Metal lithium composite material as well as preparation method and application thereof

Abstract

The invention discloses a metal lithium composite material as well as a preparation method and application thereof. The metal lithium composite material comprises a lithium-containing inner core, and a modification layer is arranged on the surface of the lithium-containing inner core; the modification layer comprises carbon nanotubes and a carbon fluoride material, the carbon nanotubes are interwoven to form a cage-shaped structure, and the carbon fluoride material exists on at least one of the surface of the lithium-containing core, the surface of the cage-shaped structure or pores of the cage-shaped structure. In the modification layer, the carbon nanotubes are interwoven to form a cage-shaped structure, so that a space can be provided for the volume change of the lithium-containing core, and meanwhile, a support is provided for the carbon fluoride material. Fluorine in the carbon fluoride material and lithium in the lithium-containing inner core are subjected to an in-situ reaction to generate lithium fluoride, and a stable SEI film is constructed on the surface of the lithium-containing inner core. The modification layer constructs a stable electron transport network while modifying the surface of the lithium-containing inner core, so that the current density is effectively regulated and controlled, and the problem that lithium dendrites are generated due to non-uniform current is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a metal lithium composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are rechargeable secondary batteries widely used in products such as mobile phones, laptops, and new energy vehicles. Lithium metal is one of the preferred negative electrode materials for lithium batteries, but it suffers from volume expansion and lithium dendrites, resulting in a short cycle life and limiting its application in high-energy-density lithium batteries.

[0003] At present, the research on metallic lithium mainly focuses on two aspects: (1) using lithium alloy as negative electrode or composite negative electrode; (2) setting a volume expansion mitigation layer on the surface of metallic lithium. Among them, CN114300654A discloses a uniformly distributed three-dimensional lithium alloy negative electrode and its preparation method, the preparation method comprising the following steps: (1) melting metallic lithium and other metals at high temperature to obtain an alloy material; (2) rolling the alloy material through a roller to obtain an alloy strip, and roughening the alloy strip; (3) polishing the surface of the pure lithium strip and then performing surface roughness treatment; (4) composite rolling the treated alloy strip and the pure lithium strip, embedding the grooves and the protrusions, and then rolling the composite strip to obtain a composite strip; (5) heat treating the rolled composite strip to obtain a uniformly distributed three-dimensional lithium alloy negative electrode material. The three-dimensional lithium alloy negative electrode material prepared by this method significantly improves its cycle life and significantly improves the problem of lithium dendrites, but does not solve the problem of metallic lithium / alloy volume expansion.

[0004] CN116504973A discloses a lithium-carbon material, its preparation method, and a lithium-ion battery. This lithium-carbon material has a cocoon structure comprising a cocoon body formed from a structural carbon material and one or more lithium metal particles contained within the cocoon body. Each lithium metal particle consists of a lithium metal core and an organic conductive layer coated on the core surface. This lithium-carbon material can effectively address the problem of lithium metal dendrites and the volume change of lithium metal during battery charge and discharge. While the organic conductive layer can effectively transport lithium ions and electrons, it cannot stabilize the interface between the lithium metal particles, resulting in poor interface stability during charge and discharge.

[0005] Based on this, how to modify powdered lithium-containing materials such as metallic lithium powder to solve the problems of volume expansion and uneven deposition of metallic lithium, while enhancing the interface stability between metallic lithium particles, has become an urgent problem to be solved. Summary of the Invention

[0006] To address the above technical issues, the present invention provides a lithium metal composite material, its preparation method, and its use. The composite material comprises a modified layer comprising carbon nanotubes and a fluorinated carbon material on the surface of a lithium-containing core. This modified layer simultaneously addresses the issues of volume expansion, uneven deposition, and interfacial instability between lithium-containing core particles in powdered lithium-containing materials such as lithium metal powder, significantly improving the cycling performance of the lithium metal composite material.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a metal lithium composite material, which includes a lithium-containing core, and a modified layer is provided on the surface of the lithium-containing core; the modified layer includes carbon nanotubes and a fluorinated carbon material, the carbon nanotubes are intertwined to form a cage structure, and the fluorinated carbon material is present at least one position on the surface of the lithium-containing core, on the surface of the cage structure, or in the pores of the cage structure; the mass ratio of the carbon nanotubes to the fluorinated carbon material is 1:(0.1-100).

