Negative pole piece, preparation method thereof and silicon-carbon soft package lithium battery

Abstract

The invention relates to a negative pole piece and a preparation method thereof and a silicon-carbon soft package lithium battery, the negative pole piece comprises a current collector and a negative active material layer located on at least one side surface of the current collector, the negative pole piece comprises an inner layer, a protective layer and a stable layer which are stacked in sequence, and the inner layer is close to the current collector; the inner layer comprises a first silicon-carbon composite material; the protective layer comprises a second silicon-carbon composite material and a first silicon-oxygen composite material; and the stable layer comprises a second silica composite material and a graphite material. The negative electrode active material layer comprises the inner layer, the protective layer and the stable layer which are stacked, the inner layer provides high specific capacity, excellent fast charging capacity and excellent conductivity, the protective layer ensures the stability of interface contact and effectively relieves negative effects caused by silicon expansion, the stable layer can improve the stability of the battery under high voltage, and the stability of the battery under high voltage is improved. Lithium separation of the battery under high magnification is avoided, long-term stability of the battery performance is ensured, and the problem of performance degradation of the silicon-carbon soft package lithium battery under fast charging and voltage window operation conditions is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pole piece preparation, and particularly relates to a negative pole piece, a preparation method thereof and a silicon-carbon soft-pack lithium battery. BACKGROUND

[0002] Silicon-carbon composite material is an ideal negative electrode material due to its high theoretical specific capacity, which can significantly improve the energy density of the battery. However, silicon will undergo a large volume expansion during charging and discharging, which will lead to instability of the negative electrode structure, and further affect the cycle life and fast charging capability of the battery. Especially under fast charging conditions (such as 3C rate charging), the volume expansion effect of silicon will cause the capacity attenuation and excessive heat of the battery, which seriously affects the safety and performance of the battery. In addition, when the silicon-carbon negative electrode battery is operated at a high voltage (such as 4.55V), an unstable reaction may occur at the interface between the electrolyte and the negative electrode, which will cause performance degradation and safety hazards of the battery.

[0003] Therefore, how to provide a negative pole piece to ensure the fast charging capability of the silicon-carbon soft-pack lithium battery while improving the cycle capability and the stability of the silicon-carbon soft-pack lithium battery at a high voltage has become a technical problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the present application provides a negative pole piece, a preparation method thereof and a silicon-carbon soft-pack lithium battery. The negative pole piece provided by the present application comprises an inner layer, a protective layer and a stable layer which are sequentially stacked in the negative active material layer, the inner layer provides high specific capacity and excellent fast charging capability, and at the same time, it performs excellently in terms of conductivity; the protective layer is close to the physical properties of the inner layer, which can ensure the stability of the interface contact and effectively alleviate the negative effects caused by silicon expansion, and prevent the structure from being damaged; the stable layer can improve the stability of the battery at a high voltage, avoid lithium precipitation of the battery at a high rate, and ensure long-term stability of the battery performance. The combination of the inner layer, the protective layer and the stable layer effectively improves the performance degradation problem of the silicon-carbon soft-pack lithium battery under fast charging (3C) and voltage window (4.55V) operating conditions, while taking into account the excellent cycle performance.

[0005] To achieve this purpose, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a negative pole piece, which comprises a current collector and a negative active material layer located on at least one side surface of the current collector;

[0007] The negative active material layer comprises an inner layer, a protective layer and a stable layer which are sequentially stacked, and the inner layer is close to the current collector;

[0008] The inner layer comprises a first silicon-carbon composite material;

[0009] The protective layer comprises a second silicon-carbon composite material and a first silicon-oxygen composite material;

[0010] The stabilizing layer comprises a second silicon-oxygen composite material and a graphite material.

[0011] In this invention, the inner layer includes a first silicon-carbon composite material (high capacity), which provides high specific capacity and excellent fast charging capability, while also exhibiting excellent conductivity. The protective layer includes a second silicon-carbon composite material and a first silicon-oxygen composite material (medium-high capacity), which have similar physical properties to the inner layer, ensuring the stability of the interface contact and effectively mitigating the negative impact of silicon expansion, thus preventing structural damage. The stabilizing layer includes a second silicon-oxygen composite material and graphite material, which can improve the fast charging capability of the negative electrode and prevent lithium plating under high-rate fast charging, ensuring the stability of the battery at high voltage, avoiding lithium plating at high rates, and ensuring long-term stable battery performance.

