Negative plate and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention provides a negative plate and a preparation method thereof, a battery, a battery pack and electric equipment, the negative plate comprises a negative active layer, and the Zeta potential of the negative active layer is less than or equal to-53 mV. According to the negative electrode plate provided by the invention, the Zeta potential of the negative electrode active layer is limited to be less than or equal to-53 mV, so that the electrostatic repulsive force among particles can be enhanced, particle aggregation is prevented, the dispersion uniformity and stability of the negative electrode active material in the negative electrode plate are improved, and black spots or dark lineation of the negative electrode plate are avoided; and the local lithium precipitation risk of the battery in the charging process is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a negative electrode sheet, a preparation method thereof, a battery, a battery pack and an electrical device. Background Art

[0002] Lithium-ion secondary 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 working voltage. With the rapid development of portable electronic products and electric vehicles, higher requirements are placed on the fast charging performance and safety of lithium-ion secondary batteries.

[0003] When a lithium-ion battery is fast charged, lithium metal precipitation is likely to occur on the negative electrode sheet, resulting in capacity loss and safety hazards. Especially when the distribution of the negative electrode active material in the negative electrode sheet is uneven, local lithium precipitation is extremely likely to occur. Therefore, how to reduce the risk of lithium precipitation on the negative electrode in a lithium-ion battery is an urgent problem to be solved in this field. Summary of the Invention

[0004] The main object of the present invention is to provide a negative electrode sheet, which can reduce the risk of lithium precipitation.

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

[0006] The present invention also provides a battery, including the above-mentioned negative electrode sheet. Therefore, the battery can reduce the risk of lithium precipitation.

[0007] The present invention also provides a battery pack, including the above-mentioned battery. Therefore, the battery pack can reduce the risk of lithium precipitation.

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

[0009] In a first aspect, the present invention provides a negative electrode sheet, 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.

[0010] For the negative electrode sheet as described above, the Zeta potential of the negative electrode active layer is -75 mV to -63 mV.

[0011] For the negative electrode sheet as described above, the negative electrode active layer includes a negative electrode active material and a dispersant, and 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] For the negative electrode sheet 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] The negative electrode sheet as described above, wherein the Zeta potential of the negative electrode active material is less than or equal to -33 mV.

[0014] The negative electrode sheet as described above, wherein the Zeta potential of the negative electrode active material is -55 mV to -40 mV.

[0015] The negative electrode sheet as described above, wherein the Zeta potential of the dispersant is less than or equal to -50 mV.

[0016] The negative electrode sheet as described above, wherein the Zeta potential of the dispersant is -70 mV to -58 mV.

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

[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] The negative electrode sheet as described above, wherein the negative electrode active layer further comprises a binder and a conductive agent.

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

[0021] Coating a negative electrode slurry comprising a negative electrode active material, a dispersant, a conductive agent, a binder, and a solvent on a negative electrode current collector, drying, and rolling to form a negative electrode active layer having a Zeta potential less than or equal to -53 mV, thereby obtaining the negative electrode sheet.

[0022] For the method for preparing a negative electrode sheet 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;

[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] In a third aspect, the present invention provides a battery comprising the negative electrode sheet as described above or a negative electrode sheet prepared by the method for preparing a negative electrode sheet as described above.

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

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

[0028] For the negative electrode sheet provided by the present invention, by defining that the Zeta potential of the negative electrode active layer is less than or equal to -53 mV, the electrostatic repulsion force between particles can be enhanced, particle aggregation can be prevented, the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet can be improved, black spots or dark scribed lines on the negative electrode sheet can be avoided, and the risk of local lithium plating during battery charging can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention or related technologies. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0030] Figure 1 It is the Zeta potential test spectrogram of the negative electrode active material in Embodiment 1 of the present invention;

[0031] Figure 2 It is the Zeta potential test spectrogram of the negative electrode active material in Embodiment 8 of the present invention;

[0032] Figure 3 It is the Zeta potential test spectrogram of the negative electrode active material in Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0034] As an efficient energy storage device, the lithium-ion secondary battery has become a core component of modern electronic products, electric vehicles, and energy storage systems due to its advantages such as high energy density, long cycle life, and high working voltage. However, with the rapid popularization of portable electronic products and electric vehicles, users have put forward higher requirements for the fast charging performance and safety of batteries. The application of fast charging technology can significantly shorten the charging time and improve the use efficiency of devices, but at the same time, it also brings new technical challenges.

