The Research Of Preparation And Modification For PEO-based Solid Electrolyte

Lithium-ion batteries?LIBs?are now widely used in 3C consumer electronics,passenger/commercial vehicles and advanced smart grid energy storage devices.The progress of society and technology also makes people pursue high-energy storage equipment.The Made in China 2025 proposed by the State Council in 2015 clearly pointed out the energy density target of power shovel in the next fifteen years.The US federal government also proposed the battery 500 plan.In terms of the battery safety,traditional LIBs contain components of liquid electrolyte.During long-term use,the formation of lithium dendrites will pierce the membrane and cause a safety accident.Solid electrolytes have a wide electrochemical stability window,good chemical compatibility and excellent mechanical properties.Applying them to LIBs can solve the above-mentioned issues of the energy density and safety.PEO-based polymer solid electrolyte is one of the representatives,and has been widely studied due to its simple preparation process and excellent interface contact.However,due to its high crystallinity,it exhibits a low lithium-ion conductivity,which limits its practical application.Aiming at this problem,the polymer solid electrolyte was prepared by tape-casting method.On the basis of this,the addition and modification of nanoparticles were carried out to prepare a composite polymer solid electrolyte,and finally all solid-state lithium ion battery with LiFePO₄ were assembled to make test.The main experimental contents and conclusions for this paper are as follows:?1?The PEO-based solid state electrolyte was prepared by tape-casting method.The effects of different molecular weight poly?ethylene oxide?and different EO:Li molar ratio on the physical properties and lithium-ion conductivity of the materials were investigated.At a ratio of EO:Li=15:1,the PEO-based solid state electrolyte prepared by using PEO having a molecular weight of 600000 has the lowest degree of crystallinity.On the basis of this,by adjusting the ratio of the polymer to LiClO₄,it is concluded that the material with EO:Li=10:1 has the lowest degree of crystallinity and the highest lithium-ion conductivity.?2?The titanium dioxide nanoparticles composite PEO-based solid electrolyte was prepared by tape-casting method,and the best mass fraction of titanium dioxide was discussed.It was proved that the as-prepared material?CPE10?having titanium dioxide nanoparticles with a mass fraction of 10%has the lower degree of crystallinity and more superior mechanical properties.Electrochemical analysis shows that CPE10 has the highest lithium-ion conductivity and the lowest activation energy.The CPE10 also has a high electrochemical window and low polarization.Finally,the all solid-state lithium-ion battery test results show that LiFePO₄/CPE10/Li has more excellent cycle stability at different current densities.?3?The walnut-like silica?WLS?was synthesized.The WLS composite PEO-based solid electrolyte?PLWLS?was prepared by the method of tape-casting,and the best mass fraction of WLS nanoparticles was discussed.Physical characterization indicates that PLWLS-15 has the lowest crystallinity and the tensile strength of the material is significantly improved.The AC impedance test results show that the room temperature conductivity of PLWLS-15 is improved.The PLWLS-15 and PLWLS-0 were assembled into the all solid-state lithium-ion battery for charge and discharge tests.The results show that LiFePO₄/PLWLS-15/Li has more excellent cycle stability at different current densities.