Negative pole piece, and secondary battery and electric device comprising same

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative pole piece comprises a current collector and a negative active layer laminated on the surface of the current collector, and the negative active layer comprises a first active layer and a second active layer which are laminated; the first active layer comprises the following materials in percentage by mass of the first active layer: 60%-94% of a silicon-based material, 0%-30% of a carbon-based material and 5%-15% of a binder; and the second active layer comprises the following materials in percentage by mass: 0-5% of a second silicon-based material, 94-99% of a second carbon-based material and 1-3% of a second binder. And the negative pole piece has relatively good cycle performance.

Description

Negative electrode sheet, secondary battery and electrical device containing the same Technical Field

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

[0002] In recent years, as the application scope of lithium-ion batteries has become increasingly wider, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] The negative electrode active materials of traditional lithium-ion batteries are mainly carbon-based materials. Later, as the requirements for energy density continued to increase, silicon-based materials were developed, and mixing carbon-based materials and silicon-based materials as negative electrode active materials became a development trend. However, the cycle performance of batteries containing such negative electrode active materials needs to be further improved.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate and a secondary battery and an electric device containing the same. The negative electrode plate has good cycle performance.

[0006] A first aspect of the present application provides a negative electrode sheet, comprising a current collector and a negative electrode active layer stacked on a surface of the current collector, wherein the negative electrode active layer comprises a first active layer and a second active layer stacked;

[0007] Calculated by mass percentage of the first active layer, the material of the first active layer includes:

[0008] 60% to 94% of a first silicon-based material, 0% to 30% of a first carbon-based material, and 5% to 15% of a first binder;

[0009] Calculated by mass percentage of the second active layer, the material of the second active layer includes:

[0010] 0% to 5% of a second silicon-based material, 94% to 99% of a second carbon-based material, and 1% to 3% of a second binder.

[0011] The above-mentioned negative electrode plate has good overall structural stability, which can effectively improve the cycle performance of the battery and extend the cycle life of the battery. It is also beneficial to improve the rate performance of the battery.

[0012] A second aspect of the present application provides a secondary battery, comprising the negative electrode sheet described in the first aspect.

[0013] A third aspect of the present application provides an electrical device comprising the secondary battery described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0015] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0016] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0017] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0018] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0019] 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0020] Description of reference numerals:

[0021] 1. Battery pack; 2. Upper case; 3. Lower case; 4. Battery module; 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover; 6. Power-consuming device;

[0022] FIG7 is a schematic structural diagram of the negative electrode sheet prepared in Example 1 of the present application;

[0023] FIG8 is a schematic structural diagram of the negative electrode sheet prepared in Example 12 of the present application;

[0024] Figure 9 is a schematic structural diagram of the negative electrode sheet prepared in Example 13 of the present application. DETAILED DESCRIPTION

[0025] Below, the embodiments of the negative electrode sheet of the present application, the secondary battery and the electric device containing the same are described in detail with appropriate reference to the accompanying drawings. However, there may be 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 structure 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 description 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.

[0026] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0028] 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.

[0029] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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.

[0030] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0031] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0032] Some examples of the present application provide a negative electrode sheet, including a current collector and a negative electrode active layer stacked on a surface of the current collector, wherein the negative electrode active layer includes a first active layer and a second active layer stacked;

[0033] Calculated by mass percentage of the first active layer, the material of the first active layer includes:

[0034] 60% to 94% of a first silicon-based material, 0% to 30% of a first carbon-based material, and 5% to 15% of a first binder;

[0035] Calculated by mass percentage of the second active layer, the material of the second active layer includes:

[0036] 0% to 5% of a second silicon-based material, 94% to 99% of a second carbon-based material, and 1% to 3% of a second binder.

[0037] Currently, batteries that use a mixture of carbon-based and silicon-based materials as negative electrode active materials have insufficient cycling performance. To address this issue, the inventors discovered that due to the high expansion and rebound properties of silicon-based materials, more binders are needed to maintain the structural stability of the electrode. Furthermore, in negative electrode active layers that use a mixture of silicon-based and carbon-based materials, the surface of the carbon-based material is also coated with a large amount of binder. However, the carbon-based material itself has a relatively good structural stability, making the actual effectiveness of this binder low. Furthermore, the resulting structural instability of the silicon-based material, which in turn leads to poor overall battery cycling performance, has been overlooked.

