Metal lithium composite electrode and preparation method and application thereof

Abstract

The invention relates to a metal lithium composite electrode and a preparation method and application thereof, the electrode comprises a current collector, at least one side of the current collector is provided with a lithium carbon material layer, and the lithium carbon material layer contains a metal lithium composite material; the metal lithium composite material comprises lithium-containing particles, carbon nanotubes are attached to the surfaces of the lithium-containing particles, the carbon nanotubes are interwoven to form a three-dimensional porous skeleton, and at least one of the surfaces of the lithium-containing particles, the surface of the three-dimensional porous skeleton or pores contains a carbon fluoride material. Lithium fluoride is generated in situ between the carbon fluoride material existing on the surfaces of the lithium-containing particles and the lithium-containing particles, and the lithium fluoride has an effect of stabilizing an interface between the composite electrode and an electrolyte, so that uniform deposition of lithium is facilitated, and growth of lithium dendrites is inhibited; the carbon nanotubes construct a three-dimensional network channel porous framework, lithium ions and electrons can be regulated and controlled at the same time, uniform deposition of lithium is facilitated, space is provided for volume expansion of lithium-containing particles, and the electrode has excellent cycle performance.

Description

Technical Field

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

[0002] In recent years, with the development of new energy vehicles, commercial graphite anodes can no longer meet actual needs. Metal lithium has a high specific capacity (3860mAh / g) and a low density (0.534g / cm 3 ) and good ductility, it has returned to the attention of researchers. However, metallic lithium has problems such as volume expansion, lithium dendrites, and dead lithium during the cycling process. In particular, the continuous growth of lithium dendrites may further cause safety issues (such as fire and explosion). These factors have greatly limited the commercial application of metallic lithium anodes.

[0003] At present, there are two main aspects of the application research on lithium metal negative electrodes: on the one hand, surface modification is performed on the surface of lithium metal to improve the interfacial stability between the lithium metal negative electrode and the electrolyte and solve the problem of lithium dendrites. CN108448058B discloses a lithium metal negative electrode with a surface rich in lithium fluoride. The preparation method of the negative electrode comprises: in a dry protective gas atmosphere, immersing the lithium metal negative electrode in a fluorine-containing ionic liquid, or applying the fluorine-containing ionic liquid to the surface of the lithium metal negative electrode, after fluorination, removing it, and forming a protective layer rich in lithium fluoride on the surface of the lithium metal negative electrode to obtain a lithium fluoride-coated lithium metal negative electrode. However, the negative electrode is modified on a two-dimensional plane, and the generated lithium fluoride has poor electronic conductivity.

[0004] On the other hand, lithium powder is used as a raw material and its surface is coated with a carbon material to solve the problems of lithium dendrites and volume expansion. CN116504973A discloses a lithium-carbon material, a preparation method thereof, and a lithium-ion battery. The lithium-carbon material has a cocoon structure, comprising a cocoon body formed of a structural carbon material and one or more metallic lithium particles contained within the cocoon body. Each metallic lithium particle consists of a metallic lithium core and an organic conductive layer coated on the core surface. However, this lithium-carbon material is only coated with carbon material on the surface of the metallic lithium powder. During the cycle, the SEI film ruptures, and the electrolyte reacts with the metallic lithium to regenerate the SEI film, consuming active lithium. This fails to stabilize the contact interface between the lithium-carbon material and the electrolyte, resulting in poor cycling performance.

[0005] Based on this, how to design a metal lithium composite electrode that is rich in lithium fluoride in three dimensions and solves the poor electronic conductivity of lithium fluoride, and overcomes the above-mentioned shortcomings such as uneven deposition of metal lithium during charging and discharging, easy formation of dendrites, volume expansion, and poor stability of the contact interface with the electrolyte, has become an urgent problem to be solved at this stage. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present application provides a metal lithium composite electrode and a preparation method thereof, wherein the electrode includes a lithium-carbon material layer, and the surface of the lithium-containing particles in the lithium-carbon material layer is provided with carbon nanotubes and carbon fluoride materials. The carbon nanotubes have dual transmission channels for ions and electrons, which can simultaneously regulate the current density and the transmission of lithium ions, thereby overcoming the problem of uneven deposition of metal lithium, which is prone to form dendrites and volume expansion during charging and discharging; at the same time, it provides position support for the carbon fluoride material and solves the problem of poor electronic conductivity of lithium fluoride; the carbon fluoride material reacts with active lithium to generate lithium fluoride and carbon, and the lithium fluoride is the main component of the SEI film, which contributes to interface stability and uniform deposition of lithium. The carbon improves the problem of poor conductivity of lithium fluoride, and at the same time cooperates with the carbon nanotubes to construct a conductive network, thereby improving the cycle stability of the electrode.

