Self-adaptive metal lithium composite electrode and preparation method thereof

Abstract

The invention relates to a metal lithium composite electrode with self-adaptability and a preparation method thereof, the electrode comprises a positive electrode active material layer, a current collector and a lithium carbon material layer, and the current collector is arranged between the positive electrode active material layer and the lithium carbon material layer; the lithium carbon material layer comprises an elastic lithium monomer, and the elastic lithium monomer comprises lithium powder and / or lithium alloy powder as an active core and a tubular carbon nanomaterial as an elastic shell. In the lithium-carbon material layer, the elastic shells are uniformly distributed between the active cores to construct a three-dimensional network channel, so that lithium ion and electron dual-channel adjustability is realized. The elastic shell can change in applicability according to the change of the active core, so that the problem of volume change caused by lithium deposition / stripping is solved; the surface of the lithium-carbon material layer is provided with micro-nano-scale protrusions, the lithium-carbon material layer can be well combined with the current collector and the solid electrolyte, and the problem of poor interface contact is solved.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and particularly relates to a self-adaptive lithium metal composite electrode and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are the most widely used secondary batteries at present, with advantages such as long cycle life and small volume. However, with the development of new energy vehicles, the energy density of commercial lithium-ion batteries cannot meet the actual needs.

[0003] Lithium metal has returned to the researchers' vision due to its high specific capacity (3860 mAh / g), low density (0.534 g / cm 3 ), and good ductility. Among them, a representative study is the application of lithium metal anodes in solid-state batteries. The reduction potential of lithium metal is -3.04 V vs SHE). Due to this low reduction potential, lithium metal will reduce most materials, such as reacting with sulfide solid electrolytes to form lithium sulfide.

[0004] CN 112703618 A discloses an electrode for a solid-state lithium battery, which has a current collector and an electrode active layer of lithium metal or a lithium metal alloy on the current collector. The lithium metal or lithium metal alloy has a surface layer of a homogeneous nano-alloy particle composition, and the homogeneous nano-alloy particle composition contains nano-particles of element M or nano-particles of a lithium alloy of element M, where M is at least one element selected from Group 2 and Groups 8-16. The surface layer is in direct contact with the solid electrolyte, isolating the lithium metal from the solid electrolyte, and can alleviate the decomposition of the electrolyte. However, the electrode still has problems such as poor contact between the active layer and the current collector and the solid electrolyte, poor ionic conductivity, and uneven current that is prone to form dendrites. In addition, during the lithium metal deposition / stripping process, the volume of the negative electrode changes, further deteriorating the contact between the negative electrode and the solid electrolyte, easily forming larger and more voids, and requiring a large pressure to control the close contact between the negative electrode and the solid electrolyte.

[0005] Based on this, how to design a self-adaptive electrode to overcome the above disadvantages such as poor interfacial contact between the active layer and the current collector and the solid electrolyte, poor ionic conductivity, and uneven current that is prone to form dendrites has become an urgent problem to be solved at the present stage. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present application provides an adaptive lithium metal composite electrode and a preparation method thereof. The electrode includes a positive electrode active material layer, a current collector, and a lithium-carbon material layer. The current collector is disposed between the positive electrode active material layer and the lithium-carbon material layer. The lithium-carbon material layer has dual transport channels for ions and electrons, can simultaneously regulate the current density and the transport of lithium ions, and inhibit the growth of dendrites. At the same time, the surface roughness of the lithium-carbon material layer is higher than that of the lithium metal negative electrode, and it has a tight contact with the current collector and the solid electrolyte, and the electrode structure has high stability.

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

[0008] In a first aspect, the present application provides an adaptive lithium metal composite electrode. The electrode includes a positive electrode active material layer, a current collector, and a lithium-carbon material layer. The current collector is disposed between the positive electrode active material layer and the lithium-carbon material layer. The lithium-carbon material in the lithium-carbon material layer includes elastic lithium monomers. The elastic lithium monomers include metal lithium and / or lithium alloy as an active core, and tubular carbon nanomaterials as an elastic outer shell. The elastic outer shells communicate with each other to construct a three-dimensional network channel, and the elastic outer shells communicate with each other to construct a three-dimensional network channel. And there are protrusions formed by tubular carbon nanomaterials on the surface of the lithium-carbon material layer.

[0009] In the present application, on the surface of the lithium-carbon material layer, the ends or bent portions of the tubular carbon nanomaterials form protrusions, which are exposed on the electrode surface, greatly increasing the roughness of the lithium-carbon material layer, making the combination between the lithium-carbon material layer and the current collector and the solid electrolyte better, and solving the problem of poor contact between the negative electrode and the current collector and the solid electrolyte.

