Surface Modification And Three-dimensional Structure Design Of Lithium Anode For Lithium Metal Battery

Lithium metal has an extremely high theoretical specific capacity(3860 m Ah·g^-1)and the most negative electrode potential?-3.04 V?among all of anode materials,which is known as the "holy grail" in lithium secondary batteries.However,the problems of lithium dendrite and low coulomb efficiency have always limited the practical application of lithium anode.In view of the above issues,the paper carried out two methods,including the surface modification and three-dimensional structure design of lithium anode to inhibit the growth of lithium dendrites,reduce the side reactions of the electrode and improve the utilization and the cycle stability of lithium anode.Regarding the surface modification,the artificial Li₂CO₃ protective layer is prepared on the surface of the lithium anode by spin coating.On the one hand,the artificial protective layer,combining the inorganic component Li₂CO₃ and the organic component PVDF,results in a very dense structure,which not only possesses high mechanical modulus to prevent the dendrites growth,but also can adapt to the volume expansion.As a direct physical barrier from electrolyte,Li₂CO₃ protective layer significantly reduced the accumulation of side reaction products.On the other hand,Li₂CO₃ as one of the main components of the routine SEI film has a high Li⁺ conductivity(10-8 S·cm^-1),which can promote the uniform deposition of Li⁺ between the protective layer and the lithium anode.The electrochemical performance is the best when the coating thickness of the slurry is 100 ?m and the ratio of Li₂CO₃:PVDF is 9:1.The characterizations before and after cyclings prove that Li₂CO₃ layer plays an important role in stabilizing the interface between electrode and electrolyte.The Li|Li symmetrical battery cycled steadily for at least 200 h at a current density of 3 m A·cm^-2,and the overpotential is maintained at ?80 m V.With the Li₂CO₃ coated lithium anode appling in Li|Li Fe PO₄ battery,the specific discharge capacity(119.6 m Ah·g^-1)and capacity retention rate?87.2%?were significantly improved after 500 cycles.Compared with a bare 400 ?m thick lithium metal anode,a 100 ?m thick anode protected by Li₂CO₃ layer exhibits superior cycle stability,greatly reducing the usage of lithium metal and battery costs.The results show that the protective layer of Li₂CO₃ exhibits higher electrochemical stability and resistance to electrolyte corrosion,and its higher Li⁺ conductivity promotes the uniform deposition of Li⁺ and inhibits the growth of dendrites.In view of the design of the three-dimensional structure of the lithium anode,a small amount of indium was deposited on the copper foam by electroplating,and then the battery was assembled to electrodeposit metal lithium to prepare graded Cu@In/Li alloy anodes.On the one hand,the graded Cu@In/Li alloy anodes use copper foam as the primary skeleton and Li/In alloy as the secondary skeleton,which obviously reduces the true current density.On the other hand,indium have the ability to regulate the uniform distribution and induce nucleation of Li⁺.Calculations show that the binding energy between In and Li atom is significantly higher than that of Cu and Li,which means that indium can preferentially alloy with Li to form Li/In alloy skeleton to regulate the deposition behavior of Li⁺.It is determined that the Cu@In/Li anode prepared by pulse plating for 180 s had the best cycle stability,which operated for at least 400 h in Li|Li symmetric batteries(1 m A·cm^-2).In Li|Cu batteries,the average coulombic efficiency of Cu@In/Li anode for 100 cycles is close to 98%.After 500 cycles of Li|Li Fe PO₄ battery,the specific discharge capacity was 105.94 m Ah·g^-1,and the capacity retention rate was 76.64%.In brief,the synergies combining the graded conductive skeleton and indium lithiophilic layer effectively suppress the growth of lithium dendrites and improve the cycle stability of the electrode.