A negative electrode sheet, a method for manufacturing the same, a battery, a battery pack, and an electric device

Abstract

This invention provides a negative electrode sheet and its preparation method, a battery, a battery pack, and an electrical device. The negative electrode sheet includes a negative electrode active layer, and the zeta potential of the negative electrode active layer is less than or equal to -53 mV. The negative electrode sheet provided by this invention, by limiting the zeta potential of the negative electrode active layer to less than or equal to -53 mV, can enhance the electrostatic repulsion between particles, prevent particle aggregation, improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, avoid the appearance of black spots or dark streaks on the negative electrode sheet, and reduce the risk of localized lithium plating during battery charging.

Description

A negative electrode sheet and its preparation method, a battery, a battery pack, and an electrical device thereof. Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a negative electrode sheet and its preparation method, a battery, a battery pack and an electrical device. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used in electronic products, electric vehicles, and energy storage devices due to their advantages such as high energy density, long cycle life, and high operating voltage. With the rapid development of portable electronic products and electric vehicles, there are higher requirements for the fast-charging performance and safety of lithium-ion rechargeable batteries.

[0003] During fast charging, lithium-ion batteries are prone to lithium metal deposition on the negative electrode, leading to capacity loss and safety hazards. This is especially true when the active material in the negative electrode is unevenly distributed, making localized lithium deposition highly likely. Therefore, reducing the risk of lithium deposition on the negative electrode in lithium-ion batteries is a pressing issue that needs to be addressed in this field. Summary of the Invention

[0004] The main objective of this invention is to provide a negative electrode that can reduce the risk of lithium plating.

[0005] The present invention also provides a method for preparing a negative electrode sheet, which can prepare the above-mentioned negative electrode sheet, and the process is simple and low in cost.

[0006] The present invention also provides a battery including the above-described negative electrode, thereby reducing the risk of lithium plating.

[0007] The present invention also provides a battery pack including the above-described battery, thereby reducing the risk of lithium plating.

[0008] The present invention also provides an electrical device including the above-mentioned battery or battery pack, therefore, the battery of the electrical device has excellent performance.

[0009] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode active layer, wherein the zeta potential of the negative electrode active layer is less than or equal to -53 mV.

[0010] As described above, the zeta potential of the negative electrode active layer is -75 mV to -63 mV.

[0011] As described above, the negative electrode active layer comprises a negative electrode active material and a dispersant, wherein the sum of the zeta potential of the dispersant and the zeta potential of the negative electrode active material is -125 mV to -90 mV.

[0012] As described above, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material is -112 mV to -100 mV.

[0013] As described above, the zeta potential of the negative electrode active material is less than or equal to -33 mV.

[0014] As described above, the zeta potential of the negative electrode active material is -55 mV to -40 mV.

[0015] As described above, the zeta potential of the dispersant in the negative electrode is less than or equal to -50 mV.

[0016] As described above, the zeta potential of the dispersant in the negative electrode is -70 mV to -58 mV.

[0017] The negative electrode sheet as described above, wherein the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, mesophase carbon microspheres, silicon oxide, and silicon-carbon.

[0018] The negative electrode sheet as described above, wherein the dispersant comprises at least one of carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0019] As described above, the negative electrode active layer further includes a binder and a conductive agent.

[0020] Secondly, the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0021] A negative electrode slurry, comprising a negative electrode active material, dispersant, conductive agent, binder, and solvent, is coated onto a negative electrode current collector, dried, and rolled to form a negative electrode active layer with a zeta potential less than or equal to -53 mV, thus obtaining the negative electrode sheet.

[0022] In the above-described method for preparing the negative electrode, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material is -112 mV to -100 mV.

[0023] And / or, the Zeta potential of the negative electrode active material is less than or equal to -33 mV, preferably -55 mV to -40 mV;

[0024] And / or, the Zeta potential of the dispersant is less than or equal to -50 mV, preferably -70 mV to -58 mV.

[0025] Thirdly, the present invention provides a battery comprising a negative electrode sheet as described above or a negative electrode sheet prepared by the method described above.

[0026] Fourthly, the present invention provides a battery pack comprising the battery as described above.

