Secondary battery and electric device

Abstract

The invention discloses a secondary battery and a power utilization device, and belongs to the technical field of batteries, the secondary battery comprises a pole piece, the pole piece comprises a current collector and an active material layer located on at least one surface of the current collector, and the surface, away from the current collector, of the active material layer is provided with a plurality of grooves arranged at intervals; the pole piece comprises a conductive agent, the conductive agent comprises a first conductive agent, and the first conductive agent comprises a fiber material; the pole piece is subjected to a repeated bending test, the number of times of repeated bending is n when the internal resistance of the pole piece is 5 times of the initial internal resistance, and n is larger than or equal to 10000 and smaller than or equal to 200000. The secondary battery disclosed by the invention has excellent flexibility and rate capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electric device. BACKGROUND

[0002] Emerging wearable electronic devices with intelligent functions are entering our daily life and gradually changing the way of human life. The full use of these wearable electronic devices urgently needs to seamlessly integrate high-energy-density deformable power sources within the limited human surface.

[0003] At present, the secondary battery has become the main power supply choice of industrial wearable devices due to its high energy density, long cycle stability, low self-discharge and mature production technology. The flexible secondary battery has the same electrochemical working mechanism as the traditional secondary battery, but in actual operation, it needs to maintain its electrochemical performance under repeated mechanical deformation. However, the rigid metal substrate commonly used in the current electrode sheet is easy to cause the electrochemical and mechanical instability of the traditional secondary battery under complex deformation.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies existing in the prior art and provide a secondary battery and an electric device, which has excellent flexibility and rate performance.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, comprising an electrode sheet, the electrode sheet comprising a current collector and an active material layer on at least one surface of the current collector, the active material layer having a plurality of recesses arranged at intervals on the surface away from the current collector; The electrode sheet comprises a conductive agent, and the conductive agent comprises a first conductive agent, and the first conductive agent comprises a fibrous material; The electrode sheet is subjected to repeated bending test, and the number of times of repeated bending when the internal resistance of the electrode sheet is 5 times the initial internal resistance is n, and 10000≤n≤200000.

[0007] As an embodiment of the present application, at least one of the following (1) to (4) is satisfied: (1) The aspect ratio of the fibrous material is 20 to 100; (2) The fibrous material comprises at least one of carbon nanotubes, carbon fibers, metalized glass fibers and metalized polymer nanofibers; (3) The mass percentage content of the first conductive agent in the conductive agent is 30 to 100%; (4) The mass percentage content of the conductive agent in the active material layer is 0.5 to 2%.

[0008] As an embodiment of the present application, the conductive agent further includes a second conductive agent including at least one of carbon black, acetylene black, and graphite; and the mass percentage content of the second conductive agent in the conductive agent is 0 to 70%.

[0009] As an embodiment of the present application, the electrode sheet satisfies -422400 ≤ 100*W*D - (1000*L+W)*D0 ≤ -7360 and 0.5 ≤ D / D0 ≤ 0.9. W μm is a width of the groove; D μm is a depth of the groove; L mm is a pitch between adjacent grooves; D0 μm is a thickness of the active material layer.

[0010] As an embodiment of the present application, the electrode sheet satisfies 2*W / D - 1 ≤ 0.

[0011] As an embodiment of the present application, the electrode sheet satisfies L / R ≤ 0.2, R mm is a minimum bending radius of the electrode sheet.

[0012] As an embodiment of the present application, at least one of the following (5) to (9) is satisfied: (5) 10 ≤ W ≤ 75; (6) 10 ≤ D ≤ 150; (7) 1 ≤ L ≤ 5; (8) 20 ≤ D0 ≤ 200; (9) 5 ≤ R ≤ 30.

[0013] As an embodiment of the present application, the electrode sheet further includes a binder including at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, sodium alginate, chitosan, guar gum, and xanthan gum.

[0014] As an embodiment of the present application, the binder includes a first binder and a second binder at a mass ratio of 1:(0.25 to 4), the first binder including at least one of polypropylene and carboxymethyl cellulose; the second binder including at least one of styrene butadiene rubber, sodium alginate, chitosan, guar gum, and xanthan gum; and / or The mass percentage content of the binder in the electrode sheet is 1 to 3%.

[0015] A second aspect of the present application provides an electric device including the secondary battery described above as a power supply for the electric device.

