Secondary battery and electric device

Abstract

The application discloses a secondary battery and an electric device, and belongs to the technical field of batteries. The negative electrode sheet comprises a negative electrode current collector, a negative electrode active material layer and a metal layer which are sequentially arranged on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer comprises a body part, the body part has a first end and a second end away from the surface of the negative electrode current collector, the body part extends along the first end and the second end to form a first extension part and a second extension part away from the negative electrode current collector, and the first negative electrode active material layer is located between the first extension part and the second extension part. The application effectively improves the surface lithium precipitation and edge lithium precipitation phenomenon, inhibits the lithium dendrite growth, and effectively improves the energy density and power density of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] The improvement of energy density in rechargeable batteries and the reduction of energy storage costs are currently receiving widespread attention. One direction for developing high-energy-density rechargeable batteries is to increase the thickness of the positive and negative electrode coatings and improve the compaction density of the positive and negative electrode sheets. However, due to the limitations of negative electrode kinetics, increasing the thickness of the negative electrode coating and improving the compaction density will lead to lithium plating on the negative electrode.

[0003] Lithium plating leads to a decrease in the capacity of secondary batteries, a reduction in energy density and power density, and serious jeopardization of safety performance. The formation of lithium dendrites consumes the number of active lithium ions in the battery, directly causing capacity decay. Secondly, fresh lithium dendrites penetrate the SEI film and come into direct contact with the electrolyte, causing more side reactions, resulting in gas production. In severe cases, they can puncture the separator, causing a short circuit between the positive and negative electrodes, leading to fire and explosion of the secondary battery.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery and power device that can effectively improve the phenomena of surface lithium deposition and edge lithium deposition, suppress lithium dendrite growth, and effectively improve the energy density and power density of the secondary battery.

[0006] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer and a metal layer disposed sequentially on at least one surface of the negative electrode current collector.

[0007] The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer; the first negative electrode active material layer includes a body portion, the body portion having a first end and a second end on a surface away from the negative electrode current collector, the body portion extending along the first end and the second end in a direction away from the negative electrode current collector to form a first extension portion and a second extension portion, and the second negative electrode active material layer being located between the first extension portion and the second extension portion.

[0008] As an embodiment of this application, the first negative electrode active material layer includes a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material, satisfying: Dv′ 50 ≥Dv 50 ;

[0009] Among them, Dv 50μm is the particle size corresponding to when the cumulative volume percentage of the first negative electrode active material reaches 50%.

[0010] Dv′ 50 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 50%.

[0011] As an implementation scheme of this application, it satisfies: Dv′ 10 ≥2Dv 10 ;

[0012] Among them, Dv 10 μm is the particle size corresponding to when the cumulative volume percentage of the first negative electrode active material reaches 10%.

[0013] Dv′ 10 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 10%.

[0014] As an implementation scheme of this application, at least one of the following (a) to (d) is satisfied:

[0015] (a) 4≤Dv 50 ≤20;

[0016] (b)6≤Dvˊ 50 ≤20;

[0017] (c)2≤D v10 ≤8;

[0018] (d)4≤Dvˊ 10 ≤16.

[0019] As an implementation scheme of this application, the following condition must be met: 2≤Dv 50 / Dv 10 ≤4.

[0020] As an implementation scheme of this application, at least one of the following (1) to (4) is satisfied:

[0021] (1) The width of the main body is W1, which satisfies: 10.2mm≤W1≤312mm;

[0022] (2) The width of the first extension is W2, which satisfies: 0.1mm≤W2≤6mm;

[0023] (3) The width of the second active material layer is W3, which satisfies: 10mm≤W3≤300mm;

[0024] (4) The width of the second extension is W3, 0.1mm≤W4≤6mm.

[0025] As an implementation scheme of this application, the following condition must be met: d2≥d1;

[0026] Wherein, d1mm is the thickness of the main body;

[0027] d2 mm is the thickness of the second negative electrode active material layer.

[0028] As an implementation scheme of this application, 0 < d1 ≤ 0.3.

[0029] As an implementation scheme of this application, 0 < d2 ≤ 0.3.

