Silicon-based negative electrode sheet, preparation method thereof, and lithium ion battery

Abstract

The application provides a silicon-based negative electrode sheet, a preparation method thereof and a lithium ion battery. The silicon-based negative electrode sheet comprises a porous current collector and a silicon-containing material, the silicon-containing material is attached to the pores of the porous current collector, and the porous current collector is a porous carbon material. On the one hand, the network structure of the porous carbon material itself greatly reduces the resistivity of the silicon-based negative electrode sheet, thereby enhancing the toughness of the silicon-based negative electrode sheet, and effectively preventing the expansion of the silicon-based negative electrode sheet. On the other hand, the network structure of the porous carbon material itself covers the particle surfaces of the silicon-carbon material and establishes a highly conductive, firm and durable connection between the silicon particles. In addition, compared with a metal current collector, the porous carbon material has the advantages of low density, low cost and corrosion resistance. Therefore, using the porous carbon material as the negative electrode current collector can reduce the content of the conductive agent in the silicon-based negative electrode sheet, and improve the proportion of the silicon-carbon material in the entire silicon-based negative electrode sheet, thereby further improving the energy density of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a silicon-based negative electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] The improvement of battery energy density mainly relies on the development of key electrode materials, such as the continuous improvement of the capacity of positive and negative electrode materials. The capacity of existing lithium-ion battery negative electrode materials is approaching its limit. Taking graphite-based negative electrodes (which account for as much as 98% of lithium-ion battery negative electrode materials) as an example, the specific capacity of graphite-based negative electrodes is above 350 mAh / g, which is close to the theoretical upper limit of 372 mAh / g. Therefore, in order to meet the energy demands of the next generation, it is urgent to develop new types of lithium-ion battery negative electrodes to improve battery energy density.

[0003] Currently, silicon-based anodes have significant advantages, with a theoretical specific capacity of up to 4200 mAh / g, more than 10 times that of graphite materials. Furthermore, silicon-based anodes provide lithium-ion insertion and extraction channels from various directions, offering excellent fast-charging performance, making them the future direction for anode development. However, issues such as severe volume expansion during lithium insertion, poor material conductivity, and poor initial efficiency and cycle performance limit their commercial application. Summary of the Invention

[0004] The main objective of this invention is to provide a silicon-based anode sheet and its preparation method, as well as a lithium-ion battery, to solve the problem of severe volume expansion of silicon-based anodes in the prior art.

[0005] To achieve the above objectives, according to one aspect of the present invention, a silicon-based negative electrode is provided, the silicon-based negative electrode comprising a porous current collector and a silicon-containing material, the silicon-containing material being attached to the pores of the porous current collector, the porous current collector being a porous carbon material.

[0006] Furthermore, the porosity of the above-mentioned porous current collector is 50-90%, and preferably the pore size of the porous current collector is 50-100 μm. More preferably, the porous current collector is selected from any one or more of carbon fiber, carbon cloth, carbon nanotubes, and carbon foam.

[0007] Furthermore, the aforementioned silicon-based negative electrode sheet also includes a functional additive used to bind the porous current collector and the silicon-containing material. Preferably, the mass ratio of the porous current collector to the silicon-containing material is 5-15:100. Preferably, the mass of the functional additive is 0.2-5% of the silicon-containing material. Preferably, the silicon-containing material is selected from any one or more of silicon oxide, silicon carbide, micron-sized silicon, nano-sized silicon, pre-lithium-intercalated modified silicon oxide, graphite, and a mixture of silicon oxide. Further, it is preferred that the silicon-containing material is a mixture of graphite and silicon oxide, and the mass ratio of silicon oxide to graphite in the mixture is 1:1-4. Preferably, the functional additive is a dopamine monomer.

[0008] Furthermore, the thickness of the aforementioned silicon-based anode sheet is 6–200 μm. Preferably, the silicon-based anode sheet also includes a binder and a conductive agent. The binder is preferably selected from any one or more of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinyl alcohol. The conductive agent is preferably selected from any one or more of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0009] According to another aspect of the present invention, a method for preparing the above-mentioned silicon-based anode sheet is provided, the method comprising: step S1, coating a negative electrode slurry comprising silicon-containing material onto the surface of a porous current collector to obtain an active current collector; step S2, drying, rolling and stamping the active current collector to obtain a silicon-based anode sheet.

