Negative electrode sheet, secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application provides a negative electrode plate, a secondary battery, a battery module, a battery pack and an electric device, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer. The second negative electrode film layer comprises a metal element M, and the atomic radius of M is r M The atomic radius of Li Li Meeting #imgabs0#This application can effectively inhibit the precipitation of lithium metal on the surface of the negative electrode, and significantly improve the kinetic performance, cycle performance and safety performance of the secondary battery.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] In recent years, with the application and promotion of secondary batteries in various electronic products and new energy vehicles, their energy density has received more and more attention. However, during the high-rate charging process of secondary batteries, lithium deposition will inevitably occur on the surface of the negative electrode. In addition, when the secondary battery is overcharged, lithium deposition will also occur on the surface of the negative electrode. Summary of the invention

[0003] The purpose of the present application is to provide a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device, which aims to solve the problem of lithium precipitation caused by secondary batteries under high-rate charging and overcharging conditions, effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate, and significantly improve the kinetic performance, cycle performance and safety performance of the secondary battery.

[0004] In a first aspect, the present application provides a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector. The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer being located between the negative electrode current collector and the first negative electrode film layer. The second negative electrode film layer comprises a metal element M, and the atomic radius of M is r M The atomic radius of Li Li satisfy

[0005] The negative electrode film layer of the present application has a multilayer structure, and the second negative electrode film layer contains a metal element M, and the atomic radius of M and Li is slightly different, and the lattice mismatch is relatively small, so that Li is more likely to be solid-dissolved on the surface of M. When the secondary battery is facing high-rate charging and overcharging, the surface of M can serve as a preferential nucleation site for lithium metal, inducing lithium metal to precipitate on the surface of the second negative electrode film layer M, effectively inhibiting the precipitation of lithium metal on the surface of the negative electrode plate, and improving the kinetic performance, cycle performance and safety performance of the secondary battery. When the atomic radius of M and Li is slightly different, the lattice structure of M is more matched with the lattice structure of Li, and Li is more likely to induce nucleation on the surface of M, so it can have a better effect of inhibiting the precipitation of lithium metal on the surface of the negative electrode plate. The negative electrode plate of the present application can effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate, so the secondary battery not only has good kinetic performance, but also has a significantly improved cycle life.

[0006] In any embodiment of the present application, the atomic radius r of M M The atomic radius of Li Li satisfy

[0007] Controlling the difference between the atomic radius of M and Li within an appropriate range can more effectively inhibit the precipitation of lithium metal on the surface of the negative electrode, further improving the kinetic performance, cycle performance and safety performance of the secondary battery.

[0008] In any embodiment of the present application, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al, Sc, Mo, W, Pt, Pd, In, Re, Ir, Ga, Os, V, Zn, Ru, and Rh. Optionally, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, and Al.

[0009] When M is selected from the above metal elements, its lattice structure is more matched with the lattice structure of Li, and Li is more easily induced to nucleate on the surface of M, so it has a better effect of inhibiting the precipitation of lithium metal on the surface of the negative electrode, further improving the kinetic performance, cycle performance and safety performance of the secondary battery.

[0010] In any embodiment of the present application, M is at least located in the main body of the negative electrode film layer.

[0011] In any embodiment of the present application, the second negative electrode film layer includes a first surface and a second surface relative to each other along its thickness direction, the first surface is arranged to face away from the negative electrode current collector, and the second surface is arranged to face the negative electrode current collector, and M is located on the first surface of the second negative electrode film layer facing away from the negative electrode current collector and / or the second surface of the second negative electrode film layer facing the negative electrode current collector.

[0012] In any embodiment of the present application, based on the total mass of the second negative electrode film layer, the mass percentage of M is 3% to 7%. Optionally, the mass percentage of M is 3% to 5%.

[0013] When the mass percentage of M is within a suitable range, it can effectively inhibit the precipitation of lithium metal on the surface of the negative electrode and effectively inhibit the shortening of the cycle life of the secondary battery.

[0014] In any embodiment of the present application, based on the total mass of the first negative electrode film layer, the mass percentage of M is ≤0.5%.

[0015] In any embodiment of the present application, the first negative electrode film layer does not contain the metal element M.

[0016] When the first negative electrode film layer does not contain or substantially does not contain the metal element M, it can effectively ensure that lithium metal is preferentially precipitated on the surface of the second negative electrode film layer M, further inhibiting the precipitation of lithium metal on the surface of the negative electrode sheet. At the same time, lithium metal is preferentially precipitated on the surface of the second negative electrode film layer M, and the first negative electrode film layer on the surface of the second negative electrode film layer can also inhibit the rapid growth of lithium dendrites, thereby further extending the cycle life of the secondary battery.

[0017] In any embodiment of the present application, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1.2. Optionally, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.5 to 0.8.

[0018] The coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is within an appropriate range, which can not only effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate, but also effectively inhibit lithium dendrites from reaching the surface of the negative electrode plate.

[0019] In any embodiment of the present application, the second negative electrode film layer includes metal particles, and the metal particles are selected from one or more of simple particles of M and alloy particles of M.

[0020] In any embodiment of the present application, the alloy of M includes an alloy formed by two or more elements in M, and an alloy formed by one or more elements in M ​​and another metal element M. 1 An alloy formed by one or more elements.

[0021] In any embodiment of the present application, M 1 Including one or more of Fe, Cu, Ni, Cr, and Mn.

[0022] In any embodiment of the present application, the volume average particle size Dv50 of the metal particles is ≤5 μm. Optionally, the volume average particle size Dv50 of the metal particles is ≤1 μm.

[0023] When the volume average particle size Dv50 of the metal particles is controlled within a suitable range, a sufficient number of nucleation sites can be formed in the second negative electrode film layer, thereby effectively inhibiting the precipitation of lithium metal on the surface of the negative electrode plate.