[0009] In this invention, the modified layer comprises a fluorinated carbon material and carbon nanotubes. The carbon nanotubes intertwine to form a cage-like structure, allowing lithium ion transport, providing space for the volume expansion of the lithium-containing core, and providing support for the fluorinated carbon material. Furthermore, the carbon nanotubes can simultaneously transport lithium ions and electrons, providing dual regulation of current density and lithium ion transport.

[0010] In the present invention, the fluorine in the carbon fluoride material located on the surface of the lithium-containing core, in the portion directly in contact with the lithium-containing core surface, reacts with the active lithium on the lithium-containing core surface to generate lithium fluoride, thereby in-situ constructing a stable SEI. Simultaneously, the carbon in the carbon fluoride material can conduct electrons, effectively regulating the interface state between the lithium-containing cores and the uniform distribution of current density. The carbon fluoride material located on the surface of the cage structure and / or in the pores of the cage structure acts as a fluorine source, reacting with the active lithium during the charge and discharge process to continuously generate lithium fluoride, stabilizing the interface of the composite material. Furthermore, it can also form a conductive network with carbon nanotubes to regulate the uniform deposition of metallic lithium.

[0011] In the present invention, the carbon nanotubes and the fluorinated carbon material work together to create a modified layer that simultaneously addresses the issues of uneven lithium metal deposition, volume expansion of lithium metal, and interface instability between the lithium-containing core and the metal. The metal-lithium composite material exhibits excellent cycling performance and safety. The modified layer can be varied according to the size of the lithium-containing core, enabling modification of the lithium-containing core at nanometer, submicron, and micrometer scales.

[0012] In the present invention, the modified layer constructed of carbon nanotubes and fluorinated carbon materials in a specific mass ratio enables the metal lithium composite material to have good cycling performance. The mass ratio can be 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:2.5, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:75, 1:90 or 1:100, including but not limited to the listed values. If the mass ratio is too large, the amount of fluorinated carbon material is small, the SEI constructed on the surface of the lithium-containing core is small, and the effect of interface regulation is limited; if the mass ratio is too small, the amount of carbon nanotubes is small, the volume expansion of the lithium-containing core is limited, and the effect of regulating lithium ions and current density uniformity is poor.

[0013] Optionally, the fluorinated carbon material includes at least one of fluorinated graphite, fluorinated carbon, fluorinated carbon black, fluorinated carbon fiber, fluorinated nanocarbon fiber VGCF, fluorinated graphene microsheets, fluorinated graphene oxide or fluorinated carbon nanotubes.

[0014] Optionally, the atomic ratio of carbon to fluorine in the fluorinated carbon material is greater than 0 and less than 1.25, for example, it can be 0.1, 0.25, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2 or 1.25, including but not limited to the listed point values. The atomic ratio can take into account both the in situ construction of a complete SEI and the regulation of electron transport, and is preferably 0.5-1.

[0015] Optionally, the size of the carbon fluoride material is 1 nm to 50 μm, preferably a nanoscale carbon fluoride material with a size of 3 nm to 500 nm, more preferably 5 to 300 nm. It should be noted that the nanoscale in the nanoscale carbon fluoride material only requires that the size in at least one of the three-dimensional directions is nanoscale.

[0016] As a preferred technical solution of the present invention, the mass ratio of the carbon nanotubes to the fluorinated carbon material is 1:(0.5-50), preferably 1:(1-20).

[0017] Optionally, the lithium-containing core comprises metallic lithium powder and / or lithium alloy powder, with an average particle size of 1-100 μm, preferably 10-50 μm.

[0018] Optionally, the alloying elements in the lithium alloy powder include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum, or zinc. During lithium extraction from the metal-lithium composite material, the alloying elements remain in place and do not participate, thereby improving the stability of the core. The alloying elements have an affinity for lithium, which can regulate the uniform deposition of the metallic lithium during deposition.

[0019] Optionally, the carbon nanotubes are 0.5 μm to 50 μm in length, preferably 1-20 μm in length. If the carbon nanotubes are too short, it is difficult to form a continuous and stable modified layer. If the carbon nanotubes are too long, they are difficult to disperse evenly, resulting in an uneven modified layer.

[0020] Optionally, the number of the carbon nanolayers is less than or equal to 15 layers, preferably 1-10 layers.

[0021] Optionally, the outer diameter of the carbon nanotube is less than 30 nm, preferably 4-20 nm.

