Construction And Electrochemical Performance Of Garnet-type Solid Electrolyte/Cathode Interlayer

In recent years,the electronics and information industries have boomed,and the demand for small mobile power sources has increased rapidly.Traditional commercial lithium-ion batteries use flammable,corrosive,and volatile organic electrolytes,which pose serious safety risks,and its energy density is close to the limit value,which is difficult to increase.These factors restrict its further application in the field of energy storage.Garnet-type solid electrolytes can simultaneously combine the advantages of high ionic conductivity,good electrochemical performance,excellent mechanical properties,and stable physicochemical properties,etc.It is hoped that these problems can be fundamentally solved.However,the solid electrolyte/electrode interface problem limits the further improvement of the electrochemical performance of solid lithium batteries.On the contact side with lithium metal,because lithium metal has the characteristics of high electronic and ionic conductivity and low melting point?180.5°C?,simple surface modification can effectively solve the problems of poor contact and high interface resistance between anode and solid electrolyte.In contrast,the cathode active material has a low electronic ion conductivity and is not flexible.The interface problem is difficult to solve,which is the main obstacle to the development of garnet-type all-solid-state lithium batteries.In this paper,the garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂?LLZTO?solid electrolyte is taken as the research object.The construction of the interlayer improves the problems of the electrolyte/electrode interface and improves the electrochemical performance of all-solid-state batteries.The research results are as follows:?1?A conversion interlayer strategy is proposed,and a graphene-lithium fluoride inorganic?Gr-Li F?composite interlayer is in-situ constructed between LLZTO and the cathode material by electrochemical reaction.The composite layer has both flexibility and ionic conductivitya and can be in good contact with LLZTO and the cathode material.The Li/LLZTO/Gr-Li F/Li Fe PO₄ all-solid-state lithium battery has an impedance of 1538?cm²,which is 5 times smaller than that one without an interlayer.The battery's first-cycle discharge capacity is 143.1 m Ah g^-1,and the capacity can be maintained at 90%after 60 cycles at 60°C and 0.05 C.?2?An interlayer of polytetrahydrofuran-based polymer electrolyte?PPEI?is constructed on the surface of both sides of LLZTO through a simple temperature-change treatment.This polymer electrolyte has a wide electrochemical window and shows good stability to both cathode and anode materials.It has good flexibility after in-situ solidification at the interface,which can ensure close contact with the electrode and LLZTO and can alleviate the interface cracks caused by the volume change of the electrode material during charging and discharging.The assembled Li/PPEI/LLZTO/PPEI/Li Fe PO₄ solid-state battery has a first-cycle discharge capacity of 142 m Ah g^-1 at room temperature and 0.1 C,and the capacity retention rate is 98%after 130 cycles.