Study On Thermoelectric Properties Of Polyoxyethylene Composite Solid Electrolyte

In consideration of the safety,environmental protection,and reliability of traditional liquid batteries,scientists have increasingly turned their research directions to solid-state batteries.Solid polymer electrolytes were proposed in the 1970s,and it has gradually become a hot spot in the field of solid electrolyte research due to its high safety and environmental protection.However,the ionic conductivity of most solid polymer electrolytes at room temperature is generally very low,and it is difficult to achieve application conditions.In the1990s,scientists discovered that a large number of oxygen atoms in polyethylene oxide（PEO）can provide lone pairs of electrons to conductive particles and form complexes with them.Therefore,in general,alkali metal salts can dissolve well in PEO,and then complete the transport of charged particles in the electrolyte through the movement of molecular chains.Studies have shown that the ionic conductivity of PEO can reach 10^-6S·cm^-1,so the solid polymer electrolyte based on PEO has the potential to meet scientists’requirements for new batteries,and the direction of composite copolymer electrolyte research on PEO is opened.In this thesis,the method that combine simulations based on molecular dynamics theory and experiments is mainly used to study the thermodynamic and electrochemical properties of composite solid electrolytes and copolymer solid electrolytes based on PEO.We also analyze the influence of the material composition ratio and temperature on the electrothermal performance of the solid electrolyte.It is composed of polyethylene oxide（PEO）,polyvinylidene fluoride（PVDF）,1,2-epoxy-4,7,10,13-tetraoxatetradecane,alkali metal salt,and inorganic filler particles to construct different solid electrolyte models,and use the Large Atomic/Molecular Mass Parallel Simulator（LAMMPS）for molecular dynamics simulation.Under different lithium salt mass concentration ratios and different temperatures,the analysis of structural parameters such as its radial distribution function and the radius of gyration shows that the composite solid electrolyte has better electrochemical stability at working temperature.Then,in the process of calculating the thermal conductivity of solid electrolytes of different components,it is found that as the temperature rises,the thermal conductivity curves increase at a slower slope.Compared with the mixed system of PEO/lithium salt,the composite solid electrolyte has a lower thermal conductivity.From the analysis of the mean square displacement curve of lithium ions in the electrolyte,it can be seen that the mean square displacement curve rises in an approximately straight line with the increase of time,and as the temperature rises and the mass fraction of lithium salt increases,the slope of the curve also changes.By calculating the ionic conductivity of different components of PEO-based electrolyte,it can be seen that the ionic conductivity of the composite electrolyte with polyvinylidene fluoride and alumina inorganic particles and the PEO-C₁₀H₂₀O₄ copolymer electrolyte are higher than that of the mixed system of PEO and lithium salt.From the simulation calculation results,it can be known that PEO-C₁₀H₂₀O₄ copolymer electrolyte has the highest ionic conductivity when the mass fraction of lithium salt is 20%.By comparing the simulation results with the experimental results,it can be known that the PEO-PVDF composite solid electrolyte has the highest ionic conductivity when the mass fraction of lithium salt is 25%.In summary,this thesis studies the structural parameters,thermal conductivity,and ionic conductivity of different component composite solid electrolytes and polymer solid electrolytes with temperature and composition ratio changes,verifying the existing experimental conclusions,and at the same time the thermodynamic and electrochemical laws of the solid electrolyte are analyzed,and the laws are summarized,explained and predicted.