Preparation And Properties Of Modified PEO-based Solid Polymer Electrolyte

With the development of technology,lithium ion battery has been widely used in our life,and its safety performance has attracted people's attention.Solid electrolyte could improve the safety of lithium battery.As a branch of solid electrolyte,polymer solid electrolyte has the advantages of low price and stability to lithium metal,and is a promising next generation electrolyte material.However,its low ionic conductivity seriously restricts its application.Therefore,it is very important to modify polymer electrolyte to improve its performance.In this paper,poly(ethylene oxide)(PEO)was selected as the polymer substrate and its modification was studied.The specific research contents are as follows:Al(OH)(1,4-NDC)(Al-MOF)was successfully synthesized by hydrothermal method and added as a filler to PEO substrate to make a composite electrolyte.The tensile and thermogravimetric results show the better mechanical properties and thermal stability of composite electrolyte.The result of XRD,FTIR and DSC showed that the crystallinity of PEO could be reduced by adding Al-MOF.When the addition amount of Al-MOF was 5 wt.%,the electrolyte has a highest conductivity.The ionic conductivity at room temperature increased from 7.71×10-7 S cm-1 to 2.09×10-5 S cm-1(PEO-MOF5%).The Lewis acid effect of Al-MOF helped to increase the lithium ion transference number to 0.46.The voltage window of PEO-MOF5%electrolyte can reach 4.7v,and the polarization voltage of lithium symmetrical battery is lower,which still remains stable after circulating for 1000 h.Under the test conditions of 30? and 0.1 C,the maximum discharge capacity of LFP/PEO-MOF5%/Li solid-state battery is 137.9 mAh g-1,this battery still operated stably after 200 cycles with the discharge capacity of 111.8 mAh g-1,which is 81.1%of the maximum.However,under the test conditions of 60? and 0.1 C,the discharge capacity of LFP/PEO-MOF5%/Li battery in the first cycle is 167.3 mAh g-1,there is 87.1%retain after 100 cycles,showing good cycle stability.PEO@CG electrolyte was prepared by filling PEO into the orifice of Celgard 2400 diaphragm.The results of SEM,photographs and FTIR showed that PEO successfully filled the orifice of diaphragm.The physical limitation of the pore allows the polymer to form directional crystallization,which is benefited the conduction of lithium ions.The ionic conductivity of PEO@CG electrolyte is 8.51×10-6 S cm-1 at 30?,and 2.08×10-4 S cm-1 at 60?.The lithium ion transference number also increased to 0.32.Due to the stable chemical properties of the diaphragm,the electrochemical stability has been improved,with an electrochemical window of 4.5 V(vs.Li/Li+)and the lithium symmetrical battery capable of cycling for more than 600 h.LFP/PEO@CG/Li solid state battery shows good stability.Under the test conditions of 60? and 0.1C,the maximum discharge capacity of LFP/PEO@CG/Li battery is 156.7 mAh g-1,which still has a capacity retention rate of 92.9%after 130 cycles.Under the test conditions of 60? and 0.1 C,the maximum discharge capacity of the battery is 158.8 mAh g-1.And the capacity retention 91.1%after 300 cycles.PEO@CG has high ion conductivity,lithium ion migration number and thin thickness,so the battery also has good multiplier performance.Moreover,the good mechanical properties of the diaphragm can greatly improve the mechanical strength of the electrolyte,which is conducive to its stability in the battery cycle.