Metallic lithium composite material, and preparation method and application thereof

Abstract

This application relates to a lithium metal composite material, its preparation method, and its application. The lithium metal composite material includes a lithium-containing core and an elastic cocoon disposed on the surface of the lithium-containing core. The elastic cocoon comprises interwoven one-dimensional carbon nanomaterials and three-dimensional graphene materials, with the three-dimensional graphene material having a honeycomb structure. The elastic cocoon has a large specific surface area and porosity, as well as high mechanical strength, acting like a spring during lithium metal deposition / stripping, effectively adapting to changes in the volume of lithium metal; simultaneously, it regulates the uniform distribution of lithium ions and electrons, which is beneficial for uniform and dense deposition of lithium metal and inhibits the generation and growth of lithium dendrites. The lithium metal composite material exhibits excellent cycle performance and rate performance.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, specifically to a lithium metal composite material, its preparation method, and its application in lithium metal batteries. Background Technology

[0002] Lithium metal, as a negative electrode material for lithium-ion batteries, possesses extremely high theoretical specific capacity and the lowest potential, making it one of the ideal negative electrode materials. However, lithium metal suffers from serious defects during cycling, such as a huge volume expansion effect, a high tendency to form lithium dendrites leading to a decrease in coulombic efficiency, and even safety hazards such as short circuits. These problems limit the commercial application of lithium metal.

[0003] Currently, constructing a three-dimensional framework to provide sufficient space for lithium dendrites and volume expansion is a research hotspot. Existing technologies typically employ carbon materials, metal foams, etc., as three-dimensional current collectors combined with lithium metal. While this improves cycle stability to some extent, lithium metal tends to deposit on the surface of the three-dimensional current collector, which is not conducive to the formation of a stable solid electrolyte membrane. In addition, these three-dimensional materials each have some problems, such as poor conductivity and wettability of polymer fiber webs with lithium metal, high density of metal foam materials, and low usable mass capacity and areal capacity of carbon materials.

[0004] CN116504973A discloses a lithium-carbon material having a cocoon structure. The cocoon structure includes a cocoon formed of structural carbon material and one or more metallic lithium particles contained in the cocoon. Each metallic lithium particle consists of a metallic lithium core and an organic conductive layer coated on the surface of the core.

[0005] CN111864180A discloses a composite lithium metal anode, comprising lithium metal and a three-dimensional framework with cavities. The three-dimensional framework includes a conductive layer and an insulating layer surrounding the conductive layer, with lithium metal filling the cavities within the three-dimensional framework. This three-dimensional framework can limit volume expansion during electrochemical cycling, and the high specific surface area of ​​the three-dimensional porous framework can reduce the actual current density to some extent, but it is far from meeting the requirements of practical applications.

[0006] In summary, existing technologies such as three-dimensional skeleton structures / cocoon structures are difficult to effectively control the uniform distribution of lithium ions and electrons, which is not conducive to the uniform and dense deposition of metallic lithium. Furthermore, they are difficult to effectively adapt to the volume changes of metallic lithium during charging and discharging, and cannot effectively suppress the generation and growth of lithium dendrites.

[0007] Therefore, how to develop a lithium metal composite material that can effectively adapt to the volume changes of lithium metal during charging and discharging while simultaneously regulating the uniform deposition of lithium metal, and possessing long cycle life and high-rate discharge capability, is a key problem that urgently needs to be solved. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention proposes a novel lithium metal composite material. Through the structural design of setting elastic cocoons on the surface of the lithium core, it can effectively adapt to the volume change of lithium metal during the charging and discharging process, regulate the uniform distribution of lithium ions and electrons, thereby suppressing the generation and growth of lithium dendrites and improving the cycle performance and rate performance of the lithium metal anode.

[0009] To achieve this objective, the following technical solution is adopted in this application:

[0010] In a first aspect, this application provides a lithium metal composite material, the lithium metal composite material comprising a lithium-containing core and an elastic cocoon disposed on the surface of the lithium-containing core, the elastic cocoon comprising interwoven one-dimensional nano-carbon material and three-dimensional graphene material, the three-dimensional graphene material having a honeycomb structure.

