Negative pole piece, secondary battery and electric device

Abstract

The invention discloses a negative pole piece, a secondary battery and a power utilization device, and belongs to the technical field of batteries, the negative pole piece comprises a negative current collector, and a metal layer and an insulating layer which are sequentially arranged on at least one surface of the negative current collector, and the insulating layer and the metal layer are provided with a plurality of pore structures. The lithium-containing metal layer and the insulating layer are provided with the pore structures, so that the quality and the thickness of the negative electrode plate can be effectively reduced, the energy density of the secondary battery can be effectively improved, pre-lithiation is not needed, a porous conductive substrate is not needed to be introduced, and the lithium-containing metal layer and the insulating layer can be effectively protected. According to the present invention, the negative electrode plate has characteristics of high lithium affinity and high utilization rate of the pore structure, can effectively reduce the volume expansion of the negative electrode plate, provides the sufficient space for the deposition of the lithium, ensures the deposition of the lithium in the pore structure, effectively avoids the occurrence of the internal lithium precipitation and the surface lithium precipitation, reduces the lithium dendrites, and effectively improves the cycle stability of the secondary battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode plate, a secondary battery and an electrical device. Background Art

[0002] The negative electrode of a secondary battery has the highest specific capacity and lowest potential, making it the ultimate means of increasing the energy density of secondary batteries. Lithium metal is a commonly used negative electrode in secondary batteries, but metal negative electrodes face numerous challenges, severely restricting their large-scale application.

[0003] Lithium metal has active chemical properties and easily reacts continuously with the electrolyte, resulting in rapid consumption of the electrolyte and lithium and the formation of a large amount of by-products, increased battery impedance, and rapid cycle decay; lithium metal is unevenly deposited and forms dendrites, which not only causes severe volume expansion of the negative electrode, but also the dendrites are easy to puncture the diaphragm and fall off, posing serious safety risks.

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

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a negative electrode plate, a secondary battery and an electrical device, which can effectively avoid internal and surface lithium deposition in the negative electrode plate, reduce the volume expansion of the negative electrode plate, and effectively improve the cycle life of the secondary battery.

[0006] To achieve the above objectives, the first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a metal layer and an insulating layer sequentially disposed on at least one surface of the negative electrode current collector; the insulating layer and the metal layer are provided with a plurality of pore structures, the pore structures penetrating the insulating layer and extending to the metal layer;

[0007] The metal layer includes at least one of lithium and a lithium alloy.

[0008] As an embodiment of the present application, the negative electrode sheet satisfies: 1<(1+D / R) 2 ≤2;

[0009] Rμm is the longest distance between adjacent insulating layers;

[0010] D μm is the shortest distance between adjacent pore structures.

[0011] As an embodiment of the present application, the R satisfies: 10≤R≤100; and / or

[0012] The D satisfies: 1≤D≤40.

[0013] As an embodiment of the present application, the shape of the pore structure is one of cylindrical and conical; or

[0014] The hole structure is cylindrical on the insulating layer and is conical on the metal layer.

[0015] As an embodiment of the present application, the ratio of the depth of the hole structure extending into the metal layer to the thickness of the metal layer is 0.5-1.

[0016] As an embodiment of the present application, the thickness of the metal layer is 1 to 200 μm.

[0017] As an embodiment of the present application, the thickness of the insulating layer is 0.1 to 10 μm.

[0018] As an embodiment of the present application, the mass percentage of lithium element in the metal layer is ≥5%; and / or

[0019] The insulating layer includes at least one of lithium oxide, lithium nitride, lithium fluoride, lithium hydroxide, lithium carbonate, aluminum oxide, silicon dioxide, lithium oxide, polyacrylonitrile, polypropylene, polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, and polyurethane.

[0020] A second aspect of the present application provides a secondary battery comprising the negative electrode plate described above.

[0021] A third aspect of the present application provides an electrical device comprising the secondary battery described above.