[0024] In any embodiment of the present application, the second negative electrode film layer includes Li-M alloy particles, Li-MM 1 One or more of the alloy particles, M 1 represents a metal element, and M 1 Including one or more of Fe, Cu, Ni, Cr, and Mn.

[0025] A second aspect of the present application provides a secondary battery, which includes the negative electrode plate of the first aspect of the present application.

[0026] A third aspect of the present application provides a battery module, which includes the secondary battery of the second aspect of the present application.

[0027] A fourth aspect of the present application provides a battery pack, which includes the secondary battery of the second aspect of the present application and one of the battery modules of the third aspect.

[0028] A fifth aspect of the present application provides an electrical device, which includes at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0029] The battery module, battery pack and electric device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0031] Figure 1 It is a schematic diagram of one embodiment of the negative electrode plate of the present application.

[0032] Figure 2 It is a schematic diagram of one embodiment of the secondary battery of the present application.

[0033] Figure 3 It is an exploded schematic diagram of one embodiment of the secondary battery of the present application.

[0034] Figure 4 It is a schematic diagram of an embodiment of a battery module of the present application.

[0035] Figure 5 It is a schematic diagram of an embodiment of the battery pack of the present application

[0036] Figure 6 yes Figure 5 Exploded diagram of .

[0037] Figure 7 It is a schematic diagram of an embodiment of an electric device using the secondary battery of the present application as a power source.

[0038] Figure 8 This is a scanning electron microscope image of the cross section of the negative electrode sheet of Example 1.

[0039] In the accompanying drawings, the drawings may not be drawn according to the actual scale. The description of the accompanying drawings numerals is as follows:

[0040] 1 Battery Pack

[0041] 2 upper box

[0042] 3 lower box

[0043] 4 Battery Module

[0044] 5 Secondary batteries

[0045] 51 Housing

[0046] 52 Electrode assembly

[0047] 53 Cover

[0048] 10 Negative electrode

[0049] 11. Negative electrode current collector

[0050] 121 First negative electrode film layer

[0051] 122 second negative electrode film layer

[0052] 1221 First Surface

[0053] 1222 second surface. DETAILED DESCRIPTION

[0054] Below, the embodiments of the negative electrode plate, secondary battery, battery module, battery pack and electric device of the present application are specifically disclosed with appropriate reference to the drawings in detail. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0058] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0060] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] Secondary battery

[0062] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can continue to be used by activating the active materials by recharging them after they are discharged.

[0063] Normally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the charge and discharge process of a secondary battery, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of conducting active ions.

[0064] [Negative electrode]

[0065] When a secondary battery is charged, lithium ions are released from the positive electrode and embedded in the negative electrode. However, when a secondary battery is charged at a high rate or overcharged, it is easy to encounter situations such as insufficient negative electrode embedding space, lithium ions being released from the positive electrode too quickly but unable to be embedded in the negative electrode in equal amounts, etc. The lithium ions that cannot be embedded in the negative electrode in time can only obtain electrons on the surface of the negative electrode and be reduced to form lithium metal. This is the lithium precipitation phenomenon. At the same time, when a secondary battery is charged at a high rate or overcharged, the negative electrode polarization is large. When the surface potential of the negative electrode continues to decrease and is lower than the Li / Li+ reference electrode potential, lithium ions will obtain electrons on the surface of the negative electrode and be reduced to form lithium metal. Lithium precipitation not only reduces the performance of the secondary battery, such as significantly shortening the cycle life, but also after the lithium precipitation phenomenon continues to occur, the lithium metal will grow into a tree-like structure, namely lithium dendrites. The growth of lithium dendrites will destroy the solid electrolyte interface (SEI) film on the surface of the negative electrode active material, causing irreversible consumption of active ions; the growth of lithium dendrites will also pierce the isolation membrane to cause internal short circuits, which may cause safety risks such as combustion and explosion. The inventors found that lithium plating occurs mainly because the negative electrode active material is usually a lithium-intercalating material. The lithium-intercalating rate of these lithium-intercalating materials is low, and it is difficult to meet the high-rate charging requirements of secondary batteries. In addition, when the secondary battery is overcharged, these lithium-intercalating materials can hardly prevent the generation of lithium metal on the surface of the negative electrode, resulting in a higher safety risk for the secondary battery.

[0066] In order to solve the problem of lithium deposition in secondary batteries under high-rate charging and overcharging conditions, as well as the resulting shortened cycle life of secondary batteries and increased safety risks, the inventors have further conducted extensive research and provided a negative electrode plate that can effectively inhibit the deposition of lithium metal on the surface of the negative electrode plate, significantly improve the kinetic performance, cycle performance and safety performance of secondary batteries, especially improve the cycle performance and safety performance of secondary batteries under high-rate charging and overcharging conditions.

[0067] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer. The second negative electrode film layer contains a metal element M, and the atomic radius of M is r M The atomic radius of Li Li satisfy

[0068] The negative electrode film layer of the present application has a multilayer structure, and the second negative electrode film layer contains a metal element M, and the atomic radius of M and Li is slightly different and the lattice mismatch is relatively small, so that Li is more likely to be dissolved on the surface of M. The inventors found that after Li is dissolved on the surface of M, the crystal structure of the solid solution formed is similar to the crystal structure of Li, so that the nucleation interface energy of Li on the surface of M is low. The interface energy is the source of nucleation resistance. When the surface nucleation resistance of M is lower, the surface of M can serve as a preferential nucleation site for lithium metal, inducing lithium metal to precipitate on the surface of M instead of on the surface of the negative electrode sheet.

