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

Abstract

The embodiment of the application provides a negative plate and a preparation method thereof, a battery, a battery pack and an electric equipment, the negative plate comprises a negative current collector and a negative active layer existing on at least one side of the negative current collector; the negative plate satisfies: lambda = (4.5 - R a ) / P, lambda is 1.3-2.9, wherein P is the compaction density of the negative plate, and the unit is g / cm 3 ; Ra is the surface roughness of the negative active layer, and the unit is mu m; the application can improve the liquid phase transmission capacity of the negative plate, reduce the battery impedance, and improve the fast charging performance and other electrochemical performances of the battery.

Description

Technical Field

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

[0002] Electrode sheets (or simply electrodes) are a crucial component of batteries. The liquid phase transport capability of the electrode sheets affects the battery's electrochemical performance, such as fast charging performance. For example, high power density and high energy density are performance advantages of power batteries, and these high power density and high energy density depend on thick electrodes. The kinetic performance of batteries with thick electrodes mainly depends on the liquid phase transport capability of the electrodes. Currently, methods to improve the liquid phase transport capability of electrodes include magnetic induction processing, laser processing, and multi-layer gradient pore design. However, these methods have limited effects on improving the liquid phase transport capability of electrodes. Furthermore, due to the high orientation and deformability of electrode active materials (such as graphite and other negative electrode active materials), a dense overpressure layer exists on the electrode surface (for example, a 5-10 micrometer thick overpressure layer is typically present on the surface of the negative electrode). This dense overpressure layer reduces the liquid phase transport capability of the electrode surface, severely degrading the electrode's liquid phase transport capability. This results in high battery impedance and poor fast charging performance. For example, it can lead to surface lithium plating during high-rate charging, thus affecting the battery's cycle stability and safety.

[0003] Therefore, how to improve the liquid phase transport capability of the electrode sheet, reduce the internal resistance of the battery, and improve the fast charging performance of the battery remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides a negative electrode sheet and its preparation method, a battery, a battery pack, and an electrical device, which can improve the liquid phase transport capability of the negative electrode sheet, reduce battery impedance, and improve the fast charging performance and other electrochemical properties of the battery.

[0005] In a first aspect, embodiments of the present invention provide a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer present on at least one side of the negative electrode current collector;

[0006] The negative electrode plate satisfies: λ = (4.5 - R) / (4.5 - R) a ) / P, λ is 1.3~2.9, where P is the compaction density of the negative electrode sheet, in g / cm³. 3 Ra is the surface roughness of the negative electrode active layer, expressed in μm.

[0007] In one possible implementation, λ is 1.8 to 2.4.

[0008] In one possible implementation, the R aThe micrometer size ranges from 0.4μm to 2.9μm, with 0.7μm to 2.2μm being preferred.

[0009] In one possible implementation, the surface porosity ρ of the negative electrode is 15% to 50%.

[0010] In one possible implementation, the compaction density P of the negative electrode sheet is greater than or equal to 1.25 g / cm³. 3 The preferred value is 1.40 g / cm³. 3 ~1.6g / cm 3 .

[0011] In one possible implementation, the thickness of the negative electrode active layer is 0.04 mm to 0.13 mm.

[0012] In one possible implementation, the negative electrode active layer comprises a carbon-based negative electrode material; preferably, the carbon-based negative electrode material comprises graphite.

[0013] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0014] The negative electrode slurry used to form the negative electrode active layer is coated on at least one side of the negative electrode current collector to form a negative electrode active layer precursor, thus obtaining an intermediate.

[0015] The negative electrode active layer precursor in the intermediate is subjected to surface roughening treatment to form the negative electrode active layer, thereby obtaining the negative electrode sheet.

[0016] In one possible implementation, the process of surface roughening the negative electrode active layer precursor in the intermediate includes: sandblasting the negative electrode active layer precursor in the intermediate to roughen the surface of the negative electrode active layer precursor, forming the negative electrode active layer, and obtaining the negative electrode sheet.

[0017] In one possible implementation, the particle size of the abrasive used in the sandblasting process is 61μm to 125μm; and / or, the conditions for the sandblasting process are: air pressure of 0.01Mpa to 0.1Mpa; and / or, linear velocity of 20HZ to 80HZ.

[0018] Thirdly, embodiments of the present invention provide a battery comprising the above-described negative electrode sheet or a negative electrode sheet prepared according to the above-described method for preparing a negative electrode sheet.

[0019] Fourthly, embodiments of the present invention provide a battery pack comprising at least two interconnected batteries as described above.

[0020] Fifthly, embodiments of the present invention provide an electrical device, including the battery or battery pack described above.