[0007] To achieve this goal, this application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a metal lithium composite electrode, comprising a current collector and a lithium-carbon material layer disposed on at least one side of the current collector; wherein the lithium-carbon material layer contains a metal lithium composite material, the metal lithium composite material comprises lithium-containing particles, carbon nanotubes attached to the surface of the lithium-containing particles, a three-dimensional porous skeleton formed by interweaving the carbon nanotubes, a fluorinated carbon material distributed on the surface of the lithium-containing particles, on the surface of the three-dimensional porous skeleton or at least one position in the pores, and lithium fluoride is generated in situ between the fluorinated carbon material present on the surface of the lithium-containing particles and the lithium-containing particles.

[0009] In the present application, the lithium-carbon material layer contains a metallic lithium composite material, which includes lithium-containing particles and carbon nanotubes distributed on the surface of the lithium-containing particles, wherein the lithium-containing particles are in a stacked distribution state in the lithium-carbon material layer, and the carbon nanotubes are interwoven to form a three-dimensional porous skeleton, and the fluorinated carbon material is distributed on the surface of the lithium-containing particles, the surface of the three-dimensional porous skeleton or at least one of the pores, thereby realizing the modification of the metallic lithium negative electrode in a three-dimensional direction. The three-dimensional porous skeleton in which the carbon nanotubes are interwoven can alleviate the volume expansion problem of the lithium-containing particles during the charge and discharge process in a three-dimensional direction. The carbon nanotubes serve as transmission channels for electrons and lithium ions, regulating the current density and lithium ion transmission uniformity in a three-dimensional direction, and inhibiting the generation and growth of lithium dendrites. At the same time, the three-dimensional porous skeleton formed by the carbon nanotubes can not only provide support sites for the fluorinated carbon material, allowing it to be stably and evenly distributed, but also improve the problem of poor electronic conductivity of the fluorinated carbon material and lithium fluoride.

[0010] In the present application, lithium fluoride and carbon are generated in situ between the carbon fluoride material located on the surface of the lithium-containing particles and the lithium-containing particles. Lithium fluoride is the main component of the SEI film, which makes the interface between the lithium-containing particles and the electrolyte more stable and the deposition of metallic lithium more uniform; carbon can improve the problem of poor electronic conductivity of lithium fluoride and improve the conductivity of the interface; the carbon fluoride material located on the surface or pores of the three-dimensional porous skeleton reacts with active lithium to generate lithium fluoride and carbon during the charge and discharge cycle, which can increase the content of lithium fluoride in the SEI, continuously stabilize the interface, contribute to the uniform deposition of lithium, and inhibit the growth of lithium dendrites; carbon provides a transmission channel for electrons and / or lithium ions, regulates the uniform distribution of current density and the uniform deposition of metallic lithium, and inhibits the generation of lithium dendrites.

[0011] In the present application, carbon nanotubes and fluorinated carbon materials cooperate with each other to stabilize the electrode interface without reducing the conductivity of the electrode. The metal lithium composite electrode has good interface stability and excellent cycle performance. Compared with the metal lithium negative electrode, the electrode of the present application converts the two-dimensional planar active lithium deposition / stripping mechanism into a three-dimensional mechanism. The internal interface of the electrode is stable in the three-dimensional direction, and the contact interface between the electrode and the electrolyte is also stable, which can achieve high-rate charge and discharge and has excellent rate performance.