[0022] Optionally, the carbon nanotubes contain lithium-phobic elements, and the lithium-phobic elements include at least one of copper, nickel, titanium, chromium, vanadium, cobalt, manganese or iron. In the prior art, the regulation of the deposition of metallic lithium is concentrated on the deposition site where lithium affinity is introduced. In the present invention, the inventors found during the experiment that the use of carbon nanotubes containing a lithium-phobic element modification layer can also achieve the regulation of metallic lithium deposition. The reason is speculated to be: the uneven deposition of metallic lithium is caused by the uneven current density on the surface of the material. Although the lithium-phobic element modification layer cannot induce the uniform deposition of metallic lithium, it has good electronic conductivity, which makes the current density on the surface of the material more uniform, thereby solving the problem of uneven deposition of metallic lithium and the generation and growth of lithium dendrites; further, the composite material composed of the carbon nanotubes and the lithium alloy core constructs a lithium-philic-lithium-phobic gradient from the inside to the outside, regulates the preferential inward deposition of metallic lithium, and improves the structural stability and cycle stability of the metallic lithium composite material.

[0023] Optionally, based on the mass of the carbon nanotubes being 100%, the mass content of the lithium-phobic element is greater than 30%, preferably 50-80%. A lower mass content may limit the uniform deposition of metallic lithium, while a higher mass content may result in a lower gram capacity of the metallic lithium composite.

[0024] Optionally, the thickness of the modified layer ranges from 0.5 μm to 20 μm. A thicker thickness results in a lower metallic lithium content and a lower gram capacity of the metallic lithium composite material. A thinner thickness has limited effect on mitigating core volume expansion, and is preferably 1-10 μm. The thickness of the modified layer can be adjusted based on the mass ratio of the carbon nanotubes to the fluorinated carbon material, thereby simultaneously achieving effective control of ions and electrons and stabilizing the interface between the lithium-containing core.

[0025] Optionally, based on the mass of the metal lithium composite material being 100%, the mass fraction of the core in the metal lithium composite material is greater than 50%, preferably greater than 70%, and more preferably greater than 85%.

[0026] In a second aspect, the present invention provides a method for preparing the metal lithium composite material as described in the first aspect, the preparation method comprising the following steps:

[0027] (1) mixing an organic solvent, carbon nanotubes, and a fluorinated carbon material to obtain a mixture;

[0028] (2) mixing the mixture with a lithium-containing powder material and spray drying the mixture to obtain the metal lithium composite material;

[0029] Alternatively, the mixture and the lithium-containing powder material are entangled at a high speed at a rotation speed of 5000 rpm or more to remove the organic solvent to obtain the metal lithium composite material; the organic solvent is inert to the lithium-containing powder material.

[0030] In the present invention, the organic solvent is not specifically limited, as long as it is inert to the lithium metal powder and / or lithium alloy powder, does not undergo violent chemical reactions, and can be used as a solvent. For example, it can be any one of liquid alkanes having 4 to 20 carbon atoms, liquid halogenated hydrocarbons having 4 to 20 carbon atoms, toluene, xylene, liquid paraffin, tetrahydrofuran, N,N-dimethylformamide, or silicone oil, or a combination of at least two thereof.

[0031] Optionally, step (1) includes the following operations: (a) pre-dispersing the carbon nanotubes in an organic solvent, and then adding the fluorinated carbon material to mix to obtain a mixture. Pre-dispersing the carbon nanotubes allows the single-walled carbon nanotubes to be more evenly dispersed, thereby better forming a stable and uniform modified layer with the fluorinated carbon material.

[0032] Optionally, the mixing method in step (2) includes at least one of mechanical stirring, ultrasonic dispersion or high-speed winding at a rotation speed of 5000 rpm or above.

[0033] In a third aspect, the present invention provides an electrode comprising the metal lithium composite material described in the first aspect. The electrode may be an electrode made of a pure metal lithium composite material, or a pre-lithiated electrode or composite electrode comprising the metal lithium composite material and graphite or silicon-based materials.

