Negative pole piece, preparation method thereof and steel shell battery

Abstract

The invention provides a negative pole piece, a preparation method thereof and a steel shell battery. The negative pole piece comprises the following raw materials: 80%-95% of graphite, 5%-20% of a silicon carbon material, 0.5%-1% of conductive carbon black, 0.1%-0.3% of a carbon nanotube, 0.1%-0.2% of a thickening agent, 0.6%-1.5% of a first binder and 0.7%-2% of a second binder, wherein the first binder is different from the second binder; graphite, a carbon nanotube, a silicon carbon material and conductive carbon black are compounded, and a plurality of conductive materials generate a synergistic effect, so that the energy density of the electrode is favorably improved; besides, the first binder and the second binder are also added in the formula, through the synergistic effect of the multiple binders, the electrode material can be bonded more firmly, friction heat caused by vibration, volume change and the like among particles is reduced, and thus the heat dissipation efficiency is improved; the negative pole piece prepared by adopting the formula has relatively high energy density and excellent heat dissipation performance, and is suitable for the steel shell battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode plate and a preparation method thereof, and a steel-shell battery. Background Art

[0002] With the advent of the AI ​​era, market demand for AI mobile phones has surged, placing higher performance requirements on the lithium-ion batteries in mobile phones. Currently, the mainstream lithium-ion batteries on the market are still soft-pack batteries. However, soft-pack batteries have problems such as low energy density, poor heat dissipation, non-removability, and poor safety, which affect the daily use experience of mobile phone users. Compared with soft-pack batteries, steel-case batteries have higher energy density, better heat dissipation performance, and higher safety. Therefore, there is an urgent need to research and develop materials for steel-case batteries to meet the long-term battery life of AI mobile phones. It can also ensure stable operation of the battery in high-temperature environments, help improve the user experience of mobile phone users, and accelerate the sustainable development of AI mobile phones.

[0003] In related technologies, lithium-ion batteries include positive electrode sheets, negative electrode sheets and separators. The active material in the positive electrode sheet accounts for a high proportion, and the main material is relatively stable, which has limitations in improving the energy density of the battery.

[0004] However, the negative electrode undergoes significant volume changes during charge and discharge, which can easily lead to damage to the battery structure and capacity decay. This is particularly true for steel-cased batteries, which is why the development of suitable negative electrode sheets for steel-cased batteries is crucial. Summary of the Invention

[0005] The embodiments of the present invention provide a negative electrode plate and a preparation method thereof, and a steel-cased battery, which have high energy density and excellent heat dissipation and are suitable for use in steel-cased batteries.

[0006] In a first aspect, an embodiment of the present invention provides a negative electrode plate. The negative electrode plate comprises the following raw materials, calculated by mass percentage, based on the total mass of the negative electrode plate:

[0007] 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder and 0.7% to 2% second binder; wherein the first binder is different from the second binder.

[0008] In one embodiment, the carbon nanotubes are multi-walled carbon nanotubes, and the specific surface area of ​​the multi-walled carbon nanotubes is 800 m 2 / g~1600m 2 / g; and / or

[0009] The aspect ratio of the multi-walled carbon nanotubes is 1000-4000.

[0010] In one embodiment, the particle size D50 of the silicon-carbon material is 6 μm to 10 μm; and / or

[0011] The mass ratio of silicon to carbon in the silicon-carbon material is 0.8 to 1.

[0012] In one embodiment, the first binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and carboxymethyl cellulose; and / or

[0013] The second binder includes at least one of polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0014] In a second aspect, an embodiment of the present invention provides a method for preparing a negative electrode sheet, the method comprising preparing a negative electrode slurry; the negative electrode slurry is prepared by the following steps:

[0015] 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder, 0.7% to 2% second binder, 1% to 3% additives, and 40% to 60% first solvent; wherein the first binder is different from the second binder;

[0016] dissolving the thickener in a portion of the first solvent and stirring to obtain a first glue solution;

[0017] Mixing the graphite, the silicon-carbon material and the conductive carbon black to obtain a mixed powder;

[0018] mixing part of the first glue solution, part of the first binder, part of the first solvent and the mixed powder, and stirring to obtain a first mixed solution;

[0019] adding the carbon nanotubes to the first mixed solution and stirring to obtain a second mixed solution;

[0020] adding the remaining first glue solution, the remaining first solvent, and the additive to the second mixed solution, and continuing stirring to obtain a third mixed solution;

[0021] The second binder is added and the viscosity is adjusted to prepare the negative electrode slurry.

[0022] In one embodiment, the thickener is dissolved in a portion of the first solvent and stirred to obtain a first glue solution, and the stirring includes a combination of stirring at a first speed and stirring at a second speed; preferably,

[0023] The first rotation speed is 10 rpm to 30 rpm; the second rotation speed is 1500 rpm to 3000 rpm.

[0024] In one embodiment, part of the first glue solution, part of the first binder and part of the first solvent are added to the mixed powder and stirred to obtain a first mixed solution, and the stirring includes stirring at a third speed and stirring at a fourth speed; preferably, the third speed is 10rpm~30rpm, and the fourth speed is 500rpm~1000rpm.

[0025] In one embodiment, the remaining first glue solution, the remaining first solvent and the additive are added to the second mixed solution, and stirring is continued to obtain a third mixed solution, and the stirring includes stirring at a fifth speed and stirring at a sixth speed; preferably,

[0026] The fifth rotation speed is 10 rpm to 30 rpm, and the sixth rotation speed is 1000 rpm to 3000 rpm.

[0027] In one embodiment, the portion of the first gel solution is 10% to 30% of the first gel solution; and / or

[0028] The remaining first glue solution is 70% to 90% of the first glue solution.

[0029] In one embodiment, the viscosity of the negative electrode slurry is 2500 cp to 4500 cp; preferably, the viscosity of the negative electrode slurry is 3000 cp to 4000 cp; and / or

[0030] The solid content of the negative electrode slurry is 40% to 50%; preferably, the solid content of the negative electrode slurry is 43% to 47%.

[0031] In a third aspect, an embodiment of the present invention provides a steel-shell battery, which includes a positive electrode sheet, a negative electrode sheet and a separator; the negative electrode sheet is made of the negative electrode slurry as described above.

[0032] In one embodiment, the positive electrode sheet is made of positive electrode slurry, and the positive electrode slurry includes the following components in percentage by mass:

[0033] 95% to 99% positive electrode material, 0.5% to 1% conductive carbon black, 0.15% to 1% first carbon nanotube, 0.05% to 1% second carbon nanotube, 0.01% to 1% dispersant, 0.29% to 1% binder, and 10% to 20% second solvent;

[0034] Wherein, the specific surface area of ​​the first carbon nanotube is 250m 2 / g~330m 2 / g, the aspect ratio of the first carbon nanotubes is 1000-2000;

[0035] The specific surface area of ​​the second carbon nanotube is 250 m 2 / g~330m 2 / g, and the aspect ratio of the second carbon nanotubes is 5000-10000.