[0069] When the secondary battery faces high-rate charging or overcharging, the negative electrode polarization is large. When the surface potential of the negative electrode is about to drop to the lithium deposition overpotential, because the surface nucleation resistance of M contained in the second negative electrode film layer is lower, its surface lithium deposition overpotential is lower than the surface potential of the negative electrode. Therefore, it can serve as a preferential nucleation site for lithium metal, inducing the precipitation of lithium metal on the surface of the second negative electrode film layer M, effectively inhibiting the precipitation of lithium metal on the surface of the negative electrode, and improving the kinetics, cycle performance and safety performance of the secondary battery.

[0070] When the atomic radius difference between M and Li is small, the lattice structure of M is more matched with the lattice structure of Li, and Li is more likely to induce nucleation on the surface of M, so it can better inhibit the precipitation of lithium metal on the surface of the negative electrode. When the atomic radius difference between M and Li is large, for example, greater than 12%, the lattice mismatch between M and Li is large, and the surface of M cannot serve as a preferential nucleation site for lithium metal, and cannot play the role of inducing lithium metal to preferentially nucleate on the surface of M in the second negative electrode film layer. When the secondary battery is charged at a high rate or overcharged, lithium metal will still precipitate on the surface of the negative electrode, and the safety performance of the secondary battery cannot be effectively guaranteed.

[0071] The negative electrode plate of the present application can realize the safe use of conventional negative electrode active materials under high-rate charging and overcharging conditions; the negative electrode plate of the present application can effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate, so the secondary battery not only has good kinetic performance, but also has a significantly improved cycle life.

[0072] In the present application, the atomic radius of the metal element M and Li can be referred to in Lange's handbook of chemistry.

[0073] In some embodiments, the atomic radius of M is r M The atomic radius of Li Li satisfy

[0074] Controlling the difference between the atomic radius of M and Li within an appropriate range can more effectively inhibit the precipitation of lithium metal on the surface of the negative electrode, further improving the kinetic performance, cycle performance and safety performance of the secondary battery.

[0075] In some embodiments, based on the total mass of the first negative electrode film layer, the mass percentage of M is ≤0.5%. Optionally, the first negative electrode film layer does not contain the metal element M.

[0076] When the first negative electrode film layer does not contain or substantially does not contain the metal element M, it can effectively ensure that lithium metal is preferentially precipitated on the surface of the second negative electrode film layer M, further inhibiting the precipitation of lithium metal on the surface of the negative electrode sheet. At the same time, lithium metal is preferentially precipitated on the surface of the second negative electrode film layer M, and the first negative electrode film layer on the surface of the second negative electrode film layer can also inhibit the rapid growth of lithium dendrites, thereby further extending the cycle life of the secondary battery.

[0077] In some embodiments, based on the total mass of the second negative electrode film layer, the mass percentage of M is 1% to 10%. Optionally, the mass percentage of M is 1% to 9%, 1% to 8%, 1% to 7%, 1% to 6%, 1% to 5%, 1% to 4%, 2% to 9%, 2% to 8%, 2% to 7%, 2% to 6%, 2% to 5%, 2% to 4%, 3% to 9%, 3% to 8%, 3% to 7%, 3% to 6%, 3% to 5%, 3% to 4%, 3.5% to 9%, 3.5% to 8%, 3.5% to 7%, 3.5% to 6%, 3.5% to 5%, or 3.5% to 4.5%.

[0078] When the mass percentage of M is low, the second negative electrode film layer has a small number of nucleation sites. When the secondary battery is facing high-rate charging or overcharging, the second negative electrode film layer has an insignificant effect in suppressing the precipitation of lithium metal on the surface of the negative electrode. When the mass percentage of M is high, the consumption of electrolyte also increases, and since the volume of M expands after Li solid dissolves on the surface of M, the volume expansion of the second negative electrode film layer and the negative electrode will increase, and the cycle life of the secondary battery will be shortened to a certain extent. When the mass percentage of M is within an appropriate range, it can effectively suppress the precipitation of lithium metal on the surface of the negative electrode while effectively suppressing the shortening of the cycle life of the secondary battery.

[0079] In some embodiments, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al, Sc, Mo, W, Pt, Pd, In, Re, Ir, Ga, Os, V, Zn, Ru, and Rh. Alternatively, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, and Al. Further, M is selected from one or more of Nb, Au, Ag, Al, Mg, Ti, Cd, and Zr.

[0080] When M is selected from the above metal elements, its lattice structure is more matched with the lattice structure of Li, and Li is more easily induced to nucleate on the surface of M, so it has a better effect of inhibiting the precipitation of lithium metal on the surface of the negative electrode, further improving the kinetic performance, cycle performance and safety performance of the secondary battery.

[0081] In some embodiments, the second negative electrode film layer includes a main body, and a first surface and a second surface opposite to each other along its thickness direction, the first surface is arranged to face away from the negative electrode current collector, and the second surface is arranged to face the negative electrode current collector, and the main body refers to the negative electrode film layer located between the first surface and the second surface. M is located at one or more positions of the main body of the second negative electrode film layer, the first surface of the second negative electrode film layer facing away from the negative electrode current collector, and the second surface of the second negative electrode film layer facing the negative electrode current collector. For example, (1) M is located only in the main body of the negative electrode film layer, (2) M is located only in the first surface of the second negative electrode film layer facing away from the negative electrode current collector, (3) M is located only in the second surface of the second negative electrode film layer facing the negative electrode current collector, (4) M is located at both the main body of the negative electrode film layer and the first surface of the second negative electrode film layer facing away from the negative electrode current collector, (5) M is located at both the main body of the negative electrode film layer and the second surface of the second negative electrode film layer facing the negative electrode current collector, (6) M is located at both the first surface of the second negative electrode film layer facing away from the negative electrode current collector and the second surface of the second negative electrode film layer facing the negative electrode current collector, (7) M is located at three positions: the main body of the negative electrode film layer, the first surface of the second negative electrode film layer facing away from the negative electrode current collector, and the second surface of the second negative electrode film layer facing the negative electrode current collector.

