| Polymer lithium battery is the new generation of high-energy battery system,which uses solid or gel electrolyte instead of liquid electrolyte.Comparing with traditional lithium-ion batteries,it can get rid of safety problems such as leakage.However there also exist some disadvantages of significantly reducing the ionic conductivity.Therefore how to improve the ionic conductivity of polymer electrolyte and performance of thermal stability under high temperature becomes a problem which needs urgently to be solved.Poly?ionic liquid?electrolyte is promising to improve the performance of safety and stability,which combines the advantages of ionic liquid of excellent conducting performance,no volatile,nonflammable etc.,with that of the polymer of easily processing,no flow and good mechanical performance.In this thesis,titanate nanotubes were synthesized and used as the matrix material and the poly?ionic liquid?electrolyte was synthesized by in situ free-radical polymerization of N-vinylimidazolium salts that was initiated by azo-type initiator grafted on surface of titanate nanotubes.Titanate nanotubes provided the function of support and fixation at high temperature by improving thermal stability of poly?ionic liquid?.By doping lithium salt and grafted alkyl chain the ionic conductivity have been sufficiently improved.In order to obtain the optimal polymerization conditions,series of experiments have been seted,which mainly research on the effect of temperature and monomer concentration.Some conclusions have been summarized as follows:1)Titanate nanotube prepared by hydrothermal process has shown excellent thermal stability,which have been characterized by TEM and FTIR and were perfectly suitable to be utilized as matrix material of poly?ionic liquid?electrolyte of lithium battery.The azo-type initiator has been fixed on the surface of titanate nanotubes and the optimum concentration of initiator was determined by elemental analysis.2)Poly?ionic liquid?was synthesized by the free-radical polymerization initiated by azo-type initiator fixed on the surface of titanate nantubes.FTIR and TG-DSC demonstrated that the prepared ionic conductor possessed excellent thermal stability,which perfectly met the requirement of poly?ionic liquid?electrolyte of lithium battery.3)With polymerization time prolonging or monomer concentration increasing,the ionic conductivity of the prepared ionic conductor would increase until the optimal value has been reached,after which opposite trend has come up.The ionic conductivities have been calculated from the electrochemical impedance spectra and different results of varing reaction temperature and monomer concentration indicated the optimum reaction time of 2-3 h and optimum monomer concentration of 10-15ml.And the ionic conductivity achieves maximum of 6.63×10-4 S cm-1 at anhydrous and 3.6×10-2 S cm-1 at 100%RH respectively.4)The optimum lithium doping amount located between 20%and 25%,the ionic conductivity reached 1.98×10-3 S cm-1 when LiBF4 doped and 5.4×10-2 S cm-1 for LiTFSI.When grafting different alkyl chain,ionic conductivity of butyl grafting of alkyl chain was obviously higher than that of octyl,and ionic conductivity of ionic conductor with anionic TFSI-was also higher than that with anionic BF4-. |
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