| Due to the existence of liquid electrolyte,the safety of traditional lithium-ion batteries has been controversial,and the use of solid polymer electrolytes can avoid the safety problems derived from many liquid electrolytes.Traditional polymer electrolytes such as polyethylene oxide have been widely studied for their ability to effectively dissolve lithium salts.However,its simple molecular chain structure results in a high degree of crystallinity.At the same time,due to its low melting point and easy melting at high temperatures,the material fails,and the ionic conductivity at room temperature is as low as 10-8S cm-1,which is far from commercialization.The requirements of use,so the development and design of new polymer electrolyte systems is the main direction of solid polymer electrolyte research,in line with the current research focus of polymer electrolytes.In view of the above problems,more heteroatoms are introduced through the structural design to provide lithium ion transition sites,and at the same time,the polymer molecular chain interaction is regulated to avoid material failure due to high temperature and improve the ionic conductivity of the polymer electrolyte.The details are as follows:?1?Using different molecular weight polyethylene glycols as soft segments and fixing two isocyanate?MDI,IPDI?feed ratios,polymers with different hydrogen bonding densities were prepared and doped with lithium perchlorate to prepare solid polymers.The electrolyte was tested by Fourier transform infrared spectroscopy and AC impedance spectroscopy to investigate the effects of changing the content of lithium perchlorate and the molecular weight of polyethylene glycol on the performance of the polymer electrolyte.The results show that changing the molecular weight of polyethylene glycol can regulate the polymer PEG-MPU-IU hydrogen bond network density.The smaller the soft segment content,the higher the hydrogen bond density.The larger the hydrogen bond density,the polymer crystallizes.The worse is until the amorphous form.The addition of lithium perchlorate is easily polarized by the strong polar groups in the polymer and most of them are in the form of free lithium ions,and can occur with groups such as urea carbonyl,etheroxy,and amino groups in the polymer main chain.Coordination complexation and the formation of cross-linking points cause the glass transition temperature of the soft and hard segments to increase.At20?,the maximum ionic conductivity in high-hydrogen bond density PEG-MPU-IU series polymer electrolyte is 2.3×10-7 S cm-1,and the maximum ionic conductivity at 80?is 3.8×10-55 S cm-1.The upper limit of the electrochemical window is 4.7 V?80??,and the electrochemical stability and thermal stability are excellent.?2?Modified on the surface of easily agglomerated nano-silica to synthesize two ureido-based nano-silicas that can form hydrogen bonds,filled with PEG-MPU-IU-1000-7%solution and formed Solid polymer electrolyte.The results show that compared with the unmodified nano-silica,the dispersion state of the modified urea-based nano-silica in the composite polymer electrolyte is obviously improved,and the addition of the urea-based nano-silica leads to the polymer electrolyte.The glass transition temperature of the soft and hard segments decreases,and SiO2-Upy,which contains more proton donors and acceptors on the surface organic chain,can promote ionic conductivity more than SiO2-Urea.When the SiO2-Upy content is only 5 wt%,the highest ionic conductivity of the solid polymer electrolyte at 20?is 4.46×10-6S cm-1,which is higher than that of polymer electrolyte ions filled with the same mass fraction of unmodified nano-silica.The electrical conductivity is increased by about an order of magnitude,and the ionic conductivity can reach 2.47×10-4S cm-11 at 80?,and the electrochemical window has a maximum width of 5.1 V,which can be applied to lithium-ion batteries. |
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