Self-supporting silicon carbon electrode plate and preparation method thereof

Abstract

The invention discloses a preparation method of a self-supporting silicon-carbon electrode plate. The preparation method comprises the following steps of expanded graphite preparation, nitrogen doping, pore forming, silicon compounding and compression molding. The innovation of the invention is that the integrated pole piece with a three-dimensional elastic conductive network is constructed through the porous design of the nitrogen-doped expanded graphite matrix and the in-situ silicon coating and mould pressing integrated forming process. By doping the nitrogen element in the expanded graphite, the wettability of the pole piece to an electrolyte can be improved, pores of the expanded graphite can be used as transmission channels of ions between graphite sheet layers, and then by utilizing a microscopic two-dimensional sheet structure of the expanded graphite and direct molding through mold pressing, efficient compounding of graphite and silicon is realized, and preparation of the negative pole piece is completed in one step. The breakthrough of the thickness of the pole piece reaches the magnitude of 1 mm (far exceeding the level of tens of microns of a traditional current collector), and meanwhile, the pole piece has high rate performance and excellent cycle stability. Wherein the three-dimensional structure maintains the integrity of the electrode through a mechanical interlocking effect, and the structure has certain elasticity, so that the structure of the material is kept stable in a repeated expansion / contraction process caused by charging and discharging, and the capacity retention ratio is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of negative electrode materials, and in particular to a self-supporting silicon-carbon electrode sheet and a preparation method thereof. Background Art

[0002] Since its inception, lithium-ion batteries, with their high specific energy, high operating voltage, low self-discharge rate, compact size, and light weight, have revolutionized the energy storage field and are widely used in various portable electronic devices and electric vehicles. However, with the improvement of people's living standards, the demand for a better user experience has placed higher demands on lithium-ion batteries: lighter weight and longer battery life. To address these issues, it is necessary to find new electrode materials with better performance.

[0003] Silicon-carbon negative electrode materials have become the focus of attention in negative electrode materials due to the high specific capacity of silicon (theoretical capacity is about 4200mAh / g, which is 10 times that of graphite); however, they still face the problem of cycle life degradation caused by electrode pulverization due to the rapid volume expansion of the silicon phase (~300%), as well as the difficulty of balancing complex nanostructure design with large-scale production costs.

[0004] Most existing methods use composite electrode materials to improve the performance of silicon-carbon anodes. For example, they use carbon-coated silicon materials or carbon-skeleton composite silicon materials to prepare silicon-carbon composite material powders, and then coat the anode material on the current collector using a binder and a conductive agent. Although such methods can effectively improve the performance of the anode, they have limited silicon loading capacity and are unable to cope with the volume expansion of the silicon anode material during the charge and discharge process, resulting in a shorter battery life. At the same time, the slurry coating process leads to poor construction of the electrode conductive network, which also limits the rate performance of the silicon anode and prevents the electrode from being thicker. Therefore, it is necessary to propose a new solution to improve the above problems. Summary of the Invention

[0005] In view of this, the present invention addresses the deficiencies in the prior art, and its main purpose is to provide a self-supporting silicon-carbon electrode sheet and a preparation method thereof, which can effectively solve the problems of limited silicon loading in the existing silicon-carbon negative electrode, difficulty in coping with the volume expansion of the silicon negative electrode material during the charge and discharge process, resulting in a shorter battery life, and the problem that the conductive network of the electrode sheet is poor due to the design of coating on the current collector, resulting in limited rate performance of the silicon-carbon negative electrode and the inability to make the electrode sheet thicker.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a self-supporting silicon-carbon electrode sheet comprises the following steps:

[0008] (1) mixing natural graphite with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:(1-15):(0.05-0.5), allowing the mixture to react at 40°C for 30 minutes, filtering, and washing to obtain expandable graphite;

[0009] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite;

[0010] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is (75-85):(15-25), heating to 1000° C. and holding the mixture for 30 min to obtain nitrogen-doped porous expanded graphite;

[0011] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor so that the interior of the reactor forms an oxygen-free environment, heating to 600-800° C., and then introducing silane gas to perform a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material;

[0012] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:(0.2-20). After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0013] As a preferred embodiment, in step (1), the natural graphite is natural flake graphite.