[0010] Further, step S1 above includes surface modification treatment of the porous current collector. Preferably, the surface modification treatment process includes: step S11, oxidizing the porous current collector with an oxidizing agent solution to obtain an oxidized current collector; step S12, washing the oxidized current collector to obtain a washed current collector; step S13, immersing the washed current collector in a functional additive solution to obtain a modified porous current collector; the oxidizing agent solution is a nitric acid solution with a concentration of 50-90 wt%, preferably the oxidation treatment time is 20-60 min, and preferably the NO3 in the washed current collector is... - The residual amount is <50ppm; the preferred functional additive solution is a dopamine monomer solution, the preferred concentration of the dopamine monomer solution is 2-3g / L, and the preferred solvent in the dopamine monomer solution is Tris-HCl buffer solution; the preferred impregnation time is 10-24h.

[0011] Further, in step S1 above, the porous current collector is simultaneously coated on its relative surfaces. Preferably, the coating speed is 10–50 m / min, the solid content of the negative electrode slurry is 35–50 wt%, and the viscosity of the negative electrode slurry is 3000–7000 mPa·s. -1 .

[0012] Furthermore, in step S2 above, the drying temperature is 60–150°C.

[0013] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned silicon-based negative electrode.

[0014] Furthermore, a metal crimp sleeve is used to connect the porous current collector of the silicon-based negative electrode to the metal wire of the lithium-ion battery.

[0015] By applying the technical solution of this invention, on the one hand, the network structure of the porous carbon material itself greatly reduces the resistivity of the silicon-based anode sheet, thereby enhancing its toughness and effectively preventing its expansion. On the other hand, the network structure of the porous carbon material covers the surface of the silicon-carbon material particles and establishes a highly conductive, strong, and durable connection between the silicon particles. Even if the silicon particles expand in volume and begin to crack, the porous carbon material can maintain a good connection between them, thus preventing the silicon-carbon material from breaking. This allows the lithium-ion battery to have high capacity while also possessing excellent cycle stability and first-efficiency performance. Furthermore, compared with metal current collectors, porous carbon materials have advantages such as low density, low cost, and corrosion resistance. Therefore, using porous carbon materials as a current collector can reduce the conductive agent content in the silicon-based anode sheet and increase the proportion of silicon-carbon material in the entire silicon-based anode sheet, further improving the energy density of the battery cell. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 SEM images of the modified carbon fibers obtained according to Example 1 of the present invention are shown;

[0018] Figure 2 A SEM image of a silicon-based negative electrode obtained according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] As analyzed in the background section of this application, there is a serious problem of volume expansion in silicon-based anodes in the prior art. In order to solve this problem, this application provides a silicon-based anode sheet and its preparation method, as well as a lithium-ion battery.

[0021] In a typical embodiment of this application, a silicon-based negative electrode is provided, which includes a porous current collector and a silicon-containing material. The silicon-containing material is attached to the pores of the porous current collector, and the porous current collector is a porous carbon material.

[0022] The silicon-based anode material of this application, on the one hand, utilizes the network structure of porous carbon material itself to greatly reduce the resistivity of the silicon-based anode material, thereby enhancing its toughness and effectively preventing its expansion. On the other hand, the network structure of the porous carbon material itself covers the surface of the silicon-containing material particles and establishes highly conductive, strong, and durable connections between the silicon particles. Even if the silicon particles expand in volume and begin to crack, the porous carbon material can still maintain good connections between the silicon particles, thereby preventing the silicon-containing material from breaking. This allows the lithium-ion battery to have high capacity while also possessing excellent cycle stability, first-efficiency performance, and other electrical properties. In addition, compared with metal current collectors, porous carbon materials have advantages such as low density, low cost, and corrosion resistance. Therefore, using porous carbon materials as a negative electrode current collector can reduce the conductive agent content in the silicon-based anode material and increase the proportion of silicon-containing material in the entire silicon-based anode material, further improving the energy density of the battery cell.