[0012] And / or, the thickness of the inner layer is 10μm-20μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm, etc.

[0013] And / or, the first silicon-carbon composite material has a spherical or blocky morphology, preferably a spherical morphology.

[0014] And / or, the median particle size of the first silicon-carbon composite material is 2μm-7μm, such as 2μm, 3μm, 4μm, 5μm, 6μm or 7μm.

[0015] And / or, based on the total mass of the inner layer as 100wt%, the content of the first silicon-carbon composite material is 78.5wt%-96.5wt%, for example 78.5wt%, 80.5wt%, 82.5wt%, 84.5wt%, 86.5wt%, 88.5wt%, 90.5wt%, 92.5wt%, 94.5wt%, or 96.5wt%, etc.

[0016] And / or, the difference between the electrode capacity of the corresponding region of the protective layer and the electrode capacity of the corresponding region of the inner layer is 10 mAh·cm. -2 -50mAh·cm -2 For example, 10mAh·cm -2 20mAh·cm -2 30mAh·cm -2 40mAh·cm -2 or 50mAh·cm -2 wait.

[0017] In this invention, the difference between the electrode capacity of the corresponding region of the control protective layer and the electrode capacity of the corresponding region of the inner layer is 10 mAh·cm. -2 -50mAh·cm -2 This can slow down the volume expansion of silicon materials during charging and discharging, preventing material shedding or battery performance degradation.

[0018] And / or, the thickness of the protective layer is 15μm-25μm, such as 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm.

[0019] And / or, the second silicon-carbon composite material has a spherical or blocky morphology, preferably a spherical morphology.

[0020] And / or, the second silicon-carbon composite material includes any one of a small-particle-size second silicon-carbon composite material, a medium-particle-size second silicon-carbon composite material, or a large-particle-size second silicon-carbon composite material, wherein the median particle size of the small-particle-size second silicon-carbon composite material is x, 1 μm ≤ x < 3.5 μm, for example 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, or 3.4 μm, etc., and the median particle size of the medium-particle-size second silicon-carbon composite material is x. The median particle size of the composite material is y, where 3.5μm≤y<6.0μm, for example 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm or 5.9μm, etc. The median particle size of the large-particle-size second silicon-carbon composite material is z, where 6μm≤z≤10μm, for example 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm, etc.

[0021] And / or, based on the total mass of the protective layer being 100wt%, the content of the second silicon-carbon composite material is 12wt%-25wt%, for example, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, or 25wt%, etc.

[0022] And / or, the first silicon-oxygen composite material includes at least one of a 4C fast-charging silicon-oxygen composite material, a 5C fast-charging silicon-oxygen composite material, or a 6C fast-charging silicon-oxygen composite material.

[0023] And / or, the first silica composite material includes any one of a small-particle-size first silica composite material, a medium-particle-size first silica composite material, or a large-particle-size first silica composite material, wherein the median particle size of the small-particle-size first silica composite material is a, where 2μm ≤ a < 3.5μm, for example, 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.2μm, or 3.4μm, etc., and the median particle size of the medium-particle-size first silica composite material is b, where 3.5μm ≤ b < The median particle size of the large-particle-size first silicon-oxygen composite material is c, where 6μm≤c≤9μm, for example, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm, or 5.9μm, and the median particle size is c, where 6μm≤c≤9μm, for example, 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, 7.5μm, 8μm, 8.2μm, 8.5μm, 8.8μm, or 9μm, etc.

[0024] And / or, based on the total mass of the protective layer as 100wt%, the content of the first silicon-oxygen composite material is 73.6wt%-83.6wt%, for example 73.6wt%, 75.6wt%, 77.6wt%, 79.6wt%, 81.6wt%, or 83.6wt%.

[0025] And / or, the thickness of the stabilizing layer is 24μm-35μm, for example 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm or 35μm, etc.

[0026] And / or, the second silicon-oxygen composite material includes at least one of a 4C fast-charging silicon-oxygen composite material, a 5C fast-charging silicon-oxygen composite material, or a 6C fast-charging silicon-oxygen composite material.

