Surface Modification Of Lithium Metal And Its Stability With Li₁₀GeP₂S₁₂

At present,commercial lithium-ion battery uses organic electrolyte and graphite anode,which has potential safety problems such as spontaneous combustion and leakage.In addition,the energy density is difficult to further improve.All-solid-state batteries using solid electrolyte instead of traditional organic electrolyte of lithium-ion battery,solves the problem such as flammable,volatile and electrolyte leakage,enhancing the security of the battery.At the same time,lithium metal can be introduced as the anode.lithium metal has the advantages of high theoretical specific capacity(3860 m Ah g^-1)and very low potential compared with standard hydrogen electrode（-3.04 V）,which can effectively improve the working voltage and energy density of lithium battery,and is an excellent choice for realizing high energy density lithium battery.Li10Ge P2S12 sulfide solid electrolyte is one of the most promising solid electrolytes because of its high ionic conductivity comparable to the organic electrolyte and good mechanical strength.However,due to the high reactivity of lithium metal,it will react spontaneously when contacting with Li10Ge P2S12electrolyte,forming an unstable solid electrolyte interface layer,resulting in rapid fade and failure of the battery.In order to improve the interface stability of lithium metal and Li10Ge P2S12 electrolyte as well as the cycling and rate performance of all-solid-state battery,the surface modification of lithium metal was conducted to reduce the reactivity of lithium metal and Li10Ge P2S12 electrolyte to inhibit the interface reaction and guide the uniform deposition of lithium ions,so as to improve the electrochemical performance of all-solid-state lithium battery.The specific works are as follows:（1）A layer of Ag film is sputtered on the surface of lithium metal by radio frequency magnetron sputtering to prepare Li@Ag anode.Ag has the highest conductivity and lowest contact resistance among metals,and Ag is a lithiphilic material.Li-Ag alloy with extremely low electrochemical potential can be formed in situ on the surface of lithium metal,thus reducing the nuclear generation of lithium metal.Thus,inhibiting the formation of lithium dendrites,improve the electrode/electrolyte interface contact,and improve the electrochemical performance of all-solid-state lithium metal battery.The results show that the lithium anode with 1μm Ag layer has the best electrochemical performance.The assembled Li@Ag 1μm/Li₁₀Ge P₂S₁₂/Li@Ag 1μm symmetrical battery can cycle stably for 1000 h at the current density of 0.1 m A cm^-2 and the surface current capacity of 1 m Ah cm^-2,and the overvoltage after cycling is only 160 m V.Li@Ag 1μm/Li₁₀Ge P₂S₁₂/Li Co O₂ all-solid-state battery shows reversible capacity of 106.5 m Ah g^-1 after 100 cycles with a capacity retention rate of 83.9%.（2）By radio frequency magnetron sputtering technology,a protective layer of Mg can be successfully sputtered on the surface of lithium metal,which can significantly decrease the reactivity of lithium metal and reduce the side interface reactions.In addition,Li-Mg alloy formed spontaneously in the cycling process has high ion diffusion coefficient,which can adjust the deposition rate of lithium from the perspective of electrochemical dynamics to achieve uniform deposition of lithium,which greatly inhibits the generation of lithium dendrites and avoids the formation of dead lithium.The results show that the lithium anode with the thickness of 700 nm Mg layer has the best electrochemical performance.The overvoltage of Li@Mg 700nm/Li10Ge P2S12/Li@Mg 700 nm symmetrical battery is stable at 400 m V after 1000 h of cycling under the current density of 0.1 m A cm^-2 and surface current capacity of0.5 m Ah cm^-2.The Li@Mg 700 nm/Li10Ge P2S12/Li Co O2 all-solid-state battery has a reversible capacity of 111.2 m Ah g^-1 and a capacity retention rate of 87% after 100 cycles.