[0022] The beneficial effects of the present invention are as follows: the negative electrode plate described in the present application includes a negative electrode current collector and a metal layer and an insulating layer sequentially arranged on at least one surface of the negative electrode current collector, and a plurality of pore structures are provided on the insulating layer and the metal layer, and the pore structure penetrates the insulating layer, and the pore structure extends to the metal layer. The present application sets a pore structure on the lithium-containing metal layer and the insulating layer, which can effectively reduce the mass and thickness of the negative electrode plate, effectively improve the energy density of the secondary battery, and does not require pre-lithiation or the introduction of a porous conductive matrix. It has a high affinity for lithium and a high utilization rate of the pore structure, which can effectively reduce the volume expansion of the negative electrode plate, provide sufficient space for the deposition of lithium, ensure that lithium is deposited inside the pore structure, effectively avoid internal lithium deposition and surface lithium deposition, reduce lithium dendrites, and effectively improve the cycle stability of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the negative electrode sheet according to one embodiment of the present invention.

[0024] Figure 2 Schematic diagram of the structure of the negative electrode sheet according to another embodiment of the present invention.

[0025] Figure 3 Schematic diagram of the structure of a negative electrode sheet according to another embodiment of the present invention.

[0026] Figure 4 Schematic diagram of the structure of a negative electrode sheet according to another embodiment of the present invention.

[0027] Figure 5 Schematic diagram of the structure of the negative electrode sheet of the comparative example.

[0028] Markings in the figure: 1. Negative electrode current collector; 2. Metal layer; 3. Insulating layer. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In this 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.

[0031] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0032] Unless otherwise specified, the components, raw materials or instruments used in the embodiments and comparative examples of the present invention are all commercially available raw materials or instruments, and the components and raw materials used in each parallel experiment are all of the same kind.

[0033] The inventors of this application have found that in order to reduce the volume expansion of lithium metal negative electrodes and improve cycle stability, a porous matrix with high conductivity (referred to as a porous conductive matrix) is usually used as a lithium metal negative electrode current collector in the prior art: the porous structure of the porous conductive matrix can provide space for lithium deposition, reducing the volume expansion of the battery; at the same time, the porous conductive matrix has a high specific surface area, which can reduce the local current density, optimize the deposition morphology of lithium, and reduce the generation of dendrites. However, the preparation process of the conductive matrix is ​​relatively complicated, and the material is usually a conductive carbon material, a porous metal network material, etc., which has a large volume and mass; resulting in a decrease in battery energy density. At the same time, the porous conductive matrix has a weak affinity for lithium: complex lithium-affinity modification is required, such as coating the conductive matrix surface with a lithium-affinity oxide, a lithium-affinity metal layer, etc., to ensure that lithium can be deposited in the reserved pore structure. In addition, the porous conductive matrix needs to be pre-lithiated in advance when used, such as melt infiltration, mechanical rolling composite method, in-situ deposition method, etc., to ensure high initial efficiency of the battery; but the preparation process is complicated and not suitable for scale.

[0034] Therefore, based on the above questions, Figure 1 As shown, an embodiment of the present application provides a negative electrode sheet, comprising a negative electrode current collector 1 and a metal layer 2 and an insulating layer 3 sequentially disposed on at least one surface of the negative electrode current collector; a plurality of pore structures are provided on the insulating layer and the metal layer, the pore structures penetrating the insulating layer and extending to the metal layer;

[0035] The metal layer includes at least one of lithium and a lithium alloy.

[0036] The negative electrode plate described in the present application includes a negative electrode current collector and a metal layer and an insulating layer sequentially arranged on at least one surface of the negative electrode current collector, and a plurality of pore structures are provided on the insulating layer and the metal layer, and the pore structure penetrates the insulating layer and extends to the metal layer. The present application sets a pore structure on the lithium-containing metal layer and the insulating layer, which can effectively reduce the mass and thickness of the negative electrode plate and effectively improve the energy density of the secondary battery. There is no need for pre-lithiation and the introduction of a porous conductive matrix. It has a high affinity for lithium and a high utilization rate of the pore structure. It can effectively reduce the volume expansion of the negative electrode plate and provide sufficient space for the deposition of lithium, ensuring that lithium is deposited inside the pore structure, effectively avoiding internal lithium deposition and surface lithium deposition, reducing lithium dendrites, and effectively improving the cycle stability of the secondary battery.

