Negative electrode and preparation method therefor, battery and electric device

Abstract

A negative electrode and a preparation method therefor, a battery and an electric device. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on a surface of the negative electrode current collector, wherein the negative electrode active material layer comprises graphite, the orientation value of the negative electrode active material layer is less than or equal to 3, and the binding force between the negative electrode current collector and the negative electrode active material layer is greater than or equal to 0.25 N / 40 mm; and the orientation value is the ratio of the peak area of the characteristic diffraction peak (004) in an X-ray diffraction spectrum of the negative electrode to the peak area of the characteristic diffraction peak (110).

Description

Negative electrode and preparation method thereof, battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202410382797X and application name “Negative electrode and preparation method thereof, battery and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a negative electrode and a preparation method thereof, a battery and an electrical device. Background Art

[0003] Graphite is widely used in battery anodes due to its low cost and high energy density. Currently, with increasing user demand, more and more electrical products require fast charging capabilities, which necessitates research and improvements in the batteries used in these products. However, the layered structure of graphite in battery anodes makes it more likely to be aligned parallel to the current collector during the production process, resulting in suboptimal fast-charging performance.

[0004] Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a negative electrode and its preparation method, a battery and an electrical device, wherein the negative electrode has excellent ion and electron diffusion capabilities and good internal stability, which is beneficial to improving the battery's charge and discharge rate, cycle capacity retention rate and service life.

[0006] In the first aspect, the present application discloses a negative electrode, comprising a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, the negative electrode active material layer comprising graphite, the orientation value of the negative electrode active material layer being less than or equal to 3, and the binding force between the negative electrode current collector and the negative electrode active material layer being greater than or equal to 0.25N / 40mm.

[0007] In a second aspect, the present application discloses a method for preparing a negative electrode, comprising: providing a negative electrode current collector, coating a negative electrode slurry containing graphite on at least one surface of the negative electrode current collector, and adjusting the orientation of the graphite in the negative electrode slurry using a magnetic field;

[0008] After drying, a negative electrode having an orientation value of the negative electrode active material layer less than or equal to 3 is obtained; and the binding force between the negative electrode current collector and the negative electrode active material layer is greater than or equal to 0.25N / 40mm.

[0009] In a third aspect, the present application discloses a battery, comprising the negative electrode described in the first aspect or the negative electrode prepared by the preparation method described in the second aspect, and a positive electrode.

[0010] In a fourth aspect, the present application discloses an electrical device comprising the battery described in the third aspect.

[0011] In combination with the above technical solutions, the graphite in the negative electrode active material layer provided by the present application has a low orientation degree, which is beneficial to improving the ion and electron transmission capacity of the negative electrode. At the same time, the bonding force between the negative electrode current collector and the negative electrode active material layer is good, which is beneficial to improving the stability and reliability of the negative electrode structure with low orientation degree to adapt to the influence of rapid lithium deintercalation on the negative electrode; the preparation method of the negative electrode is simple and easy to operate, and industrial production can be realized; the battery with the negative electrode has excellent charge and discharge rate, cycle capacity retention rate and service life, which is beneficial to its use in electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG1 is a schematic cross-sectional view of a negative electrode provided in one embodiment of the present application;

[0013] FIG2 is a flow chart of a method for preparing a negative electrode according to an embodiment of the present application;

[0014] FIG3 is a schematic diagram of a negative electrode current collector and a magnetic field according to an embodiment of the present application;

[0015] FIG4 is a schematic diagram of a negative electrode current collector and a magnetic field according to an embodiment of the present application;

[0016] FIG5 is a schematic diagram of a negative electrode current collector and a magnetic field according to an embodiment of the present application;

[0017] FIG6 is an electron microscope cross-sectional view of a negative electrode prepared in one embodiment of the present application;

[0018] FIG7 is an electron microscope cross-sectional view of a negative electrode prepared in a ratio according to the present application. DETAILED DESCRIPTION

[0019] In the embodiments of this application, the term "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0020] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] Please refer to FIG1 , which is a schematic cross-sectional view of a negative electrode provided in one embodiment of the present application. The negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the surface of the negative electrode current collector 11. The negative electrode active material layer 12 includes graphite. The orientation value of the negative electrode active material layer 12 is less than or equal to 3, and the bonding force between the negative electrode current collector 11 and the negative electrode active material layer 12 is greater than or equal to 0.25 N / 40 mm. It can be understood that the orientation value (OI value) of the negative electrode active material layer 12 is used to represent the orientation index of the graphite in the negative electrode active material layer 12, that is, the degree of anisotropy of the graphite arrangement in the negative electrode active material layer 12. The OI value is the ratio of the peak area of ​​the (004) characteristic diffraction peak to the peak area of ​​the (110) characteristic diffraction peak in the X-ray diffraction (XRD) spectrum of the negative electrode.

[0022] In the battery negative electrode manufacturing process, coating, rolling and other processes will cause the material with a layered structure (for example, graphite) to have a preferential orientation, that is, the material with a layered structure is preferentially arranged in a direction parallel to the current collector. The graphite is arranged approximately parallel to the direction of the negative electrode current collector, which hinders the transmission of ions and electrons, making it impossible to improve the charge and discharge rate of the battery. The orientation degree of the graphite in the negative electrode active material layer 12 of the present application is low, which is conducive to the transmission of ions and electrons and improves the migration rate of ions and electrons; and the expansion caused by ion embedding can be evenly dispersed in the negative electrode active material layer 12, which is beneficial to the negative electrode rate performance and cycle performance. At the same time, the bonding force between the negative electrode current collector and the negative electrode active material layer 12 is relatively high (greater than or equal to 0.25N / 40mm), which is beneficial to improving the stability of the internal structure of the negative electrode to adapt to the influence of rapid lithium deintercalation on the negative electrode, thereby facilitating the use of the negative electrode in the battery and improving the battery's charge and discharge rate and high-rate cycle capacity retention rate.

[0023] In the present application, graphite is used as the negative electrode active material in the negative electrode to ensure the performance of the negative electrode.

[0024] In one embodiment of the present application, the particle size D50 of the graphite is 1μm-30μm, so that the ion migration path is suitable, which is beneficial to improving the ion transmission capacity in the negative electrode; it is also beneficial to increase the compaction density of the negative electrode while reducing the side reactions between the electrolyte during use, thereby further improving the performance of the negative electrode and the battery. Specifically, the particle size D50 of the graphite can be, but is not limited to, 1μm, 5μm, 9μm, 10μm, 13μm, 15μm, 17μm, 20μm, 23μm, 25μm, 28μm or 30μm, etc. In one embodiment of the present application, the particle size D50 of the graphite can be 5μm-25μm. In another embodiment of the present application, the particle size D50 of the graphite can be 7μm-22μm. In another embodiment of the present application, the particle size D50 of the graphite can be 8μm-20μm, which is beneficial to further improve the electrochemical performance and performance of the negative electrode. In another embodiment of the present application, the graphite particle size D50 can be 9μm-15μm. Controlling the graphite particle size D50 within an appropriate range is beneficial for balancing the orientation of the graphite in the negative electrode active material layer 12 and the binding force between the negative electrode current collector 11 and the negative electrode active material layer 12. A smaller particle size D50 indicates an appropriate orientation of the graphite in the negative electrode active material layer 12, but a relatively weak binding force; a larger particle size D50 indicates an appropriate binding force between the negative electrode current collector 11 and the negative electrode active material layer 12, but a poor orientation of the graphite in the negative electrode active material layer 12. Particle size D50 refers to the median particle size of the graphite particles, also known as the volume average particle size, representing the particle size corresponding to a material's cumulative volume distribution percentage of 50%. The graphite particle size D50 can be measured using a laser force tester. Graphite includes at least one of artificial graphite and natural graphite.

