Study On The Optimization Of Solid Electrolyte And Lithium Metal LLZO/Li Interface And The Performance Of All Solid-state Lithium Batteries

Faced with the growing needs of the new energy industry,lithium-ion batteries have attracted more and more attention with their high energy density,high power density and long life.However,the flammable organic liquid electrolyte has the disadvantages of leakage,spontaneous combustion,even explosion,which leads to poor battery safety.All-solid-state lithium batteries using inorganic solid electrolytes instead of organic liquid electrolytes are expected to fundamentally solve battery safety issues.In addition,the energy density of all solid-state lithium batteries is expected to reach300-400 Wh/kg.At present,the main problem of all solid-state lithium batteries is the interface between the solid electrolyte and the positive or negative electrodes.In particular,the problem of lithium dendrites growth at the interface between the lithium metal anode and the solid electrolyte has become an urgent problem in the development of all-solid-state lithium batteries.In this paper,garnet-type solid electrolyte Li₇La₃Zr₂O₁₂（LLZO）was prepared by the solid state sintering method.Magnetron sputtering DC power supply and RF power supply were used to deposit Al film and LiPON film on LLZO solid electrolyte as the interface layer of lithium metal and solid electrolyte Li/LLZO,respectively.The influence of the structure and properties of the interface layer on the electrochemical performance of all solid-state lithium batteries was studied.Study on the construction and performance of Al metal interface layer:Results show that the Al film is rough and uneven under magnetron sputtering for 10 min,the impedance of the lithium symmetric battery is large（1.7×10⁴Ω）,and the charge and discharge performance is poor（The three-time polarization voltage exceeds 0.5V at the current density of 0.05 m A/cm²）.The battery with Al sputtering time of 20 min at a current density of 0.05 m A/cm² has a low polarization voltage close to 0 V,but it is short-circuited for 23 cycles.The battery with Al sputtering time of 40 min is short-circuited 95 times at a current density of 0.05 m A/cm²,and the polarization voltage is about 0.1 V.It was observed by SEM that lithium dendrites were formed in LLZO,which caused a short circuit in the battery,indicating that the electronically conductive Al interface layer could not well inhibit the growth of lithium dendrites.In addition,through XPS,SEM-EDS,it is found that the Al film has been partially oxidized before cycling,and Li-Al-O compound is formed after cycling which may be due to the insertion of lithium ions into Al₂O₃ during the charging and discharging process.The formation of Li-Al-O compounds might be beneficial to the transmission of lithium ions.Based on this,the Al/LLZO was annealed to form a dense alumina layer on the surface,and the effect of annealing on the electrochemical performance of the lithium battery was studied.Results show that Al₂O₃ is more uniform after annealing treatment.After charging and discharging,lithium ions react with Al₂O₃ to form more uniform Li-Al-O,which is beneficial to lithium ion transmission.Thus,the cell maintains good performance after 1000 cycles at a current density of 0.05 m A/cm².LiPON interface layer construction and performance research:Results show that LiPON interface layer can effectively improve the wettability between the solid electrolyte LLZO and lithium metal.(The internal resistance of the battery dropped from 10948Ω·cm^-2 to 371Ω·cm^-2)The battery cycle performance test shows that the battery with LiPON sputtering time of 40 min at 150 W power can be cycled 85 times at a current density of 0.05 m A/cm²,and the polarization voltage is<0.05 V.The polarization voltage of the battery under the sputtering time of 150 W for 1 h was>0.2V after 85 cycles at a current density of 0.05 m A/cm².The rate performance tested at the current density of 0.05～0.2 m A/cm² shows that the polarization voltage of a battery with a power of 150 W at a high current density of 0.2 m A/cm² for 15 cycles is still very small（close to 0 V）,while the polarization voltage of 200 W for 15 cycles is slightly greater than 0.1V.The cycle stability and rate performance of the battery modified by the LiPON interface layer are better than those of the Al interface layer,and no lithium dendrites are observed inside the battery,indicating that the LiPON film with low electronic conductivity and higher lithium ion conductivity can effectively inhibit lithium dendrite growth.