[0036] In one embodiment, the positive electrode slurry is prepared by the following steps:

[0037] dissolving the binder in a portion of the second solvent and stirring to obtain a second adhesive solution;

[0038] adding the dispersant and the remaining second solvent to the second glue solution, mixing, and continuing to add the conductive carbon black and the first carbon nanotubes, stirring to obtain a fourth mixed solution;

[0039] adding the positive electrode material to the fourth mixed solution and mixing to obtain a fifth mixed solution;

[0040] The second carbon nanotubes are added to the fifth mixed solution, and stirring is continued to obtain a positive electrode slurry.

[0041] In one embodiment, the viscosity of the positive electrode slurry is 3000cp to 5000cp; and / or

[0042] The solid content of the positive electrode slurry is 70% to 75%.

[0043] Beneficial effects of the embodiments of the present invention:

[0044] In an embodiment of the present invention, by adding graphite, carbon nanotubes and silicon-carbon materials to the formula, the carbon nanotubes are multi-walled, have a high aspect ratio and excellent conductivity, and can form a three-dimensional conductive network, thereby greatly improving the conductivity of the electrode; the theoretical specific capacity of silicon in the silicon-carbon material is very high, but it has a huge volume change during the charge and discharge process. The addition of graphite and carbon nanotubes can alleviate the volume change to a certain extent. Therefore, compounding graphite, carbon nanotubes, silicon-carbon materials with conductive carbon black is beneficial to improving the energy density of the electrode; in addition, a first binder and a second binder are also added to the formula. Through the synergistic effect of multiple binders, the electrode material can be more firmly bonded, reducing frictional heat generated between particles due to vibration, volume change, etc., and the tightly ordered bonding structure can reduce the obstacles to heat transfer, making it easier for heat to be transferred from the inside of the electrode to the outside, thereby improving the heat dissipation efficiency; the negative electrode sheet prepared using the above formula has a high energy density and excellent heat dissipation, and is suitable for steel-shell batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0046] Figure 1 is a flow chart of a method for preparing a negative electrode slurry in an embodiment of the present invention;

[0047] Figure 2 Schematic diagram of capacity retention rate change under normal temperature cycling provided by Example 1 of the present invention;

[0048] Figure 3 This is a schematic diagram of the change in capacity retention rate under 45°C cycling provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise specified, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inside" and "outside" refer to the outline of the device.

[0050] In related technologies, lithium-ion batteries include positive electrode sheets, negative electrode sheets and separators. The active material in the positive electrode sheet accounts for a high proportion, about 95% to 99%, and its main material is relatively stable. Therefore, there are limitations in improving the energy density of the battery.

[0051] However, the volume of the negative electrode changes greatly during the charging and discharging process, which can easily lead to damage to the battery structure and capacity attenuation. Therefore, the negative electrode has a greater impact on steel-shell batteries, and the research and development of negative electrode sheets suitable for steel-shell batteries is particularly critical.

[0052] In view of this, the embodiments of the present application provide a negative electrode plate and a preparation method thereof, and a steel-shell battery, aiming to provide a negative electrode plate suitable for a steel-shell battery, which has a high energy density and excellent heat dissipation performance.

[0053] In a first aspect, an embodiment of the present invention provides a negative electrode plate. The negative electrode plate comprises the following raw materials in terms of mass percentage, based on the total mass of the negative electrode plate:

[0054] 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder and 0.7% to 2% second binder; wherein the first binder is different from the second binder.

[0055] By adopting the above scheme, graphite, carbon nanotubes and silicon-carbon materials are added to the formula. The carbon nanotubes are multi-walled, have a high aspect ratio and excellent conductivity, and can form a three-dimensional conductive network, thereby greatly improving the conductivity of the electrode; the theoretical specific capacity of silicon in the silicon-carbon material is very high, but it has a huge volume change during the charging and discharging process. The addition of graphite and carbon nanotubes can alleviate the volume change to a certain extent. Therefore, compounding graphite, carbon nanotubes, silicon-carbon materials with conductive carbon black is beneficial to improving the energy density of the electrode; in addition, a first binder and a second binder are also added to the formula. Through the synergistic effect of multiple binders, the electrode material can be more firmly bonded, reducing frictional heat generated between particles due to vibration, volume change, etc., and the tightly ordered bonding structure can reduce the obstacles to heat transfer, making it easier for heat to be transferred from the inside of the electrode to the outside, thereby improving the heat dissipation efficiency; the negative electrode sheet prepared by the above formula has a high energy density and excellent heat dissipation, and is suitable for steel-shell batteries.

[0056] In some embodiments of the present application, the carbon nanotubes are multi-walled carbon nanotubes, and the specific surface area of ​​the multi-walled carbon nanotubes is 800 m 2 / g~1600m 2 / g.

[0057] By adopting the above solution, carbon nanotubes are limited to multi-walls, resulting in a larger specific surface area. This high specific surface area helps increase the contact area with the active material, allowing lithium ions to be more efficiently inserted and removed, thereby improving the utilization rate of motor materials and fully utilizing the lithium storage capacity of graphite and silicon-carbon materials, thereby increasing the energy density of the battery. Furthermore, the larger specific surface area also helps increase the heat exchange area with the surrounding environment, thereby accelerating heat dissipation and improving the battery's heat dissipation performance, thereby ensuring the battery's thermal stability during the charge and discharge process.

[0058] In some embodiments of the present application, the aspect ratio of the multi-walled carbon nanotubes is 1000-4000.

[0059] By adopting the above scheme, multi-walled carbon nanotubes with an aspect ratio of 1000 to 4000 help form an efficient conductive network. A larger aspect ratio means a thinner tube, which is more conducive to building a long-distance conductive path between the electrodes, reducing obstacles to electron transmission and lowering the internal resistance of the battery, thereby improving charge and discharge efficiency, reducing energy loss, and thus increasing the energy density of the electrode. At the same time, the aspect ratio in this range can penetrate the electrode material, quickly conducting away locally generated heat and preventing heat accumulation.

[0060] In some embodiments of the present application, the D50 particle size of the silicon-carbon material is 6 μm to 10 μm.

[0061] By adopting the above solution, the D50 particle size of the silicon-carbon material is limited to a moderate particle size range. The appropriate particle size can reduce the diffusion distance of lithium ions within the particles, lowering diffusion resistance and helping to improve the overall performance of the battery. In addition, the above particle size range is also conducive to reducing the stress concentration caused by silicon volume changes, which can be more evenly distributed, reducing the degree of damage to the electrode structure, and thus improving the cycle stability of the battery.