[0011] In this invention, a honeycomb-like three-dimensional graphene material is used to enhance the mechanical strength of the elastic cocoon, giving it a spring-like function that can adapt to the volume changes of lithium metal during charging and discharging. The three-dimensional graphene material enhances the specific surface area and porosity of the elastic cocoon, resulting in a rich pore structure and a large specific surface area. This provides multiple channels for lithium-ion transport, homogenizes current distribution, and also retains liquid, effectively suppressing the formation and growth of lithium dendrites and improving cycle life. The resulting lithium metal composite material exhibits excellent cycle performance and rate performance, surpassing the performance of lithium metal composite materials composed solely of one-dimensional nano-carbon materials forming the cocoon.

[0012] Optionally, the lithium-containing core comprises metallic lithium and / or a lithium alloy, wherein the alloying element in the lithium alloy comprises at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, carbon, magnesium, indium, gallium, aluminum, or zinc.

[0013] Optionally, the lithium alloy contains more than 50% metallic lithium, preferably 60-95%.

[0014] Optionally, the average particle size of the lithium-containing core is 1-100 μm, preferably 5-50 μm.

[0015] Optionally, the one-dimensional carbon nanomaterial includes at least one of carbon nanofibers, single-walled carbon nanotubes, or multi-walled carbon nanotubes.

[0016] Optionally, the outer diameter of the one-dimensional carbon nanomaterial is ≤300nm, preferably 1-20nm, and more preferably 1-10nm.

[0017] Optionally, the length of the one-dimensional carbon nanomaterial is 0.5 μm to 500 μm, preferably 1-100 μm, and more preferably 5-50 μm.

[0018] Optionally, the BET specific surface area of ​​the three-dimensional graphene is 1-50 m² / g, preferably 5-20 m² / g.

[0019] Optionally, the pore size of the three-dimensional graphene is 1-50 nm, preferably 5-50 nm.

[0020] Optionally, the pore volume of the three-dimensional graphene is 0.05-50 cm³. 3 / g, preferably 0.075-50cm 3 / g.

[0021] Optionally, the mass ratio of the one-dimensional carbon nanomaterial to the three-dimensional graphene material is 1:(0.1-10), preferably 1:(0.5-5).

[0022] As a preferred embodiment of the present invention, the mass ratio of the elastic cocoon to the lithium-containing core is 1:(0.1-100), preferably 1:(0.5-50).

[0023] Optionally, the thickness of the elastic cocoon is 0.1-5 μm, preferably 0.5-3 μm.

[0024] As a further preferred technical solution of the present invention, the ratio between the average particle size of the lithium-containing core and the thickness of the elastic cocoon is (1-20):1, preferably (5-10):1.

[0025] In a second aspect, the present invention provides a method for preparing the composite material as described in the first aspect above, the method comprising the following steps:

[0026] (1) Mix one-dimensional carbon nanomaterials, three-dimensional graphene materials and organic solvents to obtain a mixture;

[0027] (2) The mixture in step (1) is applied to the surface of the lithium-containing core by high-speed winding or spray drying to obtain the composite material;

[0028] In step (1), the organic solvent is inert to the lithium core (or does not undergo a violent chemical reaction).

[0029] Optionally, the organic solvent in step (1) includes at least one of the following: liquid alkanes with 5-20 carbon atoms, liquid cycloalkanes with 5-20 carbon atoms, benzene, toluene, xylene, solvent oil D20, solvent oil D40, solvent oil D60, solvent oil D80, silicone oil, light paraffin, N-methylpyrrolidone, or N,N-dimethylformamide.

[0030] As a preferred technical solution of the present invention, step (1) involves first mixing the one-dimensional carbon nanomaterial and the organic solvent once, and then adding the three-dimensional graphene material for a second mixing; or,

[0031] Step (1) First, mix the three-dimensional graphene material and the organic solvent once, and then add the one-dimensional nano carbon material for a second mixing.

[0032] Optionally, the mixing in step (1) may employ at least one of high-speed dispersion, high-pressure homogenization, or high-pressure turbulence.

[0033] Optionally, the pressure of the high-pressure homogenization and high-pressure turbulence is independently 500-2000 bar, preferably 600-1500 bar.

[0034] Optionally, the high-speed winding speed in step (2) is above 3000 rpm, preferably 5000-15000 rpm.

[0035] Optionally, the high-speed winding time is 5-90 minutes, preferably 10-60 minutes.

[0036] Optionally, the inlet air temperature for spray drying is 180~240℃, for example, it can be 180℃, 185℃, 190℃, 200℃, 210℃, 220℃, 230℃ or 240℃, etc., including but not limited to the values ​​listed above, preferably 200~220℃.