[0016] The beneficial effects of this application are as follows: the active material layer in the electrode sheet described in this application includes fibrous material, and multiple grooves are formed on the surface of the active material layer away from the current collector. When the electrode sheet is subjected to repeated bending tests, the number of repeated bending tests when the internal resistance of the electrode sheet is 5 times the initial internal resistance is 10,000 to 200,000. The electrode sheet has excellent bendability, which can effectively improve the lithium-ion transport rate, improve the rate performance of the electrode sheet, and effectively improve the dynamic performance of the electrode sheet while minimizing the impact on the energy density of the secondary battery, thus significantly improving the flexibility and rate performance of the secondary battery. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an electrode sheet according to an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the structure of an electrode sheet according to another embodiment of this application.

[0019] The markings in the diagram are: 1. Current collector; 2. Active material layer; 21. Groove. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0022] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0023] like Figure 1 , Figure 2As shown, this application embodiment provides a secondary battery, including an electrode sheet, the electrode sheet including a current collector 1 and an active material layer 2 located on at least one surface of the current collector, the active material layer having a plurality of grooves 21 spaced apart from each other on the surface away from the current collector; The electrode includes a conductive agent, the conductive agent includes a first conductive agent, and the first conductive agent comprises a fibrous material; The electrode is subjected to repeated bending tests. The number of repeated bending tests when the internal resistance of the electrode is 5 times the initial internal resistance is n, where 10000≤n≤200000. For example, it can be 10000, 15000, 20000, 40000, 50000, 60000, 80000, 100000, 120000, 150000, 160000, 180000, 200000, or any two of these values.

[0024] The active material layer of the electrode described in this application comprises a fibrous material. Multiple mutually spaced grooves are formed on the surface of the active material layer away from the current collector. When the electrode is subjected to repeated bending tests, the number of repeated bending cycles when the internal resistance of the electrode is 5 times the initial internal resistance is 10,000 to 200,000. The electrode exhibits excellent bendability and mechanical stability, while effectively improving the lithium-ion transport rate and rate performance. It also significantly improves the flexibility and rate performance of the secondary battery while minimizing the impact on the energy density of the secondary battery.

[0025] In some of these implementations, 19500 ≤ n ≤ 190000.

[0026] The repeated bending test specifically involves repeatedly bending the electrode sheet from 0° to 180° to 0° to 180°.

[0027] The repeated bending test was conducted on an automated reciprocating motion platform.

[0028] In some embodiments, the aspect ratio of the fiber material is 20 to 100, for example, it can be 20, 30, 40, 50, 60, 70, 80, 90, 100 or any two of these values. By controlling the aspect ratio of the fiber material within this range, the fiber material can be uniformly dispersed in the electrode, effectively improving the structural stability of the electrode, effectively improving the flexibility of the electrode, and effectively improving the bendability of the electrode.

[0029] In some embodiments, the diameter of the fiber material is 0.01 to 5 μm, for example, it can be 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 4 μm, 5 μm or any two of these values.

[0030] In some embodiments, the length of the fiber material is 1 to 100 μm, for example, it can be 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any two of these values.

[0031] In some embodiments, the fibrous material includes at least one of carbon nanotubes, carbon fibers, metallized glass fibers, and metallized polymer nanofibers.

[0032] Metallized glass fiber refers to glass fiber with one or more layers of metal or metal alloy film coated on its surface by physical or chemical methods.

[0033] More specifically, metallized glass fiber includes at least one of galvanized glass fiber, aluminized glass fiber, silver-plated glass fiber, nickel-plated glass fiber, and copper-plated glass fiber.

[0034] Metallized polymer nanofibers refer to polymer nanofibers on which metal is attached to the surface of polymer nanofibers through physical or chemical methods, forming a metal layer or metal nanoparticles on the surface of the polymer nanofibers.

[0035] Among them, the metallized polymer nanofibers include at least one of copper-plated polyimide nanofibers, nickel-plated polyimide nanofibers, silver-plated polyimide nanofibers, copper-plated polypropylene nanofibers, and copper-plated cellulose nanofibers.

[0036] In some embodiments, the mass percentage of the first conductive agent in the conductive agent is 30% to 100%, for example, it can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or any two of these values. By controlling the mass percentage of the first conductive agent in the conductive agent to be 30% to 100%, the electrode sheet can be guaranteed to have a certain degree of flexibility and bendability.

[0037] In some embodiments, the conductive agent has a mass percentage content of 0.5% to 2% in the active material layer, for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of these values. By controlling the mass percentage content of the conductive agent in the active material layer to be 0.5% to 2%, the conductivity of the active material layer can be improved, the lithium ion transport performance can be effectively improved, and the structural stability of the electrode can be improved.