[0034] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0035] 1. By using carbon nanotubes and carbon fluoride materials as a modifying layer to modify the lithium-containing core, the carbon nanotubes are interwoven to form a cage-like structure, which reduces the volume expansion problem of metallic lithium during charging and discharging, while providing support for the carbon fluoride material;

[0036] 2. Carbon nanotubes can conduct electrons and ions simultaneously, regulating lithium ion transmission and current density, effectively solving the problem of uneven lithium metal deposition and avoiding the generation and growth of lithium dendrites, thereby improving the safety and service life of lithium metal composite materials;

[0037] 3. The fluorine in the fluorinated carbon material located on the surface of the lithium-containing core can react with the active lithium in the metallic lithium or lithium alloy to generate lithium fluoride, which can in situ construct a stable SEI film and solve the problem of unstable interface between the lithium-containing cores; at the same time, the carbon in the fluorinated carbon material can improve electron conduction and solve the problem of lithium dendrite generation and growth; the fluorinated carbon material located on the surface of the cage structure and / or in the pores of the cage structure acts as a fluorine source, reacting with the active lithium during the charge and discharge process to continuously generate lithium fluoride, stabilize the interface of the composite material, and jointly construct a conductive network with the carbon nanotubes to regulate the uniform deposition of metallic lithium;

[0038] 4. The carbon nanotubes and the carbon fluoride material cooperate with each other at a specific mass ratio, and the cycle stability of the lithium metal composite material is better than the cycle performance of the lithium metal composite material modified with pure carbon nanotubes or carbon fluoride materials;

[0039] 5. By designing the mass ratio of carbon nanotubes and carbon fluoride materials, the thickness of the modified layer can be adjusted. The thickness of the modified layer, capacity and cycle performance of the metal lithium composite material can be adjusted and customized. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a SEM image of the lithium metal composite material in Example 2;

[0041] Figure 2 The lithium extraction test curves of Example 1 and Example 2 are shown;

[0042] Figure 3 These are the symmetrical battery test curves of Example 1, Example 6, and Example 7;

[0043] Figure 4 These are the symmetrical battery test curves of Example 2, Example 3, Example 4, and Example 5;

[0044] Figure 5 These are the symmetrical battery test curves of Example 2, Example 8, Example 9, and Example 10;

[0045] Figure 6 Symmetrical battery test curves of Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 5;

[0046] Figure 7 These are the symmetrical battery test curves of Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5.

[0047] Note: Some discontinuous areas in the test curve are caused by different sampling parameter settings of the test equipment. DETAILED DESCRIPTION

[0048] The present invention will be further described in detail below with reference to the examples. The following examples are only used to explain the principle of the present invention and are not to be construed as limiting the present invention.

[0049] Example 1

[0050] This embodiment provides a metal lithium composite material, the metal lithium composite material comprising metal lithium powder, a surface of the metal lithium powder being provided with a modified layer of multi-walled carbon nanotubes and graphite fluoride in a mass ratio of 1:0.1, the modified layer having a thickness of 20 μm, and the mass fraction of the metal lithium powder being approximately 50%;

[0051] The preparation method of the lithium metal composite material comprises the following steps:

[0052] (1) adding 10 g of multi-walled carbon nanotubes (GT-400, outer diameter 20-30 nm, length 3-12 μm, Shandong Dazhan Nanomaterial Co., Ltd.) and 1 g of fluorinated graphite (Aladdin, F302204, specification or purity: ≥56 wt% F, D90 ≤8 μm) to 120 L of heptane, performing ultrasonic dispersion, and mixing uniformly to obtain a first mixture;

[0053] (2) adding 11 g of passivation metal lithium powder having an average particle size of 10 μm to the mixture, and mixing at a rotation speed of 9000 rpm for 30 min to obtain a second mixture;

[0054] (3) The second mixture was filtered to remove heptane, and then dried at 110° C. under vacuum conditions for 24 hours to obtain the metal lithium composite material.

[0055] Example 2

[0056] This embodiment provides a metal lithium composite material, the metal lithium composite material comprising metal lithium powder, a surface of the metal lithium powder being provided with a modification layer of single-walled carbon nanotubes and fluorinated carbon black in a mass ratio of 1:100, the modification layer having a thickness of 1 μm, and the mass fraction of the metal lithium powder being approximately 90%;

[0057] The preparation method of the lithium metal composite material comprises the following steps:

[0058] (1) 0.1 g of single-walled carbon nanotubes (Article No. 104477, outer diameter 1-2 nm, length 5-30 μm, Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.) and 10 g of fluorinated carbon black (Shanghai Furui Fine Chemical Co., Ltd., fluorine-carbon ratio 1.0, particle size 50-100 nm) were added to 150 L of p-xylene, and the mixture was dispersed at a speed of 9000 rpm and mixed uniformly to obtain a first mixture;

[0059] (2) adding 20.2 g of metallic lithium powder having an average particle size of 50 μm to the first mixture, and mechanically stirring the mixture at a rotation speed of 3000 rpm for 60 min to obtain a second mixture;

[0060] (3) The second mixture was spray-dried at an air inlet temperature of 240° C., an air outlet temperature of 90° C., an atomization pressure of 1.1 MPa, and an injection volume of 180 mL / min to obtain the metal lithium composite material.

