Negative electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application discloses a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. The negative electrode sheet disclosed by the application comprises a negative electrode current collector and an active material layer arranged on at least one surface of the negative electrode current collector, wherein the active material layer comprises a first active material layer and a second active material layer arranged on the surface of the first active material layer, the first active material layer comprises a first active material, the second active material layer comprises a second active material, and the active material layer satisfies: alpha*CW2<=CW1, wherein alpha is an interlayer spacing relative factor, and 1<=alpha<=1.12. The secondary battery obtained by using the negative electrode sheet disclosed by the application has better rate performance and energy density.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] In recent years, the application range of lithium-ion batteries has become increasingly wide. For example, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. The widespread use of lithium-ion batteries has led to increasingly higher requirements for their overall performance. More and more application scenarios demand that power batteries possess both high energy density and good charge-discharge characteristics. As one of the most critical components of lithium-ion batteries, the design of the negative electrode directly affects the battery's performance, especially its charge-related characteristics. How to optimize the negative electrode design to obtain a battery that balances energy density and kinetic performance is a common challenge currently faced by the industry. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode sheet to address existing needs. This application also provides secondary batteries, battery modules, battery packs, and electrical devices using this negative electrode sheet. The inventors of this application have discovered that by employing double or multiple layers of active material in the negative electrode and controlling the relationship between the interlayer spacing and coating weight of each active material layer, a battery negative electrode with both higher energy density and better charge-discharge kinetics can be obtained.

[0004] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, comprising a negative current collector and an active material layer disposed on at least one surface of the negative current collector, wherein the active material layer comprises a first active material layer and a second active material layer disposed on the surface of the first active material layer, the first active material layer comprising a first active material, the second active material layer comprising a second active material, and the active material layer satisfying: α CW2≤CW1, where α: Interlayer spacing relative factor, α= And 1≤α≤1.12; d1: Interlayer spacing corresponding to the d002 peak of the first active material, in nm; d2: The interlayer spacing corresponding to the d002 peak of the second active material, in nm; CW1: The mass of the first active material layer disposed on the negative electrode current collector per unit area, in g / m². 2 ; CW2: The mass of the second active material layer disposed on the negative electrode current collector per unit area, in g / m². 2 .

[0005] Therefore, by employing double or multiple active material layers on the negative electrode and controlling the relationship between the interlayer spacing and coating weight of each active material layer, a battery negative electrode with both higher energy density and better charge-discharge kinetics can be obtained. More specifically, the inventors of this application have discovered that by coating two active material layers on the current collector on the same side of the negative electrode sheet, with the interlayer spacing of the second active material layer being larger than that of the first active material layer, lithium ions can quickly intercalate into the surface active material when migrating from the positive electrode to the negative electrode due to the larger interlayer spacing of the surface material and the lower lithium ion insertion impedance. This avoids lithium ion deposition on the surface of the negative electrode sheet due to excessive charging rate. Since a larger interlayer spacing of the negative electrode active material results in a lower material capacity, a larger coating weight of the second active material layer has a greater impact on the overall capacity of the negative electrode sheet. To balance the capacity of the negative electrode sheet and the charging window performance, this application limits the coating weight of the second active material layer. When the interlayer spacing of the active materials in the second active material layer is larger, it indicates stronger charging capability but lower capacity. Correspondingly, a smaller coating weight is sufficient to achieve a good charging level. Conversely, when the interlayer spacing of the active materials in the second active material layer is relatively small, its charging capability weakens but its capacity increases. In this case, to ensure good overall charging performance of the electrode, the ratio of the coating weight of the second active material layer to the total coating weight of the electrode should be increased. The inventors of this application unexpectedly discovered that using a double-layer active material structure, with a small interlayer spacing and high capacity in the first active material layer, the electrode and battery achieve relatively high energy density. The large interlayer spacing in the second active material layer reduces the lithium intercalation resistance on the surface of the negative electrode, preventing lithium ion deposition on the negative electrode surface during high-rate charging and improving the battery charging window. Therefore, a battery negative electrode with an active material layer satisfying the above relationships possesses both high energy density and good charge-discharge kinetics performance.

[0006] In any embodiment of this application, the active material layer satisfies: CW2 ≥ α CW1.

[0007] To balance battery energy density and charging performance, and to avoid over-designing one performance aspect at the expense of another, the inventors, based on actual test results, further limited the relationship between the coating weight and interlayer spacing of the first and second active material layers. When this relationship is satisfied, both the rate performance and energy density of the negative electrode and the battery can be significantly improved.

