Study On The Preparation And Performance Of PEO-based Polymer Composite Electrolyte

Lithium-ion batteries(LIB)are widely used in modern society from portable electronic devices to network-scale storage,and are a major energy storage device.However,organic liquid electrolytes are generally used in lithium ion batteries(LIB),which may cause many safety problems,such as leakage,reduced service life,flammability,and some side reactions.The current effective way to eliminate these safety issues is to replace organic liquid electrolytes with solid electrolytes.The solid polymer electrolyte not only does not leak,does not chemically react with the electrode and the container,but also has the advantages of high energy density,wide operability temperature range,and good thermal stability,so it has attracted extensive attention and research.Polyethylene oxide(PEO)is considered to be an important solid polymer electrolyte(SPE)matrix due to its excellent lithium salt dissolving ability and low cost.However,PEO still has many problems,such as ion conductivity at room temperature Low rate,poor interface stability between electrolyte and electrode,poor mechanical properties,flammability,etc.Aiming at the above-mentioned problems,this paper selects PEO as the polymer matrix,adds tannic acid and dopamine to modify the polymer electrolyte,and obtains a polymer electrolyte with excellent basic and electrochemical performance.The second chapter is to prepare polymer electrolyte membrane by adding different content of tannic acid to polyethylene oxide(PEO)and lithium bis(trifluoromethanesulfonamide)imide(Li TFSI)system by casting method.Under the action of hydrogen bonds,the crystallinity of PEO is destroyed to improve the ionic conductivity of the polymer electrolyte.The polymer electrolyte membrane was characterized by X-ray diffraction,differential scanning calorimeter,thermogravimetric analyzer,mechanical properties,surface morphology,AC impedance method and battery performance.The test results show that with the increase of tannic acid(TA)content,the crystallinity decreases,the elongation at break increases,up to 675%,and the thermodynamic properties are also greatly improved.At room temperature,when the tannic acid content is 1%,the tensile strength reaches 0.22MPa,the maximum ionic conductivity reaches 3.4×10^-5S/cm,and it has good electrochemical stability,and the electrochemical window reaches 5.13V.The assembled Li|PEO-Li TFSI-TA(1%)|Li Fe PO₄battery has excellent cycle stability and rate performance.At a current density of 0.1C,the battery can reach a discharge capacity of 142.15 m Ah·g^-1 and cycle200.After the lap,the capacity retention rate is as high as 99%.In Chapter 3,in order to eliminate the potential safety hazards of polymer electrolytes,dopamine is added to the polymer electrolyte system,and the dopamine is polymerized in situ in the PEO matrix to obtain the PEO polyelectrolyte compounded with polydopamine nanoparticles.On the basis of performance and electrochemical properties,further improve its thermal stability and flame retardant properties.The tensile test showed that after adding dopamine,compared with the pure polymer electrolyte membrane,its breaking strength increased by up to 40%,and its elongation at break increased by 22%.The thermodynamic performance test found that the thermal stability of the polymer electrolyte membrane was greatly improved after adding dopamine.In addition,a cone calorimeter was used to evaluate the flame retardant performance of the polymer electrolyte membrane.After adding 20%dopamine,the heat release rate(HRR)and total heat release(THR)of the electrolyte were reduced by26.6%and 33.7%,respectively.The CO release rate decreased by 22%,and the peak mass loss rate(MLR)of the polymer electrolyte membrane also decreased by 41.7%.In addition,when the dopamine content is 10%,the ion conductivity of the polymer electrolyte membrane is as high as 1.41×10^-4S/cm.The test of Li|PEO-Li TFSI-DA(10%)|Li Fe PO₄battery found that it has excellent cycle stability.At a current density of0.1C,the battery can reach a discharge capacity of 147.15 m Ah·g^-1,after 200 cycles of cycling,The capacity retention rate is still as high as 99%.