[0061] The metal lithium composite material was characterized by SEM, as shown in FIG. Figure 1 As shown in the figure, it can be clearly seen that the modified layer of the lithium metal composite material includes single-walled carbon nanotubes (tubular material in the figure) and fluorinated carbon black (granular material in the figure). The single-walled carbon nanotubes are interwoven to form a cage structure, and the fluorinated carbon black is distributed at at least one location on the surface of the lithium-containing core, on the surface of the cage structure, or in the pores of the cage structure.

[0062] The metal lithium composite materials in Example 1 and Example 2 were pressed onto the foam copper to form a button battery with the lithium sheet. The lithium extraction capacity was tested at 0.2 mA. The test curve is as follows: Figure 2 As shown. Figure 2 It can be seen that the lithium extraction capacity of the metal lithium composite material in Example 1 is 1699.77 mAh / g, and the lithium extraction capacity of the metal lithium composite material in Example 2 is 3337.34 mAh / g. This shows that the capacity of the metal lithium composite material of the present invention is adjustable and customizable.

[0063] Example 3

[0064] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to fluorinated carbon black is replaced with 1:0.5, and the other conditions are the same.

[0065] Example 4

[0066] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to fluorinated carbon black is replaced with 1:20, and the other conditions are the same.

[0067] Example 5

[0068] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to fluorinated carbon black is replaced with 1:50, and the other conditions are the same.

[0069] Example 6

[0070] Compared with Example 1, the only difference is that the multi-walled carbon nanotubes are replaced with copper-plated multi-walled carbon nanotubes (Beijing Dekedaojin Technology Co., Ltd., CNT813, copper content of 60% by mass, outer diameter 8-15 nm, length 50 μm), and the other conditions are the same.

[0071] Example 7

[0072] Compared with Example 1, the only difference is that the multi-walled carbon nanotubes are replaced with nickel-plated multi-walled carbon nanotubes (Beike Nano, HQNANO-CNTs-009-6A, nickel content greater than 60% by mass, outer diameter 8-15 nm, length 50 μm), and the other conditions are the same.

[0073] Example 8

[0074] Compared with Example 2, the only difference is that the metallic lithium powder is replaced by lithium-silver alloy powder (the mass fraction of silver is 1 wt%), and the other conditions are the same.

[0075] Example 9

[0076] Compared with Example 2, the only difference is that the metallic lithium powder is replaced with lithium-boron-silver alloy powder (the mass fraction of boron is 1 wt %, and the mass fraction of silver is 4%), and the other conditions are the same.

[0077] Example 10

[0078] Compared with Example 8, the only difference is that the single-walled carbon nanotubes are replaced by single-walled carbon nanotubes and nickel-plated multi-walled carbon nanotubes (Beike Nano, HQNANO-CNTs-009-6A, nickel content greater than 60% by mass, outer diameter 8-15 nm, length 50 μm) with a mass ratio of 2:1, and the other conditions are the same.

[0079] Comparative Example 1

[0080] Compared with Example 2, the only difference is that the modified layer contains only single-walled carbon nanotubes and does not contain fluorinated carbon black.

[0081] Comparative Example 2

[0082] Compared with Example 2, the only difference is that the modification layer contains only fluorinated carbon black and does not contain single-walled carbon nanotubes.

[0083] Comparative Example 3

[0084] Compared with Example 2, the only difference is that the modified layer includes an organic conductive layer and single-walled carbon nanotubes (lithium carbon material mentioned in CN116504973A in the background art), and does not contain fluorinated carbon black.

[0085] Comparative Example 4

[0086] Compared with Example 2, the only difference is that the modified layer includes single-walled carbon nanotubes and conductive carbon black (product model: MA-EN-CO-01, CLUDE experimental consumables), and does not contain fluorinated carbon black.

[0087] Comparative Example 5

[0088] Compared with Example 2, the only difference is that the metal lithium composite material does not include a modification layer, but only contains metal lithium powder.