[0062] In some embodiments of the present application, the mass ratio of silicon to carbon in the silicon-carbon material is 0.8 to 1. Exemplarily, the mass ratio of silicon to carbon in the silicon-carbon material is 1:1.

[0063] By adopting this approach, silicon's ultra-high theoretical specific capacity allows it to store large amounts of lithium ions, providing a foundation for increasing battery energy density. Carbon, with its excellent conductivity and structural stability, can compensate for silicon's shortcomings of poor conductivity and excessive volume expansion during charge and discharge. A 1:1 mass ratio of the two allows silicon to fully utilize its high specific capacity while leveraging carbon's structural stability and ensuring smooth electron transfer, effectively increasing the battery's energy density.

[0064] In some embodiments of the present application, the first binder may include at least one of polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0065] By adopting the above scheme, the first binder contains a large number of carboxyl groups and has good hydrophilicity. It can be evenly dispersed in the system and form a hydrogen bond network with the solvent molecules. When the battery generates heat during charging and discharging, the thermal motion of the water molecules can quickly transfer heat. Through the hydrogen bond network formed by the first binder, the heat can be conducted away more efficiently, thereby playing a role in assisting heat dissipation.

[0066] In some embodiments of the present application, the second binder may include at least one of polyvinylidene fluoride, styrene-butadiene rubber, and carboxymethyl cellulose.

[0067] By adopting the above scheme, the second binder has good flexibility and adhesion, which can effectively tightly bond the particles of the electrode material. Its molecular structure contains unsaturated bonds. During the charging and discharging process, the fluctuation of the electron cloud helps to dissipate heat in the form of radiation. The thermal conductivity of this material itself is relatively good, and it can serve as a microchannel for heat transfer.

[0068] In a second aspect, an embodiment of the present invention provides a method for preparing a negative electrode sheet, referring to Figure 1 The preparation method includes preparing a negative electrode slurry; the negative electrode slurry is prepared by the following steps:

[0069] S10. Provide raw materials for negative electrode slurry according to the following mass percentages:

[0070] 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder, 0.7% to 2% second binder, 1% to 3% additives, and 40% to 60% first solvent; wherein the first binder is different from the second binder;

[0071] S20, dissolving the thickener in part of the first solvent and stirring to obtain a first glue solution, which is set aside; mixing the graphite, silicon-carbon material and conductive carbon black to obtain a mixed powder, which is set aside;

[0072] S30, mixing part of the first glue solution, part of the first binder, and part of the first solvent with the mixed powder, and stirring to obtain a first mixed solution;

[0073] S40, adding carbon nanotubes to the first mixed solution, and stirring to obtain a second mixed solution;

[0074] S50, adding the remaining first glue solution, the remaining first binder, the remaining first solvent and the additive to the second mixed solution, and continuing stirring to obtain a third mixed solution;

[0075] S60, adding a second binder, adjusting the viscosity, and preparing a negative electrode slurry.

[0076] By adopting this approach, the thickener is first evenly dispersed in a portion of the first solvent, providing a stable foundation for subsequent mixing. Then, a portion of the first glue solution, the first binder, and a portion of the first solvent are mixed with the mixed powder to evenly disperse the components. The carbon nanotubes are then added and evenly dispersed throughout the system to build a conductive network. Furthermore, the first glue solution and the first binder are added in stages. The proportion of these additions can affect the peel strength of the electrode, and thus the characteristics of the negative electrode. If the peel strength of the electrode is too weak, it can affect the battery's internal resistance, long-cycle performance, rate capability, and safety.

[0077] Specifically, the first binder is added first to form a preliminary electrode structure, and then the second binder is added. The first binder and the second binder firmly bond the graphite, silicon-carbon material, conductive carbon black, and carbon nanotubes by physical entanglement and chemical bonding, respectively, thereby enhancing the binding force between the particles, reducing particle shedding and displacement during charging and discharging, maintaining the stability of the electrode structure, and thus improving the cycle life of the battery.

[0078] In some embodiments of the present application, the thickener is dissolved in part of the first solvent and stirred to obtain a first gum solution. The stirring includes a combination of stirring at a first speed and stirring at a second speed, and the average speed of the first speed is less than the average speed of the second speed.

[0079] In some embodiments of the present application, the first speed is 10 rpm to 30 rpm; further, the first speed is 20 rpm to 30 rpm. Exemplarily, the first speed is 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, and any value between two adjacent values.

[0080] In some embodiments of the present application, the second speed is 1500 rpm to 3000 rpm. Further, the second speed is 2000 rpm to 3000 rpm. Exemplarily, the second speed is 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm, 3000 rpm, and any value between two adjacent values.

[0081] In some embodiments of the present application, part of the first glue solution, the first binder and part of the first solvent are added to the mixed powder and stirred to obtain a first mixed solution, wherein the stirring includes stirring at a third speed and stirring at a fourth speed, and the average speed of the third speed is less than the average speed of the fourth speed.

[0082] In some embodiments of the present application, the third speed is 10 rpm to 30 rpm. Further, the third speed is 20 rpm to 30 rpm. Exemplarily, the third speed is 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, and any value between two adjacent values.

[0083] In some embodiments of the present application, the fourth speed is 500 rpm to 1000 rpm. Further, the fourth speed is 750 rpm to 1000 rpm. Exemplarily, the fourth speed is 750 rpm, 760 rpm, 770 rpm, 780 rpm, 790 rpm, 800 rpm, 810 rpm, 820 rpm, 830 rpm, 840 rpm, 850 rpm, 860 rpm, 870 rpm, 880 rpm, 890 rpm, 900 rpm, 910 rpm, 920 rpm, 930 rpm, 940 rpm, 950 rpm, 960 rpm, 970 rpm, 980 rpm, 990 rpm, 1000 rpm, and any value between two adjacent values.

[0084] In some embodiments of the present application, the remaining portion of the first gel solution, the remaining first solvent and the additive are added to the second mixed solution, and stirring is continued to obtain a third mixed solution. The stirring may include stirring at a fifth speed and stirring at a sixth speed, and the average speed of the fifth speed is less than the average speed of the sixth speed.

[0085] In some embodiments of the present application, the fifth speed may be 10 rpm to 30 rpm. Further, the fifth speed is 20 rpm to 30 rpm. Exemplarily, the fifth speed is 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, and any value between two adjacent values.

[0086] In some embodiments of the present application, the sixth speed may be 1000 rpm to 3000 rpm. Further, the sixth speed is 2000 rpm to 3000 rpm. Exemplarily, the sixth speed is 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm, 3000 rpm, and any value between two adjacent values.