[0027] And / or, the second silica composite material includes any one of small-particle-size second silica composite material, medium-particle-size second silica composite material, or large-particle-size second silica composite material. The median particle size of the small-particle-size second silica composite material is 2μm-3.5μm, such as 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.2μm, or 3.5μm. The median particle size of the medium-particle-size second silica composite material is 4μm-5.5μm, such as 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, or 5.5μm. The median particle size of the large-particle-size second silica composite material is 6μm-7.5μm, such as 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, or 7.5μm.

[0028] And / or, based on the total mass of the stabilizing layer as 100wt%, the content of the second silicon-oxygen composite material is 17wt%-33wt%, for example, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, or 33wt%, etc.

[0029] And / or, the graphite material includes at least one of 4C fast-charging graphite material, 6C fast-charging graphite material, 8C fast-charging graphite material or 10C fast-charging graphite material.

[0030] And / or, the graphite material includes any one of small-particle-size graphite material, medium-particle-size graphite material, or large-particle-size graphite material. The median particle size of the small-particle-size graphite material is m, where 2μm ≤ m < 5μm, for example, 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.2μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, or 4.9μm, etc. The median particle size of the medium-particle-size graphite material is n, where 5μm ≤ n < 8μm, for example, 5μm < m < 5μm, etc. The particle sizes are μm, 5.2μm, 5.5μm, 5.8μm, 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, 7.5μm, or 7.9μm, etc., and the median particle size of the large-particle graphite material is s, 8μm≤s≤10μm, for example 8μm, 8.2μm, 8.5μm, 8.8μm, 8.2μm, 8.5μm, 8.8μm, 9μm, 9.2μm, 9.5μm, 9.8μm, or 10μm, etc.

[0031] And / or, based on the total mass of the stabilizing layer being 100wt%, the content of the graphite material is 65wt%-75wt%, for example, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, or 75wt%, etc.

[0032] And / or, the inner layer, the protective layer, and the stabilizing layer each independently include a conductive agent and a binder.

[0033] And / or, the conductive agent includes at least one of conductive carbon black, acetylene black, carbon nanotubes, graphene, or carbon nanofibers.

[0034] And / or, based on the total mass of the inner layer as 100wt%, the content of the conductive agent is 0.7wt%-5.0wt%, for example 0.7wt%, 1.2wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%.

[0035] And / or, based on the total mass of the protective layer being 100wt%, the content of the conductive agent is 0.7wt%-3.7wt%, for example, 0.7wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3wt%, or 3.7wt%.

[0036] And / or, based on the total mass of the stabilizing layer as 100wt%, the content of the conductive agent is 0.7wt%-5.0wt%, for example 0.7wt%, 1.2wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%.

[0037] And / or, the adhesive includes polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0038] And / or, based on the total mass of the inner layer as 100wt%, the content of the polyacrylic acid is 0.3wt%-2.0wt%, for example 0.3wt%, 0.5wt%, 1.0wt%, 1.5wt%, or 2.0wt%, etc.; the content of the sodium carboxymethyl cellulose is 0.2wt%-0.6wt%, for example 0.2wt%, 0.4wt%, or 0.6wt%, etc.; and the content of the styrene-butadiene rubber is 0.2wt%-1.0wt%, for example 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, or 1.0wt%, etc.

[0039] And / or, based on the total mass of the protective layer as 100wt%, the content of the polyacrylic acid is 0.2wt%-1.1wt%, for example 0.2wt%, 0.5wt%, 0.8wt%, or 1.1wt%, etc.; the content of the sodium carboxymethyl cellulose is 0.3wt%-1.5wt%, for example 0.3wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, or 1.5wt%, etc.; and the content of the styrene-butadiene rubber is 0.2wt%-1.1wt%, for example 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, or 1.1wt%, etc.

[0040] And / or, based on the total mass of the stabilizing layer as 100wt%, the content of the polyacrylic acid is 0.2wt%-1.4wt%, for example 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, or 1.4wt%, etc.; the content of the sodium carboxymethyl cellulose is 0.3wt%-1.8wt%, for example 0.3wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, 1.5wt%, or 1.8wt%, etc.; and the content of the styrene-butadiene rubber is 0.3wt%-1.5wt%, for example 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, or 1.5wt%, etc.

[0041] Secondly, the present invention also provides a method for preparing a negative electrode sheet according to the first aspect, the method comprising the following steps:

[0042] S1. Mix the first silicon-carbon composite material, conductive agent, binder and first solvent evenly to obtain a first slurry; mix the second silicon-carbon composite material, the first silicon-oxygen composite material, conductive agent, binder and second solvent evenly to obtain a second slurry; mix the second silicon-oxygen composite material, graphite material, conductive agent, binder and second solvent evenly to obtain a third slurry.

