High-compaction silicon-carbon negative electrode plate with porous CVD (chemical vapor deposition) silicon-carbon material, preparation method of high-compaction silicon-carbon negative electrode plate and battery

Abstract

The invention discloses a high-compaction silicon-carbon negative electrode plate with a porous CVD silicon-carbon material, a preparation method of the high-compaction silicon-carbon negative electrode plate and a battery, and belongs to the technical field of lithium ion batteries. The high-compaction silicon-carbon negative electrode plate with the porous CVD silicon-carbon material comprises a negative electrode current collector, an inner coating and an outer coating, wherein the inner coating and the outer coating are provided with negative electrode active substances; the inner coating is arranged on the surface of at least one side of the negative electrode current collector, and the outer coating is arranged on the surface of one side, far away from the negative electrode current collector, of the inner coating; the negative active material of the inner coating is a carbon material, and the negative active material of the outer coating comprises a carbon material and a porous CVD silicon carbon material; and the compaction density of the outer coating is smaller than that of the inner coating. The performance of the negative plate and the battery can be improved.

Description

Technical Field

[0001] The present invention relates to a high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material, a preparation method thereof, and a battery, belonging to the technical field of lithium-ion batteries. Background Art

[0002] Porous CVD silicon-carbon materials are composite materials created by depositing nanosilicon particles onto a carbon skeleton using chemical vapor deposition. Based on theoretical analysis, their application to improving the energy density of lithium-ion batteries is highly promising. This is because the highly porous carbon skeleton can accommodate the large lithium-silicon alloy formed by the embedding of lithium ions into the silicon material, overcoming the drawbacks of adding silicon alone, such as battery volume expansion and poor cycling performance.

[0003] However, the presence of a carbon skeleton structure makes the compaction density of the negative electrode sheet containing porous CVD silicon-carbon material much lower than that of traditional graphite negative electrode sheets. Lower compaction density means lower volumetric energy density of the battery cell. However, excessive rolling of the porous CVD silicon-carbon material to increase the compaction density often causes the carbon skeleton structure to break, and the broken particles are exposed on the surface of the electrode sheet, contacting the electrolyte, which also leads to a decrease in the battery's cycle performance and is not conducive to improving the performance of the negative electrode sheet and battery. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present invention proposes a high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material, a preparation method thereof, and a battery, which can improve the performance of the negative electrode sheet and the battery.

[0005] A first aspect of the present invention relates to a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material, comprising a negative electrode current collector, and an inner coating and an outer coating having a negative electrode active material;

[0006] The inner coating is provided on at least one side of the negative electrode current collector, and the outer coating is provided on the inner coating on a side away from the negative electrode current collector;

[0007] The negative electrode active material of the inner coating layer is a carbon material, and the negative electrode active material of the outer coating layer includes a carbon material and a porous CVD silicon-carbon material;

[0008] The outer coating layer has a lower compaction density than the inner coating layer.

[0009] A second aspect of the present invention relates to a method for preparing a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material, comprising the following steps:

[0010] Providing an inner coating slurry; in terms of weight ratio, the inner coating slurry comprises 35% to 70% of a negative electrode active material carbon material, 0.1% to 1.5% of a conductive agent, 0.2% to 2.2% of a binder, 0.1% to 2.0% of a dispersant, and the remainder being a solvent;

[0011] Providing an outer coating slurry; in terms of weight ratio, the outer coating slurry comprises 20% to 50% of a negative electrode active material carbon material, 15% to 40% of a negative electrode active material porous CVD silicon carbon material, 0.2% to 0.5% of a plasticizer, 1.0% to 5.0% of a conductive agent, 3% to 15% of a binder, 0.1% to 0.6% of a dispersant, and the remainder being a solvent;

[0012] The inner coating slurry is coated on the negative electrode current collector, dried and solidified, and then preliminarily rolled to form an inner coating on the negative electrode current collector;

[0013] The outer coating slurry is coated on the inner coating, dried and solidified, and then rolled twice to form an outer coating on the negative electrode current collector; the second rolling is hot rolling at a rolling temperature of 50 to 80°C;

[0014] The negative electrode current collector provided with an inner coating and an outer coating is thermally composited with a separator to obtain a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material.