[0035] In a lithium-ion battery, the design and material selection of the negative electrode sheet have a crucial impact on the overall performance of the battery. The negative electrode sheet typically includes a negative electrode active material, a dispersant, and a binder, and is loaded on a negative electrode current collector. During fast charging, the electrochemical reactions inside the battery intensify, and the electrochemical polarization phenomenon of the negative electrode sheet increases significantly. This polarization causes lithium ions to directly deposit on the surface of the negative electrode, forming the precipitation of metallic lithium. This not only leads to a rapid decline in the battery capacity but may also trigger safety hazards such as short circuits and thermal runaway. In particular, when the distribution of the negative electrode active material in the negative electrode sheet is uneven, the increase in the local current density will exacerbate the local lithium precipitation phenomenon. Therefore, how to reduce the risk of metallic lithium precipitation by improving the material properties and structural design of the negative electrode sheet has become an urgent problem to be solved in the current lithium battery technology field. The present invention adjusts 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 sheet, thereby reducing the lithium precipitation problem of the lithium-ion battery.

[0036] In a first aspect, the present invention provides a negative electrode sheet, which includes a negative electrode active layer, and the Zeta potential of the negative electrode active layer is less than or equal to -53 mV. For example, it can be -90 mV, -80 mV, -75 mV, -71 mV, -65 mV, -63 mV, -60 mV, -53 mV, or a range composed of any two of them.

[0037] It can be understood that the Zeta potential of the negative electrode active layer can reflect the interaction between particles in the negative electrode active layer. In the present invention, the Zeta potential of the negative electrode active layer is less than or equal to -53 mV, which can enhance the electrostatic repulsive force between particles in the negative electrode active layer, prevent particle agglomeration, enable the negative electrode active material to be evenly and stably distributed in the negative electrode sheet, effectively reduce the risk of lithium precipitation under fast charging conditions of the lithium-ion battery, avoid the appearance of black spots or dark scribed lines on the negative electrode sheet, and improve the safety and service life of the battery.

[0038] In an 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 -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 a range composed of any two of them. As a preferred solution, it can further improve the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, effectively reduce the precipitation of metallic lithium, reduce the risk of lithium precipitation 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, and 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 -125 mV, -120 mV, -115 mV, -110 mV, -105 mV, -100 mV, -95 mV, -90 mV or the range composed of any two of them.

[0040] It can be 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 the present invention includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material and a dispersant, and 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, which can make the charge amounts of the dispersant and the negative electrode active material appropriate, be conducive to the dispersion of the materials in the solution, and make the prepared negative electrode sheet have better uniformity. In addition, it can also enhance the electrostatic repulsion force between the particles formed by the interaction between the negative electrode active material and the dispersant, prevent particle aggregation, thereby improving the dispersion uniformity and stability of the negative electrode active material and the dispersant in the negative electrode sheet, effectively reducing the risk of lithium precipitation under fast charging conditions of the lithium-ion battery, avoiding black spots or dark scribed lines on the negative electrode sheet, and improving the safety and service life of the battery.

[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 -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 the range composed of any two of them. As a preferred solution, it can further improve the dispersion uniformity and stability of the negative electrode active material and the dispersant in the negative electrode sheet, effectively reduce the precipitation of lithium metal, reduce the lithium precipitation risk of 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 -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 the range composed of any two of them.

[0043] It can be understood that the Zeta potential of the negative electrode active material can reflect the charged state on the surface of the negative electrode active material, affect its interaction with the dispersant, and the Zeta potential of the negative electrode active material can be adjusted by simultaneously changing the D50 particle size and specific surface area of the negative electrode active material. The negative electrode active material with a Zeta potential within this range can better combine with the dispersant, be uniformly and stably dispersed in the negative electrode sheet, avoid the appearance of black spots or dark scribed lines on the negative electrode sheet, and reduce the risk of local 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 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or a range composed of any two of them.

