Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries, a negative pole piece comprises a negative current collector, and a negative active material layer and a metal layer which are sequentially arranged on at least one surface of the negative 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 surface, far away from the negative electrode current collector, of the body part is provided with a first end and a second end, and the body part extends in the direction far away from the negative electrode current collector along the first end and the second end to form a first extension part and a second extension part; the first negative electrode active material layer is positioned between the first extension part and the second extension part; according to the invention, the phenomena of surface lithium precipitation and edge lithium precipitation are effectively improved, the growth of lithium dendrites is inhibited, and the energy density and power density of the secondary battery are effectively improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] At present, the improvement of secondary battery energy density and the reduction of energy storage cost have attracted wide attention. One of the directions for developing high energy density secondary batteries is to increase the thickness of positive and negative electrode coatings and improve the compaction density of positive and negative electrode sheets. However, due to the limitation of negative electrode kinetics, increasing the thickness of negative electrode coating and improving the compaction density will lead to lithium deposition at the negative electrode.

[0003] Lithium deposition will lead to a decrease in the capacity of secondary batteries, shorten the energy density and power density, and seriously endanger 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 membrane and directly contact the electrolyte, causing more side reactions and gas production. In severe cases, they pierce the diaphragm, causing a short circuit between the positive and negative electrodes, and causing the secondary battery to catch fire and explode.

[0004] In view of this, this application is filed. Summary of the invention

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device that can effectively improve the surface lithium deposition and edge lithium deposition phenomena, inhibit the growth of lithium dendrites, and effectively improve the energy density and power density of the secondary battery.

[0006] To achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer and a metal layer sequentially arranged 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 main body portion, the main body portion has a first end and a second end on a surface away from the negative electrode current collector, the main body portion extends 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 is located between the first extension portion and the second extension portion.

[0008] As an embodiment of the present 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 the present 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 the present 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 the present application, it satisfies: 2≤Dv 50 / Dv 10 ≤4.

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

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

[0022] (2) The width of the first extension portion is W 2 , meet: 0.1mm≤W 2 ≤6mm;

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

[0024] (4) The width of the second extension portion is W 3 , 0.1mm≤W 4 ≤6mm.

[0025] As an implementation scheme of this application, it satisfies: d 2 ≥d 1 ;

[0026] Among them, d 1 mm is the thickness of the main body;

[0027] d 2 mm is the thickness of the second negative electrode active material layer.

[0028] As an implementation scheme of the present application, 0<d 1 ≤0.3.

[0029] As an implementation scheme of the present application, 0<d 2 ≤0.3.

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

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

[0032] As an embodiment of the present 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 vapor-phase carbon fibers.

[0033] As an embodiment of the present 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 vapor-phase carbon fibers.

[0034] A second aspect of the present application provides an electrical device, comprising the secondary battery described above.

[0035] The beneficial effects of the present application are as follows: the present application forms a special electrode structure by setting a first negative electrode active material layer and a second negative electrode active material layer, and using a first extension part, a second extension part and a main body part as the first negative electrode active material layer, and the second negative electrode active material layer is located between the first extension part and the second extension part, and then setting a metal layer on the surface of the active material layer. The setting of the first extension part and the second extension part can effectively improve the lithium insertion dynamics, effectively promote the diffusion of lithium ions from the surface layer to the inner layer of the negative electrode plate, reduce the surface lithium precipitation phenomenon, and improve the edge lithium precipitation phenomenon of the electrode plate, inhibiting the growth of lithium dendrites; the setting of the metal layer can improve the conductivity of the negative electrode plate, effectively inhibit the growth of lithium dendrites, increase the overpotential of lithium metal deposition, effectively inhibit lithium metal deposition, promote electron transmission, further improve the lithium precipitation phenomenon, and effectively improve the energy density and power density of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the negative electrode plate of a secondary battery according to an embodiment of the present application.

[0037] Figure 2 Schematic diagram of the structure of the negative electrode active material layer of the negative electrode plate according to one embodiment of the present application.

[0038] Figure 3 It is a schematic structural diagram of a negative electrode sheet of a secondary battery according to another embodiment of the present application.

