A metal lithium negative electrode for improving lithium metal deposition behavior and a preparation method thereof

Abstract

The application discloses a metal lithium negative electrode and a preparation method for improving lithium metal deposition behavior, and the lithium metal deposition behavior can be improved by adding lithiumophilic sites in the through hole of an organic polymer film and under the film; different polymers are mixed and coated on the surface of the metal lithium negative electrode, one of the polymers is removed, the polymer coating on the surface of the metal lithium is in a through hole porous state, and then a lithiumophilic substance is coated and embedded into the pore channel of the polymer coating, so that the purpose of adding the lithiumophilic sites under the film is achieved. The application has the beneficial effects that: through the preparation method, lithium metal can be induced to uniformly nucleate and grow, the lithium metal deposition direction can be changed, the ionic conductivity of the composite protective film can be improved, the generation of lithium dendrites can be inhibited, and the side reaction caused by the direct contact between the negative electrode and the electrolyte can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery materials, and in particular relates to a lithium metal anode that improves lithium metal deposition behavior and its preparation method. Background Technology

[0002] With the increasing demand for energy, the next generation of lithium-ion batteries is developing towards higher energy densities (>500Wh / kg). -1 Lithium metal anodes have a low electrochemical potential (3.014 V vs. SHE) and a high theoretical capacity (3860 mAh g⁻¹), making them one of the most ideal anode materials. Although lithium anodes have excellent application potential, some serious problems still hinder their practical application: (1) the formation of a brittle and heterogeneous solid electrolyte intermediate phase (SEI); (2) the loss of electrolyte solution and active lithium leads to a decrease in coulombic efficiency. Once lithium metal comes into contact with the electrolyte solution, an SEI film is immediately formed on the lithium surface during the side reaction. Due to the insufficient Young's modulus of the generated SEI film, it is difficult to suppress the growth of lithium dendrites. Based on the considerations of artificial SEI and nucleation and grain growth, inducing uniform nucleation and growth of lithium metal and changing the lithium metal deposition direction can effectively suppress the growth of lithium dendrites and avoid lithium metal piercing the separator. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a lithium metal anode with improved lithium metal deposition behavior and a method for its preparation.

[0004] The technical solution adopted in this invention is: a method for preparing a lithium metal anode, comprising the following steps:

[0005] Step 1: Weigh out solvent A, polymer A, polymer B, and lithium salt A in a mass ratio of 9:0.8:(0.1-0.3):0.05, mix them, and stir evenly to obtain film-forming solution A;

[0006] Step 2: Spin-coating film-forming solution A at a concentration of 20-50 μL / cm 2 A certain amount is applied to the surface of the lithium metal anode, and after drying, a polymer protective layer is formed.

[0007] Step 3: Immerse the lithium metal anode from Step 2 in solvent B to create through-holes; solvent B does not dissolve polymer A, but it can dissolve polymer B;

[0008] Step 4: Prepare a 1M lithium salt solution A by mixing solvent C and lithium salt B. Mix lithium salt solution A with lithiophilic substance A at a mass ratio of 10:(0.05-0.1) and stir until homogeneous to obtain lithiophilic solution A.

[0009] Step 5: Apply the lithiophilic solution A by spin coating at a concentration of 30-60 μL / cm³.2 The amount of coating is applied to the surface of the lithium metal anode obtained in step 3 and reacted for 2-10 minutes, preferably 4-5 minutes, to form a layer with lithium-affinity sites.

[0010] Preferably, solvents A, B, and C are ethylene glycol dimethyl ether (DME), N,N-dimethylformamide (DMF), ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, γ-butyrolactone, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, succinate, sulfolane, and dimethyl... The solvent A is selected from at least two of the following: sulfone, ethylmethyl sulfone, diethyl sulfone, adiponitrile, tetrahydrofuran, N-methylpyrrolidone, acetonitrile, benzyl nitrile, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, wherein solvent A and solvent B cannot be the same.

[0011] Polymer A and polymer B are at least two of the following: polyurethane (TPU), polyacrylonitrile (PAN), polyethylene, polypropylene, poly(meth)acrylate, poly(meth)methyl acrylate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroalkyl polymer (PFA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polysiloxane, polysilazane, and polycarbosilane.

[0012] Lithium salt A and lithium salt B are LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 At least one of the following: LiPF6, LiFSI, LiTFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, and lithium imino.

[0013] The lithiophilic substance A is at least one of CuCl2, Cu(NO3)2, SiO2, TiO2, ZnO, Al2O3, Al(NO3)3, BaTiO3, silver nitrate, silver complexes, graphene oxide, graphene oxide, carbon nanotubes, Fe2O3, CuO, cage-structured silsesquioxanes, and metal-organic frameworks.