[0008] In any embodiment of this application, and Inversely proportional, and 0.2 ≤ ≤0.45, where, Da 50 Volume average particle size of the first active material, in μm; Db 50 : Volume average particle size of the second active material, in μm.

[0009] The coating weight of the active material layer is adjusted according to the interlayer spacing and particle size of each active material layer, so that the electrode and battery can take into account both fast charging performance and energy density.

[0010] In any embodiment of this application, the volume average particle size Da of the first active material is... 50 The volume average particle size Db of the second active material 50 Satisfying 0.2≤ ≤0.8.

[0011] By specifying the relative particle size of the active materials in the two active material layers, the kinetic performance can be further improved, and the processing performance can be facilitated when the amount of the second layer coating is low.

[0012] In any embodiment of this application, the interlayer spacing d1 corresponding to the d002 peak of the first active material is in the range of 0.335~0.3362nm, and the interlayer spacing d2 corresponding to the d002 peak of the second active material is in the range of 0.3356~0.38nm.

[0013] In any embodiment of this application, the volume average particle size Da50 of the first active material ranges from 8 to 20 μm, and the volume average particle size Db50 of the second active material ranges from 4 to 12 μm.

[0014] In any embodiment of this application, the mass CW1 of the first active material layer disposed on the negative electrode current collector per unit area ranges from 80 to 200 g / m². 2 The mass CW2 of the second active material layer disposed on the negative electrode current collector per unit area ranges from 10 to 110 g / m². 2 .

[0015] In any embodiment of this application, the first active material is natural graphite or artificial graphite, and / or the second active material is artificial graphite.

[0016] In any embodiment, the first active layer and / or the second active layer contains soft carbon or hard carbon.

[0017] A second aspect of this application provides a secondary battery that includes the negative electrode sheet of the first aspect of this application.

[0018] A third aspect of this application provides a battery module that includes the secondary battery of the second aspect of this application.

[0019] The fourth aspect of this application provides a battery pack, which includes one of the secondary battery of the second aspect of this application and the battery module of the third aspect.

[0020] The fifth aspect of this application provides an electrical device that includes at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0021] The battery module, battery pack, and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of one embodiment of the negative electrode sheet of this application.

[0024] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0025] Figure 3 This is an exploded view of one embodiment of the secondary battery of this application.

[0026] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0027] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0028] Figure 6 yes Figure 5 The exploded diagram.

[0029] Figure 7 This is a schematic diagram of one embodiment of the electrical device that uses a secondary battery as a power source according to this application.

[0030] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained below: 1 battery pack 2 upper box 3 lower cabinets 4 battery modules 5 Secondary batteries 51 housing 52 Electrode Assembly 53 cover plate Detailed Implementation The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0031] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0034] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the method may also 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0036] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0037] Secondary batteries Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0038] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also located between the positive and negative electrodes, mainly conducts the active ions.

[0039] [Negative electrode plate] As one of the most critical components of lithium-ion batteries, the design of the negative electrode directly affects the battery's performance, especially its charging-related characteristics. Optimizing the negative electrode design to achieve a battery that balances energy density and kinetic performance is a common challenge in the industry.

[0040] To address the aforementioned problems, the inventors conducted extensive research and provided a negative electrode sheet. The negative electrode sheet of this application employs two or more layers of active material, and by controlling the relationship between the interlayer spacing and coating weight of each active material layer, it can achieve both high energy density and excellent charge-discharge kinetic performance.

[0041] The negative electrode sheet of this application includes a negative current collector and an active material layer disposed on at least one surface of the negative current collector. The active material layer includes a first active material layer and a second active material layer disposed on the surface of the first active material layer. The first active material layer includes a first active material, and the second active material layer includes a second active material. The active material layer satisfies: α CW2≤CW1, where α: Interlayer spacing relative factor, α= And 1≤α≤1.12; d1: Interlayer spacing corresponding to the d002 peak of the first active material, in nm; d2: The interlayer spacing corresponding to the d002 peak of the second active material, in nm; CW1: The mass of the first active material layer disposed on the negative electrode current collector per unit area, in g / m². 2 If both sides of the negative electrode current collector are provided with a first active material layer and a second active material layer, then the mass of the first active material layer should be the mass of both sides.

[0042] CW2: The mass of the second active material layer disposed on the negative electrode current collector per unit area, in g / m². 2； If both sides of the negative electrode current collector are provided with a first active material layer and a second active material layer, then the mass of the second active material layer should be the mass of both sides.