[0027] Fifthly, the present invention provides an electrical device, including a battery as described above or a battery pack as described above.

[0028] The negative electrode sheet provided by the present invention, by limiting the Zeta potential of the negative electrode active layer to less than or equal to -53 mV, can enhance the electrostatic repulsion between particles, prevent particle aggregation, improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, avoid the appearance of black spots or dark streaks on the negative electrode sheet, and reduce the risk of local lithium plating during battery charging. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 is a Zeta potential test spectrum of the negative electrode active material in Example 1 of the present invention;

[0031] Figure 2 is a Zeta potential test spectrum of the negative electrode active material in Example 8 of the present invention;

[0032] Figure 3 shows the Zeta potential test spectrum of the negative electrode active material in Comparative Example 2 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Lithium-ion rechargeable batteries, as highly efficient energy storage devices, have become core components of modern electronic products, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and high operating voltage. However, with the rapid popularization of portable electronic products and electric vehicles, users have placed higher demands on the fast-charging performance and safety of batteries. The application of fast-charging technology can significantly shorten charging time and improve the efficiency of device use, but it also brings new technical challenges.

[0035] In lithium-ion batteries, the design and material selection of the negative electrode have a crucial impact on the overall battery performance. The negative electrode typically comprises a negative electrode active material, a dispersant, and a binder, and is loaded onto a negative electrode current collector. During fast charging, the electrochemical reactions within the battery intensify, significantly increasing the electrochemical polarization of the negative electrode. This polarization leads to the direct deposition of lithium ions on the negative electrode surface, forming lithium metal deposition. This not only causes rapid capacity decay but may also trigger safety hazards such as short circuits and thermal runaway. In particular, when the distribution of the negative electrode active material is uneven, the increase in local current density exacerbates localized lithium deposition. Therefore, how to reduce the risk of lithium metal deposition by improving the material properties and structural design of the negative electrode has become a pressing issue in the current lithium battery technology field. This invention reduces the lithium deposition problem in lithium-ion batteries by adjusting the Zeta potential of the negative electrode active layer to improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode.

[0036] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode active layer, wherein the zeta potential of the negative electrode active layer is less than or equal to -53 mV, for example, it can be a range of -90 mV, -80 mV, -75 mV, -71 mV, -65 mV, -63 mV, -60 mV, -53 mV or any two thereof.

[0037] It is understood that the Zeta potential of the negative electrode active layer reflects the interaction between particles within the negative electrode active layer. In this invention, the Zeta potential of the negative electrode active layer is less than or equal to -53 mV, which enhances the electrostatic repulsion between particles in the negative electrode active layer, prevents particle agglomeration, and allows the negative electrode active material to be uniformly and stably distributed in the negative electrode sheet. This effectively reduces the risk of lithium plating in lithium-ion batteries under fast charging conditions, avoids black spots or dark streaks on the negative electrode sheet, and improves battery safety and lifespan.

[0038] In one embodiment of the present invention, the Zeta potential of the negative electrode active layer is -75 mV to -63 mV, for example, it can be a range of -75 mV, -74 mV, -73 mV, -72 mV, -71 mV, -70 mV, -69 mV, -68 mV, -67 mV, -66 mV, -65 mV, -64 mV, -63 mV, or any combination thereof. As a preferred embodiment, this can further improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, effectively reduce lithium metal deposition, reduce the risk of lithium plating in the battery, and improve the overall performance and safety of the battery.

[0039] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material and a dispersant, wherein the sum of the zeta potential of the dispersant and the zeta potential of the negative electrode active material is -125 mV to -90 mV, for example, it can be a range of -125 mV, -120 mV, -115 mV, -110 mV, -105 mV, -100 mV, -95 mV, -90 mV or any two of these.

[0040] It is understood that the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material can reflect the interaction between the negative electrode active material and the dispersant. The negative electrode sheet of this invention includes a negative electrode active layer, which comprises a negative electrode active material and a dispersant. The sum of the Zeta potentials of the dispersant and the negative electrode active material is -125 mV to -90 mV, which allows for an appropriate charge on both the dispersant and the negative electrode active material, facilitating material dispersion in solution and resulting in a more uniform negative electrode sheet. Furthermore, it can enhance the electrostatic repulsion between particles formed by the interaction between the negative electrode active material and the dispersant, preventing particle aggregation. This improves the dispersion uniformity and stability of the negative electrode active material and dispersant in the negative electrode sheet, effectively reducing the risk of lithium plating in lithium-ion batteries under fast charging conditions, avoiding black spots or dark streaks on the negative electrode sheet, and improving battery safety and lifespan.

