Preparation Of Garnet-based Composite Solid Electrolyte And Study On Interface Regulation Between It And Lithium Metal Anod

Solid-state lithium-ion batteries employ solid-state electrolytes instead of flammable organic electrolytes and separators,addressing safety and low energy density concerns associated with conventional lithium-ion batteries.The solid-state electrolyte,which is the core component of solid-state batteries,plays a crucial role in determining the battery’s performance.Garnet,as a type of inorganic solid-state electrolyte,has been widely applied in solid-state batteries due to its advantages of a wide electrochemical window and high lithium-ion conductivity.However,its commercial application has been severely hindered by issues such as the large interfacial impedance between garnet and electrodes,as well as its fragility.To solve the above issues,this paper utilizes garnet-type solid electrolyte as the active filler,poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）as the polymer matrix,and lithium bis（trifluoromethane）sulfonimid（Li TFSI）as the additive,to prepare an HSE with a high ionic conductivity,a good safety performance,and a stable interface.The effects of filler and lithium salt additives on the physical and electrochemical properties of the electrolyte were systematically investigated.Subsequently,a multifunctional interfacial layer containing Li₃P and Li Cl（PCl@Li）was constructed in situ on the surface of lithium metal,achieving uniform lithium deposition in an all-solid-state lithium metal battery.The main research content and results are as follows:（1）Hybrid solid electrolyte（HSE）was prepared by the solution casting method.The effect of Li_6.75La₃Zr_1.75Ta_0.25O₁₂（LLZTO）content on HSE performance was investigated without Li TFSI.The results showed that the Li⁺conductivity of HSE first increased and then decreased with the increasing LLZTO content.The maximum lithium-ion conductivity of 3.6×10^-5 S cm^-1 was obtained when the LLZTO content was10 wt.%.The addition of LLZTO reduced the crystallinity of HSE due to the hindrance of LLZTO on the recrystallization of PVDF-HFP.In addition,the addition of LLZTO has improved the mechanical properties of HSE,endowing it with a"rigid-flexible"characteristic,thereby improving the contact between the electrolyte and electrode interfaces.Subsequently,Li TFSI was added,and when the polymer to Li TFSI mass ratio was 3:1,the total impedance of HSE decreased from 136.0Ωto 16.9Ω,and the lithium-ion conductivity increased to 3.7×10^-4 S cm^-1.At a current density of 0.1 m A cm^-2,a Li|HSE|Li symmetric battery was cycled for 1000 h.The Li|HSE|Li Fe PO₄（LFP）battery had a discharge-specific capacity of 150.8 m Ah g^-1 at 0.1 C.After 400 cycles at 1 C,the discharge-specific capacity was 108.1 m Ah g^-1,the capacity retention was 85.7%,and the average Coulombic efficiency was 97.6%.（2）Based on the above research results,a multifunctional interface layer containing Li₃P and Li Cl was in-situ constructed on the surface of lithium metal by the chemical reaction of PCl₃ and Li（PCl₃+6Li=Li₃P+3Li Cl）.Li₃P has a high Li⁺conductivity,while Li Cl has excellent electronic insulation characteristics,effectively improving the Li⁺transport performance and interface stability between the electrolyte and lithium metal anode.The PCl@Li|HSE|PCl@Li symmetric battery cycled stably for 1300 h at a current density of 0.1 m A cm^-2,with an average overpotential of 0.032 V.The PCl@Li|HSE|LFP battery had a discharge-specific capacity of up to 165.5 m Ah g^-1 at0.1 C.At 1 C rate,the initial discharge-specific capacity was 135.6 m Ah g^-1,and after500 cycles,the capacity retention rate of the battery was as high as 87.0%,with an average coulombic efficiency of 99.2%.The electronic insulation of Li Cl obstructs electrons from the lithium metal anode,preventing them from shuttling into the HSE,thereby impeding the reduction of lithium ions into dendritic lithium at the interface.On the other hand,the high lithium-ion conductivity of Li₃P provides a pathway for Li⁺diffusion and induces uniform lithium deposition,effectively suppressing dendritic lithium formation,and enhancing the electrochemical performance of all-solid-state lithium metal batteries.