[0014] Preferably, in step 1, the mass ratio of solvent A, polymer A, polymer B and lithium salt A is 9:08:0.2:0.05.

[0015] Preferably, the coating amount in step 2 is 30 μL / cm³. 2 In step 5, the coating amount is 50 μL / cm³. 2 .

[0016] Preferably, steps 2 and 5 are carried out in an anhydrous, room-temperature environment, with a spin coating speed of 500-5000 rpm and a spin coating time of 1-120 seconds.

[0017] Preferably, in step 4, lithium salt solution A and lithiophilic substance A are mixed at a mass ratio of 10:0.08.

[0018] A lithium metal anode prepared by a method for improving lithium metal deposition behavior.

[0019] A battery comprising a lithium metal anode that improves lithium metal deposition behavior.

[0020] The advantages and positive effects of this invention are: by adding lithiophilic sites to the pores and under the organic polymer film, the lithium metal deposition behavior can be improved; through this preparation method, the uniform nucleation and growth of lithium metal can be induced, the lithium metal deposition direction can be changed, the ionic conductivity of the composite protective film can be improved, and the formation of lithium dendrites can be suppressed and the side reactions caused by direct contact between the negative electrode and the electrolyte can be reduced. Attached Figure Description

[0021] Figure 1 The SEM images are those of Example 1 and Comparative Example 1.

[0022] Figure 2 The figures show the cycle performance of the pouch cells in the examples and comparative examples. Detailed Implementation

[0023] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0024] This invention discloses a lithium metal anode with improved lithium metal deposition behavior and its preparation method. By adding lithiophilic sites to the pores of an organic polymer film and beneath the film, lithium metal deposition behavior can be improved. First, different polymers are mixed and coated onto the surface of the lithium metal anode. One of the polymers is then removed, resulting in a porous polymer coating on the lithium metal surface. Next, a lithiophilic material is coated and embedded into the pores of the polymer coating, achieving the purpose of adding lithiophilic sites beneath the film. The specific preparation method is as follows:

[0025] Step 1: Weigh out solvent A, polymer A, polymer B, and lithium salt A in a mass ratio of 9:0.8:(0.1-0.3):0.05, mix them, and stir evenly to obtain film-forming solution A; the preferred mass ratio is 9:08:0.2:0.05.

[0026] Step 2: Spin-coating film-forming solution A at a concentration of 20-50 μL / cm 2 The amount of coating applied to the surface of the lithium metal anode is preferably 30 μL / cm³. 2 The coating process is carried out in an anhydrous, room-temperature environment. The spin coating speed is 500-5000 rpm and the spin coating time is 1-120 seconds. After drying, a polymer protective layer is formed.

[0027] Step 3: Immerse the lithium metal anode from Step 2 in solvent B to create through-holes; solvent B does not dissolve polymer A, but it can dissolve polymer B; the resulting polymer coating on the lithium metal surface is porous.

[0028] Step 4: Prepare a 1M lithium salt solution A by mixing solvent C and lithium salt B. Mix lithium salt solution A with lithiophilic substance A at a mass ratio of 10:(0.05-0.1), preferably at a mass ratio of 10:0.08, and stir until homogeneous to obtain lithiophilic solution A.

[0029] Step 5: Apply the lithiophilic solution A by spin coating at a concentration of 30-60 μL / cm³. 2 The coating is applied to the surface of the lithium metal anode obtained in step 3 and reacted for 2-10 minutes to form a layer with lithium-affinity sites. The preferred coating amount is 50 μL / cm³. 2 The preferred reaction time is 4-5 minutes. The coating process is carried out in an anhydrous environment at room temperature. The spin coating speed is 500-5000 rpm and the spin coating time is 1-120 seconds.

[0030] Preferably, solvents A, B, and C are ethylene glycol dimethyl ether (DME), N,N-dimethylformamide (DMF), ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, γ-butyrolactone, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, succinate, sulfolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, adiponitrile, and tetrahydrofuran. Solvent A may be any two of the following: N-methylpyrrolidone, acetonitrile, benzyl nitrile, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, wherein solvent A and solvent B cannot be the same; solvent C may be the same solvent as either solvent A or solvent B, or a solvent that is different from both solvent A and solvent B.