[0015] A third aspect of the present invention relates to a battery comprising the above-mentioned high-density silicon-carbon negative electrode sheet having porous CVD silicon-carbon material.

[0016] Compared with the prior art, the present invention has the following technical effects:

[0017] 1. A double-coated negative electrode sheet with different combinations of negative electrode active materials is used. In particular, a porous CVD silicon-carbon material is applied in the outer coating, forming a coating structure that is dense inside and loose outside. This not only fully utilizes the advantages of high volume energy density of the highly compacted active material, but also the loose outer coating structure does not damage the carbon skeleton, and can fully utilize the buffering effect of the high-porosity active material on battery volume expansion. Compared with traditional graphite negative electrode sheets, this improves the theoretical specific capacity of the battery, solves the problems of battery volume expansion and poor cycle performance compared to conventional silicon-carbon negative electrode sheets, and avoids the problem of low cell volume energy density caused by the use of porous CVD silicon-carbon materials in single-coated negative electrode sheets.

[0018] 2. Double-layer coatings are rolled separately, especially in the second rolling process, hot rolling is used, combined with plasticizers to improve the fluidity of the material, thereby promoting particle rearrangement, which can effectively increase the compaction density of the silicon-carbon negative electrode sheet from the original 1.4g / cm 3 The carbon skeleton shows obvious fragmentation under compaction density, which is increased to a maximum of 1.5g / cm 3The compaction density can still maintain a relatively complete carbon skeleton, achieve a relatively dense outer coating, and improve the performance of the negative electrode and battery;

[0019] 3. The secondary rolling process adopts a step-by-step rolling process of high speed and low pressure first and then low speed and high pressure, so that the plasticizer can fully play its role, gradually release the stress, avoid the coating breakage caused by a single high pressure, and improve the product yield and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the negative electrode sheet in Example 1;

[0021] Figure 2 This is a scanning electron microscope image of the negative electrode sheet in Comparative Example 1. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below in conjunction with specific embodiments. Experimental methods without specific conditions specified in the examples were carried out according to conventional methods and conditions.

[0023] The high-compacted silicon-carbon negative electrode sheet involved in a specific embodiment of the present invention includes: a negative electrode current collector, and an inner coating and an outer coating having a negative electrode active material; the inner coating is arranged on at least one side of the negative electrode current collector, and the outer coating is arranged on the surface of the inner coating away from the negative electrode current collector; the negative electrode active material of the inner coating is a carbon material, and the negative electrode active material of the outer coating includes a carbon material and a porous CVD silicon-carbon material; the compaction density of the outer coating is less than that of the inner coating.

[0024] To maximize the performance of the highly compacted silicon-carbon negative electrode, the present invention employs different designs for the inner and outer coatings. For the inner coating, elemental silicon is avoided; for the outer coating, in addition to the carbon material, a porous CVD silicon-carbon material is added, forming a highly porous, relatively loose structure relative to the inner coating. This allows the highly compacted inner coating to fully contact the electrolyte, maximizing battery performance and accommodating the large volume of lithium-silicon alloy produced. This avoids the direct introduction of elemental silicon into the inner coating, which could lead to structural collapse and deterioration of battery performance, and the direct introduction of porous CVD silicon-carbon material into a single-layer coating structure, which could result in low compaction density and thus reduced battery performance.

[0025] In some specific implementation schemes, the negative electrode current collector is copper foil.

[0026] In some specific embodiments, the inner coating layer may be disposed on the surface of only one side of the negative electrode current collector, or may be disposed on the surfaces of both sides of the negative electrode current collector.