[0041] In some embodiments of the present invention, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material is -112 mV to -100 mV, for example, it can be a range of -112 mV, -111 mV, -110 mV, -109 mV, -108 mV, -107 mV, -106 mV, -105 mV, -104 mV, -103 mV, -102 mV, -101 mV, -100 mV, or any combination thereof. As a preferred embodiment, this can further improve the dispersion uniformity and stability of the negative electrode active material and dispersant in the negative electrode sheet, effectively reduce lithium metal deposition, reduce the risk of lithium plating in the battery, and improve the overall performance and safety of the battery.

[0042] In some embodiments of the present invention, the zeta potential of the negative electrode active material is less than or equal to -33 mV, for example, it can be a range of -100 mV, -95 mV, -90 mV, -85 mV, -80 mV, -75 mV, -70 mV, -65 mV, -60 mV, -50 mV, -40 mV, -35 mV, -33 mV or any combination thereof.

[0043] It is understandable that the zeta potential of the negative electrode active material reflects the charge state of its surface and affects its interaction with the dispersant. The zeta potential of the negative electrode active material can be adjusted by simultaneously changing its D50 particle size and specific surface area. Negative electrode active materials with zeta potentials within this range can better bind with the dispersant and be uniformly and stably dispersed in the negative electrode sheet, avoiding black spots or dark streaks and reducing the risk of localized lithium plating during battery charging.

[0044] In some embodiments, the D50 particle size of the negative electrode active material is 6.5 μm to 14 μm, for example, it can be a range of 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or any combination thereof.

[0045] In some embodiments, the specific surface area of ​​the negative electrode active material is 0.5 g / cm³. 3 ~4g / cm 3 For example, it can be 0.5 g / cm³. 3 1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.5g / cm 3 2g / cm 3 2.5g / cm 3 3g / cm 3 3.5g / cm 3 4g / cm 3 or a range consisting of any two of them.

[0046] In some embodiments of the present invention, the Zeta potential of the negative electrode active material is -55 mV to -40 mV, for example, it can be a range of -55 mV, -50 mV, -48 mV, -47 mV, -45 mV, -42 mV, -40 mV, or any combination thereof. Preferably, the negative electrode active material can be further better combined with the dispersant, and uniformly and stably dispersed in the negative electrode sheet, avoiding black spots or dark streaks on the negative electrode sheet and reducing the risk of localized lithium plating during battery charging.

[0047] In some embodiments of the invention, the zeta potential of the dispersant is less than or equal to -50 mV, for example, it can be a range of -80 mV, -75 mV, -70 mV, -65 mV, -60 mV, -55 mV, -50 mV or any two of these.

[0048] This invention can adjust the Zeta potential of the dispersant by changing its molecular structure. For example, the degree of substitution of carboxymethyl cellulose (CMC), i.e., the average number of hydroxyl groups substituted in each monomer, can be changed; or the type of dispersant can be changed by using different polymerizable monomers. When the Zeta potential of the dispersant in this invention is within the aforementioned range, the negative electrode active material can exhibit good dispersibility and stability in the negative electrode sheet, which is beneficial for forming a uniform electrode structure. This uniformity can reduce current density fluctuations within the electrode, thereby reducing the risk of local overpotential and lithium metal deposition. It can effectively reduce the risk of local lithium plating during fast charging, thus improving battery safety.

[0049] In some embodiments, the degree of substitution of the dispersant is 0.5 to 1.1, for example, it can be a range of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or any two of these.

[0050] In some embodiments of the present invention, the zeta potential of the dispersant is -70 mV to -58 mV, for example, it can be a range of -70 mV, -68 mV, -64 mV, -62 mV, -60 mV, -58 mV, or any combination thereof. As a preferred embodiment, this can further improve the dispersibility and stability of the negative electrode active material, thereby reducing the risk of local overpotential and lithium metal deposition, effectively reducing the risk of local lithium deposition during fast charging, and thus improving battery safety.

