Method for improving thermal stability of silicon-carbon negative electrode lithium battery based on construction of porous buffer layer

Abstract

The invention discloses a method for improving thermal stability of a silicon-carbon negative electrode lithium battery based on construction of a porous buffer layer. According to the method for improving the thermal stability of the silicon-carbon negative electrode lithium battery based on the construction of the porous buffer layer, the porous buffer layer is coated on a silicon-carbon negative electrode plate of the lithium battery, and the porous buffer layer is prepared by the following steps: dissolving a negative electrode binder in deionized water to prepare mucilage; and dropwise adding hydroxylated graphene dispersion liquid into the mucus, uniformly mixing to form slurry with dense micro-bubble distribution, coating a silicon-carbon negative pole piece with the slurry, and drying to obtain the porous buffer layer. The porous buffer layer structure provided by the invention can keep effective and uniform distribution of the electrolyte on the negative pole piece, and further improves the thermal safety and reliability of the battery.

Description

Technical Field:

[0001] The present invention relates to the technical field of negative electrode materials for lithium - ion batteries, and particularly relates to a method for improving the thermal stability of a silicon - carbon negative electrode lithium battery by constructing a porous buffer layer. Background Art:

[0002] As the current mainstream energy storage device, lithium - ion batteries are widely used in fields such as electric vehicles and portable electronic devices. Silicon - carbon composite negative electrode materials have become a hot research direction for negative electrode materials of lithium - ion batteries due to their high energy density. However, during the charge - discharge process, the silicon - carbon composite negative electrode material undergoes significant volume changes, resulting in an increase in internal stress of the battery, affecting the structural stability and cycle life of the battery. In addition, in a high - temperature environment, the electrolyte is prone to local decomposition at the negative electrode sheet, further reducing the electrochemical performance of the lithium battery.

[0003] Existing technical strategies for improving the performance of silicon - carbon composite negative electrodes mainly include the following: (1) Nanostructure design, by preparing nano - silicon particles, silicon nanowires or silicon thin films to relieve volume expansion. However, the high specific surface area of nanomaterials leads to an increase in side reactions and high preparation costs, making it difficult to be applied on a large scale; (2) Coating with composite carbon materials, using amorphous carbon, etc. to coat the silicon material body. Although it can improve conductivity and structural stability, the dense coating layer will hinder the diffusion of lithium ions and it is difficult to simultaneously meet the requirement of buffering volume expansion; (3) Reserved buffer space, reserving voids or adding elastic polymers in the electrode design, but it will reduce the volumetric energy density and the compatibility between the polymer and the electrolyte is poor, affecting long - term cycle stability.

[0004] Existing technical solutions still have significant deficiencies in balancing energy density, cycle stability and safety performance. Especially at the level of electrode structure design, there is a lack of innovative solutions that can effectively buffer volume expansion and maintain an efficient electron / ion transport channel. How to achieve the coordinated optimization of the technical goals of constructing a surface layer with elastic buffering ability, maintaining an efficient electron / ion transport network and improving the overall thermal stability of the electrode has become the key. Summary of the Invention:

[0005] The present invention solves the problems existing in the prior art and provides a method for improving the thermal stability of a silicon - carbon negative electrode lithium battery by constructing a porous buffer layer. By coating a porous buffer layer containing graphene on the silicon - carbon negative electrode sheet of the lithium battery, the volume change of the silicon - carbon material is effectively relieved, and the distribution and stability of the electrolyte in a high - temperature environment are effectively improved, thereby improving the electrochemical cycle stability of the corresponding lithium battery at high temperatures.

[0006] The first object of the present invention is to provide a method for enhancing the thermal stability of a lithium-ion battery with a silicon-carbon negative electrode based on constructing a porous buffer layer. By coating a porous buffer layer on the silicon-carbon negative electrode sheet of the lithium-ion battery, the porous buffer layer is prepared by the following steps: dissolving a negative electrode binder in deionized water to prepare a mucus, and dropwise adding a hydroxylated graphene dispersion into the mucus and mixing evenly to form a slurry with a dense distribution of tiny bubbles, and then coating the slurry on the silicon-carbon negative electrode sheet and drying to obtain the porous buffer layer.

