Negative electrode and preparation method thereof, battery and electric equipment

Abstract

The invention provides a negative electrode and a preparation method thereof, a battery and electric equipment. The negative electrode comprises 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 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 / 40mm. The negative electrode has excellent ion and electron transmission capability and good internal stability, is favorable for being used in the battery, improves the charge-discharge rate and the cycle capacity retention rate of the battery, and prolongs the service life of the battery.

Description

Technical Field

[0001] 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

[0002] Graphite is widely used in battery anodes due to its low cost and high energy density. Currently, with increasing user demand, more and more electronic 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. Summary of the Invention

[0003] In view of this, the present application provides a negative electrode and its preparation method, a battery and an electrical device. 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.

[0004] In the first aspect, the present application provides 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.

[0005] Optionally, the orientation value of the negative electrode active material layer is 0.06-3.

[0006] Optionally, the bonding force between the negative electrode current collector and the negative electrode active material layer is 0.25 N / 40 mm to 2.8 N / 40 mm.

[0007] Optionally, the negative electrode active material layer further includes a conductive agent, and the distribution density of the conductive agent on the side away from the negative electrode current collector is smaller than the distribution density of the conductive agent on the side close to the negative electrode current collector.

[0008] Furthermore, 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.

[0009] Furthermore, the mass of the conductive agent in the negative electrode active material layer accounts for 0.1%-6.7% of the total mass of the negative electrode active material layer.

[0010] Optionally, the resistivity of the negative electrode is 0.1Ω·cm-2Ω·cm.

[0011] Optionally, the mass of the graphite in the negative electrode active material layer is greater than or equal to 80% of the total mass of the negative electrode active material layer.

[0012] Optionally, the particle size D50 of the graphite is 1 μm-30 μm.

[0013] In a second aspect, the present application provides 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;

[0014] After drying, a negative electrode having an orientation value of a 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 0.25 N / 40 mm.

[0015] Optionally, the negative electrode current collector includes a first surface and a second surface arranged opposite to each other, and a magnetic field is set 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°.

[0016] Optionally, the magnetic field performs at least one of reciprocating motion and rotational motion, and an angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 0°-90°.

[0017] Optionally, the intensity of the magnetic field is 0.1T-2T.

[0018] Optionally, the negative electrode slurry further includes a conductive agent, and the negative electrode current collector is positively charged before drying so that the distribution density of the conductive agent away from the negative electrode current collector is smaller than the distribution density of the conductive agent close to the negative electrode current collector.

[0019] Optionally, the voltage of the negative electrode current collector is 0.1V-120V.

[0020] Optionally, the drying temperature is 40° C.-200° C., and the drying time is 2 min-60 min.

[0021] Optionally, after the drying, roller pressing is further performed, the roller pressing pressure is 2t-35t, and the roller speed is 0.5m / s-2m / s.

[0022] In a third aspect, the present application provides 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.

[0023] In a fourth aspect, the present application provides an electrical device comprising the battery described in the third aspect.

[0024] The graphite in the negative electrode active material layer provided in the present application has a low degree of orientation, 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 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

[0025] Figure 1 A schematic cross-sectional view of a negative electrode according to one embodiment of the present application.

[0026] Figure 2 This is a flow chart of a method for preparing a negative electrode provided in one embodiment of the present application.

[0027] Figure 3 Schematic diagram of the negative electrode current collector and magnetic field provided in one embodiment of the present application.

[0028] Figure 4 Schematic diagram of the negative electrode current collector and magnetic field provided in another embodiment of the present application.

[0029] Figure 5 This is a schematic diagram of the negative electrode current collector and the magnetic field provided in another embodiment of the present application.

[0030] Figure 6 This is an electron microscope cross-sectional view of the negative electrode prepared in Example 1.

[0031] Figure 7 This is an electron microscope cross-sectional view of the negative electrode prepared in Comparative Example 2. DETAILED DESCRIPTION

[0032] 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.

[0033] See also Figure 1, 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. 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. 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, that is, the degree of anisotropy of the graphite arrangement in the negative electrode. The OI value is the area ratio of the (004) characteristic diffraction peak and the (110) characteristic diffraction peak in the X-ray diffraction (XRD) spectrum of the negative electrode.

[0034] In the related art, graphite is arranged approximately parallel to the direction of the negative electrode current collector, which hinders the transmission of ions and electrons and makes it impossible to improve the charge and discharge rate of the battery. In the present application, the graphite has a low orientation degree, which is conducive to the transmission of ions and electrons, improves the migration rate of ions and electrons, and the expansion caused by ion embedding can be evenly dispersed in the negative electrode, which is conducive to the negative electrode rate performance and cycle performance. At the same time, the binding force between the negative electrode current collector and the negative electrode active material layer is high, which is conducive 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 charge and discharge rate and high rate cycle capacity retention rate.