[0038] Based on the above findings, the negative electrode sheet provided by this application is provided with a first active layer primarily composed of a silicon-based material and a second active layer primarily composed of a carbon-based material. Based on the structures of the silicon-based and carbon-based materials and the requirements for binders, different binders within a certain range are added to the first and second active layers. This improves the overall structural stability of the negative electrode sheet, thereby enhancing the battery's cycling performance and extending its cycle life, while using a total binder amount comparable to or even less than that of traditional methods. Furthermore, by maintaining the same positional relationship between the first and second active layers and the current collector, the battery's rate performance is also improved.

[0039] Specifically, the mass percentage of the first silicon-based material includes but is not limited to: 60%, 63%, 65%, 67%, 70%, 73%, 75%, 77%, 80%, 83%, 85%, 87%, 90%, 92%, 94% or a range formed by any two of the foregoing values.

[0040] Specifically, the mass percentage of the first carbon-based material includes but is not limited to: 0%, 3%, 5%, 10%, 15%, 18%, 20%, 25%, 30% or a range formed by any two of the foregoing values.

[0041] Specifically, the mass percentage of the first binder includes but is not limited to: 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range formed by any two of the foregoing values.

[0042] Specifically, the mass percentage of the second silicon-based material includes but is not limited to: 0%, 1%, 2%, 3%, 4%, 5% or a range formed by any two of the foregoing values.

[0043] Specifically, the mass percentage of the second carbon-based material includes but is not limited to: 94%, 95%, 96%, 97%, 97.5%, 98%, 99% or a range formed by any two of the foregoing values.

[0044] Specifically, the mass percentage of the second binder includes but is not limited to: 1%, 1.5%, 2%, 2.5%, 3% or a range formed by any two of the foregoing values.

[0045] In some examples, the first active layer is further away from the current collector than the second active layer.

[0046] Compared to carbon-based materials, silicon-based materials experience greater volume expansion after lithium insertion. Therefore, the porosity of the first active layer is generally greater than that of the second active layer. This gradient pore structure helps improve cycling dynamics, thereby enhancing the battery's rate performance. It is also understandable that in these examples, the silicon-based material preferentially inserts lithium, which helps improve the battery's fast-charging performance.

[0047] In some examples, the first active layer is closer to the current collector than the second active layer. Due to the higher binder content in the first active layer, it maintains good adhesion to the current collector, enhancing the stability of the electrode structure. Furthermore, during actual battery cycling, the depth of discharge of the battery is relatively low. During discharge, carbon-based materials preferentially remove lithium, resulting in a higher utilization rate of carbon-based materials and a lower utilization rate of silicon-based materials, thereby extending the battery's cycle life.

[0048] In some examples, a primer layer is provided between the first active layer and the current collector. Furthermore, the primer layer comprises a binder and a conductive agent. When the first active layer is close to the current collector, the primer layer can enhance adhesion and electrical contact between the first active layer and the current collector, further improving cycling performance.

[0049] In addition, similar to the binder, due to the high expansion and rebound characteristics of silicon-based materials, it is usually necessary to add more conductive agents to maintain the conductive network of the electrode, and in the negative electrode active layer where silicon-based materials and carbon-based materials coexist, the surface of the carbon-based material will also be wrapped with more conductive agents, and the carbon-based material itself has good conductivity, which makes the actual benefit of this part of the conductive agent low. At the same time, the conductive network between the silicon-based materials is not perfect, and the conductivity is poor. Therefore, in some examples of the present application, by adding a certain range of conductive agents to the first active layer and the second active layer. The conductivity of the negative electrode active layer can be further improved. In particular, the proportion of conductive agent in the first active layer is relatively high. When it is closer to the current collector, it can enable better electrical contact between the first active layer and the current collector.

[0050] In some examples, the material of the first active layer further includes 1% to 5% of a first conductive agent. Specifically, the mass percentage of the first conductive agent includes but is not limited to: 1%, 2%, 3%, 4%, 5%, or a range formed by any two of the foregoing values.