[0021] This application provides a negative electrode sheet, its preparation method, a battery, a battery pack, and an electrical device. The negative electrode sheet satisfies: λ = (4.5 - Ra) / P, where λ is 1.3~2.9. This opens up the pores of the negative electrode sheet's surface structure, reduces the surface tortuosity, and reduces the transport and diffusion resistance of active ions such as lithium ions in the liquid phase. This makes it easier for active ions such as lithium ions to enter the interior of the negative electrode, promoting the diffusion of active ions such as lithium ions inside the negative electrode sheet. This allows the negative electrode sheet to withstand high current densities and avoids the accumulation of active ions such as lithium ions caused by the closed-pore structure of the surface, which can lead to lithium plating and other phenomena. This alleviates problems such as lithium plating on the surface of the battery during high-rate charging. At the same time, the above-mentioned negative electrode sheet is equivalent to opening the overvoltage layer (or overvoltage region) on the surface, which can improve the mass transfer capacity of the pore structure of the negative electrode surface, enhance the liquid phase transport capacity of the negative electrode sheet, optimize the battery dynamic performance, and thus reduce the battery impedance. This also improves the battery's energy density, cycle stability, fast charging performance, and other electrochemical performance. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0023] Figure 1 This is a schematic diagram of a sandblasting process equipment according to an embodiment of the present invention;

[0024] Figure 2 This is a SEM image of the cross-section of the negative electrode sheet in Comparative Example 2 of the present invention;

[0025] Figure 3 This is a confocal microscope image of the negative electrode surface in Embodiment 1 of the present invention.

[0026] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0027] To enable those skilled in the art to better understand the solutions of this invention, the following provides a more detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0028] In related technologies, the liquid phase transport capability of the negative electrode sheet is poor due to factors such as the presence of an overpressure layer on the surface of the negative electrode sheet. In particular, as the compaction density of the negative electrode sheet increases, the overall density of the negative electrode sheet increases, especially the density of the overpressure layer on its surface, which leads to greater resistance to liquid phase transport of the negative electrode sheet. This results in high battery impedance and poor electrochemical performance such as fast charging performance and cycle stability.

[0029] This invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer present on at least one side of the negative electrode current collector; the negative electrode sheet satisfies: λ = (4.5 - R) / ( ... a ) / P, λ is 1.3~2.9, where P is the compaction density of the negative electrode, in g / cm³ 3 Ra is the surface roughness of the negative electrode active layer, expressed in μm.

[0030] According to the inventors' research, the aforementioned negative electrode sheet is the first to focus on the mass transfer capacity of the pore structure in the electrode surface layer. Under this negative electrode sheet structure system, the liquid phase transport capacity of the negative electrode sheet can be improved, optimizing battery kinetic performance, thereby reducing battery impedance and improving electrochemical performance such as fast charging performance. The reason for this is that λ is the overpressure coefficient, which is related to the surface roughness and compaction density of the negative electrode sheet. The surface roughness and compaction density of the negative electrode sheet affect its surface structure. When λ is between 1.3 and 2.9, both the compaction density and surface roughness of the negative electrode sheet can be balanced. Specifically, on the one hand, a high compaction density can be maintained, i.e., a high capacity; on the other hand, the surface roughness of the negative electrode sheet can be increased to open the surface overpressure layer, i.e., targeted overpressure reduction. By opening up the overvoltage zone on the surface of the negative electrode and opening up the pores in the surface structure, the tortuosity of the surface layer is reduced, which helps to reduce the resistance to the transport and diffusion of active ions such as lithium ions in the liquid phase. This makes it easier for active ions such as lithium ions to enter the interior of the negative electrode, promotes the diffusion of active ions such as lithium ions inside the negative electrode, enables the negative electrode to withstand high current density, avoids the accumulation of active ions such as lithium ions caused by the closed pores on the surface of the negative electrode, alleviates the problem of surface lithium plating during high-rate charging, and can reduce battery impedance, improve the fast charging performance of the battery, and also improve the electrochemical performance such as cycle stability of the battery. Especially for batteries with high areal density and high compaction density, it can significantly improve the kinetic performance of the battery without wasting pores, and can improve the energy density of the battery.

[0031] According to further research by the inventors, in the above-mentioned negative electrode structure system, λ not less than 1.3 can open the surface structure pores, which is conducive to the passage of active ions such as lithium ions, improve the liquid phase transport capability of the negative electrode, optimize the battery dynamic performance, and the opened surface structure pores will not cause waste, which can also improve the energy density of the battery. λ not greater than 2.9 can facilitate the opening of the surface overpressure layer, reduce the surface tortuosity of the negative electrode, and increase the surface porosity of the negative electrode, thereby improving the liquid phase transport capability of the negative electrode surface, improving the dynamic performance of the battery, reducing battery impedance, and improving the battery's cycle stability and fast charging electrochemical performance. Therefore, λ of 1.3~2.9 can balance the compaction density (capacity) and liquid phase transport capability of the negative electrode, thereby improving the battery's dynamic performance and energy density, reducing the battery's internal resistance, and improving the battery's cycle stability and fast charging performance.

[0032] In this embodiment of the invention, λ is 1.3 to 2.9. For example, λ can be a range of 1.3, 1.5, 1.8, 2.0, 2.2, 2.4, 2.6, 2.9 or any combination thereof.