[0037] Optionally, the outlet air temperature of the spray dryer is 80~120℃, for example, it can be 80℃, 85℃, 90℃, 100℃, 110℃ or 120℃, etc., including but not limited to the values ​​listed above, preferably 100~110℃.

[0038] Optionally, the atomization pressure of the spray drying is 0.1~0.5 MPa, for example, it can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa or 0.5 MPa, etc., including but not limited to the values ​​listed above, and preferably 0.2~0.4 MPa.

[0039] Thirdly, the present invention provides the application of the composite material as described in the first aspect above in lithium metal batteries.

[0040] Optionally, the composite material is contained in the lithium metal anode of the lithium metal battery.

[0041] Compared with the prior art, this application has at least one of the following beneficial effects:

[0042] (1) The composite material provided in this application includes a lithium core and an elastic cocoon. The elastic cocoon includes one-dimensional nano-carbon material and three-dimensional graphene material that are intertwined and interwoven. The three-dimensional graphene material has a honeycomb structure. This structural design makes the elastic cocoon have a large specific surface area and porosity, which plays a similar role to a spring during the deposition / stripping of lithium metal and effectively adapts to the volume change of lithium metal.

[0043] (2) In the lithium metal composite material provided by the present invention, the structure design of the elastic cocoon can regulate the uniform distribution of lithium ions and electrons, which is conducive to the uniform and dense deposition of lithium metal, thereby inhibiting the generation and growth of lithium dendrites and improving the cycle performance and rate performance of the lithium metal anode.

[0044] (3) Compared with the use of polymer fiber mesh, metal foam or carbon materials as three-dimensional skeleton in the prior art, the present invention uses one-dimensional nano carbon materials and three-dimensional graphene materials to construct an elastic cocoon, which not only has good conductivity and wettability with lithium metal, but also has a low density, which is beneficial to improving the mass capacity and areal capacity of the electrode.

[0045] (4) By optimizing the structural design of the elastic cocoon, such as the thickness, porosity, and ratio of one-dimensional carbon nanomaterials and three-dimensional graphene materials, this invention can further improve the energy density and cycle performance of the lithium metal anode.

[0046] (5) The preparation method provided in this application has a short process flow, high production efficiency, and is universally applicable. Attached Figure Description

[0047] Figure 1 Here is a SEM image of the composite material in Example 2;

[0048] Figure 2 The cyclic test curves are for Examples 2, 4, 6, and 8.

[0049] Figure 3 The cyclic test curves are for Example 2 and Comparative Examples 1-4. Detailed Implementation

[0050] To facilitate understanding of this application, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of this application.

[0051] Example 1

[0052] This embodiment provides a lithium metal composite material, which includes lithium metal powder with a particle size of 100 μm and an elastic cocoon disposed on its surface. The elastic cocoon includes double-walled carbon nanotubes and three-dimensional graphene materials.

[0053] The method for preparing the composite material includes the following steps:

[0054] (1) 1g of double-walled carbon nanotubes (outer diameter 4nm, length 50μm) and 0.1g of three-dimensional graphene material (BET specific surface area 50m² / g, pore size 5nm, pore volume 0.075cm³) were added. 3 (g) and heptane were mixed and dispersed evenly using a high-pressure homogenizer at a pressure of 1000 bar to obtain a mixture;

[0055] (2) Mix 0.11% lithium metal powder with the mixture, rotate at 15000 rpm for 10 min, filter, and heat at 120°C to obtain the lithium metal composite material.

[0056] Example 2

[0057] This embodiment provides a lithium metal composite material, which includes lithium boron particles with a particle size of 50 μm (boron accounts for 40% by mass) and an elastic cocoon disposed on its surface. The elastic cocoon includes single-walled carbon nanotubes and three-dimensional graphene materials.

[0058] The method for preparing the composite material includes the following steps:

[0059] (1) 0.1g of single-walled carbon nanotubes (outer diameter 4nm, length 50μm) and 1g of three-dimensional graphene material (BET specific surface area 5m² / g, pore size 50nm, pore volume 50cm³) were added. 3 (g) and solvent oil D20 are mixed and dispersed evenly using a high-pressure turbulent flow machine at a pressure of 1200 bar to obtain a mixture;

[0060] (2) Mix 110g of lithium boron alloy powder (lithium boron particles) with the mixture, and then spray dry it with an inlet air temperature of 220°C, an outlet air temperature of 90°C, and an atomization pressure of 0.5 MPa to obtain the metal lithium composite material.

