| In recent years,lithium-ion batteries have been widely used in consumer electronics and new energy vehicles,but the development of electric vehicles is facing challenges in battery life and safety,which raised higher requirements for specific energy and safety capability of lithium-ion batteries.At present,the traditional commercial lithium-ion battery generally uses a liquid electrolyte,which faces the problems that the electrolyte is flammable,volatile,easily leaked,easy to cause side reactions and battery polarization,and the separator is easy to shrink under high temparature and cause short circuits.In response to these problems,we take the separator and electrolyte as the research object to conduct a varity of structure design:on the one hand,we designed high safety separator to improve mechanical thermal stability of the separator;on the other hand,we did structural design of the gel state and solid polymer electrolyte to reduce and further replace the use of liquid electrolyte,at the same time increase the migration number of lithium ions,reduce the polarization of electrodes and the occurrence of side reactions,maintain the safety of the battery and stable electrochemical cycle.The main research work is as follows:1.Developed a new type of core-shell structured ceramic nonwoven separator by atomic layer deposition(ALD)technology combined with electorspining techinique.The role of oxygen plasma pretreatment was studied by infrared spectroscopy and Xray photoelectron spectroscopy.The separator shows high thermal mechanical stability(does not shrink significantly at a temperature of 230℃),providing a new strategy for ultrathin high safety separator.2.A single ion conducting gel polymer electrolyte with porous membrane structure was prepared.Single ion conductor is a strategy to reduce polarization and improve the electrochemical performance of lithium ion batteries.In this paper,P(MPEGAAMPSLi)single ion conductor polymer lithium salt was prepared by free radical polymerization,and a single ion conducting gel electrolyte was prepared by electrostatic co-spinning with polyvinylidene fluoride-hexafluoropropylene(PVDFHFP).The ion conductivity of 2.8×10-5 S cm-1 at room temperature with an ion migration number of 0.75 and it has stable electrochemical cycling stability at room temperature(25℃)and high temperature(60℃).The molecular dynamic simulation results show that plasticization promotes the dissociation of lithium ions and at the same time increases the diffusion coefficient of lithium ions(8.05×10-11 cm2/s to 1.37×10-9 cm2/s).3.A quasi-solid single ion conductor polymer electrolyte with a 3D network structure was prepared.The electrolyte consists of cross-linked lithium poly(2acrylamido-2-methylpropane sulfonate)(PAMPS-Li)as a lithium source and high molecular weight linear polyethylene oxide(PEO)as an ion-conducting polymer matrix.Due to 3D network structure of the electrolyte,the two components show a good compatibility and the crystallinity of PEO decreased clearly.In addition,the lithium ion conductive film shows the Li+dominant conductivity and high lithium ion transference number(0.77).In addition,the battery shows a good cycle performance during tests.4.Prepared mesoporous silica active filler with the physically immbolization of ionic liquid and PEO-based solid electrolyte containing the active filler.The design of the active filler enhances the Li+transport kinetics at the interface between the filler and the PEO-based electrolyte and the ionic conductivity is up to 4.3×10-4 S cm-1 at 60℃,while maintaining good mechanical strength.The composite electrolyte can inhibit the growth of lithium dendrites.The assembled lithium symmetric battery has long cycle life and low polarization voltage and the Li/LiFePO4 half coin cell also showed stable cycle performance and 1C at 60℃. |
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