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

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

[0041] Figure 6 This is a schematic structural diagram of the negative electrode plate of the secondary battery of Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0043] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0044] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0045] like Figure 1 As shown, an embodiment of the present application provides a secondary battery, including a negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector 1 and a negative electrode active material layer and a metal layer 2 sequentially arranged 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 main body 4, the main body has a first end and a second end on the surface away from the negative electrode current collector, the main body extends 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 is located between the first extension portion and the second extension portion.

[0047] The present application forms a special electrode structure by setting a first negative electrode active material layer and a second negative electrode active material layer, and using a first extension part, a second extension part and a main body part as the first negative electrode active material layer, and the second negative electrode active material layer is located between the first extension part and the second extension part, and then setting a metal layer on the surface of the active material layer. The setting of the first extension part and the second extension part can effectively improve the lithium insertion dynamics, effectively promote the diffusion of lithium ions from the surface layer to the inner layer of the negative electrode plate, reduce the surface lithium precipitation phenomenon, and improve the edge lithium precipitation phenomenon of the electrode plate, inhibiting the growth of lithium dendrites; the setting of the metal layer can improve the conductivity of the negative electrode plate, effectively inhibit the growth of lithium dendrites, increase the overpotential of lithium metal deposition, effectively inhibit lithium metal deposition, promote electron transmission, further improve the lithium precipitation phenomenon, and effectively improve 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] The present invention controls the first active material and the second active material to satisfy: Dv′ 50 ≥Dv 50 , making the porosity of the first active material layer smaller than that of the second active material layer, and at the same time, the minimum pore diameter of the first active material layer is smaller than the minimum pore diameter of the second active material layer, so that the ion diffusion kinetics of the second active material layer is better than that of the first active material layer, making the electrolyte easier to infiltrate, improving the lithium ion conduction rate, and then making the lithium ions diffuse from the surface layer to the inner layer, further improving the surface lithium deposition phenomenon and the lithium deposition phenomenon at the edge of the electrode, and effectively improving the energy density and power density of the secondary battery.

[0052] In one embodiment, Dv′ satisfies: 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 In this way, the ion transfer dynamics of the negative electrode plate are further improved, the wettability of the electrolyte is further improved, the diffusion of lithium ions from the surface to the inner layer is promoted, the surface polarization phenomenon is reduced, and the energy density and power density of the secondary battery are further improved.

[0056] It should be noted that the Dv′ mentioned in this application 50 、Dv 50 , Dv′ 10 、2Dv 10 The test refers to GB-T19077-2016 and is tested using a particle size analysis laser diffractometer.

[0057] In one embodiment, 4≤Dv 50 ≤20, for example, it can be 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20 or a range consisting of any two of them. By controlling Dv 50Within 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 lithium deposition phenomenon at the edge of the electrode can be further improved, and the energy density and power density of the secondary battery can be effectively improved.

[0058] In one embodiment, 6≤Dvˊ 50 ≤20; for example, it can be 6, 8, 10, 12, 14, 15, 16, 18, 20 or a range consisting of any two values ​​therein, by controlling Dv′ 50 Within this range, the time of being wetted by the electrolyte can be improved, the side reactions of the electrolyte can be reduced, the compaction density can be increased, the lithium precipitation phenomenon can be further improved, and the energy density and power density can be increased.

[0059] In one embodiment, 2≤D v10 ≤8; for example, it can be 2, 3, 4, 5, 6, 7, 8 or a range consisting of any two values ​​therein. By controlling D v10 Within this range, the ion transfer kinetics can be further improved, the ion deintercalation path can be improved, the concentration polarization difference can be reduced, the surface lithium precipitation phenomenon can be further improved, and the energy density and power density can be increased.

[0060] In one embodiment, 4≤Dvˊ 10 ≤16, for example, it can be 4, 5, 6, 8, 10, 12, 14, 15, 16 or a range consisting of any two of them. v ' 10 Within this range, the wettability of the electrolyte can be further improved, the lithium precipitation phenomenon can be further improved, and the energy density and power density can be increased.

[0061] In one embodiment, it satisfies: 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 filled to the maximum extent, the compaction density of the negative electrode active material is effectively improved, the wettability of the electrolyte to the negative electrode active material is improved, the interface side reactions are effectively reduced, the gas production of the secondary battery is reduced, the diffusion path of lithium ions is improved, the stability of the negative electrode active material is improved, and the stability of the negative electrode active material during the tableting process is improved, thereby effectively improving the cycle performance and rate performance of the secondary battery.