[0012] Optionally, the lithium-containing particles include metallic lithium and / or lithium alloys, the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc, and the content of metallic lithium in the lithium alloy is more than 50%, preferably more than 80%, and more preferably more than 90%.

[0013] Optionally, the fluorinated carbon material includes at least one of fluorinated graphite, fluorinated activated carbon, fluorinated carbon black, fluorinated carbon nanofibers, fluorinated graphene, 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 mass ratio of the carbon fluoride material to the lithium-containing particles is 1:(0.1-500), preferably 1:(1-300), and more preferably 1:(10-100). The specific mass ratio of the carbon fluoride material and the lithium-containing particles enables the composite electrode to have good cycle 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, 1:7.5, 1:10, 1:20,

[0016] 1:30, 1:50, 1:80, 1:90, 1:100, 1:150, 1:200, 1:250, 1:270, 1:300, 1:400, 1:450 or 1:500, including but not limited to the listed values. If the mass ratio is too large, the lithium-containing particles are small, the gram capacity of the metal lithium composite negative electrode is low, the conductivity of the electrode is poor, and the cycle performance is poor; if the mass ratio is too small, the carbon fluoride material is small, the generated lithium fluoride is limited, and the effect on stabilizing the interface between the composite electrode and the electrolyte is limited.

[0017] Optionally, the size of the carbon fluoride material is 1 nm-50 μm, preferably a nanoscale carbon fluoride material with a size of 3 nm-500 nm, more preferably 5-300 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.

[0018] Optionally, the average particle size of the lithium-containing particles is 1-100 μm, preferably 10-50 μm.

[0019] Optionally, the thickness of the carbon fluoride material distribution area on the surface of the lithium-containing particles is 0.1-10 μm, preferably 0.5-5 μm. In the present invention, the thickness includes the lithium fluoride generated in situ by the contact reaction between the surface of the lithium-containing particles and the carbon fluoride material. Because the lithium-containing particles react with the contacted carbon fluoride material to generate lithium fluoride and carbon, the reaction is in situ. The generated lithium fluoride is difficult to distinguish from the carbon fluoride material on the surface of the lithium-containing particles that is not in contact, and therefore is included in the overall thickness.

[0020] Alternatively, the carbon nanotubes include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes. In the present invention, the modified substances in the modified single-walled carbon nanotubes and modified multi-walled carbon nanotubes are not limited, and can be simple substances containing lithium-philic elements such as tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc, oxides, nitrides, sulfides, carbides or phosphides, or simple substances containing lithium-phobic elements such as copper, nickel, titanium, chromium, vanadium, cobalt, manganese or iron, oxides, nitrides, sulfides, carbides or phosphides. As long as it can play a role in regulating and controlling the uniform distribution of current density and guiding the uniform deposition of metallic lithium, it belongs to the scope of protection of the present invention.

[0021] Optionally, the number of layers of the carbon nanotubes is less than or equal to 15 layers, preferably 1-10 layers.

[0022] Optionally, the outer diameter of the carbon nanotube is less than 30 nm, preferably 1-20 nm.

[0023] Optionally, the length of the carbon nanotubes is 0.5 μm to 50 μm, preferably 1-30 μm.

[0024] Optionally, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the carbon nanotubes is 0.05-50%, preferably 0.25%-30%, and more preferably 0.5-20%.

[0025] Optionally, the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, and the mass ratio of the single-walled carbon nanotubes, multi-walled carbon nanotubes and fluorinated carbon material is 1: (0.05-100): (0.05-100), preferably 1: (0.1-50): (0.1-50), and further preferably 1: (0.5-20):

[0026] (0.5-20).

[0027] Optionally, the current collector includes a base current collector and a modified current collector, wherein the base current collector includes any one of copper foil, composite copper foil, aluminum foil, nickel foil, stainless steel foil, conductive polymer film, or carbon fiber, or a combination of at least two thereof. The polymer matrix material of the conductive polymer composite film includes, but is not limited to, at least one of polyethylene, polypropylene, polystyrene, polyurethane, epoxy resin, and phenolic resin. The conductive filler of the conductive polymer composite film includes, but is not limited to, at least one of conductive carbon black, conductive graphite, nano-carbon fiber, carbon nanotubes, graphene, metal, and metal oxide.

