Study On Electrochemical Performance And Design Strategy Of Interface Alloy Layer For Lithium Metal Anode

Lithium metal has emerged as a preferred choice for the next-generation anode material due to its high specific capacity(3860 mAh g-1)and low potential(-3.040V vs.SHE.).Researchers have explored new high-density cathode materials,such as sulfur and oxygen,to enhance the performance of lithium anodes.These advancements have enabled the application of lithium anodes in power batteries,allowing them to fully utilize their capacity advantages.However,the use of lithium metal as a battery anode presents several challenges,including the formation of interfacial lithium dendrites and an unstable solid electrolyte interface(SEI).These factors have a significant impact on the safety performance and cycle life of lithium metal batteries.In this paper,we propose experimental designs that seek to address the interfacial dendrite problem associated with the lithium metal anode.The surface of the electrode will be subjected to alloying to construct a lithiophilic interface alloy layer and we assemble the battery for performance testing and analysis.We have explored regulation effect of the alloy layer on the lithium deposition morphology.The specific research contents are as follows:(1)The process of pressure self-reaction between the gold foil and lithium begets the formation of a Li15Au4 alloy layer in situ on the surface of the lithium anode with a thickness of 2 μm.Notably,this lithiophilic Li15Au4 alloy layer increases the specific surface area of the electrode,providing a plethora of nucleation sites for lithium metal.The DFT calculation results highlight that the Li15Au4 alloy has a higher adsorption energy for lithium ions than the lithium metal.In fact,the lithium ions tend to nucleate uniformly on the alloy layer,leading to a reduction in aggregation deposition of lithium metal and a dense platform shape for the surface lithium metal even when the deposition amount is different.Moreover,the three-dimensional Li15Au4 alloy layer possesses high electronic conductivity and significantly promotes the electrochemical reaction rate at the interface.This ultimately results in the assembled symmetric battery exhibiting low charge transfer resistance and stable cycling for over 200 hours at a current density of 4 mA cm-2.The LiFePO4 full battery also demonstrated great rate performance.In fact,it could stably cycle for up to 400 cycles at 3 C(1 C=170 mA g-1),with a coulombic efficiency above 98.3%and a maintained discharge capacity of 65 mAh g-1.Furthermore,in the LiCoO2 full battery test,the capacity retention rate remained 78.9%after 200 cycles at a current of 1 C(1 C=140 mA g-1).These findings demonstrate the immense potential of Li15Au4 alloy layer in enhancing battery performance and stability.(2)By modifying the separator with a Bi2O3 coating and utilizing the self-reaction process of the interface lithium metal and coating,a mixed interface layer of Li3Bi alloy and Li2O was constructed on the surface of the lithium metal during subsequent battery assembly.The Li3Bi alloy,characterized by its high electrochemical stability and lithiophilic properties,provided a stable framework structure for lithium deposition and exfoliation,while Li2O facilitated the intralayer lithium ions transport and homogenized the lithium ions flux.Furthermore,the porous morphology of the interface layer accelerated the diffusion of lithium ions and provided more nucleation and growth sites for lithium metal,resulting in more uniform and dense lithium metal growth from the bottom of the interface layer.Through DFT calculations,it was determined that the adsorption energy of the Li3Bi alloy to lithium ions was higher than the cohesive energy of lithium metal,which led to a reduction in aggregation deposition of lithium metal and enhanced uniformity and density of lithium metal deposition.The alloy layer also reinforced the interfacial lithium ion and electron transport process,resulting in a significant reduction of the interfacial charge transfer impedance of the symmetric battery to 74.2 Ω.The symmetric battery was able to cycle stably for 600 hours at a current density of 1 mA cm-2 with an overpotential of approximately 25 mV.Furthermore,the assembled LiFePO4 full battery exhibited stable cycling for 600 cycles at a current of 1 C with a capacity retention rate of up to 84%.In the test of the LiCoO2 full battery,the discharge capacity remained at 109 mAh g-1 after 200 stable cycles at a current of 1 C.