A negative electrode active material, a preparation method, and a negative electrode sheet and a lithium battery

Abstract

This invention discloses a negative electrode active material, its preparation method, a negative electrode sheet, and a lithium battery. The preparation method of the negative electrode active material includes: preparing nanoscale carbon fibers; obtaining a lithium-lithium-carbon alloy foil through a thermodynamic spontaneous reaction between lithium strip and the nanoscale carbon fibers; and embedding a titanium mesh into the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework. This invention, through the preparation of nanoscale carbon fibers, obtains a lithium-lithium-carbon alloy foil capable of embedding a titanium mesh during a thermodynamic spontaneous reaction with lithium strip, forming a negative electrode active material with a metal skeleton. This negative electrode active material is a composite material with a branch-type hierarchical skeleton, which can improve structural stability and the comprehensive mechanical properties of the composite material.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, and more specifically, to a negative electrode active material, a preparation method, a negative electrode sheet, and a lithium battery. Background Technology

[0002] Lithium metal has a capacity of up to 3860 mAh g. -1 With its theoretical capacity and ability to achieve high energy density, lithium metal is considered the best material to replace graphite electrodes. However, electrolyte systems using lithium metal as the negative electrode in secondary batteries suffer from a series of problems, such as the formation of lithium dendrites, poor overall mechanical properties of composite materials, and uncontrollable charge transfer.

[0003] Application number CN202211100676.9 discloses a lithium metal battery anode composite material and its preparation method. This material achieves lithium-ion conduction and guides uniform lithium deposition under the film layer through a protective layer, maintaining the integrity of the film structure during long cycles and thus achieving a long battery cycle life. However, the mechanical properties and expansion forces of the anode material itself do not address the impact on the anode structure. This means that later lithium insertion / extraction may still damage the anode structure, further causing uneven lithium deposition and affecting the electrical performance of the lithium battery.

[0004] Therefore, improvements are needed in multiple aspects to solve the above-mentioned technical problems, thereby improving the cycle and rate performance of lithium battery cells. Summary of the Invention

[0005] The purpose of this invention is to provide a negative electrode active material, a preparation method, a negative electrode sheet, and a lithium battery, which can solve at least one of the aforementioned technical problems. The specific solution is as follows:

[0006] According to specific embodiments disclosed in this invention, the first aspect of this invention provides a method for preparing a negative electrode active material, comprising: preparing nanoscale carbon fibers;

[0007] Lithium-lithium-carbon alloy foil was obtained by utilizing the thermodynamic spontaneous reaction between lithium tape and the nanoscale carbon fiber.

[0008] A titanium mesh is embedded in the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework.

[0009] Preferably, the preparation of nanoscale carbon fibers includes:

[0010] A polyacrylonitrile solution is dissolved in an organic solution to form a spinning solution;

[0011] The spinning solution is stretched into nanoscale polyacrylonitrile fibers using electrospinning technology.

[0012] The polyacrylonitrile fibers are subjected to staged heat treatment to obtain the nanoscale carbon fibers with fibrous carbon structures.

[0013] Preferably, lithium-lithium-carbon alloy foil is obtained by utilizing the thermodynamic spontaneous reaction between lithium tape and the nanoscale carbon fiber, comprising:

[0014] After thoroughly mixing 0.5 to 10 parts by weight of the lithium strip and 0.5 to 10 parts by weight of the nano-carbon fiber, the mixture is placed in a rare gas environment and vigorously stirred at 350°C to allow the lithium strip and the nano-carbon fiber to undergo a thermodynamic spontaneous reaction, thereby obtaining a lithium-lithium carbon alloy ingot; wherein the number of parts of the lithium strip is greater than the number of parts of the nano-carbon fiber.

[0015] The lithium-lithium-carbon alloy ingot is rolled to obtain the lithium-lithium-carbon alloy foil with a thickness of 5 to 50 μm;

[0016] The process conditions for rolling lithium-lithium-carbon alloy ingots include: adjusting the pressure between the first roll and the second roll to 0-10 MPa, and adjusting the distance between the first roll and the second roll to 0-1000 μm.

[0017] Preferably, a titanium mesh is embedded in the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework, comprising:

[0018] The titanium mesh is co-rolled with the lithium-lithium-carbon alloy foil to continuously embed the titanium mesh into the lithium-lithium-carbon alloy foil, thereby forming the negative electrode active material with a metal frame.