[0087] In some embodiments of the present application, the portion of the first gel solution is 10% to 30% of the first gel solution.

[0088] By adopting the above scheme, an appropriate amount of the first gel solution is added in the early stage to promote the physical mixing between the mixed powder and other raw materials to form a preliminary uniform system. As the remaining first gel solution and other components are subsequently added, the physical properties of the system such as viscosity and fluidity gradually change. At the same time, there may be some weak chemical interactions, which is conducive to better control of the rhythm of physical and chemical changes and ensure that a negative electrode slurry with excellent performance is finally prepared.

[0089] In some embodiments of the present application, the remaining first gel solution is 70% to 90% of the first gel solution.

[0090] By adopting this approach, the remaining first glue solution can completely encapsulate the graphite, silicon-carbon material, conductive carbon black, and carbon nanotubes, filling the weak areas of early bonding, helping to closely connect the various raw materials and build a stable electrode structure. The remaining first glue solution can strengthen the binding of the carbon-silicon material and simultaneously work synergistically with the first and second binders to buffer the volume expansion and contraction stress of the carbon-silicon material, thereby improving the battery's cycling stability.

[0091] In some embodiments of the present application, the viscosity of the negative electrode slurry is 2500 cp to 4500 cp. Further, the viscosity of the negative electrode slurry is 3000 cp to 4000 cp. Exemplarily, the viscosity of the negative electrode slurry is 3000 cp, 3100 cp, 3200 cp, 3300 cp, 3400 cp, 3500 cp, 3600 cp, 3700 cp, 3800 cp, 3900 cp, 4000 cp, and any value between two adjacent values.

[0092] By adopting the above solution, a viscosity of 2500cp to 4500cp enables the various components in the slurry to be tightly bonded to each other during the curing process, forming a uniform, continuous, and dense electrode structure. This structure can effectively prevent problems such as particle shedding and delamination during subsequent processing and use, ensuring the stability of the physical and electrochemical properties of the electrode. In addition, when the viscosity is between 2500cp and 4500cp, the slurry will not flow or have uneven thickness during coating due to too low viscosity, nor will it cause coating difficulties and scraper marks due to too high viscosity.

[0093] In some embodiments of the present application, the solid content of the negative electrode slurry is 40% to 50%. Further, the solid content of the negative electrode slurry is 43% to 47%. Exemplarily, the solid content of the negative electrode slurry is 43%, 44%, 45%, 46%, 47%, and any value between two adjacent values.

[0094] By adopting the above solution, a solid content of 40% to 50% means that the electrode contains more active materials, such as graphite and silicon-carbon materials, per unit volume. These materials are key to the battery's energy storage and release. More active materials can store more lithium ions, thereby increasing the battery's capacity. A solid content of 40% to 50% ensures that the negative electrode slurry has appropriate fluidity and coating properties. If the solid content is too low, the slurry contains too much solvent, which can easily cause flow during coating, making it difficult to accurately control the coating thickness and resulting in uneven electrode thickness. If the solid content is too high, the slurry is too viscous, making coating more difficult and potentially causing problems such as scraper marks and discontinuous coating.

[0095] In a third aspect, an embodiment of the present invention provides a steel-shell battery, which includes a positive electrode sheet, a negative electrode sheet as described above, and a separator.

[0096] By adopting the above solution, the steel-shell battery made of the above negative electrode plate has higher energy density, excellent heat dissipation performance and higher safety.

[0097] In some embodiments of the present application, the positive electrode sheet is made of a positive electrode slurry, and the positive electrode slurry includes the following components in percentage by mass:

[0098] 95% to 99% positive electrode material, 0.5% to 1% conductive carbon black, 0.15% to 1% first carbon nanotube, 0.05% to 1% second carbon nanotube, 0.01% to 1% dispersant, 0.29% to 1% binder, and 10% to 20% second solvent;

[0099] The specific surface area of ​​the first carbon nanotube is 250 m 2 / g~330m 2 / g, the aspect ratio of the first carbon nanotube is 1000-2000;

[0100] The specific surface area of ​​the second carbon nanotube is 250 m 2 / g~330m 2 / g, and the aspect ratio of the second carbon nanotubes is 5000-10000.

[0101] By adopting the above scheme, the positive electrode uses conductive carbon black, the first carbon nanotube and the second carbon nanotube. Since the aspect ratios of the first carbon nanotube and the second carbon nanotube are different, the first carbon nanotube can form dense conductive nodes, and the second carbon nanotube can connect these nodes to form a three-dimensional cross-conductive network, thereby improving the conductive efficiency of the battery.

[0102] In some embodiments of the present application, the positive electrode slurry is prepared by the following steps:

[0103] dissolving the binder in a portion of the second solvent and stirring to obtain a second adhesive solution;

[0104] Adding a dispersant and the remaining second solvent to the second glue solution and mixing, then adding conductive carbon black and the first carbon nanotubes, and stirring to obtain a fourth mixed solution;

[0105] adding a positive electrode material to the fourth mixed solution and mixing to obtain a fifth mixed solution;

[0106] The second carbon nanotubes are added to the fifth mixed solution, and stirring is continued to obtain a positive electrode slurry.

[0107] In some embodiments of the present application, the viscosity of the positive electrode slurry is 3000 cp to 5000 cp. For example, the viscosity of the positive electrode slurry is 3000 cp, 3200 cp, 3500 cp, 3700 cp, 3900 cp, 4100 cp, 4300 cp, 4500 cp, 4800 cp, 5000 cp, and any value between two adjacent values.

[0108] In some embodiments of the present application, the solid content of the positive electrode slurry is 70% to 75%. Exemplarily, the solid content of the positive electrode slurry is 70%, 71%, 72%, 73%, 74%, 75%, and any value between two adjacent values.

[0109] The present invention is described in detail below by means of specific examples, which are only some examples of the present invention and are not intended to limit the present invention. The raw materials used in the following examples, unless otherwise specified, are all commercially available products.