[0028] Optionally, the modified current collector includes a base current collector and a coating disposed on the surface of the base current collector, wherein the coating comprises any one of elemental aluminum, aluminum oxide, graphene, graphene oxide, Ketjen black, activated carbon, or biochar, or a combination of at least two. Different coating types interact differently with the lithium-carbon material layer, and preferably, a coating that forms an integral structure with the lithium-carbon material coating is selected based on actual needs, generally ranging from 3 to 10 μm.

[0029] In a second aspect, the present application provides a method for preparing the composite electrode as described in the first aspect above, the method comprising the following steps:

[0030] (1) mixing lithium-containing particles, a fluorinated carbon material, carbon nanotubes, and an organic solvent, and then spray-drying or high-speed dispersing at a rotation speed of 5000 rpm to remove the organic solvent to obtain a lithium-carbon material, wherein the organic solvent is inert to the lithium-containing particles;

[0031] (2) The lithium-carbon material in step (1) is subjected to a molding process to obtain a lithium-carbon material layer, and the layer is composited on at least one side of a current collector to obtain the composite negative electrode.

[0032] The organic solvent includes, but is not limited to, any one of liquid alkanes with 5 to 20 carbon atoms, benzene, p-xylene, solvent oil D40, solvent oil D60, solvent oil D80, liquid paraffin, or petroleum ether, or a combination of at least two thereof. As long as they are inert to metallic lithium, do not undergo violent chemical reactions, and can be used as a solvent, they all fall within the scope of protection of the present invention.

[0033] The lithium-containing particles include metallic lithium powder and / or lithium alloy powder.

[0034] Optionally, the forming method in step (2) includes at least one of mechanical rolling, twisting, screen printing or coating.

[0035] Optionally, the mechanical rolling includes the following operations: placing the lithium-carbon material between two release films, and performing mechanical rolling to obtain a lithium-carbon material layer.

[0036] Optionally, the twisting includes the following operations: placing the lithium-carbon material in a mold, and forming the material by twisting to obtain a lithium-carbon material layer.

[0037] In a third aspect, the present application provides a lithium metal battery, comprising the composite electrode described in the first aspect as a negative electrode, a positive electrode, and an electrolyte. The lithium metal battery may be a primary battery or a secondary battery. The active material in the positive electrode of the secondary battery may be at least one of elemental sulfur, polyacrylonitrile sulfide, oxygen, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, or lithium manganese iron phosphate.

[0038] Compared with the prior art, this application has at least one of the following beneficial effects:

[0039] (1) The composite electrode provided by the present application comprises a lithium-carbon material layer comprising a metal lithium composite material formed of lithium-containing particles, carbon nanotubes and a fluorinated carbon material, wherein the metal lithium composite material is in a stacked distribution state in the lithium-carbon material layer, the carbon nanotubes are distributed on the surface of the lithium-containing particles and intertwined to form a three-dimensional porous skeleton, and the fluorinated carbon material is distributed on at least one of the surface of the lithium-containing particles, the surface of the three-dimensional porous skeleton or the pores, thereby achieving modification of the metal lithium negative electrode in a three-dimensional direction;

[0040] (2) In the composite electrode provided by the present application, carbon nanotubes form a three-dimensional porous skeleton, which alleviates the problem of volume expansion of lithium-containing particles; the carbon nanotubes also have dual ion and electron channels, which effectively regulate the electrode current density and the transmission of lithium ions, and inhibit the growth of lithium dendrites; the carbon nanotubes also provide positional support for the fluorinated carbon material, improving the electronic conductivity of the fluorinated carbon material, and the cycle stability of the electrode is good;

[0041] (3) The composite electrode provided by the present application has lithium fluoride and carbon fluoride material distributed in three dimensions. Lithium fluoride is an important component of the SEI film. During the charge and discharge process, the carbon fluoride material acts as a fluorine source and reacts with active lithium to continuously generate lithium fluoride, which can stabilize the interface between the composite negative electrode and the electrolyte, regulate the deposition of lithium, and inhibit the generation and growth of dendrites.