[0019] The co-rolling process conditions include: stacking the titanium mesh and the lithium-lithium carbon alloy foil of the same size in a dry environment with a dew point temperature of -60 to -30°C and then placing them into a roll press for rolling; adjusting the pressure between the first roll and the second roll to 0-10 MPa and adjusting the distance between the first roll and the second roll to 0-1000 μm.

[0020] Preferably, the electrospinning process conditions include:

[0021] Spinning temperature 40~60℃, spinning time 1~1.5h, positive pressure 15~18kV, negative pressure -8~-1kV, receiving distance 8~20cm, relative humidity 40%~60%, and feed speed 0.8~2.0mL / h.

[0022] Preferably, the polyacrylonitrile fibers are subjected to a staged heat treatment, including:

[0023] In the first stage, the polyacrylonitrile fiber is subjected to a polymer chain crosslinking reaction at a temperature of 200℃~300℃ to improve the density and strength of the polyacrylonitrile fiber.

[0024] In the second stage, hydrogen atoms, nitrogen atoms, and oxygen atoms in the polyacrylonitrile fiber are removed at a temperature of 1000℃ to 2000℃ to form a fibrous carbon structure.

[0025] In the third stage, the carbon fibers are further heated to 2500℃~3000℃ in an inert atmosphere to obtain the nanoscale carbon fibers with high electrical conductivity and mechanical strength.

[0026] Preferably, the titanium mesh is made of titanium fibers, the thickness of the titanium mesh is 5-50 μm, the mesh side length is 5-50 μm, and the diameter of the titanium fibers is 10-30 μm.

[0027] According to the specific embodiments disclosed in this invention, a second aspect of this invention discloses a negative electrode active material prepared by the above method.

[0028] According to specific embodiments disclosed in this invention, a third aspect of this invention discloses a negative electrode sheet, comprising: a negative electrode current collector layer, and a negative electrode active material layer covering the surface of the negative electrode current collector layer, wherein the negative electrode active material layer is prepared using the aforementioned negative electrode active material.

[0029] According to specific embodiments disclosed in this invention, a fourth aspect of this invention discloses a lithium battery comprising a negative electrode sheet prepared by the above method.

[0030] Compared with the prior art, the above-described solution disclosed in this invention has at least the following beneficial effects:

[0031] This invention prepares nanoscale carbon fibers, which, upon undergoing a thermodynamic spontaneous reaction with lithium tape, yield a lithium-lithium-carbon alloy foil capable of embedding a titanium mesh, forming a negative electrode active material with a metallic skeleton. This negative electrode active material is a composite material with a branched hierarchical skeleton, a structure that enhances structural stability and the overall mechanical properties of the composite material. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the disclosure of this invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0033] Figure 1 A flowchart of the method for preparing the negative electrode active material provided in the first embodiment of the present invention;

[0034] Figure 2An electron microscope schematic diagram of nanoscale carbon fibers provided in the first embodiment of the present invention;

[0035] Figure 3 This is an electron microscope schematic diagram of the negative electrode active material provided in the first embodiment of the present invention;

[0036] Figure 4 A schematic diagram of the composite layered structure of the negative electrode sheet provided in the third embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram of the internal single-layer structure of a lithium battery cell provided in the fourth embodiment of the present invention.

[0039] 1. Aluminum current collector; 2. Positive electrode material; 3. Separator; 4. Negative electrode active material layer; 5. Copper current collector. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments disclosed in this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments disclosed in this invention without creative effort are within the protection scope of this invention.

[0041] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0042] The following is in conjunction with the appendix Figures 1-5 Detailed description of optional embodiments of the present invention.

[0043] During the charge-discharge cycle of a lithium battery, uneven deposition of lithium metal at the electrode interface can lead to the formation of lithium dendrites. To prevent the unlimited growth of lithium dendrites from piercing the battery separator and causing a short circuit, which could pose a safety hazard, it is necessary to guide the uniform deposition of metallic lithium and reduce the probability of lithium dendrite formation. Therefore, the first embodiment of this invention provides a method for preparing a negative electrode active material, such as... Figure 1 As shown, it includes the following steps:

[0044] Step S1: Prepare nanoscale carbon fibers;

[0045] Step S2: Obtain lithium-lithium-carbon alloy foil by utilizing the thermodynamic spontaneous reaction between lithium tape and the nanoscale carbon fiber;

[0046] Step S3: Embed the titanium mesh into the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework.