[0025] In the present application, graphite is used as the negative electrode active material in the negative electrode active material layer. It can be understood that the negative electrode active material in the negative electrode can be only graphite, or can include graphite and other negative electrode active materials. Specifically, other negative electrode active materials can include but are not limited to at least one of silicon-based materials, intermediate phase microcarbon beads, hard carbon and soft carbon. In one embodiment of the present application, the mass content of graphite in the negative electrode active material layer is greater than or equal to 80% of the total mass content of the negative electrode active material layer, thereby ensuring the orientation of the negative electrode active material in the negative electrode active material layer, further improving the ion and electron transmission capacity, and improving the rate and cycle performance of the negative electrode. Specifically, the mass content of graphite in the negative electrode active material layer may be, but is not limited to, 80%, 82%, 85%, 88%, 90%, 91%, 95%, 96%, 96.2%, 96.5%, 96.8%, 97%, 97.3%, 97.5%, 97.9%, 98%, 98.3%, 98.5%, 98.6%, 99%, 99.1%, 99.5%, or 99.8%. In one embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 80%-99.9%. In another embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 96%-98%. In yet another embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 96.5%-99%. In yet another embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 97%-99%. In another embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 80%-96%. In another embodiment of the present application, the mass content of graphite in the negative electrode active material layer may be 85%-93%. In another embodiment of the present application, when the negative electrode active material in the negative electrode active material layer includes graphite and other negative electrode active materials, the mass content of graphite in the negative electrode active material layer may be greater than or equal to 50%, which helps to improve the migration rate of ions and electrons in the negative electrode active material layer.

[0026] In the present application, the orientation value of the negative electrode active material layer 12 is less than or equal to 3, thereby aligning the graphite in the negative electrode active material layer to facilitate ion and electron transport, thereby improving the rate performance of the negative electrode. In one embodiment of the present application, the orientation value of the negative electrode active material layer 12 is between 0.06 and 3. This not only ensures the ion and electron transport capabilities during use of the negative electrode, thereby increasing the rate performance and cycle performance of the negative electrode, but also reduces the difficulty and cost of manufacturing the negative electrode, thereby facilitating its commercial application. It is understood that when the orientation value of the negative electrode active material layer 12 is too small, on the one hand, the energy consumption of inducing graphite orientation in the negative electrode active material layer 12 is high, increasing manufacturing costs; on the other hand, during battery charge and discharge, the graphite in the active material layer 12 has too low an orientation value, resulting in a significant expansion direction of the graphite, causing cracking in the negative electrode active material layer 12 and affecting the battery's cycle life. When the orientation value of the negative electrode active material layer 12 is too large, the ion and electron transport capabilities are reduced, which is detrimental to the rate performance of the negative electrode. Therefore, the orientation value of the negative electrode active material layer 12 should be within an appropriate range. Specifically, the orientation value of the negative electrode active material layer 12 may be, but is not limited to, 0.06, 0.09, 0.1, 0.2, 0.5, 0.8, 1, 1.33, 1.5, 1.7, 2, 2.4, 2.5 or 2.8, etc. In one embodiment of the present application, the orientation value of the negative electrode active material layer 12 may be 0.06-2.5. In another embodiment of the present application, the orientation value of the negative electrode active material layer 12 may be 0.09-2.5. In yet another embodiment of the present application, the orientation value of the negative electrode active material layer 12 may be 0.09-1.33, thereby further improving the ion and electron transfer rate of the negative electrode and improving the performance of the negative electrode. In yet another embodiment of the present application, the orientation value of the negative electrode active material layer 12 may be 0.1-2.5.

[0027] In one embodiment of the present application, the graphitization degree of graphite is greater than or equal to 60%, so that there are fewer defects in the graphite crystal and the graphite is more stable, which is beneficial to improving the specific capacity and ion deintercalation ability of graphite, thereby helping to improve the negative electrode and battery cycle performance and energy density. Specifically, the graphitization degree of graphite can be, but is not limited to, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, etc. The graphitization degree of graphite can be measured using X-ray diffraction (XRD). The XRD spectrum of the negative electrode is obtained, and the interlayer spacing d of the graphite (002) in the negative electrode is calculated based on the spectrum. 002 , and then substitute it into the Mering–Maire formula (also known as the Franklin formula) to calculate: G = (0.3440–d 002) / (0.3440–0.3354)×100%. Where G is the degree of graphitization (%); 0.3440 is the interlayer spacing of non-graphitized carbon (nm); 0.3354 is the interlayer spacing of ideal graphite crystal (nm), which is also 1 / 2 of the c-axis lattice constant of hexagonal graphite; d 002 is the interlayer spacing of the (002) crystal plane of graphite material (nm).

[0028] In one embodiment of the present application, the negative electrode active material layer further includes a conductive agent. The addition of the conductive agent to the negative electrode active material layer can improve the conductivity of the negative electrode, reduce the resistivity, accelerate the mobility of electrons, increase the migration rate of ions, and improve the charge and discharge efficiency and output power of the battery.

[0029] In one embodiment of the present application, the mass content of the conductive agent in the negative electrode active material layer accounts for 0.1%-6.7% of the total mass content of the negative electrode active material layer, which can not only reduce the resistivity of the negative electrode, but also ensure the liquid absorption capacity of the negative electrode active material layer, thereby improving the rate performance of the negative electrode and the battery. Specifically, the mass content of the conductive agent in the negative electrode active material layer can be, but is not limited to, 0.1%, 0.5%, 0.7%, 1%, 1.1%, 1.4%, 1.5%, 1.7%, 2.2%, 2.5%, 2.6%, 3%, 3.3%, 3.7%, 4%, 4.2%, 4.5%, 5%, 5.5%, 5.8%, 6%, 6.3%, 6.5% or 6.7%, etc. In one embodiment of the present application, the mass content of the conductive agent in the negative electrode active material layer can be 0.1%-2%. In another embodiment of the present application, the mass content of the conductive agent in the negative electrode active material layer can be 1%-3%. In another embodiment of the present application, the mass content of the conductive agent in the negative electrode active material layer may be 1%-3.5%. In another embodiment of the present application, the mass content of the conductive agent in the negative electrode active material layer may be 4%-6.5%. In the present application, the conductive agent may be selected from materials that can be used in the art to perform a conductive role in the negative electrode. Specifically, the conductive agent may include, but is not limited to, at least one of acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, carbon nanofibers, and the like.