[0033] In some embodiments, λ can be 1.8 to 2.4, which can further enhance the liquid phase transport capability of the negative electrode, improve the kinetic performance of the battery, and further improve the energy density and cycle stability of the battery. The reason is that λ not less than 1.8 can further open the surface structure pores to build transport channels for active ions such as lithium ions, further improve the liquid phase transport capability of the negative electrode, which is more conducive to optimizing the battery kinetic performance and further avoids waste caused by the surface structure pores of the negative electrode, which is conducive to further improving the energy density of the battery. λ not greater than 2.4 helps to further open the overvoltage layer on the surface of the negative electrode, further reduce the surface tortuosity of the negative electrode, thereby further improving the liquid phase transport capability on the surface of the negative electrode, which is conducive to further improving the kinetic performance of the battery, improving the cycle stability and electrochemical performance such as fast charging, and reducing the internal resistance of the battery.

[0034] In some embodiments, the surface roughness R of the negative electrode active layer a The micrometer value can range from 0.4 μm to 2.9 μm, for example, it can be a range of 0.4 μm, 0.7 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.9 μm, or any combination thereof, R. a With a diameter of not less than 0.5 μm, it can further open up the surface structure pores, allowing the passage of active ions such as lithium ions. aA surface roughness R of no more than 2.9 μm can further avoid excessively large pores, preventing waste of pore space and thus avoiding a reduction in the quality of the negative electrode active material. This further prevents a decrease in the lithium intercalation capacity of the negative electrode sheet and the energy density of the battery. Therefore, based on λ of 1.3~2.9, the surface roughness R of the negative electrode active layer is... a Within the range of 0.4μm to 2.9μm, it helps to further open the overpressure layer on the surface of the negative electrode, which is beneficial to the transport of active ions such as lithium ions, further improving the liquid phase transport capability of the negative electrode, improving the dynamic performance of the battery, while maintaining a high compaction density of the negative electrode and improving the energy density and other performance of the battery.

[0035] In some embodiments, the surface roughness R of the negative electrode active layer a The thickness can range from 0.7μm to 2.2μm, which can further improve the capacity and liquid phase transport capability of the negative electrode, while also improving the kinetic performance and energy density of the battery.

[0036] In this embodiment of the invention, the surface roughness Ra of the negative electrode active layer is the average roughness (or arithmetic mean roughness). The surface of the negative electrode active layer (i.e., the surface area) refers to the side of the negative electrode active layer facing away from the negative electrode current collector (also the interface where the negative electrode active layer and the electrolyte directly contact each other in the battery). As mentioned above, the thickness of this surface area is approximately 10 μm ± 3 μm. The surface roughness of the negative electrode active layer refers to the unevenness of the negative electrode sheet surface with small spacing and tiny peaks and valleys. In this invention, it is represented by the profile arithmetic mean deviation Ra, that is, by the arithmetic mean of the absolute values ​​of the profile deviations within a sampling length of 6 mm. The surface roughness Ra can be tested using the following method: Wipe the surface of the negative electrode sheet and the test platform of the precision roughness tester clean with a lint-free cloth (the model and specification of the precision roughness tester used is SPR1103G-sak). Place the negative electrode sheet stably on the test platform, ensuring that there is no shaking or tilting in the contact area between the negative electrode sheet and the probe. Set the probe position to automatically adjust so that the probe gently contacts the surface of the negative electrode sheet. Set the measurement length of the negative electrode sheet surface to 6 mm and record Ra.

[0037] In some embodiments, the surface porosity ρ of the negative electrode sheet can be 15% to 50%, for example, ρ can be a range of 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any combination thereof. A surface porosity ρ of not less than 15% can construct ion transport channels, which is beneficial to further reduce battery impedance. A surface porosity ρ of not more than 50% can improve the liquid phase transport capability of the negative electrode sheet, avoid waste of pores, further improve the energy density of the battery, and avoid poor contact between negative electrode active material particles, which can further improve the cycle stability of the battery and reduce the internal resistance of the battery. Therefore, a ρ of 15% to 50% is more conducive to balancing the improvement of the liquid phase transport capability of the negative electrode sheet and the energy density of the battery.

[0038] In this embodiment of the invention, the surface porosity ρ of the negative electrode sheet is the proportion of pore structure on the surface of the negative electrode active layer. The surface of the negative electrode active layer (hereinafter referred to as the surface region) refers to the side of the negative electrode active layer away from the negative electrode current collector (also the interface in which the negative electrode active layer and the electrolyte are in direct contact in the battery). The thickness of this surface region is approximately 10 μm ± 3 μm. The surface porosity ρ of the negative electrode sheet can be obtained by the following method: Take the negative electrode sheet, use nano-CT (nano ct) to test and obtain the surface image of the negative electrode sheet, correct the surface image of the negative electrode sheet, and obtain the surface porosity ρ of the negative electrode sheet by layer-by-layer statistical analysis. The resolution of the nano CT device is 0.2 μm.

[0039] In some embodiments, the compaction density P of the negative electrode can be greater than or equal to 1.25 g / cm³. 3 By improving the liquid phase transport capability of the negative electrode and enhancing the battery's kinetic performance, it is beneficial to further improve the battery's energy density and cycle stability. The reason for this is that the compaction density P of the negative electrode is greater than or equal to 1.25 g / cm³. 3 This can reduce the porosity of the negative electrode sheet, improve its structural stability, and further enhance the contact between the negative electrode active material particles. This avoids problems such as poor contact between particles caused by excessively large pores, increased battery resistance, and decreased battery cycle stability. At the same time, a higher compaction density also helps retain more negative electrode active material in the negative electrode sheet, increasing its capacity and further improving the battery's energy density.