[0037] In some embodiments, the negative electrode plate satisfies: 1<(1+D / R) 2 ≤2, for example, it can be 1.001, 1.01, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range consisting of any two values ​​therein;

[0038] Rμm is the longest distance between adjacent insulating layers;

[0039] D μm is the shortest distance between adjacent pore structures.

[0040] The inventors of this application have found that the longest distance (R) between adjacent insulating layers and the shortest distance (D) between adjacent pore structures can affect the performance of the negative electrode sheet, and thus affect the performance of the secondary battery. This application controls the longest distance (R) between adjacent insulating layers and the shortest distance (D) between adjacent pore structures to satisfy: 1 ​​< (1 + D / R) 2 ≤2, which can ensure that the negative electrode sheet has sufficient space for lithium deposition, while improving the stability of the negative electrode sheet, avoiding the increase of foot current, reducing lithium dendrites, promoting the deposition and extraction of lithium elements, avoiding the collapse of pore structure, improving the wettability of the electrolyte to the negative electrode sheet, effectively reducing the volume expansion of the negative electrode sheet, and improving the cycle life.

[0041] In some embodiments, the negative electrode plate satisfies: 1.21≤(1+D / R) 2 ≤1.96.

[0042] In some embodiments, the R satisfies: 10≤R≤100, for example, it can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 64, 70, 75, 80, 85, 90, 95, 100 or a range consisting of any two of these values; by controlling R within this range, the specific surface area can be increased, the wettability of the electrolyte can be improved, the impedance can be reduced, and the cycle life of the secondary battery can be increased.

[0043] In some embodiments, the D satisfies: 1≤D≤40, for example, it can be 1, 2, 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40 or a range consisting of any two of these values. By controlling D within this range, the structural stability of the negative electrode sheet can be improved, the energy density can be increased, the utilization rate of the pore structure can be improved, the volume expansion of the negative electrode sheet can be reduced, the deposition and extraction of lithium elements can be promoted, and the cycle life of the secondary battery can be effectively improved.

[0044] In some embodiments, such as Figure 1 、 Figure 2 As shown, the shape of the pore structure is cylindrical. By setting the pore structure to be cylindrical, it has a higher pore volume, which can more effectively improve the deposition effect of lithium elements and promote the deposition and removal of lithium elements.

[0045] In some embodiments, such as Figure 3As shown, the hole structure is cylindrical on the insulating layer and conical on the metal layer. By setting it in this way, internal lithium deposition and surface lithium deposition are avoided, lithium dendrites are reduced, and impedance can be further reduced.

[0046] In some embodiments, such as Figure 4 As shown, the shape of the pore structure is conical. By setting the pore structure to be conical, the structural stability of the negative electrode plate can be improved, the wetting effect of the electrolyte on the negative electrode plate can be improved, and the rate performance can be improved.

[0047] In the present application, the hole structure is achieved by laser drilling and / or mechanical drilling.

[0048] In the present application, the method of forming the insulating layer includes but is not limited to evaporation, ion sputtering, electrochemical deposition, in-situ reaction, coating, and transfer.

[0049] Exemplarily, the insulating layer may be formed by the following method:

[0050] 1. In-situ reaction method: Polish the surface of the metallic lithium to remove the original impurity layer; expose it to a reaction environment (such as standing in an oxygen atmosphere, or coating the surface with a trace amount of polar solvent), react for a certain period of time, clean and dry it, and complete the preparation of the insulating layer.