[0045] In some embodiments, the specific surface area of the negative electrode active material is 0.5 g / cm 3 ~4 g / cm 3 For example, it can be 0.5 g / cm 3 、1 g / cm 3 、1.2 g / cm 3 、1.3 g / cm 3 、1.5 g / cm 3 、2 g / cm 3 、2.5 g / cm 3 、3 g / cm 3 、3.5 g / cm 3 、4 g / cm 3 or a range composed 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 -55 mV, -50 mV, -48 mV, -47 mV, -45 mV, -42 mV, -40 mV, or a range composed of any two of them. As a preferred solution, the negative electrode active material can further better combine with the dispersant, be uniformly and stably dispersed in the negative electrode sheet, avoid the appearance of black spots or dark scribed lines on the negative electrode sheet, and reduce the risk of local lithium plating during battery charging.

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

[0048] The present invention can adjust the Zeta potential of the dispersant by changing the molecular structure of the dispersant. For example, by changing the degree of substitution of carboxymethyl cellulose (CMC), that is, the average number of hydroxyl groups substituted in each monomer; or by changing the type of dispersant and using different polymerization monomers. When the Zeta potential of the dispersant in the present invention is within the above range, the negative electrode active material can have good dispersibility and stability in the negative electrode sheet, which is beneficial to the formation of a uniform electrode structure. This uniformity can reduce the current density fluctuation inside the electrode, thereby reducing the local overpotential and the risk of lithium metal precipitation, and can effectively reduce the risk of local lithium precipitation during fast charging, thus improving the safety of the battery.

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

[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 -70 mV, -68 mV, -64 mV, -62 mV, -60 mV, -58 mV or any range composed of any two of them. As a preferred solution, it can further improve the dispersibility and stability of the negative electrode active material, thereby reducing the local overpotential and the risk of lithium metal precipitation, and can effectively reduce the risk of local lithium precipitation during fast charging, thus improving the safety of the battery.

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

[0052] The above 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 scribes on the negative electrode sheet and reducing the risk of local lithium precipitation 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), and preferably carboxymethyl cellulose (CMC).

[0054] The above dispersant can effectively disperse the negative electrode active material particles, prevent particle agglomeration, is beneficial to the formation of a uniform electrode structure, reduces the current density fluctuation inside the electrode, thereby reducing the risk of local lithium precipitation during fast charging and improving the safety of the battery.

[0055] In some embodiments of the present invention, the negative electrode active layer further comprises a binder and a conductive agent. Among them, the binder comprises 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, and preferably styrene-butadiene rubber (SBR).

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

[0057] The binder in the present invention can improve the mechanical strength of the negative electrode sheet, prevent the material from falling off due to volume change during the charge and discharge cycle, improve the stability of the negative electrode sheet during the electrochemical cycle, reduce the peeling of the material and the damage of the electrode structure, thereby prolonging the service life of the battery.

[0058] The addition of the conductive agent can improve the conductivity of the negative electrode sheet, ensure that electrons can be quickly transmitted to the negative electrode active material particles, facilitate the uniform distribution of current, and reduce the overpotential and lithium plating phenomenon caused by too high local current density.

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

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

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

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

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

[0064] Coat a negative electrode slurry including a negative electrode active material, a dispersant, a conductive agent, a binder, and a solvent on a negative electrode current collector, dry it, and roll it to form a negative electrode active layer with a Zeta potential less than or equal to -53 mV, thereby 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) Mix the negative electrode active material, the dispersant, the binder, the conductive agent, the solvent, and other components by dry mixing and / or wet mixing to prepare a negative electrode slurry. For example, first dissolve the dispersant in the solvent to obtain a dispersion colloidal solution; then dry-mix the negative electrode active material and the conductive agent powder, and then add a part of the dispersion colloidal solution for kneading. Subsequently, add the remaining dispersion colloidal solution and an appropriate amount of solvent for dilution and stirring. Finally, add the binder and stir evenly to obtain the corresponding negative electrode slurry.

[0067] 2) Transfer the uniformly mixed negative electrode slurry obtained above to a coater, and use the coater to coat the negative electrode slurry on the negative electrode current collector, which can be coated on either one side or both sides of the negative electrode current collector. Among them, the negative electrode current collector is usually made of a conductive structure made of a metal with good conductivity and no reaction with the active material (such as copper, nickel, titanium, and stainless steel, etc.). The present invention does not limit the shape of the negative electrode current collector. For example, it can be in the form of a foil, a sheet, a mesh, etc. The negative electrode current collector is preferably a copper foil. When the negative electrode current collector is a copper foil, its thickness is not particularly limited and can be between 6 μm and 20 μm. In addition, the negative electrode slurry can be coated on only one side of the negative electrode current collector or on both sides of the negative electrode current collector. Preferably, it is coated on both sides. The areal density of the negative electrode active material on the negative electrode sheet can be regulated through the coating process.