[0040] As mentioned earlier, in related technologies, the higher the compaction density of the negative electrode, the greater the density of the negative electrode as a whole and its surface overpressure layer, resulting in a greater resistance to liquid phase transport. Therefore, it is usually difficult to simultaneously achieve high compaction density (high capacity) and low liquid phase transport resistance (low impedance) in the negative electrode. However, in the embodiments of this application, by synergistically controlling the compaction density P and surface roughness Ra of the negative electrode, the overpressure coefficient λ of the negative electrode is kept within the range of 1.3 to 2.9, even for compaction densities as high as 1.25 g / cm³. 3 The above-mentioned negative electrode sheets can also effectively improve their liquid phase transport capability, achieving a balance between high capacity and low impedance, thereby improving the battery's energy density, fast charging performance, and cycle stability.

[0041] In some embodiments, the compaction density P of the negative electrode can be 1.40 g / cm³. 3 ~1.60g / cm 3 For example, it can be 1.40 g / cm³. 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 1.60g / cm 3 Or a range consisting of any two of these, which can further improve the energy density and dynamic performance of the battery.

[0042] In this embodiment of the invention, the compaction density P of the negative electrode sheet refers to the mass per unit volume of the negative electrode active layer, that is, the compaction density of the negative electrode sheet = the total mass of the negative electrode active layer / the total volume of the negative electrode active layer. The compaction density of the negative electrode active layer can be measured by the following process: Take a negative electrode sheet sample, and test the total mass m1, the total thickness T1, and the surface area of ​​one side of the negative electrode sheet sample (i.e., the surface area of ​​the side of the negative electrode active layer facing away from the negative electrode current collector) S; then scrape off the negative electrode active layer on the negative electrode sheet sample, and test the mass m2 and the thickness T2 of the obtained negative electrode current collector. Then, the total thickness of the negative electrode active layer = T1 - T2, the total volume of the negative electrode active layer = (T1 - T2) × S, the total mass of the negative electrode active layer = (m1 - m2), and the compaction density of the negative electrode active layer = (m1 - m2) / ((T1 - T2) × S).

[0043] In some embodiments, the thickness of the negative electrode active layer can be greater than or equal to 0.04 mm, which is beneficial to further improve the capacity of the negative electrode on the basis of improving the liquid phase transport capability of the negative electrode.

[0044] Thick electrodes help improve battery energy density, but in related technologies, the thickness of thick electrodes is relatively large. Due to the presence of a surface overpressure layer and long ion transport paths, the liquid phase transport resistance of the negative electrode sheet is greater and difficult to overcome. In the embodiments of this application, by synergistically controlling the compaction density P and surface roughness Ra of the negative electrode sheet, the overpressure coefficient λ of the negative electrode sheet is made within the range of 1.3 to 2.9. Even for negative electrode sheets with a thickness of more than 0.04 mm, its liquid phase transport capability can be effectively improved, achieving a balance between high capacity and low impedance of the negative electrode sheet, thereby improving the battery's energy density, fast charging performance, and cycle stability.

[0045] In some embodiments, the thickness of the negative electrode active layer can be 0.04 mm to 0.13 mm, for example, it can be 0.04 mm, 0.06 mm, 0.08 mm, 0.10 mm, 0.12 mm, 0.125 mm, 0.13 mm or any combination thereof. A thickness of 0.04 mm to 0.13 mm can further balance the lithium intercalation capacity and the liquid phase transport capability of the negative electrode sheet. Specifically, a thickness of no more than 0.13 mm is beneficial to further improve the transport rate of active ions such as lithium ions on the surface of the negative electrode sheet, further improve the liquid phase transport capability of the negative electrode sheet, and further improve the kinetic performance of the battery. A thickness of no less than 0.04 mm can further improve the lithium intercalation capacity of the negative electrode sheet and further improve the energy density of the battery.

[0046] Specifically, the thickness of the negative electrode active layer can be 0.04mm to 0.13mm, which refers to the thickness of the negative electrode active layer on one side.

[0047] In some embodiments, the thickness of the negative electrode sheet can be 0.12 mm to 0.25 mm, for example, it can be a range of 0.12 mm, 0.15 mm, 0.18 mm, 0.21 mm, 0.24 mm, 0.25 mm or any combination thereof.

[0048] In this embodiment of the invention, the thickness of the negative electrode active layer can be measured by conventional methods, such as using a micrometer to measure the thickness of the negative electrode active layer.

[0049] In some embodiments, the negative electrode active layer may include a negative electrode active material, which may include a carbon-based negative electrode material, and the carbon-based negative electrode material may include graphite. Carbon-based negative electrode materials such as graphite have relatively high conductivity and stable cycle performance. Using carbon-based negative electrode materials such as graphite as the negative electrode active material is beneficial to further improve the conductivity and cycle stability of the negative electrode sheet. Simultaneously, within the range of λ of 1.3 to 2.9, not only can a high-throughput ion transport pathway be constructed, further enhancing the liquid phase transport capability of the negative electrode sheet, thereby further improving the battery's kinetic performance, reducing internal resistance, and improving electrochemical performance such as cycle stability and fast charging, but it can also further increase the battery's energy density.

