Safety evaluation method for silicon-based negative electrode material

Abstract

The invention provides a silicon-based negative electrode material safety evaluation method, and particularly relates to the technical field of negative electrode material safety tests.The silicon-based negative electrode material safety evaluation method comprises the steps that S1, a silicon-based negative electrode material, a binder and a conductive agent are mixed with deionized water according to the mass ratio of (1-a-b): a: b to obtain evenly-mixed slurry, copper foil is coated with the slurry, and drying and rolling are conducted to obtain a negative electrode piece; s2, cutting the negative plate into three strip-shaped samples, and reserving 1 cm of blank copper foil at one end of each sample; s3, vertically hanging the sample, firing by aligning a butane spray gun to the lower end of the sample, recording time t0, t1 and t2 through a camera, and stopping testing if the sample is not ignited after 10 seconds of firing; the ignition time T = t1-t0 and the combustion speed V = L / (t2-t1) are calculated, and finally the arithmetic mean value of the three pieces of sample data is obtained. By adopting the technical scheme of the invention, an objective and reproducible negative electrode material safety evaluation system can be constructed, and the test is safe, environment-friendly and efficient.

Description

Technical Field

[0001] This invention relates to the field of anode material safety testing technology, and in particular to a method for evaluating the safety of silicon-based anode materials. Background Technology

[0002] With the rapid development of consumer electronics and new energy vehicles, lithium-ion batteries have placed higher demands on energy density and safety. Silicon-based anode materials, due to their high specific capacity, are increasingly being used in digital products and electric vehicle batteries. Currently, most cell manufacturers use a mixture of silicon and graphite, but to further improve energy density, some manufacturers have begun researching all-silicon anode materials without graphite, especially silicon-carbon materials prepared using vapor deposition processes, which exhibit higher activity.

[0003] However, silicon-based anode materials, especially those containing a large amount of nano-silicon, pose certain safety risks during battery manufacturing and use. For example, during the electrode die-cutting process, laser cutting may cause the material to burn; during battery use, if a fire breaks out, the silicon material may support the combustion, increasing the risk of an accident.

[0004] Existing safety tests primarily focus on the cell level, using methods such as hot box testing, combustion, and needle penetration, which cannot directly reflect the safety of silicon-based anode materials themselves. Furthermore, these tests are highly hazardous and polluting, making them unsuitable for material screening and early assessment. Therefore, there is an urgent need for a method to evaluate the safety of silicon-based anodes at the material level, in order to identify potential risks earlier and improve the overall safety level of lithium batteries.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for evaluating the safety of silicon-based anode materials, so as to solve the technical problems in the prior art.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a method for safety evaluation of silicon-based anode materials, comprising: Step S1: The silicon-based anode material, binder and conductive agent are mixed with deionized water at a mass ratio of (1-ab):a:b to obtain a uniformly mixed slurry, which is then coated onto copper foil and dried and rolled to obtain anode sheet. Step S2: Cut the negative electrode sheet into 3 long strip samples, and leave 1 cm of blank copper foil at one end of each sample; Step S3: The sample is suspended vertically, and a butane spray gun is used to burn the lower end of the sample. At the same time, the start time of burning t0, the ignition time t1, and the end time of combustion t2 are recorded by a camera. If the sample fails to ignite after 10 seconds of burning, the test is stopped. The ignition time T = t1 - t0 and the combustion rate V = L / (t2 - t1) are calculated for the ignited sample, where L is the length from the lower end of the sample to the end point of combustion. Finally, the arithmetic mean of the three sample data is taken, and the ignition time of the unignited sample is recorded as T > 10s.

[0008] Further, in step S1, adhesive a is 3.5%-10%; preferably, adhesive a is 4.5%-7%. And / or, in step S1, the conductive agent b is 0.5%-5%; preferably, the conductive agent b is 0.5%-3%; And / or, in step S1, the silicon-based anode material (1-ab) is 85%-96%; preferably, the silicon-based anode material is 90%-95%.

[0009] Furthermore, the binder is selected from at least one of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber, and the conductive agent is selected from one or more combinations of conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0010] Further, the solid content of the slurry is 25-45%; preferably, the solid content of the slurry is 30-40%. And / or, the thickness of the copper foil is 5-15 μm; preferably, the thickness of the copper foil is 6-10 μm; And / or, the areal density of the negative electrode sheet is 35-150 g / m2; preferably, the areal density of the negative electrode sheet is 40-90 g / m2; And / or, the compaction density of the negative electrode sheet is 0.65-1.0 g / cm3; preferably, the compaction density of the negative electrode sheet is 0.7-0.9 g / cm3.