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

[0069] 4) After the negative electrode sheet is dried, rolling can be carried out. By rolling, the thickness of the negative electrode sheet and the compaction density of the negative electrode active material can be controlled.

[0070] It should be noted that in step 1), the solid content of the negative electrode slurry can be 40% or more, 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 preparation process of the negative electrode sheet, but also improve the stability and fluidity of the negative electrode slurry, make the coating process more uniform, and make the distribution of the active material and the dispersant on the obtained negative electrode sheet more uniform.

[0071] The negative electrode sheet prepared by the above method is not prone to local lithium precipitation. This is because the above method can avoid the agglomeration of the negative electrode active material in the slurry and the black spots and dark scribed lines formed during the coating process, so that the negative electrode active material, dispersant, binder, conductive agent, etc. are all 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 -125 mV, -120 mV, -115 mV, -112 mV, -110 mV, -105 mV, -100 mV, -95 mV, -90 mV or the range composed of any two of them, 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 -100mV, -95mV, -90 mV, -85 mV, -80 mV, -75 mV, -70 mV, -65 mV, -60 mV, -50 mV, -40 mV, -35mV, -33 mV or the range composed of any two of them, 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 -80 mV, -75mV, -70 mV, -65 mV, -60 mV, -55 mV, -50 mV or the range composed of any two of them, preferably -70 mV to -58 mV.

[0075] In the present 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 within the above ranges, which is beneficial to improving the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet, effectively reducing the precipitation of lithium metal, reducing the risk of lithium precipitation in the battery, and improving the overall performance and safety of the battery.

[0076] During the preparation process of the negative electrode sheet provided by the present invention, there may be deviations between the Zeta potential of the negative electrode active material, the Zeta potential of the dispersant, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material, and the Zeta potential of the negative electrode active layer, and the Zeta potential of the negative electrode active material, the Zeta potential of the dispersant, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material, and the Zeta potential of the negative electrode active layer measured from the negative electrode sheet obtained after disassembling from the battery. However, within the error range, therefore, the Zeta potential of the negative electrode active material, the Zeta potential of the dispersant, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material, and the Zeta potential of the negative electrode active layer during the preparation process of the negative electrode sheet are basically the same as the Zeta potential of the negative electrode active material, the Zeta potential of the dispersant, the sum of the Zeta potential of the dispersant and the Zeta potential of the negative electrode active material, and the Zeta potential of the negative electrode active layer in the negative electrode sheet.

[0077] The parameters of the present invention can be measured from the negative electrode sheet obtained after disassembling from the battery in the following manner: After obtaining the negative electrode sheet, the negative electrode active layer on the negative electrode sheet can be scraped off and placed in water at 70°C to 80°C for ultrasonic dispersion. After centrifugation, the supernatant and the precipitate are vacuum dried at 80°C respectively. The dispersant is obtained after the supernatant is dried; after the precipitate is dried, it is heated to 700°C in an N 2 atmosphere and kept warm for 5 h to remove the binder, and then cooled to obtain the negative electrode active material. There may be some residues of the binder and the conductive agent in the finally obtained negative electrode active material, but it has 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 on the negative electrode sheet, it is mixed with water at a mass ratio of 1:200 and ultrasonically dispersed for 30 min to form a solution, and the Zeta potential of the solution is measured with an electrophoretic light scattering instrument.

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

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

[0081] 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 plus the Zeta potential of the negative electrode active material.

[0082] In a third aspect, the present invention provides a battery, including the negative electrode sheet as described above. The battery has corresponding advantages to those of the above-mentioned negative electrode sheet, which will not be elaborated herein.

[0083] In addition to the negative electrode sheet, the battery of the present invention further includes a separator, a positive electrode sheet, and an electrolyte. Among them, the composition of the positive electrode sheet can refer to the conventional positive electrode sheets in the art, and the separator can also adopt the separators commonly used in the art, such as PP films, PE films, etc.