[0050] Taking graphite as an example, graphite has a layered structure and is characterized by high orientation and variability. In related technologies, when graphite is used to prepare negative electrode sheets (graphite negative electrodes), a dense overpressure layer (typically 5-10 μm thick) easily forms on the surface of the graphite negative electrode, severely affecting the liquid phase transport capability of the negative electrode sheet, thereby increasing battery impedance and affecting the battery's fast-charging performance. In the embodiments of this application, graphite is used as the negative electrode active material (i.e., the negative electrode sheet is a graphite negative electrode). By synergistically controlling the compaction density P and surface roughness Ra of the negative electrode sheet, the overpressure coefficient λ of the negative electrode sheet is kept within the range of 1.3 to 2.9. This effectively solves the problem of poor liquid phase transport capability of the graphite negative electrode caused by the presence of an overpressure layer on the surface of the graphite negative electrode, improves the kinetic performance of the negative electrode sheet, thereby reducing the battery's internal resistance and improving the battery's fast-charging performance and other electrochemical performance.

[0051] Specifically, in the negative electrode sheet, a negative electrode active layer can be provided on one side of the negative electrode current collector, or a negative electrode active layer can be provided on both sides of the negative electrode current collector in the thickness direction.

[0052] Specifically, the negative electrode active layer may also include a conductive agent and a binder, both of which can be conventional materials in the art. For example, the conductive agent may include one or more of carbon black, conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0053] Generally, in the negative electrode active layer, the mass percentage of the negative electrode active material (i.e., the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0054] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0055] In this embodiment of the invention, the negative electrode sheet can be specifically prepared by coating method, that is, coating a negative electrode slurry containing negative electrode active material and other materials onto a negative electrode current collector, and then performing processes such as drying and rolling to form a negative electrode active layer, thereby obtaining a negative electrode sheet.

[0056] The present invention also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps: coating a negative electrode slurry for forming a negative electrode active layer onto at least one side of a negative electrode current collector to form a negative electrode active layer precursor, thereby obtaining an intermediate; and subjecting the negative electrode active layer precursor in the intermediate to surface roughening treatment to form a negative electrode active layer, thereby obtaining a negative electrode sheet.

[0057] In this embodiment of the invention, the material composition of the negative electrode active layer precursor is basically the same as that of the negative electrode active layer. The only difference is that the negative electrode active layer precursor has not undergone surface roughening treatment. After surface roughening treatment, the negative electrode active layer is formed.

[0058] Specifically, the aforementioned intermediate can be prepared by a coating method. Specifically, components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying and rolling processes, the intermediate is obtained. The coating, drying, and rolling processes are standard operations in the preparation of negative electrode sheets using the coating method and are not particularly limited thereto.

[0059] In this embodiment of the invention, the surface roughening treatment of the negative electrode active layer precursor can be performed by sandblasting, that is, sand is used to sandblast the surface of the negative electrode active layer precursor to control its surface roughness, form the above-mentioned negative electrode active layer, and obtain the negative electrode sheet.

[0060] Specifically, in some embodiments, the process of surface roughening treatment of the negative electrode active layer precursor in the intermediate includes: sandblasting the negative electrode active layer precursor in the intermediate to roughen the surface of the negative electrode active layer precursor, forming a negative electrode active layer, and obtaining a negative electrode sheet.

[0061] In some embodiments, the abrasive used in the sandblasting process may include one or more of the following: garnet sand, steel shot / steel grit, brown corundum sand, silicon carbide sand, iron sand, quartz sand, nylon sand, and graphite particles. This is beneficial for improving the surface roughness of the negative electrode sheet, further opening the surface pores of the negative electrode sheet, and improving the liquid phase transport capability of the negative electrode sheet.

[0062] In some embodiments, the particle size of the abrasive used in the sandblasting process can be 61μm to 125μm, for example, it can be 61μm, 71μm, 81μm, 91μm, 101μm, 111μm, 121μm, 125μm or any combination thereof. This can further open the overpressure layer on the surface of the negative electrode, further reduce the surface tortuosity of the negative electrode, improve the surface porosity of the negative electrode, and facilitate the preparation of the negative electrode. The reason for this is that if the particle size of the abrasive is not less than 61μm, it can prevent the abrasive from embedding into the surface of the negative electrode, affecting the liquid phase transport capability of the negative electrode and the battery performance. Also, if the particle size is too small, it is not conducive to the recycling and reuse of the abrasive, which will cause waste of the abrasive. If the particle size of the abrasive is not greater than 125μm, it is more conducive to controlling the surface roughness of the negative electrode, opening the surface pores of the electrode, and opening the overpressure layer on the surface of the electrode.