[0035] 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. 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, and it is beneficial to the transmission capacity of ions and electrons and the improvement of the compaction density, while reducing the side reactions between the electrolyte when used in the battery, 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 graphite particle size D50 can be 8 μm to 20 μm, which can further enhance the electrochemical performance and usability of the negative electrode. In another embodiment of the present application, the graphite particle size D50 can be 9 μm to 15 μm. D50 refers to the median particle size of the graphite particles, as measured using a laser force meter. The graphite can include at least one of artificial graphite and natural graphite.

[0036] In this application, graphite is used as the negative electrode active material in the negative electrode active material layer. It is understood that the negative electrode active material in the negative electrode may be solely graphite, or may include graphite and other negative electrode active materials. Specifically, the other negative electrode active materials may include, but are not limited to, at least one of silicon-based materials, mesophase carbon microspheres, hard carbon, and soft carbon. In one embodiment of this application, the mass of the graphite in the negative electrode active material layer is greater than or equal to 80% of the total mass 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 enhancing ion and electron transport capabilities, and improving the 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.

[0037] In the present application, the orientation value of the negative electrode active material layer 12 is less than or equal to 3, so that the orientation of the graphite in the negative electrode active material layer is more conducive to the transmission of ions and electrons, thereby improving the performance of the negative electrode. In one embodiment of the present application, the orientation value of the negative electrode active material layer 12 is 0.06-3, which can not only ensure the transmission capacity of ions and electrons during the use of the negative electrode, but also reduce the difficulty and cost of preparing the negative electrode, which is conducive to the commercial application of the negative electrode. Specifically, the orientation value of the negative electrode active material layer 12 can 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 can be 0.06-2.5. In another embodiment of the present application, the orientation value of the negative electrode active material layer 12 can be 0.09-2.5. In another embodiment of the present application, the orientation value of the negative electrode active material layer 12 can be 0.09-1.33, thereby further improving the ion and electron transport rate of the negative electrode and improving the performance of the negative electrode. In another embodiment of the present application, the orientation value of the negative electrode active material layer 12 can be 0.1-2.5.

[0038] In one embodiment of the present application, the graphite has a degree of graphitization greater than or equal to 60%, resulting in fewer defects in the graphite crystals, better graphite stability, increased specific capacity of the graphite, and facilitated rapid ion deintercalation, thereby improving the negative electrode and battery cycle performance and energy density. Specifically, the graphite degree of graphitization 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.

[0039] 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 conductivity, reduce resistivity, accelerate electron mobility, and increase ion migration, thereby improving the battery's charge and discharge efficiency and output power.

[0040] In one embodiment of the present application, the mass of the conductive agent in the negative electrode active material layer accounts for 0.1%-6.7% of the total mass 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.

[0041] 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.

[0042] In one embodiment of the present application, the distribution density of the conductive agent in the negative electrode active material layer is lower on the side away from the negative electrode current collector than on the side closer to the negative electrode current collector. The distribution density of the conductive agent refers to the amount of conductive agent per unit area. This improves the conductivity of the negative electrode active material layer closer to the negative electrode current collector, further enhancing the performance of the negative electrode. Furthermore, the higher distribution density of the conductive agent on the negative electrode current collector side helps 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.

[0043] 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. For example, the direction from the negative electrode active material layer to the negative electrode current collector is Figure 1In other words, the conductive agent has a higher distribution density in the region of the negative electrode active material layer close to the negative electrode current collector, which makes the side of the negative electrode active material layer close to the negative electrode current collector more conductive, further improving the performance of the negative electrode.

[0044] 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.

[0045] In this application, 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, which provides the negative electrode with excellent stability. In this application, the length measured during the binding force test is 40mm. In one embodiment of this application, the binding force between the negative electrode current collector and the negative electrode active material layer is between 0.25N / 40mm and 2.8N / 40mm, which ensures high stability and reliability within the negative electrode, thereby improving the negative electrode's cycle 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.

[0046] 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.

[0047] 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.

[0048] This application also provides a method for preparing a negative electrode. Figure 2 , is a flow chart of a method for preparing a negative electrode provided in one embodiment of the present application, comprising:

[0049] 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.

[0050] 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.