[0007] The hydroxylated graphene dispersion is dropwise added into the mucus and mixed evenly by magnetic force or high-speed spiral stirring until a dense distribution of tiny bubbles is generated. The stirring speed of the magnetic force or high-speed spiral stirring is 300-500 revolutions per minute.

[0008] Preferably, the negative electrode binder is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and polyacrylonitrile.

[0009] Preferably, the mass fraction of the negative electrode binder in the mucus is 3%-6%, and 2-5 mg of the hydroxylated graphene dispersion is added per milliliter of the mucus.

[0010] More preferably, the mass fraction of the negative electrode binder in the mucus is 4%, and 4 mg of the hydroxylated graphene dispersion is added per milliliter of the mucus.

[0011] Preferably, the specific drying steps are as follows: placing the coated silicon-carbon negative electrode sheet in a high-temperature vacuum drying container, and at this time, the vacuum drying container is preheated to 100°C-110°C and the vacuum is not turned on. Before the coated slurry is completely dried, vacuum pumping is started (the vacuum degree is <-0.085 MPa) to accelerate the rupture of the bubbles in the coating layer, so as to form a porous buffer layer structure containing graphene on the silicon-carbon negative electrode sheet, and then complete drying is carried out. The conditions for complete drying are: the drying temperature is 80°C-100°C, and the drying time is ≥24 hours. More preferably, vacuum pumping is started before the coated slurry is completely dried, that is, 24 hours after the coated slurry is dried.

[0012] Preferably, the coating thickness is 20-50 μm. The slurry is coated on the negative electrode sheet by a coater, and the thickness can be set by the doctor blade according to needs.

[0013] The second object of the present invention is to provide a silicon-carbon negative electrode sheet for a lithium-ion battery with a porous buffer layer, which is prepared by the following steps:

[0014] (1) Mix the silicon-carbon negative electrode material, the first negative electrode binder, the conductive agent, and deionized water evenly, then coat them on a copper current collector, dry, and roll to obtain a silicon-carbon negative electrode sheet;

[0015] (2) Dissolve the second negative electrode binder in deionized water to prepare a mucilage, dropwise add the hydroxylated graphene dispersion into the mucilage and mix evenly to form a slurry with a dense distribution of tiny bubbles, then coat the slurry on the silicon-carbon negative electrode sheet and dry it to obtain the silicon-carbon negative electrode sheet for lithium batteries with a porous buffer layer.

[0016] In step (1), the silicon-carbon negative electrode material, the first negative electrode binder, the conductive agent, and deionized water are uniformly blended by planetary ball milling or propeller stirring.

[0017] Dropwise add the hydroxylated graphene dispersion into the mucilage, and through magnetic force or high-speed spiral stirring, mix the two evenly to form a slurry with a dense distribution of tiny bubbles. Coat the slurry on the initial negative electrode sheet by a coater, place it in a high-temperature vacuum oven, the temperature is close to the boiling point of the solvent in the above slurry, so that the solvent in the coating layer rapidly generates bubbles and evaporates synchronously, gradually becoming thicker. Before the coated slurry is completely dried, turn on the vacuum pump to accelerate the rupture of the bubbles in the coating layer, and form a porous buffer layer structure containing graphene on the silicon-carbon negative electrode sheet. After complete drying, the silicon-carbon negative electrode sheet for lithium-ion batteries with a porous buffer layer can be obtained.

[0018] Preferably, the mass ratio of the silicon-carbon negative electrode material, the first negative electrode binder, and the conductive agent in step (1) is 93-96:3-5:1-2, and the mass ratio of the silicon-carbon negative electrode material to deionized water is 0.90-0.96:1. Further preferably, the mass ratio of the silicon-carbon negative electrode material, the first negative electrode binder, and the conductive agent is 95:3.5:1.5, and the mass ratio of the silicon-carbon negative electrode material to deionized water is 0.95:1.

[0019] Preferably, the conductive agent in step (1) is selected from one or more of acetylene black, conductive carbon black, and Super-P.

[0020] Preferably, the first negative electrode binder in step (1) or the negative electrode binder in step (2) is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and polyacrylonitrile.

[0021] Preferably, the mass fraction of the second negative electrode binder in the mucilage in step (2) is 3% - 6%, and the addition amount of the hydroxylated graphene dispersion is 2 - 5 mg of the hydroxylated graphene dispersion added per milliliter of the mucilage. Further preferably, the mass fraction of the second negative electrode binder in the mucilage is 4%, and the addition amount of the hydroxylated graphene dispersion is 4 mg of the hydroxylated graphene dispersion added per milliliter of the mucilage.