[0063] In some embodiments, the conditions for sandblasting can be: the air pressure can be 0.01 MPa to 0.1 MPa, for example, it can be a range of 0.01 MPa, 0.03 MPa, 0.05 MPa, 0.07 MPa, 0.09 MPa, 0.1 MPa or any combination thereof, with the air pressure not exceeding 0.1 MPa. This allows for opening the pores on the surface of the negative electrode sheet while further avoiding damage to the surface structure of the negative electrode sheet. At the same time, the air pressure is not less than 0.01 MPa, which can further open the overpressure layer on the surface of the negative electrode sheet, which is beneficial to further improving the liquid phase transport capability of the negative electrode sheet. Therefore, the air pressure in the sandblasting process is in the range of 0.01 MPa to 0.1 MPa, which is more conducive to the preparation of the negative electrode sheet, improves the preparation efficiency of the negative electrode sheet, and can further improve the liquid phase transport capability and surface structure stability of the negative electrode sheet.

[0064] In some embodiments, the conditions for sandblasting are: the linear velocity can be 20Hz~80Hz, for example, it can be a range of 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz or any combination thereof, which is more conducive to surface roughening of the negative electrode sheet, improving the preparation efficiency of the negative electrode sheet. At the same time, on the basis of improving the liquid phase transport capability of the prepared negative electrode sheet, it further improves the uniformity of the surface roughness of the negative electrode sheet and the uniformity of the surface pore distribution, and further optimizes the performance of the prepared negative electrode sheet.

[0065] In this embodiment of the invention, a conventional sandblasting device can be used for sandblasting. The sandblasting process includes spraying sand from the nozzle of the sandblasting device onto the surface of the negative electrode active layer precursor. The aforementioned air pressure refers to the air pressure of the nozzle, and the aforementioned linear velocity refers to the linear velocity of the nozzle oscillation. Figure 1 As shown, when performing sandblasting (sandblasting processing) on ​​the rolled electrode sheet (i.e., the precursor of the negative electrode active layer in the intermediate), the specific steps can be as follows: Figure 1 As shown in the conveyor belt direction, the negative electrode active layer precursor is sequentially sandblasted through nozzles. During the sandblasting process, the nozzles spray sand towards the negative electrode active layer precursor to roughen its surface and form the negative electrode active layer. Surface roughening through sandblasting is beneficial for the preparation of the negative electrode sheet. This sandblasting method is simple and convenient, and the areal density loss of the negative electrode sheet is small. Compared with other methods such as laser processing to control the surface roughness of the negative electrode coating, sandblasting results in less loss of the main negative electrode material (negative electrode active material), lower processing costs, and faster operation. Furthermore, the sand can be reused, which helps reduce preparation costs. The prepared negative electrode sheet has advantages such as high roughness, high wettability, and high surface porosity, which helps to further improve the ion transport rate on the surface of the negative electrode sheet and further enhance its liquid phase transport capability.

[0066] In this embodiment of the invention, the compaction density of the negative electrode sheet is basically equal to the compaction density of the intermediate, and the thickness of the negative electrode active layer is basically equal to the thickness of the negative electrode active layer precursor in the intermediate. That is, the surface roughening treatment of the negative electrode active layer precursor in the intermediate does not affect the compaction density of the intermediate and the thickness of the negative electrode active layer precursor in the intermediate.

[0067] This invention also provides a battery comprising the above-described negative electrode sheet or a negative electrode sheet prepared according to the above-described method for preparing the negative electrode sheet. This battery has advantages corresponding to the above-described negative electrode sheet, which will not be elaborated further.

[0068] In this embodiment of the invention, the battery may include a power battery, which can be applied to the fields of lithium-ion power batteries, solar cells, and new energy storage batteries, and has significant advantages.

[0069] Generally, a battery includes a cell and a casing that encapsulates the cell. Electrolyte is injected into the cell within the casing. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of positive electrode, separator, and negative electrode layers stacked sequentially and then wound together.

[0070] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0071] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0072] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0073] Specifically, the diaphragm can be a polymer membrane, which can be a conventional diaphragm material in the art, for example, the diaphragm includes a polyethylene (PE) membrane.

[0074] In this embodiment of the invention, conventional positive electrode sheets in the art can be used, and there are no particular limitations. For example, the positive electrode sheet may include a positive current collector and a positive active layer located on at least one side surface of the positive current collector. Specifically, the positive active layer may be provided on one side surface of the positive current collector, or the positive active layers may be provided on both opposite sides of the positive current collector in the thickness direction (i.e., the two surfaces of the positive current collector).

[0075] Generally, the positive electrode active layer may include a positive electrode active material (positive electrode active substance), a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium nickel oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary positive electrode materials. The ternary positive electrode material may include nickel cobalt manganese ternary material (NCM) and / or nickel cobalt aluminum ternary material (NCA). The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0076] Generally, in the positive electrode active layer, the mass percentage of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0077] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0078] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0079] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence to obtain a battery cell. Then the battery cell is placed in a casing (outer packaging) and after conventional battery assembly processes such as electrolyte injection, baking and wetting, the battery is obtained.

[0080] This invention also provides a battery pack comprising at least two interconnected batteries as described above. This battery pack has advantages corresponding to the negative electrode or the battery described above, which will not be elaborated further.

[0081] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0082] This invention also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the positive electrode or battery described above, which will not be elaborated further.

[0083] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0084] The present invention will be further described below through specific embodiments.