[0042] (4) The present application uses carbon nanotubes and carbon fluoride materials to cooperate with each other, so that the composite electrode has both interface stability and conductivity. The mass ratio of specific lithium-containing particles and carbon fluoride materials, the types of carbon fluoride materials and carbon nanotubes, and other parameters are designed to further optimize the interface stability and electrochemical performance of the electrode;

[0043] (5) The preparation method provided in this application has a short process flow, high production efficiency, and universal applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is an SEM image of the metal lithium composite material in the lithium-carbon material layer in Example 2;

[0045] Figure 2 The cyclic test curves of Example 2 and Example 5 are shown;

[0046] Figure 3 1 is the cycle test curve of Example 2, Example 7 and Example 9;

[0047] Figure 4 These are the cycle test curves of Example 2, Comparative Example 2, Comparative Example 3 and Comparative Example 5. DETAILED DESCRIPTION

[0048] To facilitate understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only provided to help understand the present application and should not be considered as specific limitations of the present application.

[0049] Example 1

[0050] This embodiment provides a composite electrode, wherein the composite negative electrode includes a 10μm copper foil, and lithium-carbon material layers are provided on both sides of the copper foil. The raw materials of the lithium-carbon material layers include metallic lithium powder, and a three-dimensional porous skeleton formed by interweaving multi-walled carbon nanotubes is provided on the surface of the metallic lithium powder. Fluorinated carbon black is distributed on the surface of the metallic lithium powder, on the surface of the three-dimensional porous skeleton, or at least one position in the pores. Lithium fluoride and carbon are generated in situ between the fluorinated carbon black present on the surface of the metallic lithium and the metallic lithium powder.

[0051] The preparation method of the electrode comprises the following steps:

[0052] (1) Multi-walled carbon nanotubes (Xianfeng Nano, XFM67, length 10-20 μm, outer diameter 4-6 nm), fluorinated carbon black (Shanghai Furui Fine Chemical Co., Ltd., fluorine-carbon ratio 1.0, particle size 50-100 nm), metallic lithium powder with an average particle size of 10 μm, and petroleum ether were mixed at a rotation speed of 9000 rpm for 20 min, with the mass ratio of metallic lithium powder to fluorinated carbon black being 1:0.1, and the mass fraction of multi-walled carbon nanotubes in the lithium-carbon material being controlled to be 0.25%, filtered, and dried to obtain a lithium-carbon material;

[0053] (2) In a clean room with a dew point of -45°C, a lithium-carbon material is spread between two layers of release films and mechanically rolled into a foil. Then, one layer of the release film is peeled off to obtain a composite foil. The composite foil is mechanically rolled and laminated on both sides of a copper foil. The thickness of the lithium-carbon material layer is controlled to be 20 μm to obtain the composite electrode.

[0054] Example 2

[0055] This embodiment provides a composite electrode, which includes a 6μm copper foil, with lithium-carbon material layers provided on both sides of the copper foil. The raw materials of the lithium-carbon material layers include metallic lithium powder, and a three-dimensional porous skeleton formed by interweaving single-walled carbon nanotubes is provided on the surface of the metallic lithium powder. Graphite fluoride is distributed on the surface of the metallic lithium powder, on the surface of the three-dimensional porous skeleton, or at least one position in the pores. Lithium fluoride and carbon are generated in situ between the graphite fluoride present on the surface of the metallic lithium and the metallic lithium powder.

[0056] The preparation method of the electrode comprises the following steps:

[0057] (1) A single-walled carbon nanotube dispersion (Okoshiel, diameter 1 nm, length 5 μm, 3 wt%), fluorinated graphite (Aladdin, F302204, F content ≥ 56 wt.%, D90 ≤ 8 μm), metal lithium powder with an average particle size of 50 μm, and solvent oil D40 were mixed, the mass fraction of the single-walled carbon nanotubes in the lithium-carbon material was controlled to be 30%, the mass ratio of the metal lithium powder to the fluorinated graphite was 1:10, and the mixture was spray-dried to obtain a metal lithium composite material;

[0058] (2) In a clean room with a dew point of -45°C, the lithium carbon material is twisted into shape by a mold, and the thickness of the lithium carbon material layer is 50 μm. It is then mechanically rolled and laminated on both sides of the copper foil to obtain the composite electrode.