[0027] For some specific embodiments, the compacted density of the inner coating is 1.65 to 1.7 g / cm 3The compacted density of the outer coating is 1.3 to 1.5 g / cm 3 ;

[0028] For example, the compacted density of the inner coating may be 1.65 g / cm 3 , 1.66g / cm 3 , 1.67g / cm 3 , 1.68g / cm 3 , 1.69g / cm 3 , 1.70g / cm 3 wait;

[0029] For example, the topcoat layer may have a tap density of 1.30 g / cm 3 , 1.31g / cm 3 , 1.32g / cm 3 , 1.33g / cm 3 , 1.34g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.37g / cm 3 , 1.38g / cm 3 , 1.39g / cm 3 , 1.40g / cm 3 , 1.41g / cm 3 , 1.42g / cm 3 , 1.43g / cm 3 , 1.44g / cm 3 , 1.45g / cm 3 , 1.46g / cm 3 , 1.47g / cm 3 , 1.48g / cm 3 , 1.49g / cm 3 , 1.50g / cm 3 wait.

[0030] For some specific embodiments, the carbon material is selected from at least one of natural graphite, artificial graphite, hard carbon, soft carbon and carbon fiber.

[0031] In some specific embodiments, the inner coating and the outer coating both include a conductive agent, a dispersant, and a binder;

[0032] Preferably, the conductive agent includes at least one of conductive carbon black, carbon nanotubes and graphene;

[0033] Preferably, the dispersant comprises at least one of sodium carboxymethyl cellulose and sodium polyacrylate;

[0034] Preferably, the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose and styrene-butadiene rubber.

[0035] In some specific embodiments, the outer coating layer further comprises a plasticizer, and the plasticizer is at least one of dibutyl phthalate (DBP) and triethyl citrate (TEC).

[0036] The high-density silicon-carbon negative electrode sheet is prepared by the following steps:

[0037] Providing an inner coating slurry; in terms of weight ratio, the inner coating slurry comprises 35% to 70% of a negative electrode active material carbon material, 0.1% to 1.5% of a conductive agent, 0.2% to 2.2% of a binder, 0.1% to 2.0% of a dispersant, and the remainder being a solvent;

[0038] Providing an outer coating slurry; in terms of weight ratio, the outer coating slurry comprises 20% to 50% of a negative electrode active material carbon material, 15% to 40% of a negative electrode active material porous CVD silicon carbon material, 0.2% to 0.5% of a plasticizer, 1.0% to 5.0% of a conductive agent, 3% to 15% of a binder, 0.1% to 0.6% of a dispersant, and the remainder being a solvent;

[0039] The inner coating slurry is coated on the negative electrode current collector, dried and solidified, and then preliminarily rolled to form an inner coating on the negative electrode current collector;

[0040] The outer coating slurry is coated on the inner coating, dried and solidified, and then rolled twice to form an outer coating on the negative electrode current collector; the second rolling is hot rolling at a rolling temperature of 50 to 80°C;

[0041] The negative electrode current collector provided with an inner coating and an outer coating is thermally compounded with a separator to obtain a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material.

[0042] In some specific embodiments, the solvent includes at least one of deionized water, ethanol, isopropanol, acetone, NMP, THF, EC, and PC.

[0043] For inner coating slurry:

[0044] The weight proportion of the carbon material can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.;

[0045] The weight proportion of the conductive agent can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.;

[0046] The weight proportion of the binder can be 0.2%, 0.5%, 0.7%, 1.0%, 1.3%, 1.5%, 1.7%, 1.8%, 2.0%, 2.2%, etc.;

[0047] The weight proportion of the dispersant can be 0.1%, 0.4%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 1.8%, 2.0%, etc.

[0048] For the outer coating slurry:

[0049] The weight proportion of the carbon material can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.;

[0050] The weight proportion of the porous CVD carbon material can be 15%, 20%, 25%, 30%, 35%, 40%, etc.;

[0051] The weight proportion of the plasticizer can be 0.2%, 0.3%, 0.4%, 0.5%, etc.;

[0052] The weight proportion of the conductive agent can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, etc.;

[0053] The weight proportion of the binder can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.;

[0054] The weight proportion of the dispersant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, etc.

[0055] For some specific implementation schemes, the preliminary rolling can be room temperature rolling or heated rolling; in addition, it is obvious that compared with the outer coating layer added with porous CVD silicon-carbon material, in order to make the inner coating layer as dense as possible, the rolling pressure of the inner coating layer will be significantly higher than that of the outer coating layer; the specific process parameters depend on the type of carbon material and are conventional technologies. For example, for graphite, a linear pressure rolling of 300kN / m is more appropriate.