[0031] Polymer A and polymer B are at least two of the following: polyurethane (TPU), polyacrylonitrile (PAN), polyethylene, polypropylene, poly(meth)acrylate, poly(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroalkyl polymer (PFA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polysiloxane, polysilazane, and polycarbosilane; when selecting polymer categories, polymer A should be insoluble in solvent B, while polymer B should be soluble in solvent B. Lithium salt A and lithium salt B are LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 At least one of the following: LiPF6, LiFSI, LiTFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, and lithium imino.

[0032] The lithiophilic substance A is at least one of CuCl2, Cu(NO3)2, SiO2, TiO2, ZnO, Al2O3, Al(NO3)3, BaTiO3, silver nitrate, silver complexes, graphene oxide, graphene oxide, carbon nanotubes, Fe2O3, CuO, cage-structured silsesquioxanes, and metal-organic frameworks.

[0033] By adding lithiophilic sites to the pores and under the membrane of the organic polymer membrane, the lithium metal deposition behavior can be improved. Lithium ions are first deposited at the lithiophilic sites in the pores, and the lithiophilic sites induce uniform nucleation and growth of lithium metal. Subsequently, lithium metal spreads along the lithiophilic sites in the pores to the lithiophilic sites under the membrane, thereby changing the lithium metal deposition direction and realizing two-dimensional spreading growth of lithium metal. The protective layer composed of organic polymer and lithiophilic sites can also effectively suppress the side reactions between lithium metal and electrolyte and prevent lithium metal from piercing the membrane.

[0034] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0035] Example 1

[0036] Weigh and mix DMF, PVDF, TPU, and LiPF6 in a mass ratio of 9:08:0.2:0.05, stir thoroughly, and then apply at a concentration of 30 μL / cm³. 2 The coating amount was spin-coated onto the lithium metal surface and dried for 30 minutes. The dried lithium metal anode was then immersed in DME solution for 10 minutes to create pores.

[0037] Prepare a 1M lithium salt solution of LiPF6 and DME. Weigh and mix the lithium salt solution and AgNO3 at a mass ratio of 10:0.08, stir thoroughly, and then dilute at a concentration of 50 μL / cm³. 2 The coating amount was applied to the lithium metal anode after pore formation, and the reaction was carried out for 4 minutes to form sample A.

[0038] Example 2

[0039] Weigh and mix DMF, PVDF, PAN, and LiPF6 in a mass ratio of 9:08:0.2:0.05, stir thoroughly, and then apply at a concentration of 30 μL / cm³. 2 The coating amount was spin-coated onto the lithium metal surface and dried for 30 minutes. The dried lithium metal anode was then immersed in DMF solution for 10 minutes to create pores.

[0040] Prepare a 1M lithium salt solution of LiPF6 and DME. Weigh and mix the lithium salt solution and AgNO3 at a mass ratio of 10:0.08, stir thoroughly, and then dilute at a concentration of 50 μL / cm³. 2 The coating amount was applied to the pore-forming lithium metal anode, and the reaction was carried out for 4 minutes to form sample C. The pouch cell made from sample C maintained a coulombic efficiency of over 99% and a capacity retention of over 80% after 200 cycles at 0.2C.

[0041] Example 3

[0042] Weigh and mix DMF, PVDF, PAN, and LiPF6 in a mass ratio of 9:08:0.2:0.05, stir thoroughly, and then apply at a concentration of 30 μL / cm³. 2 The coating amount was spin-coated onto the lithium metal surface and dried for 30 minutes. The dried lithium metal anode was then immersed in DMAC solution for 10 minutes to create pores.

[0043] Prepare a 1M lithium salt solution of LiPF6 and DME. Weigh and mix the lithium salt solution and AgNO3 at a mass ratio of 10:0.08, stir thoroughly, and then dilute at a concentration of 50 μL / cm³. 2 The coating amount was applied to the pore-forming lithium metal anode, and the reaction was carried out for 4 minutes to form sample D. The pouch cell made from sample D maintained a coulombic efficiency of over 99% and a capacity retention of over 80% after 200 cycles at 0.2C.

[0044] Comparative Example 1

[0045] Weigh and mix DMF, PVDF, TPU, and LiPF6 in a mass ratio of 9:08:0.2:0.05, stir thoroughly, and then apply at a concentration of 30 μL / cm³. 2 The coating amount was spin-coated onto the lithium metal surface, and after drying for 30 minutes, sample B was obtained.

[0046] The products obtained in Example 1 and Comparative Example 1 were subjected to morphological analysis under a scanning electron microscope, such as... Figure 1 As shown in the figure; the protective film of sample A is porous with through-holes, and the lithiophilic sites are located in the pores and below the film; the protective film of sample B is relatively dense. Samples A and B were assembled with ternary cathode materials into a pouch cell and cycled at 0.2C rate. The experimental results are as follows. Figure 2 As shown, sample A pouch cell maintained a coulombic efficiency of over 99% and a capacity retention of over 80% after 200 cycles at 0.2C. Sample B pouch cell, however, experienced dendrite punctures in the separator after 60 cycles, resulting in a micro-short circuit and a sharp drop in battery performance.