[0010] In the bulk phase of the lithium-carbon material layer, the elastic outer shells formed by the tubular carbon nanomaterials communicate with each other to construct a three-dimensional network channel, which plays a role in modifying the bulk phase and stabilizing the structure of the lithium-carbon material layer. The structure of the electrode is relatively stable. And even if the active core undergoes volume changes during the deposition / stripping process, the elastic outer shell can adaptively change with the metal lithium and / or lithium alloy by virtue of its ability to restore its original shape, and always maintain good contact with the solid electrolyte, solving the problem of deteriorating the contact between the negative electrode and the solid electrolyte during the lithium metal deposition / stripping process.

[0011] The tubular carbon nanomaterials have good electronic conductivity and can effectively regulate the current density. The tubular carbon nanomaterials also have a hollow structure and can effectively regulate the transport of lithium ions. The tubular carbon materials are connected to each other to construct a three-dimensional network channel, realizing the simultaneous regulation of electrons and ions, and inhibiting the growth of lithium dendrites. Compared with the lithium metal negative electrode, the electrode of the present application converts the mechanism of two-dimensional planar active lithium deposition / stripping into a three-dimensional mechanism, can achieve high-rate charge and discharge, and has excellent rate performance.

[0012] Optionally, the lithium alloy includes any one or a combination of at least two of a binary lithium alloy, a ternary lithium alloy, or a multi-component lithium alloy, wherein the mass content of metallic lithium exceeds 50%, preferably more than 80%, more preferably more than 90%; for example, the alloying elements in the lithium alloy include, but are not limited to, any one or a combination of at least two of boron, silicon, aluminum, gallium, antimony, silver, tin, indium, magnesium, or gold.

[0013] Optionally, the tubular carbon nanomaterial includes any one or a combination of at least two of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes, preferably a combination of single-walled carbon nanotubes and at least one of double-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes. Single-walled carbon nanotubes have higher flexibility than other tubular carbon materials and can better construct an elastic outer shell while supporting other tubular carbon materials to build a stable elastic outer shell. The mass ratio of the single-walled carbon nanotubes to other tubular carbon materials is 1:(0.1 - 10). If the ratio is too high, the amount of single-walled carbon nanotubes is large, the production cost is high, and they are prone to self-aggregation with poor dispersion uniformity; if the ratio is too low, the content of single-walled carbon nanotubes is small and cannot effectively construct an elastic outer shell. Preferably, it is 1:(0.5 - 5).

[0014] Optionally, the modifying elements in the modified carbon nanotubes include any one or a combination of at least two of nitrogen, oxygen, sulfur, aluminum, silver, silicon, magnesium, tin, or zinc.

[0015] As a preferred technical solution of the present invention, the elastic outer shell further includes an elastic filler, and the elastic filler includes a thermoplastic elastomer and a conductive material. Utilizing the good elasticity and softness of the thermoplastic elastomer and the excellent conductivity of the conductive material, the elastic filler has both conductive performance and toughness, effectively increasing the flexibility of the elastic outer shell and the ability to recover deformation, and making the interface contact closer.

[0016] Optionally, the mass ratio of the thermoplastic elastomer to the conductive material is (0.1 - 10):(90 - 99.9). If the mass ratio is too low, the amount of the thermoplastic elastomer is small, and its role in adapting to the deformation of the elastic outer shell is limited; if the mass ratio is too high, the amount of the thermoplastic elastomer is large, its role in adapting to the deformation of the elastic outer shell is strong, but the conductivity is greatly reduced, which is not conducive to the performance of the electrode. Preferably, it is (0.5 - 5):(95 - 99.5), and more preferably (1 - 3):(97 - 99).

[0017] Optionally, the thermoplastic elastomeric material includes, but is not limited to, any one or a combination of at least two of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butene-styrene block copolymer (SEBS), and styrene-ethylene-propylene-styrene block copolymer (SEPS).

[0018] Optionally, the conductive material includes at least one of, but is not limited to, Ketjen black, acetylene black, Cabot carbon black, conductive graphite, Super P, graphene, graphene oxide, mesophase carbon microspheres, carbon nanofibers, or nano metal particles.

[0019] Preferably, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the elastic filler is below 5%. If the mass fraction is too large, the content of the elastic filler is relatively high, which hinders the electron and ion transport of the lithium-carbon material layer. If the mass fraction is too small, the content of the elastic filler is relatively low, and the adaptability to the volume change of the lithium-carbon material layer is weak. Preferably, it is 0.5 - 3%.

[0020] Optionally, the lithium-carbon material layer further includes linear carbon nanomaterials, preferably carbon nanofibers and / or modified carbon nanofibers; the modifying elements in the modified carbon nanofibers include any one or a combination of at least two of nitrogen, oxygen, sulfur, aluminum, silver, silicon, magnesium, tin, or zinc, which may be the same as or different from the modifying elements in the modified carbon nanotubes.