[0047] This invention prepares nanoscale carbon fibers, which undergo a thermodynamic spontaneous reaction with lithium tape to obtain a lithium-carbon alloy foil capable of embedding a titanium mesh, forming a negative electrode active material with a metallic skeleton. This negative electrode active material possesses a branched, hierarchical framework structure, which not only inhibits the growth of lithium dendrites during cycling but also increases the structural stability and mechanical strength of the lithium alloy foil.

[0048] In this embodiment, nanoscale carbon fibers are prepared through the following steps.

[0049] Step S11: Dissolve the polyacrylonitrile solution in an organic solution to form a spinning solution;

[0050] Step S12: The spinning solution is stretched into nanoscale polyacrylonitrile fibers using electrospinning technology;

[0051] Step S13: Perform staged heat treatment on the polyacrylonitrile fiber to obtain the nanoscale carbon fiber with a fibrous carbon structure.

[0052] Specifically, in step S11, the purified acrylonitrile is reacted with a comonomer to prepare a polyacrylonitrile solution. The comonomer can be polylactic-co-glycolic acid copolymer (PLGA), polycaprolactone (PCL), polyvinyl alcohol (PVA), etc.

[0053] The prepared polyacrylonitrile solution is dissolved in solvents with strong dissolving power and high dielectric constant, such as N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), acetone, etc., to form a uniform spinning solution.

[0054] In step S12, the electrospinning process involves spraying the spinning solution into fibers. Under the influence of an electrostatic field, the fine stream of spinning solution is stretched into nanoscale polyacrylonitrile fibers. The electrospinning process conditions include:

[0055] Spinning temperature 40~60℃, spinning time 1~1.5h, positive pressure 15~18kV, negative pressure -8~-1kV, receiving distance 8~20cm, relative humidity 40%~60%, and feed speed 0.8~2.0mL / h.

[0056] The staged heat treatment of polyacrylonitrile fibers in step S13 includes the following three stages:

[0057] In the first stage, the polyacrylonitrile fiber is placed in an oxidation furnace. At a temperature of 200℃ to 300℃, oxygen molecules in the air combine with the polyacrylonitrile fiber to carry out a cross-linking reaction of the polymer chain. The cross-linking reaction time is controlled within 5 to 48 hours. The density and strength of the polyacrylonitrile fiber are improved by oxidation.

[0058] In the second stage, hydrogen, nitrogen, and oxygen atoms in the polyacrylonitrile fiber are removed at a temperature of 1000℃ to 2000℃ to form a fibrous carbon structure.

[0059] In this stage, relatively pure nanoscale carbon fibers are obtained by removing impurity elements, avoiding porosity in subsequent processes that would affect the thickness and mechanical properties of the anode. Simultaneously, the fibrous carbon structure improves conductivity, accelerating lithium migration within the anode and preventing gaps between the solid electrolyte and the anode caused by the lithium ion migration rate within the anode being slower than the lithium ion extraction rate on the anode surface during discharge, thus reducing voids.

[0060] In the third stage, the nanoscale carbon fibers are further heated to 2500℃~3000℃ in an inert atmosphere for graphitization treatment to obtain nanoscale carbon fibers with high conductivity and mechanical strength.

[0061] Further surface treatment and sizing processes, including washing and drying, can be applied to nanoscale carbon fibers to improve their surface and processing properties, and increase their flexibility and tensile strength.

[0062] In this embodiment, the nanoscale carbon fibers prepared by the above method have good mechanical properties, providing lithium transport carriers and mechanical frameworks for the subsequent preparation of lithium-lithium carbon alloys, and ensuring the stability of the alloy skeleton when inlaid with titanium mesh.

[0063] Step S2, obtaining lithium-lithium-carbon alloy foil through the thermodynamic spontaneous reaction of lithium tape and nanoscale carbon fiber, includes:

[0064] Step 21: 0.5–10 parts of lithium strip with a purity of 99.9% and 0.5–10 parts of nano-sized carbon fiber are placed under argon protection and stirred at 350°C to fully mix and react. The mixture is then solidified in a crucible to form a lithium-lithium-carbon alloy ingot. The number of parts of the lithium strip is greater than the number of parts of the nano-sized carbon fiber.