[0082] In some embodiments, M is located at least in the main portion of the second negative electrode film layer.

[0083] In some embodiments, when M is located on the first surface of the second negative electrode film layer facing away from the negative electrode current collector, M may form a layered structure at the first surface position of the second negative electrode film layer. Optionally, the layered structure is discontinuous. For example, M is distributed in intervals or arrays at the first surface position of the second negative electrode film layer. At this time, on the one hand, it is beneficial for the electrolyte to fully infiltrate the second negative electrode film layer, and on the other hand, it is beneficial for the lithium ions from the positive electrode to be smoothly embedded in the second negative electrode film layer when the secondary battery is charged, and for the lithium ions embedded in the second negative electrode film layer to be fully released and smoothly migrate to the positive electrode when the secondary battery is discharged.

[0084] In some embodiments, when M is located at the second surface of the second negative electrode film layer facing the negative electrode current collector, M may form a layered structure at the second surface position of the second negative electrode film layer. Optionally, the layered structure is discontinuous. For example, M is distributed in intervals or arrays on the second surface of the second negative electrode film layer. At this time, on the one hand, it is beneficial for the second negative electrode film layer to maintain a high bonding strength with the negative electrode current collector to prevent powder from falling, and on the other hand, it is beneficial for the conduction from electrons.

[0085] In some embodiments, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1.2. Optionally, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1, 0.4 to 1, 0.5 to 1, 0.3 to 0.8, 0.4 to 0.8, 0.5 to 0.8, 0.3 to 0.7, 0.4 to 0.7, 0.5 to 0.7, 0.3 to 0.6, 0.4 to 0.6, or 0.5 to 0.6.

[0086] When the coating weight of the first negative electrode film layer is relatively large compared to the second negative electrode film layer, the nucleation sites of the second negative electrode film layer are relatively few, and the effect of inhibiting the precipitation of lithium metal on the surface of the negative electrode plate is not obvious. When the coating weight of the first negative electrode film layer is relatively small compared to the second negative electrode film layer, the thickness of the first negative electrode film layer is relatively small, and the lithium dendrites formed by the second negative electrode film layer are more likely to pass through the first negative electrode film layer to reach the surface of the negative electrode plate, and the risk of short circuit in the battery increases. The coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is within an appropriate range, which can not only effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate, but also effectively inhibit lithium dendrites from reaching the surface of the negative electrode plate.

[0087] In some embodiments, the second negative electrode film layer may include metal particles, and the metal particles are selected from one or more of simple particles of M and alloy particles of M.

[0088] In some embodiments, the alloy of M includes an alloy formed by two or more elements in M, and an alloy formed by one or more elements in M ​​and another metal element M.1 Alternatively, the alloy of M includes an alloy formed by two or more elements in M.

[0089] In some embodiments, M 1 Including one or more of Fe, Cu, Ni, Cr, and Mn.

[0090] In some embodiments, the volume average particle size Dv50 of the metal particles is ≤5 μm. Alternatively, the volume average particle size Dv50 of the metal particles is ≤1 μm. More specifically, the volume average particle size Dv50 of the metal particles is ≤0.5 μm.

[0091] When the volume average particle size Dv50 of the metal particles is controlled within a suitable range, a sufficient number of nucleation sites can be formed in the second negative electrode film layer, thereby effectively inhibiting the precipitation of lithium metal on the surface of the negative electrode plate.

[0092] In the present application, the volume average particle size Dv50 of the material has a well-known meaning in the art and can be measured by methods and instruments known in the art. For example, it can be measured with a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) with reference to GB / T 19077-2016 particle size distribution laser diffraction method.

[0093] In some embodiments, the second negative electrode film layer may include Li-M alloy particles, Li-MM 1 One or more of the alloy particles, M 1 represents a metal element, and M 1 Including one or more of Fe, Cu, Ni, Cr, Mn. Li-M alloy refers to the alloy formed by Li and one or more of the metal elements M. Li-MM 1 Alloy means Li and one or more of the metal elements M and the metal element M 1 An alloy formed by one or more of the above.

[0094] As examples, Li-M alloys are Li-Sn, Li-Bi, Li-Cd, Li-Ti, Li-Nb, Li-Ta, Li-Sb, Li-Hf, Li-Mg, Li-Zr, Li-Ag, Li-Au, Li-Al, Li-Sc, Li-Mo, Li-W, Li-Pt, Li-Pd, Li -One or more of In, Li-Re, Li-Ir, Li-Ga, Li-Os, Li-V, Li-Zn, Li-Ru, Li-Rh, Li-Mg-Al, Li-Mg-Zr, Li-Mg-Zn, Li-Ag-Al, Li-Ag-Zn, Li-Ag-Mg, Li-Ti-Al.

[0095] As an example, Li-MM 1 The alloy is selected from one or more of Li-Mg-Mn, Li-Al-Mn, Li-Al-Fe, Li-Al-Cu, Li-Ti-Ni, and Li-Ti-Cr.

[0096] In some embodiments, the second negative electrode film layer includes the above metal particles, Li-M alloy particles, Li-MM 1 In addition to one or more of the alloy particles, the second negative electrode active material, an optional conductive agent, an optional binder and other optional auxiliary agents may also be included.

[0097] In some embodiments, the first negative electrode film layer includes a first negative electrode active material, an optional conductive agent, an optional binder, and other optional auxiliary agents.