[0038] In some embodiments, the conductive agent further comprises a second conductive agent, which includes at least one of carbon black, acetylene black, and graphite; the second conductive agent has a mass percentage content of 0-70% in the conductive agent, for example, it can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any two of these values. By controlling the mass percentage content of the second conductive agent in the conductive agent within this range, it is possible to promote the formation of a three-dimensional conductive network, effectively improve the conductivity, and enhance the flexibility of the electrode.

[0039] In some embodiments, the electrode satisfies: -422400≤100*W*D-(1000*L+W)*D0≤-7360, for example, it can be -422400, -420000, -400000, -350000, -300000, -250000, -200000, -150000, -100000, -80000, -60000, -50000, -40000, -20000, -10000, -8000, -7360 or a range of any two of these values; Wμm is the width of the groove; Dμm is the depth of the groove; L mm is the spacing between adjacent grooves; D0μm is the thickness of the active material layer.

[0040] The inventors of this application have discovered that in active materials containing fibrous materials and grooves, the flexibility and rate performance of the electrode are closely related to the parameters of the grooves and the thickness of the active material layer. This application effectively improves the lithium-ion transport rate by controlling the following parameters: -422400≤100*W*D-(1000*L+W)*D0≤-7360 and 0.5≤D / D0≤0.9. Under the synergistic regulation of the groove width, depth, spacing, and active material layer, the lithium-ion transport rate is improved. This ensures the continuity of the conductive network and the structural stability of the electrode when it is bent. With minimal impact on the energy density of the secondary battery, the dynamic performance of the electrode is effectively improved, significantly enhancing the flexibility and rate performance of the secondary battery.

[0041] In some embodiments, the electrode satisfies: 2*W / D-1≤0. By controlling 2*W / D-1 within this range, the loss of energy density can be effectively reduced, and the flexibility of the electrode and the secondary battery can be improved.

[0042] In some embodiments, the electrode satisfies: -0.56≤2*W / D-1≤0, for example, it can be -0.25, -0.2, -0.15, -0.1, -0.05, 0, 0.05, 0.1, 0.2, 0.3, 0.33, 0.34 or any two of these values.

[0043] In some embodiments, the electrode sheet satisfies: L / R ≤ 0.2, where R mm is the minimum bending radius of the electrode sheet.

[0044] In some embodiments, the electrode satisfies: 0.12≤L / R≤0.2, for example, it can be 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or any two of these values, where R mm is the minimum bending radius of the electrode.

[0045] In some implementations, 10≤W≤75, for example, can be a range consisting of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or any two of these values. By controlling W within this range, the lithium-ion diffusion rate can be effectively improved, thereby effectively improving the rate performance of the secondary battery.

[0046] In some implementations, 10 ≤ D ≤ 150; for example, it can be a range consisting of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 or any two of these values, which can effectively balance the energy density and rate performance of the secondary battery.

[0047] In some implementations, 1≤L≤5, for example, it can be a range consisting of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two of these values. By controlling L within this range, the flexibility of the electrode can be improved, the loss of energy density can be reduced, and the rate performance can be improved.

[0048] In some implementations, 20 ≤ D0 ≤ 200, for example, can be 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 150, 160, 180, 200 or a range of any two of these values.

[0049] In some implementations, 5 ≤ R ≤ 30, for example, it can be a range consisting of 5, 6, 8, 10, 15, 20, 25, 30 or any two of these values.

[0050] In some embodiments, the electrode further includes a binder, the binder comprising at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, chitosan, guar gum, and xanthan gum. In some embodiments, the binder comprises a first binder and a second binder in a mass ratio of 1:(0.25-4), the first binder comprising at least one of polypropylene and carboxymethyl cellulose; the second binder comprising at least one of styrene-butadiene rubber, sodium alginate, chitosan, guar gum, and xanthan gum, for example, 1:0.25, 1:0.5, 1:1, 1:2, 1:3, 1:4, or any range of two such values.

[0051] In some embodiments, the binder has a mass percentage content of 1 to 3% in the electrode sheet, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any two of these values.

[0052] In some embodiments, the Dv50 particle size of the active material is 3 to 15 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm or any two of these values.

[0053] In some embodiments, the thickness of the current collector is 4 to 15 μm. For example, it can be 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or any two of these values.

[0054] In some embodiments, this application does not limit the shape of the groove, as long as its dimensional parameters meet the requirements of this invention.