[0022] Compared with the prior art, the present invention has the following advantages: The method for improving the thermal stability of a silicon-carbon anode lithium battery based on constructing a porous buffer layer provided by the present invention sets a porous graphene buffer layer on the silicon-carbon anode material layer. The buffer layer is designed with a porous structure and has excellent thermal conductivity and certain elastic buffering ability. The graphene material with good thermal conductivity can effectively improve the heat conduction efficiency of the electrode sheet body, enabling the heat generated by the electrode sheet to spread quickly and maintaining the balance of the working temperature of the battery. It also effectively alleviates the volume change of the silicon-carbon material during charge and discharge through its structural characteristics, reducing the internal stress of the battery. At the same time, the porous structure can maintain the effective and uniform distribution of the electrolyte on the negative electrode sheet, solving the problem of uneven local decomposition of the electrolyte that is prone to occur in a high-temperature environment, and further improving the thermal safety and reliability of the battery. Description of the Drawings:

[0023] Figure 1 It is the surface microstructural diagram (a) of the initial negative electrode sheet prepared in Example 1 of the present invention and the surface microstructural diagram (b) of the silicon-carbon negative electrode sheet containing a porous buffer layer.

[0024] Figure 2 It is the charge and discharge long cycle diagram at high temperature of the lithium-ion battery (B-2) without a porous buffer layer on the negative electrode sheet and the lithium-ion battery (B-1) with a graphene porous buffer layer on the negative electrode sheet in Example 1 of the present invention.

[0025] Figure 3 It is the heat generation distribution diagram of the lithium-ion battery (a) without a porous buffer layer on the negative electrode sheet and the lithium-ion battery (b) with a graphene porous buffer layer on the negative electrode sheet in Example 1 of the present invention during the 300th charge in the charge and discharge test under high-temperature conditions.

[0026] Figure 4 It is the CT image of the lithium-ion battery (a) without a porous buffer layer on the negative electrode sheet and the lithium-ion battery (b) with a graphene porous buffer layer on the negative electrode sheet in Example 1 of the present invention after 300 charge and discharge tests under high-temperature conditions. Detailed Embodiments:

[0027] The following embodiments are further illustrations of the present invention rather than limitations thereof.

[0028] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specified, the experimental materials and reagents in this article are all conventional commercially available products in this technical field.

[0029] Example 1

[0030] The silicon-carbon negative electrode material (specific capacity of the material is 450 mAh / g), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber, and Super-P were added to deionized water according to a mass ratio of 95:2:1.5:1.5, and the solid content of the mixture was 49%. After being stirred and blended evenly by a propeller, it was coated on a copper foil, thoroughly dried in an oven at 80 °C, and then roll-pressed into an initial negative electrode sheet for use. The compaction density of the sheet was 16.5 g / cm 2 . Sodium carboxymethyl cellulose was dissolved in deionized water to prepare a mucilage with a solid content of 4%. The hydroxylated graphene dispersion was added dropwise to the above mucilage, and the addition amount was 4 mg / mL. Through high-speed stirring with a double-helix agitator at a rotation speed of 400 revolutions per minute, the two were mixed evenly to form a slurry with a dense distribution of tiny bubbles. The above viscous mixed slurry was coated on the initial negative electrode sheet by a coater, and the thickness of the coating knife was set to 30 μm. After coating, the above sheet was placed in a high-temperature vacuum oven at 110 °C to quickly generate bubbles and simultaneously evaporate the water solvent in the coating layer, gradually becoming thicker. Before the coated slurry was completely dried, vacuum was pumped to < -0.085 MPa to accelerate the rupture of the bubbles in the coating layer. After complete drying, a silicon-carbon negative electrode sheet for a lithium-ion battery with a graphene porous buffer layer was constructed.

[0031] From Figure 1 the scanning electron microscope images, it can be seen that the surface microstructure of the initial negative electrode sheet is granular ( Figure 1 a), and the surface microstructure of the silicon-carbon negative electrode sheet with a graphene porous buffer layer constructed presents a porous structure similar to a honeycomb ( Figure 1 b). The generation of this porous structure is due to the rupture of bubbles in the slurry. After drying, graphene and sodium carboxymethyl cellulose binder jointly form this honeycomb-like porous buffer layer film covering the surface of the negative electrode sheet.