[0085] Example 1

[0086] (1) Preparation of negative electrode

[0087] Graphite, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), and conductive agent carbon black were mixed in a mass ratio of 96:1.5:1:1.5. Water was added as a solvent, and the mixture was thoroughly mixed to prepare a negative electrode slurry. This slurry was then coated onto both sides of a copper foil. After baking and rolling, a compacted density of 1.50 g / cm³ was obtained. 3 Intermediates;

[0088] The intermediate negative electrode active layer precursor was sandblasted. The sand used for sandblasting was quartz sand with a particle size of 65μm. The sandblasting conditions were: air pressure of 0.01Mpa and linear velocity of 20HZ. The negative electrode sheet was obtained after sandblasting.

[0089] The compaction density of the negative electrode is 1.5 g / cm³. 3 The surface roughness is 1.3 μm.

[0090] (2) Preparation of positive electrode sheet

[0091] Lithium iron phosphate cathode material, carbon black, and PVDF are mixed in a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) solvent is added and stirred until the mixture is uniform to obtain a cathode slurry. The cathode slurry is coated on both sides of an aluminum foil. After drying and rolling, a cathode active layer is formed on both sides of the aluminum foil to obtain a cathode sheet.

[0092] (3) Battery assembly

[0093] The negative electrode, separator, positive electrode, and separator are stacked in sequence to form a battery cell;

[0094] The battery cells are packaged in aluminum-plastic film and assembled into lithium-ion batteries after processes such as baking, electrolyte injection, and immersion.

[0095] The solute in the electrolyte is LiPF6, and the solution consists of EC, EMC, DEC, and DMC, with a mass ratio of LiPF6:EC:EMC:DEC:DMC = 13:30:34:11:12.

[0096] Examples 2-23, Comparative Example 1, and Comparative Example 3 differ from Example 1 in that the overpressure coefficient λ of the negative electrode, the surface roughness Ra of the negative electrode active layer, the surface porosity ρ of the negative electrode, the compaction density P of the negative electrode, the thickness of the negative electrode active layer, the particle size of the sand, the air pressure of the sandblasting process, and the linear velocity of the sandblasting process are different. See Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same as those in Example 1.

[0097] Comparative Example 2: The difference from Example 1 is that the overpressure coefficient λ of the negative electrode is 3.0, the surface roughness Ra of the negative electrode active layer is 0.4, the surface porosity ρ of the negative electrode is 41, the compaction density P of the negative electrode is 1.37, and no sandblasting is performed during the preparation of the negative electrode. All other conditions are the same as in Example 1.

[0098] The overpressure coefficient λ, compaction density P, and thickness testing methods of the negative electrode sheet in each embodiment and comparative example are as described above and will not be repeated here.

[0099] The surface roughness Ra of the negative electrode active layer, the surface porosity ρ of the negative electrode sheet, the liquid phase diffusion resistance of the negative electrode sheet, the DCIR of the battery at 50% SOC, and the capacity retention rate of the battery after 500 fast charging cycles were tested for each embodiment and comparative example through the following process. The results are shown in Table 2.

[0100] (1) Surface roughness Ra test of the negative electrode active layer: Wipe the surface of the negative electrode and the test platform of the precision roughness tester with a lint-free cloth (the model and specification of the precision roughness tester used is SPR1103G-sak). Place the prepared negative electrode on the test platform stably, ensuring that there is no shaking or tilting in the contact area between the negative electrode and the probe. Set the probe position to automatically adjust so that the probe gently touches the surface of the negative electrode. Set the measurement length of the negative electrode surface to 6mm and measure Ra.

[0101] (2) Test of surface porosity ρ of negative electrode sheet: Take negative electrode sheet and use nano CT to test to obtain surface image of negative electrode sheet. Correct the surface image of negative electrode sheet and obtain the surface porosity ρ of negative electrode sheet by layer statistics. The resolution of nano CT equipment is 0.2μm.

[0102] (3) Negative electrode liquid phase diffusion impedance test: The two negative electrodes and the separator were assembled into an electrode core in sequence; the electrode core was placed in the outer packaging shell, baked and then injected with electrolyte (the formula is the same as the electrolyte in the assembly of the above battery). After battery assembly processes such as immersion, a liquid phase diffusion impedance battery was obtained. The liquid phase diffusion impedance was tested using an electrochemical workstation (model: VMP-300) in the frequency range of 300000Hz-0.05Hz. The measured liquid phase diffusion impedance of the negative electrode is shown in Table 2.

[0103] (4) DC internal resistance test of lithium-ion battery at 50% SOC: At room temperature (25±5℃), take the lithium-ion battery prepared above, use the Blue Electric room temperature test channel (5V, 12A), discharge it to 2.0V with a constant current of 1 / 3C, then charge it to 50% SOC (50% state of charge) with a constant current of 1 / 3C, and let it rest for 30min; then discharge it with a constant current of 1.5C for 30s, and detect the DC internal resistance of the battery at 50% SOC.