[0065] In this step, the reaction of lithium intercalation into carbon fibers has a negative Gibbs free energy (-10.59 kJ / mol), so the in-situ interaction between lithium and carbon fibers to form LiC6 is a thermodynamically spontaneous process. After lithium atoms intercalate into carbon fibers, the transfer of electrons from lithium to carbon increases the anisotropy of carbon atoms, thereby enhancing the binding force between the carbon framework and lithium ions. This enhanced binding force, especially in repeated lithium plating / stripping cycles, helps improve the uniformity and stability of lithium deposition.

[0066] On the other hand, the formation of the LiC6 interface layer enhances the bonding force between Li and the carbon framework, giving LiC6 lithium-affinity properties. By acting as a buffer layer, it strengthens the bonding force between the electrode and the electrolyte, reduces the overpotential for lithium nucleation, and promotes uniform lithium deposition. Simultaneously, the formed LiC6 interface layer effectively alleviates volume expansion and suppresses the dendritic and powdery morphology of lithium deposits, thereby improving the stability of the composite anode.

[0067] Furthermore, by adding excess lithium, more lithium is provided in subsequent cycles, thereby increasing the number of cycles.

[0068] Therefore, in this embodiment, by adjusting the doping ratio of lithium to nanoscale carbon fibers, the electronic pathway is increased, the uniformity of lithium deposition is improved, and the lithium void problem during delithiation is avoided.

[0069] Step S22: Roll the lithium-lithium carbon alloy ingot.

[0070] During the rolling process, by adjusting the pressure between the first and second rolls of the rolling mill to 0-10 MPa and the distance between the first and second rolls to 0-1000 μm, a lithium-lithium-carbon alloy foil with a thickness of 5-50 μm is obtained. Figure 2 As shown, it is used for embedding a titanium mesh.

[0071] Step S3: Co-roll the titanium metal mesh with the lithium-lithium carbon alloy foil to continuously embed the titanium metal mesh into the lithium-lithium carbon alloy foil, forming the negative electrode active material with a metal frame.

[0072] Titanium mesh is a mesh structure made of titanium alloy. The ultra-fine diameter of titanium fibers allows titanium mesh to have a smaller grid structure, which can be finely processed and implanted into the human body. It is mainly used in the medical field.

[0073] In this embodiment, as Figure 3As shown, ultrafine titanium fibers with a diameter of 20 μm are woven into a titanium mesh with a certain mesh side length and thickness. The surface of the titanium mesh is flat and without bumps, which is conducive to the uniform deposition of lithium. In a dry environment with a dew point temperature of -60 to -30℃, a layer of titanium mesh of the same size is co-rolled with the lithium-lithium-carbon alloy foil synthesized in step S2 through a rolling mill. The gap between the rollers of the rolling mill is adjusted to 0-1000 μm, and the larger the diameter of the titanium fiber, the larger the gap between the rollers. The pressure between the first and second rollers is adjusted to 0-10 MPa, and the greater the thickness of the titanium mesh, the lower the pressure. The titanium mesh is continuously embedded into the lithium-lithium-carbon alloy foil, so that the titanium mesh and the lithium-lithium-carbon alloy foil are tightly bonded to form the negative electrode active material of the lithium-lithium-carbon-titanium composite foil.

[0074] The negative electrode active material of the present invention utilizes the difference in lithium affinity between carbon fiber and titanium mesh to induce lithium to be deposited in a directional manner within the mesh, thereby increasing the lithium pathway, enhancing lithium diffusion, further reducing the gap between the negative electrode and the electrolyte layer, and slowing down the precipitation of lithium dendrites.

[0075] Meanwhile, the lithium-lithium-carbon-titanium mesh forms a branch-type hierarchical skeleton, which can improve the stability of the skeleton structure and the comprehensive mechanical properties of the composite material.

[0076] The second embodiment of the present invention provides a negative electrode active material, prepared according to the above method, as a material for making a lithium battery negative electrode.

[0077] The third embodiment of the present invention provides a negative electrode sheet, comprising: a negative electrode current collector layer, and a negative electrode active material layer 4 covering the surface of the negative electrode current collector layer. The negative electrode active material layer is made of a negative electrode active material, thus forming a structure as shown in the figure. Figure 4 The composite structure shown has three layers: a copper current collector, a lithium-lithium-carbon alloy layer, and a titanium mesh.