[0059] The metal lithium composite material in step (1) was sampled and characterized by SEM. The structure was characterized as follows: Figure 1 As shown in the figure, it can be clearly seen that the fluorinated graphite is located on the surface (as shown by the black circle in the figure) and pores (as shown by the white circle in the figure) of the three-dimensional porous skeleton.

[0060] Example 3

[0061] Compared with Example 2, the only difference is that the mass ratio of metallic lithium powder to graphite fluoride is replaced with 1:1, and the other conditions are the same.

[0062] Example 4

[0063] Compared with Example 2, the only difference is that the mass ratio of metallic lithium powder to graphite fluoride is replaced with 10:1, and the other conditions are the same.

[0064] Example 5

[0065] Compared with Example 2, the only difference is that the mass ratio of metallic lithium powder to graphite fluoride is replaced with 50:1, and the other conditions are the same.

[0066] Example 6

[0067] Compared with Example 2, the only difference is that the mass ratio of metallic lithium powder to graphite fluoride is replaced with 100:1, and the other conditions are the same.

[0068] Example 7

[0069] Compared with Example 2, the only difference is that the metallic lithium powder is replaced by lithium-indium alloy particles (the mass fraction of indium is 15%).

[0070] Example 8

[0071] Compared with Example 2, the only difference is that the metallic lithium powder is replaced by lithium-tin-silver alloy particles (the mass fraction of tin is 7%, and the mass fraction of silver is 3%).

[0072] Example 9

[0073] Compared with Example 2, the only difference is that the single-walled carbon nanotube dispersion is replaced by a combination of single-walled carbon nanotube dispersion (Okoshiel, 1 nm in diameter, 5 μm in length, 3 wt%) and multi-walled carbon nanotubes (Xianfeng Nano, XFM67, 10-20 μm in length, 4-6 nm in outer diameter), and the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is controlled to be 1:1.

[0074] Comparative Example 1

[0075] Compared with Example 2, the only difference is that the lithium-carbon material layer is replaced by a metal lithium strip, and the other conditions are the same as those in Example 2.

[0076] Comparative Example 2

[0077] Compared with Example 2, the only difference is that the lithium-carbon material in the lithium-carbon material layer is replaced by a physical mixture of metallic lithium powder, single-walled carbon nanotubes and graphite fluoride (not the structure of this application, and the rotation speed in the preparation process is 2000 rpm), and the other conditions are the same as Example 2.

[0078] Comparative Example 3

[0079] Compared with Example 2, the only difference is that the lithium-carbon material layer contains only single-walled carbon nanotubes and does not contain fluorinated graphite.

[0080] Comparative Example 4

[0081] Compared with Example 2, the only difference is that the fluorinated graphite in the lithium-carbon material layer is replaced with ordinary graphite (purchased from CLUDE experimental consumables).

[0082] Comparative Example 5

[0083] Compared with Example 2, the only difference is that the lithium-carbon material layer contains only graphite fluoride but no single-walled carbon nanotubes.

[0084] Test data:

[0085] The electrodes in Examples 1-9 and Comparative Examples 1-5 were assembled into soft-pack batteries with NCM811 positive electrodes for testing. The electrolyte was an ether electrolyte. The cycle performance was tested at 25°C and 0.1C / 0.5C charge and discharge conditions. The cycle data are shown in Table 1.

[0086] Table 1 Test data of electrodes

[0087]

[0088]

[0089] From Table 1 we can see that:

[0090] (1) Combining Example 2 and Examples 3-6, it can be seen that the cycle performance of the soft-pack battery of Examples 3-6 is better than that of Example 2. This is because the mass ratio of the metal lithium powder to the fluorinated graphite in Example 2 is not within the preferred range, the fluorinated graphite content is high, the conductivity is poor, and the performance of the composite negative electrode cannot be brought into play; combined with Figure 2 It can be seen that the soft-pack batteries of Examples 2 and 5 both experienced capacity recovery during the charge and discharge process. This may be because the single-walled carbon nanotubes and the fluorinated carbon material located on the surface and in the pores of the three-dimensional porous skeleton formed by the single-walled carbon nanotubes have the effect of stabilizing the interface. Furthermore, the ratio of metallic lithium powder and graphite fluoride in Example 5 is better than that in Example 2, and its composite negative electrode and electrolyte interface is more stable, and the cycle performance is better than that of Example 2.