[0043] S2. The first slurry is coated on at least one side surface of the current collector to form an inner layer;

[0044] S3. The second slurry is coated on the surface of the inner layer away from the current collector to form a protective wet film. The third slurry is then coated on the surface of the protective wet film to obtain the negative electrode sheet.

[0045] And / or, in step S1, the first solvent includes at least one of ethylene carbonate, ethanol, acetone, deionized water, or butanone.

[0046] And / or, in step S1, the second solvent includes N-methylpyrrolidone and / or deionized water.

[0047] And / or, in step S1, the solid content of the first slurry is 40wt%-45wt%, for example, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, or 45wt%, etc.

[0048] And / or, in step S1, the solid content of the second slurry is 35wt%-50wt%, for example, 35wt%, 38wt%, 40wt%, 42wt%, 45wt%, 48wt%, or 50wt%.

[0049] And / or, the solid content of the third slurry in step S1 is 50wt%-60wt%, for example, 50wt%, 52wt%, 55wt%, 58wt% or 60wt%.

[0050] And / or, after the coating process described in step S2 is completed, a high-temperature curing step is also included.

[0051] And / or, the high-temperature curing temperature is 65℃-120℃, such as 65℃, 75℃, 85℃, 95℃, 105℃, 115℃ or 120℃.

[0052] And / or, the high-temperature curing time is 15s-60s, for example 15s, 30s, 45s or 60s.

[0053] And / or, after the third slurry described in step S3 is further coated on the surface of the protective wet film, the process further includes heat treatment and drying steps to obtain the negative electrode sheet.

[0054] And / or, the temperature of the heat treatment is 75℃-150℃, for example 75℃, 85℃, 95℃, 105℃, 115℃, 125℃, 135℃ or 150℃, etc.

[0055] And / or, the heat treatment time is 1 min to 30 min, for example, 1 min, 5 min, 10 min, 15 min, 20 min, 25 min or 30 min, etc.

[0056] It should be noted that the present invention does not impose specific requirements or special limitations on the coating method of the first slurry in step S2. Commonly used coating methods in the art are applicable to the present invention. Those skilled in the art can make adaptive selections and adjustments according to actual conditions, such as scraping or extrusion coating.

[0057] It should be noted that the present invention does not impose specific requirements or special limitations on the coating method of the second slurry in step S3. Commonly used coating methods in the art are applicable to the present invention. Those skilled in the art can make adaptive selections and adjustments according to actual conditions, such as spraying or dipping.

[0058] It should be noted that the present invention does not impose specific requirements or special limitations on the coating method of the third slurry in step S3. Commonly used coating methods in the art are applicable to the present invention. Those skilled in the art can make adaptive selections and adjustments according to actual conditions, such as spraying.

[0059] Thirdly, the present invention also provides a silicon-carbon soft-pack lithium battery, the silicon-carbon soft-pack lithium battery comprising a negative electrode sheet as described in the first aspect, or a negative electrode sheet prepared by the preparation method described in the second aspect.

[0060] Compared with the prior art, the present invention has at least the following beneficial effects:

[0061] The negative electrode sheet provided by this invention has the following advantages when used in silicon-carbon soft-pack lithium batteries: 1) Enhanced fast charging capability: The inner layer improves the specific capacity of the silicon-carbon soft-pack lithium battery, while the outer protective layer and stabilizing layer reduce the volume expansion of silicon and improve the high voltage stability of the silicon-carbon soft-pack lithium battery, ensuring the stable charging process of the silicon-carbon soft-pack lithium battery under 3C fast charging conditions; 2) Improved voltage window stability: The stabilizing layer can effectively suppress the side reactions between the electrolyte and the negative electrode material, enabling the silicon-carbon soft-pack lithium battery to work stably at a high voltage of 4.55V, thus extending the service life of the silicon-carbon soft-pack lithium battery; 3) Extended cycle life: The first silicon-carbon composite material included in the inner layer can enhance the stability and conductivity of the silicon-carbon soft-pack lithium battery, the protective layer effectively reduces the impact of silicon expansion on the negative electrode structure, and the stabilizing layer ensures that the silicon-carbon soft-pack lithium battery does not experience premature degradation during long-term use at high voltage, thereby extending the cycle life of the silicon-carbon soft-pack lithium battery. Detailed Implementation

[0062] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0063] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0064] The structure of the silicon-carbon composite material used in the specific embodiments of the present invention is as follows: spherical porous carbon serves as the skeleton, the pores are filled with silicon particles, and the surface is coated with an amorphous carbon coating layer (silicon content 46.3 wt%, carbon content 53.7 wt%).