[0062] It should be noted that the present invention can change the Dv of the first negative electrode active material and the second negative electrode active material by selecting the first negative electrode active material and the second negative electrode active material of different brands and production batches or by treating the negative electrode active material according to the existing method of changing the particle size of the material. 50 、Dv 10 , Dv′ 50 , Dv′ 10 .

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

[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 vapor-phase 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 vapor-phase carbon fibers.

[0066] In one embodiment, the first conductive agent includes a dot-structured carbon material, and the dot-structured carbon material includes carbon black.

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

[0068] Among them, the first active material layer contains a point-structured carbon material, and the second negative electrode active material layer contains a surface-structured 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 of the negative electrode active material, reducing surface concentration polarization, and improving the battery rate performance.

[0069] like Figure 2 As shown, in one embodiment, the width of the main body is W 1 , meet: 10.2mm≤W 1 ≤312 mm, for example, it can be 10.2, 12, 15, 20, 30, 50, 60, 80, 120, 150, 180, 200, 220, 250, 280, 300, 310, 312 or a range consisting of any two of the values.

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

[0071] In one embodiment, the width of the second active material layer is W 3 , meet: 10mm≤W 3 ≤300mm; for example, it can be 10, 12, 15, 20, 30, 50, 60, 80, 120, 150, 180, 200, 220, 250, 280, 300 or a range consisting of any two of the values.

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

[0073] This application is controlled by W 1 , W 2 , W 3 , W 4 The width is within the above range, and the widths of the first extension portion, the second extension portion and the second active material layer are controlled within this range. During the charging process, it is ensured that there are sufficient negative electrode lithium vacancies at the edge to embed lithium ions from the positive electrode, avoid lithium precipitation at the edge, and effectively improve the cycle performance.

[0074] like Figure 3 As shown, in one embodiment, it satisfies: d 2 ≥d 1 , the thickness of the main body and the thickness of the main body are controlled within this range, the porosity of the second negative electrode active material layer is larger and the tortuosity is smaller, so that the lithium ions are transmitted faster in this layer, the ion transport kinetics of this layer is higher than that of the first active material layer, and the overall ion transport kinetics of the electrode is significantly improved, further improving the lithium precipitation phenomenon.

[0075] Among them, d 1 mm is the thickness of the main body;

[0076] d 2 mm is the thickness of the second negative electrode active material layer.

[0077] In one embodiment, 0<d 1 ≤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 consisting of any two of the values.

[0078] In one embodiment, 0<d 2 ≤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 consisting of any two of the values.

[0079] As an implementation scheme of the present application, the metal layer includes at least one of Ni, Pt, Ti, Sr, Pb, Sn, Fe, Ni-based alloy, Fe-based alloy, and Ti-based alloy. By adopting 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, can effectively inhibit the growth of lithium dendrites, increase the overpotential of lithium metal deposition, effectively inhibit lithium metal deposition, promote electron transmission and uniform current, and prevent 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 a range consisting of any two of these values. By controlling the thickness of the metal layer within this range, it is possible to promote the embedding of lithium ions into the first negative electrode active material layer and the second negative electrode active material layer, effectively inhibit local lithium deposition, and improve lithium precipitation.

[0081] In one embodiment, the first negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , spinel structure lithium titanate Li 4 Ti 5 O 12 , at least one of Li-Al alloy and metallic lithium.

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

[0083] In one embodiment, the second negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , spinel structure lithium titanate Li 4 Ti 5O 12 , at least one of Li-Al alloy and metallic lithium.

[0084] In one embodiment, the second negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon beads (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 mass percentage of the first conductive agent in the first negative electrode active material layer is 0.2%-5%.

[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 mass percentage of the second conductive agent in the second negative electrode active material layer is 0.5%-5%.

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

[0091] In the present application, there is no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

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

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

[0094] In one embodiment, the type of the 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 metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper.

[0095] There is no particular restriction on the form of the positive electrode current collector. When the positive electrode current collector is a metal material, the positive electrode current collector may be in the form of metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal plate mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may include but is not limited to a carbon plate, a carbon film, a 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, the type of the binder mentioned in the present application is not limited, and any known positive electrode binder can be used.