[0051] In some embodiments of the present invention, the negative electrode active material includes at least one selected from natural graphite, artificial graphite, hard carbon, mesophase carbon microspheres, silicon dioxide, and silicon-carbon, preferably artificial graphite. Furthermore, the artificial graphite can be selected from primary granules or secondary granulated granules, or from granules with amorphous carbon coated on their surface.

[0052] The aforementioned negative electrode active material can be well combined with the dispersant and uniformly and stably dispersed in the negative electrode sheet, avoiding black spots or dark streaks on the negative electrode sheet and reducing the risk of local lithium plating during battery charging.

[0053] In some embodiments of the present invention, the dispersant includes at least one of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS), preferably carboxymethyl cellulose (CMC).

[0054] The aforementioned dispersant can effectively disperse the negative electrode active material particles, prevent particle agglomeration, facilitate the formation of a uniform electrode structure, reduce fluctuations in current density inside the electrode, thereby reducing the risk of local lithium plating during fast charging and improving battery safety.

[0055] In some embodiments of the present invention, the negative electrode active layer further includes a binder and a conductive agent, wherein the binder includes at least one of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), acrylic rubber (ACM), fluororubber (FKM), modified styrene-butadiene rubber, modified acrylonitrile-butadiene rubber, modified acrylic rubber, and modified fluororubber, preferably styrene-butadiene rubber (SBR).

[0056] In some embodiments, the conductive agent includes at least one of conductive carbon black, Ketjen black, graphene, conductive carbon fiber, and conductive carbon nanotubes, preferably conductive carbon black and conductive carbon nanotubes.

[0057] The binder in this invention can improve the mechanical strength of the negative electrode, prevent material shedding due to volume changes during charge-discharge cycles, improve the stability of the negative electrode during electrochemical cycles, reduce material peeling and electrode structure damage, thereby extending the battery's service life.

[0058] The addition of conductive agents can improve the conductivity of the negative electrode, ensuring that electrons can be quickly transferred to the negative electrode active material particles, which is conducive to achieving uniform current distribution and reducing overpotential and lithium plating caused by excessive local current density.

[0059] In some embodiments of the present invention, the mass percentage of the negative electrode active material in the negative electrode active layer is greater than or equal to 50%, for example, it can be a range of 50%, 55%, 60%, 65%, 70%, 80%, 90%, 95%, 97%, 99% or any two of these, preferably 90% to 99%.

[0060] In some embodiments, the mass percentage of the dispersant in the negative electrode active layer is 0.1% to 10%, for example, it can be a range of 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two of these, preferably 0.3% to 1.5%.

[0061] In some embodiments, the mass percentage of the binder in the negative electrode active layer is 0.1% to 10%, for example, it can be a range of 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two of these, preferably 0.5% to 2.5%.

[0062] In some embodiments, the mass percentage of the conductive agent in the negative electrode active layer is 0.2% to 20%, for example, it can be a range of 0.2%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20% or any two of these, preferably 0.5% to 1.5%.

[0063] Secondly, the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0064] A negative electrode slurry, comprising negative electrode active material, dispersant, conductive agent, binder, and solvent, is coated onto a negative electrode current collector, dried, and rolled to form a negative electrode active layer with a zeta potential less than or equal to -53 mV, thus obtaining a negative electrode sheet.

[0065] Specifically, the method for preparing the negative electrode sheet of the present invention may include the following steps:

[0066] 1) Anode slurry is prepared by mixing negative electrode active material, dispersant, binder, conductive agent, solvent, and other components using dry and / or wet mixing methods. For example, the dispersant is first dissolved in a solvent to obtain a dispersion solution; then, the negative electrode active material and conductive agent dry powder are mixed, and then a portion of the dispersion solution is added and kneaded. The remaining dispersion solution and an appropriate amount of solvent are then added for dilution and stirring. Finally, the binder is added and stirred until homogeneous to obtain the corresponding negative electrode slurry.