[0065] The silicon-oxygen composite material was purchased from Ningbo Shanshan New Material Technology Co., Ltd.

[0066] Example 1

[0067] This embodiment provides a negative electrode sheet, which includes a copper foil. On one side surface of the copper foil, an inner layer with a thickness of 15 μm, a protective layer with a thickness of 23 μm, and a stabilizing layer with a thickness of 27 μm are sequentially stacked.

[0068] The inner layer contains 96.5 wt% first silicon-carbon composite material (spherical morphology, median particle size 3 μm), 2.5 wt% conductive carbon black, 0.3 wt% PAA binder, 0.2 wt% CMC, and 0.5 wt% SBR;

[0069] The protective layer contains 83.6 wt% of a first silicon-oxygen composite material (6C fast-charging silicon-oxygen composite material, median particle size 5 μm), 15 wt% of a second silicon-carbon composite material (spherical morphology, median particle size 3 μm), 0.7 wt% conductive carbon black, 0.2 wt% PAA binder, 0.3 wt% CMC, and 0.2 wt% SBR.

[0070] The stabilizing layer contains 73wt% graphite material (6C fast-charging graphite material, median particle size 7μm), 25wt% second silicon-oxygen composite material (6C fast-charging silicon-oxygen composite material, median particle size 5μm), 0.7wt% conductive carbon black, 0.3wt% PAA binder, 0.4wt% CMC, and 0.6wt% SBR.

[0071] This embodiment provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0072] S1. According to the above formula, the first silicon-carbon composite material, conductive carbon black, PAA binder, CMC, SBR latex (solid content of 37%), ethylene carbonate and deionized water are mixed and stirred evenly to obtain a first slurry with a solid content of 45wt%. The first silicon-oxygen composite material, the second silicon-carbon composite material, conductive carbon black, PAA binder, CMC, SBR latex (solid content of 37%), N-methylpyrrolidone and deionized water are mixed and stirred evenly to obtain a second slurry with a solid content of 50wt%. The graphite material, the second silicon-oxygen composite material, conductive carbon black, PAA binder, CMC, SBR latex (solid content of 37%), N-methylpyrrolidone and deionized water are mixed and stirred evenly to obtain a third slurry with a solid content of 50wt%.

[0073] S2. Apply the first slurry to one side of the copper foil and cure at 95°C for 30 seconds to form the inner layer;

[0074] S3. Spray the second slurry onto the surface of the inner layer to form a protective wet film. Continue to spray the third slurry onto the surface of the protective wet film. Heat treat at 110℃ for 3 minutes and dry to obtain the negative electrode sheet.

[0075] Examples 2-3

[0076] Examples 2 and 3 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of Example 1 are shown in Table 1. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0077] Table 1

[0078]

[0079] Examples 4-7

[0080] Examples 4-7 provide a negative electrode sheet and its preparation method. The differences in structure, composition, and preparation method between the negative electrode sheet and Example 1 are shown in Table 2. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0081] Table 2

[0082]

[0083] Examples 8-11

[0084] Examples 8-11 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 3. The remaining structures, compositions, preparation methods, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0085] Table 3

[0086]

[0087] Examples 12-13

[0088] Examples 12-13 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 4. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0089] Table 4

[0090]

[0091] Examples 14-17

[0092] Examples 14-17 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 5. The remaining structures, compositions, preparation methods, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0093] Table 5

[0094]

[0095] Examples 18-22

[0096] Examples 18-22 provide a negative electrode sheet and its preparation method. The differences in structure, composition, and preparation method between the negative electrode sheet and Example 1 are shown in Table 6. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0097] Table 6

[0098]

[0099] Examples 23-24

[0100] Examples 23-24 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 7. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0101] Table 7

[0102]

[0103] Examples 25-29

[0104] Examples 25-29 provide a negative electrode sheet and its preparation method. The differences in structure, composition, and preparation method between the negative electrode sheet and Example 1 are shown in Table 8. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0105] Table 8

