LAGP ASPE）formed,which is because of the thermally initiating in-situ polymerization.Owing to the structural advantages,the ionic conductivity of PEG@LAGP ASPE reaches 1.45×10^-4 S cm^-1 at room temperature.Under a current density of 0.5 m A cm^-2,Li/PEG@LAGP ASPE/Li symmetric battery cycled stably for more than 400 hours.At 2.5 C(0.5 m A cm^-2)and60 ℃,the LiFePO₄/PEG@LAGP ASPE/Li battery achieved a maximum discharge specific capacity of 130.8 m Ah g^-1with its capacity retention rate of 87.2%after 1000cycles.