[0030] In one embodiment of the present application, the negative electrode active material layer is made of graphite and a conductive agent. In another embodiment of the present application, the negative electrode active material layer includes graphite, a conductive agent, and an additive. Adding an additive further enhances the performance of the negative electrode. In one embodiment of the present application, the additive includes at least one of a binder and a dispersant. Adding a binder can improve the bonding strength within the negative electrode active material layer and between the negative electrode active material layer and the negative electrode current collector, thereby improving the structural stability of the negative electrode. Adding a dispersant can improve the uniformity of the dispersion of graphite and the conductive agent in the negative electrode active material layer, thereby improving the performance of the negative electrode. In one embodiment, the weight content of the binder in the negative electrode active material layer is less than or equal to 2.5%. Specifically, the weight content of the binder in the negative electrode active material layer can be, but is not limited to, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.4%, 1.5%, 1.7%, 2%, 2.1%, or 2.5%. In a specific embodiment, the weight content of the binder in the negative electrode active material layer may be 0.05%-2.5%. In the present application, the binder may include, but is not limited to, at least one of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene latex, and nitrile rubber. In one embodiment, the weight content of the dispersant in the negative electrode active material layer is less than or equal to 2.5%. Specifically, the weight content of the dispersant in the negative electrode active material layer may be, but is not limited to, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.4%, 1.5%, 1.7%, 2%, 2.1%, or 2.5%. In a specific embodiment, the weight content of the dispersant in the negative electrode active material layer may be 0.05%-2.5%. In the present application, the dispersant may include, but is not limited to, at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, and nanocellulose.

[0031] In one embodiment of the present application, in the negative electrode active material layer, the distribution density of the conductive agent on the side away from the negative electrode current collector is less than the distribution density of the conductive agent on the side close to the negative electrode current collector. The distribution density of the conductive agent refers to the amount of conductive agent per unit area. In this way, the conductivity of the negative electrode active material layer close to the negative electrode current collector is better, further improving the rate performance of the negative electrode. At the same time, the higher distribution density of the conductive agent on the negative electrode current collector side is beneficial to increase the bonding strength between the negative electrode active material layer and the negative electrode current collector, thereby increasing the cycle life of the battery. The distribution density of the conductive agent can be tested by SEM. For example, the negative electrode is subjected to a cross section polisher and CP (argon ion beam cutting and polishing of the negative electrode sheet, with the cutting direction being perpendicular to the negative electrode current collector) to obtain a cross section of the electrode sheet. The electrode sheet interface is scanned separately to obtain the distribution density of the conductive agent, and the distribution density trend of the conductive agent on the side away from the negative electrode current collector and the conductive agent on the side close to the negative electrode current collector can be further statistically analyzed.

[0032] In one embodiment of the present application, the distribution density of the conductive agent gradually increases along the direction from the negative electrode active material layer to the negative electrode current collector. In this way, the migration rate of ions and electrons in the negative electrode is uniformly improved, and the binding force between the negative electrode active material layer 12 and the negative electrode current collector, as well as between the negative electrode active materials in the negative electrode active material layer 12, is more stable, which is beneficial to improving the stability of the battery. Exemplarily, the direction from the negative electrode active material layer to the negative electrode current collector is the direction indicated by the arrow in Figure 1. In one embodiment of the present application, the negative electrode current collector is made of metal. The metal material includes at least one of copper, nickel, iron, cobalt and stainless steel. In a specific embodiment, the negative electrode current collector is copper foil.

[0033] In this application, the bonding force between the negative electrode current collector and the negative electrode active material layer is greater than or equal to 0.25N / 40mm, so that the negative electrode has better stability.

[0034] In one embodiment of the present application, the bonding force between the negative electrode current collector and the negative electrode active material layer is 0.25N / 40mm-2.8N / 40mm, which improves the internal stability and reliability of the negative electrode, helps improve the negative electrode's cycle performance, and also has higher rate performance. It is understandable that when the orientation value of the negative electrode active material layer 12 decreases (i.e., within the scope of this application), the state of the graphite in the negative electrode active material layer 12 changes from the arrangement parallel to the current collector in the prior art to the arrangement perpendicular to the negative electrode current collector. At this time, the contact area between the graphite in the negative electrode active material layer 11 and the current collector is reduced, and the bonding force is weakened, which is not conducive to the battery's cycle performance. When the bonding force between the negative electrode current collector and the negative electrode active material layer is too high, the amount of binder required to be added to the negative electrode increases, and the battery's rate performance will be affected. Therefore, when the bonding force between the negative electrode current collector and the negative electrode active material layer is 0.25N / 40mm-2.8N / 40mm, it is beneficial to improve the negative electrode's cycle performance and have higher rate performance. Specifically, the binding force between the negative electrode current collector and the negative electrode active material layer may be, but is not limited to, 0.25 N / 40 mm, 0.3 N / 40 mm, 0.5 N / 40 mm, 0.8 N / 40 mm, 1 N / 40 mm, 1.2 N / 40 mm, 1.4 N / 40 mm, 1.5 N / 40 mm, 1.6 N / 40 mm, 1.7 N / 40 mm, 1.8 N / 40 mm, 1.9 N / 40 mm, 2 N / 40 mm, 2.1 N / 40 mm, 2.2 N / 40 mm, 2.3 N / 40 mm, 2.4 N / 40 mm, 2.5 N / 40 mm, 2.6 N / 40 mm, 2.7 N / 40 mm or 2.8 N / 40 mm, etc. In one embodiment of the present application, the binding force between the negative electrode current collector and the negative electrode active material layer is 0.25N / 40mm-2.2N / 40mm, the binding force between the negative electrode current collector and the negative electrode active material layer is high and the preparation is convenient. In another embodiment of the present application, the binding force between the negative electrode current collector and the negative electrode active material layer is 0.3N / 40mm-2.2N / 40mm. In yet another embodiment of the present application, the binding force between the negative electrode current collector and the negative electrode active material layer is 0.8N / 40mm-1.3N / 40mm. In yet another embodiment of the present application, the binding force between the negative electrode current collector and the negative electrode active material layer is 0.25N / 40mm-1.8N / 40mm. In yet another embodiment of the present application, the binding force between the negative electrode current collector and the negative electrode active material layer is 1N / 40mm-2.5N / 40mm.

[0035] In one embodiment of the present application, the resistivity of the negative electrode is 0.1Ω·cm-2Ω·cm. The orientation value of the negative electrode active material layer 12 in the present application is relatively low, which can form a directional and orderly transmission channel, which is beneficial to the transmission of ions and electrons, and reduces the ion transfer impedance, reduces the resistivity of the negative electrode, is more conducive to fast charging and discharging of the battery, and improves the performance of the battery. Specifically, the resistivity of the negative electrode can be, but is not limited to, 0.1Ω·cm, 0.5Ω·cm, 0.9Ω·cm, 1Ω·cm, 1.2Ω·cm, 1.5Ω·cm, 1.8Ω·cm or 2Ω·cm, etc. In one embodiment of the present application, the resistivity of the negative electrode can be 0.1Ω·cm-1.8Ω·cm. In another embodiment of the present application, the resistivity of the negative electrode can be 0.1Ω·cm-1.5Ω·cm.

[0036] In the present application, the thickness of the negative electrode current collector and the negative electrode active material layer can be selected as needed and is not limited thereto.

[0037] The present application also provides a method for preparing a negative electrode. Please refer to Figure 2, which is a flow chart of the method for preparing a negative electrode provided in one embodiment of the present application, including:

[0038] S101: providing a negative electrode current collector, coating a negative electrode slurry containing graphite on at least one surface of the negative electrode current collector, and adjusting the orientation of the graphite in the negative electrode slurry using a magnetic field.

[0039] S102: After drying, a negative electrode is obtained in which the orientation value of the negative electrode active material layer is less than or equal to 3, and the bonding force between the negative electrode current collector and the negative electrode active material layer is greater than or equal to 0.25 N / 40 mm.