[0056] For some specific embodiments, for the secondary rolling, the rolling temperature can be 50°C, 53°C, 55°C, 57°C, 60°C, 62°C, 65°C, 69°C, 70°C, 74°C, 75°C, 76°C, 80°C, etc.

[0057] For some specific embodiments, the secondary rolling is carried out in two steps, the first step is rolling at a first speed under a first pressure, followed by a second step of rolling at a second speed under a second pressure; the first pressure is less than the second pressure, the second pressure is less than the initial rolling pressure, and the first speed is greater than the second speed.

[0058] Preferably, the first pressure is 2-7 kN / m, the first speed is 5-8 m / min, the second pressure is 20-30 kN / m, and the second speed is 0.5-1 m / min;

[0059] For example, the first pressure can be 2kN / m, 3kN / m, 4kN / m, 5kN / m, 6kN / m, 7kN / m, etc.; the first speed can be 5m / min, 6m / min, 7m / min, 8m / min, etc.; the second pressure can be 20kN / m, 21kN / m, 22kN / m, 23kN / m, 24kN / m, 25kN / m, 26kN / m, 27kN / m, 28kN / m, 29kN / m, 30kN / m, etc.; the second speed can be 0.5m / min, 0.6m / min, 0.7m / min, 0.8m / min, 0.9m / min, 1.0m / min, etc.

[0060] For some specific embodiments, the temperature of the thermal compounding is 80-120°C; for example, the temperature is 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, etc.

[0061] Example 1

[0062] This embodiment relates to a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material, and the preparation process thereof is as follows:

[0063] S1: 5 kg of artificial graphite (HJ-Ta-1, Qingdao Huajin New Materials Technology Development Co., Ltd.), 0.06 kg of conductive carbon black, 0.21 kg of a 50% solid content styrene-butadiene rubber aqueous solution, and 6.329 kg of a 1.5% solid content sodium carboxymethyl cellulose aqueous solution were mixed to prepare an inner coating slurry with a graphite mass fraction of 43%. The inner coating slurry was coated on both sides of the copper foil at a surface density of 150 g / m² according to the process requirements, and then rolled on a roller press with a linear pressure of 300 kN / m to obtain a compacted density of 1.7 g / cm 3 inner coating;

[0064] S2: 3.656 kg of porous CVD silicon-carbon material (SC-1, Jiangsu Naborn New Materials Co., Ltd.), 5 kg of artificial graphite (HJ-Ta-1), 0.457 kg of carbon nanotubes (BP2000, Cabot Corporation, USA), 0.075 kg of plasticizer dibutyl phthalate, 0.457 kg of a 6% solid content polyacrylic acid aqueous solution, 3.047 kg of a 50% solid content styrene-butadiene rubber aqueous solution, and 3.047 kg of a 1.5% solid content sodium carboxymethyl cellulose aqueous solution were mixed to prepare an outer coating slurry;

[0065] The outer coating slurry was applied to the fully rebounded inner coating and heated and rolled in two steps at 80°C; the first step was a line pressure of 5 kN / m and a speed of 6 m / min; the second step was a line pressure of 25 kN / m and a speed of 0.8 m / min. The final compaction density of the outer coating reached 1.5 g / cm³.

[0066] S3, thermally compounding the copper foil provided with the outer coating and the adhesive-coated separator by using a heating roller at a temperature of 100° C., and then rolling it up to obtain a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material.

[0067] The scanning electron microscope image of the outer coating of the high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material is as follows: Figure 1 shown.

[0068] Example 2

[0069] Compared with Example 1, the difference of this embodiment is:

[0070] Inner coating formula: artificial graphite 4.65kg, conductive carbon black 0.12kg, styrene-butadiene rubber aqueous solution with a mass solid content of 50% 0.25kg, sodium carboxymethyl cellulose aqueous solution with a mass solid content of 1.5% 7.075kg, and the rest is deionized water. After rolling with a linear pressure of 300kN / m, the compacted density is 1.65g / cm 3 inner coating.