[0067] 2) Transfer the uniformly mixed negative electrode slurry obtained above to a coating machine, and coat the negative electrode slurry onto the negative electrode current collector. The coating can be applied to either side or both sides of the negative electrode current collector. The negative electrode current collector is typically a conductive structure made of a metal with good conductivity and that does not react with the active material (such as copper, nickel, titanium, and stainless steel). This invention does not limit the shape of the negative electrode current collector; for example, it can be foil, sheet, mesh, etc. Copper foil is preferred as the negative electrode current collector. When the negative electrode current collector is copper foil, its thickness is not particularly limited and can be between 6 μm and 20 μm. Furthermore, the negative electrode slurry can be coated on only one side of the negative electrode current collector or on both sides, preferably on both sides. The areal density of the negative electrode active material on the negative electrode sheet can be controlled through the coating process.

[0068] 3) The negative electrode current collector loaded with negative electrode slurry is dried in an oven to obtain a negative electrode sheet with a layer of negative electrode active material. The drying temperature and time are appropriately selected based on the solvent used and the solid content of the slurry. For example, the drying temperature can be between 70℃ and 110℃, and the drying time can be between 10s and 300s.

[0069] 4) After the negative electrode sheet is dried, it can be rolled. Rolling can control the thickness of the negative electrode sheet and the compaction density of the negative electrode active material.

[0070] It should be noted that in step 1), the solid content of the negative electrode slurry can be above 40%, preferably between 45% and 60%. When the solid content of the negative electrode slurry is within the above range, it can not only effectively improve the drying efficiency in the negative electrode sheet preparation process, but also improve the stability and fluidity of the negative electrode slurry, making the coating process more uniform and the distribution of active materials and dispersants on the obtained negative electrode sheet more uniform.

[0071] The negative electrode sheet prepared by the above method is less prone to local lithium plating. This is because the above method can avoid the agglomeration of negative electrode active material in the slurry and the black spots and dark streaks formed during the coating process, so that the negative electrode active material, dispersant, binder and conductive agent are uniformly dispersed in the negative electrode sheet.

[0072] In some embodiments of the present invention, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material is -125 mV to -90 mV. For example, it can be a range of -125 mV, -120 mV, -115 mV, -112 mV, -110 mV, -105 mV, -100 mV, -95 mV, -90 mV or any two of these, preferably -112 mV to -100 mV.

[0073] In some embodiments, the zeta potential of the negative electrode active material is less than or equal to -33 mV, for example, it can be a range of -100 mV, -95 mV, -90 mV, -85 mV, -80 mV, -75 mV, -70 mV, -65 mV, -60 mV, -50 mV, -40 mV, -35 mV, -33 mV or any two of these, preferably -55 mV to -40 mV.

[0074] In some embodiments, the zeta potential of the dispersant is less than or equal to -50 mV, for example, it can be a range of -80 mV, -75 mV, -70 mV, -65 mV, -60 mV, -55 mV, -50 mV or any two thereof, preferably -70 mV to -58 mV.

[0075] In this invention, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material, the Zeta potential of the negative electrode active material, and the Zeta potential of the dispersant are all within the above-mentioned range. This is beneficial to improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, effectively reduce lithium metal deposition, reduce the risk of lithium deposition in the battery, and improve the overall performance and safety of the battery.

[0076] In the preparation process of the negative electrode sheet provided by this invention, the Zeta potential of the negative electrode active material, the Zeta potential of the dispersant, the sum of the Zeta potentials of the dispersant and the negative electrode active material, and the Zeta potential of the negative electrode active layer may deviate from the Zeta potentials of the negative electrode active material, the dispersant, the dispersant, the negative electrode active material, and the negative electrode active layer obtained from the negative electrode sheet obtained after disassembly from the battery. However, the deviation is within the error range. Therefore, the Zeta potentials of the negative electrode active material, the dispersant, the dispersant, the negative electrode active material, and the negative electrode active layer in the negative electrode sheet preparation process are basically consistent with the Zeta potentials of the negative electrode active material, the dispersant, the dispersant, the negative electrode active material, and the negative electrode active layer in the negative electrode sheet.