[0051] In the preparation method of the negative electrode provided in the present application, the orientation mode of graphite in the negative electrode slurry is changed under the action of a magnetic field, the orientation degree of graphite is improved, a reasonable and orderly arrangement of graphite is achieved, a path that is easier for ion and electron transmission is generated, the migration rate of ions and electrons is increased, and the transmission obstruction and negative electrode degradation problems caused by the natural parallel layered arrangement structure of graphite can be improved. 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 increased, which is beneficial for use in batteries and improves the battery's charge and discharge rate, cycle capacity retention rate and service life.

[0052] In one embodiment of the present application, the negative electrode current collector includes a first surface and a second surface arranged opposite to each other, and a magnetic field is set 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° (such as 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 unobstructed ion and electron transmission paths.

[0053] 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.

[0054] See also Figure 3 , is a schematic diagram of a negative electrode current collector and a magnetic field provided in one embodiment of the present application, wherein the negative electrode current collector 11 includes a first surface 111 and a second surface arranged opposite to each other, the arrow indicates the magnetic moment direction of the magnetic field, the magnetic field can be generated by a magnetic field device 20, and 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 to be vertically arranged, reduce the tortuosity of the negative electrode, optimize the ion transmission path in the thickness direction of the negative electrode, and further improve the performance of the negative electrode.

[0055] 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 improving the arrangement of graphite and improving the performance of the negative electrode. 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 can be further optimized, and the performance of the negative electrode can be improved. Please refer to Figure 4 , 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 111, and the direction indicated by arrow b is the extension direction of the negative electrode current collector 11. The angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector 11 is θ2. In one embodiment of the present application, the angle between the direction of 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 direction of 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 direction of 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 direction of the reciprocating motion and the extension direction of the negative electrode current collector is 50°-90°.

[0056] In this application, the uniformity of graphite distribution can be improved by rotational motion; rotational motion is rotation along an axis. In one 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, thereby causing the magnetic field to generate rotational motion. Of course, in other embodiments, the magnetic field device can rotate along other axes. Please refer to Figure 5, is a schematic diagram of a negative electrode current collector and a magnetic field provided in another embodiment of the present application. The magnetic field can be generated by a magnetic field device 20, and the magnetic field device 20 rotates along the central axis c of the magnetic field device 20. In one embodiment of the present application, the rotation speed of the magnetic field device can be 10 r / min (round / min)-60 r / min. Specifically, the rotation speed of the magnetic field device can be, but is not limited to, 15 r / min, 20 r / min, 25 r / min, 30 r / min, 35 r / min, 40 r / min, 45 r / min, or 50 r / min.

[0057] In one embodiment of the present application, the intensity of the magnetic field is 0.1T-2T, which can produce a directional induction effect on graphite and improve the orientation of graphite, while reducing the difficulty of preparation and not affecting the negative electrode fluid, and can obtain a negative electrode with excellent performance. Specifically, the intensity 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 intensity of the magnetic field can be 0.2T-2T. In another embodiment, the intensity of the magnetic field can be 0.5T-2T. In yet another embodiment, the intensity of the magnetic field can be 0.2T-1T. In yet another embodiment, the intensity of the magnetic field can be 0.8T-2T, which is conducive to further improving the performance of the negative electrode.

[0058] In this application, the graphite in the negative electrode slurry is oriented under the influence of a magnetic field, and the graphite moves under the influence of an electric charge, 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.

[0059] 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 performance of the negative electrode. 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 and facilitate coating of 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.

[0060] In one embodiment of the present application, the viscosity of the negative electrode slurry is 1500mPa·s-5000mPa·s. This suitable viscosity facilitates the uniform dispersion of graphite and the conductive agent, and also facilitates the coating and drying of the negative electrode slurry on the surface of the negative electrode current collector. 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.

[0061] 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 of the negative electrode slurry and the effect of the magnetic field on graphite.

[0062] 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.

[0063] 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.

[0064] 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 conducive to the bonding of the negative electrode current collector and the negative electrode active material layer. 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 it is also conducive 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 can 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 can be, but is not limited to, 1min, 5min, 10min, 15min, 20min, 25min or 30min, etc. In one embodiment, the final baking temperature is 60°C-180°C, and the time is 5min-25min. In another embodiment, the final baking temperature is 140° C.-180° C., and the time is 5 min-15 min.

[0065] 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.