[0078] The fourth embodiment of the present invention provides a lithium battery, such as... Figure 5 As shown, the lithium battery cell sequentially includes: an aluminum current collector 1, a positive electrode material 2, a separator 3, a negative electrode active material layer 4, and a copper current collector 5.

[0079] Copper foil is the most common negative electrode current collector in lithium batteries. During the initial charge and discharge process, lithium metal is deposited on the surface of the copper foil. The increased charge density at the deposition site further induces the rapid growth of lithium metal at the protruding tips, forming lithium dendrites. A uniform lithium negative electrode deposition substrate can promote the homogenization of current density and effectively reduce local current density, which can alleviate the growth of lithium dendrites to some extent. However, it is difficult to maintain this ideal deposition state during long-term cycling. Therefore, in order to suppress or alleviate the formation of lithium dendrites, the negative electrode active material of this invention is used as the negative electrode active material layer. A titanium mesh is introduced by rolling, and a lithium-lithium carbon alloy material is sandwiched between the copper current collector and the titanium mesh to form a sandwich structure. The mesh is used to construct the physical boundary to form a micro-electrode, thereby suppressing the excessive dissolution of lithium along local hot spots to form large pits.

[0080] The following comparative experiments illustrate how the negative electrode active material provided by this invention can improve the cycle performance of lithium metal batteries by suppressing lithium dendrites and solving the gap problem that may exist between the solid electrolyte and the negative electrode.

[0081] In this embodiment, the cathode material provided for preparing the soft-pack full battery is a nickel-cobalt-manganese ternary cathode material with the molecular formula Ni0.8Co0.1Mn0.1 (NCM811) and the formulation is NCM811:SP:PVDF = 96%:1.5%:2.5%; the separator is a 9μm PE base film coated with a 2μm Al2O3 ceramic layer on both sides; the electrolyte system used for preparing the soft-pack full battery is EC / DMC / EMC, and all operations are carried out at the dew point (-30℃) environment.

[0082] Comparative Example 1:

[0083] This comparative example is a graphite negative electrode lithium battery, which was prepared using the following steps:

[0084] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode includes a positive electrode current collector and an active material layer covering the surface of the positive electrode current collector;

[0085] (2) Fabricating a graphite anode for a lithium-ion battery, wherein the lithium-ion battery anode includes a negative electrode current collector and an active material layer covering the surface of the negative electrode current collector.

[0086] (3) Lithium battery fabrication: The positive electrode, negative electrode and separator obtained in steps (1) and (2) are assembled into a battery for testing.

[0087] Example 1:

[0088] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0089] (1) To make a positive electrode for a lithium-ion battery, wherein the positive electrode layer of the lithium-ion battery includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0090] The materials used to prepare the active material layer include: NCM811 with the molecular formula Ni0.8Co0.1Mn0.1, polyvinylidene fluoride, and a conductive agent, in a ratio of 96%:1.5%:2.5%.

[0091] (2) To prepare lithium-ion battery negative electrode active material, lithium strip and nano-scale carbon fiber with a mass ratio of 9:1 were placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0092] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0093] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0094] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 30 μm, and a diameter of 20 μm.

[0095] (3) Fabricating a lithium-ion battery negative electrode, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0096] (4) Assemble the separator, positive electrode and negative electrode into a battery and test it.

[0097] Example 2:

[0098] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0099] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0100] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 4:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0101] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0102] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0103] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 30 μm, and a diameter of 20 μm.

[0104] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0105] (4) The separator, positive electrode layer and negative electrode layer are assembled into a battery for testing.

[0106] Example 3:

[0107] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0108] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0109] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 1:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0110] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0111] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0112] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 30 μm, and a diameter of 20 μm.

[0113] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0114] (4) The separator, positive electrode layer and negative electrode layer are assembled into a battery for testing.

[0115] Example 4:

[0116] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0117] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0118] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0119] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0120] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0121] A negative electrode active material with a thickness of 60 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 50 μm, and a diameter of 20 μm.

[0122] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0123] (4) The separator, positive electrode layer and negative electrode layer are assembled into a battery for testing.

[0124] Example 5:

[0125] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0126] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0127] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0128] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0129] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0130] A negative electrode active material with a thickness of 110 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 100 μm, and a diameter of 20 μm.

[0131] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0132] (4) Assemble the separator, positive electrode layer and negative electrode layer into a battery and test it.