[0106]

[0107] Examples 30-35

[0108] Examples 30-35 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 9. The remaining structures, compositions, preparation methods, and parameters are consistent with those of Example 1. The preparation method is adapted to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0109] Table 9

[0110]

[0111] Examples 36-37

[0112] Examples 36-37 provide a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of the negative electrode sheet and Example 1 are shown in Table 10. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0113] Table 10

[0114]

[0115] Example 38

[0116] Example 38 provides a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of Example 1 are shown in Table 11. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0117] Table 11

[0118]

[0119] Example 39

[0120] Example 39 provides a negative electrode sheet and its preparation method. The differences between the structure and composition of the negative electrode sheet and the preparation method of Example 1 are shown in Table 12. The remaining structure, composition, preparation method, and parameters are consistent with those of Example 1. The preparation method is adaptively adjusted according to the negative electrode sheet, while the remaining preparation methods and parameters are consistent with those of Example 1.

[0121] Table 12

[0122]

[0123] Comparative Example 1

[0124] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the protective layer and the stabilizing layer are omitted, while the remaining structure and composition are consistent with those of Example 1.

[0125] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0126] Comparative Example 2

[0127] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the inner layer and the stabilizing layer are omitted, while the remaining structure and composition are consistent with those of Example 1.

[0128] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0129] Comparative Example 3

[0130] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the inner layer and protective layer are omitted, while the remaining structure and composition are consistent with those of Example 1.

[0131] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0132] Comparative Example 4

[0133] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the second silicon-carbon composite material is omitted in the protective layer, and the corresponding content is increased in the first silicon-oxygen composite material (6C fast-charging silicon-oxygen composite material, median particle size 5μm). The remaining structure and composition are consistent with those of Example 1.

[0134] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0135] Comparative Example 5

[0136] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the first silicon-oxygen composite material is omitted in the protective layer, and the corresponding content is increased in the second silicon-carbon composite material (spherical morphology, median particle size 3 μm). The remaining structure and composition are consistent with those of Example 1.

[0137] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0138] Comparative Example 6

[0139] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the second silicon-oxygen composite material is omitted in the stabilizing layer, and the corresponding content is increased in the graphite material (6C fast-charging graphite material with a median particle size of 7μm). The remaining structure and composition are consistent with those of Example 1.

[0140] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0141] Comparative Example 7

[0142] This comparative example provides a negative electrode sheet and its preparation method. The structure of the negative electrode sheet differs from that of Example 1 in that the graphite material is omitted in the stabilizing layer, and its content is increased in the second silicon-oxygen composite material (6C fast-charging silicon-oxygen composite material with a median particle size of 5μm). The remaining structure and composition are consistent with those of Example 1.

[0143] The preparation method is adapted to the negative electrode sheet, while the other preparation methods and parameters remain the same as in Example 1.

[0144] Application Example 1-39 and Comparative Application Example 1-7

[0145] The negative electrode, 65μm thick lithium iron phosphate positive electrode, separator and electrolyte provided in Examples 1-39 and Comparative Examples 1-7 were used to assemble silicon-carbon soft-pack lithium batteries, corresponding to Application Examples 1-39 and Comparative Application Examples 1-7, respectively.

[0146] The batteries provided in Application Examples 1-39 and Comparative Application Examples 1-7 were subjected to performance tests under the following conditions: fast charging to 90% capacity at a constant rate of 3C, discharging to 3.0V at 0.2C, cycling 5 times, and taking the time to reach the constant rate on the 5th cycle to evaluate the 3C fast charging capability, and taking the capacity on the 5th cycle to evaluate the stability of the voltage window (full charge voltage 4.55V), and then charging and discharging at a constant rate of 3C for 1800 cycles to evaluate the battery capacity decay. The test results are shown in Table 13.

[0147] Table 13

[0148]

[0149]

[0150]

[0151] The test results show that:

[0152] (1) As can be seen from Application Examples 1 to 37, the negative electrode active material layer in the negative electrode sheet provided by the present invention includes an inner layer, a protective layer, and a stabilizing layer stacked sequentially. The combination of the inner layer, the protective layer, and the stabilizing layer effectively improves the performance degradation problem of silicon-carbon soft-pack lithium batteries under fast charging (3C) and voltage window (4.55V) operating conditions, while also taking into account better cycle performance. Specifically, the capacity decay is less than 5% when 3C charging to 90% in less than 20 minutes, the capacity decay is less than 10% after the 5th discharge, and the capacity decay is less than 5% during 3C cycling.