[0077] The parameters of this invention can be obtained from the negative electrode sheet obtained after disassembling the battery, as follows: After obtaining the negative electrode sheet, the negative electrode active layer on the negative electrode sheet can be scraped off and ultrasonically dispersed in water at 70°C~80°C. After centrifugation, the supernatant and precipitate are vacuum dried at 80°C. After drying the supernatant, a dispersant is obtained; after drying the precipitate, it is heated to 700°C in a N2 atmosphere and kept at that temperature for 5 hours to remove the binder, and then cooled to obtain the negative electrode active material. The final negative electrode active material may contain some binder and conductive agent residues, but these have no significant impact on the Zeta potential test of the negative electrode active material.

[0078] Test of the zeta potential of the negative electrode active layer: After scraping off the negative electrode active layer from the negative electrode sheet, it is mixed with water at a mass ratio of 1:200, ultrasonically dispersed for 30 minutes to form a solution, and the zeta potential of the solution is tested using an electrophoretic light scattering instrument.

[0079] Test of Zeta potential of negative electrode active material: The negative electrode active material and ethanol were mixed at a mass ratio of 1:1000 and ultrasonically dispersed for 10 min to form a solution. The Zeta potential of the solution was then tested using an electrophoretic light scattering instrument.

[0080] Test of Zeta potential of dispersant: Disperse the dispersant in water to form a solution with a mass fraction of 0.01 wt%, and test the solution Zeta potential using an electrophoretic light scattering instrument.

[0081] The sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material: the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material.

[0082] Thirdly, the present invention provides a battery comprising the negative electrode sheet as described above, which has advantages corresponding to the aforementioned negative electrode sheet, and will not be elaborated further.

[0083] In addition to the negative electrode, the battery of the present invention also includes a separator, a positive electrode, and an electrolyte. The composition of the positive electrode can refer to conventional positive electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as a PP film or a PE film.

[0084] The battery of the present invention can be prepared using conventional methods in the art. Specifically, the positive electrode, separator and negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding. Then, the battery can be obtained by baking, liquid injection, formation and packaging.

[0085] Fourthly, the present invention provides a battery pack including the battery as described above, which has advantages corresponding to the negative electrode sheet described above, and will not be elaborated further.

[0086] Fifthly, the present invention provides an electrical device comprising the battery or battery pack described above, which has advantages corresponding to the negative electrode sheet described above, and will not be elaborated further.

[0087] The electrical equipment of this invention can be any conventional electrical equipment in the art, including, in addition to batteries, controllers, transformers, motors, etc. Examples of electrical equipment include power equipment (such as electric vehicles), electronic equipment (such as computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (such as watches, wristbands, VR glasses, etc.), and home appliances (such as air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without particular limitation.

[0088] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0089] Example 1

[0090] The method for preparing the negative electrode sheet in this embodiment includes the following steps:

[0091] Artificial graphite was selected as the negative electrode active material, with a D50 particle size of 8.70 μm and a specific surface area of ​​1.41 g / cm³. 3 The zeta potential is -42 mV. Carboxymethyl cellulose (CMC) is used as a dispersant with a degree of substitution of 0.92 and a zeta potential of -63 mV. The sum of the zeta potentials of the dispersant and the negative electrode active material is -105 mV. Commercially available styrene-butadiene rubber (SBR) and conductive carbon black are used as binders and conductive agents, respectively. The mass ratio of artificial graphite:CMC:SBR:conductive carbon black is 100:1.2:1.9:1.2.

[0092] First, CMC is dissolved in water to obtain a CMC dispersion. Then, artificial graphite and conductive carbon black powder are mixed evenly, and a portion of the CMC dispersion is added and kneaded. Next, the remaining dispersion is added, and an appropriate amount of water is added to dilute and stir until homogeneous. Finally, SBR is added and stirred evenly to obtain the negative electrode slurry.

[0093] The negative electrode slurry is coated onto both sides of a Cu foil using a coating machine. After drying, it is rolled to obtain a negative electrode sheet. The areal density of the negative electrode sheet is 172 g·m³. -2 The compacted density is 1.5 g·cm³. -3 The negative electrode includes a negative electrode active layer.