[0051] In some examples, the material of the second active layer further includes 0.5% to 2% of a second conductive agent. Specifically, the mass percentage of the first conductive agent includes, but is not limited to, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, or a range formed by any two of the foregoing values.

[0052] Without limitation, the first conductive agent and the second conductive agent may be conventional conductive agents in the art, such as one or more conductive carbons, specifically one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0053] In some examples, in the first active layer, the Dv50 of the first silicon-based material is ≤ 15 μm. Specifically, the Dv50 of the first silicon-based material includes, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range formed by any two of the foregoing values. Furthermore, the Dv50 of the first silicon-based material is between 5 μm and 10 μm.

[0054] In some examples, in the first active layer, the Dv50 of the first carbon-based material is ≤ 10 μm. Specifically, the Dv50 of the first carbon-based material includes, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range formed by any two of the foregoing values. Furthermore, the Dv50 of the first carbon-based material is 2 μm to 6 μm.

[0055] Furthermore, the Dv99 of the first carbon-based material is ≤ 15 μm. Specifically, the Dv99 of the first carbon-based material includes but is not limited to: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range formed by any two of the foregoing values.

[0056] Reasonable control of the particle size of the silicon-based material and the carbon-based material in the first active layer can further improve the cycle performance and rate performance of the battery, while also improving the compaction ability of the negative electrode active layer, thereby further reducing the amount of binder, conductive agent, etc. required. In some examples, the compaction density of the negative electrode active layer is 1.2 to 2.0 g / cm 3 .

[0057] Without limitation, in the second active layer, the Dv50 of the second silicon-based material is ≤ 15 μm. Specifically, the Dv50 of the second silicon-based material includes, but is not limited to, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, or a range formed by any two of the foregoing values. In some examples, the Dv50 of the second silicon-based material is between 5 μm and 10 μm.

[0058] Without limitation, in the second active layer, the second carbon-based material Dv50 ≤ 25 μm. Specifically, the second carbon-based material Dv50 includes but is not limited to: 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm or a range formed by any two of the foregoing values. In some examples, the second carbon-based material Dv50 is 5 μm to 20 μm. Further, the second carbon-based material Dv99 ≤ 40 μm. Specifically, the second carbon-based material Dv99 includes but is not limited to: 1 μm, 5 μm, 10 μm, 15 μm, 17 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or a range formed by any two of the foregoing values.

[0059] Without limitation, the material of the first active layer may further include other additives, such as a thickener. In some examples, the thickener includes sodium carboxymethyl cellulose. Without limitation, the weight ratio of the thickener is 0 to 15% by weight based on the total weight of the first active layer.

[0060] Without limitation, the material of the second active layer may further include other additives, such as a thickener. In some examples, the thickener includes sodium carboxymethyl cellulose. Without limitation, the weight ratio of the thickener is 0 to 15% by weight, based on the total weight of the second active layer.

[0061] Without limitation, the first binder may be a conventional binder in the art, such as one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Furthermore, the first binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, and polyacrylamide.

[0062] Without limitation, the second binder can be a conventional binder in the art, such as one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Furthermore, the second binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, and polyacrylamide. Selecting the appropriate type of binder can further improve the cycle performance and rate performance of the battery.

[0063] Without limitation, the first silicon-based material may be a conventional silicon-based material in the art, such as one or more of pure silicon, silicon-oxygen, and silicon-carbon materials. Furthermore, the first silicon-based material includes one or more of silicon-carbon and silicon-oxygen materials.

[0064] Without limitation, the second silicon-based material may be a conventional silicon-based material in the art, such as one or more of pure silicon, silicon-oxygen, and silicon-carbon materials. Furthermore, the second silicon-based material includes one or more of silicon-carbon and silicon-oxygen materials.

[0065] Without limitation, the first carbon-based material may be a conventional carbon-based material in the art, such as one or more of graphite, graphene, hard carbon, soft carbon, porous carbon, and activated carbon. Further, the second carbon-based material includes one or more of graphite and hard carbon.

[0066] Without limitation, the second carbon-based material may be a conventional carbon-based material in the art, such as one or more of graphite, graphene, hard carbon, soft carbon, porous carbon, and activated carbon. Furthermore, the second carbon-based material includes one or more of graphite and hard carbon.