[0032] The above negative electrode sheet, the ternary material positive electrode sheet of the lithium battery, the commercial electrolyte of the lithium battery, and the battery separator were assembled into a soft-pack lithium-ion battery, denoted as Battery B-1, and its electrochemical performance at high temperature was tested. The temperature was 45 °C, the current was 1C, and the charge-discharge voltage range was 3.0 - 4.3 V. And the silicon-carbon negative electrode sheet for a lithium-ion battery without a coated graphene porous buffer layer (i.e., the initial negative electrode sheet) was used as a control group to carry out the same high-temperature electrochemical test, denoted as Battery B-2. From Figure 2It can be seen that the initial discharge capacity of the lithium-ion battery with a graphene porous buffer layer on the negative electrode (B-1) at high temperature is 1.01 Ah, while that of the lithium-ion battery without a porous buffer layer on the negative electrode (B-2) is 1.03 Ah. By comparison, the initial discharge capacity of the lithium-ion battery with a graphene porous buffer layer on the negative electrode is slightly lower (about 0.02 Ah lower). This may be because the porous buffer layer on the negative electrode surface forms a larger area of solid-liquid interface film (SEI film) during the first lithium deintercalation and intercalation process of the battery, resulting in a slight decrease in the discharge specific capacity of the battery due to the loss of some active lithium. From the perspective of long-term cycling, at 45 °C, the lithium-ion battery with a graphene porous buffer layer on the negative electrode (B-1) shows significantly improved electrochemical stability. After 300 charge-discharge cycles, the discharge capacity is 0.83 Ah, and the capacity retention rate is as high as 82.2%. However, after 300 charge-discharge cycles, the discharge capacity of battery B-2 is 0.64 Ah, and the capacity retention rate is only 62.1%. This indicates that the porous buffer layer structure can effectively alleviate the volume change of the silicon-carbon material during charge and discharge, reduce the internal stress of the battery, and improve the long-term cycling stability of the battery at high temperature.

[0033] An infrared thermal imager was used to test the heat generation of the lithium-ion battery during charging at the 300th high-temperature cycle under the condition of 45 °C. As Figure 3 shown, when the lithium-ion battery with a graphene porous buffer layer on the negative electrode (B-1) undergoes long-term cycling tests under high-temperature environmental conditions during charging, the temperature can be effectively controlled and evenly distributed. The highest temperature at different positions of the battery is 46.0 °C, the lowest temperature is 42.4 °C, and the average temperature is 45.0 °C. The difference between the highest temperature and the lowest temperature at different positions of the battery is 3.6 °C. However, when the lithium-ion battery without a porous buffer layer on the negative electrode (B-2) undergoes long-term cycling tests under high-temperature environmental conditions during charging, there is an obvious uneven temperature distribution, and there is a situation of concentrated high heat in a local area. The highest temperature at different positions of the battery is 47.7 °C, the lowest temperature is 41.9 °C, and the average temperature is 46.4 °C. The difference between the highest temperature and the lowest temperature at different positions of the battery is as high as 5.8 °C. This indicates that the graphene material with good thermal conductivity can effectively improve the heat conduction efficiency of the electrode sheet body, enabling the heat generated by the electrode sheet to spread quickly and maintaining the balance of the working temperature of the battery.

[0034] The non-destructive three-dimensional imaging CT technology was used to detect the internal structure of the lithium-ion battery after 300 high-temperature cycles. As Figure 4As shown, in the lithium-ion battery (B-1) with a graphene porous buffer layer on the negative electrode sheet, the internal electrolyte is evenly distributed. However, in the lithium-ion battery (B-2) without a porous buffer layer on the negative electrode sheet, the electrolyte shows uneven distribution inside, and lithium salt residue particles generated by the volatilization or decomposition of the electrolyte solvent appear in local areas of the electrode sheet. It can be seen that the porous structure buffer layer can maintain the effective and uniform distribution of the electrolyte on the negative electrode sheet, solving the problem of uneven local decomposition of the lithium battery electrolyte in a high-temperature environment.

