Study On Gel Polymer Electrolyte With Graphene Oxide As Filler

If the polymer electrolyte exists in a gel state,it can well solve the safety problem of conventional lithium ion batteries.In order to meet the commercial application of polymer batteries and improve the electrochemical performance of polymer electrolytes,we take fillers as the main measures to modify the polymer.The aim to prepare high energy density and cycle polymer LFP/Li battery,we systematically study the effect of filler content on the electrolyte.The main research contents are as follows:(1)The gel-type polymer electrolyte(GPE)was prepared simply and quickly by hot pouring method,in which graphene oxide(GO)was used as a filler.The addition of GO reduced the crystallinity of the polymer,from the original 41.4%to 20.5%,which achieved the effect of reducing by more than 50%.The results show the decrease in crystallinity that increases the ionic conductivity of GPE nearly 300%,up to 1.3m S/cm.The smallest ion transport activation energy of Ea is 1.076J/mol.At the same time,the addition of GO significantly increased the lithium ion transferring number of GPE,up to 0.79.Under the combined effect of GO modified GPE,the specific capacity of the battery is increased about 20%after being assembled into LFP/Li battery,and the battery shows more stable cycling performance.After 100 cycles of 0.2C cycle the specific capacity retention rate was 94.4%.When GO modified GPE,it was unevenly distributed in the polymer matrix.GO may have some curling and clustering in the polymer.The reason is because GO is poorly compatible with the PVDF-HFP matrix.On this basis,it was also found that the contact resistance of GO modified GPE to the lithium electrode is poor,which results in an increase in interface impedance and is not conducive to the conduction of lithium ions at the two-phase interface.(2)Based on the above problems,we grafted the PEO segment on the carbon network of GO(GO-PEO)to achieve the effect of increasing the dispersion of the filler in the PVDF-HFP matrix.GO-PEO as a filler can further reduce the crystallinity of GPEP up to 19.7%,further increase the ionic conductivity up to 1.6m S/cm.It shows the smallest ion transport activation energy of Ea up to 0.603J/mol,and maintains high lithium ions number of transferring.It is worth noting that the interface resistance of GO-PEO modified GPEP to the lithium metal anode is reduced,which significantly improves the compatibility with the lithium metal anode.The GPE assembled Li/Li battery can perform stable cycling when the current is 2m A/cm~2,and the polarization voltage is only 0.2V.After the modified GPE is assembled into an LFP/Li battery,the specific capacity of the battery is increased by nearly 40%.While maintaining cycle stability,it shows better rate performance.It can still maintain 40m Ah/g of discharge specific capacity under 5C current cycling.