[0021] Optionally, the ratio of the tubular carbon nanomaterials to the linear carbon nanomaterials is 1:(0.1 - 10), preferably 1:(0.5 - 5), and this ratio range can take into account the structural stability and cycling stability of the lithium-carbon material layer.

[0022] Optionally, the diameter of the linear and / or tubular carbon nanomaterials is below 200 nm, preferably 1 - 50 nm, and more preferably 2 - 10 nm.

[0023] Optionally, the length of the linear and / or tubular carbon materials is above 1 μm, preferably 3 - 50 μm, and more preferably 5 - 30 μm.

[0024] Optionally, the aspect ratio of the linear and / or tubular carbon materials is 10 - 100000, preferably 2000 - 50000, and more preferably 5000 - 30000.

[0025] Optionally, the average thickness of the elastic outer shell is 0.05 - 10 μm, preferably 0.5 - 5 μm.

[0026] Optionally, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the elastic outer shell is 0.05 - 50%, preferably 0.25% - 30%.

[0027] Optionally, the surface roughness Ra of the lithium-carbon material layer is greater than 0.3 μm, preferably Ra is 0.5 - 5 μm. The surface roughness has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, it can be measured with a surface roughness meter. In this application, the NDT110 type device of Beijing Kaida Keyi Technology Co., Ltd. is used for measurement.

[0028] Optionally, the peel force between the lithium-carbon material layer and the current collector is greater than 0.2 kgf, preferably 0.5 - 5 kgf. The peel force has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, it can be measured with a universal tensile machine. In this application, the Shimadzu AG-X50N universal tensile machine is used for testing.

[0029] Optionally, the thickness of the lithium-carbon material layer is 5 - 100 μm, preferably 20 - 50 μm.

[0030] Optionally, the N / P ratio of the lithium-carbon material layer to the positive electrode active material layer is 1.05 - 1.25, preferably 1.08 - 1.15. The N / P ratio is designed according to actual requirements.

[0031] Optionally, the positive electrode active material layer includes any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganate, lithium cobaltate, sublimed sulfur, sulfonated polyacrylonitrile, vanadium pentoxide, or MS2 (M = Fe, Mn, Mo, V, Ti, Co, or Cr).

[0032] Optionally, the current collector includes a base current collector and a modified current collector. The base current collector includes any one or a combination of at least two of copper foil, composite copper foil, aluminum foil, nickel foil, stainless steel foil, conductive polymer film, or carbon fiber. 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, carbon nanofibers, carbon nanotubes, graphene, metals, and metal oxides.

[0033] Optionally, the modified current collector includes a base current collector and a coating disposed on the surface of the base current collector. The coating includes any one or a combination of at least two of graphene, graphene oxide, chromate, manganese oxide, or aluminum oxide. Different types of coatings have different interactions with the lithium-carbon material layer. Preferably, a coating that can form an integral structure with the lithium-carbon material coating is selected. The thickness of the coating is selected according to actual requirements and is generally 3-10 μm.

[0034] In a second aspect, the present application provides a method for preparing the electrode as described in the first aspect above. The method includes the following steps:

[0035] (1) Mix the positive electrode active material, conductive agent, and binder, and dispose them on one side of the current collector; or dispose the lithium-carbon material on one side of the current collector.

[0036] (2) Dispose the material containing the active material with the opposite polarity to that in step (1) on the other side of the current collector to obtain the electrode structure.

[0037] The preparation method of the lithium-carbon material is illustrated but not limited to the preparation method of the lithium-carbon material:

[0038] (1`) Mix the lithium-containing core, tubular carbon nanomaterial, and non-polar organic solvent; (2`) Spray granulation or high-speed winding under the condition of a rotation speed above 6000 rpm, and the tubular carbon nanotube material forms an elastic shell, and at least one lithium-containing core is included in the elastic shell to obtain the lithium-carbon material.

[0039] For the lithium-carbon material containing elastic fillers, its preparation method is not limited. For example, it may include the following steps: uniformly mix the thermoplastic elastic material and the conductive agent to obtain an elastic slurry, and add the elastic slurry to the mixture in (1`), or the elastic slurry can also be added after step (1`) is completed for secondary mixing. After mixing, step (2`) is carried out. It is also possible to mix the lithium-carbon material and the elastic slurry in step (2`) for secondary spray granulation or high-speed mixing, and the rotation speed of the mixing is above 5000 rpm.

[0040] The non-polar organic solvent includes but is not limited to any one or a combination of at least two of liquid alkanes with 5-10 carbon atoms, benzene, p-xylene, or petroleum ether.