[0011] Further, the length of the sample strip is 11-51 cm and the width is 0.5-3 cm; preferably, the length of the sample strip is 21-31 cm and the width is 1-1.5 cm.

[0012] Furthermore, in step S3, the flame temperature of the butane spray gun is 1000-1300℃; preferably, the flame temperature is 1200℃-1300℃, and the recording frame rate of the camera is ≥240 fps.

[0013] The basic principles and beneficial effects of this invention are as follows: This invention constructs a standardized direct evaluation system for the intrinsic safety of silicon-based anode materials. By precisely controlling the mass ratio of silicon-based anode materials, binders, and conductive agents, and combining process parameters such as electrode surface density and compaction density, samples that highly simulate the structure of real battery cell electrodes are prepared. The oxidation reaction of silicon materials is triggered by a high-energy butane flame. The material's resistance to ignition is characterized by quantifying the ignition time (T = t1 - t0) (the larger the T value, the stronger the thermal stability), and the combustion intensity is characterized by the combustion rate (V = sample length / (t2 - t1)) (the lower the V value, the lower the fire risk). Thus, an objective and reproducible material-level safety evaluation standard is established.

[0014] This invention also overcomes the limitation of existing cell testing methods that cannot trace material defects. By directly outputting the intrinsic safety parameters (T value, V value) of the silicon-based anode through electrode combustion testing, it identifies high-risk materials at the source, preventing them from entering the cell manufacturing process (especially the laser die-cutting process) or end applications, thus intercepting safety hazards at the front end. Furthermore, compared to cell-level testing, this invention requires only a small amount of material, completes the test in a short time, and is safe, environmentally friendly, and efficient. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating a safety evaluation method for silicon-based anode materials according to the present invention. Detailed Implementation

[0017] The embodiments and examples of the present invention will be described in detail below with reference to the implementation methods and examples. However, those skilled in the art will understand that the following implementation methods and examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a method for safety evaluation of silicon-based anode materials. A schematic diagram of the specific process steps of this method is attached. Figure 1 As shown, it includes: Step S1: The silicon-based negative electrode material, binder, and conductive agent are mixed with deionized water at a mass ratio of (1-ab):a:b to obtain a uniformly mixed slurry. This slurry is then coated onto copper foil, dried, and rolled to obtain a negative electrode sheet. The binder can be selected from at least one of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber. The conductive agent can be selected from one or more of conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. Appropriate binder and conductive agent materials can be selected according to the specific testing scenario.

[0019] Step S2: Cut the negative electrode sheet into 3 long strip samples, and leave 1 cm of blank copper foil at one end of each sample.

[0020] Step S3: The sample is suspended vertically, and a butane torch is used to burn the lower end of the sample. At the same time, the burning start time t0 (the initial moment when the flame contacts the sample), the ignition time t1, and the combustion end time t2 (the moment when the sample flame is completely extinguished) are recorded by a camera. If the sample does not ignite after 10 seconds of burning, the test is stopped. The ignition time T = t1 - t0 and the combustion rate V = L / (t2 - t1) are calculated for the ignited sample, where L is the length from the lower end of the sample to the combustion end point. Finally, the arithmetic mean of the three sample data is taken, and the ignition time of the unignited sample is recorded as T > 10 s.

[0021] The butane spray gun has a flame temperature of 1000-1300℃, and typical but non-limiting flame temperatures include: 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, 1150℃, 1200℃, 1250℃, and 1300℃. However, it is not limited to these, and a further preferred temperature is 1200℃-1300℃. The camera has a recording frame rate ≥240 fps. By controlling the flame temperature of the butane spray gun (1000-1300℃), the thermal runaway environment of the battery can be simulated, and the frame rate ≥240 fps accurately captures the ignition moment (error <4 ms), ensuring that high-speed combustion can be recorded.

