Research On Anode And Interfacial Modification Of Lithium-boron Alloy

Lithium metal anode is considered to be the most promising anode in the next generation of secondary battery due to its high theoretical specific capacity and low redox potential.However,the irregular dendrite growth during the cycles,the rupture of fragile Solid Electrolyte Interphase（SEI）,the formation of"dead lithium"and infinite volume expansion all seriously reduce the cycle life of lithium metal battery and limit its further application.In order to solve the above problems,composite anodes or artificial SEI can be used to limit its volume expansion,guide the uniform deposition of Li⁺and inhibit the dendrite growth.However,the poor lipophilicity of some composite anodes,and the inevitable extra mass burden due to the existence of inactive substances,affecting the realization of high specific energy density battery.Lithium-boron（LiB）alloy has a lightweight alloy skeleton structure,and its electrochemical potential is close to that of lithium,which can reduce the local current density without introducing too much mass burden.Therefore,in this thesis,LiB alloy was selected as the substrate,and lithium-zinc alloy（LiZn）protection layer was introduced on the surface of LiB by solution treatment and magnetron sputtering to further improve the lipophilicity of alloy anode,uniform Li⁺flux and guide homogeneous lithium deposition.The LiZn alloy protection layer was formed on the surface of LiB by solution treatment to prepare LiBZn anode.The alloy protection layer not only improved the lipophilicity of the surface,but also accelerated the migration of Li⁺in the plane,which effectively homogenized the local current density and stabilized the plating/stripping process,so that LiBZn cycled stably for 1800 h with a minimum overpotential of 14 m V at 1 m A·cm^-2 and 1 m Ah·cm^-2.The full cell paired with NCM811 maintained a specific capacity of 160 m Ah·g^-1 after 300 cycles at 1 C.In addition,the effective effect of alloy protection layer on inhibiting dendrite growth was explored by observing the macroscopic and microscopic morphology of the anode surface after cycling.The oxide layer on the surface of LiB was removed by argon etching,and then the LiZn alloy protection layer was introduced by magnetron sputtering.Because of the strong Li⁺rectifying ability and good lipophilicity of the alloy protection layer,the prepared LiBZn-ES anode guided orderly lithium deposition and exhibited a longer cycle life(stably cycled with a low overpotential of 15 m V for 1200 h at 1 m A·cm^-2 and 1m Ah·cm^-2).The effect of alloy protection layer on uniform lithium deposition was studied by comparing the micro-morphology after cycling.In addition,the alloy protection layer prepared by magnetron sputtering was uniform and compact,which reduced the negative effect of air on the electrochemical performance of alloy anode to a certain extent,so that the anode placed in the air still cycled stably at 1 m A·cm^-2 and 1m Ah·cm^-2 for 800 h.Uniform LiZn alloy protection layers were prepared by both chemical and physical surface modification,which effectively improved the performance of anode and inhibit dendrite growth,provided a new idea for the preparation of long cycle life alloy anode which can replace pure lithium anode.