[0067] Selecting appropriate silicon-based and carbon-based materials can further improve the battery's cycle performance and rate performance.

[0068] Some examples of the present application also provide a secondary battery comprising the negative electrode sheet as described above.

[0069] Some examples of the present application further provide an electric device including the secondary battery as described above.

[0070] The secondary battery, battery module, battery pack, and electric device of the present application are described below with reference to the accompanying drawings as appropriate.

[0071] In one embodiment of the present application, a secondary battery is provided.

[0072] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0073] Positive electrode

[0074] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0075] As an 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.

[0076] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. Polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.)

[0077] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100 weight%, based on the total weight of the positive electrode film layer.

[0078] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0-20 weight%, based on the total weight of the positive electrode film layer.

[0079] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0080] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40-80 wt % and a viscosity at room temperature adjusted to 5000-25000 mPa·s, the positive electrode slurry is coated on the surface of the positive electrode current collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit area density is 15-35 mg / cm 2 The compaction density of the positive electrode is 3.0-3.6g / cm 3 , optional 3.3-3.5g / cm 3 The calculation formula of the compacted density is

[0081] Compaction density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0082] Negative electrode

[0083] As shown above, the negative electrode sheet includes a current collector and a negative electrode active layer stacked on the surface of the current collector.

[0084] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0085] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0086] In some embodiments, the negative electrode sheet can be prepared by the following method: the material of the first active layer and the material of the second active layer are dispersed in a solvent (e.g., deionized water) to form a first active layer slurry and a second active layer slurry, wherein the solid content of the slurry can be 30-70wt%, and the viscosity at room temperature is adjusted to 2000-10000mPa·s; the obtained first active layer slurry and second active layer slurry are sequentially coated on the negative electrode current collector, and after a drying process, cold pressing, such as rolling, is performed to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 3-17mg / cm 2 , the compaction density of the negative electrode is 1.2-2.0g / cm 3 .

[0087] electrolytes

[0088] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0089] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0090] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0091] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), 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), 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), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0092] In some embodiments, the electrolyte may further 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, and additives that improve battery high or low temperature performance.

[0093] Isolation film

[0094] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0095] In some embodiments, the material of the separator can be selected from at least one 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, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0096] In some embodiments, the isolation film has a thickness of 6-40 μm, and optionally 12-20 μm.

[0097] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0098] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0099] 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.

[0100] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0101] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. 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 enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into 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, and those skilled in the art can select according to specific actual needs.

[0102] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0103] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0104] 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.

[0105] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0106] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0107] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in 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 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 is not limited thereto.

[0108] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0109] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high rate performance requirements of the secondary battery, a battery pack or battery module can be used.

[0110] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0111] Example

[0112] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0113] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0114] Example 1

[0115] 1) Preparation of positive electrode sheet

[0116] The positive electrode active material NCM811, conductive carbon black SP and binder PVDF were dispersed in the solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried and cold pressed to obtain a positive electrode sheet. The coating amount per unit area was 0.3g / 1540.25mm 2 .

[0117] 2) Preparation of negative electrode sheet

[0118] Coating of carbon-based material active layer: The negative electrode active material artificial graphite (Dv50 = 4 μm, Dv99 = 13 μm), conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed in deionized water at a weight ratio of 97%: 0.8%: 1.5%: 0.7%, and then coated on copper foil and dried to obtain a carbon-based material active layer. The coating amount was 0.055 g / cm 2 ;

[0119] Silicon-based material active layer coating: The negative electrode active material artificial graphite (Dv50 = 4μm, Dv99 = 13μm), silicon oxide material (Dv50 = 8μm), conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) were mixed in deionized water at a weight ratio of 18%: 70%: 3%: 7%: 2%, and then coated on the electrode with the carbon-based material active layer and dried to obtain the silicon-based material active layer. The coating amount was 0.055g / cm 2 After obtaining the double-layer coated electrode, it is cold pressed and the compaction density is 1.6g / cm 3 .

[0120] The structure of the prepared negative electrode plate is shown in FIG7 , which includes a copper foil 701 , and a carbon-based material active layer 702 and a silicon-based material active layer 703 sequentially stacked on the surface of the copper foil 701 .