[0040] In the preparation method of the negative electrode provided in the present application, the orientation of the graphite in the negative electrode slurry is changed under the action of a magnetic field, the orientation of the graphite in the negative electrode active material layer is improved, and a reasonable and orderly arrangement of the graphite in the negative electrode active material layer is achieved, thereby creating a path that makes it easier for ions and electrons to be transported, and improving the migration rate of ions and electrons. This can improve the transmission obstruction and negative electrode performance degradation caused by the natural parallel arrangement of graphite in the negative electrode active material layer. At the same time, while ensuring that the bonding force between the negative electrode active material layer and the negative electrode current collector is greater than or equal to 0.25N / 40mm, the migration rate of ions and electrons is improved, which is beneficial for use in batteries and improves the battery's charge and discharge rate, cycle capacity retention rate, and service life.

[0041] In one embodiment of the present application, the negative electrode current collector includes a first surface and a second surface disposed opposite to each other, and a magnetic field is provided on one side of the first surface and / or the second surface, and the angle between the magnetic moment direction of the magnetic field and the negative electrode current collector is 10°-90°. In the present application, by controlling the angle between the magnetic moment direction of the magnetic field and the surface of the negative electrode current collector to be 10°-90° (e.g., 20°, 30°, 40°, 50°, 60°, 70°, 75°, 80°, or 90°, etc.), after the negative electrode slurry is coated on the negative electrode current collector, the graphite in the negative electrode slurry can be oriented under the action of the magnetic field, achieving directional induction, and obtaining a negative electrode active material layer that facilitates ion transport and electron transport.

[0042] In this application, the magnetic field may be, but is not limited to, generated by a magnetic field device. The magnetic field device may be, but is not limited to, an electromagnet, a permanent magnet, or the like, and may be selected as needed. In one embodiment of this application, the magnetic field device may be disposed on a side of the first surface facing away from the second surface, and spaced apart from the first surface; and / or the magnetic field device may be disposed on a side of the second surface facing away from the first surface, and spaced apart from the second surface.

[0043] Please refer to Figure 3, which is a schematic diagram of the negative electrode current collector and the magnetic field provided in one embodiment of the present application. The negative electrode current collector 10 includes a first surface 111 and a second surface arranged opposite each other. The arrow indicates the direction of the magnetic moment of the magnetic field. The magnetic field can be generated by a magnetic field device 20. The angle between the magnetic moment direction of the magnetic field and the first surface is θ1. In one embodiment of the present application, the angle between the magnetic moment direction of the magnetic field and the first surface is 30°-90°, which is conducive to further optimizing the arrangement of graphite and improving the performance of the negative electrode. In another embodiment of the present application, the angle between the magnetic moment direction of the magnetic field and the first surface is 40°-80°. In yet another embodiment of the present application, the angle between the magnetic moment direction of the magnetic field and the first surface is 60°-90°, which can further cause the graphite in the negative electrode active material layer to tend to be perpendicular to the negative electrode current collector, reduce the tortuosity of the negative electrode, optimize the ion transmission path in the thickness direction of the negative electrode, and further improve the rate performance of the negative electrode.

[0044] In one embodiment of the present application, the magnetic field performs at least one of reciprocating motion and rotational motion. That is, under the premise of maintaining the angle between the magnetic moment direction of the magnetic field and the first surface at 10 ° -90 °, the magnetic field can perform reciprocating motion and / or rotational motion, thereby further optimizing the arrangement of graphite, improving the rate performance of the negative electrode, and increasing the cycle performance. The magnetic field can perform reciprocating motion, rotational motion, and reciprocating motion and rotational motion at the same time. In one embodiment of the present application, the angle between the direction of reciprocating motion and the extension direction of the negative electrode current collector is 0 ° -90 ° (such as 10 °, 20 °, 30 °, 40 °, 45 °, 50 °, 60 °, 70 °, 80 ° or 90 °, etc.). It can be understood that the extension direction of the negative electrode current collector is the length direction of the negative electrode current collector. By adopting reciprocating motion, the arrangement angle of graphite can be improved, the diffusion path of ions in the direction parallel to the negative electrode current collector and the diffusion path in the electron transport direction are further optimized, and the performance of the negative electrode is improved.

[0045] Please refer to Figure 4, which is a schematic diagram of a negative electrode current collector and a magnetic field according to another embodiment of the present application. The magnetic field can be generated by a magnetic field device 20, which reciprocates in the direction indicated by arrow a. The direction indicated by arrow a is parallel to the first surface, and the direction indicated by arrow b is the extension direction of the negative electrode current collector. The angle between the reciprocating motion and the extension direction of the negative electrode current collector is θ2. In one embodiment of the present application, the angle between the reciprocating motion and the extension direction of the negative electrode current collector is 10°-80°. In another embodiment of the present application, the angle between the reciprocating motion and the extension direction of the negative electrode current collector is 30°-90°. In yet another embodiment of the present application, the angle between the reciprocating motion and the extension direction of the negative electrode current collector is 40°-90°. In yet another embodiment of the present application, the angle between the reciprocating motion and the extension direction of the negative electrode current collector is 50°-90°.

[0046] In the present application, the uniformity of graphite distribution can be improved by rotational motion; rotational motion is rotation along the axis. In a specific embodiment, the magnetic field device generates a magnetic field, and the magnetic field device can rotate along the central axis of the magnetic field device, so that the magnetic field generates a rotational motion. Of course, in other embodiments, the magnetic field device can rotate along other axial directions. Please refer to Figure 5, which is a schematic diagram of the negative electrode current collector and the magnetic field provided in another embodiment of the present application. The magnetic field can be generated by the magnetic field device 20, and the magnetic field device rotates along the central axis c of the magnetic field device. In one embodiment of the present application, the rotation speed of the magnetic field device can be 10r / min (round / min)-60r / min. Specifically, the rotation speed of the magnetic field device can be, but is not limited to, 15r / min, 20r / min, 25r / min, 30r / min, 35r / min, 40r / min, 45r / min or 50r / min, etc.

[0047] In one embodiment of the present application, the strength of the magnetic field is 0.1T-2T, which can not only produce a directional induction effect on graphite, improve the orientation of graphite in the negative electrode active material layer, but also reduce the difficulty of preparation, and will not affect the negative electrode current collector, so as to obtain a negative electrode with excellent performance. Specifically, the strength of the magnetic field can be, but is not limited to, 0.1T, 0.2T, 0.3T, 0.5T, 0.8T, 0.9T, 1T, 1.2T, 1.5T, 1.7T or 2T, etc. In one embodiment, the strength of the magnetic field can be 0.2T-2T. In another embodiment, the strength of the magnetic field can be 0.5T-2T. In yet another embodiment, the strength of the magnetic field can be 0.2T-1T. In yet another embodiment, the strength of the magnetic field can be 0.8T-2T, which is conducive to further improving the performance of the negative electrode.

[0048] In this application, the graphite in the negative electrode slurry is oriented and moved under the influence of a magnetic field, thereby producing a high-performance negative electrode. In one embodiment of this application, the graphite particle size D50 can be 1μm-30μm, which facilitates the transport of ions and electrons and reduces side reactions with the electrolyte. In one embodiment of this application, the graphite has a degree of graphitization greater than or equal to 60%, which is beneficial for improving the negative electrode and battery cycle performance and energy density.

