Research On Flexible Fiber-shaped Battery Based On Iongel Electrolyte

As an important part of flexible wearable electronic devices,flexible energy devices should possess high security,high energy density and excellent flexibility.Among many flexible energy devices,flexible fiber-shaped batteries have become promising candidates due to their high volumetric energy density,excellent flexibility and the ability to be woven into fabrics.However,conventional organic electrolytes are toxic,leaky,and flammable and most of the aqueous electrolytes have a low decomposition voltage and a narrow operating temperature range,which cannot meet the flexibility and safety requirements of fiber-shaped batteries.To solve the problems of organic and aqueous electrolytes,this dissertation uses ionic liquids as electrolytes and polymetric ionic liquids as polymer substrates to synthesize high ionic conductivity and thermal stable iongel electrolytes.The operating temperature range and thermal safety of the fiber-shaped batteries based on the iongel electrolytes were carried out.A high ionic conductivity iongel electrolyte was prepared by thermal polymerization and crosslinking of 1-vinyl-3-ethylimidazolium dicyanamide（[VEIm][DCA]）in ionic liquid 1-ethyl-3-methylimidazolium dicyanamide（[EMIm][DCA]）in which zinc acetate（Zn（CH₃COO）₂）is dissolved.The strong chemical affinity of [EMIm][DCA] with [VEIm][DCA] allows [EMIm][DCA] to be well defined in polymetric ionic liquids networks without phase separation.The Zn//MnO₂ fiber-shaped battery based on the electrolyte exhibits a volumetric capacity of 3.3 m Ah cm^-3 at room temperature,and the volumetric capacity of the battery has a retention of 73% at 0 ℃ and gets 1.4-fold enhancement at 60 ℃.In order to further optimize the poly[VEIm][DCA] gel electrolyte,the effect of adding manganese sulfate（MnSO₄）to the liquid electrolyte on the battery capacity was first studied.The capacity of the Zn//MnO₂ battery increased with the addition of MnSO₄ in the liquid electrolyte.At a current density of 0.1 A g^-1,the capacity of the battery in the ionic liquid electrolyte containing MnSO₄ is 1.3-fold higher than that without MnSO₄.The method of doping silica（SiO₂）nanoparticles in iongel electrolyte improves the flame resistance of poly[VEIm][DCA] gel electrolyte.In addition,the fiber-shaped Zn//MnO₂ battery based on the iongel electrolyte with 40 wt% SiO₂ nanoparticles delivers a specific capacity of 277.0 m Ah g^-1 at a current density of 0.1 A g^-1.To further achieve the thermal safety of the fiber-shaped battery,a nonflammable iongel was prepared by the polymerization and crosslinking of the 1-vinyl 3-methylimidazolium bistrifluoromethanesulfonimide（[VMIm][TFSI]）in ionic liquid electrolyte in which lithium bistrifluoromethanesulfonimide（Li TFSI）and vinylene carbonate（VC）are dissolved.The iongel electrolyte possesses a glass transition temperature of-74.2 ℃ and a decomposition temperature of 350 ℃.Applying the iongel electrolyte into the Li₄Ti₅O₁₂//LiFePO₄ fiber-shaped lithium ion battery,the battery delivers a capacity of 135 m Ah g^-1 at room temperature and the capacity retention keeps at 89 and 60% at 0 and 40 ℃.