Research On Liquid Metal-based Cathode And In-situ Solidified Gel Electrolyte For Flexible Li-air Battery

In recent years,the rapid development of flexible electronics has greatly improved the living quality of people in modern society.With the continuous advancement of flexible electronics technology,higher requirements have been placed on flexible power supplies.Meanwhile,the energy storage device used for flexible devices should also meet the standards of portability and flexibility,and remians stable under bending and other crush conditions.However,the present batteries still cannot meet the rapid development of flexible devices in terms of energy density,bendability,and service life.Lithium-air batteries（LABs）,as the battery system with the highest theoretical energy density,are the most promising candidate as a new generation of energy storage equipment for flexible devices.However,the current flexible lithium-air battery still faces some urgent problems:1.The current conventional electrode of LABs does not have excellent flexibility,and it is easy to break during the repeated bending and result in cathode materials falling off of the current collector;2.The air cathode has poor catalystic activity,higher charging overpotential reduces the energy efficiency of the battery;3.The organic liquid electrolyte is prone to volatilization and leakage in the flexible lithium-air battery,which undoubtedly lead to battery failure.4.In ambient air,the Li andoe can be corroded by moisture and CO₂,which would deteriorate the battery life.To address the aforementioned challenges,in this paper,I designed a flexible cathode based on a liquid metal substrate to solve the problems of poor electrode stability and low electrode reaction catalytic efficiency during the bending process;an in-situ gel electrolyte based on small molecule reactions was developed to solve the problem of electrolyte volatilization and pulverization of lithium anode.The research includes the following three parts:First,the Ru-modified Ga Sn（Ru/LM）composite material displays as liquid metal at room temperature,which can be easily fabricated,is designed and explored as the positive electrode of a flexible lithium-air battery.The introduction of Ru in the composite not only decreases the surface tension and promoting the spreading of LM,but also enhances the catalytic performance of cathode.;meanwhile,the Ru component in Ru/LM exhibits high efficiency towards the O₂reduction and decomposition of discharge products during battery cycling.The liquid metal substrate endows the electrode good flexibility,it also has excellent adhesion on the current collector,which prevents the active material from falling off during cycling under bending and deformation states.Compared with pure carbon cloth current collectors,the Ru/LM composite cathode exhibits excellent catalytic activity and achieves a full discharge capacity of 3.64 m Ah/cm²in ambient air condition.Combining XRD and SEM techniques to characterize the cathode during different charge state,it was found that the discharge products were mainly crystalline Li₂O₂and amorphous Li₂CO₃,and the Ru/LM cathode could efficiently promote their decomposition during battery charging,which proved that the Ru/LM cathode has excellent catalytic activity.The assembled flexible pouch Li-air battery with Ru/LM cathode exhibits excellent mechanical and electrochemical properties under bending,folding,and wrinkling conditions.Second,the residual discharged products on passivated cathode after cycles under air condition can be easily washed off and the cathode can be re-used in LAB.Even after refreshed for 4 times,the cathode shows no obvious performance fading.This is mainly due to the fact that various auxiliary materials such as additional binders and conductive agents are not used in the electrode manufacturing process.Furthermore,the Ru/LM cathode can be facilely recycled from spent batteries,which the Ru precious metal and liquid metal separately through ultrasonic recovery,showing good cost and efficiency in the full life cycle of the battery.performance advantage.Third,the in-situ solidification study of the small molecule electrolyte was carried out to fabricated gel electrolyte,to solve the problems of volatilization and leakage of liquid organic electrolytes in Li-air batteries,and the existence of solid-solid interfaces between gels and solid electrolytes.It was found that the reaction of metallic lithium with N,N-dimethylformamide（DMF）,a polar,low-melting organic solvent,formed a polymeric cross-linker in situ,and formed a relatively close relationship with tetraethylene glycol dimethyl ether（G4）molecules with strong interactions to form gel electrolytes.The gel electrolyte can not only protect the Li anode from air corrosion,but also effectively reduce the charging voltage and improve the energy efficiency and cycling life.The G4/DMF gel electrolyte is formed in situ between the electrolyte and the Li anode,which ensures the interface contact of the electrolyte/electrode and the ionic conductivity of the electrolyte is maximized after gelation.The performance of the battery was tested in the air environment,the battery with gel electrolyte exhibited a low overpotential of0.95 V in the first cycle,and the overpotential only increased to 1.29 V after 60 cycles,and the cycle stability is significantly better than G4 liquid electrolyte,G4/DMF gel electrolyte significantly prolongs the cycle life of Li-air battery and improves the energy efficiency of the battery,After 60 cycles of the battery,the energy efficiency is still 70.56%.The pouch battery was further assembled based on the in-situ solid-state gel electrolyte,and the battery still maintained excellent electrochemical performance under various deformation conditions,showing application prospect of flexible lithium-air batteries in the future.