[0049] In one embodiment of the present application, to improve the conductivity of the negative electrode, the negative electrode slurry preferably also includes a conductive agent. In another embodiment of the present application, the negative electrode slurry may include an additive to further enhance the structural stability of the negative electrode active material layer. In one embodiment of the present application, the additive includes at least one of a binder and a dispersant. In one embodiment, the binder content in the negative electrode slurry may be less than or equal to 2%. Specifically, the binder content in the negative electrode slurry may be, but is not limited to, 0.1%, 0.5%, 0.9%, 1%, 1.5%, 1.8%, or 2%. For example, the binder content in the negative electrode slurry may be between 0.5% and 2%. In one embodiment, the dispersant content in the negative electrode slurry may be less than or equal to 2%. Specifically, the dispersant content in the negative electrode slurry may be, but is not limited to, 0.1%, 0.5%, 0.9%, 1%, 1.5%, 1.8%, or 2%. For example, the dispersant content in the negative electrode slurry may be between 0.5% and 2%. In another embodiment of the present application, the negative electrode slurry may include a solvent to adjust the viscosity of the negative electrode slurry, which is beneficial for coating the negative electrode slurry and orienting the graphite in the negative electrode slurry. Specifically, the solvent may be, but is not limited to, at least one of water, ethanol, toluene, xylene, anisole, acetonitrile, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, N-methylpyrrolidone, and acetone.

[0050] In one embodiment of the present application, the viscosity of the negative electrode slurry is 1500mPa·s-5000mPa·s. This suitable viscosity of the negative electrode slurry is conducive to the uniform dispersion of graphite and the conductive agent, and is also conducive to the coating of the negative electrode slurry and the reasonable orientation of the graphite in the negative electrode slurry. Specifically, the viscosity of the negative electrode slurry can be, but is not limited to, 1500mPa·s, 2000mPa·s, 2500mPa·s, 3000mPa·s, 3500mPa·s, 4000mPa·s, 4500mPa·s, 5000mPa·s, etc.

[0051] In one embodiment of the present application, the negative electrode active material is coated on the surface of the negative electrode current collector at 10°C-40°C (such as 20°C, 25°C, 30°C, 35°C or 40°C, etc.), which is beneficial to the leveling and stable purity of the negative electrode slurry, and is also beneficial to the induction of the magnetic field on graphite, promoting the reasonable orientation of graphite.

[0052] In one embodiment of the present application, the magnetic field acts on the negative electrode slurry for a time of 1 minute to 30 minutes, thereby obtaining excellently oriented graphite and a negative electrode with excellent performance. Specifically, the time the negative electrode slurry is in the magnetic field can be, but is not limited to, 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes. It is understood that when the negative electrode slurry is subjected to the magnetic field, it will also be affected by the positive charge on the negative electrode current collector, that is, the time the charge acts on the negative electrode slurry is 1 minute to 30 minutes. In one embodiment of the present application, the magnetic field acts on the negative electrode slurry for a time of 1 minute to 10 minutes. In another embodiment of the present application, the magnetic field acts on the negative electrode slurry for a time of 5 minutes to 20 minutes. In one embodiment of the present application, the temperature of the negative electrode slurry in the magnetic field is 40°C to 60°C (such as 40°C, 45°C, 50°C, 55°C, 60°C, etc.), thereby producing a pre-drying effect, which is conducive to the adhesion of the negative electrode slurry to the surface of the negative electrode current collector and the fixation of the graphite after orientation induction. That is to say, the negative electrode slurry is pre-dried, and the pre-drying temperature is 40°C-60°C, and the time is 1min-30min.

[0053] In the present application, the magnetic field can be applied after the negative electrode slurry is set on the surface of the negative electrode current collector, or the magnetic field can be set on one side of the negative electrode current collector before the negative electrode slurry is set. In one embodiment of the present application, the negative electrode current collector can be placed in a conveying device, and the negative electrode current collector can move with the movement of the conveying device. During the movement, the negative electrode slurry is set on the surface of the negative electrode current collector, and at the same time, the magnetic field is set on one side of the negative electrode current collector. In the present application, the magnetic field can be set on one side of the first surface or the second surface. In one embodiment of the present application, the magnetic field can be set on one side of the second surface, so as to avoid affecting the negative electrode slurry. For example, when a magnetic field device is used to generate a magnetic field, the magnetic field device is set on one side of the second surface to avoid contact with the negative electrode slurry, which is more conducive to the setting of the negative electrode slurry.

[0054] In one embodiment of the present application, the drying temperature is 40°C-200°C, and the time is 2min-60min. In one embodiment of the present application, the drying includes pre-drying and final baking, which is beneficial to the bonding of the negative electrode current collector and the negative electrode active material layer. In one embodiment of the present application, the pre-drying temperature is lower than the final baking temperature, which is beneficial to controlling the evaporation rate and evaporation amount of the solvent in the negative electrode slurry after magnetic induction, increasing the bonding force between the negative electrode active material layer and the current collector, and between the negative electrode active materials in the negative electrode active material layer, and ensuring the structural stability of the negative electrode. In one embodiment of the present application, the final baking temperature is 60°C-200°C, and the time is 1min-30min, so that the graphite can maintain the orientation after induction, and is also beneficial to the bonding of the negative electrode current collector and the negative electrode active material layer, thereby improving the performance of the negative electrode. Specifically, the final baking temperature may be, but is not limited to, 10°C, 50°C, 70°C, 100°C, 130°C, 150°C, 180°C, or 200°C, and the final baking time may be, but is not limited to, 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes. In one embodiment, the final baking temperature is 60°C-180°C, and the time is 5 minutes-25 minutes. In another embodiment, the final baking temperature is 140°C-180°C, and the time is 5 minutes-15 minutes.

[0055] In one embodiment of the present application, after drying, roller pressing is further included. By roller pressing, the thickness of the negative electrode is controlled, the compaction density and the bonding force are improved, and it is also beneficial to further improve the orderliness of the graphite arrangement. In one embodiment of the present application, the pressure of the roller pressing is 2t (ton)-35t, and the roller speed is 0.5m / s-2m / s. Specifically, the pressure of the roller pressing can be, but is not limited to, 2t, 5t, 9t, 10t, 12t, 15t, 20t, 25t, 30t or 35t, and the roller speed can be, but is not limited to, 0.5m / s, 1m / s, 1.5m / s, 1.8m / s or 2m / s, etc.

[0056] In one embodiment of the present application, the negative electrode slurry further comprises a conductive agent. Before the negative electrode slurry is dried on the negative electrode current collector, the negative electrode current collector is positively charged so that the distribution density of the conductive agent on the side away from the negative electrode current collector is less than the distribution density of the conductive agent on the side closer to the negative electrode current collector. In this embodiment, a magnetic field and an electric field are used together. The magnetic field alters the orientation of graphite in the negative electrode slurry to be parallel or approximately parallel to the negative electrode current collector, thereby increasing the angle between the graphite and the negative electrode current collector. This increases the tendency of the graphite to be perpendicular to the current collector, improves the orientation of the graphite, and achieves a rational and orderly stacking of the graphite, creating a path that facilitates ion and electron transport and improves the migration rate of ions and electrons. An electric field is applied to the negative electrode current collector to impart a positive charge to the negative electrode current collector. Under the action of this electric field, the conductive agent is attracted to move toward one side of the negative electrode current collector, thereby improving the conductivity of the negative electrode active material layer near the negative electrode current collector, thereby reducing the resistivity of the negative electrode. Under the action of the charge, the graphite also moves toward the current collector, thereby improving the density of the graphite arrangement, optimizing the liquid phase transmission pores, and increasing the liquid storage capacity of the negative electrode active material layer, thereby ensuring the cycle life and rate performance of the battery. Under the action of the magnetic field and electric field, the conductive agent and graphite are in closer contact near the negative electrode current collector, and the contact surface between the conductive agent and the graphite and the negative electrode current collector is larger. This increases the bonding strength between the negative electrode active material layer and the negative electrode current collector, improving the bonding reliability, which is beneficial for use in the battery and improves the battery's rate performance and rate performance.