[0041] The lithium-containing core includes metallic lithium powder and / or lithium alloy powder.

[0042] As a preferred technical solution of the present application, the method includes the following steps:

[0043] (a) Prepare a positive electrode active material layer from a positive electrode active material, a conductive agent, and a binder through a dry process, and then dispose it on one side of a current collector through a mechanical rolling and / or bonding process;

[0044] (b) Dispose a material containing a lithium-carbon material on the other side of the current collector described in step (1) through any one or a combination of at least two of mechanical rolling, twisting, spraying, or stamping to obtain the electrode structure;

[0045] Or (a`) Dispose a material containing a lithium-carbon material on one side of a current collector through any one or a combination of at least two of mechanical rolling, twisting, spraying, or stamping;

[0046] (b`) Prepare a positive electrode active material layer from a positive electrode active material, a conductive agent, and a binder through a dry process, and then dispose it on the other side of the current collector through a mechanical rolling and / or bonding process to obtain the electrode structure.

[0047] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0048] (1) For the electrode provided by the present application, the tubular carbon nanomaterials are exposed on the surfaces of both sides of the electrode to form protrusions, greatly increasing the roughness of the lithium-carbon material layer, enabling the lithium-carbon material layer to better combine with the current collector and the solid electrolyte, and at the same time forming a skeleton existing in the entire body phase of the lithium-carbon material layer, with good electrode structure stability;

[0049] (2) For the electrode provided by the present application, the tubular carbon nanomaterials have both ion and electron channels, effectively regulating the electrode current density and the transport of lithium ions, inhibiting the growth of lithium dendrites, and the electrode has good cycle stability and excellent rate performance;

[0050] (3) For the electrode provided by the present application, the elastic outer shell formed by the tubular carbon nanomaterials utilizes its own performance of restoring deformation, and can adaptively change with the volume change of metallic lithium and / or lithium alloy, ensuring that the lithium-carbon material layer, the current collector, and the solid electrolyte layer always maintain good contact during charge and discharge;

[0051] (4) Through the design of parameters such as the type and mass fraction of the elastic outer shell material, the present application regulates the surface roughness and peeling force of the electrode, further optimizing the structural stability and electrochemical performance of the electrode;

[0052] (5) The preparation method provided by the present application has a short process flow, high production efficiency, and universality. Description of the Drawings

[0053] Figure 1 It is a comparative schematic diagram of the electrode in the prior art and the electrode of the present application during charge and discharge,

[0054] 1 - Lithium metal anode, 1' - Lithium-carbon material layer, 2 - Current collector, 3 - Solid electrolyte layer, 4 - Cathode active material layer;

[0055] Figure 2 SEM cross-sectional view of the electrode of Example 1;

[0056] Figure 3 Rate performance test curves of Example 1 and Comparative Examples 1 - 4. Detailed implementation manners

[0057] For ease of understanding this application, the following examples are listed in this application. Those skilled in the art should understand that the said examples are only for helping to understand this application and should not be regarded as specific limitations to this application.

[0058] For example, there are differences in the negative electrode interface between the lithium metal composite electrode of this application and the lithium metal electrode in the prior art during the charge and discharge process. The comparison schematic diagram is as Figure 1 shown. For the lithium metal anode 1 in the prior art, during the charge and discharge process, voids or holes appear at the position where the surface of the lithium metal anode 1 contacts the solid electrolyte 3, resulting in the problems of uneven current density on the surface of the lithium metal anode 1 and poor interface contact between the lithium metal anode 1 and the solid electrolyte 3; while in this application, the lithium-carbon material layer 1' uses elastic lithium monomers, and utilizes the performance of the elastic shell to restore deformation, and adaptively changes with the volume change of lithium metal and / or lithium alloy, ensuring that the lithium-carbon material layer 1' always maintains good contact with the current collector 2 and the solid electrolyte layer 3 during the charge and discharge process. The tubular carbon nanomaterials forming the elastic shell in the lithium-carbon material layer 1' form protrusions on both sides of the surface of the lithium-carbon material layer 1', and have good contact with the current collector 2 and the solid electrolyte layer 3; bulk modification is carried out in the lithium-carbon material layer, and the electrode structure has good stability; the elastic shell provides dual channels for ions and electrons, regulates the current density and lithium ion transport of the lithium-carbon material layer 1', inhibits the growth of lithium dendrites, and has excellent cycle performance and rate performance.

[0059] Example 1

[0060] This example provides a lithium metal composite electrode. The electrode includes a copper foil, a lithium-carbon material layer is provided on one side of the copper foil, and the lithium-carbon material in the lithium-carbon material layer includes an elastic shell formed by single-walled carbon nanotubes and lithium metal powder contained in the elastic shell; a material layer containing the single-crystalline nickel cobalt manganese oxide cathode material NCM811 is provided on the other side, and the N / P ratio is 1.05.