[0066] In one embodiment of the present application, the negative electrode slurry also contains a conductive agent, and the negative electrode current collector is positively charged before drying 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 close to the negative electrode current collector. In this embodiment, a magnetic field and an electric field are used together, wherein the orientation of the graphite in the negative electrode slurry is changed to be parallel or approximately parallel to the negative electrode current collector under the action of the magnetic field, so that the angle between the graphite and the negative electrode current collector is increased, the orientation degree of the graphite is improved, and the reasonable and orderly stacking of the graphite is achieved, thereby creating a path that is easier for ion and electron transmission and increasing the migration rate of ions and electrons; an electric field is applied to the negative electrode current collector to make the negative electrode current collector positively charged. Under the action of the electric field, the conductive agent is attracted to move toward the side of the negative electrode current collector, so that the negative electrode current collector close to the negative electrode current collector is moved to the negative electrode current collector. The conductive performance of the active material layer is better, which is beneficial to reducing the resistivity of the negative electrode, and under the action of charge, the graphite will also move, thereby improving the density of the graphite arrangement and optimizing the liquid phase mass transfer pores; under the action of the magnetic field and the electric field, the conductive agent and the graphite are in closer contact near the negative electrode current collector side, and at the same time, the contact area between the two and the negative electrode current collector is larger, the bonding force between the negative electrode active material layer and the negative electrode current collector is increased, and the bonding reliability is improved, which is beneficial for use in the battery and improves the battery's charge and discharge rate, cycle capacity retention rate and service life.

[0067] 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. In one embodiment of the present application, the negative electrode current collector can be connected to the positive electrode of a power source 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, and the two rollers clamp the negative electrode current collector in the thickness direction of the negative electrode current collector, and the rollers apply a voltage to the negative electrode current collector to make the negative electrode current collector positively charged.

[0068] 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 effect of graphite, improve the compaction density and rate performance. 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 the safety of preparation. At the same time, it is beneficial to further optimize the distribution of graphite and conductive agent in the negative electrode active material layer, and further improve 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.

[0069] In the present application, the negative electrode current collector may be positively charged in any step before drying. For example, after the negative electrode slurry is placed on the surface of the negative electrode current collector, a magnetic field may be applied and the negative electrode current collector may be positively charged. Alternatively, the negative electrode slurry may be placed after the magnetic field is set on one side of the negative electrode current collector and the negative electrode current collector is positively charged. In one embodiment of the present application, the negative electrode current collector may be placed in a conveying device, and the negative electrode current collector may be moved with the movement of the conveying device. During the movement, the negative electrode slurry is placed on the surface of the negative electrode current collector, and at the same time, the negative electrode collector is connected to a power source and positively charged, and a magnetic field is set on one side of the negative electrode current collector.

[0070] Under the same preparation conditions, compared to 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 to the ordinary electrode piece without applying a magnetic field, greatly improving the conductivity 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 improves the ion and electron diffusion capacity, binding force, resistivity, etc. of the negative electrode, obtains a negative electrode with excellent performance, can improve the battery's charge and discharge rate and high-rate cycle capacity retention rate, especially conducive to the performance of high-area density and compacted batteries, breaking through the bottleneck of traditional battery charge and discharge rate and capacity.

[0071] 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.

[0072] 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 is beneficial for 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 (such as a solar cell), and the like.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The effects of the technical solution of this application are further illustrated below through specific examples.

[0077] Example 1

[0078] 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%, 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%.

[0079] 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.

[0080] Example 2

[0081] The process is similar to that of Example 1, except that the voltage applied to the copper foil is 5V.

[0082] Example 3

[0083] The process is substantially the same as that of Example 1, except that the voltage applied to the copper foil is 35V.

[0084] Example 4

[0085] It is substantially the same as Example 1, except that the magnetic field strength is 0.2T.

[0086] Example 5

[0087] It is substantially the same as Example 1, except that the magnetic field strength is 2T.

[0088] Example 6

[0089] 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°.

[0090] Example 7

[0091] 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°.

[0092] Example 8

[0093] 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°.

[0094] Example 9

[0095] 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°.

[0096] Example 10

[0097] 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°.

[0098] Example 11

[0099] 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.

[0100] Example 12

[0101] 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.

[0102] Example 13

[0103] 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.

[0104] Example 14

[0105] It is substantially the same as Example 1, except that the particle size D50 of the graphite is 19.5 μm.

[0106] Example 15

[0107] 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.

[0108] Example 16

[0109] It is roughly the same as Example 1, except that the rolling pressure is 45t.

[0110] Example 17

[0111] The process is substantially the same as that of Example 1, except that no voltage is applied to the copper foil.

[0112] Example 18

[0113] 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.

[0114] Comparative Example 1

[0115] It is substantially the same as Example 1, except that no magnetic field device is provided.

[0116] Comparative Example 2

[0117] 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.