[0023] To improve the permeation efficiency and effect of silicon-containing materials in the pores of porous current collectors, the porosity of the porous current collectors is preferably 50-90%, and the pore size of the porous current collectors is preferably 50-100 μm. Further, the porous current collectors are preferably selected from any one or more of carbon fibers, carbon cloth, carbon nanotubes, and carbon foam.

[0024] In one embodiment of this application, the silicon-based negative electrode further includes a functional additive used to bond the porous current collector and the silicon-containing material. Preferably, the mass ratio of the porous current collector to the silicon-containing material is 5-15:100. Preferably, the mass of the functional additive is 0.2-5% of the silicon-containing material. Preferably, the silicon-containing material is selected from any one or more of silicon oxide, silicon carbide, micron-sized silicon, nano-sized silicon, pre-lithium-intercalated modified silicon oxide, graphite, and a mixture of silicon oxide. Further, it is preferred that the silicon-containing material is a mixture of graphite and silicon oxide, and the mass ratio of silicon oxide to graphite in the mixture is 1:1-4. Preferably, the functional additive is a dopamine monomer.

[0025] Functional additives enhance the penetration of the negative electrode slurry into the pores of the porous current collector, and improve the adhesion between the negative electrode slurry, especially the silicon-carbon material, and the pores of the porous current collector. Preferred types of silicon-containing materials and functional additives, as well as preferred mass ratios of the porous current collector, silicon-containing materials, and functional additives, help to maximize the proportion of silicon-containing materials in an equivalent mass of negative electrode sheet while ensuring firm adhesion of the silicon-containing material to the porous current collector, thereby improving the electrical performance of the lithium-ion battery, such as capacity.

[0026] In one embodiment of this application, the thickness of the silicon-based negative electrode sheet is 6 to 200 μm. Preferably, the silicon-based negative electrode sheet further includes a binder and a conductive agent. Preferably, the binder is selected from any one or more of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinyl alcohol. Preferably, the conductive agent is selected from any one or more of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0027] For current collectors of the same thickness, coating the negative electrode slurry onto the surface of the porous current collector helps reduce the thickness of the silicon-based negative electrode sheet. Preferably, the thickness of the silicon-based negative electrode sheet is within the aforementioned range, which facilitates the fabrication of thinner silicon-based negative electrode sheets with higher rate capability and higher energy density. Binders improve the bonding effect between the various components and the porous current collector, while conductive agents improve the overall conductivity of the silicon-based negative electrode sheet. Preferred types of binders and conductive agents help to leverage their respective advantages and achieve better synergistic effects among the components, resulting in a lithium-ion battery with excellent overall electrical performance.

[0028] In another typical embodiment of this application, a method for preparing the aforementioned silicon-based negative electrode sheet is provided. The method includes: step S1, coating a negative electrode slurry containing silicon material onto the surface of a porous current collector to obtain an active current collector; step S2, drying, rolling, and stamping the active current collector to obtain a silicon-based negative electrode sheet.

[0029] The above preparation method utilizes the network structure of porous carbon materials to significantly reduce the resistivity of silicon-based anode sheets, thereby enhancing their toughness and effectively preventing expansion. Furthermore, the network structure of the porous carbon materials covers the surface of silicon-containing material particles and establishes highly conductive, robust, and durable connections between them. Even if silicon particles expand in volume and begin to crack, the porous carbon materials maintain good connections, preventing the silicon-containing material from breaking. This results in lithium-ion batteries with high capacity, excellent cycle stability, and good first-efficiency performance. In addition, compared to metal current collectors, porous carbon materials have advantages such as low density, low cost, and corrosion resistance. Therefore, using porous carbon materials as a current collector can reduce the conductive agent content in silicon-based anode sheets and increase the proportion of silicon-containing materials in the entire anode sheet, further improving the energy density of the battery cell. Moreover, the above preparation method is simple and easy to industrialize.

[0030] The above-mentioned methods for coating the negative electrode slurry can be conventional coating methods in existing technologies such as extrusion coating, which will not be elaborated here.

[0031] To improve the uniformity of the negative electrode slurry, it is preferable to first dry mix the silicon carbon material and the conductive agent. The preferred dry mixing speed is 20-40 r / min and the time is 20-50 min. Then, the binder is added and kneaded at a speed of 20-50 r / min. The dispersion speed is controlled at 40-100 r / min, the dispersion disc speed is 3000-5000 r / min, and the dispersion time is 3-5 h. After uniform dispersion, the remaining water is added, the resulting slurry is stirred, and then sieved to obtain the negative electrode slurry.