[0091] (2) Based on Example 2 and Examples 7-8, it can be seen that the cycle performance of the soft-pack battery of Examples 7-8 is better than that of Example 2. This is because lithium alloy is used as the active material in Examples 7 and 8. During the charge and discharge process, the alloy element can induce the uniform deposition of metallic lithium, and cooperate with the single-walled carbon nanotubes and fluorinated graphite to significantly improve the cycle performance of the composite negative electrode; the test curves of Example 2 and Example 7 are as follows: Figure 3 As shown, the cycle stability of the soft pack battery of Example 7 is better than that of Example 2;

[0092] (3) Combining Example 2 and Example 9, it can be seen that the cycle performance of Example 9 is better than that of Example 2. This is because Example 9 uses a three-dimensional porous skeleton formed by single-walled carbon nanotubes and double-walled carbon nanotubes. By utilizing the difference in flexibility and rigidity between the two, the stability of the constructed three-dimensional porous skeleton is better than that of the three-dimensional porous skeleton constructed by single-walled carbon nanotubes alone in Example 2. The test curves of Example 2 and Example 9 are as follows: Figure 3 As shown, the cycle stability of the soft pack battery of Example 9 is better than that of Example 2;

[0093] (4) Combining Example 2 with Comparative Examples 1 and 2, it can be seen that the cycle performance of Example 2 is better than that of Comparative Examples 1-2. This is because the selection of raw materials for the lithium-carbon material layer in Example 2 is better than that in Comparative Examples 1-2. Specifically, Comparative Example 1 is only a metallic lithium strip, and the volume expansion and interface problems during the charge and discharge process are more prominent; although carbon nanotubes and fluorinated graphite are used in Comparative Example 2, the structure of the raw materials in the present application is not formed, which can stabilize the interface and alleviate the volume expansion to a certain extent, but the effect is worse than that of the present application. The test curves of Example 2 and Comparative Example 2 are as follows: Figure 4 As shown, when the cycle reaches about 120 cycles, the capacity decay rate of the soft-pack battery in Comparative Example 2 is faster than that in Example 2;

[0094] (5) Combining Example 2 and Comparative Examples 3 to 5, it can be seen that the cycle performance of Example 2 is better than that of Comparative Examples 3 to 5. This is because Comparative Example 3 contains only single-walled carbon nanotubes and does not contain fluorinated graphite. It only regulates the volume change of the lithium-carbon material layer during the cycle, which cannot improve the interface stability between the negative electrode and the electrolyte and cannot achieve a stable interface in the three-dimensional direction. Figure 4 It can be seen that the capacity of the soft-pack battery in Comparative Example 3 is lower than that in Example 2 at the beginning of the 100th cycle, and then the capacity decays without recovery. Ordinary graphite is used in Comparative Example 4, which cannot play the role of fluorinated graphite in stabilizing the interface in the three-dimensional direction. In Comparative Example 5, only fluorinated graphite is used, and it does not contain single-walled carbon nanotubes. Although it can stabilize the interface, it has no single-walled carbon nanotubes for support, and displacement will occur during the charge and discharge process. It has a weak effect on regulating the volume change of the lithium-carbon material layer, and the capacity decays rapidly. The test curve shows Figure 4 .

[0095] In summary, the electrode designed in this application adopts a metal lithium composite material with a three-dimensional structure, which has both interface stability and cycle stability in the three-dimensional direction and is a composite electrode with excellent performance.

