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Studies On Phosphate-type All-Solid-State Polymer Electrolytes For Lithium Ion Batteries

Posted on:2008-01-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z J LingFull Text:PDF
GTID:1101360272477718Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Polymer electrolytes are the key to development of lithium ion batteries. Research in this area is valuable in either theory or application consideration. Polymer with branch-shaped structure is helpful to improve polymer electrolyte's electrochemical performance. Though great progresses have been made in the research on PEO-based all-solid-state polymer electrolyte, localization especially low ionic conductivity at room temperature is so obvious, which directly influences the application to lithium-ion batteries. We put attention mainly on the research of polymer electrolyte system based on branch-shaped structure. Results showed potential application as well as academic meaning to lithium-ion batteries.In this work, branch-shaped phosphate-type molecular structure was designed. Reacting phosphoryl oxychloride with polyethylene glycol (abbreviated as PEG) and other compounds, branch-shaped polyether phosphate-type macromolecular monomers were successfully prepared. Following complexing monomers with lithium percholorate. polymer(PEP) electrolyte was obtained after UV-curing The performance of the phosphate type polymer electrolyte was found to be determined by the composition,molecular weight of macromolecular monomers and content of lithium percholorate as well as temperature. The molecular weight and content of PEG used greatly influence the final performances of obtained polymer electrolyte. For some one series of polymer electrolyte using PEG with the same molecular weight, ionic conductivity at room temperature exhibits a maximum value with growth of molecular weight of phosphate macromolecular monomers and then decreases, which is similar to that of the variation of ionic conductivity depending on PEG with different molecular weight and salt content. Ionic conductivity reaches the maximum value of 4.41×10-5S/cm when PEG and macromolecular monomers'average molecular weights are around 400 and 1600 respectively and content of lithium perchlorate is 5% mass of polymer matrix at the same time. Polymer electrolyte is amorphous at ambient temperature. The electrochemical stable window and thermal decomposition temperature of phosphate type polymer electrolyte is up to 10V and 250℃respectively.PEP-type polymer is difficult to be modified because of its cross linkage. Soluble comb-shaped polyether phosphate type polymer LPEP was obtained by polymerizing the phosphate macromolecular monomers with long side chain, which was prepared by reacting polyethylene glycol mono methyl ether and other compound with phosphoryl oxychloride. The performance of the phosphate type polymer electrolyte was found to be determined by the molecular weight of polyethylene glycol mono methyl ether, salt content and temperature. The maximum ionic conductivity of polymer electrolyte at room temperature declines with the growth of the chain length of polyethylene glycol mono methyl ether, while the corresponding salt content rises. The phosphate-type polymer electrolyte is stable up to 10V and lithium ion transference number increases a little appreciably with the side chain length increases. System shows a little better on both ionic conductivity at room temperature and thermal stability compared to PEP-LiClO4 polymer electrolyte system.To decrease the crystallization of LPEP- LiClO4 type polymer electrolyte and to further improve system's performance, nano-scale alumina and self-prepared ion-conducting Li1.3Al0.3Ti1.7(PO4)3 particles were introduced into polymer electrolyte independently. The addition of nano-particles decreases the crystallization remarkably. The influence of particles'content on glass transition temperature shows difference for these two type materials. Ionic conductivity could reach about 10-4S/cm at room temperature after complexing LPEP750-8%LiClO4 with nano-particles. Lithium transference number was also enhanced. The thermal stability and the stability of interface between polymer electrolyte and lithium electrode could be effectively improved after the addition of nano-particles as well.Polymer electrolyte was fabricated into lithium ion batteries. The batteries show favorable cycle performance under small current charging and discharging.
Keywords/Search Tags:Lithium ion battery, Phosphate, All-solid-state polymer electrolyte, Nano-particle, Ionic conductivity
PDF Full Text Request
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