[0098] In some embodiments, the types of the first negative electrode active material and the second negative electrode active material are not specifically limited, and negative electrode active materials for secondary batteries known in the art may be used. The types of the first negative electrode active material and the second negative electrode active material may be the same or different. As an example, the first negative electrode active material and the second negative electrode active material each independently include one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0099] In some embodiments, the type and content of the conductive agent and the binder are not subject to specific restrictions and can be selected according to actual needs. The types of conductive agents of the first negative electrode film layer and the second negative electrode film layer can be the same or different. As an example, the conductive agent may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers. The types of binders of the first negative electrode film layer and the second negative electrode film layer can be the same or different. As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). The types of other optional additives of the first negative electrode film layer and the second negative electrode film layer can be the same or different. As an example, other optional additives may include thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0100] In the negative electrode sheet of the present application, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be selected from one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0101] In some embodiments, the negative electrode film layer is disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0102] Figure 1 A schematic diagram of an embodiment of the negative electrode sheet 10 of the present application is shown. The negative electrode sheet 10 may be composed of a negative electrode current collector 11, a second negative electrode film layer 122 respectively disposed on both sides of the negative electrode current collector 11, and a first negative electrode film layer 121 disposed on the second negative electrode film layer 122, wherein the second negative electrode film layer 122 is located between the negative electrode current collector 11 and the first negative electrode film layer 121. The second negative electrode film layer 122 includes a first surface 1221 and a second surface 1222 opposite to each other along its thickness direction, wherein the first surface 1221 is disposed away from the negative electrode current collector 11, and the second surface 1222 is disposed toward the negative electrode current collector 11.

[0103] Of course, the negative electrode plate 10 of the present application may also have other embodiments. For example, the negative electrode plate 10 is composed of a negative electrode current collector 11, a second negative electrode film layer 122 arranged on one side of the negative electrode current collector, and a first negative electrode film layer 121 arranged on the second negative electrode film layer 122.

[0104] In addition, the negative electrode plate of the present application does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the second negative electrode film layer. In other embodiments, the negative electrode plate of the present application also includes a protective layer covering the surface of the first negative electrode film layer.

[0105] In some embodiments, the preparation method of the negative electrode plate of the present application may include the following steps: forming a second negative electrode film layer on at least one side of the negative electrode current collector, the second negative electrode film layer includes metal particles, and the metal particles are selected from one or more of the elemental particles of M and the alloy particles of M; forming a first negative electrode film layer on the surface of the second negative electrode film layer.

[0106] The negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material and optional conductive agent, optional binder, other optional auxiliary agents, etc. in a solvent and stirring them evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto. In some embodiments, the first negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents can be dispersed in a solvent and stirred evenly to form a first negative electrode slurry, and the second negative electrode active material, metal particles, optional conductive agent, optional binder, and other optional auxiliary agents are dispersed in a solvent and stirred evenly to form a second negative electrode slurry.

[0107] In the method for preparing the negative electrode sheet, the first negative electrode slurry and the second negative electrode slurry can be coated simultaneously at one time or in two times.

[0108] In some embodiments, the first negative electrode slurry and the second negative electrode slurry are coated at the same time. Coating at the same time can improve the adhesion between the first negative electrode film layer and the second negative electrode film layer, help reduce the overall interface resistance of the negative electrode film layer, and further improve the cycle performance of the battery.

[0109] In some embodiments, the preparation method of the negative electrode plate may include the following steps: forming a second negative electrode film layer on at least one side of the negative electrode current collector, forming a layer of metal M on the surface of the second negative electrode film layer, and then continuing to form a first negative electrode film layer, and after cold pressing, M is located on the first surface of the second negative electrode film layer facing away from the negative electrode current collector. Optionally, the layered structure of the metal M is a discontinuous form, for example, in an interval distribution state or an array distribution state. Methods for forming metal M on the surface of the second negative electrode film layer include coating, shot peening, spraying, vapor deposition, etc., but are not limited thereto. For example, the metal M is deposited on the surface of the second negative electrode film layer by vapor deposition. The vapor deposition method can be one or more of atomic layer deposition, chemical vapor deposition, and physical vapor deposition.

[0110] In some embodiments, the preparation method of the negative electrode plate may include the following steps: forming a layer of metal M on at least one side of the negative electrode current collector, then forming a second negative electrode film layer on the surface of the negative electrode current collector, and then forming a first negative electrode film layer on the surface of the second negative electrode film layer, and after cold pressing, M is located on the second surface of the second negative electrode film layer facing the negative electrode current collector. Optionally, the layered structure of the metal M is a discontinuous form, for example, in an interval distribution state or an array distribution state. Methods for forming metal M on the surface of the negative electrode current collector include coating, vapor deposition, gravure process, etc., but are not limited thereto. For example, the metal M is deposited on the surface of the negative electrode current collector by vapor deposition. The vapor deposition method can be one or more of atomic layer deposition, chemical vapor deposition and physical vapor deposition.

[0111] The mass percentage content of M in the second negative electrode film layer can be obtained by the following method.

[0112] The thickness of the first negative electrode film layer and the second negative electrode film layer are obtained by using a scanning electron microscope (e.g., ZEISS Sigma 300). First, the negative electrode sheet is cut into a sample of a certain size (e.g., 2 cm×2 cm), and the negative electrode sheet is fixed on the sample stage by paraffin. Then, the sample stage is placed in the sample holder, locked and fixed, and the power and vacuum (e.g., 10 -4 Pa), set the argon flow rate (e.g. 0.15MPa) and voltage (e.g. 8KV) and polishing time (e.g. 2 hours), adjust the sample stage to the swing mode and start polishing. Sample testing can refer to JY / T010-1996. In order to ensure the accuracy of the test results, multiple (e.g. 5) different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (e.g. 500 times), read the thickness of the first negative electrode film layer and the second negative electrode film layer in the ruler test area, and take the average value of multiple test areas as the test result.

[0113] Since the content of the metal element M in the second negative electrode film layer is low and has little effect on the density of the second negative electrode film layer, it is believed that the densities of the first negative electrode film layer and the second negative electrode film layer are consistent. Furthermore, the coating weight ratio of the first negative electrode film layer and the second negative electrode film layer can be obtained through the thickness ratio of the first negative electrode film layer and the second negative electrode film layer.