[0084] The battery of the present invention can be prepared by conventional methods in the art. Specifically, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in sequence, and then a battery core can be obtained through a stacking or winding process. Subsequently, through processes such as baking, liquid injection, formation, and encapsulation, the above-mentioned battery can be obtained.

[0085] In a fourth aspect, the present invention provides a battery pack, including the battery as described above. The battery pack has corresponding advantages to those of the above-mentioned negative electrode sheet, which will not be elaborated herein.

[0086] In a fifth aspect, the present invention provides an electrical device, including the battery or the battery pack as described above. The electrical device has corresponding advantages to those of the above-mentioned negative electrode sheet, which will not be elaborated herein.

[0087] The electrical device of the present invention can be a conventional electrical device in the art. In addition to including a battery, it can also include a controller, a transformer, a motor, etc. The electrical device can be, for example, a power device (such as an electric vehicle), an electronic device (such as a computer, a mobile phone, a digital camera, a printer, a fax machine, etc.), a wearable device (such as a watch, a bracelet, a VR glasses, etc.), a household electrical appliance (such as an air conditioner, a refrigerator, a washing machine, a microwave oven, etc.), etc., and no special limitation is made thereto.

[0088] Hereinafter, the technical solutions of the present invention will be further described in conjunction with specific embodiments.

[0089] Example 1

[0090] The preparation method of the negative electrode sheet in this example includes the following steps:

[0091] Select artificial graphite as the negative electrode active material, with a D50 particle size of 8.70 μm, a specific surface area of 1.41 g / cm 3 , and a Zeta potential of -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 potential of the dispersant and the Zeta potential of the negative electrode active material is -105 mV. Commercially available styrene-butadiene rubber (SBR) and conductive carbon black are used as a binder and a conductive agent respectively. Among them, the mass ratio of artificial graphite: CMC: SBR: conductive carbon black is 100: 1.2: 1.9: 1.2.

[0092] First, dissolve CMC in water to obtain a CMC dispersion gel. Subsequently, mix artificial graphite and conductive carbon black dry powder evenly, and then add a part of the CMC dispersion gel for kneading. Then add the remaining dispersion gel and add an appropriate amount of water for dilution and stir evenly. Finally, add SBR and stir evenly to obtain the negative electrode slurry.

[0093] Coat the negative electrode slurry on both side surfaces of the Cu foil with a coater, and after drying, roll press to obtain the negative electrode sheet. Among them, the surface density of the negative electrode sheet is 172 g·m -2 , and the tap density is 1.5 g·cm -3 . The negative electrode sheet 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, the difference being 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, the difference being 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, the difference being 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, the difference being that the type of the dispersant is changed to PAA, and 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, the difference being that the D50 particle size of the artificial graphite as the negative electrode active material is changed to 11.31 μm, and the specific surface area is 0.76 g / cm 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, the difference being that the D50 particle size of the artificial graphite as the negative electrode active material is changed to 13.55 μm, and the specific surface area is 1.30 g / cm 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, the negative electrode active material, is changed to 11.50 μm, and the specific surface area is 1.25 g / cm 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, the negative electrode active material, is changed to 11.34 μm, and the specific surface area is 1.32 g / cm 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, the D50 particle size is 10.79 μm, and the specific surface area is 3.23 g / cm 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, the D50 particle size is 6.96 μm, and the specific surface area is 3.58 g / cm 3 .

[0114] Example 12

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

[0116] Example 13

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

[0118] Example 14

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

[0120] Example 15

[0121] The preparation method of the negative electrode sheet in Example 15 is basically the same as that in Example 10, 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 was basically the same as that of Example 1, except that the degree of substitution of the dispersant CMC was changed to 0.68.

[0124] Comparative Example 2

[0125] The preparation method of the negative electrode sheet of Comparative Example 2 was basically the same as that of Example 6, except that the degree of substitution of the dispersant CMC was changed to 0.68.