[0071] Example 3

[0072] Compared with Example 1, the difference of this embodiment is:

[0073] The outer coating formula is as follows: 4.875 kg of porous CVD silicon carbon material, 3.75 kg of artificial graphite, 0.562 kg of carbon nanotubes, 0.562 kg of polyacrylic acid aqueous solution with a mass solid content of 6%, 3.75 kg of styrene-butadiene rubber aqueous solution with a mass solid content of 50%, 3.75 kg of sodium carboxymethyl cellulose aqueous solution with a mass solid content of 1.5%, and 0.037 kg of plasticizer dibutyl phthalate. The resulting compacted density is 1.30 g / cm 3inner coating.

[0074] Comparative Example 1

[0075] Compared with Example 1, the difference of this comparative example is that a single coating layer is used instead of a double coating layer. Specifically:

[0076] 3.656 kg of porous CVD silicon-carbon material, 10 kg of artificial graphite, 0.06 kg of conductive carbon black, 0.457 kg of carbon nanotubes, 0.457 kg of a polyacrylic acid aqueous solution with a mass solid content of 6%, 3.257 kg of a styrene-butadiene rubber aqueous solution with a mass solid content of 50%, and 6.329 kg of a sodium carboxymethyl cellulose aqueous solution with a mass solid content of 1.5% were mixed to prepare a slurry;

[0077] According to the process requirements, the slurry is coated on the copper foil at a surface density of 150g / m², and then rolled by a roller press with a line pressure of 300kN / m to a compaction density of 1.4g / cm 3 ;

[0078] The coated copper foil and the adhesive-coated separator were thermally laminated at a temperature of 100° C. using a heating roller and then rolled up to produce a silicon-carbon negative electrode sheet.

[0079] The scanning electron microscope image of the coating in the silicon carbon negative electrode sheet is as follows Figure 2 Compare Figure 1 and Figure 2 It can be found that the degree of particle fragmentation in Example 1 is significantly less than that in Comparative Example 1 at the compaction density. This is due to the fragmentation of the porous CVD silicon-carbon material caused by the standard roller pressing of the high-compaction negative electrode active material.

[0080] Comparative Example 2

[0081] Compared with Example 1, the difference of this comparative example is:

[0082] A single coating was used instead of a double coating. The single coating was the same as the inner coating in Example 1 and was rolled according to the standard of the inner coating in Example 1.

[0083] Comparative Example 3

[0084] Compared with Example 1, the difference of this comparative example is:

[0085] A single coating was used instead of a double coating. The single coating was the same as the outer coating in Example 1 and was rolled according to the standard for the outer coating.

[0086] Comparative Example 4

[0087] Compared with Example 1, the difference of this comparative example is:

[0088] The outer coating is formulated without carbon materials, specifically:

[0089] 7.5kg of porous CVD silicon-carbon material, 0.75kg of carbon nanotubes, 0.75kg of polyacrylic acid aqueous solution with a mass solid content of 6%, 3.75kg of styrene-butadiene rubber aqueous solution with a mass solid content of 50%, 3.75kg of sodium carboxymethyl cellulose aqueous solution with a mass solid content of 1.5%, 0.075kg of plasticizer dibutyl phthalate, and 0.054kg of solvent NMP. Rolling was performed at a linear pressure of 10kN / m and a speed of 2m / min to obtain a compacted density of 1.1g / cm 3 outer coating.

[0090] The negative electrode sheets and positive electrode sheets (Rongbai Technology NCM811-G5), separators (Zhuogao PV-12C) and electrolytes (Xinzhoubang LBC-304D) prepared in the above examples and comparative examples were assembled into lithium-ion batteries, and then the electrical properties were tested, and the results shown in Table 1 were obtained.