[0061] The preparation method of the electrode includes the following steps:

[0062] (1) Mix a single-walled carbon nanotube dispersion (Okoshi Ayer, with a diameter of 1 nm and a length of 5 μm, 3 wt%), lithium metal powder, and n-hexane at a rotation speed of 7000 rpm for 15 min. Control the mass fraction of single-walled carbon nanotubes in the lithium-carbon material to be 0.05%. Then, perform suction filtration and drying to obtain the lithium-carbon material;

[0063] (2) In a clean room with a dew point of -45°C, lay the lithium-carbon material flat between two layers of release films, and roll it into a foil by mechanical rolling. Then, remove one layer of the release film to obtain a composite foil. Roll the composite foil onto one side of a copper foil with a thickness of 15 μm by mechanical rolling. The thickness of the lithium-carbon material layer is 20 μm;

[0064] (3) Prepare a positive electrode mixture from single-crystal nickel cobalt manganese oxide positive electrode material NCM811, ionic conductor lithium lanthanum zirconium oxide LLZTO, acetylene black, and PTFE according to a mass ratio of 75:15:5:5. After high-speed shearing, hot press it into a shape to obtain a positive electrode active material layer. In a clean room with a dew point of -45°C, laminate the positive electrode active material layer onto the other side of the copper foil and dry it under vacuum to obtain the electrode.

[0065] Test the cross-section SEM of the lithium-carbon material layer (excluding the copper foil) in step (2). The test results are as Figure 2 shown. It can be clearly seen from the figure that the lithium-carbon material layer includes an elastic outer shell formed by single-walled carbon nanotubes and lithium metal powder contained in the elastic outer shell. The cocoon-like bodies are interconnected to form a three-dimensional network channel, and there are protrusions formed by exposed carbon nanotubes on both side surfaces of the lithium-carbon material layer.

[0066] Example 2

[0067] This example provides a lithium metal composite electrode. The electrode includes a stainless steel foil, with a lithium-carbon material layer provided on one side of the stainless steel foil. The lithium-carbon material in the lithium-carbon material layer includes an elastic outer shell formed by single-walled carbon nanotubes and nanofibers and lithium-tin alloy powder contained in the elastic outer shell; a material layer containing lithium iron phosphate is provided on the other side, and the N / P ratio is 1.25.

[0068] The preparation method of the electrode includes the following steps:

[0069] (1) Mix lithium iron phosphate, ionic conductor lithium lanthanum zirconium oxide LLZO, Ketjen black, single-walled carbon nanotubes, and binder polytetrafluoroethylene PTFE evenly according to a mass ratio of 75:15:4:1:5. After high-speed shearing, hot roll it into a film layer, and then roll the film layer onto one side of a stainless steel foil with a thickness of 12 μm;

[0070] (2) Mix the single-walled carbon nanotube dispersion (Okeshier, with a diameter of 1 nm and a length of 5 μm, 3 wt%), carbon nanofibers (with a diameter of 200 nm and a length of 15 μm, Beijing Decodaojin Technology Co., Ltd.), lithium-tin alloy powder (with a mass fraction of tin of 5%), and N-methylpyrrolidone, and control the total mass fraction of single-walled carbon nanotubes and carbon nanofibers in the lithium-carbon material to be 50%. The mass ratio of single-walled carbon nanotubes to carbon nanofibers is 1:0.5. Spray dry to obtain the lithium-carbon material;

[0071] (3) In a clean room with a dew point of -45°C, mix the lithium-carbon material and the binder PTFE, and then spray the mixture on the other side of the stainless steel foil. The thickness of the lithium-carbon material layer is 100 μm to obtain the electrode described.

[0072] Example 3

[0073] Compared with Example 1, the difference is only that the mass fraction of single-walled carbon nanotubes is adjusted to 0.25%, and the other conditions are the same.

[0074] Example 4

[0075] Compared with Example 1, the difference is only that the mass fraction of single-walled carbon nanotubes is adjusted to 30%, and the other conditions are the same.

[0076] Example 5

[0077] Compared with Example 1, the difference is only that the copper foil is replaced with a copper foil with an alumina coating with a thickness of 5 μm, and the other conditions are the same.

[0078] Example 6

[0079] Compared with Example 1, the difference is only that the single-walled carbon nanotubes are replaced with a mixture of single-walled carbon nanotubes and double-walled carbon nanotubes, and the mass ratio of the two is 1:0.5.

[0080] Example 7

[0081] Compared with Example 1, the difference is only that the single-walled carbon nanotubes are replaced with a mixture of single-walled carbon nanotubes and double-walled carbon nanotubes, and the mass ratio of the two is 1:5.

