Preparation And Properties Of PEO-based Composite Polymer Electrolyte For Lithium Ion Batteries

Lithium ion batteries have been widely used in portable electronic devices and electric vehicles,but their energy density and safety are difficult to meet the demand.Using lithium metal anode can greatly improve the energy density of batteries,but it also brings greater challenges to the safety of batteries.Polymer electrolytes are considered as the next generation electrolyte,due to their good safety and stability to lithium metal.However,it is still a challenge to obtain a polymer electrolyte that integrates excellent electrochemical and mechanical properties.In this paper,surface-grafted nano-SiO2 was introduced into polyethylene oxide(PEO)based polymers as crosslinking agent to improve the performance of polymer electrolytes.Two kinds of PEO-based composite polymer electrolytes with different structures were prepared.The main contents are as follows:(1)The nano-SiO2 was first grafted by ?-Glycidoxypropyltrimethoxysilane,after that,it could be used as crosslinking agent to polymerize with poly(ethylene glycol)diglycidyl ether(PEGDE)and diamino-poly(propylene glycol)(DPPO)under heating conditions to form a 3D crosslinked PEO-based composite polymer electrolyte.Test results show that the ionic conductivity of the electrolyte at room temperature reach to 4.65×10-3 S cm-1,the ionic transfer number reach to 0.45,and there is a wide electrochemical window of 5.4 V(vs.Li+/Li).The electrolyte also has good mechanical properties.The tensile strength and brea:king strain are 8.95 MPa and 181.9%respectively.The electrolyte also has good stability to lithium metal.The assembled Li/3D-GCPE4/LiFePO4 exhibits excellent cycle performance and rate performance,the cell maintains over 90%capacity after cycled 500 cycles at 1C,and the cell exhibits 124 mAh g-1 at 10C.In addition,when the electrolyte combined with high voltage cathode materials LiNi0.8Co0.1Mn0.1O2 and LiNi0.5Mn1.5O4 also exhibited superior cycling performance.(2)Nano-SiO2 which grafted with ?-Methacryloylpropyltrimethoxysilane,poly(ethylene glycol)diacrylate(PEGDA)and poly(ethylene glycol)ether acrylate(PEGEMA)were used to copolymerize to form A comb-like PEO-based network,which was cured by simple ultraviolet light.In the process of polymerization,the PEO network interspersing with linear PVDF-HFP network formed a PEO-based composite polymer electrolyte with semi-interpenetrating network structure.Test results show that the ionic conductivity of the electrolyte is 2.71 X 10-3 S cm-1 at room temperature,the electrochemical stability window is 5 V,the tensile strength and breaking strain are 7.01 MPa and 248.1%respectively,and the thermal decomposition temperature reaches to 330?.The electrolyte also has good stability to lithium metal,the assembled Li/Semi-IPN-GCPE/LiFePO4 battery showed excellent cycle performance and rate performance.The reversible capacity of cell remained 141,3 mAh g-1 after 300 cycles at 1C cycle.and the cell exhibits 103.4 mAh-1 at 10C,which was much higher than traditional liquid electrolyte.