[0030] As an embodiment of this application, the metal layer includes at least one of Ni, Pt, Ti, Sr, Pb, Sn, Fe, Ni-based alloys, Fe-based alloys, and Ti-based alloys.

[0031] As an embodiment of this application, the thickness of the metal layer is 0.5 to 30 nm.

[0032] As an embodiment of this application, the first negative electrode active material layer includes a first conductive agent; the first conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers.

[0033] As an embodiment of this application, the second negative electrode active material layer includes a second conductive agent; the second conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers.

[0034] A second aspect of this application provides an electrical device comprising the aforementioned secondary battery.

[0035] The beneficial effects of this application are as follows: This application forms a special electrode structure by setting a first negative electrode active material layer and a second negative electrode active material layer, with a first extension, a second extension, and a body portion as the first negative electrode active material layer, and the second negative electrode active material layer located between the first extension and the second extension. A metal layer is then disposed on the surface of the active material layer. The setting of the first extension and the second extension can effectively improve the lithium intercalation kinetics, effectively promote the diffusion of lithium ions from the surface layer to the inner layer of the negative electrode, reduce surface lithium deposition, and improve the edge lithium deposition phenomenon of the electrode, suppressing lithium dendrite growth. The setting of the metal layer can improve the conductivity of the negative electrode, effectively suppress lithium dendrite growth, increase the lithium metal deposition overpotential, effectively suppress lithium metal deposition, promote electron transport, further improve the lithium deposition phenomenon, and effectively improve the energy density and power density of the secondary battery. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the negative electrode of a secondary battery according to an embodiment of this application.

[0037] Figure 2 This is a schematic diagram of the structure of the negative electrode active material layer of a negative electrode sheet according to an embodiment of this application.

[0038] Figure 3 This is a schematic diagram of the negative electrode of a secondary battery according to another embodiment of this application.

[0039] Figure 4 This is a schematic diagram of the negative electrode of the secondary battery in Comparative Example 1 of this application.

[0040] Figure 5 This is a schematic diagram of the negative electrode of the secondary battery in Comparative Example 2 of this application.

[0041] Figure 6 This is a schematic diagram of the negative electrode of the secondary battery in Comparative Example 3 of this application. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] 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.

[0045] like Figure 1 As shown, this application provides a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector 1 and a negative electrode active material layer and a metal layer 2 disposed sequentially on at least one surface of the negative electrode current collector;

[0046] The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer 3; the first negative electrode active material layer includes a body portion 4, the body portion having a first end and a second end on the surface away from the negative electrode current collector, the body portion extending along the first end and the second end in a direction away from the negative electrode current collector to form a first extension portion 5 and a second extension portion 6, and the second negative electrode active material layer being located between the first extension portion and the second extension portion.

[0047] This application constructs a unique electrode structure by setting a first negative electrode active material layer and a second negative electrode active material layer, with a first extension, a second extension, and a body portion forming the first negative electrode active material layer. The second negative electrode active material layer is located between the first extension and the second extension. A metal layer is then disposed on the surface of the active material layers. The first and second extensions effectively improve lithium intercalation kinetics, promote the diffusion of lithium ions from the surface to the inner layer of the negative electrode, reduce surface lithium deposition, and improve edge lithium deposition, thus inhibiting lithium dendrite growth. The metal layer enhances the conductivity of the negative electrode, effectively inhibits lithium dendrite growth, increases the lithium metal deposition overpotential, effectively suppresses lithium metal deposition, promotes electron transport, further improves lithium deposition, and effectively increases the energy density and power density of the secondary battery.

[0048] In one embodiment, the first negative electrode active material layer includes a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material, satisfying: Dv′ 50 ≥Dv 50 ;

[0049] Among them, Dv 50 μm is the particle size corresponding to when the cumulative volume percentage of the first negative electrode active material reaches 50%.

[0050] Dv′ 50 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 50%.