[0089] Testing of the performance of metal lithium composite materials:

[0090] The lithium metal composite materials in Examples 1-10 and Comparative Examples 1-5 were pressed onto copper foam to make electrodes, and then assembled into symmetrical cells. The electrolyte was 1M LiTFSIDOL / DME (volume ratio 1:1), and the cycling performance was tested. 2 and 1mAh / cm 2 Under the conditions of , the test results are shown in Table 1. The test cutoff condition is that the overpotential exceeds 1V or a short circuit occurs.

[0091] Table 1

[0092] Sources Number of cycles Example 1 545 Example 2 560 Example 3 683 Example 4 581 Example 5 572 Example 6 589 Example 7 578 Example 8 803 Example 9 851 Example 10 883 Comparative Example 1 337 Comparative Example 2 300 Comparative Example 3 361 Comparative Example 4 372 Comparative Example 5 205

[0093] From Table 1 we can see that:

[0094] (1) The cycle performance of the lithium metal composite material in Example 1 is poorer than that in Example 6 and Example 7 (test curves are shown in FIG. Figure 3 This is because the multi-walled carbon nanotubes in Examples 6 and 7 contain a lithium-repelling element modification layer, which not only provides space for the volume expansion of metallic lithium, but also has good electronic conductivity of lithium-repelling elements, making the surface current density of the material more uniform, and the modification effect on metallic lithium powder is better than that of the multi-walled carbon nanotubes without a lithium-repelling element modification layer in Example 1;

[0095] (2) The cycle performance of the lithium metal composite material of Examples 3-5 is better than that of Example 2 (test curves are shown in FIG. Figure 4 This is because the quality of the single-walled carbon nanotubes and the fluorinated carbon black in the modified layer of the metal lithium composite material in Examples 3-5 is suitable, and the two cooperate with each other to better solve the problems of metal lithium volume expansion, uneven deposition, and the generation and growth of lithium dendrites than in Example 2;

[0096] (3) The cycle performance of the metal lithium composite material of Example 8 and Example 9 is better than that of Example 2 (test curves as shown in FIG. Figure 5 This is because the core in Examples 8 and 9 is lithium alloy powder. When the metallic lithium is stripped, the alloy elements do not participate in the lithium extraction and remain in place, playing a role in stabilizing the core. When the metallic lithium is deposited, the alloy elements have an affinity for lithium and regulate the uniform deposition of the metallic lithium.

[0097] (4) The cycle performance of the metal lithium composite material of Example 10 is better than that of Example 2 and Example 8 (test curve as shown in FIG. Figure 5This is because the core in Example 10 is lithium alloy powder, which induces the inward deposition of metallic lithium. The multi-walled carbon nanotubes modified with a lithium-repellent element are not affinity-repellent to metallic lithium, forming a lithium-repellent gradient, regulating the inward transport of lithium ions and the uniformity of the current density on the surface. The single-walled carbon nanotubes, nickel-plated multi-walled carbon nanotubes, and fluorinated carbon black cooperate with each other to jointly regulate the uniform deposition of metallic lithium and the stability of the interface.

[0098] (5) The cycle performance of the lithium metal composite material of Example 2 is better than that of the comparative examples 1-5 (test curves as shown in FIG. Figure 6 and Figure 7 As shown), this is because the modified layer of the metal lithium composite material in Comparative Example 1 contains only single-walled carbon nanotubes and does not contain fluorinated carbon black. There are only single-walled carbon nanotubes between the metal lithium powder particles, lithium fluoride will not be generated, and the interface is unstable; in Comparative Example 2, the modified layer of the metal lithium composite material contains only fluorinated carbon black and does not contain single-walled carbon nanotubes. The modified layer has limited relief of the volume expansion of metal lithium, and the lithium fluoride generated by fluorinated carbon black and active lithium has poor electronic conductivity, and there is no single-walled carbon nanotube to regulate the electronic conductivity; Comparative Example 3 is a lithium-carbon material in the prior art. Although it has an organic conductive layer, it only transmits lithium ions and electrons and does not work on the interface stability between the metal lithium powder particles; in Comparative Example 4, the modified layer of the metal lithium composite material includes single-walled carbon nanotubes and conductive carbon black, does not contain fluorinated carbon black, cannot generate lithium fluoride on the surface of the metal lithium powder, in situ constructs the SEI film, and the interface stability between the metal lithium powders is poor; in Comparative Example 5, there is only metal lithium powder and no modified layer, which characterizes the performance of the metal lithium powder itself.