[0061] The lithium metal composite material was characterized by SEM, and the characterization results are as follows: Figure 1 As shown in the figure, the elastic cocoon of the lithium metal composite material comprises linear single-walled carbon nanotubes and honeycomb-shaped three-dimensional graphene. The three-dimensional graphene and single-walled carbon nanotubes intertwine to form a stable elastic cocoon.

[0062] Example 3

[0063] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotubes is replaced with 0.2g, while the other conditions remain unchanged.

[0064] Example 4

[0065] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotubes is replaced with 2g, while the other conditions remain unchanged.

[0066] Example 5

[0067] Compared with Example 2, the only difference is that the mass of lithium boron particles is replaced with 55g, while the other conditions remain unchanged.

[0068] Example 6

[0069] Compared with Example 2, the only difference is that the mass of lithium boron particles is replaced with 0.55g, while the other conditions remain unchanged.

[0070] Example 7

[0071] Compared with Example 2, the only difference is that the lithium boron particles are replaced with lithium boron indium particles, the mass percentage of boron is 25% and the mass percentage of indium is 5%, and the other conditions remain unchanged.

[0072] Example 8

[0073] Compared with Example 2, the only difference is that lithium boron particles are replaced with lithium magnesium silver particles, with magnesium accounting for 5% of the mass and silver accounting for 5% of the mass, while the other conditions remain unchanged.

[0074] Comparative Example 1

[0075] Compared to Example 2, the only difference is that the composite material includes lithium boron particles and single-walled carbon nanotubes, but does not include three-dimensional graphene materials.

[0076] Comparative Example 2

[0077] Compared to Example 2, the only difference is that the composite material includes lithium boron particles and three-dimensional graphene material, but does not include single-walled carbon nanotubes.

[0078] Comparative Example 3

[0079] Compared to Example 2, the only difference is that the materials include lithium boron particles, but do not include single-walled carbon nanotubes and three-dimensional graphene materials.

[0080] Comparative Example 4

[0081] Compared to Example 2, the only difference is that the composite material comprises a mechanical mixture of lithium boron particles, single-walled carbon nanotubes, and three-dimensional graphene materials, and does not form the structure described in this invention.

[0082] Comparative Example 5

[0083] Compared with Example 2, the only difference is that the composite material includes lithium boron particles, single-walled carbon nanotubes, and graphene material, wherein the graphene material is two-dimensional graphene.

[0084] Performance testing:

[0085] The materials from Examples 1-8 and Comparative Examples 1-4 were pressed onto copper foam to prepare electrodes. These electrodes were then assembled into symmetrical cells. The electrolyte was an ether-based solution purchased from Shenzhen Kejing Materials Technology Co., Ltd. The symmetrical cells were tested for cycle performance at 2 mA and 2 mAh, with the cutoff condition being the occurrence of a short circuit or an overpotential reaching 1V. The measurement results are shown in Table 1 and... Figure 2-3 ,in, Figure 2 The cyclic test curves for Examples 2, 4, 6, and 8 are shown. Figure 3 The cyclic test curves of Example 2 and Comparative Examples 1-4 are shown.

[0086] Table 1

[0087]

[0088] As can be seen from Table 1:

[0089] (1) Comparing Example 2 and Example 3-4, it can be seen that the number of cycles in Example 3-4 is more than that in Example 2. This is because the quality of single-walled carbon nanotubes and three-dimensional graphene materials in Example 3-4 is more suitable, and the elastic cocoon constructed by single-walled carbon nanotubes and three-dimensional graphene materials significantly improves the cycle performance.

[0090] (2) Comparing Example 2 and Example 5-6, it can be seen that the number of cycles in Example 5-6 is more than that in Example 2. This is because the mass of lithium boron particles and elastic cocoon is more suitable in Example 5-6. The two work together to effectively adapt to the volume change of metallic lithium during charging and discharging.

[0091] (3) Comparing Example 2 and Example 8-9, it can be seen that the number of cycles in Example 8-9 is more than that in Example 2. This is because there are alloying elements in Example 8 and Example 9 that regulate the uniform deposition of metallic lithium.

[0092] (4) Comparing Example 2 and Comparative Examples 1-5, it can be seen that the number of cycles in Example 2 is more than that in Comparative Examples 1-5. This is because the cocoon composition materials and structures of the materials in Comparative Examples 1-4 are different from those in Example 2, and the adaptability to changes in the volume of metallic lithium and the uniformity of regulating lithium ions and electrons are poor. The graphene material used in Comparative Example 5 is a two-dimensional structure, which is different from the three-dimensional honeycomb graphene material used in this invention. The improvement of the composite material performance is not as good as that of the composite material of this invention.