[0051] This application controls the first and second active materials to satisfy: Dv′ 50 ≥Dv 50 This design ensures that the porosity of the first active material layer is less than that of the second active material layer, and that the minimum pore diameter of the first active material layer is also less than that of the second active material layer. As a result, the ion diffusion kinetics of the second active material layer are superior to those of the first active material layer, making it easier for the electrolyte to be wetted, increasing the lithium-ion conduction rate, and thus enabling lithium ions to diffuse from the surface layer to the inner layer. This further improves the surface lithium deposition phenomenon and the electrode edge lithium deposition phenomenon, effectively increasing the energy density and power density of the secondary battery.

[0052] In one implementation, the following condition is satisfied: Dv′ 10 ≥2Dv 10 ;

[0053] Among them, Dv 10 μm is the particle size corresponding to when the cumulative volume percentage of the first negative electrode active material reaches 10%.

[0054] Dv′ 10 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 10%.

[0055] This application controls Dv′ 10 ≥2Dv 10 This further improves the ion transport dynamics of the negative electrode, further improves the wettability of the electrolyte, promotes the diffusion of lithium ions from the surface to the inner layer, reduces surface polarization, and further improves the energy density and power density of the secondary battery.

[0056] It should be noted that the Dv′ mentioned in this application 50 Dv 50 、Dv′ 10 2Dv 10 The test was conducted in accordance with GB-T19077-2016, using a particle size analysis laser diffractometer.

[0057] In one implementation, 4≤Dv 50 ≤20, for example, can be a range of 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, or any two of these values, controlled by Dv. 50 Within this range, the lithium-ion conduction rate can be further improved, the diffusion of lithium ions from the surface to the inner layer can be further promoted, the surface lithium deposition phenomenon and the electrode edge lithium deposition phenomenon can be further improved, and the energy density and power density of the secondary battery can be effectively improved.

[0058] In one implementation, 6≤Dvˊ 50 ≤20; for example, it can be a range of 6, 8, 10, 12, 14, 15, 16, 18, 20, or any two of these values, controlled by Dv′. 50 Within this range, it is possible to improve the wetting time of the electrolyte, reduce the side reactions of the electrolyte, increase the compaction density, further improve the lithium plating phenomenon, and increase the energy density and power density.

[0059] In one implementation, 2≤D v10 ≤8; for example, it can be a range of 2, 3, 4, 5, 6, 7, 8, or any two of these values, controlled by D.v10 Within this range, it is possible to further improve ion transport dynamics, improve ion insertion / extraction pathways, reduce concentration polarization differences, further improve surface lithium deposition, and increase energy density and power density.

[0060] In one implementation, 4≤Dvˊ 10 ≤16, for example, can be a range of 4, 5, 6, 8, 10, 12, 14, 15, 16 or any two of these values, controlled by D. v ′ 10 Within this range, the wettability of the electrolyte can be further improved, the lithium plating phenomenon can be further reduced, and the energy density and power density can be increased.

[0061] In one implementation, the following condition is satisfied: 2≤Dv 50 / Dv 10 ≤4, by controlling Dv 50 / Dv 10 Within this range, the first negative electrode active material has better particle uniformity, the particle pores of the negative electrode active material are maximized, effectively improving the compaction density of the negative electrode active material, increasing the wettability of the electrolyte to the negative electrode active material, effectively reducing interfacial side reactions, reducing gas production in the secondary battery, improving the diffusion path of lithium ions, improving the stability of the negative electrode active material, and improving the stability of the negative electrode active material during the pressing process, thereby effectively improving the cycle performance and rate performance of the secondary battery.

[0062] It should be noted that this application can modify the Dv of the first and second negative electrode active materials by selecting different grades and production batches of the first and second negative electrode active materials, or by using existing methods to change the particle size of the materials. 50 Dv 10 、Dv′ 50 、Dv′ 10 .

[0063] It should be noted that the methods mentioned above for changing the particle size of materials include, but are not limited to, grinding, ball milling, and sieving.

[0064] In one embodiment, the first negative electrode active material layer includes a first conductive agent; the first conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers.

[0065] In one embodiment, the second negative electrode active material layer includes a second conductive agent; the second conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers.

[0066] In one embodiment, the first conductive agent comprises a dotted carbon material, wherein the dotted carbon material comprises carbon black.

[0067] In one embodiment, the second conductive agent comprises a planar carbon material, which includes at least one of carbon nanotubes and graphene.