[0022] In some preferred embodiments, the adhesive a in step S1 is 3.5%-10%, and typical but non-limiting mass ratios of adhesive a can be, for example: 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%, 5.5%, 6.0%, 7.0%, 8.0%, 9.0%, 10%. However, it is not limited to this, and can be further preferably 4.5%-7%. And / or, in step S1, the conductive agent b is 0.5%-5%, and its typical but non-limiting mass ratio can be, for example: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%. However, it is not limited to this, and can be further preferably 0.5%-3%. And / or, in step S1, the silicon-based anode material (1-ab) is 85%-96%, and the typical but not limiting mass ratio of the silicon-based anode material (1-ab) can be, for example, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or 96%. However, it is not limited to this, and it is more preferably 90%-95%. By limiting the ratio of binder (3.5%-10%), conductive agent (0.5%-5%), and silicon-based material (85%-96%), the combustion stability of the electrode sheet (anti-detachment / flame retardant) is ensured.

[0023] In some preferred embodiments, the slurry has a solids content of 25-45%, and typical but non-limiting solids contents may be: 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 45%. However, it is not limited to these, and may be further preferred to be 30%-40%. And / or, the thickness of the copper foil is 5-15 μm, and typical but non-limiting copper foil thicknesses can be, for example: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm. However, it is not limited to this, and 6-10 μm is more preferably preferred; And / or, the areal density of the negative electrode sheet is 35-150 g / m², and typical but non-limiting areal densities of the negative electrode sheet can be, for example: 35 g / m², 36 g / m², 40 g / m², 45 g / m², 50 g / m², 60 g / m², 70 g / m², 80 g / m², 85 g / m², 90 g / m², 100 g / m², 110 g / m², 120 g / m², 130 g / m², 140 g / m², 150 g / m². However, it is not limited to this, and may be further preferably 40-90 g / m². And / or, the compaction density of the negative electrode sheet is 0.65-1.0 g / cm³, and its typical but non-limiting areal density can be, for example, 0.65 g / cm³, 0.7 g / cm³, 0.8 g / cm³, 0.9 g / cm³, or 1.0 g / cm³. However, it is not limited to these, and 0.7-0.9 g / cm³ is more preferably preferred. By setting the boundaries of slurry solid content (25%-45%), copper foil thickness (5-15 μm), areal density (35-150 g / m²), and compaction density (0.65-1.0 g / cm³), the coating processability and combustion controllability (prevention of ignition failure / deflagration) are balanced.

[0024] In some preferred embodiments, the length of the sample strip is 11-51 cm, and typical but non-limiting sample strip lengths can be, for example: 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, 21 cm, 22 cm, 24 cm, 26 cm, 28 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 cm, and more preferably 21-31 cm. The width of the sample strip is 0.5-3 cm, and typical but non-limiting sample strip widths can be, for example: 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1 cm, 1.1 cm, 1.2 cm, 1.4 cm, 1.6 cm, 1.8 cm, 2.0 cm, 2.5 cm, 3.0 cm, and more preferably 1-1.5 cm. By optimizing the sample size (11-51 cm long × 0.5-3 cm wide), the minimum size ensures the effectiveness of the combustion length, while the maximum size prevents the flame from getting out of control.

[0025] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0026] Example 1

[0027] This embodiment provides a method for evaluating the safety of silicon-based anode materials, including the following steps: Step S1: The silicon-carbon anode material with a silicon content of 49.6% prepared by phenolic resin-based porous carbon-silane vapor deposition method is mixed with binder polyacrylic acid and conductive agent conductive carbon black at a mass ratio of 95:4.5:0.5 and deionized water to obtain a uniformly mixed slurry with a solid content of 35.4%. The slurry is coated on a copper foil with a thickness of 9μm and dried and rolled to obtain an anode sheet with an areal density of 55 g / m2 and a compaction density of 0.75 g / cm3.

[0028] Step S2: Cut the negative electrode sheet into 3 long strip samples, each 20 cm long and 1 cm wide, with 1 cm of blank copper foil left at one end of each sample.

[0029] Step S3: The sample is suspended vertically and the lower end of the sample is ignited with a butane torch at 1200 ℃. The start time of ignition t0, ignition time t1, and combustion end time t2 are recorded with a 240 fps camera. If the sample fails to ignite after ignition for >10 s, the test is stopped. The ignition time T = t1 - t0 and the combustion rate V = L / (t2 - t1) are calculated for the ignited sample, where L is the length from the lower end of the sample to the combustion end point. Finally, the arithmetic mean of the three sample data is taken. The ignition time of the unignited sample is recorded as T > 10 s. The test results are shown in Table 1 below.