[0082] Example 8

[0083] Compared with Example 1, the difference is only that the elastic outer shell further includes a thermoplastic elastic filler, and the elastic filler includes SEBS, Ketjenblack, and multi-walled carbon nanotubes (with a diameter of 8-10 nm and a length of 15 μm) with a mass ratio of 0.5:80:19.5.

[0084] The difference between the preparation method and that of Example 1 is only that in step (1), SEBS is first dissolved in n-hexane according to a mass ratio, and Ketjen black and multi-walled carbon nanotubes are added and mixed to obtain an elastic slurry. Then, a single-walled carbon nanotube dispersion (Axensil, with a diameter of 1 nm and a length of 5 μm, 3 wt%), lithium metal powder, the elastic slurry, and n-hexane are mixed at a rotation speed of 7000 rpm for 15 min, controlling the mass fraction of single-walled carbon nanotubes in the lithium-carbon material to be 0.05%. After suction filtration and drying, a lithium-carbon material is obtained. The mass of the elastic filler accounts for 0.5% of the total mass of the lithium-carbon material, and the remaining steps are the same as those in Example 1.

[0085] Example 9

[0086] Compared with Example 1, the difference is only that the elastic outer shell further includes a thermoplastic elastic filler, and the elastic filler includes SBS, conductive graphite, and double-walled carbon nanotubes (with a diameter of 8 - 10 nm and a length of 15 μm) with a mass ratio of 5:70:25.

[0087] The difference between the preparation method and that of Example 1 is only that in step (1), SBS is first dissolved in n-hexane according to a mass ratio, and conductive graphite and double-walled carbon nanotubes are added and mixed to obtain an elastic slurry. Then, a single-walled carbon nanotube dispersion (Axensil, with a diameter of 1 nm and a length of 5 μm, 3 wt%), lithium metal powder, the elastic slurry, and n-hexane are mixed at a rotation speed of 7000 rpm for 15 min, controlling the mass fraction of single-walled carbon nanotubes in the lithium-carbon material to be 0.05%. After suction filtration and drying, a lithium-carbon material is obtained. The mass of the elastic filler accounts for 5% of the total mass of the lithium-carbon material, and the remaining steps are the same as those in Example 1.

[0088] Example 10

[0089] Compared with Example 1, the difference is only that the elastic outer shell further includes a thermoplastic elastic filler, and the elastic filler includes SIS, Super P, and graphene oxide (flake diameter 5 μm) with a mass ratio of 3:60:37.

[0090] The difference between the preparation method and that of Example 1 is only that in step (1), SIS is first dissolved in n-hexane according to a mass ratio, and Super P and graphene oxide are added and mixed to obtain an elastic slurry. Then, a single-walled carbon nanotube dispersion (Axensil, with a diameter of 1 nm and a length of 5 μm, 3 wt%), lithium metal powder, the elastic slurry, and n-hexane are mixed at a rotation speed of 7000 rpm for 15 min, controlling the mass fraction of single-walled carbon nanotubes in the lithium-carbon material to be 0.05%. After suction filtration and drying, a lithium-carbon material is obtained. The mass of the elastic filler accounts for 3% of the total mass of the lithium-carbon material, and the remaining steps are the same as those in Example 1.

[0091] Comparative Example 1

[0092] Compared with Example 1, the difference is only that the lithium-carbon material layer is replaced with a lithium metal strip, and the other conditions are the same as those in Example 1.

[0093] Comparative Example 2

[0094] Compared with Example 1, the difference is only that the lithium-carbon material in the lithium-carbon material layer is replaced with a mixture of lithium metal powder and single-walled carbon nanotubes (not the structure of the present application), and the other conditions are the same as those in Example 1.

[0095] Comparative Example 3

[0096] Compared with Example 1, the difference is only that the single-walled carbon nanotubes in the lithium-carbon material layer are replaced with nanofibers.

[0097] Comparative Example 4

[0098] Compared with Example 1, the difference is only that the single-walled carbon nanotubes in the lithium-carbon material layer are replaced with particulate acetylene black.

[0099] The electrodes of Example 1 and Comparative Examples 1-4 were assembled into a solid-state battery, which included the above 1 electrode and 2 single-sided electrodes with opposite polarities to the electrode (i.e., 2 layers of positive electrode active material layers and 2 layers of negative electrode active material layers). The solid electrolyte was LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ), and the rate performance was tested at 60 °C. The rate data are as Figure 3 shown.