[0043] Therefore, this application achieves a battery negative electrode with both higher energy density and better charge-discharge kinetics by employing double or multiple active material layers on the negative electrode and controlling the relationship between the interlayer spacing and coating weight of each active material layer. More specifically, the inventors of this application discovered that by coating two active material layers on the current collector on the same side of the negative electrode sheet, with the interlayer spacing of the second active material layer being larger than that of the first active material layer, lithium ions can quickly intercalate into the surface active material when migrating from the positive electrode to the negative electrode due to the larger interlayer spacing and lower lithium ion insertion impedance. This avoids lithium ion deposition on the surface of the negative electrode sheet due to excessive charging rate. Since a larger interlayer spacing of the negative electrode active material results in lower material capacity, a larger coating weight of the second active material layer has a greater impact on the overall capacity of the negative electrode sheet. To balance the capacity of the negative electrode sheet and the charging window performance, this application sets requirements on the coating weight of the second active material layer. When the interlayer spacing of the active materials in the second active material layer is larger, it indicates stronger charging capability but lower capacity. Correspondingly, a smaller coating weight is sufficient to achieve a good charging level. Conversely, when the interlayer spacing of the active materials in the second active material layer is relatively small, its charging capability weakens but its capacity increases. In this case, to ensure good overall charging performance of the electrode, the ratio of the coating weight of the second active material layer to the total coating weight of the electrode should be increased. The inventors of this application have discovered that using a double-layer active material structure, the first active material layer has a small interlayer spacing and high capacity, resulting in a relatively high energy density for the electrode and battery. The second active material layer has a large interlayer spacing, reducing the lithium intercalation resistance on the surface of the negative electrode, preventing lithium ion deposition on the negative electrode surface during high-rate charging, and improving the battery charging window. Therefore, a battery negative electrode with an active material layer that satisfies the above relationships possesses both high energy density and good charge-discharge kinetics performance.

[0044] In some embodiments, the active material layer satisfies: CW2 ≥ α CW1.

[0045] The weight of the second active material layer is adjusted based on the interlayer spacing and the weight of the first active material layer. Overall, to ensure that the negative electrode sheet possesses both high energy density and kinetic performance, the coating weight of the second active material layer should satisfy CW2 ≥ α CW1.

[0046] The inventors of this application discovered that a smaller weight of the active material layer coated on the negative electrode and a larger interlayer spacing of the active materials result in lower internal resistance of the electrode and the battery, leading to better charge and discharge performance. However, a smaller active material layer weight and a larger interlayer spacing, for the same battery capacity, lead to a decrease in battery energy density due to the increased amount of auxiliary materials such as foil and the increased material usage. To balance battery energy density and charging performance, and to avoid over-designing one performance characteristic at the expense of another, the inventors, based on actual test results, further defined the relationship between the coating weight and interlayer spacing of the first and second active material layers. When this relationship is satisfied, both the rate performance and energy density of the negative electrode and the battery can be significantly improved.

[0047] In some implementations... and Inversely proportional, and 0.2 ≤ ≤0.45, where Da 50 Volume average particle size of the first active material, in μm; Db 50 : Volume average particle size of the second active material, in μm.

[0048] Based on the interlayer spacing and particle size of each active material layer, adjust the coating weight of the active material layer and the particle size of the active material between each active material layer to meet the following requirements: and Inversely proportional and 0.2≤ When the value is ≤0.45, the electrode and battery can balance fast charging performance and energy density.

[0049] In some embodiments, the volume average particle size Da of the first active material is... 50 The volume average particle size Db of the second active material 50 Satisfying 0.2≤ ≤0.8.

[0050] The relative particle size of the active materials in the two active material layers is specified to further improve the kinetic performance and facilitate the realization of processing performance when the amount of the second layer coating is low.

[0051] In some embodiments, the interlayer spacing d1 corresponding to the d002 peak of the first active material is in the range of 0.335~0.3362nm, and the interlayer spacing d2 corresponding to the d002 peak of the second active material is in the range of 0.3356~0.38nm.

[0052] In some embodiments, the volume average particle size Da50 of the first active material ranges from 8 to 20 μm, and the volume average particle size Db50 of the second active material ranges from 4 to 12 μm.

[0053] In some embodiments, the mass CW1 of the first active material layer disposed on the negative electrode current collector per unit area ranges from 80 to 200 g / m². 2 The mass CW2 of the second active material layer disposed on the negative electrode current collector per unit area ranges from 10 to 110 g / m². 2 .

