Modification And Performance Of PEO-based Composite Polymer Electrolyte

Solid lithium batteries have attracted the focus of many researchers due to its advantages of high energy density,safety and long cycle life.As the main component of solid lithium battery,composite solid electrolyte has attracted wide attention because of its characteristics of both organic polymer and inorganic compounds.However,composite solid electrolytes still face many problems such as low ionic conductivity at room temperature,narrow electrochemical window,unstable interface and use of toxic solvent in the preparation process,which restrict the industrial application of solid lithium batteries.Therefore,this work studied the composition optimization,compatibility with the positive and negative electrode,film-forming property and green solvent substitution of the composite solid electrolyte.The details are as follows:In this work,polyethylene oxide(PEO)was selected as the matrix of composite polymer electrolyte,which has excellent dissociation ability for lithium salts.The PEO-Li TFSI-LLZTO-Ti O₂composite polymer electrolyte was prepared by using Li_6.4La₃Zr_1.4Ta_0.6O₁₂(LLZTO)as active filler and Ti O₂as inert filler.The optimal ratio of composite polymer electrolyte was determined.The ionic conductivity could reach5.8×10^-5S/cm at 25°C and 4.1×10^-4S/cm at 70°C.The voltage compatibility could up to 5.2V.Solid lithium batteries were assembled using PEO-Li TFSI-LLZTO-Ti O₂as electrolyte,LFP as cathode and lithium as anode.The discharge specific capacity was165 m Ah/g at 0.1 C and 153 m Ah/g at 0.2C(170 m Ah/g).After 150 cycles,the battery capacity was maintained by 95%.Symmetrical battery of lithium/electrolyte/lithium was tested,and showed that the battery has excellent interface stability and reversible transfer of Li ion after 2000 h cycling at 0.2 m A/cm².The battery with NCM811 and NCM622 cathode materials could achieve 193 m Ah/g and 165 m Ah/g at 0.1C,respectively.This indicates that the electrolyte can combine with high-voltage materials to improve the energy density of the battery.In order to improve the film-forming property of the composite polymer electrolyte,PEG/PEO blend was used as the polymer matrix.At the same time,the ethanol solvent as substitute of acetonitrile was used to prepare the electrolyte.The results showed that the ethanol had little effect on the performance of battery.These results will contribute to the further development and application of solid lithium batteries.