[0032] In some embodiments of this application, step S1 includes surface modification of the porous current collector. Preferably, the surface modification process includes: step S11, oxidizing the porous current collector with an oxidizing agent solution to obtain an oxidized current collector; step S12, washing the oxidized current collector to obtain a washed current collector; and step S13, immersing the washed current collector in a functional additive solution to obtain a modified porous current collector. The oxidizing agent solution is a nitric acid solution with a concentration of 50–90 wt%, and the oxidation treatment time is preferably 20–60 min. Preferably, the NO3- in the washed current collector is... - The residual amount is <50ppm; the preferred functional additive solution is a dopamine monomer solution, the preferred concentration of the dopamine monomer solution is 2-3g / L, and the preferred solvent in the dopamine monomer solution is Tris-HCl buffer solution; the preferred impregnation time is 10-24h.

[0033] The above-mentioned surface modification treatment of porous current collectors is beneficial to change the surface roughness, the functional groups contained on the surface, and other properties, thereby increasing the probability of negative electrode slurry penetrating into the pores of the porous current collector, and thus incorporating negative electrode slurry including silicon carbon materials into the porous current collector.

[0034] Oxidation treatment of porous current collectors with an oxidizing agent solution can generate active groups such as carboxyl and hydroxyl groups on their surface. The amount of these groups increases with the extension of oxidation time and the increase of temperature. The preferred oxidation treatment time is 20 to 60 minutes, which significantly increases the various oxygen-containing polar groups and grooves on the surface of the porous current collector. This is beneficial to improving the bonding force between the porous current collector and the negative electrode slurry, and further helps the negative electrode slurry to penetrate into the pores of the porous current collector.

[0035] If the concentration of the nitric acid solution is too low, it will hinder the improvement of oxidation efficiency; if the concentration is too high, the porous current collector will be corroded by the strong acid during the oxidation process, resulting in a significant loss of strength and thus affecting its performance. A nitric acid solution with a concentration of 50–90 wt% is preferred as the oxidant solution. Ideally, the NO3 in the carbon material after washing should also be minimized. - Residual levels <50 ppm are beneficial for reducing NO3. -The impact on the performance of silicon-based anode sheets.

[0036] The preferred soaking time is 10 to 24 hours, which helps to more fully adsorb the functional additives into the collector after washing.

[0037] To prevent the negative electrode slurry from leaking out of the pores of the porous current collector during the coating process, it is preferable that the opposing surfaces of the porous current collector be coated simultaneously in step S1 above. The preferred coating speed is 10–50 m / min, which helps to balance coating efficiency and coating effect. Negative electrode slurry that is too thin or too thick is detrimental to coating. Preferably, the solid content of the negative electrode slurry is 35–50 wt%, and the preferred viscosity is 3000–7000 mPa·s. -1 This facilitates a smoother coating and minimizes the workload of subsequent drying, thus making it easier to adhere the slurry to the porous current collector.

[0038] To improve the efficiency and effectiveness of drying and to save energy as much as possible, the drying temperature in step S2 is preferably 60-150°C.

[0039] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned silicon-based negative electrode.

[0040] Lithium-ion batteries, including the silicon-based anode sheet of this application, have high capacity and excellent electrical performance such as cycle stability and first-efficiency.

[0041] The aforementioned porous current collector is a non-metallic material. To better integrate the silicon-based negative electrode sheet with the metal wire, a metal crimp sleeve is preferably used to connect the porous current collector of the silicon-based negative electrode sheet to the metal wire of the lithium-ion battery. A pressure of 50–1000 MPa is preferred to achieve a tighter connection between the silicon-based negative electrode sheet and the metal wire, thereby improving the reliability of the lithium-ion battery. Furthermore, the porous current collector of this application has high thermal conductivity, resulting in rapid heat dissipation at the junction of the silicon-based negative electrode sheet and the metal wire, thus improving its service life.

