Research On Preparation,Modification And Electrochemical Performance Of PEO/PVA Polymer Solid Electrolyte

Lithium-ion batteries(LIBs)have undoubtedly become ideal choices for consumer electronics and electric vehicles due to their high energy density.Lithium metal anodes are considered to be the most promising anode materials for improving battery energy density due to their ultra-high theoretical capacity and lowest redox potential.However,the inherent safety,poor thermal stability,lithium dendrites,and poor cycle performance of traditional electrolytes make it difficult to match with metal lithium anodes.Replacing liquid electrolyte with solid electrolyte is the best way to solve the above problems.The research and development of all-solid-state batteries has also become an important research direction in the field of lithium-ion batteries.It is expected to further increase energy density and ensure extremely high safety.The polymer electrolyte is considered to be an effective solution to replace the current organic liquid electrolyte in many solid electrolytes to build a safer lithium ion battery.On the one hand,in addition to components with good electrochemical and physical properties,polymer electrolytes can also suppress the growth of lithium dendrites and improve the unstable cathode electrolyte interface due to their unique properties,such as flexibility and good mechanical properties.Optimize the dissolution and migration of lithium ions.At present,polymer electrolytes based on polyethylene oxide(PEO)are the focus of research.When PEO is complexed with lithium salt(LiTFSI),it has good lithium ion conductivity.However,most of the current research work is only to modify the Li+transport capacity of a single PEO matrix from the perspective of blending,crosslinking,plasticizing or compounding,and it is difficult to fundamentally change its high crystallinity characteristics.From the perspective of "similar compatibility",this paper innovatively proposes to introduce polyvinyl alcohol(PVA)into the PEO segment to increase the carrier concentration to construct a two-component Li+carrier framework and solve the PEO matrix room temperature The problem of high crystallinity;secondly,the high-speed Li+permeation network of PEO-PVA is constructed by the action of polyphenylene sulfone(PESf)organic additives;finally,maleic anhydride(MAH)is added to the PEO-PVA system to play a small molecule Lubricating properties further improve the interface of the PEO-PVA system;from three levels of "two-component Li+ carrier framework construction-small molecule interface lubrication-Li+ percolation network construction",PEO-PVA polymer compounding of lithium ion secondary batteries was progressively studied The preparation and performance of the electrolyte membrane,the main research contents and conclusions of this article are as follows:1.Construction of lithium ion active carrier:Use the organic additive polyvinyl alcohol(PVA)that is prone to crosslinking reaction of PEO and blend PEO-PVA.Because PVA and PEO have similar molecular structures and their molecular weights are small,they can be used in To a certain extent,it disrupts its regularity and improves the ionic conductivity of the system,thereby improving the electrochemical performance of the solid-state battery(electrochemical window 5.12 V);improving the stability and compatibility of the electrode and electrolyte interface,half-cell LiFePO4/PEO-LiTFSI-30%PVA/Li shows better cycle performance than LiFePO4/PEO-LiTFSI/Li.After LiFePO4/PEO-LiTFSI-30%PVA/Li can cycle for about 20 cycles,its capacity begins to decay,while LiFePO4/PEO-LiTFSI/Li can only circulate for about 10 cycles,its capacity is greatly attenuated,and finally the capacity is close to 0.2.Construction of lithium ion permeation network:adding polyphenylene ether sulfone(PESf)to the PEO/PVA system to improve the lithium ion conductivity of the system.To study the effect of PESf on the performance of organic polymer electrolytes,by adding PESf as a plasticizer,the electrochemical window of the polymer electrolyte of this system can reach 5.38 V,and compared with the pure PEO system,at 60℃,it can Stable circulation is at least 100 cycles,and its Coulomb efficiency is maintained at about 98%.Moreover,the modified polymer electrolyte has a certain elasticity and plasticity,therefore,it can weaken the influence of lithium dendrite growth and puncture during the charge and discharge cycle,which causes battery short circuit.3.Improvement of interfacial stability:maleic anhydride with stable structure is added to PEO/PVA system,and maleic anhydride is a small molecule,which can be dissolved in the solvent acetonitrile.Moreover,at 60℃,maleic anhydride can ring-open to form smaller molecular weight organics.In the microstructure,the addition of maleic anhydride can disrupt the regularity of the PEO segment,increase the amorphous area of PEO,and reduce the PEO.Crystallinity,thereby enhancing the lithium ion conductivity of the polymer electrolyte.At the same time,maleic anhydride can be stable under high pressure.The electrolyte electrochemical window can be increased to 5.22 V.In summary,based on the research idea of two-component Li+ conductive matrix,through the modification method of blending small molecules and organic particles,the electrochemical performance of PEO-based polymer electrolytes has been improved to a certain extent,and a relative The composite polymer electrolyte with higher lithium ion conductivity,wider electrochemical window and higher lithium ion migration number in PEO-LiTFSI provides a possible idea for the research and development of polymer electrolytes in the future.