[0100] It can be seen from Figure 3 that at 0.1C and 0.2C, the rate performance of the electrodes of Example 1 and Comparative Examples 1-4 is similar. At 0.5C-2C, the electrode performance of Example 1 is significantly better. This is because the electrode of Example 1 adopts the electrode of the present application, which has a stable structure and can simultaneously regulate the transport of lithium ions and electrons, showing excellent rate performance.

[0101] Test data:

[0102] The electrodes in Examples 1-10 and Comparative Examples 1-4 were tested for surface roughness and peel strength. The data are shown in Table 1. The test method for peel strength is as follows: The electrode was cut into a rectangle with a length of 20 mm and a width of 10 cm as the test piece. The test piece was adhered to a clean stainless steel plate with a 20-mm-wide double-sided tape, and a Shimadzu AG-X50N universal tensile machine was used to perform a 180° peel at a speed of 300 mm / min from one end of the test piece. The test was repeated 3 times, and the average value was taken as the peel strength. The greater the peel strength, the better the bonding state between the electrode active material layer and the current collector.

[0103] Assembling a solid-state battery for testing: The solid-state battery includes the above 1 electrode and 2 single-sided electrodes with opposite polarities to the electrode. The solid electrolyte is LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ). It was tested under cycling at 60 °C and 0.2C, and the cycling data is shown in Table 1.

[0104] Table 1 Test data of electrode surface roughness and peel strength

[0105]

[0106]

[0107] It can be seen from Table 1 that:

[0108] (1) Considering Examples 1, 3, and 4 comprehensively, in Example 1, the surface roughness, peel strength, and cycling performance of the lithium-carbon material layer are all worse than those in Examples 3 and 4. This is because the mass fraction of single-walled carbon nanotubes in Example 1 is relatively low, with fewer exposed or protruding ones on the surface, resulting in limited effects on improving surface roughness and peel strength and providing fewer channels for ion and electron transport;

[0109] (2) In Example 2, the surface roughness, peel strength, and cycling performance of the lithium-carbon material layer are all relatively excellent. This is because in Example 2, single-walled carbon nanotubes and nanofibers are used and a suitable ratio is selected to construct the lithium-carbon material layer, which has excellent structural stability and cycling stability;

[0110] (3) Considering Examples 1 and 5 comprehensively, the peel strength and cycling performance of Example 5 are better than those of Example 1. This is because the copper foil in Example 5 contains an alumina coating, which not only has a higher surface roughness than the copper foil in Example 1 but also can undergo an in-situ reaction with lithium in the lithium-carbon material layer to form an integrated structure; at the same time, aluminum has a good affinity with lithium, which can induce the deposition of lithium during cycling;

[0111] (4) Considering Examples 1, 6, and 7 comprehensively, the surface roughness and peel strength of Examples 1, 6, and 7 are close, but the cycling stability of the electrodes varies greatly. This is because the rigidity of double-walled carbon nanotubes is stronger than that of single-walled carbon nanotubes, and the formed elastic shell is more stable, which can simultaneously regulate ion and electron transport;

[0112] (5) Combining Example 1 with Examples 8 - 10, the capacity retention rate after 50 cycles in Example 1 is lower than that in Examples 8 - 10. This is because elastic fillers are added to the elastic outer shell of the lithium-carbon material in Examples 8 - 10. The elastic fillers further increase the flexibility of the elastic outer shell and its ability to recover its own deformation. The interfacial contact between the lithium-carbon material layer, the current collector, and the solid electrolyte layer is closer, and the electrode structure has good stability. The capacity retention rate of Example 9 is smaller than that of Examples 8 and 10. This is because the proportion of thermoplastic elastomeric materials in the elastic seasoning in Example 9 is relatively high and the mass fraction in the lithium-carbon material layer is also high, which hinders the electron and ion transport in the lithium-carbon material layer and reduces its cycling performance.

[0113] (6) Combining Example 1 with Comparative Examples 1 - 4, the surface roughness, peel strength, and cycling performance of Example 1 are higher than those of Comparative Examples 1 - 4. This is because the single-walled carbon nanotubes selected in Example 1 are tubular carbon materials, which are exposed on the electrode surface and form protrusions, greatly increasing the roughness of the lithium-carbon material layer, enabling the lithium-carbon material layer to better combine with the current collector and the solid electrolyte. At the same time, a framework exists throughout the lithium-carbon material layer, and the electrode structure has good stability. The single-walled carbon nanotubes have a hollow tubular structure, which can simultaneously regulate the transport of ions and electrons, enabling the electrode to have excellent cycling performance. In Comparative Examples 1 and 3 - 4, tubular carbon nanomaterials are not used. Although tubular carbon nanomaterials are used in Comparative Example 2, an elastic outer shell structure containing metallic lithium powder is not formed.

[0114] In summary, the electrode designed in this application combines structural stability and cycling stability and is a highly stable electrode.