[0057] In the present application, there is no limitation on the method of applying an electric field to the negative electrode current collector, as long as the negative electrode current collector can be positively charged. It is understandable that the conductive agents commonly used in the art have small particle sizes and large relative areas. When dispersed in the negative electrode slurry, they usually have a small amount of negative charge. Therefore, when the current collector is positively charged, the conductive agent will sink due to electrostatic attraction, thereby increasing the distribution density of the conductive agent on the current collector side. In one embodiment of the present application, the negative electrode current collector can be connected to the positive pole of a power supply to make it positively charged. In another embodiment of the present application, the negative electrode current collector is connected to a DC electric field to make the negative electrode current collector positively charged. In one embodiment of the present application, a rolling conductive device can be used to connect to the negative electrode current collector to make the negative electrode current collector positively charged. In a specific embodiment, the rolling conductive device has two rollers that clamp the negative electrode current collector in the thickness direction of the negative electrode current collector. The rollers apply a voltage to the negative electrode current collector to make the negative electrode current collector positively charged.

[0058] In the present application, an electric field is applied to the negative electrode current collector to make the negative electrode current collector positively charged. The conductive agent and / or graphite surface can be modified to be negatively charged, and then the conductive agent and / or graphite move to one side of the current collector under the action of electrostatic attraction.

[0059] In one embodiment of the present application, an electric field is applied to the negative electrode current collector to make the negative electrode current collector negatively charged. The conductive agent and / or graphite surface can be modified to be positively charged, and then the conductive agent and / or graphite move to one side of the current collector under the action of electrostatic attraction.

[0060] In one embodiment of the present application, the voltage of the negative electrode current collector is 0.1V-120V. This can not only make the conductive agent move toward the negative electrode current collector, but also ensure the distribution of the conductive agent in the negative electrode active material layer on the side away from the negative electrode current collector, and it is also beneficial to enhance the dense arrangement of graphite, improve the compaction density and rate performance of the negative electrode. Specifically, the voltage of the negative electrode current collector can be, but is not limited to, 0.1V, 1V, 5V, 10V, 15V, 20V, 25V, 30V, 50V, 75V, 90V, 100V, 110V, 115V, etc. In one embodiment of the present application, the voltage of the negative electrode current collector is 5V-35V, which further reduces the difficulty of preparation and ensures preparation safety. At the same time, it is beneficial to further optimize the distribution of graphite and conductive agent in the negative electrode active material layer, further improving the electrochemical performance of the negative electrode. In another embodiment of the present application, the voltage of the negative electrode current collector is 10V-50V. In another embodiment of the present application, the voltage of the negative electrode current collector is 10 V to 80 V. In one embodiment, the negative electrode current collector is connected to a DC electric field and maintains a voltage of 0.1 V to 120 V. In the present application, during the preparation process of the negative electrode, the voltage of the negative electrode current collector remains stable, which is more conducive to improving the performance of the negative electrode.

[0061] In the present application, the negative electrode current collector may be positively charged in any step before the negative electrode slurry on the negative electrode current collector is dried. For example, the negative electrode slurry may be applied to the surface of the negative electrode current collector before an electric field is applied and the negative electrode current collector is positively charged. Alternatively, the negative electrode slurry may be applied after an electric field is applied to one side of the negative electrode current collector and the negative electrode current collector is positively charged.

[0062] In one embodiment of the present application, the negative electrode current collector can be placed in a conveying device, and the negative electrode current collector can move with the movement of the conveying device. During the movement, the negative electrode slurry is set on the surface of the negative electrode current collector. At the same time, the negative electrode current collector is connected to the power supply with a positive charge, and the magnetic field is set on one side of the negative electrode current collector.

[0063] Under the same preparation conditions, compared with the negative electrode prepared without applying a magnetic field or without applying a magnetic field and an electric field, the resistivity of the negative electrode prepared by applying a magnetic field and / or an electric field in the present application is reduced by 5%-60% compared with the ordinary pole piece without applying a magnetic field, which greatly improves the rate performance of the negative electrode and the battery. The preparation method provided by the present application is simple to operate, has controllable process conditions, and low energy consumption. It can effectively improve the ion and electron diffusion capacity, binding force, resistivity, etc. of the negative electrode to obtain a negative electrode with excellent performance. This will thereby improve the charge and discharge rate of the battery and the high-rate cycle capacity retention rate, especially conducive to the electrochemical performance of batteries with high surface density and high compaction density, breaking through the charge and discharge rate and capacity bottlenecks of traditional batteries.

[0064] In the present application, the above ions may include, but are not limited to, one of lithium ions, sodium ions, potassium ions, magnesium ions and aluminum ions.

[0065] The present application also provides a battery comprising a negative electrode according to any of the above embodiments and a positive electrode. The battery having the negative electrode has excellent charge and discharge rates, cycle capacity retention, and service life, which facilitates its use in electrical devices. The battery may be, but is not limited to, a power battery (such as a lithium-ion power battery), an energy storage battery, or the like.

[0066] In one embodiment of the present application, the battery further comprises an electrolyte. In one embodiment of the present application, at least a portion of the positive electrode is immersed in the electrolyte, and at least a portion of the negative electrode is immersed in the electrolyte, thereby ensuring normal operation of the battery. In one embodiment of the present application, the electrolyte comprises a lithium salt and an organic solvent. Specifically, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium hexafluoroborate, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, LiC(CF3SO3)2, and LiN(C4F9SO2)(CF3SO3); the organic solvent may include, but is not limited to, at least one of an ether-based solvent, a nitrile-based solvent, a cyanate-based solvent, a fluoroester-based solvent, a tetrazole-based solvent, a fluorosulfonyl solvent, a chlorosulfonyl solvent, a nitro solvent, a carbonate-based solvent, a dicarbonate-based solvent, a nitrate-based solvent, a fluoroamide-based solvent, a diketone-based solvent, an azole-based solvent, and a triazine-based solvent. For example, the organic solvent may include, but is not limited to, at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0067] In one embodiment of the present application, the battery further comprises a separator disposed between the positive electrode and the negative electrode. The present application has no particular restrictions on the positive electrode and the separator, and can employ, but is not limited to, materials that can be used as battery positive electrodes and separators in the art.

[0068] The present application also provides an electrical device comprising a battery according to any of the above embodiments. The electrical device can achieve rapid charging and discharging, meeting usage requirements, and has a long service life, thereby enhancing product competitiveness. Specifically, the electrical device may be a vehicle, electronic device, energy storage system, or the like, and the battery may be provided in the electrical device in the form of a single cell, battery module, or battery pack.

[0069] The effects of the technical solution of this application are further illustrated below through specific examples.

[0070] Example 1

[0071] At 25°C, graphite (particle size D50 is 9.5 μm), carbon black, styrene-butadiene rubber, carboxymethyl cellulose and water are mixed and stirred evenly to obtain a negative electrode slurry. The mass content of graphite (artificial graphite) in the negative electrode slurry is 96.5%, the mass content of carbon black is 1.5%, the mass content of styrene-butadiene rubber is 1%, and the mass content of carboxymethyl cellulose is 1%.