[0030] Example 2

[0031] This embodiment provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Embodiment 1 in that the anode sheet density in step S1 is 35 g / m2.

[0032] Example 3

[0033] This embodiment provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Embodiment 1 in that the solid content of the slurry in step S1 is 45%, the surface density of the anode sheet is 150 g / m2, and the compaction density is 0.9 g / cm3.

[0034] Example 4

[0035] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 3 in that, in step S1, the solid content of the slurry is 25%, and the compaction density of the anode sheet is 0.65 g / cm³. In step S2, the length of the elongated sample is 51 cm.

[0036] Example 5

[0037] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that the anode sheet density in step S1 is 50 g / m². In step S2, the width of the elongated sample is 3 cm. In step S3, the butane torch flame temperature is 1300℃.

[0038] Example 6

[0039] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 5 in that, in step S2, the elongated sample is 11 cm long and 0.5 cm wide. In step S3, the butane torch flame temperature is 1000℃.

[0040] Example 7

[0041] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the silicon-carbon anode material, the binder polyacrylic acid, and the conductive agent conductive carbon black are mixed in a mass ratio of 85:10:5.

[0042] Example 8

[0043] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the mass ratio of silicon-carbon anode material to binder polyacrylic acid and conductive agent conductive carbon black is 90:8:2.

[0044] Example 9

[0045] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the silicon-carbon anode material is prepared by phenolic resin-based porous carbon-silane vapor deposition method, and the silicon content is 53.7%.

[0046] Example 10

[0047] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the silicon-carbon anode material is prepared by phenolic resin-based porous carbon-silane vapor deposition method, and the silicon content is 47.3%.

[0048] Example 11

[0049] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the silicon-carbon anode material is prepared by biomass-based porous carbon-silane vapor deposition and has a silicon content of 53.8%.

[0050] Example 12

[0051] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the silicon-carbon anode material is prepared by biomass-based porous carbon-silane vapor deposition and has a silicon content of 47.2%.

[0052] Example 13

[0053] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the mass ratio of silicon-carbon anode material to binder sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive agents conductive carbon black and single-walled carbon nanotubes is 95:1.5:3:0.4:0.1.

[0054] Example 14

[0055] This embodiment provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Embodiment 1 in that, in step S1, the mass ratio of silicon-carbon anode material to binder sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive agents conductive carbon black and multi-walled carbon nanotubes is 93:1.5:3:1.5:1.

[0056] Comparative Example 1

[0057] This comparative example provides a safety evaluation method for silicon-based anode materials. The steps differ from those in Example 9 in that, in step S1, the mass ratio of silicon-carbon anode material to binder polyacrylic acid and conductive agent conductive carbon black is 80:10:10.

[0058] Comparative Example 2

[0059] This comparative example provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Example 9 in that the anode sheet density is 30 g / m2 in step S1.

[0060] Comparative Example 3

[0061] This comparative example provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Example 1 in that the anode sheet density is 200 g / m2 in step S1.

[0062] Comparative Example 4

[0063] This comparative example provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Example 1 in that the butane torch flame temperature is 600°C in step S3.

[0064] Comparative Example 5

[0065] This comparative example provides a method for evaluating the safety of silicon-based anode materials. The steps differ from those in Example 1 in that the compaction density of the anode sheet is 1.2 g / cm3 in step S1.

[0066] The above embodiments and comparative examples were tested, and the test results are shown in Table 1: Table 1. Combustion Test Data of Silicon-based Anode

[0067] Table 1 shows that Examples 1, 2, and 3 were designed with different electrode areal densities. It can be seen that the higher the areal density, the shorter the ignition time and the faster the combustion speed. When the areal density of Comparative Example 3 was increased to 200 g / m², deflagration occurred during the actual ignition process, making time recording difficult and posing a certain danger. Examples 3 and 4, and Examples 5 and 6 compared the dimensions of the samples. The results showed that the length and width of the samples within the scope of the claims had no significant effect on the ignition time T and the combustion speed V. Examples 1, 7, and 8 adjusted the proportion of silicon-based anodes in the electrodes. It was found that the lower the proportion of silicon-based anodes, the longer the ignition time and the slower the combustion speed. When the proportion of silicon-based anodes was 85%, the sample would stop burning after a portion of the sample burned. In Comparative Example 1, when the proportion of silicon-based anodes was 80%, the sample could not be ignited. Examples 1, 9, and 12 compared silicon-based anode materials of different types and silicon contents. The results showed that the lower the silicon content, the longer the ignition time, the slower the combustion speed, and ultimately, the anode could not be ignited. Finally, Comparative Examples 3, 4, and 5 demonstrated that when the electrode surface density is too low, the butane torch temperature is too low, and the electrode compaction density is too high, the silicon-based anode is difficult to ignite.