[0042] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0043] Example 1

[0044] Ten parts by weight of carbon fiber TGP-H-60 were oxidized for 30 minutes using 60 wt% nitric acid to obtain oxidized carbon fiber. The residual oxidant on the oxidized carbon fiber was removed by washing with water, and NO3 was tested after eight washes. -The residual concentration was 40 ppm, yielding washed carbon fibers. These washed carbon fibers were then immersed in a dopamine monomer buffer solution (2 g / L, containing 3 parts by weight of dopamine monomer) for 24 h to obtain modified carbon fibers. The modified carbon fibers had a porosity of 80% and a pore size of 50-95 μm. SEM images of the modified carbon fibers are shown below. Figure 1 As shown.

[0045] The specific mixing process involves first dry mixing 25 parts by weight of silicon oxide (SiO), 75 parts by weight of graphite, and 2 parts by weight of carbon black at a stirring speed of 20 r / min for 30 minutes. Then, 5 parts by weight of polyacrylic acid are added and stirred at a stirring speed of 25 r / min for 30 minutes. The mixture is then dispersed at a dispersion speed of 40 r / min and a dispersion disc speed of 4000 r / min for 3 hours. Water is added to adjust the solid content, resulting in a negative electrode slurry with a solid content of 35 wt% and a viscosity of 4200 mPa·s. -1 .

[0046] Using a double-sided coating technique and controlling the coating speed at 30 m / min, the negative electrode slurry is coated onto the surface of the modified carbon fiber. After drying at 100℃, rolling, and stamping, a silicon-based negative electrode sheet is formed. The SEM image of this silicon-based negative electrode sheet is shown below. Figure 2 As shown.

[0047] Example 2

[0048] The difference from Example 1 is that the dopamine monomer buffer solution contains 0.2 parts by weight of dopamine monomer, and a silicon-based anode sheet is finally obtained.

[0049] Example 3

[0050] The difference from Example 1 is that the dopamine monomer buffer solution contains 5 parts by weight of dopamine monomer, and a silicon-based anode sheet is finally obtained.

[0051] Example 4

[0052] The difference from Example 1 is that the dopamine monomer buffer solution contains 0.1 parts by weight of dopamine monomer, and a silicon-based anode sheet is finally obtained.

[0053] Example 5

[0054] The difference from Example 1 is that a porous current collector (carbon cloth) is added, and the resulting modified carbon fiber has a porosity of 90% and a pore size of 50-80 μm, ultimately yielding a silicon-based anode sheet.

[0055] Example 6

[0056] The difference from Example 1 is that the concentration of the dopamine monomer buffer solution is 3 g / L, the porosity of the modified carbon fiber is 45%, the pore size is 50-60 μm, and a silicon-based anode sheet is finally obtained.

[0057] Example 7

[0058] The difference from Example 1 is that a 50wt% nitric acid solution was added, resulting in a modified carbon fiber with a porosity of 50% and a pore size of 50-70μm, ultimately yielding a silicon-based anode sheet.

[0059] Example 8

[0060] The difference from Example 1 is that a 90wt% nitric acid solution was added, resulting in a modified carbon fiber with a porosity of 80% and a pore size of 50-80μm, ultimately yielding a silicon-based anode sheet.

[0061] Example 9

[0062] The difference from Example 1 is that a 40wt% nitric acid solution was added, resulting in a modified carbon fiber with a porosity of 45% and a pore size of 50-70μm, ultimately yielding a silicon-based anode sheet.

[0063] Example 10

[0064] The difference from Example 1 is that the oxidation treatment time is 20 min, the porosity of the modified carbon fiber is 50%, the pore size is 50-70 μm, and a silicon-based anode sheet is finally obtained.

[0065] Example 11

[0066] The difference from Example 1 is that the oxidation treatment time is 60 min, the porosity of the modified carbon fiber is 80%, the pore size is 50-80 μm, and a silicon-based anode sheet is finally obtained.

[0067] Example 12

[0068] The difference from Example 1 is that the oxidation treatment time is 15 min, the porosity of the modified carbon fiber is 45%, the pore size is 30-48 μm, and a silicon-based anode sheet is finally obtained.

[0069] Example 13

[0070] The difference from Example 1 is that the impregnation time is 10 hours, the porosity of the modified carbon fiber is 80%, the pore size is 50-80 μm, and a silicon-based anode sheet is finally obtained.