[0072] The negative electrode slurry and copper foil are placed in a continuous coating device. The negative electrode slurry is applied to the first surface of the copper foil. At the same time, a voltage of 25V is applied to the copper foil to make the copper foil positively charged. A magnetic field device is placed at the negative electrode slurry coating outlet. The magnetic field device is set on the side of the second surface opposite to the first surface. The magnetic field strength is 0.8T. The magnetic moment direction of the magnetic field is at an angle of 90° with the first surface of the copper foil. The magnetic field device simultaneously reciprocates. The angle between the reciprocating motion direction and the extension direction of the copper foil (i.e., the moving direction) is 90°, maintaining a uniform and stable magnetic field. The coated negative electrode slurry passes through the magnetic field area for 10 minutes. The temperature of the negative electrode slurry in the magnetic field is 40°C. After drying at 140°C for 10 minutes, it is rolled under a pressure of 10t and a roller speed of 0.5m / s to obtain a negative electrode.

[0073] Example 2

[0074] The process is similar to that of Example 1, except that the voltage applied to the copper foil is 5V.

[0075] Example 3

[0076] The process is substantially the same as that of Example 1, except that the voltage applied to the copper foil is 35V.

[0077] Example 4

[0078] It is substantially the same as Example 1, except that the magnetic field strength is 0.2T.

[0079] Example 5

[0080] It is substantially the same as Example 1, except that the magnetic field strength is 2T.

[0081] Example 6

[0082] It is substantially the same as Example 1, except that the angle between the magnetic moment direction of the magnetic field and the first surface is 10°.

[0083] Example 7

[0084] It is substantially the same as Example 1, except that the angle between the magnetic moment direction of the magnetic field and the first surface is 30°.

[0085] Example 8

[0086] It is substantially the same as Example 1, except that the angle between the magnetic moment direction of the magnetic field and the first surface is 60°.

[0087] Example 9

[0088] It is substantially the same as Example 1, except that the angle between the reciprocating motion direction and the copper foil extension direction is 10°.

[0089] Example 10

[0090] It is substantially the same as Example 1, except that the angle between the reciprocating motion direction and the copper foil extension direction is 40°.

[0091] Example 11

[0092] It is substantially the same as Example 1, except that the magnetic field device does not reciprocate, but rotates around its own central axis at a rotation speed of 25 r / min.

[0093] Example 12

[0094] It is substantially the same as Example 1, except that the magnetic field device performs a rotational motion while performing a reciprocating motion. The rotational motion is a rotation around its own central axis at a rotation speed of 50 r / min.

[0095] Example 13

[0096] The method is substantially the same as Example 1, except that the time for the coated negative electrode slurry to pass through the magnetic field region is 1 minute.

[0097] Example 14

[0098] It is substantially the same as Example 1, except that the particle size D50 of the graphite is 19.5 μm.

[0099] Example 15

[0100] The process is substantially the same as that of Example 1, except that the magnetic field strength is 3 T and a voltage of 0.3 V is applied to the copper foil.

[0101] Example 16

[0102] It is roughly the same as Example 1, except that the rolling pressure is 45t.

[0103] Example 17

[0104] The process is substantially the same as that of Example 1, except that no voltage is applied to the copper foil.

[0105] Example 18

[0106] The method is substantially the same as Example 1, except that the negative electrode slurry consists of 98% by mass of graphite, 1% by mass of styrene-butadiene rubber, 1% by mass of carboxymethyl cellulose, and the balance of water.

[0107] Comparative Example 1

[0108] It is substantially the same as Example 1, except that no magnetic field device is provided.

[0109] Comparative Example 2

[0110] The process is substantially the same as that of Example 1, except that no voltage is applied to the copper foil and no magnetic field device is provided.

[0111] Comparative Example 3

[0112] Similar to Example 1, the magnetic field was adjusted so that the orientation value of the negative electrode active material layer was 2.5, and the bonding force between the negative electrode current collector and the negative electrode active material layer was 0.24 N / 40 mm.

[0113] Performance testing

[0114] The negative electrodes prepared in Example 1 and Comparative Example 2 were subjected to electron microscopy, where Figure 6 is an electron microscopic cross-sectional view of the negative electrode prepared in Example 1, and Figure 7 is an electron microscopic cross-sectional view of the negative electrode prepared in Comparative Example 2. It can be seen that the arrangement of graphite in the negative electrode of Example 1 tends to be perpendicular to the current collector or stacked at an angle to the current collector, while the arrangement of graphite in the negative electrode of Comparative Example 2 tends to be stacked parallel to the current collector. At the same time, the electron microscopic image of the negative electrode prepared in Comparative Example 1 is similar to that of Comparative Example 2, and the graphite in the negative electrode tends to be stacked parallel to the current collector. Therefore, the preparation method provided in the present application can modify the orientation of graphite, thereby improving the performance of the negative electrode.

[0115] The surface density, compaction density, orientation value, bonding strength and resistivity of the negative electrodes prepared in the above examples and comparative examples were tested under the following test conditions. The results are shown in Table 1.

[0116] Surface density test: Use a 1.5 cm diameter cutter to take samples from the negative electrode (the negative electrode includes the current collector and the negative electrode active material layer disposed on the current collector) and the negative electrode current collector foil, weigh the weight on an electronic scale, and calculate the surface density of the negative electrode in g / m2 Among them, the mass content of the negative electrode is m1, the mass content of the negative electrode collector is m2, and the surface density of the negative electrode is m0 = (m1-m2) / (π×(1.5 / 2)×(1.5 / 2)).

[0117] Compaction density test: Use a micrometer to measure and calculate the thickness h0 of the negative electrode active material layer. The thickness h1 of the negative electrode minus the thickness h2 of the current collector can be obtained to obtain the thickness h0 of the negative electrode active material layer = h1-h2. By calculating the ratio of the surface density m0 to the thickness h0 of the negative electrode active material layer, the compaction density of the negative electrode can be obtained, in units of g / cm 3 .

[0118] Orientation value (OI value) test: The 004 peak intensity and 110 peak intensity of the negative electrode (the negative electrode includes the current collector and the negative electrode active material layer arranged on the current collector) are measured by XRD (scanning range 5°-90°, voltage 1mV, scanning speed 0.5° / min), and the OI value of the negative electrode active material layer is calculated.

[0119] Adhesion (peel strength) test: Apply transparent tape evenly to one side of the negative electrode, tear off one end, and secure it to a test fixture. Use a tensile tester to record the force (N) applied as the tape peels off the electrode sheet. The measurement length is 40 mm, which is the length of time the transparent tape peels from the electrode sheet at the start of the measurement, also known as the device's measurement length.

[0120] Resistivity test: Cut the negative electrode into 40mm x 100mm pieces and place them in a sheet resistance tester. Set the pressure to 400kg and press the start button to automatically test the negative electrode. The negative electrode consists of a current collector and an active material layer.