[0110] Example 1

[0111] A steel shell battery is prepared by the following steps:

[0112] S100, preparing the negative electrode sheet:

[0113] The raw materials of the negative electrode slurry are provided according to the following mass percentages:

[0114] Graphite 90%, silicon carbon material 7.3%, conductive carbon black 0.5%, carbon nanotubes 0.1%, thickener CMC 0.1%, styrene-butadiene rubber SBR 1%, polyacrylic acid 1%, additive EC 1% and deionized water 40%; among them, carbon nanotubes are multi-walled carbon nanotubes with a specific surface area of ​​1000m 2 / g, and the aspect ratio of the multi-walled carbon nanotubes is 2000; the D50 particle size of the silicon-carbon material is 6μm to 10μm; the mass ratio of silicon to carbon in the silicon-carbon material is 1:1;

[0115] Dissolve the thickener CMC in 20% deionized water and mix them, stir at 15 rpm for 30 minutes, scrape the thickener off the stirring shaft, and then continue stirring at 25 rpm and a dispersion speed of 2500 rpm for 300 minutes to obtain the first glue solution;

[0116] Graphite, silicon-carbon material and conductive carbon black were mixed and stirred at 20 rpm for 30 min to obtain a mixed powder;

[0117] 30% of the first glue solution, 30% of polyacrylic acid, and 30% of deionized water were mixed with the mixed powder, stirred at 15 rpm for 10 minutes, and then scraped the cylinder. The mixture was further stirred at 20 rpm and a dispersion speed of 800 rpm for 80 minutes to prepare a first mixed solution.

[0118] Add carbon nanotubes to the first mixed solution, stir at 15 rpm for 10 min, scrape the cylinder, and continue stirring at 20 rpm and 2000 rpm for 75 min to obtain a second mixed solution;

[0119] Add the remaining first glue solution, the remaining polyacrylic acid, the remaining deionized water and the EC additive to the second mixed solution, stir at a speed of 15 rpm for 15 minutes, and continue stirring at a speed of 20 rpm and a dispersion speed of 2500 rpm for 200 minutes to obtain a third mixed solution;

[0120] SBR was added, the viscosity was adjusted to 3500 cp, and the mixture was sieved with a 100-300 mesh sieve to obtain a negative electrode slurry.

[0121] Finally, the negative electrode slurry is coated, cold pressed, and die-cut to form negative electrode sheets.

[0122] S200, preparing positive electrode sheet:

[0123] The raw materials of the positive electrode slurry are provided according to the following mass percentage components:

[0124] 98% positive electrode material, 0.5% conductive carbon black, 0.6% first carbon nanotube, 0.2% second carbon nanotube, 0.3% polyvinyl pyrrolidone dispersant, 0.4% PVDF binder and 15% methyl pyrrolidone; wherein, the first carbon nanotube is multi-walled carbon nanotube MWCNT with an aspect ratio of 1500; the second carbon nanotube is single-walled carbon nanotube SWCNT with an aspect ratio of 8000;

[0125] Dissolve the binder in part of the second solvent, stir at a speed of 15 rpm for 30 minutes, scrape the binder off the stirring shaft, and continue stirring at a speed of 25 rpm and a dispersion speed of 2500 rpm for 300 minutes to obtain a second adhesive solution;

[0126] Add the dispersant and the remaining second solvent to the second glue solution, mix, stir at 15 rpm for 10 minutes, scrape the cylinder, add the conductive carbon black and the first carbon nanotubes, and continue stirring at 25 rpm and a dispersion speed of 2500 rpm for 60 minutes to obtain a fourth mixed solution;

[0127] Add the positive electrode material to the fourth mixed solution, stir at a speed of 20 rpm for 10 minutes, scrape the cylinder, and continue stirring at a speed of 25 rpm and a dispersion speed of 2500 rpm for 80 minutes to prepare a fifth mixed solution;

[0128] The second carbon nanotubes were added to the fifth mixed solution, and the mixture was stirred at a rotation speed of 20 rpm for 10 min, then the cylinder was scraped, and the mixture was stirred at a rotation speed of 25 rpm and a dispersion speed of 2500 rpm for 30 min to prepare a positive electrode slurry.

[0129] Finally, the positive electrode slurry is coated, cold pressed, and die-cut to form positive electrode sheets.

[0130] S300, Preparation of Steel Shell Battery:

[0131] The positive electrode sheets, negative electrode sheets and diaphragms are stacked to form a stacked core. After the stacked core is made, the tabs are welded to the bottom shell. After the stacked core is placed in the shell, the top cover and the bottom shell are welded with fillets and four sides. After welding, hot pressing is performed, and after hot pressing, the battery is baked in an oven, liquid is injected, and hot pressing, formation, liquid replenishment and capacity separation are performed before formation to form a steel shell battery.

[0132] Example 2

[0133] A steel shell battery, which differs from Example 1 in that the specific surface area of ​​the multi-walled carbon nanotubes in the negative electrode slurry is different. The specific surface area of ​​the multi-walled carbon nanotubes in this embodiment is 500m 2 / g, and the aspect ratio of the multi-walled carbon nanotubes is 500; wherein the preparation method of the negative electrode plate comprises the following steps:

[0134] S100, preparing the negative electrode sheet:

[0135] The raw materials of the negative electrode slurry are provided according to the following mass percentages:

[0136] 90% graphite, 7.3% silicon-carbon material, 0.5% conductive carbon black, 0.1% carbon nanotubes, 0.1% thickener CMC, 1% styrene-butadiene rubber (SBR), 1% polyacrylic acid, 1% EC additive, and 40% deionized water; wherein the carbon nanotubes are multi-walled carbon nanotubes with a specific surface area of ​​500 m2 / g and an aspect ratio of 500; the D50 particle size of the silicon-carbon material is 6 μm to 10 μm; and the mass ratio of silicon to carbon in the silicon-carbon material is 1:1;

[0137] Dissolve the thickener CMC in 20% deionized water and mix them, stir at 15 rpm for 30 minutes, scrape the thickener off the stirring shaft, and then continue stirring at 25 rpm and a dispersion speed of 2500 rpm for 300 minutes to obtain the first glue solution;

[0138] Graphite, silicon-carbon material and conductive carbon black were mixed and stirred at 20 rpm for 30 min to obtain a mixed powder;

[0139] 30% of the first glue solution, 30% of polyacrylic acid, and 30% of deionized water were mixed with the mixed powder, stirred at 15 rpm for 10 minutes, and then scraped the cylinder. The mixture was further stirred at 20 rpm and a dispersion speed of 800 rpm for 80 minutes to prepare a first mixed solution.

[0140] Add carbon nanotubes to the first mixed solution, stir at 15 rpm for 10 min, scrape the cylinder, and continue stirring at 20 rpm and 2000 rpm for 75 min to obtain a second mixed solution;

[0141] Add the remaining first glue solution, the remaining polyacrylic acid, the remaining deionized water and the EC additive to the second mixed solution, stir at a speed of 15 rpm for 15 minutes, and continue stirring at a speed of 20 rpm and a dispersion speed of 2500 rpm for 200 minutes to obtain a third mixed solution;

[0142] SBR was added, the viscosity was adjusted to 3500 cp, and the mixture was sieved with a 100-300 mesh sieve to obtain a negative electrode slurry.

[0143] Finally, the negative electrode slurry is coated, cold pressed, and die-cut to form negative electrode sheets.