[0099] In one embodiment, the binder 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 hydrogenate, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, isotactic-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 the present application, a separator is usually provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator are not particularly limited as long as the effect of the present application is not significantly impaired.

[0101] In one embodiment, the separator includes a porous sheet or non-woven fabric having excellent liquid retention. The materials of the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like.

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

[0103] In one embodiment, the secondary battery may include an outer package, which can be used to encapsulate the electrode assembly and the 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, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

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

[0106] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0107] An embodiment of the present application provides an electric device, comprising the secondary battery described above, wherein the secondary battery serves as a power supply for the electric device.

[0108] Exemplarily, the above-mentioned 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 described below with specific embodiments:

[0110] Example 1

[0111] A method for preparing a secondary battery comprises 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 uniformly mixed in a mass ratio of 95:1.5:2:1.5, and water is added and stirred under vacuum to obtain slurry A;

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

[0115] Use double-layer coating method to mix slurry A and slurry B at a certain pump speed ratio of 2:3. Figure 1 The negative electrode sheet shown in the figure is coated on the current collector (8μm copper foil), and the outlet of the two slurries is restricted by the shape of the coating die outlet; the coating amount can be controlled by controlling the flow rate of the outlet, thereby changing the thickness; by controlling the shape of the coating die, W can be changed 1、 W 2 , W 3 , W 4 Width;

[0116] The slurry A is coated closely to the current collector (forming the first negative electrode active material layer) and dried using an air blower;

[0117] The composite electrode was pressed by a roller press until the compaction density was 1.5 g / cm 3 , obtaining the double-layer composite negative electrode sheet;

[0118] The double-layer composite electrode was coated on the surface by using a magnetron sputtering coating apparatus. In an Ar atmosphere of 8 mTorr, the target material was pure nickel metal. After 20 seconds of power-on at a power of 100 W, a negative electrode was obtained.

[0119] Among them, the Dv of the first graphite 50 、Dv 10 ; Dv′ of the second graphite 50、 Dv′ 10 and W 1、 W 2 , W 3 , W 4 and d 1 d 2 As shown in Table 1.

[0120] (2) Preparation of positive electrode sheet

[0121] The lithium iron phosphate positive electrode material, the conductive agent acetylene black, the dispersant PVP and the binder polyvinylidene fluoride were dispersed in NMP according to the mass ratio of 97.3:0.6:0.2:1.9 to prepare a slurry, which was then coated on both sides of the aluminum foil. After baking, rolling and cutting, the positive electrode sheet (surface density 0.22g / 1540.25mm 2 );

[0122] (3) Preparation of electrolyte

[0123] EC and DMC were mixed in 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 order, with the separator placed between the positive and negative electrode sheets. A bare cell is obtained by winding, hot pressing, and welding the tabs. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10°C for 24 hours. The electrolyte is injected into the dried battery, and a secondary battery is obtained by standing, forming, and dividing the capacity.

[0126] Embodiments 2 to 7

[0127] The difference between Examples 2 to 7 and Example 1 is that the first graphite and the second graphite are ball milled to change the Dv of the first graphite. 50 、Dv 10 ; Dv′ of the second graphite 50 , Dv′ 10 .

[0128] Embodiments 8 to 11

[0129] The difference between Examples 8 to 11 and Example 1 is that the W is changed by changing the shape of the coating die outlet. 2 , W 3 , W 4 .

[0130] Embodiments 12 to 15

[0131] The difference between Examples 12 to 15 and Example 1 is that by changing the coating amount of slurry A and slurry B, d 1 d 2 .

[0132] Embodiments 16 to 19

[0133] The difference between Examples 16 to 19 and Example 1 is that the power-on time is changed, thereby changing d 3 .

[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 a main body, such as Figure 4 shown.

[0136] Comparative Example 2

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

[0138] Comparative Example 3

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

[0140] Table 1 Parameters

[0141]

[0142]

[0143] Performance Testing

[0144] Normal temperature discharge specific capacity test: At 25±2° C., the secondary batteries obtained in the embodiments and comparative examples were subjected to constant current charge and discharge tests at a rate of 0.33C in a working range of 2.5 to 3.65V.

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

[0146] Rate performance test: At 25±2° C., the secondary batteries obtained in the embodiments and comparative examples were charged to 3.65 V at a charge rate of 0.33 C, and discharged to 2.5 V at a discharge rate of 4 C. This was repeated three times, and the average value of the discharge capacity was taken.