[0068] The first active material layer contains dot-shaped carbon material, and the second negative electrode active material layer contains planar conductive carbon, which is conducive to building a long-distance conductive network. The kinetic performance of the second negative electrode active material layer is better than that of the first negative electrode active material layer, which is beneficial to improving the overall kinetic performance of the negative electrode sheet under thick coating and high pressure density, improving the capacity utilization of the negative electrode active material, reducing surface concentration polarization, and improving the rate performance of the battery.

[0069] like Figure 2 As shown, in one embodiment, the width of the body portion is W1, which satisfies: 10.2mm≤W1≤312mm. For example, it can be a range of 10.2, 12, 15, 20, 30, 50, 60, 80, 120, 150, 180, 200, 220, 250, 280, 300, 310, 312, or any two of these values.

[0070] In one embodiment, the width of the first extension is W2, which satisfies: 0.1mm≤W2≤6mm, for example, it can be a range of 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6 or any two of these values.

[0071] In one embodiment, the width of the second active material layer is W3, which satisfies: 10mm≤W3≤300mm; for example, it can be a range of 10, 12, 15, 20, 30, 50, 60, 80, 120, 150, 180, 200, 220, 250, 280, 300 or any two of these values.

[0072] In one embodiment, the width of the second extension is W3, 0.1mm≤W4≤6mm, for example, it can be a range of 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6 or any two of these values.

[0073] This application controls the widths of W1, W2, W3, and W4 within the aforementioned range, and controls the widths of the first extension, the second extension, and the second active material layer within this range. During charging, this ensures that there are sufficient negative electrode lithium vacancies at the edges, allowing lithium ions from the positive electrode to be inserted, thus avoiding edge lithium plating and effectively improving cycle performance.

[0074] like Figure 3 As shown, in one embodiment, the following condition is satisfied: d2≥d1. The thickness of the body portion and the thickness of the body portion are controlled within this range. The porosity of the second negative electrode active material layer is larger and the tortuosity is smaller, which makes the lithium ion transport speed in this layer faster. The ion transport dynamics of this layer are higher than those of the first active material layer. The overall ion transport dynamics of the electrode are significantly improved, and the lithium plating phenomenon is further improved.

[0075] Wherein, d1mm is the thickness of the main body;

[0076] d2 mm is the thickness of the second negative electrode active material layer.

[0077] In one implementation, 0 < d1 ≤ 0.3, for example, it can be 0.01, 0.1, 0.2, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3 or a range of any two of these values.

[0078] In one implementation, 0 < d2 ≤ 0.3, for example, it can be 0.01, 0.1, 0.2, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3 or a range of any two of these values.

[0079] As an embodiment of this application, the metal layer includes at least one of Ni, Pt, Ti, Sr, Pb, Sn, Fe, Ni-based alloys, Fe-based alloys, and Ti-based alloys. By employing such metals or alloys, the structure of the metal layer is non-body-centered cubic, while the structure of lithium metal is body-centered cubic, which has excellent conductivity, effectively suppresses lithium dendrite growth, increases lithium metal deposition overpotential, effectively suppresses lithium metal deposition, promotes electron transport and uniform current, and prevents excessive local current.

[0080] In one embodiment, the thickness of the metal layer is 0.5 to 30 nm, for example, it can be 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 28 nm, 30 nm or any two of these values. By controlling the thickness of the metal layer within this range, lithium ion insertion into the first negative electrode active material layer and the second negative electrode active material layer can be promoted, effectively suppressing local lithium deposition and improving lithium plating.

[0081] In one embodiment, the first negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0082] In one embodiment, the first negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, and soft carbon.

[0083] In one embodiment, the second negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0084] In one embodiment, the second negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, and soft carbon.

[0085] In one embodiment, the first negative electrode active material layer further includes a binder.

[0086] In one embodiment, the second negative electrode active material layer further includes a binder.

[0087] In one embodiment, the first conductive agent has a mass percentage content of 0.2%-5% in the first negative electrode active material layer.

[0088] In one embodiment, the mass percentage of the first negative electrode active material in the first negative electrode active material layer is 90%-98%.