[0055] In some embodiments, the groove may be trapezoidal, elliptical, semi-circular, triangular, or rectangular in shape.

[0056] In some embodiments, the groove is triangular in shape. When a triangle is used, the electrode can effectively improve its energy density while satisfying flexibility and rate capability.

[0057] In some embodiments, the active material layer includes a positive electrode active material or a negative electrode active material.

[0058] In some embodiments, the active material layer includes a positive electrode active material, the positive electrode active material having a mass content of 95-98.5% in the active material layer, for example, it can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5% or any two of these values.

[0059] In some embodiments, the positive electrode active material may be a known positive electrode active material for secondary batteries. As a non-limiting example, the positive electrode active material may include lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials or substances, and other conventional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Non-limiting examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0060] In some embodiments, the active material layer includes a negative electrode active material, the negative electrode active material having a mass content of 95-98.5% in the active material layer, for example, it can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5% or any two of these values.

[0061] In some embodiments, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 At least one of the following.

[0062] In some embodiments, the current collector includes a positive current collector or a negative current collector.

[0063] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0064] In some embodiments, the positive current collector includes metal foil materials such as aluminum, stainless steel, nickel plating, and titanium.

[0065] In some embodiments, there are no particular limitations on the negative current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, or composite current collector.

[0066] In the secondary battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0067] In one embodiment, the diaphragm comprises a porous sheet-like or nonwoven material with excellent liquid retention properties. Materials for resin or glass fiber diaphragms include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0068] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is at least one of polypropylene and polyethylene. The materials of the diaphragm described above can be used alone or in any combination.

[0069] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0070] In some embodiments, the outer packaging of the secondary battery can be a pouch-type soft case. The soft case can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0071] This application does not impose any particular restrictions on the shape of the secondary battery; it can be square or any other arbitrary shape.

[0072] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0073] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, wearable electronic devices, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0074] The present application is further illustrated below with specific embodiments: Example 1 A method for preparing a secondary battery includes the following steps: (1) Preparation of negative electrode sheet: Natural graphite (active material), binder, and conductive agent were mixed in a mass ratio of 96.0%:2.5%:1.5%, and 50% water (solvent by mass) was added and stirred to form a negative electrode slurry. The negative electrode slurry was then coated on both sides of a 6μm thick copper foil current collector. After cold pressing and vacuum drying, a 126μm thick negative electrode sheet was obtained. Figure 1As shown, the thickness D0 of the single-sided negative electrode active material layer is 60 μm.

[0075] The surface of the negative electrode active material layer away from the negative electrode current collector is laser-etched to form a rectangular groove, thus obtaining the negative electrode sheet.

[0076] The parameters of the negative electrode are shown in Table 1.

[0077] (2) Preparation of the positive electrode sheet: The active material lithium cobalt oxide, binder and conductive agent are mixed in a mass ratio of 97.0%:1.8%:1.2%, and 40% of the total mass of solvent NMP is added and stirred to form a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil current collector with a thickness of 8μm. After cold pressing and vacuum drying, a positive electrode sheet is obtained. The thickness of the positive electrode is controlled to correspond to the negative electrode surface capacity design of the example. (3) Preparation of electrolyte: At room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate) are mixed evenly in a volume ratio of 1:1:1 to obtain a mixed organic solvent. Lithium salt LiPF6 (lithium hexafluorophosphate) is added to the mixed organic solvent and stirred evenly to obtain an electrolyte.

[0078] The concentration of lithium salt LiPF6 in the electrolyte is 1 mol / L.

[0079] (4) Separator: PE separator with a thickness of 12μm.

[0080] (5) Assembly of secondary battery: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive electrode and negative electrode. After stacking, hot pressing and shaping, the tabs are welded to obtain the bare cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24h. The electrolyte prepared above is injected into the dried battery. After standing, formation and capacity testing, the preparation of secondary battery is completed.

[0081] Example 2 The difference between Example 2 and Example 1 is that the shape of the groove is as follows: Figure 2 The triangle shown has the same dimensions.

[0082] Examples 3-11, Comparative Examples 3-5 Examples 3-11 and Comparative Examples 3-5 differ from Example 1 in that the parameters of the groove are changed, as shown in Table 2.

[0083] Examples 12-16 Examples 12-16 differ from Example 1 in that the aspect ratio of the carbon nanotubes is changed, as shown in Table 1.