[0091] Table 1 Volumetric energy density (Wh / L) 500-cycle capacity retention rate Volume expansion rate after 500 cycles Example 1 720 85% 7% Example 2 705 83% 10% Example 3 735 80% 9% Comparative Example 1 650 65% 30% Comparative Example 2 680 88% 35% Comparative Example 3 600 70% 40% Comparative Example 4 580 60% 45%

[0092] Comparing Examples 1 to 3, it can be found that both the inner coating and the outer coating have a significant impact on the battery performance;

[0093] Comparing Example 1 and Comparative Example 1, it can be found that the fragmentation of the carbon skeleton of the porous CVD silicon-carbon material in a single coating layer will lead to a decrease in the overall performance of the lithium-ion battery. In particular, the lack of pores to accommodate the lithium-silicon alloy makes it impossible to suppress the volume expansion of the battery.

[0094] Comparing Example 1 with Comparative Examples 1 to 3, it can be found that the double coating structure with dense inner layer and loose outer layer can give full play to the advantages of high-density negative electrode active material and porous CVD silicon-carbon material;

[0095] Comparing Example 1 and Comparative Example 4, it can be found that the outer coating layer uses a single porous CVD silicon-carbon material, resulting in a limited compaction density. Although larger pores are theoretically conducive to accommodating lithium-silicon alloys, they cannot fully exert the performance of the battery.

[0096] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple 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 high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material, characterized in that: comprising a negative electrode current collector, and an inner coating and an outer coating having a negative electrode active material; The inner coating is provided on at least one side of the negative electrode current collector, and the outer coating is provided on the surface of the inner coating away from the negative electrode current collector; The negative electrode active material of the inner coating layer is a carbon material, and the negative electrode active material of the outer coating layer includes a carbon material and a porous CVD silicon-carbon material; The outer coating layer has a lower compaction density than the inner coating layer.

2. The high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material according to claim 1, characterized in that: The compacted density of the inner coating is 1.65 to 1.7 g / cm 3 The compacted density of the outer coating is 1.3 to 1.5 g / cm 3 .

3. The high-density silicon-carbon negative electrode sheet with porous CVD silicon-carbon material according to claim 1, characterized in that: The carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon and carbon fiber.

4. A method for preparing a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material, characterized in that: The following steps are involved: Providing an inner coating slurry; in terms of weight ratio, the inner coating slurry comprises 35% to 70% of a negative electrode active material carbon material, 0.1% to 1.5% of a conductive agent, 0.2% to 2.2% of a binder, 0.1% to 2.0% of a dispersant, and the remainder being a solvent; Providing an outer coating slurry; in terms of weight ratio, the outer coating slurry comprises 20% to 50% of a negative electrode active material carbon material, 15% to 40% of a negative electrode active material porous CVD silicon carbon material, 0.2% to 0.5% of a plasticizer, 1.0% to 5.0% of a conductive agent, 3% to 15% of a binder, 0.1% to 0.6% of a dispersant, and the remainder being a solvent; The inner coating slurry is coated on the negative electrode current collector, dried and solidified, and then preliminarily rolled to form an inner coating on the negative electrode current collector; The outer coating slurry is coated on the inner coating, dried and solidified, and then rolled twice to form an outer coating on the negative electrode current collector; the second rolling is hot rolling at a rolling temperature of 50 to 80°C; The negative electrode current collector provided with an inner coating and an outer coating is thermally compounded with a separator to obtain a high-density silicon-carbon negative electrode sheet having a porous CVD silicon-carbon material.

5. The preparation method according to claim 4, characterized in that The secondary rolling is carried out in two steps, the first step is rolling at a first speed under a first pressure, followed by a second step of rolling at a second speed under a second pressure; the first pressure is less than the second pressure, the second pressure is less than the initial rolling pressure, and the first speed is greater than the second speed.

6. The preparation method according to claim 5, characterized in that The first pressure is 2-7 kN / m, the first speed is 5-8 m / min, the second pressure is 20-30 kN / m, and the second speed is 0.5-1 m / min.

7. The preparation method according to claim 4, characterized in that The compacted density of the inner coating is 1.65 to 1.7 g / cm 3 The compacted density of the outer coating is 1.3 to 1.5 g / cm 3 .

8. A battery, characterized in that: A high-density silicon-carbon negative electrode sheet comprising a porous CVD silicon-carbon material as claimed in any one of claims 1 to 7.

Images