[0126] Comparative Example 3

[0127] The preparation method of the negative electrode sheet of Comparative Example 3 was basically the same as that of Example 5, except that the negative electrode active material was changed to hard carbon, the D50 particle size was 6.96 μm, and the specific surface area was 3.58 g / cm 3 。

[0128] Test Example:

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

[0130] 2. Lithium precipitation kinetics test: Cut 10 circular pieces from the same negative electrode sheet and assemble them with lithium metal sheets into coin-type lithium-ion batteries. Discharge at 3C to 0.01V, then charge at 1C to 2V, cycle 20 times and then discharge at 3C to 0.01V. Subsequently, disassemble the battery and observe the lithium precipitation situation on the surface of each negative electrode circular piece, and count the number of negative electrode sheets with different degrees of lithium precipitation among the 10 negative electrode sheets. Among them, when the lithium precipitation area of the circular piece is less than 5%, it is slight lithium precipitation; when the lithium precipitation area is 5% - 30%, it is moderate lithium precipitation; when the lithium precipitation area is greater than 30%, it is severe lithium precipitation.

[0131] 3. Zeta potential of the negative electrode active layer: After scraping off the negative electrode active layer on the negative electrode sheet, mix it with water at a mass ratio of 1:200, and ultrasonically disperse for 30 min to form a solution, and measure the Zeta potential of the solution with an electrophoretic light scattering instrument.

[0132] Among them, Figure 1 is the Zeta potential test spectrogram of the negative electrode active material in Example 1. From the figure, the Zeta potential of this negative electrode active material can be obtained as -42 mV.

[0133] Figure 2 is the Zeta potential test spectrogram of the negative electrode active material in Example 8. From the figure, the Zeta potential of this negative electrode active material can be obtained as -54 mV.

[0134] Figure 3 is the Zeta potential test spectrogram of the negative electrode active material in Comparative Example 2. From the figure, the Zeta potential of this negative electrode active material can be obtained as -27 mV.

[0135] Table 1

[0136]

[0137] As can be seen from Table 1, compared with the comparative example, for the negative electrode sheet provided by the present invention, by defining that the Zeta potential of the negative electrode active layer is less than or equal to -53 mV, the electrostatic repulsion force between particles can be enhanced, particle aggregation can be prevented, the dispersion uniformity and stability of the negative electrode active material in the negative electrode sheet can be improved, black spots or dark scribes on the negative electrode sheet can be avoided, and the risk of local lithium deposition during the charging process of the battery can be reduced.

[0138] Finally, it should be noted that: those skilled in the art will easily think of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include common general knowledge or conventional technical means in the technical field not disclosed by the present invention. It is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A negative electrode sheet, characterized in that: 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.

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 negative electrode active layer includes a negative electrode active material and a dispersant, and 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.

4. The negative electrode sheet according to claim 3, 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.

5. The negative electrode sheet according to claim 3 or 4, characterized in that: The negative electrode active material has a zeta potential less than or equal to -33 mV.

6. The negative electrode sheet according to any one of claims 3 to 5, characterized in that: The zeta potential of the negative electrode active material is -55 mV to -40 mV.

7. The negative electrode sheet according to any one of claims 3 to 6, characterized in that: The zeta potential of the dispersant is less than or equal to -50 mV.

8. The negative electrode sheet according to any one of claims 3 to 7, characterized in that: The Zeta potential of the dispersant is -70 mV to -58 mV.

9. The negative electrode sheet according to any one of claims 3 to 8, characterized in that: The negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, mesophase carbon microbeads, silicon oxide and silicon carbon.

10. The negative electrode sheet according to any one of claims 3 to 9, characterized in that: The dispersant includes at least one of carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that: The negative electrode active layer further includes a binder and a conductive agent.

12. A method for preparing a negative electrode sheet according to any one of claims 1 to 11, characterized in that: The following steps are involved: A negative electrode slurry including a negative electrode active material, a dispersant, a conductive agent, a binder, and a solvent is coated on 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 to obtain the negative electrode sheet.

13. The method for preparing a negative electrode sheet according to claim 12, characterized in that: 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, preferably -112 mV to -100 mV; 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; And / or, the Zeta potential of the dispersant is less than or equal to -50 mV, preferably -70 mV to -58 mV.

14. A battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 11 or a negative electrode sheet prepared by the method for preparing the negative electrode sheet according to claim 12 or 13.

15. A battery pack, characterized in that: Comprising the battery of claim 14.

16. An electrical equipment, characterized in that: Comprising the battery according to claim 14 or the battery pack according to claim 15.

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