[0068] In summary, this method demonstrates that the safety evaluation results of silicon-based anode materials are directly controlled by material composition and process parameters. A silicon-based material content of 85%-96% constitutes the core basis for effective evaluation; reducing this content significantly prolongs the ignition time T (e.g., T=2.903 s when the content is 85%) and decreases the combustion rate V (V=2.61 cm / s). The electrode surface density must be strictly controlled between 35-150 g / m² (exceeding 200 g / m² triggers deflagration), and the compaction density should be 0.65-1.0 g / cm³ (exceeding 1.2 g / cm³ prevents ignition). The sample size (11-51 cm long × 0.5-3 cm wide) and flame temperature ≥1000℃ (low-temperature failure) form rigid boundaries that cannot be breached in the test. This method, through the quantification of indicators T (ignition sensitivity) and V (combustion intensity), achieves early screening of safety risks at the material level for the first time, providing direct guidance for the safe design of high-energy-density power batteries.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating safety of a silicon-based negative electrode material, characterized by, The application relates to a method for testing the flammability of a silicon-based negative electrode material. The method comprises the following steps: S1, mixing a silicon-based negative electrode material, a binder and a conductive agent with deionized water according to a mass ratio (1-a-b):a:b to obtain a uniformly mixed slurry, and coating the slurry on a copper foil to perform drying and roller pressing to obtain a negative electrode sheet; S2, cutting the negative electrode sheet into three long strip-shaped samples, and reserving 1 cm of blank copper foil at one end of each sample; 2. The method for evaluating the safety of a silicon-based negative electrode material according to claim 1, characterized by, S3, vertically hanging the samples, using a butane spray gun to burn the lower end of the samples, recording the start burning time t0, the ignition time t1 and the end burning time t2 by using a camera, and stopping the test if the sample is not ignited after 10 seconds of burning; calculating the ignition time T=t1-t0 and the burning speed V=L / (t2-t1) of the ignited sample, wherein L is the length from the lower end of the sample to the end of the burning; finally, taking the arithmetic mean of the data of the three samples, and recording the ignition time T>10 s of the unignited sample. In the step S1, the binder a is 3.5%-10%; preferably, the binder a is 4.5%-7%; And / or, in the step S1, the conductive agent b is 0.5%-5%; preferably, the conductive agent b is 0.5%-3%; 3. The method for evaluating the safety of a silicon-based negative electrode material according to claim 2, characterized by, And / or, in the step S1, the silicon-based negative electrode material (1-a-b) is 85%-96%; preferably, the silicon-based negative electrode material is 90%-95%.

4. The method for evaluating the safety of a silicon-based anode material according to claim 1, characterized by, The binder is selected from at least one of polyacrylic acid, sodium carboxymethyl cellulose and butadiene styrene rubber, and the conductive agent is selected from one or more combinations of conductive carbon black, single-walled carbon nanotubes and multi-walled carbon nanotubes. The solid content of the slurry is 25%-45%; preferably, the solid content of the slurry is 30%-40%; And / or, the thickness of the copper foil is 5-15 mu m; preferably, the thickness of the copper foil is 6-10 mu m; And / or, the area density of the negative electrode sheet is 35-150 g / m2; preferably, the area density of the negative electrode sheet is 40-90 g / m2; 5. The method for evaluating the safety of a silicon-based anode material according to claim 1, wherein And / or, the compacted density of the negative electrode sheet is 0.65-1.0 g / cm3; preferably, the compacted density of the negative electrode sheet is 0.7-0.9 g / cm3.

6. The method for evaluating the safety of a silicon-based anode material according to claim 1, wherein The length of the sample strip is 11-51 cm, and the width is 0.5-3 cm; preferably, the length of the sample strip is 21-31 cm, and the width is 1-1.5 cm. In the step S3, the flame temperature of the butane spray gun is 1000-1300 DEG C; preferably, the flame temperature is 1200 DEG C-1300 DEG C, and the recording frame rate of the camera is greater than or equal to 240 fps.

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