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The New Lithium-ion Battery Polymer Electrolytes Preparation And Performance Study

Posted on:2011-10-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:P ZhangFull Text:PDF
GTID:1111360305497028Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
With the development of the economy and society, much more attention has been paid to the utilization of the new energy for the shortage of traditional energy. Lithium ion batteries, with the advantages as high energy density, high voltage, good cycling performance, low self discharge, have been widely used in mobile communication devices, portable electronics and military equipments. The use of polymer electrolyte could overcome the safety problems caused by the leakage of traditional liquid electrolyte and gain higher energy density. Up to now, researches are mostly focused on composite polymer electrolyte and porous polymer electrolyte, both of which are based on gel polymer electrolyte.This dissertation includes three major parts. Firstly, composite polymer electrolytes were prepared by adding fillers with modified surface properties or morphology to improve their electrochemical, thermal and mechanical performance. Secondly, porous polymer electrolyte was prepared by a novel microwave assisted effervescent disintegrable reaction. Compared to bellcore technology and phase inversion process, this method presents an easy fabrication way to prepare porous polymer electrolyte for practical use. Thirdly, composite porous polymer electrolytes were prepared by adding some novel filler to merge the advantages of the composite polymer electrolyte and porous polymer electrolyte.1. Researches on the composite polymer electrolytes to improve their performance.(1) Initially, nano-TiO2 was modified by coating with a layer of poly(methyl methacrylate) (PMMA) by emulsion polymerization. Composite polymer electrolytes with this modified nano-TiO2 were then prepared by in situ copolymerization of poly(methyl methacrylate-acrylonitrile) (P(MMA-AN)). Morphology, thermal, electrochemical and spectroscopic measurements were used to characterize the electrolytes. The PMMA-coated nano-TiO2 was well dispersed in the polymer matrix due to the PMMA coating layer making the nanoparticles hydrophobic to effectively avoid the aggregation of the nanoparticles. The homogeneous composite polymer electrolytes of this PMMA-coated nano-TiO2 have better thermal tolerance, higher ionic conductivity and wider electrochemical stability.(2) Composite polymer electrolytes were prepared by adding SiO2 nanowires into P(VDF-HFP). The electrochemical and mechanical properties were enhanced by 3-dimensional network interaction between the nanowires and the polymer chains. The composite polymer membrane can tolerate the maximal stress of 27.8 MPa. The ionic conductivity of the prepared gelled polymer electrolyte is up to 1.08×10-3 S·cm-1 and electrochemical window 4.8 V. The assembled Li/CPE-10/LiFePO4 cell also shows good capacity retention. The composite polymer electrolyte with SiO2 nanowires and 1-dimensional nanofiller provides a new way to prepare polymer electrolytes with better electrochemical and mechanical performance for practical application in lithium ion batteries.2. Researches on easy fabrication method to prepare porous polymer electrolyte.Porous polymer membranes have been prepared by a microwave assisted effervescent disintegrable reaction. The fine connected porous structure was obtained by promoting effervescent disintegrable reaction between citric acid and sodium bicarbonate due to the assistance of the microwave. The effects of different reaction conditions such as temperature, time and amount of the added effervescent disintegrant on the porous structures were investigated. Shorter reaction time at higher temperature is beneficial to higher porosity of the membrane. The ionic conductivity of the prepared porous polymer electrolytes based on the porous polymer membranes is up to 1.17×10-3 S/cm and their electrochemical window is above 5 V. This method is convenient and will greatly promote the practical application of porous polymer membranes in various areas.3. Researches on composite porous polymer electrolyte to merge the advantages of composite polymer electrolyte and porous polymer electrolyte.(1) Composite porous polymer electrolyte was prepared by phase inversion process and SiO2 aerogel was used as the filler. The combination of the mesoporous structure in SiO2 aerogel and submicron pores in the polymer matrix help this polymer electrolyte gain better electrochemical performance.(2) Porous structure in the polymer electrolyte was introduced by added micro and nano SiO2 shell which of the structure could be thought as the separated pores in the polymer matrix. This kind of composite polymer electrolyte merges better mechanical strength and good electrochemical performance such high ionic conductivity and wide electrochemical window compared with the polymer electrolyte obtained by traditional method.(3) We have successfully developed a new process to prepare porous poly(methyl methacrylate-co-acrylonitrile) (P(MMA-AN)) copolymer based gel electrolyte. The porous structure in the polymer matrix is achieved by adding SnO2 nanoparticles which are mostly used as gas sensor materials. The space charge layer on the surface of SnO2 nanoparticles forms a special gas-liquid phase interface with the solvent NMP. Once the cast polymer solution is stored at an elevated temperature to evaporate the solvent, gas-liquid phase separation happens and spherical pores are obtained. The ionic conductivity at room temperature of the prepared gel polymer electrolyte based on the porous membrane is as high as 1.54 x 10-3 S·cm-1 with the electrochemical stability up to 5.10 V (vs. Li/Li+). This method presents another promising way to prepare porous polymer electrolyte for practical use.
Keywords/Search Tags:Lithium ion batteries, polymer electrolyte, composite polymer electrolyte, porous polymer electrolyte, SiO2, TiO2, SnO2, nanoparticle, nanowire, aerogel, shell structure, surface modified, microwave assisted, effervescent disintegrable reaction
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