[0133] Example 6:

[0134] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0135] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0136] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0137] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0138] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0139] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 30 μm, a thickness of 30 μm, and a diameter of 20 μm.

[0140] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0141] (4) Assemble the separator, positive electrode layer and negative electrode layer into a battery and test it.

[0142] Example 7:

[0143] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0144] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0145] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0146] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0147] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0148] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 50 μm, a thickness of 30 μm, and a diameter of 20 μm.

[0149] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0150] (4) Assemble the separator, positive electrode layer and negative electrode layer into a battery and test it.

[0151] Example 8:

[0152] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0153] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0154] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0155] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0156] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0157] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 30 μm, and a diameter of 30 μm.

[0158] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0159] (4) Assemble the separator, positive electrode layer and negative electrode layer into a battery and test it.

[0160] Example 9:

[0161] This embodiment describes a lithium battery using a negative electrode active material, prepared according to the following steps:

[0162] (1) Fabricating a lithium-ion battery NCM811 positive electrode, wherein the lithium-ion battery positive electrode layer includes a positive electrode current collector layer and a positive electrode active material layer covering the surface of the positive electrode current collector layer.

[0163] (2) To prepare lithium-ion battery negative electrode active material, lithium strip: nano-scale carbon fiber with a mass ratio of 9:1 was placed under argon protection, mixed and heated to 350°C to undergo a thermodynamic spontaneous reaction to obtain lithium-lithium carbon alloy ingot.

[0164] The rolling pressure is set to 6MPa and the roll gap between the first and second rolls is 40μm. The lithium-lithium-carbon alloy ingot is rolled to obtain a lithium-lithium-carbon alloy foil with a size of 55mm×60mm and a thickness of 15μm.

[0165] In a dry environment with a dew point temperature of -30℃, the rolling pressure of the rolling mill is set to 6MPa and the gap between the first and second rolling mills is 40μm. The titanium metal mesh and lithium-lithium carbon alloy foil are co-rolled.

[0166] A negative electrode active material with a thickness of 40 μm and a metal framework was obtained; wherein the titanium mesh has a mesh side length of 20 μm, a thickness of 30 μm, and a diameter of 50 μm.

[0167] (3) Fabricating a lithium-ion battery negative electrode layer, wherein the lithium-ion battery negative electrode layer includes a negative electrode current collector layer and a negative electrode active material layer covering the surface of the negative electrode current collector layer.

[0168] (4) Assemble the separator, positive electrode layer and negative electrode layer into a battery and test it.

[0169] The data from the tests conducted on the lithium batteries obtained in Comparative Example 1, Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, and Example 9 are compared, and the specific data is summarized in Table 1.

[0170] Table 1 Comparison of battery test data between comparative and example samples.

[0171]

[0172]

[0173] 1. As can be seen from the comparison of data between Comparative Example 1 and Examples 2-9 in Table 1:

[0174] (1) The battery in the embodiment has no significant increase in capacity, but its first efficiency is significantly improved, indicating that the negative electrode active material has a significant advantage in improving the first efficiency.

[0175] (2) The battery in the embodiment also showed a significant improvement in 0.5C cycle and 2C rate capacity retention, indicating that the negative electrode active material improves cycle and rate performance.

[0176] 2. As can be seen from the data comparison between Example 1 and Examples 2-3 in Table 1:

[0177] (1) The initial coulombic efficiency and cycle rate performance of Example 1 are significantly higher than those of Examples 2-3, which indicates that the performance of lithium to nano-carbon fiber mass ratio of 9:1 is better than that of 4:1 and 1:1.

[0178] 3. As can be seen from the comparison of data in Table 1 between Example 1 and Examples 4-5:

[0179] (2) The initial coulombic efficiency and cycle rate performance of Example 1 are significantly higher than those of Examples 4-5, which indicates that the performance of titanium mesh with a thickness of 30 μm is better than that of 50 μm and 100 μm.

[0180] 4. As can be seen from the comparison of data in Table 1 between Example 1 and Examples 6-7:

[0181] (3) The initial coulombic efficiency and cycle rate performance of Example 1 are significantly higher than those of Examples 6-7, which indicates that the performance of the titanium mesh with a side length of 20 μm is better than that of 30 μm and 50 μm.

