Preparation Of Solid Polymer Composite Electrolyte Based On PEO And Its Application In Lithium-ion Battery

In recent years,there have been frequent problems in commercial lithium batteries,such as leakage of organic electrolyte,volatilization,poor thermal stability,flammability and explosion,and so on.The effective solution to these problems is the use of solid electrolyte.Due to the absence of organic liquid,the probability of chemical reactions between solid electrolytes and electrodes and containers can be greatly reduced.At the same time,solid electrolyte also has the advantages of flexible geometry,wide operating temperature range and high energy density,so it has attracted extensive attention.However,there are still some problems in the practical application of solid electrolyte,such as the interface stability between solid electrolyte and electrode in the solid-state battery is poor,the ion transfer number and the ion conductivity at room temperature are low.The charge-discharge specific capacity of the battery is small,etc.In view of the problems existing in the above-mentioned solid electrolyte,this paper uses different methods to modify it.The main research contents are as follows:1.Inorganic fast ionic conductor LLTO nanowires with high ionic conductivity were prepared by electrospinning and filled into polymer PEO matrix as fillers to prepare a new type of PEO/LiTFSI/LLTO polymer electrolyte.The results of scanning,XRD,impedance and cycle texts showed that the addition of LLTO nanowires can effectively reduce the crystallinity,improve electrochemical window and the ionic conductivity.When the percentage of LLTO nanowires is 5%,the ionic conductivity reaches the highest,it is 3.63×10^-4 S·cm^-1 at 60?,and the specific discharge capacity of the cells assembled with LiFePO₄ as positive electrode and lithium as negative electrode is still 123 mAh·g^-1,and the coulombic efficiency is about 100%.2.The modification of PEO-based polymer electrolyte with amorphous polymer PPC was studied.The PPC is an amorphous polymer.By blending with PEO matrix,the amorphous region of polymer composite electrolyte can be effectively increased and the crystallinity of PEO matrix can be decreased.Furthermore,the migration rate of ions was increased.The results show that the addition of PPC can effectively reduce the crystallinity of polymer,improve the electrochemical window of solid electrolyte,the mechanical properties and the interface stability of lithium through the measurement of DSC,XRD,ionic conductivity and cycle,etc.Compared with pure PEO polymer electrolyte,when the addition of PPC is 50%,the ion migration number reaches the highest,from 0.156 to 0.184,and the electrochemical window reaches 4.9V.The charge-discharge test of the battery shows that the solid-state polymer composite electrolyte has excellent cycle performance.3.An organic-inorganic composite solid electrolyte based on PEO was prepared by adding inorganic fast ionic conductor LLTO nanowires on the basis of adding amorphous polymer PPC to prepare a new type of PEO/PPC/LLTO organic-inorganic composite solid electrolyte.The experimental data show that when the content of PPC is 50%and the addition of LLTO is 8%,the performance reaches the best,compared with pure PEO-based solid electrolyte and PEO-50%PPC composite electrolyte.The ionic conductivity of the modified PEO-50%PPC-8%LLTO solid polymer composite electrolyte was the highest,4.72×10^-4 S·cm^-1 at 60?.The electrochemical window was 5.1 V and the ion migration number was 0.227.The interfacial stability of lithium was also improved significantly.The test results show that the discharge specific capacity of the battery is over 130 mAh·g^-1 at 0.5 C and 60?,the capacity retention is 96%,and the coulombic efficiency is about 100%.