[0051] 2. Coating method: Inorganic fillers are mixed with adhesives, polymers, etc. to prepare slurry, or without adding inorganic fillers, polymer slurry or melt is directly used: Method 1, directly applied to the surface of lithium metal, methods include but are not limited to coating, spraying, dipping, etc., after drying and solidification, strong adhesion, simple operation, suitable for solvent systems that are stable to lithium; Method 2, first apply to the surface of a blank substrate, methods include but are not limited to coating, spraying, dipping, sputtering, evaporation, in situ polymerization, etc., after drying and solidification, transfer to the surface of the negative electrode, and a wide range of applicable solvent systems.

[0052] In some embodiments, the pore structure extends to the depth of the metal layer (e.g. Figures 1 to 4 The ratio of S) to the thickness of the metal layer is 0.5 to 1, for example, it can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or a range consisting of any two of these values. By controlling the ratio of the depth of the pore structure extending to the metal layer to the thickness of the metal layer within this range, the pore structure in the metal layer can provide sufficient space for lithium deposition, reduce volume expansion, and inhibit dendrite formation.

[0053] In some embodiments, the thickness of the metal layer is 1 to 200 μm, for example, it can be 1 μm, 2 μm, 4 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 160 μm, 180 μm, 200 μm or a range consisting of any two of these values. By controlling the thickness of the metal layer within this range, when the thickness of the metal layer is too small, it cannot provide sufficient space for lithium deposition, resulting in increased volume expansion and dendrite formation; when the thickness of the metal layer is too large, the high thickness and large mass brought by the negative electrode will cause the battery energy density to decrease.

[0054] In some embodiments, the metal layer has a thickness of 10 to 100 μm.

[0055] In some embodiments, the thickness of the insulating layer is 0.1 to 10 μm, for example, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm or a range consisting of any two of these values. By controlling the thickness of the insulating layer within this range, it can be ensured that the insulating layer has good mechanical strength and insulation, avoids dendrite puncture, maintains structural stability, and also avoids the problem of decreased energy density due to increased volume and mass caused by an overly thick insulating layer.

[0056] In some embodiments, the insulating layer has a thickness of 1 to 5 μm.

[0057] In some embodiments, the mass percentage of lithium element in the metal layer is ≥5%.

[0058] In some embodiments, the lithium alloy includes at least one of lithium aluminum alloy, lithium magnesium alloy, lithium indium alloy, lithium gallium alloy, lithium tin alloy, lithium zinc alloy, lithium magnesium aluminum alloy, lithium aluminum silicon copper alloy, lithium zinc silver tin alloy, and lithium magnesium aluminum zinc silicon alloy.

[0059] In some embodiments, the insulating layer includes at least one of lithium oxide, lithium nitride, lithium fluoride, lithium hydroxide, lithium carbonate, aluminum oxide, silicon dioxide, lithium oxide, polyacrylonitrile, polypropylene, polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, and polyurethane.

[0060] In some embodiments, the electronic conductivity of the insulating layer is 10 -18 ~10 -8 s / cm.

[0061] In some embodiments, the thickness of the negative electrode current collector is 1 to 20 μm, for example, it can be 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm or a range consisting of any two values ​​therein.

[0062] In the present application, there is no particular limitation on the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, conductive carbon, graphene, foamed copper or a composite current collector.

[0063] One embodiment of the present application provides a secondary battery, comprising the negative electrode sheet described above.

[0064] In one embodiment, the secondary battery includes a positive electrode sheet, the positive electrode sheet 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.

[0065] In one embodiment, the positive electrode active material may be a positive electrode active material for secondary batteries known in the art.

[0066] As non-limiting examples, the positive electrode active material may include lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials or substances, and other traditional materials or substances that can be used as secondary battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, non-limiting examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0067] In one embodiment, the positive electrode active material layer further includes a binder and a conductive agent.

[0068] In some embodiments, the type of the positive electrode current collector is not particularly limited, and the positive electrode current collector can be any material known to be suitable for use as a positive electrode current collector.

[0069] In some embodiments, 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.

