Investigation Of Organosilicon Ionic Liquid Based Electrolytes And Ion-gel Electrolytes

Faced with a sharp increase in energy consumption and environmental pollution problems,we turned to renewable energy research.Among them,lithium secondary batteries dominate the new energy battery market under the circumstance of various miniaturized electronic devices and large-scale technology products.However,most of commercial lithium secondary batteries currently use the traditional organic carbonate electrolytes and present potential safety risks such as leakage,combustion and even explosion,so how to improve battery safety has become to the foucus of research.Ionic liquids electrolytes have entered the eyes of investigators due to their flame retardancy,good chemical and thermal stability,high ionic conductivity and wide electrochemical windows.However,its shortcomings such as high viscosity and easy redox reaction on the surface of carbon negative electrode materials affect the practical application.The structure of ionic liquids is regulatable.Introducing differnet functional groups on the anions and cations of ionic liquids or adjusting the combination of anions and cations can make them have special physicochemical properties,and overcome the above shortcomings in a targed manner to meet different applications.In this paper,two novel ionic liquids were prepared by introducing organosilicon functional groups into imidazolium cation.Its structure,physicochemical properties and compatibility of many kinds of positive and negative materials were studied.The main results are as follows:1.Application of 1-trimethylsiylmethyl-3-butylimidazolium bis（trifluoromethane-sulfonyl）imide ionic liquid（[Si M-BIM]TFSI）in lithium-ion batteries.Chloro-1-trimethylsilylmethyl-3-butylimidazolium ionic liquid（[Si M-BIM]Cl）was synthesized by the reaction of N-butylimidazole and chloromethyltrimethylsilane.[Si M-BIM]TFSI was generated by anion exchange between[Si M-BIM]Cl and lithium bis（trifluoromethanesulfonyl）imide（Li TFSI）.The viscosity test showed that the introduction of organosilicon group（-Si（CH₃）₃）significantly reduced the room temperature viscosity of imidazolium ionic liquid by 1.2 times and enhanced its room temperature conductivity.The group also contributes to the formation of cathodic electrolyte interface（CEI）film on the surface of Li Fe PO₄（LFP）electrode,making the Li/LFP cell have good cycling performance at room temperature and 60°C.The feasibility of using this electrolyte as a high voltage electrolyte was tested with 4.4 V Li Co O₂（LCO）positive electrode.The results showed that the initial discharge capacity was 164.1 m Ah g^-1 and the coulombic efficiency was 94.7%.Moreover,the electrolyte also has good compatibility with Li Ni_1/3Co_1/3Mn_1/3O₂ and Li₄Ti₅O₁₂（LTO）electrode materials,indicating that the electrolyte is a new type of ionic liquid electrolyte with a low viscosity and wide range of applications.2.Preparation of[Si M-BIM]TFSI iongel electrolyte and its application in lithium-ion batteries.In this study,the[Si M-BIM]TFSI was immobilized in situ into the nanoporous Si O₂ framework by sol-gel method.Through a series of reactions,the[Si M-BIM]TFSI ionic liquid is filled into the porous Si O₂ skeleton to form the interpenetrating Si O₂-based iongel electrolyte.FT-IR test showed that there is no strong chemical interaction between[Si M-BIM]TFSI ionic liquid and Si O₂ skeleton,and[Si M-BIM]TFSI is confined by liquid nanosphere in Si O₂ framework.XRD result showed that tetramethoxysilane forms amorphous Si O₂ patricles under formic acid catalysis.The solid electrolyte and LFP,LTO electrode assembled into half-cell exhibit excellent electrochemical performace,which depends on the electrolyte and electrode material to form a stable and uniform interface structure.3.Application of 1-trimethylsiylmethyl-3-butylimidazolium bis（fluoromethane-sulfonyl）imide ionic liquid（[Si M-BIM]FSI）in lithium-ion batteries.In this study,Li TFSI was chosen as the lithium salt,[Si M-BIM]FSI was used as the solvent to prepare pure ionic liquid electrolyte.It had good compatibility with LFP and MCMB electrode materials.Both half-cells were charged and discharged at constant current of 0.2 C at room temperature.The discharge capacity of Li/LFP cell was 129.7 m Ah g^-1 after 120 cycles,and the capacity retention rate was as high as 94.6%.The charge/discharge capacities of Li/MCMB battery after 300 cycles were 341.5 and 340 m Ah g^-1,respectively.