[0089] In one embodiment, the second conductive agent has a mass percentage content of 0.5%-5% in the second negative electrode active material layer.

[0090] In one embodiment, the second negative electrode active material has a mass percentage content of 90%-98% in the second negative electrode active material layer.

[0091] In this application, there are no particular restrictions on the negative electrode 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, foamed nickel, foamed copper, or composite current collector, etc.

[0092] In one embodiment, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material.

[0093] In one embodiment, the positive electrode active material may be selected from sodium-iron composite oxides, sodium-cobalt composite oxides, sodium-manganese composite oxides, sodium-nickel composite oxides, sodium-nickel-titanium composite oxides, sodium-nickel-manganese composite oxides, sodium-iron-manganese composite oxides, sodium-nickel-cobalt-manganese composite oxides, sodium-iron phosphate compounds, sodium-manganese phosphate compounds, sodium-cobalt phosphate compounds, lithium nickel cobalt-manganese oxide, and lithium nickel cobalt-aluminum oxide, etc. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0094] In one embodiment, the type of positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0095] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0096] In one embodiment, the positive electrode active material layer further includes a third conductive agent and a binder.

[0097] In one embodiment, the third conductive agent includes at least one of carbon materials such as carbon black, needle coke, carbon nanotubes, and graphene.

[0098] In one embodiment, there is no limitation on the type of adhesive mentioned in this application, and any known positive electrode adhesive can be used.

[0099] In one embodiment, the adhesive includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0100] 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.

[0101] 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.

[0102] In one embodiment, the polyolefin is polyethylene or polypropylene. The materials of the diaphragm described above can be used alone or in any combination.

[0103] In one embodiment, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0104] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] In one embodiment, the type of electrolyte is not specifically limited. The electrolyte includes an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and organic solvent are not specifically limited and can be selected according to actual needs. The electrolyte may also include additives, and the types of additives are not particularly limited. These additives can be film-forming additives for the positive and / or negative electrodes, or additives that can improve certain battery performance characteristics, such as additives that improve the battery's high or low temperature performance.

[0106] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0107] 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.

[0108] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, 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.

[0109] The present application is further illustrated below with specific embodiments:

[0110] Example 1

[0111] A method for preparing a secondary battery includes the following steps:

[0112] (1) Preparation of negative electrode sheet:

[0113] First, the first graphite (first negative electrode active material), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 95:1.5:2:1.5, and water is added and stirred under vacuum to obtain slurry A.

[0114] Then, the second graphite (second negative electrode active material), conductive carbon black, carbon nanotubes, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 95:1:0.5:2:1.5, and water is added and stirred under vacuum to obtain slurry B.

[0115] Using a double-layer coating method, slurry A and slurry B are pumped at a certain speed ratio of 2:3 according to... Figure 1 The negative electrode pattern shown is coated onto the current collector (8μm copper foil). The outlet shape of the coating die restricts the flow of the two slurries. By controlling the flow rate at the outlet, the coating amount can be controlled, thereby changing the thickness. By controlling the shape of the coating die, the W value can be changed. 1、 The widths of W2, W3, and W4;

[0116] Slurry A is coated closely to the current collector (forming the first negative electrode active material layer) and dried using a blower box;

[0117] The composite electrode was pressed using a roller press until the compaction density reached 1.5 g / cm³. 3 The double-layer composite negative electrode sheet was obtained.

[0118] A double-layer composite electrode was coated using a magnetron sputtering coating instrument. In an Ar atmosphere of 8 mTorr, with pure nickel metal as the target material, and a power of 100 W, the negative electrode sheet was obtained after 20 seconds of energization.

[0119] Among them, the first graphite Dv 50 Dv 10 ; Dv′ of the second graphite 50、 Dv′ 10 and W 1、 W2, W3, W4 and d1, d2 are shown in Table 1.