[0118] Comparative Example 3

[0119] 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.

[0120] Performance testing

[0121] The negative electrodes prepared in Example 1 and Comparative Example 2 were examined by electron microscopy. Figure 6 This is an electron microscope cross-sectional view of the negative electrode obtained in Example 1. Figure 7 This is an electron micrograph of a cross-sectional view of the negative electrode prepared in Comparative Example 2. It can be seen that the graphite in the negative electrode of Example 1 is oriented and stacked in a vertical or oblique direction, while the graphite in the negative electrode of Comparative Example 2 is stacked horizontally. The electron micrograph of the negative electrode prepared in Comparative Example 1 is similar to that of Comparative Example 2, with the graphite in the negative electrode stacked horizontally. Therefore, the preparation method provided in this application can modify the orientation of graphite, thereby improving the performance of the negative electrode.

[0122] 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.

[0123] Surface density test: Use a 1.5 cm diameter cutter to take samples from the negative electrode and negative electrode current collector foil, weigh them on an electronic scale, and calculate the surface density of the negative electrode in g / m 2 .

[0124] Compaction density test: Use a micrometer to measure and calculate the average thickness of the negative electrode. By calculating the ratio of surface density to thickness, the compaction density of the negative electrode can be obtained in g / cm 3 .

[0125] Orientation value (OI value) test: XRD test (scanning range 5°-90°, voltage 1mV, scanning speed 0.5° / min) was used to measure the 004 peak intensity and 110 peak intensity of the negative electrode, thereby calculating the OI value of the negative electrode active material layer.

[0126] Adhesion (peeling) force test: Evenly stick transparent tape on one side of the negative electrode and tear off one end to fix it on the test fixture. Use a tensile tester to measure the force when the tape peels off the electrode. The measurement length is 40mm to obtain the bonding strength between the negative electrode current collector and the negative electrode active material layer.

[0127] Resistivity test: Cut the electrode into a size of 40mm×100mm and place it in the electrode resistance meter test equipment for testing. Set the pressure to 400kg and press the start button of the equipment to perform automatic testing to obtain the resistivity of the negative electrode.

[0128] Table 1 Negative electrode performance test results

[0129]

[0130]

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] Table 2 Battery performance test results

[0136]

[0137]

[0138] 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 setting an electric field can further improve the distribution density of the conductive agent, further reduce the resistivity of the negative electrode, further improve the graphite content, and enhance 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 battery.

[0139] 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 and a negative electrode active material layer arranged on the 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 0.25N / 40mm.

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

3. The negative electrode according to claim 1, wherein The negative electrode active material layer further includes a conductive agent, and a distribution density of the conductive agent on a side away from the negative electrode current collector is smaller than a distribution density of the conductive agent on a side close to the negative electrode current collector.

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

5. The negative electrode according to claim 3, wherein The mass of the conductive agent in the negative electrode active material layer accounts for 0.1% to 6.7% of the total mass of the negative electrode active material layer.

6. The negative electrode according to claim 1, wherein The resistivity of the negative electrode is 0.1Ω·cm-2Ω·cm.

7. The negative electrode according to claim 1, wherein The mass of the graphite in the negative electrode active material layer is greater than or equal to 80% of the total mass of the negative electrode active material layer; 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, coating a negative electrode slurry containing graphite on at least one side of the negative electrode current collector, and adjusting the orientation of the graphite in the negative electrode slurry using a magnetic field; After drying, a negative electrode having an orientation value of a 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 0.25 N / 40 mm.

9. The preparation method according to claim 8, wherein The negative electrode current collector includes a first surface and a second surface arranged opposite to each other. A magnetic field is set on one side of the first surface and / or the second surface. The angle between the magnetic moment direction of the magnetic field and the negative electrode current collector is 10°-90°.

10. The preparation method according to claim 8, characterized in that The magnetic field performs at least one of reciprocating motion and rotating motion, and an angle between a motion direction of the reciprocating motion and an extension direction of the negative electrode current collector is 0°-90°.

11. The preparation method according to any one of claims 8 to 10, characterized in that: The intensity of the magnetic field is 0.1T-2T.

12. The preparation method according to claim 8, wherein The negative electrode slurry further contains a conductive agent, and before drying, 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 close to the negative electrode current collector; The voltage of the negative electrode current collector is 0.1V-120V.

13. The preparation method according to claim 8, wherein The drying temperature is 40° C.-200° C., and the drying time is 2 min-60 min.

14. The preparation method according to claim 8, 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 the negative electrode according to any one of claims 1 to 7 or the negative electrode prepared by the preparation method 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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