[0096] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed structural features of the present application, the present application is not limited to the above-mentioned detailed structural features, which does not mean that the present application must rely on the above-mentioned detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for selected components, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A metallic lithium composite electrode, characterized in that: The electrode includes a current collector and a lithium-carbon material layer disposed on at least one side of the current collector; The lithium-carbon material layer contains a metallic lithium composite material, which includes lithium-containing particles, carbon nanotubes attached to the surface of the lithium-containing particles, and a three-dimensional porous skeleton formed by the carbon nanotubes interwoven with each other. Fluorinated carbon material is distributed on the surface of the lithium-containing particles, on the surface of the three-dimensional porous skeleton, or at least one position in the pores. Lithium fluoride is generated in situ between the fluorinated carbon material on the surface of the lithium-containing particles and the lithium-containing particles.

2. The composite electrode according to claim 1, characterized in that The lithium-containing particles include metallic lithium and / or lithium alloys, the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc, and the content of metallic lithium in the lithium alloy is greater than 50%.

3. The composite electrode according to claim 1 or 2, characterized in that 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 fluoride material to the lithium-containing particles is 1:(0.1-500), preferably 1:(1-300), more preferably 1:(10-100); Preferably, the size of the carbon fluoride material is 1 nm-50 μm, preferably the size of the nano-scale carbon fluoride material is 3 nm-500 nm, more preferably 5-300 nm.

4. The composite electrode according to any one of claims 1 to 3, characterized in that: The thickness of the carbon fluoride material distribution area on the surface of the lithium-containing particles is 0.1-10 μm, preferably 0.5-5 μm.

5. The composite electrode according to any one of claims 1 to 4, characterized in that: The carbon nanotubes include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes; Preferably, 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; Preferably, the length of the carbon nanotubes is 0.5 μm to 50 μm, preferably 1-30 μm.

6. The composite electrode according to any one of claims 1 to 5, characterized in that: Based on the total mass of the lithium-carbon material layer as 100%, the mass fraction of the carbon nanotubes is 0.05-50%, preferably 0.25-30%, and more preferably 0.5-20%; Preferably, the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, and the mass ratio of the single-walled carbon nanotubes, multi-walled carbon nanotubes and fluorinated carbon material is 1:(0.05-100):(0.05-100), preferably 1:(0.1-50):(0.1-50), and further preferably 1:(0.5-20):(0.5-20).

7. The composite electrode according to any one of claims 1 to 6, characterized in that: The current collector includes a basic current collector and a modified current collector, wherein the basic current collector includes any one or a combination of at least two of copper foil, composite copper foil, nickel foil, stainless steel foil, conductive polymer film or carbon fiber; The modified current collector includes a base current collector and a coating disposed on the surface of the base current collector, wherein the coating includes any one of elemental aluminum, aluminum oxide, graphene, graphene oxide, Ketjen black, activated carbon or biochar, or a combination of at least two thereof.

8. A method for preparing the composite electrode according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (1) mixing lithium-containing particles, a fluorinated carbon material, carbon nanotubes, and an organic solvent, and then spray-drying or high-speed dispersing at a rotation speed of 5000 rpm to remove the organic solvent to obtain a lithium-carbon material, wherein the organic solvent is inert to the lithium-containing particles; (2) The lithium-carbon material in step (1) is subjected to a molding process to obtain a lithium-carbon material layer, and the layer is composited on at least one side of a current collector to obtain the composite negative electrode.

9. The method according to claim 8, characterized in that In step (1), the organic solvent comprises any one or a combination of at least two of liquid alkanes having 5 to 20 carbon atoms, benzene, p-xylene, solvent oil D40, solvent oil D60, solvent oil D80, liquid paraffin or petroleum ether; Preferably, the forming method in step (2) includes at least one of mechanical rolling, twisting, screen printing or coating; Preferably, the mechanical rolling comprises the following operations: placing the lithium-carbon material between two release films and performing mechanical rolling to obtain a lithium-carbon material layer; Preferably, the twisting includes the following operations: placing the lithium-carbon material in a mold, and forming the material by twisting to obtain a lithium-carbon material layer.

10. A metal lithium battery, characterized in that: The metal lithium battery comprises the composite electrode according to any one of claims 1 to 7 as a negative electrode, and further comprises a positive electrode and an electrolyte.

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