[0114] Take a negative electrode sheet that has been coated on one side and cold pressed (if it is a negative electrode sheet coated on both sides, the negative electrode film layer on one side can be wiped off first), cut it into a certain size of test samples (for example, 2cm×2cm), and then scrape the powder; all the obtained powders are tested with an inductively coupled plasma-optical emission spectrometer (ICP-OES) to obtain the mass concentration of the metal element M in the negative electrode film layer; the mass percentage of the metal element M in the second negative electrode film layer is calculated by the coating weight ratio of the first negative electrode film layer and the second negative electrode film layer. In order to ensure the accuracy of the test results, the negative electrode sheet can be cut into multiple test samples of a certain size (for example, 5), and the average value of multiple test samples is taken as the test result.

[0115] [Positive electrode]

[0116] The secondary battery includes a positive electrode sheet, which generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0117] In the positive electrode sheet of the present application, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, the positive current collector may be an aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be selected from one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0118] In the positive electrode sheet of the present application, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for a secondary battery known in the art. As an example, the positive electrode active material may include one or more of a lithium transition metal oxide, a lithium-containing phosphate with an olivine structure, and their respective modified compounds. 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. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0119] In the positive electrode sheet of the present application, the modified compounds of the above-mentioned positive electrode active materials can be the positive electrode active materials subjected to doping modification, surface coating modification, or doping and surface coating modification.

[0120] In the positive electrode sheet of the present application, the positive electrode film layer generally comprises a positive electrode active material and optionally a binder and optionally a conductive agent. The positive electrode film layer is generally formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is generally formed by dispersing the positive electrode active material, the optional conductive agent, the optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. It should be noted that the composition or parameters of each positive electrode film layer given in this application refer to the composition or parameter range of the single-sided film layer of the positive electrode current collector. When the positive electrode film layer is arranged on two opposite surfaces of the positive electrode current collector, the composition or parameters of the positive electrode film layer on any one of the surfaces meet the requirements of this application and are considered to fall within the protection scope of this application.

[0121] [Electrolytes]

[0122] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The secondary battery of the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

[0123] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0124] In some embodiments, the type of electrolyte salt is not specifically limited and can be selected according to actual needs. As an example, the electrolyte salt can be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate).

[0125] In some embodiments, the type of solvent is not specifically limited and can be selected according to actual needs. As an example, the solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

[0126] In some embodiments, optionally, the solvent is a non-aqueous solvent.

[0127] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.

[0128] [Isolation film]

[0129] Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include a separator. The separator is arranged between the positive electrode plate and the negative electrode plate to play an isolating role. The present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected. In some embodiments, the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0131] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0132] In some embodiments, 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, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0133] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 2 The secondary battery 5 is a square structure as an example.

[0134] In some embodiments, reference Figure 3 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to needs.

[0135] In some embodiments, secondary batteries may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0136] Figure 4 4 is an example of a battery module. Figure 4In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0137] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0138] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0139] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0140] Electrical devices

[0141] The embodiments of the present application also provide an electric device, which includes at least one of the secondary battery, battery module, and battery pack of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0142] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0143] Figure 7 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the power consumption device for high power and high energy density, a battery pack or a battery module can be used.

[0144] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0145] Example

[0146] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0147] Example 1

[0148] Preparation of positive electrode

[0149] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and solvent N-methylpyrrolidone (NMP) is added. The mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0150] Preparation of negative electrode

[0151] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, and the solvent deionized water was added. The mixture was stirred under the action of a vacuum stirrer until the system was uniform to obtain a first negative electrode slurry.

[0152] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single substance particles (volume average particle size Dv50 is 0.05 μm) in a mass ratio of 98:2, and deionized water solvent was added. The mixture was stirred under the action of a vacuum stirrer until the system was uniform to obtain a second negative electrode slurry.

[0153] The first negative electrode slurry and the second negative electrode slurry are uniformly coated on the two surfaces of the negative electrode current collector copper foil at the same time, and then transferred to an oven for further drying after drying at room temperature, and then cold pressed and cut to obtain a negative electrode sheet. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3 mg / cm 2The coating weight of the second negative electrode film is 6.7 mg / cm 2 The mass proportion of Ag single substance particles in the second negative electrode film layer is 2%.

[0154] Preparation of electrolyte

[0155] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0156] Preparation of isolation membrane

[0157] A polyethylene film was used as a separator.

[0158] Preparation of secondary batteries

[0159] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0160] Example 2

[0161] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 97:3, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Ag single substance particles in the second negative electrode film layer is 3%.

[0162] Example 3

[0163] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 95:5, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Ag single substance particles in the second negative electrode film layer is 5%.

[0164] Example 4

[0165] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 90:10, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Ag single substance particles in the second negative electrode film layer is 10%.

[0166] Example 5

[0167] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Al single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 95:5, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Al single substance particles in the second negative electrode film layer is 5%.

[0168] Example 6

[0169] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Mg single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 95:5, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Mg single substance particles in the second negative electrode film layer is 5%.

[0170] Example 7

[0171] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Nb single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 95:5, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Nb single substance particles in the second negative electrode film layer is 5%.

[0172] Comparative Example 1

[0173] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the negative electrode plate, which specifically includes the following steps.

[0174] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed in a mass ratio of 96.4:1:1.2:1.4, and the solvent deionized water is added. Stir until the system is uniform under the action of a vacuum mixer to obtain a negative electrode slurry, and the negative electrode slurry is divided into two parts, respectively as the first negative electrode slurry and the second negative electrode slurry. The first negative electrode slurry and the second negative electrode slurry are uniformly coated on the two surfaces of the negative electrode collector copper foil at the same time, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain a negative electrode sheet. The second negative electrode film layer is located between the negative electrode collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3mg / cm 2 The coating weight of the second negative electrode film is 6.7 mg / cm 2 .

