Construction And Electrochemical Properties Of Transition Metal Nitride-Based Functional Materials For Lithium Metal Batteries

Lithium metal batteries have become the current international research frontier and hotspot due to it's extremely low redox potential and ultra-high theoretical energy density based on the lithium metal anode.However,the poor cycle stability and low safety caused by the uncontrollable growth of lithium dendrites seriously restrict the commercialization of lithium metal batteries.To address these problems,this dissertation takes low-cost transition metal nitrides as the research object.The lithiophilic transition metal nitride-based functional nanomaterials are designed and constructed on the surface of the separator,the surface of the lithium metal anode and the three-dimensional framework,respectively.The law of its influence on lithium dendrite growth and electrochemical performance was systematically studied.The theoretical calculation combined with experimental characterization analysis revealed the mechanism of its enhanced electrochemical performance.The main research contents and results are as follows:1.Nitride-based functional interlayers were constructed on separator and their performances of lithium metal batteries were investgated.(1)Nitrogen-doped graphene wrapped Fe₃N nanospheres(FNG)were prepared by layer-by-layer self-assembly and subsequent ammonia treatment strategy,and constructed as a functional interlayer on the surface of PP separator for improving the performance of lithium metal batteries.It is shown that the FNG/PP separator exhibits high lithium ion conductivity and ion transference number,which can effectively improve the transport and diffusion rate of lithium ion,thereby ensuring the uniform deposition of Li;Li|FNG/PP|Li symmetric cells exhibits ultra-long cycling stability of 2300 h at current density of 5 m A cm^-2;the Li|FNG/PP|LFP full cell presents stable cycling performance over 350 cycles at 2C.(2)VN embedded nitrogen-doped graphene nanosheet(VNG)functional interlayer was constructed on a commercial PP separator and used to improve the performance of lithium metal batteries.It is shown that the Li|VNG/PP|Li symmetric cell exhibits ultra-long cycling stability more than 2500 h at a high current density of 10 m A cm^-2;The specific capacity retention rate of Li|VNG/PP|LFP full cell reaches 84.6%,and the coulombic efficiency approaches 99.5%.(3)The heterostructural Mo₃N₂/Mo N(Mo N_x)nanobelt interlayer material prepared by one step ammoniation treatment was constructed on the surface of PP separator and applied to improve the performance of lithium metal batteries.It is shown that the The heterostructural Mo N_x nanobelt can accelerate the diffusion and transport rate of lithium ions,realizing the uniform deposition without dendrites;the Li|Mo N_x/PP|Li symmetric cell exhibits long-term cycling stability more 1500 h at a current density of 5 m A cm^-2;the specific capacity retention rate of the Li|Mo N_x/PP|LFP full cell is still as high as 83.2%after 500 cycles at 3C.(4)The highly lithiophilic W₂N₃ nanosheet-embedded nitrogen-doped graphene(WNG)nanoflower functional interlayer material was optimized and controllably prepared by DFT calculations,and used to improve the performance of lithium metal batteries.It is shown that the lithiophilic WNG interlayer can effectively regulate and redistribute the interfacial ion flux as a lithium ion redistributor,and realize uniform deposition with dendrite-free growth.Li|WNG/PP|Li symmetric cell can be cycled stably for more than 2000 h at 5 m Ah cm^-2 current density and the nucleation overpotential is stable at 49.6 m V.The Li|WNG/PP|LFP full cell exhibits a very low capacity decay rate of 0.06%/cycle after 300 cycles.(5)Based on the research on the improvement of lithium metal battery performance by the functional interface layer of metal nitride modified separator,the influencing factors on the inhibition of lithium dendrite growth by the metal nitride interlayer was analyzed and summarized.The electrochemical mechanism of the metal nitride interlayer optimization and modification of lithium metal battery performance was further revealed.2.Nitride-based protective layer were constructed on lithium anode surface and their performances of lithium metal batteries were investgated.(1)The core-shell structured FNG was constructed as an artificial protective layer on the surface of lithium anode(FNG-Li)by drop coating method and used to improve the performance of lithium metal batteries.It is shown that the FNG-Li|PP|FNG-Li symmetric cell exhibits a stable cycle life of over 1200 h at current densities of 1,2 and5 m A cm^-2,respectively.The specific capacity retention rate of FNG-Li|PP|LFP full cell reaches 95.1%after 260 cycles at 1C.(2)An artificial protective layer based on VNG was constructed on the lithium anode surface(VNG-Li)by drop coating and used to improve the performance of lithium metal batteries.It is shown that the growth of lithium dendrites and the consumption of electrolyte is effectively alleviated under the synergistic effect of VN and NG.VNG-Li|PP|VNG-Li symmetrical cell exhibits stable cycling over 850 h at a current density of5 m A cm^-2.The VNG-Li|PP|LFP full cell shows 84.9%specific capacity retention after350 cycles at 1C.(3)The heterostructured Mo N_x nanobelt was constructed on the surface of lithium metal anode(Mo N_x-Li),and the mechanism of its performance enhancement for lithium metal batteries was investigated.It is shown that the new interfacial protective layer can effectively promote the transfer and diffusion of lithium ions,homogenize the concentration distribution and the flux of lithium ions,which can suppress the growth of lithium dendrites and alleviate the consumption of electrolyte.Mo N_x-Li|PP|Mo N_x-Li symmetric cell exhibits a stable cycle life of over 2000 h at 5 m A cm^-2 current density.The specific capacity retention rate of Mo N_x-Li|PP|LFP full cell reaches 82.3%after 500cycles at 1C.(4)An artificial WNG protective layer was constructed on the surface of lithium metal anode(WNG-Li)to improve the performance of lithium metal batteries.It is shown that the existence of artificial WNG protective layer can promote the uniform deposition of lithium at anode interface.The WNG-Li|PP|WNG-Li symmetric cell exhibits stable cycling for over 1500 h at current density of 5 m A cm^-2.The capacity retention rate of the WNG-Li|PP|LFP full cell reaches 86.9%after 220 cycles at 3C.(5)Base on the research of the lithium metal batteries performance by constructed the artificial protective layer of metal nitride on Li metal anode,the reasons and mechanism of metal nitride artificial protective layer inhibiting lithium dendrite growth are analyzed and discussed.The electrochemical mechanism of the metal nitride protective layer enhancement of lithium metal battery performance was further revealed.3.Tungsten nitride three-dimensional functional composite anode were constructed and their performances of lithium metal batteries were investgated.(1)Lithium was impregnated onto W₂N₃-anchored three-dimensional nickel foam(W₂N₃@NF)framework by fusion method for improving the performance of lithium metal batteries.It is shown that the synergistic effect of the porous conductive metal framework and the lithiophilic interface enables the W₂N₃@NF-Li composite anode with excellent electrochemical performance,which has a reversible specific capacity of 132.1m Ah g^-1 and a specific capacity retention rate of is 92.5%after 200 cycles at 1C.(2)The lithium metal battery based on W₂N₃@NF-Li composite anode and W₂N₃/PP modified separator was assembled and its electrochemical performance was investigated.It is shown that the redistribution of guided lithium ion flow and the uniform deposition of lithium can be realized under the synergistic effect between W₂N₃@NF-Li and W₂N₃/PP.The symmetric cell based on W₂N₃@NF-Li and W₂N₃/PP exhibits an ultra-long cycle life of more than 2200 h at a current of 2 m A cm^-2.The specific capacity retention rate of the full cell is as high as 94.0%after 200 cycles at 1C and the Coulombic efficiency reaches 98.2%.