[0121] Table 1 Negative electrode performance test results

[0122] The negative electrodes prepared in the above examples and comparative examples were cut and made into a negative electrode with a surface density of 230±23 g / m 2 The negative electrode sheet has the corresponding size and surface density of 500±50g / m 2 The positive electrode lithium iron phosphate pole piece (the mass ratio of lithium iron phosphate, conductive carbon black, and PVDF is 96:2:2); 1 mol of LiPF6 is dissolved in 1 L of organic solvent (the volume ratio of ethylene carbonate and diethyl carbonate is 1:1) to obtain an electrolyte; in a glove box, under an argon atmosphere, the positive electrode, separator, and negative electrode are alternately stacked, and the electrolyte is injected to prepare a soft-pack battery with a designed battery capacity of 1.8 Ah. The prepared battery is tested as follows, and the results are shown in Table 2.

[0123] DC internal resistance test: The battery was adjusted to 50% SOC at 25°C, and then charged at 1.5C for 30 seconds. The voltage drop of each battery was recorded and the DC resistance (DCIR) was calculated.

[0124] Discharge capacity ratio: The battery is tested at 25°C to measure the variation of discharge capacity with cycle number at different rates of 0.2C, 2C and 5C, with a voltage range of 2.0V-3.8V. The ratio of the first-cycle discharge capacity at 5C rate to the first-cycle discharge capacity at 0.2C (5C / 0.2C discharge ratio) is calculated, as is the ratio of the battery capacity after 1000 charge and discharge cycles at 2C rate to the first-cycle 0.2C discharge capacity (2C / 0.2C-1000 cycle capacity). These two ratios can be used to evaluate the battery's high-rate charge and discharge capabilities.

[0125] Liquid phase diffusion impedance test: The negative electrode, separator, and negative electrode stack are made into a symmetrical battery. At a frequency of 0.02Hz-200000Hz and a voltage of 5V, the AC impedance of the symmetrical battery is tested and analyzed as the liquid phase diffusion impedance.

[0126] Table 2 Battery performance test results

[0127] It can be seen that in Comparative Example 1, no magnetic field is applied, and the orientation degree of graphite cannot be effectively adjusted, which affects the performance of the negative electrode; in Comparative Example 2, no magnetic field and electric field are applied, and the orientation degree of graphite cannot be effectively adjusted, nor can the dense arrangement of graphite in the negative electrode active material layer be adjusted, resulting in poor performance of the obtained negative electrode; although the orientation degree of the negative electrode active material layer in Comparative Example 3 is appropriate, the binding force between the negative electrode active material layer and the negative electrode current collector is weak, resulting in poor overall performance of the negative electrode; and in the embodiment of the present application, by applying a magnetic field, the orientation degree of graphite can be improved, the tortuosity of the negative electrode can be reduced, the distribution of the conductive agent can be optimized, and the binding force between the negative electrode current collector and the negative electrode active material layer can be enhanced, thereby obtaining a negative electrode with excellent performance, which is beneficial to improving the rate performance of the battery and facilitating the use of the battery. SEM analysis reveals that in the negative electrode prepared in Example 1, the distribution density of the conductive agent gradually increases along the direction from the negative electrode active material layer to the negative electrode current collector. In the negative electrode prepared in Example 17, the conductive agent is roughly evenly distributed throughout the negative electrode active material. This indicates that applying an electric field can further improve the distribution density of the conductive agent, further reducing the resistivity of the negative electrode, and further improving the distribution of graphite, thereby enhancing battery performance. Compared to Example 18, the overall performance of the battery in Example 1 is improved, indicating that the addition of a conductive agent can further enhance the electrochemical performance of the negative electrode and the battery.

[0128] The above is a preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A negative electrode, characterized in that The invention comprises a negative electrode current collector (11) and a negative electrode active material layer (12) arranged on the surface of the negative electrode current collector (11), wherein the negative electrode active material layer (12) comprises graphite, an orientation value of the negative electrode active material layer (12) is less than or equal to 3, and a bonding force between the negative electrode current collector (11) and the negative electrode active material layer (12) is greater than or equal to 0.25N / 40mm; The orientation value is the ratio of the peak area of ​​the (004) characteristic diffraction peak to the peak area of ​​the (110) characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.

2. The negative electrode according to claim 1, wherein The orientation value of the negative electrode active material layer (12) is 0.06-3; and / or the bonding force between the negative electrode current collector (11) and the negative electrode active material layer (12) is 0.25N / 40mm-2.8N / 40mm.

3. The negative electrode according to claim 1 or 2, characterized in that The negative electrode active material layer (12) further comprises a conductive agent, and the distribution density of the conductive agent on the side away from the negative electrode current collector (11) is smaller than the distribution density of the conductive agent on the side close to the negative electrode current collector (11).

4. The negative electrode according to claim 3, wherein The distribution density of the conductive agent gradually increases along the direction from the negative electrode active material layer (12) to the negative electrode current collector (11).

5. The negative electrode according to claim 3 or 4, characterized in that The mass content of the conductive agent in the negative electrode active material layer (12) accounts for 0.1%-6.7% of the total mass content of the negative electrode active material layer (12).

6. The negative electrode according to any one of claims 1 to 5, characterized in that The resistivity of the negative electrode (10) is 0.1Ω·cm-2Ω·cm.

7. The negative electrode according to any one of claims 1 to 6, characterized in that The mass content of the graphite in the negative electrode active material layer (12) is greater than or equal to 80% of the total mass content of the negative electrode active material layer (12); and / or The particle size D50 of the graphite is 1 μm-30 μm.

8. A method for preparing a negative electrode, characterized in that: include: Providing a negative electrode current collector (11), coating a negative electrode slurry containing graphite on at least one surface of the negative electrode current collector (11), and adjusting the orientation of the graphite in the negative electrode slurry using a magnetic field; After drying, a negative electrode (10) having an orientation value of a negative electrode active material layer (12) less than or equal to 3 is obtained; and the bonding force between the negative electrode current collector (11) and the negative electrode active material layer (12) is greater than or equal to 0.25N / 40mm.

9. The method for preparing a negative electrode according to claim 8, wherein: The negative electrode current collector (11) comprises a first surface (111) and a second surface that are arranged opposite to each other, a magnetic field is arranged on one side of the first surface (111) and / or the second surface, and the angle between the magnetic moment direction of the magnetic field and the negative electrode current collector is 10°-90°.

10. The method for preparing a negative electrode according to claim 8 or 9, wherein: The magnetic field performs at least one of a reciprocating motion and a rotating motion, and the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector (11) is 0°-90°.

11. The method for preparing a negative electrode according to any one of claims 8 to 10, wherein: The intensity of the magnetic field is 0.1T-2T.

12. The method for preparing a negative electrode according to any one of claims 8 to 11, wherein: The negative electrode slurry further contains a conductive agent, and before drying, the negative electrode current collector (11) is positively charged so that the distribution density of the conductive agent on the side away from the negative electrode current collector (11) is less than the distribution density of the conductive agent on the side close to the negative electrode current collector (11); The voltage of the negative electrode current collector (11) is 0.1V-120V.

13. The method for preparing a negative electrode according to any one of claims 8 to 12, wherein: The drying temperature is 40° C.-200° C., and the drying time is 2 min-60 min.

14. The method for preparing a negative electrode according to any one of claims 8 to 13, wherein: After the drying, the process further comprises roller pressing, wherein the pressure of the roller pressing is 2t-35t and the roller speed is 0.5m / s-2m / s.

15. A battery, characterized in that: The invention comprises a negative electrode (10) according to any one of claims 1 to 7 or a negative electrode (10) prepared by the method for preparing a negative electrode according to any one of claims 8 to 13, and a positive electrode.

16. An electrical device, characterized in that: Including the battery according to claim 15.

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