Theoretical Study On Ion Transport And Mechanical Properties Of Graphene-lithium Nitride Heterostructure SEI

After spontaneously formed,the non-uniform composition and thickness of the solid electrolyte interface(SEI)can cause the irreversible growth of the dendrites of the lithium negative electrode and the degradation of battery performance.At the same time,when the metal lithium negative electrode undergoes unlimited volume expansion during the cycle,the SEI with low mechanical strength cannot adapt to the interface change caused by this volume expansion and cause its own fracture,which also reduce the coulombic efficiency of the battery.The artificial solid electrolyte interface(SEI)of the graphene composite lithium salt has a good driving effect on the lithium deposition behavior on the surface of the lithium metal negative electrode,and can also improve the mechanical strength to alleviate the interface fluctuations caused by volume changes.The better driving behavior of the layered composite SEI for the deposition of lithium atoms can inhibit the growth of dendrites on the surface of the lithium negative electrode.First-principles method was used to calculate graphene/lithium nitride(Li₃N)heterostructure SEI.It was first calculated that the structure and stability of intrinsic graphene(G),single-vacancy defect graphene(SVG),and double-vacancy defect graphene(DVG)in defect states,as well as low-concentration doped graphene(NG-1,NG-2 and NG-3)with 1-3 nitrogen atoms,graphene nitride(C₂N)and graphite-like carbon nitride(g-C₃N₄).It was further calculated that the adsorption and migration behavior of lithium ions on the surface and interface of the heterostructure,the ideal tensile strength of the heterostructure,and the adsorption and migration behavior of lithium ions at the interface of the heterostructure under the critical stress.Studies have shown that the modification of double-vacancy defect graphene improves the stability of the heterostructure,enhances the bonding between the heterostructure interfaces,and the adhesion work(58.48 me V/(?)²)of the composite SEI reaches the highest of the three.The opposite adsorption energy changes between the heterostructure surface and the interface and the reduction of the migration energy barrier are more conducive for lithium atoms to pass through the defect center,fully diffuse at the interface,and drive the uniform deposition of lithium.The mechanical strength enhances the stability of lithium adsorption on the DVG/Li₃N heterostructure interface.Under the doping effect of nitrogen,the NG-2/Li₃N heterostructure strengthens the stability of the structure and has a higher adhesion work.The optimal diffusion path of the heterostructure graphene terminal and interface is the same,and their diffusion energy barrier difference(0.114 e V)is significantly smaller than the other two heterostructures.The higher mechanical strength slows down the interface deformation caused by the adsorption of lithium intercalation heterostructure interface,and drives the uniform deposition of lithium on the interface.The C₂N/Li₃N heterostructure drives the full diffusion of the lithium nitride terminal lithium due to the structural flatness and the adhesion work much larger than other structures.And it enhances the stability of the surface and interface adsorption lithium configuration.The mechanical strength enhances the stability of the configuration of interfacial adsorption of lithium and drives the interfacial diffusion of lithium.But it is not easy to diffuse because it is much larger than the diffusion energy of other structures.A physical model of graphene and Li₃N heterostructure SEI with interfacial synergistic effect was built,a new type of interface that is mechanically stable while retaining high ionic conductivity.