[0093] The applicant declares that this application illustrates its detailed structural features through the above embodiments, but this application is not limited to the above detailed structural features, that is, it does not mean that this application must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the components selected in this application, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A lithium metal composite material, characterized in that, The lithium metal composite material includes a lithium-containing core and an elastic cocoon disposed on the surface of the lithium-containing core. The elastic cocoon includes interwoven one-dimensional carbon nanomaterials and three-dimensional graphene materials, and the three-dimensional graphene materials have a honeycomb structure.

2. The composite material according to claim 1, characterized in that, The lithium-containing core includes metallic lithium and / or lithium alloys, wherein the alloying element in the lithium alloy includes at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, carbon, magnesium, indium, gallium, aluminum, or zinc. Preferably, the lithium alloy contains more than 50% metallic lithium, and more preferably 60-95% metallic lithium. Preferably, the average particle size of the lithium-containing core is 1-100 μm, and more preferably 5-50 μm.

3. The composite material according to claim 1 or 2, characterized in that, The one-dimensional carbon nanomaterial includes at least one of carbon nanofibers, single-walled carbon nanotubes, or multi-walled carbon nanotubes. Preferably, the outer diameter of the one-dimensional carbon nanomaterial is ≤300nm, more preferably 1-20nm, and even more preferably 1-10nm; Preferably, the length of the one-dimensional carbon nanomaterial is 0.5 μm to 500 μm, more preferably 1-100 μm, and even more preferably 5-50 μm.

4. The composite material according to any one of claims 1-3, characterized in that, The BET specific surface area of ​​the three-dimensional graphene is 1-50 m² / g, preferably 5-20 m² / g; Preferably, the pore size of the three-dimensional graphene is 1-50 nm, and more preferably 5-50 nm; Preferably, the pore volume of the three-dimensional graphene is 0.05-50 cm³. 3 / g, preferably 0.075-50cm 3 / g.

5. The composite material according to any one of claims 1-4, characterized in that, The mass ratio of the one-dimensional carbon nanomaterial to the three-dimensional graphene material is 1:(0.1-10), preferably 1:(0.5-5). Preferably, the mass ratio of the elastic cocoon to the lithium-containing core is 1:(0.1-100), more preferably 1:(0.5-50).

6. The composite material according to any one of claims 1-5, characterized in that, The thickness of the elastic cocoon is 0.1-5 μm, preferably 0.5-3 μm; Preferably, the ratio between the average particle size of the lithium-containing core and the thickness of the elastic cocoon is (1-20):1, and more preferably (5-10):

1.

7. A method for preparing the composite material according to any one of claims 1-6, characterized in that, The method includes the following steps: (1) Mix one-dimensional carbon nanomaterials, three-dimensional graphene materials and organic solvents to obtain a mixture; (2) The mixture in step (1) is applied to the surface of the lithium-containing core by high-speed winding or spray drying to obtain the composite material; In step (1), the organic solvent is inert to the lithium-containing core.

8. The method according to claim 7, characterized in that, The organic solvent in step (1) includes at least one of the following: liquid alkanes with 5-20 carbon atoms, liquid cycloalkanes with 5-20 carbon atoms, benzene, toluene, xylene, solvent oil D20, solvent oil D40, solvent oil D60, solvent oil D80, silicone oil, light paraffin, N-methylpyrrolidone, or N,N-dimethylformamide; Preferably, in step (1), the one-dimensional carbon nanomaterial and the organic solvent are mixed once, and then the three-dimensional graphene material is added for a second mixing; or, Step (1) First, mix the three-dimensional graphene material and the organic solvent once, then add the one-dimensional nano carbon material and mix again; Preferably, the mixing in step (1) employs at least one of high-speed dispersion, high-pressure homogenization, or high-pressure turbulence; Preferably, the pressure of the high-pressure homogenization and high-pressure turbulence is independently 500-2000 bar, more preferably 600-1500 bar.

9. The method according to claim 7 or 8, characterized in that, In step (2), the high-speed winding speed is above 3000 rpm, preferably 5000-15000 rpm; Preferably, the high-speed winding time is 5-90 minutes, and more preferably 10-60 minutes.

10. The application of the composite material as described in any one of claims 1-6 in lithium metal batteries.

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