[0035] Example 2

[0036] The silicon-carbon negative electrode material (specific capacity of the material is 450 mAh / g), polyvinyl alcohol, and conductive carbon black were added to deionized water according to a mass ratio of 96:3:1, and the solid content of the mixture was 49%. After being stirred and blended evenly by a propeller, it was coated on a copper foil. After being thoroughly dried in an oven at 80°C, it was rolled into an initial negative electrode sheet for use, and the compaction density of the electrode sheet was 16.5 g / cm 2 . Sodium carboxymethyl cellulose was dissolved in deionized water to prepare a mucus with a solid content of 3%. The hydroxylated graphene dispersion was added dropwise to the above mucus, and the addition amount was 2 mg / mL. Through high-speed stirring with a double-helical agitator at a rotation speed of 300 revolutions per minute, the two were mixed evenly to form a slurry with a dense distribution of tiny bubbles. The above viscous mixed slurry was coated on the initial negative electrode sheet by a coater, and the thickness of the coating knife was set to 20 μm. After coating, the above electrode sheet was placed in a high-temperature vacuum oven at 100°C to quickly generate bubbles and synchronously evaporate the water solvent in the coating layer, gradually becoming thicker. Before the coated slurry was completely dried, the vacuum was pumped to < -0.085 MPa to accelerate the rupture of the bubbles in the coating layer. After complete drying (drying temperature 80°C - 100°C, drying time ≥ 24 hours), a silicon-carbon negative electrode sheet for a lithium-ion battery with a graphene porous buffer layer was obtained.

[0037] The above negative electrode sheet, the ternary material positive electrode sheet of the lithium battery, the commercial electrolyte of the lithium battery, and the battery separator were assembled into a soft-pack lithium-ion battery, and its electrochemical performance at 35°C was tested, with a current of 1C and a charge-discharge voltage range of 3.0 - 4.3V. And the silicon-carbon negative electrode sheet for a lithium-ion battery without coating a graphene porous buffer layer (i.e., the initial negative electrode sheet) was used as a control group to carry out the same high-temperature electrochemical test. As shown in Table 1, Table 1 is a summary of the performance parameters of the lithium-ion battery without a porous buffer layer on the negative electrode sheet and the lithium-ion battery with a graphene porous buffer layer on the negative electrode sheet after 200 charge-discharge tests under high-temperature conditions.

[0038] Table 1

[0039]

[0040] As shown in Table 1, the silicon-carbon negative electrode sheet for lithium-ion batteries containing a graphene porous buffer layer can effectively improve the capacity retention rate at high temperatures and maintain the temperature balance at different positions during battery operation.

[0041] Example 3

[0042] The silicon-carbon negative electrode material (specific capacity of the material is 450 mAh / g), polyacrylonitrile, and acetylene black were added to deionized water according to a mass ratio of 93:5:2, and the solid content of the mixture was 49%. After being uniformly blended by a propeller stirrer, it was coated on a copper foil. After being thoroughly dried in an oven at 80 °C, it was roll-pressed into an initial negative electrode sheet for use, and the compaction density of the sheet was 16.5 g / cm 2 . Sodium carboxymethyl cellulose was dissolved in deionized water to prepare a mucilage with a solid content of 6%. The hydroxylated graphene dispersion was added dropwise to the above mucilage, and the addition amount was 5 mg / mL. Through high-speed stirring with a double-helix agitator at a rotation speed of 500 revolutions per minute, the two were mixed evenly to form a slurry with a dense distribution of tiny bubbles. The above viscous mixed slurry was coated on the initial negative electrode sheet by a coater, and the thickness of the coating blade was set to 50 μm. After coating, the above electrode sheet was placed in a high-temperature vacuum oven at 110 °C to allow the water solvent in the coating layer to quickly generate bubbles and evaporate synchronously, gradually becoming thicker. Before the coated slurry was completely dried, the vacuum was pumped to < -0.085 MPa to accelerate the rupture of the bubbles in the coating layer. After complete drying (drying temperature 80 °C to 100 °C, drying time ≥ 24 hours), a silicon-carbon negative electrode sheet for lithium-ion batteries containing a graphene porous buffer layer was obtained.

