Study On The Modification Of Metal Lithium Anode For Solid-state Batteries

Metal lithium is an ideal high energy density anode material,since its specific capacity is up to ten times of the graphite anode.However,its cycling stability and safety performance could be seriously affected by several factors,such as lithium dendrite growth,side reactions between lithium anode and electrolyte,and large volume changes during charge and discharge,which consequently hindered the application of lithium anode.Surface modification and protection of lithium metal are widely regarded as effective methods to improve lithium deposition behaviors as well as suppress lithium dendrites.In this paper,passivation layers of PVDF-LLZTO or CH₃COOLi were designed on the surface of metal lithium foil to prepare PVDF-LLZTO/Li anode and CH₃COOLi-Li anode,and the electrochemical performance was studied.Based on this,the modified lithium metal anode was used to assemble solid-state batteries with composite solid electrolyte membrane,and the performance of the solid-state batteries was tested and studied.The main work of this thesis is as follows:?1?PVDF-LLZTO/Li anode was prepared by blade coating method,and lithium symmetrical battery and lithium cobact oxide battery were assembled for testing.It was found that compared with pure Li anode,PVDF-LLZTO/Li anode has a lower polarization voltage and better cycling stability.Its lithium symmetrical battery can stably cycle for 400 h at a current density of 1 mA/cm².At the same time,the ratio of the composite electrolyte membrane material was optimized.In the lithium cobact oxide full battery,when the LLZTO content is 20%of the PVDF content and the LiTFSI content is100%of the PVDF content,the PVDF-LLZTO/Li anode has the best cycle performance and the battery has a specific discharge capacity of 73 mA·h/g after 400 cycles.?2?CH₃COOLi-Li anode was obtained by using acrtic acid gas to react with lithium metal,and lithium symmetrical battery,lithium copper battery,and lithium cobact oxide battery were assembled for testing.The study found that the CH₃COOLi-Li anode assembled lithium battery has significantly improved cycling performance compared to the pure Li anode,and its polarization voltage was almost unchanged after cycling for400 h at a current density of 1 mA/cm².The effects of different reaction times on the CH₃COOLi-Li anode were also explored.The results showed that long reaction time had an adverse effect on the lithium anode.The lithium acetate passivation film with the reaction time of 1 min had the best electrochemical performance.The lithium copper battery assembled with the CH₃COOLi-Li anode with reaction time of 1 min can stably cycle more than 100 cycles,and the Coulomb efficiency is maintained at 97%.The assembled lithium cobact oxide full battery has a discharge specific capacity of 95mA·h/g after 1000 cycles,and the capacity retention rate is still 74%.?3?The solid-state battery was assembled based on the PVDF-LLZTO-LiTFSI composite electrolyte membrane.The performance of the solid-state battery was improved after the lithium metal was modified with acetic acid.The specific discharge capacity of the solid battery was 90 mA·h/g after 200 cycles,and the capacity retention rate was still 65%.At the same time,the metal lithium solid soft packing battery was prepared based on the composite electrolyte membrane.It was found that the thinner the electrolyte,the better the solid-state battery performance.The battery performance is best when the composite electrolyte membrane thickness is 26?m.The discharge specific capacity is still 112 mA·h/g after 50 cycles,its capacity retention rate is 82%.