| Secondary lithium batteries are widely used in the field of new energy vehicles,due to their high energy density and long cycle life.However,they also have the safety hazards such as flammability and explosion.Using solid electrolyte instead of organic electrolyte was one of the effective ways to solve these problems.Polyethylene oxide(PEO)-based solid polymer electrolyte,as a kind of solid electrolyte,is considered to have excellent industrial application prospect due to its high flexibility,excellent machinability and good compatibility with electrode.However,the ionic conductivity of PEO at room temperature is lower than 10-5 S·cm-1,which limits its application in solid-state lithium batteries.It will be a significant task to design PEO-based solid polymer electrolyte(SPE)materials with good comprehensive properties.In this study,PEO was used as the matrix,and micro-and nano-fillers on different scales were selected to blend with PEO.The interaction among components was regulated on the molecular level,so as to improve the comprehensive performance of the composite solid polymer electrolyte.Results are as follows:1.Allophane(AL)was prepared by the sol-gel method and the PEO/LiClO4/AL electrolyte was obtained by the solution blending method.It is found that the noncovalent bonding interactions(complexation,hydrogen bonding and Lewis acid-base interaction)among AL,LiClO4 and PEO significantly inhibit the crystallization of PEO.When the molar ratio of EO/Li+was 10:1 and the content of AL was 5%compared with the mass of PEO,the crystallinity of PEO in the electrolyte membrane was only 4.1%.The ionic conductivity of the sample at 40℃ was 2.5×10-5 S·cm-1.And the electrochemical stability window and the lithium-ion transference numberat 80℃ were 5.0 V and 0.24,respectively.The initial discharge capacity of the assembled LiFePO4/SPE/Li solid state battery was 110.6 mAh·g-1.And the discharge capacity was 90.9mAh·g-1 after 80 cycles.In this process,the charge-discharge efficiency decayed from 95.2%to 41.8%,and the discharge capacity retention rate was 82.1%.2.PEO/LiClO4/Halloysite(HNTs)electrolytes were prepared by solution casting method.It is found that the special nanotube structure of HNTs can not only promote the dissociation of LiClO4,but also provide a channel for the transmission of Li+.When the molar ratio of EO/Li+was 10:1 and the content of HNTs was 30%of the mass of PEO,the crystallinity of PEO in the electrolyte membrane was only 7.5%.The ionic conductivity of this electrolyte membrane at 30℃ was 3.7×10-5 S·cm-1.The electrochemical stability window and the lithium-ion transference number were 4.5 V and 0.38 at 80℃,respectively.The initial discharge capacity of the assembled LiFePO4/SPE/Li solid state battery was 115.0 mAh·g-1.And the discharge specific capacity was 110.3 mAh·g-1 after 150 cycles.In this process,the battery capacity retention rate was 96%and the charge-discharge efficiency was higher than 90%.3.PEO/LiClO4/Hexagonal boron nitride(h-BN)electrolytes were also prepared by solution casting method.It is found that the Lewis acid-base interactions between h-BN and LiClO4 can increase the concentration of Li+in the system.When the molar ratio of EO/Li+was 10:1 and the content of h-BN was 5%of the mass of PEO,the ionic conductivity of the electrolyte was 3.3×10-5 S·cm-1 at 30℃.And the electrochemical stability window and the lithium-ion transference number were 5.1 V and 0.25 at 80℃,respectively.After the hydroxylation modification of h-BN(m-BN),the ionic conductivity of PEO/LiClO4/m-BN electrolyte membrane at 30℃ was 4.4×10-5 S·m-1.The electrochemical stability window and the lithium-ion transference number at 80℃ were 5.3 V and 0.31,respectively.The assembled LiFePO4/SPE/Li solid-state battery exhibited the best performance.The initial discharge capacity of was 108.1 mAh·g-1 and the discharge specific capacity was 117.5 mAh·g-1 after 200 cycles.In this process,the battery capacity retention rate was 108%and the charge and discharge efficiency was greater than 90%. |
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