[0121] 3) Isolation film

[0122] A 12μm thick polypropylene isolation film was selected.

[0123] 4) Preparation of electrolyte

[0124] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0125] 5) Battery Preparation

[0126] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrode sheets to serve as an isolation. After winding into a square bare battery cell, an aluminum-plastic film is placed in it. After baking at 80°C to remove water, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0127] The preparation methods of Examples 2 to 8 are the same as those of Example 1, with the main difference being that the mass percentages of the components are changed, as shown in Table 1 below (wherein the silicon-oxygen material added to the carbon-based material active layer of Example 8 is the same as the silicon-oxygen material in the silicon-based material active layer).

[0128] The preparation methods of Examples 9 to 11 are the same as those of Example 1, with the main difference being that the particle sizes of the silicon-based material and the carbon-based material are changed, as shown in Table 2 below.

[0129] Table 1

[0130] Table 2

[0131] The preparation method of Example 12 is the same as that of Example 1, with the main difference being that the materials of the upper and lower layers are interchanged and a primer layer is added. Specifically, the preparation steps of the negative electrode sheet in step 2) are as follows:

[0132] Primer coating gravure coating: Superconducting carbon, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed evenly in deionized water at a weight ratio of 70%:27%:3%, and then coated on copper foil by gravure coating and dried to obtain a primer coating with a coating amount of 0.0004 g / cm 2 .

[0133] Silicon-based material active layer coating: The negative electrode active material artificial graphite (Dv50 = 4 μm, Dv99 = 13 μm), silicon oxide material (Dv50 = 8 μm), conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed in deionized water at a weight ratio of 18%: 70%: 3%: 7%: 2%, and then coated on the electrode with the primer and dried to obtain the silicon-based material active layer. The coating amount was 0.055 g / cm 2 .

[0134] Coating of carbon-based material active layer: The negative electrode active material artificial graphite (Dv50 = 4 μm, Dv99 = 13 μm), conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed in deionized water at a weight ratio of 97%: 0.8%: 1.5%: 0.7%, and then coated on the silicon-based material active layer and dried to obtain a carbon-based material active layer. The coating amount was 0.055 g / cm 2 After obtaining the double-layer coated electrode, it is cold pressed and the compaction density is 1.6g / cm 3 .

[0135] The structure of the prepared negative electrode sheet is shown in FIG8 , which includes a copper foil 801 , and a primer layer 804 , a silicon-based material active layer 803 , and a carbon-based material active layer 802 sequentially stacked on the surface of the copper foil 801 .

[0136] Example 13 was prepared using the same method as Example 12, with the primary difference being that the primer layer was not provided. The resulting negative electrode sheet structure is shown in FIG9 , comprising a copper foil 901 , and a silicon-based active layer 903 and a carbon-based active layer 902 sequentially laminated on the surface of the copper foil 901 .

[0137] The preparation method of Example 14 is the same as that of Example 1, with the main difference being that an equal amount of pure silicon material is used to replace the silicon oxide material therein, and an equal amount of graphene is used to replace the graphite therein.

[0138] The preparation method of Example 15 is the same as that of Example 1, with the main difference being that an equal amount of silicon-carbon material is used to replace the silicon-oxygen material therein, and an equal amount of hard carbon is used to replace the graphite therein.

[0139] The preparation methods of Examples 16 to 18 are the same as those of Example 1, with the main difference being that polyacrylic acid, polyacrylamide, and polyvinyl alcohol are used in equal amounts to replace the styrene-butadiene rubber.

[0140] The preparation methods of Comparative Examples 1 to 3 are the same as those of Example 1, with the main difference being that the proportions of the components are changed, as shown in Table 3 below:

[0141] Table 3

[0142] Test example:

[0143] 1. Maximum charge rate @10% capacity

[0144] Prepare a three-electrode battery. The battery is fully discharged to 2.5V and charged to 10% capacity at room temperature using different rates of 0.4C, 0.6C, 0.8C, 1C, and 1.2C, while monitoring the anode potential during the process. Then, the anode potential at 10% capacity at different rates is fitted to obtain the charge rate when the anode potential is 0V (the default lithium plating potential), which is the maximum acceptable charge rate at 10% capacity.