[0153] (2) As can be seen from Application Example 1 and Application Example 38, the present invention can achieve high capacity cycling stability by adjusting the content of the first silicon-oxygen composite material in the protective layer to 73.6wt%-83.6wt% and the content of the second silicon-carbon composite material to 12wt%-25wt%. However, if the content of the second silicon-carbon composite material is higher than the content of the first silicon-oxygen composite material, it will lead to a significant capacity decay after multiple cycles.

[0154] (3) As can be seen from Application Example 1 and Application Example 39, by adjusting the content of graphite material in the stabilizing layer to 65wt%-75wt% and the content of the second silicon-oxygen composite material to 17wt%-33wt%, the present invention can achieve high-rate fast charging and maintain a high capacity. However, if the content of the second silicon-oxygen composite material is higher than the content of graphite material, it will lead to the decay of fast charging capability.

[0155] (4) As can be seen from Application Examples 1-37 and Comparative Application Examples 1-3, the negative electrode active material layer in the negative electrode sheet provided by the present invention includes an inner layer, a protective layer and a stabilizing layer stacked in sequence. The combination of the inner layer, the protective layer and the stabilizing layer effectively improves the performance degradation problem of silicon-carbon soft-pack lithium battery under fast charging (3C) and voltage window (4.55V) operating conditions, and takes into account the overall superior performance of silicon-carbon soft-pack lithium battery. However, if only a single arbitrary layer structure is set, the silicon-carbon soft-pack lithium battery cannot take into account the overall performance, and the stability of 3C fast charging, 4.55V voltage window and 3C cycle performance are all greatly reduced.

[0156] (5) As can be seen from Application Examples 1-37 and Comparative Application Examples 4-7, the protective layer of the present invention includes a second silicon-carbon composite material and a first silicon-oxygen composite material, and the stabilizing layer includes a second silicon-oxygen composite material and a graphite material. Using the second silicon-carbon composite material and the first silicon-oxygen composite material together can maintain a higher voltage window stability and thus maintain a better capacity compared to using the second silicon-carbon composite material alone (Comparative Example 5) and the first silicon-oxygen composite material alone (Comparative Example 4). Using the second silicon-oxygen composite material and the graphite material together can better improve the high-rate fast charging performance compared to using the second silicon-oxygen composite material alone (Comparative Example 7) and the graphite material alone (Comparative Example 6).

[0157] In summary, the negative electrode active material layer in the negative electrode sheet provided by this invention comprises an inner layer, a protective layer, and a stabilizing layer stacked sequentially. The inner layer provides high specific capacity and excellent fast-charging capability, while also exhibiting superior conductivity. The protective layer has similar physical properties to the inner layer, ensuring the stability of the interface contact and effectively mitigating the negative impacts of silicon expansion, preventing structural damage. The stabilizing layer improves the battery's stability at high voltages, preventing lithium plating at high rates and ensuring long-term stable battery performance. The combination of the inner layer, protective layer, and stabilizing layer effectively improves the performance degradation problem of silicon-carbon soft-pack lithium batteries under fast-charging (3C) and voltage window (4.55V) operating conditions, while also maintaining superior cycle performance.

[0158] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active material layer located on at least one side surface of the current collector; The negative electrode active material layer includes an inner layer, a protective layer, and a stabilizing layer stacked sequentially, with the inner layer close to the current collector; The inner layer comprises a first silicon-carbon composite material; The protective layer comprises a second silicon-carbon composite material and a first silicon-oxygen composite material; The stabilizing layer comprises a second silicon-oxygen composite material and a graphite material.