[0175] Comparative Example 2

[0176] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the negative electrode plate, which specifically includes the following steps.

[0177] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single-substance particles (volume average particle size Dv50 is 0.05μm) in a mass ratio of 95:5, and deionized water is added as a solvent. Stir until the system is uniform under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain a negative electrode sheet. The coating weight of the negative electrode film layer is 11.0mg / cm 2 .

[0178] Comparative Example 3

[0179] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the negative electrode plate, which specifically includes the following steps.

[0180] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ag single substance particles (volume average particle size Dv50 is 0.05 μm) in a mass ratio of 95:5, and deionized water was added as a solvent. The mixture was stirred under the action of a vacuum stirrer until the system was uniform to obtain a first negative electrode slurry.

[0181] The negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water as a solvent was added, and the mixture was stirred under the action of a vacuum stirrer until the system was uniform to obtain a second negative electrode slurry.

[0182] The first negative electrode slurry and the second negative electrode slurry are uniformly coated on the two surfaces of the negative electrode current collector copper foil at the same time, and then transferred to an oven for further drying after drying at room temperature, and then cold pressed and cut to obtain a negative electrode sheet. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3 mg / cm 2 The coating weight of the second negative electrode film is 6.7 mg / cm 2 The mass proportion of Ag single substance particles in the first negative electrode film layer is 5%.

[0183] Comparative Example 4

[0184] The preparation method of the secondary battery is similar to that of Example 1, except that the negative electrode active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene butadiene rubber (SBR) are mixed at a mass ratio of 96.4:1:1.2:1.4, and then mixed with Ni single substance particles (volume average particle size Dv50 is 0.05 μm) at a mass ratio of 95:5, and solvent deionized water is added, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a second negative electrode slurry. The mass proportion of Nb single substance particles in the second negative electrode film layer is 5%.

[0185] Test Section

[0186] (1) Maximum charge rate test of secondary batteries

[0187] At 25°C, discharge the secondary battery at a constant current of 1C to 2.8V. Then charge it at a constant current of 1C to 4.2V, and continue to charge it at a constant voltage until the current is 0.05C. At this time, the secondary battery is fully charged. After the fully charged secondary battery is left to stand for 5 minutes, discharge it at a constant current of 1C to 2.8V. The discharge capacity at this time is the actual capacity of the secondary battery at 1C rate, recorded as C0. Charge the secondary battery at a constant current of x C0 (indicates the gradient charging rate, 1C0, 1.1C0, 1.2C0, 1.3C0, 1.4C0...) to 4.2V, and then continue to charge it at a constant voltage until the current is 0.05C0. Let it stand for 5 minutes, disassemble the secondary battery and observe the lithium deposition on the surface of the negative electrode. If there is no lithium deposition on the surface of the negative electrode, increase the charging rate and test it again until lithium deposition occurs on the surface of the negative electrode. Record the maximum charging rate at which there is no lithium deposition on the surface of the negative electrode.

[0188] (2) Overcharge performance test of secondary batteries

[0189] At 25°C, discharge the secondary battery at a constant current of 1C to 2.8V. Then charge at a constant current of 1C, designing a gradient charging time of 1h, 1.1h, 1.2h, 1.3h, 1.4h... After each charge, disassemble the secondary battery, observe the lithium deposition on the surface of the negative electrode, and record the charging time t(h) when lithium deposition just begins on the surface of the negative electrode. Use the charging time t×100% to indicate the SOC state when the secondary battery is overcharged to the point where lithium deposition begins.

[0190] (3) Cycle performance test of secondary batteries

[0191] At 25°C, discharge the secondary battery at a constant current of 1C to 2.8V. Then charge the secondary battery at a constant current of 1C to 4.2V, and continue to charge at a constant voltage until the current is 0.05C. At this time, the secondary battery is fully charged. Record the charging capacity at this time, which is the charging capacity of the first cycle; let the secondary battery stand for 5 minutes and then discharge it at a constant current of 1C to 2.8V. This is a cyclic charge and discharge process. Record the discharge capacity at this time, which is the discharge capacity of the first cycle. Perform a cyclic charge and discharge test on the secondary battery according to the above method, and record the discharge capacity after each cycle until the discharge capacity of the secondary battery decays to 80% of the discharge capacity of the first cycle. The number of cycles at this time is used to characterize the cycle performance of the secondary battery under 1C rate conditions. The higher the number of cycles of the secondary battery, the better the cycle performance.

[0192] At 25°C, discharge the secondary battery at a constant current of 1C to 2.8V. Then charge the secondary battery at a constant current of 3C to 4.2V, and continue to charge at a constant voltage until the current is 0.05C. At this time, the secondary battery is fully charged. Record the charging capacity at this time, which is the charging capacity of the first cycle. After the secondary battery is left to stand for 5 minutes, discharge it at a constant current of 3C to 2.8V. This is a cyclic charge and discharge process. Record the discharge capacity at this time, which is the discharge capacity of the first cycle. Perform a cyclic charge and discharge test on the secondary battery according to the above method, and record the discharge capacity after each cycle until the discharge capacity of the secondary battery decays to 80% of the discharge capacity of the first cycle. The number of cycles at this time is used to characterize the cycle performance of the secondary battery under 3C rate conditions. The higher the number of cycles of the secondary battery, the better the cycle performance.

[0193] The specific parameters of Examples 1 to 7 and Comparative Examples 1 to 4 are shown in Table 1, and the test results are shown in Table 2.