[0094] Example 2

[0095] The preparation method of the negative electrode sheet in Example 2 is basically the same as that in Example 1, except that the degree of substitution of the dispersant CMC is changed to 0.77.

[0096] Example 3

[0097] The preparation method of the negative electrode sheet in Example 3 is basically the same as that in Example 1, except that the degree of substitution of the dispersant CMC is changed to 0.89.

[0098] Example 4

[0099] The preparation method of the negative electrode sheet in Example 4 is basically the same as that in Example 1, except that the degree of substitution of the dispersant CMC is changed to 1.03.

[0100] Example 5

[0101] The preparation method of the negative electrode sheet in Example 5 is basically the same as that in Example 1, except that the type of dispersant is changed to PAA. PAA is obtained by polymerizing acrylonitrile, acrylamide and acrylic acid, wherein the molar ratio of acrylonitrile:acrylamide:acrylic acid is 58:13:32.

[0102] Example 6

[0103] The preparation method of the negative electrode sheet in Example 6 is basically the same as that in Example 1, except that the D50 particle size of the artificial graphite active material is changed to 11.31 μm and the specific surface area is changed to 0.76 g / cm³. 3 .

[0104] Example 7

[0105] The preparation method of the negative electrode sheet in Example 7 is basically the same as that in Example 1, except that the D50 particle size of the artificial graphite active material is changed to 13.55 μm and the specific surface area is changed to 1.30 g / cm³. 3 .

[0106] Example 8

[0107] The preparation method of the negative electrode sheet in Example 8 is basically the same as that in Example 1, except that the D50 particle size of the artificial graphite active material is changed to 11.50 μm and the specific surface area is changed to 1.25 g / cm³. 3 .

[0108] Example 9

[0109] The preparation method of the negative electrode sheet in Example 9 is basically the same as that in Example 1, except that the D50 particle size of the artificial graphite active material is changed to 11.34 μm and the specific surface area is changed to 1.32 g / cm³. 3 .

[0110] Example 10

[0111] The preparation method of the negative electrode sheet in Example 10 is basically the same as that in Example 1, except that the negative electrode active material is changed to natural graphite with a D50 particle size of 10.79 μm and a specific surface area of ​​3.23 g / cm³. 3 .

[0112] Example 11

[0113] The preparation method of the negative electrode sheet in Example 11 is basically the same as that in Example 1, except that the negative electrode active material is changed to hard carbon, with a D50 particle size of 6.96 μm and a specific surface area of ​​3.58 g / cm³. 3 .

[0114] Example 12

[0115] The preparation methods of the negative electrode sheet in Example 12 and Example 7 are basically the same, except that the degree of substitution of the dispersant CMC is changed to 0.77.

[0116] Example 13

[0117] The preparation methods of the negative electrode sheet in Example 13 and Example 9 are basically the same, except that the degree of substitution of the dispersant CMC is changed to 1.03.

[0118] Example 14

[0119] The preparation methods of the negative electrode sheet in Example 14 and Example 9 are basically the same, except that the degree of substitution of the dispersant CMC is changed to 0.68.

[0120] Example 15

[0121] The preparation methods of the negative electrode sheet in Example 15 and Example 10 are basically the same, except that the degree of substitution of the dispersant CMC is changed to 1.03.

[0122] Comparative Example 1

[0123] The preparation method of the negative electrode sheet of Comparative Example 1 is basically the same as that of Example 1, except that the degree of substitution of the dispersant CMC is changed to 0.68.

[0124] Comparative Example 2

[0125] The preparation methods of the negative electrode sheets in Comparative Example 2 and Example 6 are basically the same, except that the degree of substitution of the dispersant CMC is changed to 0.68.

[0126] Comparative Example 3

[0127] The preparation methods of the negative electrode sheets in Comparative Example 3 and Example 5 are basically the same, except that the negative electrode active material is changed to hard carbon, with a D50 particle size of 6.96 μm and a specific surface area of ​​3.58 g / cm³. 3 .

[0128] Experimental example:

[0129] 1. Observation of the appearance of the negative electrode: Place the negative electrode under strong light and observe whether there are black spots, dark scratches, cracks or other defects on the surface.

