Interfacial Modification Of The Interface Of Solid-State Electrolyte/Metallic Lithium And Their Electrochemical Performance

Solid-metal lithium batterie has attracted much attention due to its higher energy density and better safety performance compared with traditional liquid batterie.Solid electrolyte is the core of solid lithium battery.In solid electrolytes,Garnet ceramic solid electrolyte has high room temperature ionic conductivity wide electrochemical window and good chemical stability to lithium metal,which is considered to be a good match for the use of high voltage anode material.In addition,Garnet ceramic solid electrolyte can also be used as active fillers for Polyethylene oxide（PEO）solid electrolyte to improve the electrochemical performance.However,whether it is a PEO based solid electrolyte or a garnet type solid electrolyte,the solid interface between them and the positive and negative electrodes is a physical contact,the interface contact is poor,resulting in a large interface impedance,thus affecting the final battery performance.Therefore,this paper mainly focuses on the problems of low room temperature conductivity of PEO solid electrolyte and poor interface contact between solid electrolyte/lithium metal.The main results of this study are as follows.First,The nanometer powder of garnet solid electrolyte can be used as an active filler to modify PEO to increase the amorphous area in PEO,so as to improve the performance of solid electrolyte such as conductivity and electrochemical window.In this paper,Li_6.5Mg_0.05La₃Zr_1.6Ta_0.4O₁₂（LLZO）powder of nanoparticles was synthesized with graphene,and LLZO powder was added to PEO in proportion.By comparison,we found that 20%LLZO powder content could make the ionic conductivity of PEO electrolyte reach 3.08×10^-5 S cm^-1 and the electrochemical window reach more than 5V.To further improve the performance of the solid electrolyte,we also added 30%Emim FSI（1-ethyl-3-methylimidazolium bis（fluorosulfonyl）imide）,an ionic liquid.The composite electrolyte membrane with room temperature ionic conductivity at 8.9×10^-5 S cm^-1 and electrochemical window still around 5V was obtained.In this paper,the composite electrolyte membrane and high-voltage anode material NCM622 are used to assemble the full battery,and the first discharge can reach 145 m Ah g^-1.Second,due to the poor affinity between lithium and garnet-type ceramic solid electrolyte,the interface impedance is very large,which makes it difficult for solid metal lithium battery to work normally at room temperature.This paper takes the synthesized Li_6.4La₃Zr_1.4Ta₆O₁₂（LLZTO）ceramic solid electrolyte which has high lithium ion conductivity at room temperature as object of study.For the first time,two-dimensional NiAl layered double hydroxide（NiAl LDHs）was used as the interface modification material to load a dense and flat layer of NiAl LDHs on the surface of LLZTO.It has been discovered that LDH decomposed and formed alloy interface with molten lithium after decomposition under 300 ^OC heating,and then interface impedance successfully reduced from 252Ωcm^-2 to 40Ωcm^-2.Based on this,the symmetrical battery of Li║LLZTO║Li can work stably at room temperature,which shows excellent performance.At room temperature,the symmetrical battery of LLZTO electrolyte after modification was found that it could stabilize the circulation for more than 1000 hours and at the current density of 0.1 m A cm^-1 and 690 hours at the current density of 0.2 m A cm^-1,and the overpotential was only 29 and 59 m V.The modified LLZTO was combined with lithium iron phosphate（Li Fe PO₄）for the full battery test.The positive electrode material load reached 5.5 mg cm^-2and the discharge capacity of the first cycle at room temperature reaches 133 m Ah g^-1at 0.1C multiplier and after 48 cycles,the capacity still has 127.5 m Ah g^-1,and the coulomb efficiency can reach 97%.Finally,in this paper,LLZO nanoparticles were added to PEO solid electrolyte to successfully improve the electrochemical performance of PEO electrolyte,and the ionic liquid was added to further improve the ionic conductivity of the electrolyte membrane,and finally a high-performance composite PEO electrolyte was obtained.In addition,NiAl LDHs was coated on the surface of LLZTO for interface modification.At high temperature,it forms a stable and dense interface layer with lithium metal cathode,and improves the definite chemical properties of LLZTO electrolyte.