[0120] (2) Preparation of positive electrode sheet

[0121] A slurry was prepared by dispersing lithium iron phosphate cathode material, conductive agent acetylene black, dispersant PVP, and binder polyvinylidene fluoride in NMP at a mass ratio of 97.3:0.6:0.2:1.9. This slurry was then coated onto both sides of aluminum foil. After baking, rolling, and cutting, the cathode sheet (area density 0.22 g / 1540.25 mm²) was obtained. 2 );

[0122] (3) Preparation of electrolyte

[0123] EC and DMC were mixed at a volume ratio of 1:1, and then lithium hexafluorophosphate was added in a glove box to prepare an electrolyte with a concentration of 1 mol / L.

[0124] (4) Assembly of secondary batteries

[0125] The prepared positive electrode sheet, polyethylene separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and welding of the tabs, a bare battery is obtained. The bare battery is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte is injected into the dried battery. After standing, formation, and capacity testing, a secondary battery is obtained.

[0126] Examples 2-7

[0127] Examples 2-7 differ from Example 1 in that the Dv of the first graphite is changed by ball milling the first graphite and the second graphite. 50 Dv 10 ; Dv′ of the second graphite 50 、Dv′ 10 .

[0128] Examples 8-11

[0129] The difference between Examples 8-11 and Example 1 is that W2, W3, and W4 are changed by altering the shape of the coating mold outlet.

[0130] Examples 12-15

[0131] The difference between Examples 12-15 and Example 1 is that the coating amounts of slurry A and slurry B are changed, thereby altering d1 and d2.

[0132] Examples 16-19

[0133] The difference between Examples 16-19 and Example 1 is that the energizing time is changed, thereby changing d3.

[0134] Comparative Example 1

[0135] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain a second active material layer, and the first active material layer of Comparative Example 1 only includes the body portion, such as... Figure 4 As shown.

[0136] Comparative Example 2

[0137] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain a first active material layer, and the width of the second active material layer in Comparative Example 2 is the same as that of the current collector, such as... Figure 5 As shown.

[0138] Comparative Example 3

[0139] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not contain a first extension and a second extension, and the width of the second active material layer in Comparative Example 3 is the same as that of the current collector. Figure 6 As shown.

[0140] Table 1 Parameter Table

[0141]

[0142]

[0143] Performance testing

[0144] Room temperature discharge specific capacity test: At 25±2℃, the secondary batteries obtained from each example and comparative example were subjected to constant current charge and discharge test at a rate of 0.33C in the working range of 2.5 to 3.65V.

[0145] Internal resistance test: The secondary batteries obtained in the examples and comparative examples were subjected to a cycle test. After 10 cycles, the batteries were removed, the SOC of the battery was adjusted to 50%, and the batteries were discharged at a 5C rate for 10 seconds. The voltage difference before and after the discharge was recorded, and the resistance value was obtained using Ohm's law.

[0146] Rate performance test: At 25±2℃, the secondary batteries obtained from each example and comparative example were charged to 3.65V at a charging rate of 0.33C and discharged to 2.5V at a discharging rate of 4C. This was repeated three times, and the average discharge capacity was taken.

[0147] Lithium plating test: At 25±2℃, the secondary batteries obtained in the examples and comparative examples were subjected to constant current charge-discharge test at a 6C rate in the working range of 2.5 to 3.65V. After 10 cycles, the batteries were taken out and charged to 3.65V at a charging rate of 0.33C. The batteries were then disassembled in a drying room and the lithium plating area on the negative electrode surface was calculated.

[0148] Table 2 Performance Test Results

[0149]

[0150] As can be seen from Table 2, this application, by setting a first negative electrode active material layer and a second negative electrode active material layer, and using a first extension, a second extension, and a body portion as the first negative electrode active material layer, and the second negative electrode active material layer located between the first extension and the second extension, can effectively improve lithium intercalation kinetics, effectively promote the diffusion of lithium ions from the surface layer to the inner layer of the negative electrode sheet, reduce surface lithium deposition, improve the edge lithium deposition phenomenon of the first extension and the second extension, and suppress lithium dendrite growth, thereby effectively improving the energy density and power density of the secondary battery.

[0151] As can be seen from the comparison of Examples 1 to 4, this application controls Dv′ 50 ≥Dv 50 This further improves the specific capacity and cycle performance of secondary batteries, and reduces internal resistance and lithium plating area.