[0084] Examples 17-19, Comparative Example 2 Examples 17-19 and Comparative Example 2 differ from Example 1 in that the composition of the conductive agent is changed, as shown in Table 1.

[0085] Examples 20-24 Examples 20-24 differ from Example 1 in that the composition of the adhesive is changed, as shown in Table 1.

[0086] Examples 25-27 Examples 25-27 differ from Example 1 in that the Dv50 particle size of the natural graphite is changed, as shown in Table 1.

[0087] Example 28 The difference between Example 28 and Example 1 is that the groove is formed on the positive electrode sheet.

[0088] A method for preparing a secondary battery includes the following steps: (1) Preparation of negative electrode sheet: The active material natural graphite, binder, and conductive agent are mixed in a mass ratio of 96.0%:2.5%:1.5%, and 50% of the total mass of solvent water is added and stirred to form a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil current collector with a thickness of 6μm. After cold pressing and vacuum drying, a negative electrode sheet with a thickness of 126μm is obtained, and the thickness D0 of the negative electrode active material layer on one side is 60μm.

[0089] (2) Preparation of the positive electrode sheet: Lithium cobalt oxide positive electrode material, binder, and conductive agent were mixed in a mass ratio of 97.0%:1.8%:1.2%. 40% NMP solvent was added and stirred to form a positive electrode slurry. The positive electrode slurry was then coated on both sides onto an 8μm thick aluminum foil current collector. After cold pressing and vacuum drying, an 88μm thick negative electrode sheet was obtained. Figure 1 As shown, the thickness D0 of the single-sided positive electrode active material layer is 40 μm.

[0090] The surface of the positive electrode active material layer away from the positive electrode current collector is laser-etched to form a rectangular groove, thus obtaining the positive electrode sheet.

[0091] (3) Preparation of electrolyte: At room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate) are mixed evenly in a volume ratio of 1:1:1 to obtain a mixed organic solvent. Lithium salt LiPF6 (lithium hexafluorophosphate) is added to the mixed organic solvent and stirred evenly to obtain the electrolyte.

[0092] The concentration of lithium salt LiPF6 in the electrolyte is 1 mol / L.

[0093] (4) Separator: PE separator with a thickness of 12μm.

[0094] (5) Assembly of secondary battery: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive electrode and negative electrode. After stacking, hot pressing and shaping, the tabs are welded to obtain the bare cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24h. The electrolyte prepared above is injected into the dried battery. After standing, formation and capacity testing, the preparation of secondary battery is completed.

[0095] Example 29 The difference between Example 29 and Example 1 is that the positive electrode sheet is different.

[0096] The positive electrode in this embodiment is the same as the positive electrode in Example 28.

[0097] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not have a groove.

[0098] Table 1 Table 2 Performance testing 1. Rate performance test: At 25°C, the secondary batteries prepared in the examples and comparative examples were charged to 4.25V with a constant current and constant voltage of 0.33C, and then discharged to 2.8V with a constant current of 0.33C. This charge-discharge cycle was repeated for two cycles, and the average discharge specific capacity was recorded as C1 (mAh / g). Using the same charging cycle, the batteries were then discharged to 2.8V with a constant current of 5C, and the average discharge specific capacity was recorded as C2 (mAh / g). The ratio C2 / C1*100% represents the rate performance.

[0099] 2. Flexibility Test: The secondary battery electrodes corresponding to the examples and comparative examples were repeatedly bent on an automated reciprocating motion platform to evaluate the bending resistance of the samples at a specific radius of curvature. In the electrode sample evaluation, a digital meter was used with a four-probe method to monitor the resistance change of the electrode sample or the voltage change of the secondary battery online. The number of bends was recorded when r / r0 = 5 or V0-V = 0.2V, allowing for a quantitative comparison of the bendability and flexibility of the electrodes and secondary batteries.

[0100] The testing process is as follows: The electrode sample is a 2.0cm*6.0cm strip. The strip is placed on an automated reciprocating motion platform, and both ends of the strip are fixed to the sliding module with clamps. The sliding module and the strip have a four-electrode probe contact connection line, which is connected to a digital meter to test the resistance of the strip at high frequency. The initial resistance r0 is recorded. The repeated bending radius R (corresponding to R in Table 2) and bending angle (180°) are set. The automated reciprocating device is started, and the sliding module performs reciprocating application. The counter automatically records the number of reciprocations. During the reciprocating motion of the slider, the bending angle of the electrode changes repeatedly from 0°→180°→0°→180°… The digital meter collects the real-time resistance r of the electrode at high frequency. When r / r0=500%, the number of slider reciprocations n is the number of times the electrode sample can be bent under R.

