Characteristics Of In-situ Polymerized Quasi-solid Electrolytes And Regulation Of Ion Migration Behavior At The Interface

For energy system in the future,energy storage system occupies a crucial position.As a product which adapts to the goals of sustainable development in new era,the emergence of lithium-ion battery technology has greatly promoted to energy structure transformation all around the world.At present,researchers are exploring electrode materials with higher specific capacity and matching high-performance electrolytes in cell design so as to develop the new generation lithium-ion battery with higher energy density.Lithium metal is considered to be one of the most promising anode material due to its high specific capacity,extremely low electrochemical potential and abundant reserves in place of graphite anode.However,because of its poor compatibility with organic liquid electrolyte,the uncontrolled growth of lithium dendrites and the internal short circuit of the cell lead to a series of serious safety hazards such as thermal runaway,which greatly limit the application of lithium metal battery.Solid or quasi-solid electrolytes can be used to replace traditional liquid electrolytes,and the conducticity of the electrolyte can be improved by doping inorganic fillers and introducing plasticizers/additives,thereby improving the cycle life and safety of the battery based on the performance of the liquid battery.In fact,the poor physical contact and low ionic conductivity of all-solid electrolyte are still unsolved problems.In contrast,the quasi-solid electrolyte prepared by in-situ polymerization uses polymer as the skeleton and increases the solvent component,which can not only produce good interface contact with the electrode,but also improve the ionic conductivity and mechanical strength of the electrolyte.Furthermore,the inward introduction of various inorganic fillers can integrate the advantages of inorganic solid electrolytes and polymer solid electrolytes,and solve the problem of insufficient performance of single material systems.In this paper,a gel polymer electrolyte was obtained by in-situ polymerization,and we investugated its electrochemical performance and compatibility with lithium anode.And on this basis,a kind of inorganic conductor powder with high ion conductivity was tried to dope the above electrolyte,and we verified the improvement of the cell performance through electrochemical tests.Finally,in order to improve the compatibility of organic-inorganic electrolytes,we constructed a stable interface of organic-inorganic hybrid electrolyte by using the protection strategy of self-assembled monolayer,which effectively regulated the lithium-ion migration path on interface according to the reaction mechanism of these two-phase electrolytes.The main research contents and results are as follows.（1）We selected the polyethylene glycol dimethacrylate（PEGDA）as monomer,and organic solvent was introduced to prepare gel polymer electrolyte by in-situ polymerization.The electrolyte with different polymer content was electrochemically tested and the optimal formula was chosen.Subsequently,we tested the Li||Li cell assembled with the electrolyte.It is found that the conductivity of the electrolyte was close to 10^-3 m S·cm^-1 at room temperature,and it owns a high oxidation stability of 5.26 V.The Li||Li cell could maintain a low overpotential stable cycle for more than 300 h at a current density of 0.5 m A·cm^-2 and a capacity of 0.5 m Ah·cm^-2.A uniformly deposited lithium coating was produced on the surface of the lithium metal.The Li||Li Fe PO₄cell has a capacity retention rate of 92.95%after 200 cycles at 0.2 C.And it shows good reversibility in rate performance test.（2）The submicron-class cubic phase Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）powder was doped into the PEGDA-based gel electrolyte to prepare a blended hybrid quasi-solid electrolyte.Through the electrochemical test of the electrolyte with different ceramic powder doping amounts,the most stable formula was selected as the key research object.It is found that the electrochemical properties such as ion conductivity and lithium-ion transfer number were better than those of gel polymer electrolyte.After the cell charged and discharged for 50 cycles,the capacity retention rate is 98.21%,but the cell shows a high overpotential.（3）We used XPS surface element analysis to study the interface composition of ceramic powders after organic system electrolyte treatment.Combined with the interface reaction mechanism analysis of LLZO-type solid electrolyte,an intrinsic acidic organic molecule was used to modify the surface of LLZTO powders.The results of XPS characterization show that the treatment method can not only significantly reduce the content of surface by-products,but also stably anchor on the surface of the powder to build a stable interfacial protective monolayer.In the subsequent electrochemical performance test,it is realized that the internal impedance of the lithium batteries assembled with the modified hybrid quasi-solid electrolyte is significantly reduced,and the cycle performance of the cells is also significantly improved.In summary,this paper systematically studied the PEGDA quasi-solid electrolyte and the electrochemical performance of its assembled cell by in-situ polymerization.On the basis of obtaining a gel polymer electrolyte with excellent lithium metal compability,an organic-inorganic hybrid quasi-solid electrolyte with higher lithium ion conductivity was developed by blending fast ion conductor LLZTO.It is worth mentioning that the single-molecule self-assembled strategy,which is based on the reaction mechanism at the interface of organic-inorganic two-phase electrolyte,is used to artificially regulate the internal interface of the hybrid electrolyte,and an organic-inorganic hybrid quasi-solid electrolyte cell with long-term cycle stability is obtained,which has certain reference value in the structural design,interface regulation and performance optimization of high-performance hybrid solid electrolyte.