[0130] 2. Lithium Plasma Kinetics Test: Ten discs were cut from the same negative electrode sheet and assembled with lithium metal sheets into coin-type lithium-ion batteries. The batteries were discharged at 3C to 0.01V, then charged at 1C to 2V, cycled 20 times, and then discharged again at 3C to 0.01V. Subsequently, the batteries were disassembled to observe the lithium plating on the surface of each negative electrode disc, and the number of discs with different degrees of lithium plating was counted. Discs with less than 5% lithium plating were classified as having slight lithium plating, 5%–30% as having moderate lithium plating, and more than 30% as having severe lithium plating.

[0131] 3. Zeta potential of negative electrode active layer: After scraping off the negative electrode active layer from the negative electrode sheet, mix it with water at a mass ratio of 1:200, and ultrasonically disperse it for 30 minutes to form a solution. The zeta potential of the solution is then tested using an electrophoretic light scattering instrument.

[0132] Figure 1 shows the Zeta potential test spectrum of the negative electrode active material in Example 1. From the figure, it can be seen that the Zeta potential of the negative electrode active material is -42 mV.

[0133] Figure 2 shows the Zeta potential test spectrum of the negative electrode active material in Example 8. From the figure, it can be seen that the Zeta potential of the negative electrode active material is -54 mV.

[0134] Figure 3 shows the Zeta potential test spectrum of the negative electrode active material in Comparative Example 2. From the figure, it can be seen that the Zeta potential of the negative electrode active material is -27 mV.

[0135] Table 1

[0136]

[0137] As shown in Table 1, compared with the comparative example, the negative electrode sheet provided by the present invention can enhance the electrostatic repulsion between particles by limiting the Zeta potential of the negative electrode active layer to less than or equal to -53mV, prevent particle aggregation, improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, avoid the appearance of black spots or dark lines on the negative electrode sheet, and reduce the risk of local lithium plating during battery charging.

[0138] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode includes a negative electrode active layer with a Zeta potential of -75 mV to -53 mV; the negative electrode active layer includes a negative electrode active material and a dispersant, the sum of the Zeta potentials of the dispersant and the negative electrode active material being -125 mV to -90 mV; the Zeta potential of the negative electrode active material is -55 mV to -40 mV; and the Zeta potential of the dispersant is -70 mV to -58 mV. mV; the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, mesophase carbon microspheres, silicon dioxide, and silicon-carbon; the dispersant includes at least one of carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan; the zeta potential of the negative electrode active layer is tested by the following method: after scraping off the negative electrode active layer from the negative electrode sheet, it is mixed with water at a mass ratio of 1:200, ultrasonically dispersed for 30 min to form a first solution, and the zeta potential of the first solution is tested using an electrophoretic light scattering instrument; the zeta potential of the negative electrode active material is tested by the following method: after mixing the negative electrode active material and ethanol at a mass ratio of 1:1000, it is ultrasonically dispersed for 10 min to form a second solution, and then the zeta potential of the second solution is tested using an electrophoretic light scattering instrument; the zeta potential of the dispersant is tested by the following method: the dispersant is dispersed in water to form a third solution with a mass fraction of 0.01 wt%, and the zeta potential of the third solution is tested using an electrophoretic light scattering instrument.

2. The negative electrode sheet according to claim 1, characterized in that, The zeta potential of the negative electrode active layer is -75 mV to -63 mV.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material is -112 mV to -100 mV.

4. The negative electrode sheet according to claim 1 or 2, characterized in that, The negative electrode active layer also includes a binder and a conductive agent.

5. A method for preparing a negative electrode sheet according to any one of claims 1-4, characterized in that, Includes the following steps: A negative electrode slurry, comprising a negative electrode active material, dispersant, conductive agent, binder, and solvent, is coated onto a negative electrode current collector, dried, and rolled to form a negative electrode active layer, thereby obtaining the negative electrode sheet.

6. A battery, characterized in that, The negative electrode sheet includes the negative electrode sheet prepared by any one of claims 1-4 or the negative electrode sheet prepared by the method of claim 5.

7. A battery pack, characterized in that, Includes the battery as described in claim 6.

8. An electrical appliance, characterized in that, Includes the battery as described in claim 6 or the battery pack as described in claim 7.

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