[0071] Example 14

[0072] The difference from Example 1 is that the impregnation time is 24 hours, the porosity of the modified carbon fiber is 80%, the pore size is 50-100 μm, and a silicon-based anode sheet is finally obtained.

[0073] Example 15

[0074] The difference from Example 1 is that the impregnation time is 5 hours, the porosity of the modified carbon fiber is 40%, the pore size is 30-45 μm, and a silicon-based anode sheet is finally obtained.

[0075] Example 16

[0076] The difference from Example 1 is that the double-sided coating technology is used, and the coating speed is controlled at 50m / min. The resulting modified carbon fiber has a porosity of 80% and a pore size of 50-80μm, ultimately yielding a silicon-based anode sheet.

[0077] Example 17

[0078] The difference from Example 1 is that the solid content of the negative electrode slurry is 50wt%, the porosity of the modified carbon fiber is 80%, the pore size is 50-80μm, and finally a silicon-based negative electrode sheet is obtained.

[0079] Example 18

[0080] The difference from Example 1 is that the viscosity of the negative electrode slurry is 7000 mPa·s. -1 The resulting modified carbon fiber has a porosity of 80% and a pore size of 50-80 μm, ultimately yielding a silicon-based anode sheet.

[0081] Example 19

[0082] The difference from Example 1 is that the negative electrode slurry is coated on the surface of the modified carbon fiber, and after drying at 60°C, rolling and stamping, a silicon-based negative electrode sheet is formed.

[0083] Example 20

[0084] The difference from Example 1 is that the amount of silicon oxide (SiO) is 50 parts by weight and the amount of graphite is 50 parts by weight, resulting in a silicon-based anode sheet.

[0085] Example 21

[0086] The difference from Example 1 is that the amount of silicon oxide (SiO) is 20 parts by weight and the amount of graphite is 80 parts by weight, resulting in a silicon-based anode sheet.

[0087] Example 22

[0088] The difference from Example 1 is that the amount of silicon oxide (SiO) is 60 parts by weight and the amount of graphite is 40 parts by weight, resulting in a silicon-based anode sheet.

[0089] Example 23

[0090] The difference from Example 1 is that the carbon fiber TGP-H-60 is 15 parts by weight, and a silicon-based anode sheet is finally obtained.

[0091] Example 24

[0092] The difference from Example 1 is that the carbon fiber TGP-H-60 is 5 parts by weight, and a silicon-based anode sheet is finally obtained.

[0093] Example 25

[0094] The difference from Example 1 is that the carbon fiber TGP-H-60 is 4 parts by weight, and a silicon-based anode sheet is finally obtained.

[0095] Example 26

[0096] The difference from Example 1 is that the negative electrode slurry is directly coated on the surface of carbon fibers that have not been surface modified, and then dried at 100°C, rolled and stamped to form a silicon-based negative electrode sheet.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that the negative electrode slurry is directly coated on the surface of the copper current collector, and then dried at 100°C, rolled, and stamped to form a copper-based negative electrode sheet.

[0099] The porosity, pore size, and electrode sheet thickness of the carbon fibers obtained in Examples 1 to 26 are listed in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] The silicon-based negative electrode sheets of Examples 1 to 26 above were assembled with NCM ternary positive electrode (model WXO4Mg) to form batteries, and the copper-based negative electrode sheet of Comparative Example 1 was assembled with NCM ternary positive electrode (model WXO4Mg) to form batteries. The number of cycles when the cycle capacity retention rate of the batteries was 80% was tested at 25°C, voltage range of 2.5 to 4.25V, and 1C. The test results are listed in Table 2.

[0104] Table 2

[0105]

[0106]

[0107] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0108] On the one hand, the network structure of porous carbon materials significantly reduces the resistivity of silicon-based anode sheets, thereby enhancing their toughness and effectively preventing expansion. On the other hand, the network structure of porous carbon materials covers the surface of silicon-carbon particles and establishes highly conductive, robust, and durable connections between them. Even if silicon particles expand in volume and begin to crack, the porous carbon material maintains good connections between them, preventing the silicon-carbon material from breaking. This allows lithium-ion batteries to have high capacity while also exhibiting excellent cycle stability and first-efficiency performance. Furthermore, compared to metal current collectors, porous carbon materials offer advantages such as low density, low cost, and corrosion resistance. Therefore, using porous carbon materials as a current collector can reduce the conductive agent content in silicon-based anode sheets and increase the proportion of silicon-carbon materials in the entire anode sheet, further improving the energy density of the battery cell.