2. The negative electrode sheet according to claim 1, characterized in that, The thickness of the inner layer is 10μm-20μm; And / or, the first silicon-carbon composite material includes a spherical morphology or a blocky morphology; And / or, the median particle size of the first silicon-carbon composite material is 2 μm-7 μm; And / or, based on the total mass of the inner layer being 100wt%, the content of the first silicon-carbon composite material is 78.5wt%-96.5wt%.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The difference between the electrode capacity of the corresponding electrode region in the protective layer and the electrode capacity of the corresponding electrode region in the inner layer is 10 mAh·cm⁻¹. -2 -50mAh·cm -2 ; And / or, the thickness of the protective layer is 15μm-25μm; And / or, the second silicon-carbon composite material includes a spherical morphology or a blocky morphology; And / or, the second silicon-carbon composite material includes any one of small-particle-size second silicon-carbon composite material, medium-particle-size second silicon-carbon composite material, or large-particle-size second silicon-carbon composite material, wherein the median particle size of the small-particle-size second silicon-carbon composite material is x, 1 μm ≤ x < 3.5 μm, the median particle size of the medium-particle-size second silicon-carbon composite material is y, 3.5 μm ≤ y < 6.0 μm, and the median particle size of the large-particle-size second silicon-carbon composite material is z, 6 μm ≤ z ≤ 10 μm; And / or, based on a total mass of 100wt% of the protective layer, the content of the second silicon-carbon composite material is 12wt%-25wt%.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The first silicon-oxygen composite material includes at least one of 4C fast-charging silicon-oxygen composite material, 5C fast-charging silicon-oxygen composite material, or 6C fast-charging silicon-oxygen composite material; And / or, the first silica composite material includes any one of small-particle-size first silica composite material, medium-particle-size first silica composite material, or large-particle-size first silica composite material, wherein the median particle size of the small-particle-size first silica composite material is a, 2μm≤a<3.5μm, the median particle size of the medium-particle-size first silica composite material is b, 3.5μm≤b<6μm, and the median particle size of the large-particle-size first silica composite material is c, 6μm≤c≤9μm; And / or, based on a total mass of 100wt% of the protective layer, the content of the first silicon-oxygen composite material is 73.6wt%-83.6wt%.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the stabilizing layer is 24μm-35μm; And / or, the second silicon-oxygen composite material includes at least one of 4C fast-charging silicon-oxygen composite material, 5C fast-charging silicon-oxygen composite material, or 6C fast-charging silicon-oxygen composite material; And / or, the second silica composite material includes any one of small-particle-size second silica composite material, medium-particle-size second silica composite material, or large-particle-size second silica composite material, wherein the median particle size of the small-particle-size second silica composite material is 2μm-3.5μm, the median particle size of the medium-particle-size second silica composite material is 4μm-5.5μm, and the median particle size of the large-particle-size second silica composite material is 6μm-7.5μm; And / or, based on a total mass of 100wt% of the stabilizing layer, the content of the second silicon-oxygen composite material is 17wt%-33wt%.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The graphite material includes at least one of 4C fast-charging graphite material, 6C fast-charging graphite material, 8C fast-charging graphite material, or 10C fast-charging graphite material; And / or, the graphite material includes any one of small-particle-size graphite material, medium-particle-size graphite material, or large-particle-size graphite material, wherein the median particle size of the small-particle-size graphite material is m, 2μm≤m<5μm, the median particle size of the medium-particle-size graphite material is n, 5μm≤n<8μm, and the median particle size of the large-particle-size graphite material is s, 8μm≤s≤10μm; And / or, based on a total mass of 100wt% of the stabilizing layer, the content of the graphite material is 65wt%-75wt%.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The inner layer, the protective layer, and the stabilizing layer each independently include a conductive agent and a binder.

8. A method for preparing a negative electrode sheet according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: S1. Mix the first silicon-carbon composite material, conductive agent, binder and first solvent evenly to obtain a first slurry; mix the second silicon-carbon composite material, the first silicon-oxygen composite material, conductive agent, binder and second solvent evenly to obtain a second slurry; mix the second silicon-oxygen composite material, graphite material, conductive agent, binder and second solvent evenly to obtain a third slurry. S2. The first slurry is coated on at least one side surface of the current collector to form an inner layer; S3. The second slurry is coated on the surface of the inner layer away from the current collector to form a protective wet film. The third slurry is then coated on the surface of the protective wet film to obtain the negative electrode sheet.

9. The preparation method according to claim 8, characterized in that, Step S1: The solid content of the first slurry is 40wt%-45wt%; And / or, in step S1, the solid content of the second slurry is 35wt%-50wt%; And / or, the solid content of the third slurry in step S1 is 50wt%-60wt%.

10. A silicon-carbon soft-pack lithium battery, characterized in that, The silicon-carbon soft-pack lithium battery includes a negative electrode sheet as described in any one of claims 1-7, or a negative electrode sheet prepared by the preparation method described in claim 8 or 9.

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