[0099] In summary, the metal lithium composite material provided by the present invention is provided with a modification layer on the surface of the lithium-containing core, and the modification layer includes carbon nanotubes and a fluorinated carbon material. The fluorinated carbon material reacts with the lithium-containing core to generate lithium fluoride, thereby realizing in situ construction of an SEI film, so that the interface between the lithium-containing core particles is relatively stable; the carbon nanotubes are interwoven into a cage-like structure, which effectively alleviates the volume expansion of the lithium-containing core; in addition, the carbon nanotubes and the fluorinated carbon material cooperate with each other to simultaneously regulate lithium ion transmission and electron transmission, effectively solving the problems of volume expansion of the lithium-containing core, uneven deposition of metallic lithium, and generation and growth of lithium dendrites.

Claims

1. A lithium metal composite material, characterized in that: The metal lithium composite material includes a lithium-containing core, and a modified layer is provided on the surface of the lithium-containing core; the modified layer includes carbon nanotubes and a fluorinated carbon material, the carbon nanotubes are intertwined to form a cage structure, and the fluorinated carbon material is present at at least one position on the surface of the lithium-containing core, on the surface of the cage structure, or in the pores of the cage structure; the mass ratio of the carbon nanotubes to the fluorinated carbon material is 1:(0.1-100).

2. The lithium metal composite material according to claim 1, wherein: The fluorinated carbon material comprises at least one of fluorinated graphite, fluorinated activated carbon, fluorinated carbon black, fluorinated carbon nanofibers, fluorinated graphene, fluorinated graphene oxide or fluorinated carbon nanotubes; Preferably, the atomic ratio of carbon to fluorine in the fluorinated carbon material is greater than 0 and less than 1.25, preferably 0.5-1; Preferably, the mass ratio of the carbon nanotubes to the fluorinated carbon material is 1:(0.5-50), preferably 1:(1-20).

3. The lithium metal composite material according to claim 1 or 2, characterized in that: The lithium-containing core comprises metallic lithium powder and / or lithium alloy powder, with an average particle size of 1-100 μm, preferably 10-50 μm; Preferably, the alloying elements in the lithium alloy powder include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc.

4. The lithium metal composite material according to any one of claims 1 to 3, characterized in that: The length of the carbon nanotubes is 0.5 μm to 50 μm, preferably 1-20 μm.

5. The lithium metal composite material according to any one of claims 1 to 4, characterized in that: The number of layers of the carbon nanotubes is less than or equal to 15 layers, preferably 1-10 layers; Preferably, the outer diameter of the carbon nanotubes is less than 30 nm, preferably 1-20 nm.

6. The lithium metal composite material according to any one of claims 1 to 5, characterized in that: The carbon nanotubes contain lithium-phobic elements, and the lithium-phobic elements include at least one of copper, nickel, titanium, chromium, vanadium, cobalt, manganese or iron; Preferably, based on the mass of the carbon nanotubes being 100%, the mass content of the lithium-phobic element is greater than 30%, preferably 50-80%.

7. The lithium metal composite material according to any one of claims 1 to 6, characterized in that: The thickness of the modified layer is between 0.5 μm and 20 μm, preferably 1-10 μm; Preferably, based on the mass of the metal lithium composite material being 100%, the mass fraction of the lithium core in the metal lithium composite material is 50% or more, preferably 70% or more, and more preferably 85% or more.

8. A method for preparing the metal lithium composite material according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) mixing an organic solvent, carbon nanotubes, and a fluorinated carbon material to obtain a mixture; (2) mixing the mixture with a lithium-containing powder material and spray drying the mixture to obtain the metal lithium composite material; Alternatively, the mixture and the lithium-containing powder material are entangled at a high speed at a rotation speed of 5000 rpm or more to remove the organic solvent to obtain the metal lithium composite material; the organic solvent is inert to the lithium-containing powder material.

9. The preparation method according to claim 8, characterized in that Step (1) includes the following operations: Pre-dispersing carbon nanotubes in an organic solvent, and then adding a fluorinated carbon material and mixing to obtain a mixture; Preferably, the mixing in step (2) comprises at least one of mechanical stirring, ultrasonic dispersion or high-speed winding at a rotation speed of 5000 rpm or above.

10. An electrode, characterized in that: The electrode comprises the metal lithium composite material according to any one of claims 1 to 7.

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