[0152] Comparing Examples 1-3 and 5, it can be seen that this application controls Dv′ 10 ≥2Dv 50 This further improves the specific capacity and cycle performance of secondary batteries, and reduces internal resistance and lithium plating area.

[0153] Comparing Examples 1-3 with Examples 6-7, it can be seen that this application controls 4≤Dv 50 ≤20、6≤Dvˊ 50 ≤20、2≤D v10 ≤8、4≤Dvˊ 10 ≤16, further improving the specific capacity and cycle performance of secondary batteries, and reducing internal resistance and lithium plating area.

[0154] Comparing Examples 1, 8 to 11, it can be seen that this application can further improve lithium plating by controlling 0.1≤W2≤6 and 0.1≤W4≤6.

[0155] Comparing Examples 1 and 12-15, it can be seen that controlling d2≥d1 further improves the lithium plating phenomenon.

[0156] Comparative examples 16-19 show that by further optimizing the thickness of the metal layer, the performance of the balanced secondary battery can be further improved. If the thickness is too large within the design range, it will cause an increase in internal resistance and a decrease in capacity retention. If it is too small, there will be a risk of lithium plating.

[0157] 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, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer and a metal layer sequentially disposed on at least one surface of the negative electrode current collector; The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer; the first negative electrode active material layer includes a body portion, the body portion having a first end and a second end on a surface away from the negative electrode current collector, the body portion extending along the first end and the second end in a direction away from the negative electrode current collector to form a first extension portion and a second extension portion, the second negative electrode active material layer being located between the first extension portion and the second extension portion, and the metal layer being located on the surfaces of the first extension portion, the second extension portion, and the second negative electrode active material layer; The metal layer includes at least one of Ni, Pt, Ti, Sr, Pb, Sn, Fe, Ni-based alloys, Fe-based alloys, and Ti-based alloys; The first negative electrode active material layer includes a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material, satisfying: Dv´ 50 ≥Dv 50 ; Among them, Dv 50 The particle size is the size corresponding to a cumulative volume percentage of 50% for the first negative electrode active material, in μm. Dv´ 50 The particle size is the particle size corresponding to a cumulative volume percentage of 50% for the second negative electrode active material, expressed in μm.

2. The secondary battery according to claim 1, characterized in that, Satisfy: Dv´ 10 ≥2Dv 10 ; Among them, Dv 10 The particle size is the size corresponding to a cumulative volume percentage of 10% for the first negative electrode active material, in μm. Dv´ 10 The particle size is the particle size corresponding to a cumulative volume percentage of 10% for the second negative electrode active material, expressed in μm.

3. The secondary battery according to claim 2, characterized in that, Satisfy at least one of the following (a) to (d): (a)4≤Dv 50 ≤20; (b)6≤Dv´ 50 ≤20; (c)2≤D v10 ≤8; (d)4≤Dv´ 10 ≤16。 4. The secondary battery according to claim 2, characterized in that, Satisfy: 2≤Dv 50 / Dv 10 ≤4.

5. The secondary battery according to claim 1, characterized in that, Satisfy at least one of the following (1) to (4): (1) The width of the main body is W1, which satisfies: 10.2mm≤W1≤312mm; (2) The width of the first extension is W2, which satisfies: 0.1mm≤W2≤6mm; (3) The width of the second negative electrode active material layer is W3, which satisfies: 10mm≤W3≤300mm; (4) The width of the second extension is W4, 0.1mm≤W4≤6mm.

6. The secondary battery according to claim 1, characterized in that, Satisfy: d2≥d1; Wherein, d1 is the thickness of the main body, in mm; d2 is the thickness of the second negative electrode active material layer, in mm.

7. The secondary battery according to claim 6, characterized in that, 0 < d1 ≤ 0.3; and / or 0＜d2≤0.3。 8. The secondary battery according to claim 1, characterized in that, The thickness of the metal layer is 0.5~30nm.

9. The secondary battery according to claim 1, characterized in that, The first negative electrode active material layer includes a first conductive agent; the first conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers; and / or The second negative electrode active material layer includes a second conductive agent; the second conductive agent includes at least one of carbon black, graphene, carbon nanotubes, and fumed carbon fibers.

10. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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