[0070] The form of the positive electrode current collector is not particularly limited. 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 coil, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may be in the form of, but not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0071] In some embodiments, the type of the conductive agent mentioned in the present application is not limited, and known conductive agents can be used.

[0072] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0073] In some embodiments, the type of the binder mentioned in this application is not limited, and known binders can be used.

[0074] In some embodiments, the binder mentioned 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 hydride, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0075] In some embodiments, the secondary battery further comprises an electrolyte, the type of which is also not specifically limited. The electrolyte comprises an electrolyte salt and an organic solvent, the specific types of which are not specifically limited and can be selected based on actual needs. The electrolyte may further comprise additives, the types of which are not particularly limited and may include film-forming additives for the positive and / or negative electrodes, or additives that improve certain battery properties, such as high or low temperature performance.

[0076] In the secondary battery mentioned in this application, a separator is usually provided between the positive electrode and the negative electrode to prevent short circuit. There is no particular limitation on the material and shape of the separator, as long as it does not significantly impair the effect of this application.

[0077] In one embodiment, the separator comprises a porous sheet or non-woven fabric having excellent liquid retention. Materials for the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like.

[0078] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned diaphragm can be used alone or in any combination.

[0079] In some embodiments, the secondary battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0080] In some embodiments, 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0081] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0082] 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.

[0083] 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 to these.

[0084] The following examples are provided to facilitate understanding of the present invention. These examples are not provided to limit the scope of the claims.

[0085] Example 1

[0086] A preparation method of a secondary battery comprises the following steps:

[0087] (1) Preparation of negative electrode sheet:

[0088] Using 8μm copper foil as the negative electrode current collector, lithium foil was roll-pressed onto the copper foil surface to form a 20μm thick lithium metal layer on the copper foil surface;

[0089] Alumina and polyacrylonitrile were dispersed in dimethylformamide (DMF) at a mass ratio of 1:4 and stirred thoroughly to form a slurry with a solid content of 20%. The slurry was coated on the surface of a PET film and dried at 60°C for 6 hours. The PET film was removed to obtain an insulating layer with a thickness of 1 μm.

[0090] An insulating layer is placed on the surface of the lithium metal layer and rolled onto the surface of the lithium metal layer to obtain a composite membrane. The composite membrane is rolled using a roller with a needle. The shape of the needle is cylindrical (with a diameter of 50 μm and a depth (also known as height) of 17 μm). The spacing D of the pore structure formed by rolling is controlled to be 10 μm to obtain a negative electrode sheet.

[0091] Among them, the thickness of the negative electrode collector of this embodiment is 8μm, the thickness of the lithium metal layer is 20μm, the thickness of the insulating layer is 1μm, D=10μm, R=50μm, S=17-1μm=16μm, and the ratio of the depth of the pore structure extending to the metal layer to the thickness of the metal layer is recorded as M, M=0.8.

[0092] The parameters of the negative electrode are shown in Table 1.

[0093] (2) Preparation of positive electrode: lithium cobalt oxide, PVDF (polyvinylidene fluoride), and SP (conductive carbon black) were added to NMP (N-methylpyrrolidone) in a mass ratio of 90:5:5. After stirring for 4 hours, the mixed slurry was evenly coated on the surface of aluminum foil and dried at 80°C in a vacuum oven for 8 hours to obtain a positive electrode. The surface capacity was 3 mAh / cm 2 .

[0094] (3) Diaphragm: PE (polyethylene) film, thickness 16 μm.

[0095] (4) Preparation of electrolyte: Ethylene carbonate (EC): diethyl carbonate (DEC): fluoroethylene carbonate (FEC) were mixed in a ratio of 30:70:5. The molecular sieve is used to remove water to obtain a mixed solvent, and LiPF6 with a final concentration of 1 M is added to the mixed solvent and stirred to obtain an electrolyte.