[0144] Example 3

[0145] A steel shell battery, which differs from Example 1 in that the D50 particle size of the silicon-carbon material is different. In this embodiment, the D50 particle size of the silicon-carbon material is 10 μm to 16 μm. ；

[0146] The method for preparing the negative electrode sheet includes the following steps:

[0147] S100, preparing the negative electrode sheet:

[0148] The raw materials of the negative electrode slurry are provided according to the following mass percentages:

[0149] 90% graphite, 7.3% silicon-carbon material, 0.5% conductive carbon black, 0.1% carbon nanotubes, 0.1% thickener CMC, 1% styrene-butadiene rubber (SBR), 1% polyacrylic acid, 1% EC additive, and 40% deionized water; wherein the carbon nanotubes are multi-walled carbon nanotubes with a specific surface area of ​​1000 m2 / g and an aspect ratio of 2000; the D50 particle size of the silicon-carbon material is 10 μm to 16 μm; and the mass ratio of silicon to carbon in the silicon-carbon material is 1:1;

[0150] Dissolve the thickener CMC in 20% deionized water and mix them, stir at 15 rpm for 30 minutes, scrape the thickener off the stirring shaft, and then continue stirring at 25 rpm and a dispersion speed of 2500 rpm for 300 minutes to obtain the first glue solution;

[0151] Graphite, silicon-carbon material and conductive carbon black were mixed and stirred at 20 rpm for 30 min to obtain a mixed powder;

[0152] 30% of the first glue solution, 30% of polyacrylic acid, and 30% of deionized water were mixed with the mixed powder, stirred at 15 rpm for 10 minutes, and then scraped the cylinder. The mixture was further stirred at 20 rpm and a dispersion speed of 800 rpm for 80 minutes to prepare a first mixed solution.

[0153] Add carbon nanotubes to the first mixed solution, stir at 15 rpm for 10 min, scrape the cylinder, and continue stirring at 20 rpm and 2000 rpm for 75 min to obtain a second mixed solution;

[0154] Add the remaining first glue solution, the remaining polyacrylic acid, the remaining deionized water and the EC additive to the second mixed solution, stir at a speed of 15 rpm for 15 minutes, and continue stirring at a speed of 20 rpm and a dispersion speed of 2500 rpm for 200 minutes to obtain a third mixed solution;

[0155] SBR was added, the viscosity was adjusted to 3500 cp, and the mixture was sieved with a 100-300 mesh sieve to obtain a negative electrode slurry.

[0156] Finally, the negative electrode slurry is coated, cold pressed, and die-cut to form negative electrode sheets.

[0157] Example 4

[0158] A steel-cased battery differs from Example 1 in that the rotational speeds used in each step of the negative electrode slurry preparation process are different. In this example, the thickener CMC is dissolved in 20% deionized water and mixed, with stirring at a constant speed of 300 rpm. Simultaneously, when 30% of the first gel solution, 30% of the first binder, and 30% of deionized water are added to the mixed powder, stirring is maintained at a constant speed of 300 rpm.

[0159] Example 5

[0160] A steel-shell battery differs from Example 1 in that the positive electrode slurry formulation is different. In this example, only multi-walled carbon nanotubes with an aspect ratio of 3000 are used in the positive electrode slurry.

[0161] Comparative Example 1:

[0162] A steel-shell battery differs from Example 1 in that the binder in the negative electrode slurry and the order in which the binder is added are different. The preparation method of the negative electrode slurry in this comparative example is as follows:

[0163] Dissolve the thickener CMC in part of the deionized water and mix, stir at 15 rpm for 30 min, scrape the thickener off the stirring shaft, and then continue stirring at 25 rpm and a dispersion speed of 2500 rpm for 300 min to obtain a first glue solution;

[0164] Graphite, silicon-carbon material and conductive carbon black were mixed and stirred at 20 rpm for 30 min to obtain a mixed powder;

[0165] The first glue solution, styrene-butadiene rubber (SBR), the remaining ionized water and the mixed powder were mixed, stirred at a speed of 15 rpm for 10 minutes, and then scraped the cylinder. The stirring was continued at a speed of 20 rpm and a dispersion speed of 800 rpm for 80 minutes to prepare a first mixed solution.

[0166] Add carbon nanotubes to the first mixed solution, stir at 15 rpm for 10 min, scrape the cylinder, and continue stirring at 20 rpm and 2000 rpm for 75 min to obtain a second mixed solution;

[0167] Adding additive EC to the second mixed solution, stirring at a speed of 15 rpm for 15 min, and continuing stirring at a speed of 20 rpm and a dispersion speed of 2500 rpm for 200 min to obtain a third mixed solution;

[0168] Styrene-butadiene rubber (SBR) was added, the viscosity was adjusted to 3500 cp, and the mixture was sieved through a 100-300 mesh sieve to obtain a negative electrode slurry.

[0169] Comparative Example 2:

[0170] A soft pack battery differs from Example 1 in that the proportions of the components in the negative electrode slurry are different, and the order of adding materials and the stirring speed are different. The preparation method of the negative electrode slurry in this comparative example is as follows:

[0171] (1) The negative electrode graphite material (accounting for 96%), conductive carbon black (accounting for 1.3%), thickener (accounting for 1.2%), and binder (accounting for 1.5%) are prepared.

[0172] (2) After mixing the thickener and deionized water, stir at a speed of 15 rpm for 30 min, continue stirring at a speed of 25 rpm and a dispersion speed of 2000 rpm for 200 min, and then vacuum to obtain a glue solution.

[0173] (3) Mix the negative electrode material graphite and conductive carbon black and stir at 15 rpm for 15 minutes. Add the 28% glue solution and deionized water from step (1) to the mixture and stir at 30 rpm and a dispersion speed of 200 rpm for 10 minutes. After scraping the cylinder, continue stirring at 20 rpm and a dispersion speed of 200 rpm for 40 minutes. After scraping the cylinder again, continue stirring at 20 rpm and a dispersion speed of 200 rpm for 40 minutes.

[0174] (4) Add 36% of the glue solution from step (1) to the mixture, scrape the cylinder, stir at a speed of 25 rpm and a dispersion speed of 500 rpm for 30 minutes, and then evacuate. Add the remaining 36% glue solution and deionized water to the mixture, stir at a speed of 25 rpm and a dispersion speed of 4000 rpm for 120 minutes, and then evacuate.

[0175] (5) Add a binder to adjust the slurry viscosity to 3500cp and the solid content to 45%, then sieve it with a 150-mesh screen to form the negative electrode slurry;

[0176] The positive electrode uses lithium cobalt oxide, and the separator is a single-sided ceramic double-sided adhesive separator. The soft-pack battery production process: After the positive and negative electrodes are stacked, they are packaged (top and side seals), injected, formed, molded, and then divided into different capacities to obtain a soft-pack battery.