[0115] The applicant declares that the detailed structural features of this application are illustrated through the above examples, 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 improvement to this application, the equivalent replacement of the components selected in this application, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A self-adaptive composite lithium metal electrode, characterized in that, The electrode includes a positive electrode active material layer, a current collector, and a lithium-carbon material layer, and the current collector is disposed between the positive electrode active material layer and the lithium-carbon material layer; Wherein the lithium-carbon material in the lithium-carbon material layer includes elastic lithium monomers, and the elastic lithium monomers include metallic lithium and / or lithium alloy as an active core, and tubular carbon nanotubes as an elastic outer shell. The elastic outer shells communicate with each other to form a three-dimensional network channel, and there are protrusions formed by tubular carbon nanotubes on the surface of the lithium-carbon material layer.

2. The lithium metal composite electrode according to claim 1, wherein The alloying elements in the lithium alloy include any one or a combination of at least two of boron, silicon, aluminum, gallium, antimony, silver, tin, indium, magnesium, or gold, and the content of metallic lithium in the lithium alloy is more than 50%.

3. The lithium metal composite electrode according to claim 1 or 2, characterized in that, The tubular carbon nanotubes include any one or a combination of at least two of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes, preferably a combination of single-walled carbon nanotubes and at least one carbon nanotube selected from double-walled carbon nanotubes, multi-walled carbon nanotubes, and modified carbon nanotubes; Preferably, the modifying elements in the modified carbon nanotubes include any one or a combination of at least two of nitrogen, oxygen, sulfur, aluminum, silver, silicon, magnesium, tin, or zinc; Preferably, the lithium-carbon material layer further includes linear carbon nanotubes, preferably nanofibers and / or modified nanofibers; the ratio of the tubular carbon nanotubes to the linear carbon nanotubes is 1:(0.1-10), preferably 1:(0.5-5).

4. The lithium metal composite electrode according to any one of claims 1-3, characterized in that The average thickness of the elastic outer shell is 0.05-10 μm, preferably 0.5-5 μm; Preferably, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the elastic outer shell is 0.05-50%, preferably 0.25%-30%; Preferably, the elastic outer shell further includes an elastic filler, and the elastic filler includes a thermoplastic elastomer and a conductive material, and the mass ratio of the thermoplastic elastomer to the conductive material is (0.1-10): (90-99.9), preferably (0.5-5):(95-99.5), more preferably (1-3);(97-99); Preferably, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the elastic filler is below 5%, preferably 0.5-3%.

5. The lithium metal composite electrode according to any one of claims 1-4, characterized in that, The surface roughness Ra of the lithium-carbon material layer is greater than 0.3 μm, preferably Ra is 0.5-5 μm.

6. The lithium metal composite electrode according to any one of claims 1-5, characterized in that, The peel force between the lithium-carbon material layer and the current collector is greater than 0.2 kgf, preferably 0.5-5 kgf.

7. The lithium metal composite electrode according to any one of claims 1-6, characterized in that, The current collector includes a base current collector and a modified current collector. The base 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, and the coating includes any one or a combination of at least two of graphene, graphene oxide, chromate, manganese oxide, or aluminum oxide.

8. The lithium metal composite electrode according to any one of claims 1-7, characterized in that, The positive electrode active material layer includes any one or a combination of at least two of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium cobalt oxide, sublimated sulfur, sulfonated polyacrylonitrile, vanadium pentoxide, or MS2 (M = Fe, Mn, Mo, V, Ti, Co, or Cr).

9. A method for preparing a metallic lithium composite electrode as described in any one of claims 1-8, characterized in that, The method includes the following steps: (1) Mix the positive electrode active material, conductive agent, and binder, and dispose them on one side of the current collector; or dispose the lithium-carbon material on one side of the current collector; (2) Dispose an active material layer having a polarity opposite to that in step (1) on the other side of the current collector to obtain the electrode described above.

10. The method according to claim 9, characterized in that, The method includes the following steps: (a) Prepare a positive electrode active material layer from the positive electrode active material, conductive agent, and binder through a dry process, and then dispose it on one side of the current collector through mechanical rolling and / or bonding processes; (b) Dispose the material containing the lithium-carbon material on the other side of the current collector described in step (1) through any one or a combination of at least two of mechanical rolling, twisting, spraying, or stamping to obtain the electrode; Or (a`) Dispose the material containing the lithium-carbon material on one side of the current collector through any one or a combination of at least two of mechanical rolling, twisting, spraying, or stamping; (b`) Prepare a positive electrode active material layer from the positive electrode active material, conductive agent, and binder through a dry process, and then dispose it on the other side of the current collector through mechanical rolling and / or bonding processes to obtain the electrode.

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