[0096] (5) Assembly of secondary batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets to provide safety isolation, and stack the sheets to obtain an electrode assembly; place the electrode assembly in a packaging shell, inject the electrolyte, and package to obtain a secondary battery.

[0097] Examples 2 to 4

[0098] The difference between Examples 2 to 4 and Example 1 is that the thickness of the insulating layer is adjusted, as shown in Table 1.

[0099] Example 5

[0100] The difference between Example 5 and Example 1 is that the thickness of the lithium metal layer is adjusted, as shown in Table 1.

[0101] Examples 6 to 8

[0102] The difference between Examples 6 to 8 and Example 1 is that the depth of the cylindrical needle roller (i.e., the height of the cylindrical needle roller) is adjusted, and then the S value is adjusted, and thus the M value is adjusted, as shown in Table 1.

[0103] Examples 9 to 14

[0104] The difference between Examples 9 to 14 and Example 1 is that the spacing D of the hole structure formed by rolling and / or the diameter of the cylindrical needle are adjusted, thereby adjusting the D value and / or R value of the negative electrode sheet, as shown in Table 1.

[0105] Example 15

[0106] The difference between Example 15 and Example 1 is that the cylindrical needle roller is adjusted to a conical shape (the diameter and depth remain unchanged); the positive electrode surface capacity used is 1 mAh / cm 2 .

[0107] Example 16

[0108] The difference between Example 16 and Example 1 is that in Example 16, the cylindrical needle roller is replaced by a needle roller with a cylindrical upper portion (diameter = 50 μm, height 1 μm, corresponding to the thickness of the insulating layer) and a conical lower portion (depth 16 μm), thereby forming a Figure 4 The negative electrode sheet shown; the positive electrode surface capacity used is 1mAh / cm 2 .

[0109] Comparative Example 1

[0110] The difference between Comparative Example 1 and Example 1 is that the preparation method of the negative electrode plate is different, Comparative Example 1 does not contain an insulating layer, and Comparative Example 1 does not contain a pore structure.

[0111] Preparation of the negative electrode sheet of this comparative example:

[0112] An 8 μm copper foil was used as the negative electrode current collector, and a lithium foil was roll-pressed and laminated on the surface of the copper foil to form a lithium metal layer with a thickness of 20 μm on the surface of the copper foil to obtain a negative electrode sheet.

[0113] Comparative Example 2

[0114] The difference between Comparative Example 2 and Example 1 is that the preparation method of the negative electrode plate is different, and Comparative Example 2 does not contain a porous structure.

[0115] Preparation of the negative electrode sheet of this comparative example:

[0116] Using 8μm copper foil as the negative electrode current collector, lithium foil was roll-pressed onto the copper foil surface to form a 20μm thick lithium metal layer on the copper foil surface;

[0117] Alumina and polyacrylonitrile were dispersed in dimethylformamide (DMF) in a mass ratio of 1:4, and the mixture was stirred and dispersed to form a slurry with a solid content of 20%. The slurry was coated on the surface of a PET film, dried at 60°C for 6 hours, and the PET film was removed to obtain an insulating layer with a thickness of 1 μm to obtain a negative electrode.

[0118] Comparative Example 3

[0119] The difference between Comparative Example 3 and Example 1 is that the preparation method of the negative electrode plate is different, and the lithium metal layer of Comparative Example 3 does not contain a porous structure.

[0120] (1) Preparation of negative electrode sheet:

[0121] Using 8μm copper foil as the negative electrode current collector, lithium foil was roll-pressed onto the copper foil surface to form a 20μm thick lithium metal layer on the copper foil surface;

[0122] Alumina and polyacrylonitrile were dispersed in dimethylformamide (DMF) at a mass ratio of 1:4 and stirred thoroughly to form a slurry with a solid content of 20%. The slurry was coated on the surface of a PET film and dried at 60°C for 6 hours. The PET film was removed to obtain an insulating layer with a thickness of 1 μm.