[0047] The results above show that the impedance of the lithium metal anode coated with a porous polymer protective film with lithiophilic sites is significantly reduced and the polarization voltage is significantly lower. In addition, the improved lithium-ion conductivity results in uniform lithium deposition, which significantly improves the cycle life of the lithium symmetric battery. Therefore, it can be concluded that the polymer protective film has a significant protective effect on the lithium metal anode.

[0048] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a lithium metal anode, characterized in that: Includes the following steps: Step 1: Mix solvent A, polymer A, polymer B, and lithium salt A in a ratio of 9:0.8:(0.1-0.3): Weigh out the contents at a mass ratio of 0.05, mix them, and stir until homogeneous to obtain film-forming solution A; Step 2: Apply film-forming solution A by spin coating at a concentration of 20-50 μL / cm³. 2 A certain amount is applied to the surface of the lithium metal anode, and after drying, a polymer protective layer is formed. Step 3: Immerse the lithium metal anode from Step 2 in solvent B to create through-holes; solvent B does not dissolve polymer A, but it can dissolve polymer B; Step 4: Prepare lithium salt solution A by mixing solvent C and lithium salt B. Mix lithium salt solution A and lithiophilic substance A at a mass ratio of 10:(0.05-0.1) and stir until homogeneous to obtain lithiophilic solution A. Step 5: Apply the heliophilic solution A by spin coating at a concentration of 30-60 μL / cm³. 2 The amount of coating is applied to the surface of the lithium metal anode prepared in step 3 and reacted for 2-10 minutes to form a layer with lithium-affinity sites; By adding lithiophilic sites to the pores and under the organic polymer membrane, lithium ions are first deposited at the lithiophilic sites in the pores. The lithiophilic sites induce uniform nucleation and growth of lithium metal, which then spreads along the lithiophilic sites in the pores to the lithiophilic sites under the membrane, thereby changing the direction of lithium metal deposition and achieving two-dimensional spreading growth of lithium metal.

2. The method for preparing a lithium metal anode according to claim 1, characterized in that: Solvents A, B, and C are ethylene glycol dimethyl ether (DME), N,N-dimethylformamide (DMF), ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, γ-butyrolactone, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, succinate, sulfolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, adiponitrile, tetrahydrofuran, N-methylpyrrolidone, acetonitrile, benzyl nitrile, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1 Solvent A and solvent B are selected from at least two of the following: 2-dimethoxyethane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, wherein solvent A and solvent B cannot be the same. Polymer A and polymer B are at least two of the following: polyurethane (TPU), polyacrylonitrile (PAN), polyethylene, polypropylene, poly(meth)acrylate, poly(meth)methyl acrylate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroalkyl polymer (PFA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polysiloxane, polysilazane, and polycarbosilane. Lithium salt A and lithium salt B are LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 At least one of the following: LiPF6, LiFSI, LiTFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, and lithium imino. The lithiophilic substance A is at least one of CuCl2, Cu(NO3)2, SiO2, TiO2, ZnO, Al2O3, Al(NO3)3, BaTiO3, silver nitrate, silver complexes, graphene oxide, graphene oxide, carbon nanotubes, Fe2O3, CuO, cage-structured silsesquioxanes, and metal-organic frameworks.

3. The method for preparing a lithium metal anode according to claim 1, characterized in that: In step 1, the mass ratio of solvent A, polymer A, polymer B and lithium salt A is 9:08:0.2:0.

05.

4. The method for preparing a lithium metal anode according to claim 1, characterized in that: The coating amount in step 2 is 30 μL / cm³. 2 In step 5, the coating amount is 50 μL / cm³. 2 .

5. The method for preparing a lithium metal anode according to claim 1 or 4, characterized in that: Steps 2 and 5 are carried out in an anhydrous, room-temperature environment. The spin coating speed is 500-5000 rpm, and the spin coating time is 1-120 seconds.

6. The method for preparing a lithium metal anode according to claim 1, characterized in that: In step 4, lithium salt solution A and lithiophilic substance A are mixed at a mass ratio of 10:0.

08.

7. The lithium metal anode with improved lithium metal deposition behavior prepared by the method of any one of claims 1-6.

8. A battery comprising a lithium metal anode with improved lithium metal deposition behavior as described in claim 7.

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