[0194] Table 1

[0195]

[0196] Table 2

[0197]

[0198] It can be seen from the data in Table 2 that the secondary battery of the present application has a higher maximum charging rate and better overcharge performance, which can effectively solve the lithium plating problem of the secondary battery under high-rate charging and overcharge conditions, and significantly improve the kinetic performance, cycle performance and safety performance of the secondary battery. Figure 8 is a cross-sectional scanning electron microscope image of the negative electrode sheet prepared in Example 1. Figure 8 It can be seen that the Ag single-substance particles are evenly distributed in the main part of the second negative electrode film layer. The surface of Ag, as the preferential nucleation site of lithium metal, can induce the surface nucleation of lithium metal in the second negative electrode film layer, and effectively inhibit the precipitation of lithium metal on the surface of the negative electrode sheet. Therefore, the secondary battery still has good kinetic performance and safety performance under high-rate charging and overcharging conditions, and the cycle performance of the secondary battery is also better.

[0199] No metal particles are added to the negative electrode film layer of Comparative Example 1, and the negative electrode film layer does not contain nucleation sites, so the precipitation of lithium metal on the surface of the negative electrode plate cannot be effectively inhibited. The kinetic performance and cycle performance of the secondary battery under high-rate charging and overcharging conditions are poor.

[0200] The negative electrode film layer of comparative example 2 is a single layer, and Ag single particles are added to the negative electrode film layer. The surface of Ag can be used as a preferential nucleation site for lithium metal, but since the Ag single particles are evenly distributed in the negative electrode film layer, they cannot inhibit the precipitation of lithium metal on the surface of the negative electrode plate. Therefore, the kinetic performance and cycle performance of the secondary battery under high-rate charging and overcharging conditions are poor. No metal particles are added to the second negative electrode film layer of comparative example 3, and Ag single particles are added to the first negative electrode film layer. The surface of Ag can be used as a preferential nucleation site for lithium metal, but since the Ag single particles are evenly distributed in the first negative electrode film layer, they cannot inhibit the precipitation of lithium metal on the surface of the negative electrode plate. Therefore, the kinetic performance and cycle performance of the secondary battery under high-rate charging and overcharging conditions are poor.

[0201] In Comparative Example 4, the metal particles added to the second negative electrode film layer are Ni single-element particles. The atomic radius of Ni and Li is too different. The surface of Ni cannot serve as the preferential nucleation site of Li, and cannot induce the surface nucleation of Li in the second negative electrode film layer. It cannot effectively inhibit the precipitation of lithium metal on the surface of the negative electrode plate. The kinetic performance of the secondary battery under high-rate charging and overcharging conditions is very poor, and it is difficult for the secondary battery to have a longer cycle life.

[0202] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A negative electrode sheet, comprising A negative electrode current collector; and A negative electrode film layer is disposed on the negative electrode current collector, wherein the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, The second negative electrode film layer comprises a second negative electrode active material and metal particles containing a metal element M, wherein the metal particles are selected from one or more of simple particles of M and alloy particles of M, and the atomic radius of M is r M The atomic radius of Li Li satisfy Based on the total mass of the second negative electrode film layer, the mass percentage of M is 1% to 10%.

2. The negative electrode sheet according to claim 1, wherein:

3. The negative electrode sheet according to claim 1, wherein: M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al, Sc, Mo, W, Pt, Pd, In, Re, Ir, Ga, Os, V, Zn, Ru, and Rh.

4. The negative electrode sheet according to claim 3, wherein: M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, and Al. 5 . The negative electrode sheet according to claim 1 , wherein M is at least located in the main body of the second negative electrode film layer.

6. The negative electrode sheet according to claim 1, wherein: The second negative electrode film layer includes a first surface and a second surface opposite to each other along its thickness direction, wherein the first surface is arranged away from the negative electrode current collector and the second surface is arranged toward the negative electrode current collector. M is located on the first surface of the second negative electrode film layer facing away from the negative electrode current collector and / or the second surface of the second negative electrode film layer facing the negative electrode current collector.

7. The negative electrode sheet according to claim 1, wherein: Based on the total mass of the second negative electrode film layer, the mass percentage of M is 3% to 7%.

8. The negative electrode sheet according to claim 7, wherein: Based on the total mass of the second negative electrode film layer, the mass percentage of M is 3% to 5%.

9. The negative electrode sheet according to claim 1, wherein: Based on the total mass of the first negative electrode film layer, the mass percentage of M is ≤0.5%.

10. The negative electrode sheet according to claim 1, wherein: The first negative electrode film layer does not contain the metal element M.

11. The negative electrode sheet according to claim 1, wherein: The coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1.

2.

12. The negative electrode sheet according to claim 11, wherein: The coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.5 to 0.

8.

13. The negative electrode sheet according to claim 1, wherein: The first negative electrode active material and the second negative electrode active material independently include one or more of graphite, soft carbon, hard carbon, mesophase carbon microbeads, carbon fibers, carbon nanotubes, silicon-based materials, tin-based materials, and lithium titanate.

14. The negative electrode sheet according to claim 1, wherein: The alloys of M include alloys formed by two or more elements in M, and alloys formed by one or more elements in M ​​and another metal element M. 1 An alloy formed by one or more elements in a 15. The negative electrode sheet according to claim 14, wherein: M 1 Including one or more of Fe, Cu, Ni, Cr, and Mn.

16. The negative electrode sheet according to claim 1, wherein: The volume average particle size Dv50 of the metal particles is ≤5 μm.

17. The negative electrode sheet according to claim 16, wherein: The volume average particle size Dv50 of the metal particles is ≤1 μm.

18. The negative electrode sheet according to claim 1, wherein: The metal particles include Li-M alloy particles, Li-MM 1 One or more of the alloy particles, M 1 represents a metal element, and M 1 Including one or more of Fe, Cu, Ni, Cr, and Mn.

19. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 18. 20 . A battery module comprising the secondary battery according to claim 19 . 21 . A battery pack comprising one of the secondary battery according to claim 19 and the battery module according to claim 20. 22 . An electric device comprising at least one of the secondary battery according to claim 19 , the battery module according to claim 20 , and the battery pack according to claim 21 .

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