Preparation And Research Of Low-salt Concentration Solid State Hydrogel Electrolytes For Lithium-ion Batteries

To solve the safety issues that the flammability of the electrolyte in the traditional organic liquid lithium-ion battery.Using safe aqueous electrolyte instead of traditional organic electrolytes is an effective solution.However,pure water is prone to hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,which has the disadvantage of narrow electrochemical window（1.23 V）.Broadening the electrochemical stability window by increasing the concentration of Li TFSI（21 mol/kg）in aqueous electrolytes is an effective solution now.However,the lithium salt is expensive,which is difficult to apply to large-scale energy storage systems.Therefore,it is necessary to adopt a rational strategy to reduce the concentration of Li TFSI in the electrolyte and continue to broaden the electrochemical window.In this paper,the concentration of Li TFSI in H₂O is reduced to 10 mol/kg by introducing small molecule and polymerizing to obtain hydrogel electrolytes,which improves the specific capacity and cycle stability of the Li Mn₂O₄/C-Li Ti₂（PO₄）₃ and Li Mn₂O₄/Mo₆S₈ full cells.This work mainly include the following items:（1）On the basis of Li TFSI aqueous solution,acrylamide（AM）is added,and polyacrylamide（PAM）hydrogel electrolyte is prepared by heating polymerization.The cured PAM can effectively inhibit the free diffusion of water molecules.The experimental results show that the hydrogel electrolyte has a wide electrochemical stability window（～3 V）and good flame retardancy.（2）According to the window of the electrolyte,the anode materials are prepared:carbon-coated C-Li Ti₂（PO₄）₃（2.5 V）and Mo₆S₈（2.1 V）.The cathode material:Li Mn₂O₄（4.1 V）is selected,the electrochemical performance are characterized.The results show that all three materials have good crystal structure,uniform particle dispersion and excellent electrochemical performance.（3）The hydrogel electrolyte is matched with the Li Mn₂O₄/C-Li Ti₂（PO₄）₃full cell to explore the effects of Li TFSI concentration and AM concentration on the cycling performance of the full cell.The optimal molar ratio is Li TFSI:AM:H₂O=1:2:5.5(Li TFSI-AM₂-H₂O_5.5)（Li TFSI to H₂O is 10 mol/kg）,The Li Mn₂O₄/C-Li Ti₂（PO₄）₃ full cells at this ratio have good cycling performance at room temperature and low temperature（-18^oC）.The optimal molar ratio of the hydrogel electrolyte is applied to the Li Mn₂O₄/Mo₆S₈ full battery with a wider voltage window.The experiments found that its cycle performance and rate performance are good.