[0177] Performance testing:

[0178] (1) Steel shell battery capacity:

[0179] Charging: At 25°C, charge at a constant current and constant voltage of 1.0 C / min until the voltage reaches 4.47 V, with a cut-off current of 0.02 C / min.

[0180] Shelf: 30min;

[0181] Discharge: At 25°C, discharge at 0.2 C min to 2.75 V and record the discharge capacity.

[0182] (2) Capacity retention rate of normal temperature cycle:

[0183] At 25°C,

[0184] a) Charging: 1.3C to 4.16V, 1C to cut off; 1C to 4.28V, 0.8C to cut off; 0.8C to 4.5V,

[0185] 0.1C cut-off;.

[0186] b) Standing time: 10 min;

[0187] c) Discharge: Discharge at 0.5C to a cut-off voltage of 3.3V;

[0188] d) Standing time: 10 min;

[0189] According to the above charge and discharge cycle requirements (800 cycles);

[0190] Among them, 1 week, 100 weeks, 200 weeks, 300 weeks, 400 weeks, 500 weeks, 600 weeks, 700 weeks, 800 weeks, 900 weeks, 1000 weeks, 1100 weeks and 1200 weeks are tested according to the following steps:

[0191] At 23±2℃,

[0192] a) Charging: Charge at 0.2C to 4.47V, and cut off at 0.02C;

[0193] b) Standing time: 10 min;

[0194] c) Discharge: Discharge at 0.2C to a cut-off voltage of 2.75V;

[0195] d) Standing time: 10 min;

[0196] After the cycle is completed, the capacity retention rate is recorded (the capacity of each week is compared with the capacity of the second cycle: C / capacity of the second cycle).

[0197] (3) Capacity retention rate after 45℃ cycling:

[0198] At 45±2℃,

[0199] a) Charging: Charge at 1.3C to 4.16V, then cut off at 1C; Charge at 1C to 4.28V, then cut off at 0.8C; Charge at 0.8C to 4.47V, then cut off at 0.1C;

[0200] b) Standing time: 10 min;

[0201] c) Discharge: Discharge at 1C to a cut-off voltage of 3.0V;

[0202] d) Standing time: 10 min;

[0203] According to the above charge and discharge cycle requirements (600 cycles);

[0204] Among them, 1 week, 100 weeks, 200 weeks, 300 weeks, 400 weeks, 500 weeks and 600 weeks are tested according to the following steps:

[0205] At 45±2℃,

[0206] a) Charging: Charge at 0.2C to 4.47V, and cut off at 0.02C;

[0207] b) Standing time: 10 min;

[0208] c) Discharge: Discharge at 0.2C to a cut-off voltage of 2.75V;

[0209] d) Standing time: 10 min;

[0210] After the cycle is completed, the capacity retention rate is recorded (the capacity of each week is compared with the capacity of the second cycle: C / capacity of the second cycle).

[0211] (4) Thermal abuse test:

[0212] a) Place the fully charged battery cell after charging at 0.5C and ending at 0.05C for 30 minutes in a test chamber. Raise the temperature to 130±2°C at a rate of (5±2°C) / min. When the temperature reaches 130±2°C, maintain the constant temperature for 60 minutes.

[0213] b) After the test, remove the battery cell and visually inspect the battery cell at room temperature to see if there is fire, explosion, or smoke, and whether the surface temperature of the battery cell is less than 200°C.

[0214] (5) Temperature rise in normal temperature cycle:

[0215] The battery was cycled at 25°C for 100 cycles using the following steps: a) Charge: 1.3C to 4.16V, 1C cutoff; 1C to 4.28V, 0.8C cutoff; 0.8C to 4.5V, 0.1C cutoff; b) Rest time: 10 minutes; c) Discharge: 0.5C to a cutoff voltage of 3.3V. The surface temperature rise of the battery was recorded before and after 100 cycles. Observe whether the temperature rise was >5°C.

[0216] The test results are shown in Table 1

[0217] Table 1

[0218]

[0219]

[0220] Combining Examples 1 and 2 with Table 1, it can be seen that the reduced specific surface area and aspect ratio of Example 2 reduce the electrode material's charge storage capacity, conductivity, and charge-discharge rate, leading to reduced cycle performance. Furthermore, the reduced specific surface area increases the thermal resistance of the battery interface, affecting heat dissipation efficiency. The reduced aspect ratio complicates the three-dimensional arrangement of carbon nanotubes, creating thermal resistance in directions where efficient heat conduction is required, reducing heat dissipation efficiency.

[0221] Combining Example 1, Example 3 and Table 1, it can be seen that when the particle size of the silicon-carbon material becomes larger, the stability of the battery during the cycle is poor. The large-particle silicon material expands significantly in volume during the lithium insertion process, which may cause damage to the material structure, thereby reducing the cycle life of the battery.

[0222] In addition, the conductivity of large-particle silicon-carbon materials is relatively low, which is due to the uneven distribution of the silicon phase and the increased distance between the conductive carbon phases. Poor conductivity will lead to an increase in the internal resistance of the battery and reduce the overall performance of the battery. Moreover, when the particle size of the silicon-carbon material is large, it will have a negative impact on the heat dissipation of the battery. This is because large-particle silicon-carbon particles occupy more space inside the battery, resulting in a decrease in the wettability of the electrolyte, thereby affecting the battery's charge and discharge performance and heat conduction efficiency. In addition, large-particle silicon-carbon particles are more likely to cause particle breakage and electrical contact failure due to the large volume change during the battery charge and discharge process, further deteriorating the heat dissipation performance of the battery.

[0223] Combining Examples 1 and 4 with Table 1, it can be seen that the low rotational speed in Example 4 means insufficient shear force on the slurry, which can lead to uneven dispersion of the conductive agent and active material in the slurry, forming agglomerated particles. These agglomerated particles not only lead to poor conductivity of the battery but also increase the resistance of the electrode sheet, thereby affecting the overall performance of the battery.

[0224] Combining Examples 1 and 5 with Table 1, it can be seen that Example 5 utilizes single-walled carbon nanotubes. Single-walled carbon nanotubes have high electrical conductivity, which can reduce electrode resistance and heat generation, thereby improving the battery's charge-discharge performance and safety. During the charge-discharge process, when the volume of the positive electrode material changes, the large aspect ratio of single-walled carbon nanotubes forms a good conductive network with the positive electrode material, preventing the material from breaking or falling off, thereby improving the battery's cycle life. Furthermore, single-walled carbon nanotubes have a higher thermal conductivity per unit mass than multi-walled carbon nanotubes, allowing them to withstand higher temperatures.