[0101] The testing process is as follows: The secondary battery is packaged as a 2.5cm*6.5cm soft-pack cell. The fully charged secondary battery (voltage > 4.2V) is placed on an automated reciprocating motion platform, and both ends are fixed to the sliding module with clamps. The positive and negative electrodes of the secondary battery are connected to the digital meter or charge / discharge equipment to test the voltage of the secondary battery sample at high frequency. The initial voltage V0 is recorded. The bending radius R and bending angle (180°) are set. The automated reciprocating equipment is started, and the sliding module performs reciprocating operation. The counter automatically records the number of reciprocations. During the reciprocating motion of the slider, the bending angle changes repeatedly from 0°→180°→0°→180°… The digital meter or charge / discharge equipment collects the real-time electrode voltage V at high frequency. When V0-V=0.2V, the number of slider reciprocations N is the number of times the secondary battery sample can be bent under R.

[0102] 3. Loss of active ingredient: Loss of active ingredient = 100% * W * D / ((W + 1000L) * D0).

[0103] Table 3 As can be seen from Table 3, the active material layer in the electrode of this application includes fibrous material. Multiple grooves are spaced apart on the surface of the active material layer away from the current collector. When the electrode is subjected to repeated bending tests, the number of repeated bending cycles when the internal resistance of the electrode is 5 times the initial internal resistance is 10,000 to 200,000. The electrode has excellent bendability, which can effectively improve the lithium-ion transport rate and the rate capability of the electrode. It also effectively improves the dynamic performance of the electrode while minimizing the impact on the energy density of the secondary battery, significantly improving the flexibility and rate performance of the secondary battery.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, characterized in that, The electrode includes a current collector and an active material layer on at least one surface of the current collector, the active material layer having a plurality of spaced grooves on the surface away from the current collector. The electrode includes a conductive agent, the conductive agent includes a first conductive agent, and the first conductive agent comprises a fibrous material; The electrode is subjected to repeated bending tests. The number of repeated bending tests when the internal resistance of the electrode is 5 times the initial internal resistance is n, where 10000≤n≤200000.

2. The secondary battery according to claim 1, characterized in that, Satisfy at least one of the following conditions (1) to (4): (1) The aspect ratio of the fiber material is 20 to 100; (2) The fiber material includes at least one of carbon nanotubes, carbon fibers, metallized glass fibers, and metallized polymer nanofibers; (3) The first conductive agent has a mass percentage content of 30-100% in the conductive agent; (4) The conductive agent has a mass percentage content of 0.5% to 2% in the active material layer.

3. The secondary battery according to claim 1, characterized in that, The conductive agent further comprises a second conductive agent, which includes at least one of carbon black, acetylene black, and graphite; the second conductive agent comprises 0-70% by mass in the conductive agent.

4. The secondary battery according to claim 1, characterized in that, The electrode sheet satisfies: -422400≤100*W*D-(1000*L+W)*D0≤-7360 and 0.5≤D / D0≤0.9; Wμm is the width of the groove; Dμm is the depth of the groove; L mm is the spacing between adjacent grooves; D0μm is the thickness of the active material layer.

5. The secondary battery according to claim 4, characterized in that, The electrode sheet satisfies: 2*W / D-1≤0.

6. The secondary battery according to claim 4, characterized in that, The electrode sheet satisfies the following condition: L / R≤0.2, where R mm is the minimum bending radius of the electrode sheet.

7. The secondary battery according to any one of claims 4 to 6, characterized in that, Satisfy at least one of the following conditions (5) to (9): (5)10≤W≤75； (6)10≤D≤150； (7)1≤L≤5； (8)20≤D0≤200； (9)5≤R≤30。 8. The secondary battery according to claim 1, characterized in that, The electrode also includes a binder, which includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, chitosan, guar gum, and xanthan gum.

9. The secondary battery according to claim 1, characterized in that, The adhesive comprises a first adhesive and a second adhesive in a mass ratio of 1:(0.25-4), wherein the first adhesive comprises at least one of polypropylene and carboxymethyl cellulose; and the second adhesive comprises at least one of styrene-butadiene rubber, sodium alginate, chitosan, guar gum, and xanthan gum; and / or The binder comprises 1-3% by mass in the electrode.

10. An electrical device, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 9, wherein the secondary battery serves as the power supply for the electrical device.

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