[0014] As a preferred embodiment, in step (1), the natural graphite is 50-mesh natural flake graphite.

[0015] As a preferred embodiment, in step (3), the inert gas is argon and the nitrogen-containing gas is ammonia.

[0016] As a preferred solution, in step (5), the density of the self-supporting silicon-carbon negative electrode sheet is 0.5-1.0 g / cm 3 , the mass proportion of silicon element is 10%-80%.

[0017] As a preferred embodiment, in step (1), the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalant is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

[0018] A method for preparing a self-supporting silicon-carbon electrode sheet is provided, which is prepared by the above-mentioned method for preparing a self-supporting silicon-carbon electrode sheet.

[0019] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, it can be seen from the above technical solution that:

[0020] By doping expanded graphite with nitrogen, the electrode's wettability with the electrolyte is improved. The pores in the expanded graphite serve as channels for ion transport between the graphite sheets. Utilizing the expanded graphite's microscopic, two-dimensional lamellae, the electrode can be directly molded through compression, achieving efficient graphite and silicon composites and completing the negative electrode fabrication in a single step. This breakthrough allows the electrode thickness to reach the 1mm mark (far exceeding the tens of microns of conventional current collectors), eliminating the need for binders, conductive agents, or metal current collectors while achieving both high-rate performance and excellent cycling stability. The three-dimensional structure maintains electrode integrity through mechanical interlocking, and its structural elasticity ensures structural stability during the repeated expansion and contraction caused by charge and discharge, significantly improving capacity retention.

[0021] In order to more clearly illustrate the structural features and effects of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the self-supporting silicon-carbon electrode sheet prepared by the present invention. DETAILED DESCRIPTION

[0023] The present invention discloses a method for preparing a self-supporting silicon-carbon electrode sheet, which comprises the following steps:

[0024] (1) Natural graphite is mixed with a certain amount of an oxidant and an intercalant, wherein the mass ratio of natural graphite to the intercalant and the oxidant is 1:(1-15):(0.05-0.5), and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalant is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

[0025] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0026] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is (75-85):(15-25), heating to 1000° C. and holding the mixture for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0027] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 600-800° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0028] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:(0.2-20). After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet; the density of the self-supporting silicon-carbon negative electrode sheet is 0.5-1.0 g / cm 3 , the mass proportion of silicon element is 10%-80%; it should be noted that the present invention application makes specific requirements on the size of the molding pressure and the length of the pressing time. Since the bottom area of ​​the pressing cavity of the mold is certain, the pressing area is also certain. A certain amount of material is placed in the pressing cavity of the mold, and the electrode sheet is pressed to a certain thickness through appropriate pressure and pressing time, so that the electrode sheet reaches the target density.

[0029] The following describes it in detail with reference to specific embodiments.

[0030] Example 1

[0031] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:8:0.4, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is hydrogen peroxide, and the intercalant is concentrated sulfuric acid.

[0032] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0033] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 75:25, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0034] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 700° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0035] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:9. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0036] Example 2

[0037] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:11:0.1, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is potassium permanganate, and the intercalant is concentrated nitric acid.

[0038] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0039] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 85:15, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0040] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 750° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0041] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:9. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0042] Example 3

[0043] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:7:0.3, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is potassium dichromate, and the intercalant is perchloric acid.

[0044] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0045] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 80:20, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0046] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 800° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0047] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:4. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0048] Example 4

[0049] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:10:0.5, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is hydrogen peroxide, and the intercalant is concentrated phosphoric acid.

[0050] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0051] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 75:25, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0052] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 600° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0053] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:1. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0054] Example 5

[0055] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:3:0.5, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is hydrogen peroxide, and the intercalant is perchloric acid.