[0145] 2. Cycles @ 80% capacity retention

[0146] The battery is charged at a constant current rate of 0.5C to 4.25V at room temperature, then charged at a constant voltage rate of 4.25V to a rate of 0.05C, and then discharged at a constant current rate of 1C to 2.5V. This is considered one cycle. Repeat the above cycle test until the discharge capacity decays to 80% of the initial capacity, and the test is stopped to obtain the cycle number.

[0147] The test results are shown in Table 4 below.

[0148] Table 4

[0149] In Examples 1-11 and Comparative Examples 1-3, the silicon-based material active layer is positioned further away from the current collector than the carbon-based material active layer. This shows that, given the same silicon-based material position, Examples 1-11 achieve better cycle performance and higher rate performance than Comparative Examples 1-3. In Examples 12 and 13, the silicon-based material active layer is positioned closer to the current collector than the carbon-based material active layer. Although the silicon-based material's location inside the active layer structure (i.e., closer to the current collector) results in the battery's overall rate performance being comparable to or only slightly improved compared to Comparative Examples 1-3, the cycle performance is significantly improved compared to Comparative Examples 1-3.

[0150] Furthermore, a comparison between Example 1 and Examples 12-13 shows that when the carbon-based material active layer is closer to the current collector, higher rate performance can be achieved, while when the silicon-based material active layer is closer to the current collector, better cycle performance can be achieved. A comparison between Example 12 and Example 13 shows that when the silicon-based material active layer is closer to the current collector, adding a primer layer can further improve cycle performance.

[0151] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode sheet, comprising a current collector and a negative electrode active layer stacked on the surface of the current collector, wherein the negative electrode active layer comprises a first active layer and a second active layer stacked; Measured in terms of mass percentage of the first active layer, the material of the first active layer includes: 60% to 94% of a first silicon-based material, 0% to 30% of a first carbon-based material, and 5% to 15% of a first binder; Measured in terms of mass percentage of the second active layer, the material of the second active layer includes: 0% to 5% of the second silicon-based material, 94% to 99% of the second carbon-based material and 1% to 3% of the second binder.

2. The negative electrode sheet according to claim 1, characterized in that: Compared with the second active layer, the first active layer is closer to the current collector.

3. The negative electrode sheet according to claim 2, characterized in that: A primer layer is further provided between the first active layer and the current collector; optionally, the material of the primer layer includes a third binder and a third conductive agent; Further optionally, the third conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; Further optionally, the third binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The material of the first active layer also includes 1% to 5% of a first conductive agent; optionally, the first conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: In the first active layer, the Dv50 of the first silicon-based material is ≤15 μm; optionally, the Dv50 of the first silicon-based material is 5 μm to 10 μm; In the first active layer, the Dv50 of the first carbon-based material is ≤10 μm; optionally, the Dv50 of the first carbon-based material is 2 μm to 6 μm; optionally, the Dv99 of the first carbon-based material is ≤15 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The first binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan; optionally, the first binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate and polyacrylamide.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The material of the second active layer also includes 0.5% to 2% of a second conductive agent; optionally, the second conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: In the second active layer, Dv50 of the second silicon-based material is ≤15 μm; optionally, Dv50 of the second silicon-based material is 5 μm to 10 μm.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: In the second active layer, the second carbon-based material has a Dv50≤25 μm; optionally, the second carbon-based material has a Dv50 of 5 μm to 20 μm; optionally, the second carbon-based material has a Dv99≤40 μm.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The second binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan; optionally, the first binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate and polyacrylamide.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that: The first silicon-based material and the second silicon-based material each independently include one or more of pure silicon material, silicon-oxygen material and silicon-carbon material; optionally, the first silicon-based material and the second silicon-based material each independently include one or more of silicon-carbon material and silicon-oxygen material.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that: The first carbon-based material and the second carbon-based material each independently include one or more of graphite, graphene, hard carbon, soft carbon, porous carbon and activated carbon; optionally, the first carbon-based material and the second carbon-based material each independently include one or more of graphite and hard carbon.

13. The negative electrode sheet according to any one of claims 1 to 12, characterized in that: The compaction density of the negative electrode active layer is 1.2 to 2.0 g / cm 3 .

14. A secondary battery, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 13.

15. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 14.

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