[0123] The insulating layer is placed on the surface of the lithium metal layer and rolled onto the surface of the lithium metal layer to obtain a composite membrane. The composite membrane is rolled using a roller with a needle. The needle is cylindrical (with a diameter of 50 μm and a depth (also known as a height) of 1 μm). The spacing D of the pore structure formed by rolling is controlled to be 10 μm, and the following is obtained: Figure 5 The negative electrode is shown.

[0124] Table 1 Parameters

[0125]

[0126]

[0127] Performance Testing

[0128] Number of cycles: The secondary batteries prepared in the comparative examples and the embodiments were repeatedly charged and discharged by the following steps: first, the first charge and discharge were performed in an environment of 25°C, and constant current and constant voltage charging was performed at a charging current of 0.1C (i.e., the current value at which the theoretical capacity is completely discharged within 10 hours) until the upper limit voltage reached 4.5V, and then constant current discharge was performed at a discharge current of 1C until the final voltage reached 3V, and the discharge capacity of the first cycle was recorded; then, charge and discharge cycles were performed until the cycle capacity retention rate was 80%; cycle capacity retention rate = (cycle discharge capacity / first cycle discharge capacity) × 100%.

[0129] Expansion rate measurement: Initial thickness: Before assembling the negative electrode sheet into a secondary battery, use a micrometer to measure the thickness of the center area of ​​the negative electrode sheet. Take 3 points and measure 3 times. The average thickness is taken as the initial thickness T0;

[0130] Thickness after expansion: After the secondary battery is fully charged, disassemble and remove the negative electrode; use a micrometer to measure the thickness of the center area of ​​the electrode, select 3 points, measure 3 times, and the average thickness is the thickness after expansion T1;

[0131] Calculation of expansion rate: (T1-T0) / T0×100%.

[0132] Table 2

[0133]

[0134]

[0135] As can be seen from Table 2, the present invention provides a pore structure on the lithium-containing metal layer and the insulating layer, which can effectively reduce the mass and thickness of the negative electrode sheet, effectively improve the energy density of the secondary battery, and does not require pre-lithiation or the introduction of a porous conductive matrix. It has a high affinity for lithium and a high utilization rate of the pore structure, which can effectively reduce the volume expansion of the negative electrode sheet, provide sufficient space for the deposition of lithium, ensure that lithium is deposited inside the pore structure, effectively avoid internal and surface lithium deposition, reduce lithium dendrites, and effectively improve the cycle stability of the secondary battery.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a metal layer and an insulating layer sequentially provided on at least one surface of the negative electrode current collector; the insulating layer and the metal layer are provided with a plurality of pore structures, the pore structures penetrate the insulating layer and extend to the metal layer; The metal layer includes at least one of lithium and a lithium alloy.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet satisfies: 1<(1+D / R) 2 ≤2; Rμm is the longest distance between adjacent insulating layers; D μm is the shortest distance between adjacent pore structures.

3. The negative electrode sheet according to claim 2, characterized in that: The R satisfies: 10≤R≤100; and / or The D satisfies: 1≤D≤40.

4. The negative electrode sheet according to claim 1, characterized in that: The shape of the hole structure is one of cylindrical and conical; or The hole structure is cylindrical on the insulating layer and is conical on the metal layer.

5. The negative electrode sheet according to claim 1, characterized in that: The ratio of the depth of the hole structure extending into the metal layer to the thickness of the metal layer is 0.5-1.

6. The negative electrode sheet according to claim 1, characterized in that: The thickness of the metal layer is 1 to 200 μm.

7. The negative electrode sheet according to claim 1, characterized in that: The thickness of the insulating layer is 0.1-10 μm.

8. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of lithium element in the metal layer is ≥5%; and / or The insulating layer includes at least one of lithium oxide, lithium nitride, lithium fluoride, lithium hydroxide, lithium carbonate, aluminum oxide, silicon dioxide, lithium oxide, polyacrylonitrile, polypropylene, polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, and polyurethane.

9. A secondary battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The secondary battery according to claim 9 is included.

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