[0056] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0057] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 80:20, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0058] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 800° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0059] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:19. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0060] Example 6

[0061] (1) Natural graphite is mixed with a certain amount of oxidant and intercalant, with the mass ratio of natural graphite to intercalant and oxidant being 1:1:0.2, and the mixture is allowed to stand for reaction at 40°C for 30 minutes, filtered, and washed to obtain expandable graphite; the natural graphite is 50-mesh natural flake graphite, the oxidant is hydrogen peroxide, and the intercalant is concentrated nitric acid.

[0062] (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite.

[0063] (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is 80:20, heating the mixture to 1000° C., and keeping the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite; the inert gas is argon, and the nitrogen-containing gas is ammonia.

[0064] (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor to form an oxygen-free environment inside the reactor, heating it to 800° C., and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material.

[0065] (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:0.4. After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

[0066] Performance tests were conducted on the above-mentioned embodiments, and the test results are shown in Table 1. The reversible gram capacity was tested using a half-button battery, and the value was calculated based on the mass of the electrode.

[0067]

[0068] Table 1

[0069] Combining the observations of the experimental process and the above data, it can be clearly seen that the greater the proportion of silicon-porous expanded graphite composite material, the greater the amount of active material loaded on the electrode; the higher the proportion of nitrogen-doped porous expanded graphite, the easier the electrode is to form, and the three-dimensional bulk structure is more stable, the conductive network is richer, and the lithium insertion and delithiation performance of the electrode can be improved. Therefore, the higher the proportion of nitrogen-doped porous expanded graphite in the electrode, the higher its cycle retention rate.

[0070] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a self-supporting silicon-carbon electrode sheet, characterized in that: The following steps are included: (1) mixing natural graphite with an oxidant and an intercalant, wherein the mass ratio of natural graphite to the intercalant and the oxidant is 1:(1-15):(0.05-0.5), allowing the mixture to react at 40° C. for 30 minutes, filtering, and washing to obtain expandable graphite; (2) placing the expandable graphite obtained in step (1) under an inert gas atmosphere and heating it to 1000° C. to obtain expanded graphite; (3) placing the expanded graphite obtained in step (2) in an atmosphere of a mixed gas consisting of an inert gas and a nitrogen-containing gas, wherein the volume ratio of the inert gas to the nitrogen-containing gas is (75-85):(15-25), heating to 1000° C. and holding the mixture for 30 min to obtain nitrogen-doped porous expanded graphite; (4) taking part of the nitrogen-doped porous expanded graphite obtained in step (3) and placing it in a reactor, introducing an inert gas to replace the air inside the reactor so that the interior of the reactor forms an oxygen-free environment, heating to 600-800° C., and then introducing silane gas to perform a chemical vapor deposition reaction to obtain a silicon-porous expanded graphite composite material; (5) The nitrogen-doped porous expanded graphite obtained in step (3) is mixed with the silicon-porous expanded graphite composite material obtained in step (4), wherein the mass ratio of the nitrogen-doped porous expanded graphite to the silicon-porous expanded graphite composite material is 1:(0.2-20). After uniform mixing, the mixture is flattened and molded to obtain a self-supporting silicon-carbon negative electrode sheet.

2. The method for preparing a self-supporting silicon-carbon electrode sheet according to claim 1, wherein: In the step (1), the natural graphite is natural flake graphite.

3. The method for preparing a self-supporting silicon-carbon electrode sheet according to claim 2, wherein: In the step (1), the natural graphite is 50-mesh natural flake graphite.

4. The method for preparing a self-supporting silicon-carbon electrode sheet according to claim 1, wherein: In the step (3), the inert gas is argon, and the nitrogen-containing gas is ammonia.

5. The method for preparing a self-supporting silicon-carbon electrode sheet according to claim 1, wherein: In the step (5), the density of the self-supporting silicon-carbon negative electrode sheet is 0.5-1.0 g / cm 3 , the mass proportion of silicon element is 10%-80%.

6. The method for preparing a self-supporting silicon-carbon electrode sheet according to claim 1, wherein: In the step (1), the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalant is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

7. A method for preparing a self-supporting silicon-carbon electrode sheet, characterized in that: The self-supporting silicon-carbon electrode sheet is prepared by the preparation method of any one of claims 1 to 6.

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