[0043] The above negative electrode sheet, the lithium battery ternary material positive electrode sheet, the lithium battery commercial electrolyte, and the battery separator were assembled into a soft-pack lithium-ion battery, and its electrochemical performance at 55 °C was tested. The current was 1C, and the charge-discharge voltage range was 3.0 to 4.3V. And the silicon-carbon negative electrode sheet for lithium-ion batteries without coating the graphene porous buffer layer (i.e., the initial negative electrode sheet) was used as a control group to carry out the same high-temperature electrochemical test. As shown in Table 2, Table 2 is a summary of the performance parameters of the lithium-ion battery with a negative electrode sheet without a porous buffer layer and the lithium-ion battery with a negative electrode sheet containing a graphene porous buffer layer after 100 charge-discharge tests under high-temperature conditions.

[0044] Table 2

[0045]

[0046] As shown in Table 2, the silicon-carbon negative electrode sheet for lithium-ion batteries containing a graphene porous buffer layer can effectively improve the capacity retention rate at high temperatures and maintain the temperature balance at different positions during battery operation.

[0047] The description of the above embodiments is only used to help understand the technical solution and its core idea of the present invention. It should be noted that for those skilled in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for improving the thermal stability of a silicon-carbon negative electrode lithium battery based on constructing a porous buffer layer, characterized in that: A porous buffer layer is coated on a lithium battery silicon-carbon negative electrode plate, wherein the porous buffer layer is prepared by the following steps: a negative electrode binder is dissolved in deionized water to form a mucus, a hydroxylated graphene dispersion is added dropwise into the mucus and mixed evenly to form a slurry with densely distributed tiny bubbles, and the slurry is then coated on the silicon-carbon negative electrode plate and dried to obtain the porous buffer layer.

2. The method according to claim 1, characterized in that The negative electrode binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol and polyacrylonitrile.

3. The method according to claim 1, characterized in that The mass fraction of the negative electrode binder in the mucus is 3% to 6%, and the amount of hydroxylated graphene dispersion added is 2 to 5 mg of hydroxylated graphene dispersion per milliliter of mucus.

4. The method according to claim 1, characterized in that: The specific steps of drying are: placing the coated silicon-carbon negative electrode sheet in a high-temperature vacuum drying container. At this time, the vacuum drying container is heated to 100°C~110°C in advance, and the vacuum is not turned on. Before the coated slurry becomes completely dry, the vacuum is turned on to form a porous buffer layer structure containing graphene on the silicon-carbon negative electrode sheet, and then it is thoroughly dried. The conditions for thorough drying are: drying temperature 80°C~100°C, drying time ≥24 hours.

5. The method according to claim 1, characterized in that The coating thickness is 20 to 50 μm.

6. A silicon-carbon negative electrode sheet for a lithium battery having a porous buffer layer, characterized in that: Prepared by the following steps: (1) mixing a silicon-carbon negative electrode material, a first negative electrode binder, a conductive agent, and deionized water uniformly, coating the mixture on a copper current collector, drying the mixture, and rolling the mixture to obtain a silicon-carbon negative electrode sheet; (2) The second negative electrode binder is dissolved in deionized water to form a viscous liquid, and the hydroxylated graphene dispersion is added dropwise to the viscous liquid and mixed evenly to form a slurry with densely distributed tiny bubbles, and then the slurry is coated on the silicon-carbon negative electrode plate, and dried to obtain the silicon-carbon negative electrode plate for lithium battery with a porous buffer layer.

7. The silicon-carbon negative electrode sheet for lithium battery with a porous buffer layer according to claim 6, characterized in that: The mass ratio of the silicon-carbon negative electrode material, the first negative electrode binder and the conductive agent in step (1) is 93-96:3-5:1-2, and the mass ratio of the silicon-carbon negative electrode material to deionized water is 0.90-0.96:

1.

8. The silicon-carbon negative electrode sheet for lithium battery with a porous buffer layer according to claim 6, characterized in that: The conductive agent described in step (1) is selected from one or more of acetylene black, conductive carbon black and Super-P.

9. The silicon-carbon negative electrode sheet for lithium battery with a porous buffer layer according to claim 6, characterized in that: The first negative electrode binder described in step (1) or the second negative electrode binder described in step (2) is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol and polyacrylonitrile.

10. The silicon-carbon negative electrode sheet for lithium battery with a porous buffer layer according to claim 6 or 9, characterized in that: The mass fraction of the second negative electrode binder in the mucus described in step (2) is 3% to 6%, and the amount of hydroxylated graphene dispersion added is 2 to 5 mg of hydroxylated graphene dispersion per milliliter of mucus.

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