Effect Of Morphology Regulation Of Polymer Interface Protective Layer On The Performance Of Lithium Metal Electrode

Lithium metal anode has ideal theoretical specific capacity(about 3860 m Ah/g)and lowest electrochemical potential(-3.04 V vs.standard hydrogen electrode),so it is called"Holy Grail electrode".However,there is a significant hot spot effect in the deposition of Li~+,which tends to grow in the form of strip dendrites on the electrode surface,leading to a series of problems such as unstable solid electrolyte interface(SEI),dead lithium generation,electrolyte consumption,battery short circuit,etc.,which cannot be applied in practice.The addition of artificial SEI layer is considered to be one of the effective strategies to alleviate lithium dendrite growth and improve electrode performance.In recent years,researchers have paid attention to it.Among them,the use of polymer artificial SEI layer is the most effective.Many polymer materials with different functional groups have been proved to have the ability to improve the lithium deposition hot spot effect.Under this background,this topic has innovatively carried out a series of explorations on the influence of morphology regulation of polymer SEI layer on the performance of lithium metal electrode,mainly including the following three parts:(1)The PFMA protective layer on the electrode surface is thermally annealed above the chain segment T_g to form a polar Guiselin brush-like adsorption layer structure on the electrode.The results showed that the content of Li F in SEI layer increased significantly with the addition of large amount of fluoroalkyl structure;The formation of the adsorption layer effectively improves the stability of the film in the organic environment.The brush mounted structure reduces the interface impedance of the polymer SEI layer from about 70Ωto about 30Ω,and can achieve the deposition morphology of dendrite free growth on the electrode surface;The battery assembled with LFP cathode can still maintain a capacity of about 138 m Ah/g after 200 cycles at 1 C.In addition,the strategy of forming adsorption layer by high temperature annealing was also extended to other types of polar polymer SEI layers,which have improved effects to varying degrees.(2)The amphiphilic block copolymer PS-b-PEG formed a polymer SEI layer with heterogeneous structure on the electrode surface by using a selective solvent.The PS-rich phase in the heterogeneous layer provides high mechanical strength to inhibit the growth of dendrites.The PEG-rich phase homogenizes and transfers Li~+rapidly at a high Li~+conductivity rate,which can finally achieve a uniform and dense lithium deposition morphology on the electrode surface.Compared with homogeneous membrane structure formed by good solvent,heterogeneous SEI layer has batter deposition effect and lower interface impedance.Under the protection of heterogeneous PS-b-PEG film,the electrode can be tested at 1 m A/cm~2 and 1 m Ah/cm~2 in a half cell for more than 95%CE to about 210 cycles,and the electrode can be tested at 1 m A/cm~2,1m Ah/cm~2 and 3 m A/cm~2,1 m Ah/cm~2 in a symmetrical cell for 720 hours and 180 hours,respectively.(3)PMMA materials are dissolved in chloroform and toluene mixed solvents with different volatile properties.PMAA films with different pore morphology can be formed on the electrodes in different temperature and humidity environments.Under the appropriate conditions,the polymer can form a special array of through-hole structure film on the electrode.The copper electrode surface protected by this special structure has the best uniform spherical lithium deposition morphology.The assembled semi battery can stably cycle for about 150 cycles under the test conditions of 1m A/cm~2 and 1 m Ah/cm~2.