[0109] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon-based negative electrode sheet, characterized by, The silicon-based negative electrode sheet comprises a porous current collector and a silicon-containing material, the silicon-containing material is attached to the pores of the porous current collector, and the porous current collector is a porous carbon material; The porosity of the porous current collector is 50-90%, and the pore size of the porous current collector is 50-100 μm; The silicon-based negative electrode sheet further comprises a functional additive, and the functional additive is used to bond the porous current collector and the silicon-containing material; The mass ratio of the porous current collector to the silicon-containing material is 5-15:100, the functional additive is a dopamine monomer, the mass of the functional additive is 0.2-5% of the silicon-containing material, and the silicon-containing material is a mixture of graphite and silicon oxide, and the mass ratio of the silicon oxide to the graphite in the mixture is 1:1-4; The preparation method of the silicon-based negative electrode sheet comprises the following steps: S1, coating negative electrode slurry comprising a silicon-containing material on the surface of a porous current collector to obtain an active current collector; S2, drying, rolling and punching the active current collector to obtain a silicon-based negative electrode sheet; In the step S1, the porous current collector is subjected to surface modification treatment, and the surface modification treatment process comprises the following steps: S11, oxidizing the porous current collector by an oxidizing agent solution to obtain an oxidized current collector; S12, washing the oxidized current collector to obtain a washed current collector; S13, immersing the washed current collector in a functional additive solution to obtain a modified porous current collector; The oxidizing agent solution is a nitric acid solution with a concentration of 50-90 wt%, the oxidation treatment time is 20-60 min, and the immersion time is 10-24 h.

2. The silicon-based negative electrode sheet according to claim 1, characterized by The porous current collector is selected from any one or more of carbon fibers, carbon cloth, carbon nanotubes and foamed carbon.

3. The silicon-based negative electrode sheet according to claim 1 or 2, characterized by, The thickness of the silicon-based negative electrode sheet is 6-200 μm.

4. The silicon-based negative electrode sheet according to claim 3, characterized by The silicon-based negative electrode sheet further comprises a binder and a conductive agent.

5. The silicon-based negative electrode sheet according to claim 4, characterized by The binder is selected from any one or more of styrene-butadiene rubber, sodium carboxymethyl cellulose and polyvinyl alcohol.

6. The silicon-based negative electrode sheet according to claim 4, wherein The conductive agent is selected from any one or more of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes and graphene.

7. The silicon-based negative electrode sheet according to claim 1, wherein NO3in the post-wash current collector - residual amount < 50 ppm.

8. The silicon-based negative electrode sheet according to claim 1, wherein The functional additive solution is a dopamine monomer solution.

9. The silicon-based negative electrode sheet according to claim 8, wherein The concentration of the dopamine monomer solution is 2-3 g / L.

10. The silicon-based negative electrode sheet according to claim 8, wherein The solvent in the dopamine monomer solution is a Tris-HCl buffer solution.

11. The silicon-based negative electrode sheet according to claim 1, characterized by, In the step S1, The relative surface of the porous current collector is simultaneously coated.

12. The silicon-based negative electrode sheet according to claim 11, characterized by The coating speed is 10-50 m / min.

13. The silicon-based negative electrode sheet according to claim 11, characterized by The solid content of the negative electrode slurry is 35-50 wt%.

14. The silicon-based negative electrode sheet according to claim 11, characterized by, The viscosity of the negative electrode slurry is 3000-7000 mPa.s -1 .

15. The silicon-based negative electrode sheet according to claim 1, wherein In the step S2, The drying temperature is 60-150 ℃.

16. A lithium-ion battery comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, characterized by, The negative electrode sheet is the silicon-based negative electrode sheet according to any one of claims 1-15.

17. The lithium-ion battery of claim 16, wherein, The porous current collector of the silicon-based negative electrode sheet is connected with the metal lead wire of the lithium ion battery by a metal crimping sleeve.

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