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

[0148] Table 2 Performance test results

[0149]

[0150] As can be seen from Table 2, the present application sets a first negative electrode active material layer and a second negative electrode active material layer, and uses the first extension portion, the second extension portion and the main body portion as the first negative electrode active material layer, and the second negative electrode active material layer is located between the first extension portion and the second extension portion. This can effectively improve the lithium insertion dynamics, effectively promote the diffusion of lithium ions from the surface layer to the inner layer of the negative electrode sheet, reduce the surface lithium deposition phenomenon, improve the edge lithium deposition phenomenon of the first extension portion and the second extension portion, and at the same time can inhibit the growth of lithium dendrites, effectively improving the energy density and power density of the secondary battery.

[0151] Comparison of Examples 1 to 4 shows that the present invention controls Dv′ 50 ≥Dv 50 , further improving the specific capacity and cycle performance of the secondary battery, and reducing the internal resistance and lithium plating area.

[0152] Comparing Examples 1 to 3 and 5, it can be seen that the present invention controls Dv′ 10 ≥2Dv 50 , further improving the specific capacity and cycle performance of the secondary battery, and reducing the internal resistance and lithium plating area.

[0153] Comparing Examples 1 to 3 with Examples 6 to 7, it can be seen that the present invention 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 the secondary battery, and reducing the internal resistance and lithium plating area.

[0154] By comparing Examples 1, 8 to 11, it can be seen that the present invention controls 0.1≤W 2 ≤6, 0.1≤W 4 ≤6, which can further improve lithium precipitation.

[0155] Comparison of Examples 1, 12 to 15 shows that by controlling d 2 ≥d 1 , further improving the lithium precipitation phenomenon.

[0156] It can be seen from the comparison of Examples 16 to 19 that the performance of the balanced secondary battery can be further improved by further optimizing the thickness of the metal layer. If the thickness is too large within the design range, it will cause an increase in internal resistance and a decrease in capacity retention rate, while if the thickness is too small, there will be a risk of lithium deposition.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, comprising a negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer and a metal layer sequentially arranged 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 main body portion, the main body portion has a first end and a second end on a surface away from the negative electrode current collector, the main body portion extends 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 is located between the first extension portion and the second extension portion.

2. The secondary battery according to claim 1, characterized in that: 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 μm is the particle size corresponding to when the cumulative volume percentage of the first negative electrode active material reaches 50% Dv′ 50 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 50%.

3. The secondary battery according to claim 2, characterized in that: Satisfy: Dv′ 10 ≥2Dv 10 ; 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% Dv′ 10 μm is the particle size corresponding to when the cumulative volume percentage of the second negative electrode active material reaches 10%.

4. The secondary battery according to any one of claims 2 to 3, characterized in that: Satisfy at least one of the following (a) to (d): (a)4≤Dv 50 ≤20; (b)6≤Dvˊ 50 ≤20; (c)2≤D v10 ≤8; (d)4≤Dvˊ 10 ≤16。 5. The secondary battery according to claim 3, characterized in that: Satisfy: 2≤Dv 50 / Dv 10 ≤4.

6. 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: 10.2 mm ≤ W1 ≤ 312 mm; (2) The width of the first extension portion is W2, which satisfies: 0.1 mm ≤ W2 ≤ 6 mm; (3) The width of the second active material layer is W3, satisfying: 10 mm ≤ W3 ≤ 300 mm; (4) The width of the second extension portion is W3, 0.1 mm ≤ W4 ≤ 6 mm.

7. The secondary battery according to claim 1, characterized in that: Satisfies: d2 ≥ d1; Wherein, d1mm is the thickness of the main body; d2 mm is the thickness of the second negative electrode active material layer.

8. The secondary battery according to claim 7, characterized in that: 0<d1≤0.3; and / or 0<d2≤0.

3.

9. The secondary battery according to claim 1, characterized in that: The metal layer comprises at least one of Ni, Pt, Ti, Sr, Pb, Sn, Fe, Ni-based alloy, Fe-based alloy, and Ti-based alloy; and / or The thickness of the metal layer is 0.5-30 nm.

10. 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 vapor-phase 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 vapor-phase carbon fibers.

11. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 10.

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