The Preparation Of Composite Artificial Solid Electrolyte Membrane And The Study Of Lithium Metal Anode Protection

Lithium metal has a very high theoretical specific capacity of 3860 mAh/g,the lowest electrochemical potential of-3.04v?compared to the standard hydrogen electrode?and a low density of 0.534g/cm³,and good conductivity,making it a potential"candidate"for the next generation of high energy density battery cathode materials.However,the high reactivity,uneven lithium deposition,huge volume expansion and dendrite growth in the electrochemical reaction of lithium make it difficult to commercialize lithium.At present,in order to solve these problems,the main methods are:lithium metal structure design,electrolyte modification,artificial solid electrolyte interface membrane?SEI?,membrane modification.This paper mainly starts with the construction of artificial SEI film,and through modifying the functional polyurethane based artificial solid electrolyte film on the surface of lithium metal,the uniform deposition of lithium ions on the surface of lithium metal can be promoted to avoid the formation of lithium dendrites,so as to improve the stability of lithium metal.The main research contents are as follows:?1?A layer of artificial SEI film was constructed on the surface of lithium metal by simple means of uniform coating.In this chapter,PEG₅₀₀ and diphenylmethane diisocyanate?MDI?are reacted to form linear polyurethane,and then combined with lithium fluoride?LiF?to form lithium compound artificial SEI membrane?AMF?.The AMF membrane has good thermal stability and mechanical properties,which can play a physical isolation role and avoid the electrolyte continuous decomposition problem caused by the contact between electrolyte and lithium metal.At the same time,AMF can also regulate the deposition mode of lithium ions,promote more uniform lithium deposition,and play a role in inhibiting lithium dendrites.In addition,the performance of the whole battery has been greatly improved under the protection of AMF.With lithium iron phosphate?LFP?as the positive electrode and lithium metal under AMF protection as the negative electrode,the LFP-Li battery was assembled with an initial specific capacity of123.8mAh/g at a 2 C multiplier,and the specific capacity was still 117 mAh/g after cycling to 600 cycles,with a capacity retention rate of up to 94%.Through SEM observation on the lithium electrode after cycling,it was found that the lithium electrode after AMF modification was very uniform and dense,without obvious lithium dendrites.It indicates that AMF artificial SEI membrane can improve the cycle stability of batteries.?2?In order to solve the interface problem of lithium metal,the effect of the combination of solid electrolyte polymer and lithium halide as artificial SEI membrane on battery performance was studied.Four different artificial SEI membranes A-LiF A-LiCl,A-LiBr and A-LiI were modified on the surface of lithium by evenly coated.By analyzing the thermal stability,mechanical properties and electrochemical properties of four artificial SEI,it is found that A-LiCl artificial SEI membrane can significantly improve the electrochemical properties of batteries.The uniform and dense A-LiCl membrane can effectively isolate lithium metal from electrolyte and avoid side reactions.Moreover,it can provide a larger channel for the shuttle of lithium ions,homogenize the ion flow rate,promote the uniform deposition of lithium ions,and avoid the growth of lithium dendrites.With lithium titanate?LTO?as the pair electrode and lithium metal under the protection of A-LiCl as the negative electrode,the preparation of the LTO-Li battery was cycled at A 5 C ratio,with an initial capacity of up to 144.4mAh/g and A stable circulation of 3500 laps.The specific capacity at 3500 laps was 112.7mAh/g,with A capacity retention rate of 78%,and the performance was far better than that of pure lithium electrode battery.In Li-Cu battery,when the current density is 0.5 mA/cm²,it can circulate steadily for 240 h.Through SEM,it can be observed that the lithium electrode under the protection of A-LiCl deposits more evenly,the surface is more flat and dense,and there is no obvious crack or loose structure,effectively slowing down the volume expansion effect.