[0104] (5) Lithium-ion battery capacity retention test after 500 fast charging cycles: The lithium-ion batteries prepared above were tested according to the following steps:

[0105] S1: Discharge to 2.0V at a constant current of 1 / 3C and let stand for 30 minutes;

[0106] S2: Charged at 4C constant current for 0.73 minutes, cutoff voltage 3.8V;

[0107] S3: Charged at a constant current of 3.5C for 1.18 minutes, cutoff voltage 3.8V;

[0108] S4: Charged at 3C constant current for 1.38 minutes, cutoff voltage 3.8V;

[0109] S5: Charged at a constant current of 2.5C for 1.66 minutes, cutoff voltage 3.8V;

[0110] S6: Charged at 2C constant current for 2.07 minutes, cutoff voltage 3.8V;

[0111] S7: Charged at 1.5C constant current for 2.76 minutes, cutoff voltage 3.8V;

[0112] S8: Charged at 1C constant current for 24.35 minutes, cutoff voltage 3.8V;

[0113] S9: Charge to 3.8V with a constant current of 1 / 3C, then let stand for 10 minutes;

[0114] S10: Discharge at a constant current of 1C to 2.0V and let stand for 10 minutes;

[0115] S11: Discharge at a constant current of 1 / 3C to 2.0V, let stand for 30 minutes, and record the discharge capacity of S10 as R. 10 The discharge capacity of S11 is R 11 Then the total discharge capacity is R1 = R 10 +R 11 Repeat the above steps 500 times, and record the discharge capacity R of S10 after 500 cycles. 20 The discharge capacity of S11 is R 21 Then the total discharge capacity is R2 = R 20 +R 21 The capacity retention rate of a lithium-ion battery after 500 fast charging cycles is R2 / R1×100%.

[0116] Table 1. Preparation and parameters of the negative electrode.

[0117]

[0118] Table 2 Performance of Anode Sheets and Lithium-ion Batteries

[0119]

[0120] Compared to Comparative Examples 1-3, the negative electrode sheets in Examples 1-23 satisfy the following: λ is 1.3~2.9, which can improve the liquid phase transport capability of the negative electrode sheet, optimize the battery dynamic performance, thereby reducing the battery impedance, and can also improve the battery's fast charging performance and cycle stability and other electrochemical performance.

[0121] Specifically, the negative electrode sheet prepared in Comparative Example 2 was cut along a direction perpendicular to the copper foil. The cross-sectional SEM image of the negative electrode sheet in Comparative Example 2 was obtained using a scanning electron microscope (SEM). Figure 2 , Figure 2The overvoltage layer on the surface of the negative electrode sheet exhibits a flat, densely packed, closed-cell structure with a λ of 3.0. This results in poor liquid phase transport capability, high internal resistance, and poor fast-charging performance. The surface state of the negative electrode sheet in Example 1, as shown in the confocal microscopy test image, is as follows. Figure 3 It can be seen that the surface of the negative electrode after sandblasting has obvious pore structure, with λ being 2.4. The negative electrode has good liquid phase transport capability, low battery internal resistance, and good fast charging performance.

[0122] 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 what has been described above. 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, It includes a negative electrode current collector and a negative electrode active layer present on at least one side of the negative electrode current collector; The negative electrode plate satisfies: λ = (4.5 - R) / (4.5 - R) a ) / P, λ is 1.3~2.9, where P is the compaction density of the negative electrode sheet, in g / cm³. 3 Ra is the surface roughness of the negative electrode active layer, expressed in μm.

2. The negative electrode sheet according to claim 1, characterized in that, The value of λ is 1.8 to 2.

4.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The R a The micrometer size ranges from 0.4μm to 2.9μm, with 0.7μm to 2.2μm being preferred.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The surface porosity ρ of the negative electrode is 15%~50%.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The compaction density P of the negative electrode sheet is greater than or equal to 1.25 g / cm³. 3 The preferred value is 1.40 g / cm³. 3 ~1.6g / cm 3 .

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The thickness of the negative electrode active layer is 0.04 mm to 0.13 mm.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The negative electrode active layer comprises a carbon-based negative electrode material; preferably, the carbon-based negative electrode material comprises graphite.

8. A method for preparing a negative electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: The negative electrode slurry used to form the negative electrode active layer is coated on at least one side of the negative electrode current collector to form a negative electrode active layer precursor, thus obtaining an intermediate. The negative electrode active layer precursor in the intermediate is subjected to surface roughening treatment to form the negative electrode active layer, thereby obtaining the negative electrode sheet.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The process of surface roughening treatment of the negative electrode active layer precursor in the intermediate includes: sandblasting the negative electrode active layer precursor in the intermediate to roughen the surface of the negative electrode active layer precursor, forming the negative electrode active layer, and obtaining the negative electrode sheet.

10. The method for preparing the negative electrode sheet according to claim 9, characterized in that, The particle size of the sand used in the sandblasting process is 61μm~125μm; And / or, the conditions for the sandblasting treatment are: air pressure of 0.01 MPa to 0.1 MPa; and / or, linear velocity of 20 Hz to 80 Hz.

11. A battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1-7 or the negative electrode sheet prepared according to the preparation method of the negative electrode sheet according to any one of claims 8-10.

12. A battery pack, characterized in that, It includes at least two interconnected batteries as described in claim 11.

13. An electrical appliance, characterized in that, Includes the battery of claim 11 or the battery pack of claim 12.

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