[0225] Combining Example 1, Comparative Examples 1-2 and Table 1, it can be seen that graphite, carbon nanotubes and silicon-carbon materials are added to the formula of Example 1. Carbon nanotubes are multi-walled, have a high aspect ratio and excellent conductivity, and adding graphite and carbon nanotubes can alleviate volume changes to a certain extent. Figure 2-3, compounding graphite, carbon nanotubes, silicon-carbon materials with conductive carbon black helps to increase the energy density of the electrode, thereby ensuring that the battery has a high capacity retention rate. In addition, a first binder and a second binder are added to the formula. Through the synergistic effect of multiple binders, the electrode materials can be more firmly bonded, reducing frictional heat generated between particles due to vibration, volume change, etc., and the tightly ordered bonding structure can reduce obstacles to heat transfer, making it easier for heat to transfer from the inside of the electrode to the outside, thereby improving heat dissipation efficiency and being suitable for steel-shell batteries. Comparative Example 1, however, only uses conventional thickener CMC, which affects the battery's cycle performance and heat dissipation performance. Comparative Example 2 uses conventional soft-pack batteries, but the effect is not as good as Comparative Example 1.

[0226] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A negative electrode plate, characterized in that: Based on the total mass of the negative electrode sheet, The negative electrode sheet comprises the following components in terms of mass percentage: 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder and 0.7% to 2% second binder; wherein the first binder is different from the second binder.

2. The negative electrode sheet according to claim 1, characterized in that: The carbon nanotubes are multi-walled carbon nanotubes with a specific surface area of ​​800 m 2 / g~1600m 2 / g; and / or The aspect ratio of the multi-walled carbon nanotubes is 1000-4000.

3. The negative electrode sheet according to claim 1, characterized in that: The D50 particle size of the silicon-carbon material is 6 μm to 10 μm; and / or The mass ratio of silicon to carbon in the silicon-carbon material is 0.8 to 1.

4. The negative electrode sheet according to claim 1, characterized in that: The first binder comprises at least one of polyacrylic acid, polyacrylonitrile and polyacrylate; and / or The second binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and carboxymethyl cellulose.

5. A method for preparing a negative electrode sheet, characterized in that: The preparation method includes preparing a negative electrode slurry; the negative electrode slurry is prepared by the following steps: 80% to 95% graphite, 5% to 20% silicon-carbon material, 0.5% to 1% conductive carbon black, 0.1% to 0.3% carbon nanotubes, 0.1% to 0.2% thickener, 0.6% to 1.5% first binder, 0.7% to 2% second binder, 1% to 3% additives, and 40% to 60% first solvent; wherein the first binder is different from the second binder; dissolving the thickener in a portion of the first solvent and stirring to obtain a first glue solution; Mixing the graphite, the silicon-carbon material and the conductive carbon black to obtain a mixed powder; Mixing part of the first glue solution, part of the first binder, part of the first solvent and the mixed powder, and stirring to prepare a first mixed solution; adding the carbon nanotubes to the first mixed solution and stirring to obtain a second mixed solution; adding the remaining first glue solution, the remaining first binder, the remaining first solvent, and the additive to the second mixed solution, and continuing stirring to obtain a third mixed solution; The second binder is added and the viscosity is adjusted to prepare the negative electrode slurry.

6. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The thickener is dissolved in part of the first solvent and stirred to obtain a first glue solution, wherein the stirring includes a combination of stirring at a first rotational speed and stirring at a second rotational speed, and the average speed of the first rotational speed is less than the average speed of the second rotational speed; preferably, The first rotation speed is 10 rpm to 30 rpm; and / or The second rotation speed is 1500 rpm to 3000 rpm.

7. The method for preparing a negative electrode sheet according to claim 5, characterized in that: adding part of the first glue solution, part of the first binder and part of the first solvent to the mixed powder and stirring to obtain a first mixed solution, wherein the stirring includes stirring at a third speed and stirring at a fourth speed, and the average speed of the third speed is less than the average speed of the fourth speed; preferably, the third speed is 10 rpm to 30 rpm; and / or The fourth rotation speed is 500 rpm to 1000 rpm.

8. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The remaining first glue solution, the remaining first binder, the remaining first solvent and the additive are added to the second mixed solution, and stirring is continued to obtain a third mixed solution, wherein the stirring includes stirring at a fifth speed and stirring at a sixth speed, and the average speed of the fifth speed is less than the average speed of the sixth speed; preferably, The fifth rotation speed is 10 rpm to 30 rpm; and / or The sixth rotation speed is 1000 rpm to 3000 rpm.

9. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The portion of the first gel solution is 10% to 30% of the first gel solution; and / or The remaining first glue solution is 70% to 90% of the first glue solution.

10. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The viscosity of the negative electrode slurry is 2500 cp to 4500 cp; preferably, the viscosity of the negative electrode slurry is 3000 cp to 4000 cp; and / or The solid content of the negative electrode slurry is 40% to 50%; preferably, the solid content of the negative electrode slurry is 43% to 47%.

11. A steel shell battery, characterized in that: The steel-shell battery comprises a positive electrode sheet, a negative electrode sheet according to any one of claims 1 to 5, and a separator.

12. The steel shell battery according to claim 11, characterized in that: The positive electrode sheet is made of positive electrode slurry, and the positive electrode slurry includes the following components in percentage by mass: 95% to 99% positive electrode material, 0.5% to 1% conductive carbon black, 0.15% to 1% first carbon nanotube, 0.05% to 1% second carbon nanotube, 0.01% to 1% dispersant, 0.29% to 1% binder, and 10% to 20% second solvent; Wherein, the specific surface area of ​​the first carbon nanotube is 250m 2 / g~330m 2 / g, the aspect ratio of the first carbon nanotubes is 1000-2000; The specific surface area of ​​the second carbon nanotube is 250 m 2 / g~330m 2 / g, and the aspect ratio of the second carbon nanotubes is 5000-10000.

13. The steel shell battery according to claim 12, characterized in that: The positive electrode slurry is prepared by the following steps: dissolving the binder in a portion of the second solvent and stirring to obtain a second adhesive solution; adding the dispersant and the remaining second solvent to the second glue solution, mixing, and continuing to add the conductive carbon black and the first carbon nanotubes, stirring to obtain a fourth mixed solution; adding the positive electrode material to the fourth mixed solution and mixing to obtain a fifth mixed solution; The second carbon nanotubes are added to the fifth mixed solution, and stirring is continued to obtain a positive electrode slurry.

14. The steel shell battery according to claim 12 or 13, characterized in that: The viscosity of the positive electrode slurry is 3000cp~5000cp; and / or The solid content of the positive electrode slurry is 70% to 75%.

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