[0182] 5. As can be seen from the comparison of the data in Example 1 with Examples 8-9 in Table 1:

[0183] (4) The initial coulombic efficiency and cycle rate performance of Example 1 are significantly higher than those of Examples 8-9, which indicates that the performance of titanium mesh fiber with a diameter of 20 μm is better than that of 30 μm and 50 μm.

[0184] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0185] The above embodiments are only used to illustrate the technical solutions disclosed in this invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments disclosed in this invention.

Claims

1. A method for preparing a negative electrode active material, characterized in that, include: Preparation of nanoscale carbon fibers; Lithium-lithium-carbon alloy foil was obtained by utilizing the thermodynamic spontaneous reaction between lithium tape and the nanoscale carbon fiber. A titanium mesh is embedded in the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework.

2. The method according to claim 1, characterized in that, The preparation of nanoscale carbon fibers includes: A polyacrylonitrile solution is dissolved in an organic solution to form a spinning solution; The spinning solution is stretched into nanoscale polyacrylonitrile fibers using electrospinning technology. The polyacrylonitrile fibers are subjected to staged heat treatment to obtain the nanoscale carbon fibers with fibrous carbon structures.

3. The method according to claim 1, characterized in that, The method of obtaining lithium-lithium-carbon alloy foil by utilizing the thermodynamic spontaneous reaction between lithium strip and nanoscale carbon fiber includes: After thoroughly mixing 0.5 to 10 parts by weight of the lithium strip and 0.5 to 10 parts by weight of the nano-carbon fiber, the mixture is placed in a rare gas environment and stirred at 350°C to allow the lithium strip and the nano-carbon fiber to undergo a thermodynamic spontaneous reaction, thereby obtaining a lithium-lithium carbon alloy ingot; wherein the number of parts of the lithium strip is greater than the number of parts of the nano-carbon fiber. The lithium-lithium-carbon alloy ingot is rolled to obtain the lithium-lithium-carbon alloy foil with a thickness of 5 to 50 μm; The process conditions for rolling lithium-lithium-carbon alloy ingots include: adjusting the pressure between the first roll and the second roll to 0-10 MPa, and adjusting the roll gap between the first roll and the second roll to 0-1000 μm.

4. The method according to claim 1, characterized in that, The step of embedding a titanium mesh into the lithium-lithium-carbon alloy foil to form a negative electrode active material with a metal framework includes: The titanium mesh is co-rolled with the lithium-lithium-carbon alloy foil to continuously embed the titanium mesh into the lithium-lithium-carbon alloy foil, thereby forming the negative electrode active material with a metal frame. The co-rolling process conditions include: stacking titanium mesh and lithium-lithium carbon alloy foil of the same size in a dry environment with a dew point temperature of -60 to -30°C and then placing them into a rolling mill for rolling; adjusting the pressure between the first roll and the second roll to 0-10 MPa and adjusting the rolling gap between the first roll and the second roll to 0-1000 μm.

5. The method according to claim 2, characterized in that, The electrospinning process conditions include: Spinning temperature 40~60℃, spinning time 1~1.5h, positive pressure 15~18kV, negative pressure -8~-1kV, receiving distance 8~20cm, relative humidity 40%~60%, and feed speed 0.8~2.0mL / h.

6. The method according to claim 2, characterized in that, The step-by-step heat treatment of polyacrylonitrile fibers includes: In the first stage, the polyacrylonitrile fiber is subjected to a polymer chain crosslinking reaction at a temperature of 200℃~300℃ to improve the density and strength of the polyacrylonitrile fiber. In the second stage, hydrogen atoms, nitrogen atoms, and oxygen atoms in the polyacrylonitrile fiber are removed at a temperature of 1000℃ to 2000℃ to form a fibrous carbon structure. In the third stage, the carbon fibers are further heated to 2500℃~3000℃ in an inert atmosphere to obtain the nanoscale carbon fibers with high electrical conductivity and mechanical strength.

7. The method according to claim 1 or 4, characterized in that, The titanium mesh is made of titanium fibers, the thickness of the titanium mesh is 5-50 μm, the mesh side length is 5-50 μm, and the diameter of the titanium fibers is 10-30 μm.

8. A negative electrode active material, characterized in that, Prepared using the method described in any one of claims 1-7.

9. A negative electrode sheet, characterized in that, include: A negative electrode current collector layer, and a negative electrode active material layer covering the surface of the negative electrode current collector layer, the negative electrode active material layer being prepared using the negative electrode active material as described in claim 8.

10. A lithium battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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