[0054] In this application, the volume average particle size D50 of the material has a well-known meaning in the art and can be determined using methods and instruments known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0055] In some embodiments, the negative electrode sheet further comprises a conductive agent and a binder, the types and amounts of which are not specifically limited and can be selected according to actual needs. As an example, the conductive agent may include one or more of superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives may be the same or different; as an example, other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0056] In the negative electrode of this application, the negative current collector can be a metal foil or a composite current collector. As an example of a metal foil, copper foil can be used. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material can be selected from one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material substrate can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0057] In some embodiments, the active material 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 each other in its thickness direction, and the active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0058] Figure 1 The negative electrode current collector and its surface active material layer are shown, wherein... Figure 1The negative electrode current collector shown has a first active material layer and a second active material layer on both surfaces.

[0059] Of course, the negative electrode 10 of this application may also have other implementations. For example, the negative electrode 10 is composed of a negative current collector 11, a first active material layer 121 disposed on one side of the negative current collector, and a second active material layer 122 disposed on the first active material layer 121.

[0060] Furthermore, the negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may also include a conductive undercoat 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 sheet of this application also includes a protective layer covering the surface of the first negative electrode film layer.

[0061] In some embodiments, the method for preparing the negative electrode sheet of this application may include the following steps: 1. Prepare slurry A containing a first active material and slurry B containing a second active material, respectively; 2. Calculate CW1 and CW2 based on the interlayer spacing of the first active material and the interlayer spacing of the second active material; 3. Coat slurry A onto the current collector and dry it to obtain electrode A coated with the first active material layer; 4. Coat the surface of electrode A with slurry B, dry it, and then cold press and slit it to obtain the negative electrode sheet described in this application; The coating amounts of the first active material layer and the second active material layer satisfy CW1 and CW2, respectively.

[0062] In some embodiments, the slurry A comprises one or more of a first active material, a conductive agent, a binder, and a thickener.

[0063] In some embodiments, the slurry B comprises a second active material, one or more of a conductive agent, a binder, and a thickener.

[0064] For specific methods of preparing the negative electrode, please refer to the specific embodiments provided in this application, which will not be repeated here.

[0065] [Positive electrode plate] A secondary battery includes a positive electrode sheet, which typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite 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 current collector.

[0066] In the positive electrode of this application, the positive current collector can be a metal foil or a composite current collector. As an example of a metal foil, the positive current collector can be aluminum foil. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material can be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material substrate can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0067] In the positive electrode sheet of this application, the positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. As an example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This 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.

[0068] In the positive electrode sheet of this application, the modified compounds of the above-mentioned positive electrode active materials can be used to modify the positive electrode active materials by doping, surface coating, or doping and surface coating at the same time.

[0069] In the positive electrode sheet of this application, the positive electrode film layer typically comprises a positive electrode active material, and optionally a binder and optionally a conductive agent. The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder used for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent used 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 disposed on two opposite surfaces of the positive electrode current collector, if the composition or parameters of the positive electrode film layer on either surface meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0070] [Electrolytes] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The secondary battery of this application does not have specific limitations on the type of electrolyte and can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0071] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0072] 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 bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0073] In some embodiments, the type of solvent is not specifically limited and can be selected according to actual needs. As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl 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), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0074] In some embodiments, the solvent may optionally be a non-aqueous solvent.

[0075] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0076] [Isolation membrane] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material 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.

[0077] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0078] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0079] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0080] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0081] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0082] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0083] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0084] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0085] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0086] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0087] Electrical appliances This application also provides an electrical device, which includes at least one of the secondary battery, battery module, and battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0088] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0089] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0090] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0091] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents, first active materials, and second active materials used in the embodiments are commercially available or synthesized by conventional methods, as are the instruments used in the embodiments.

[0092] Examples 1-9 The lithium-ion batteries containing the negative electrode of this application in Examples 1-9 were prepared according to the following method.

[0093] Preparation of negative electrode sheet 1. According to Table 1, the first active material of the first active material layer, the conductive agent Super-P, the binder SBR, and the thickener CMC are mixed in a mass ratio of 96:1:2:1. After being thoroughly stirred and mixed evenly in a deionized water solvent system, slurry A is obtained. 2. According to Table 1, the second active material of the second active material layer, conductive agent Super-P, binder SBR, thickener CMC are mixed at a mass ratio of 96:1:2:1. After being thoroughly stirred and mixed evenly in a deionized water solvent system, slurry B is obtained. 3. According to Table 1, first coat slurry A onto Cu foil and dry it to obtain electrode A coated with the first active material layer; 4. According to Table 1, slurry B is coated on the surface of electrode A, dried, and then cold-pressed and slit to obtain a negative electrode with a double active material layer. The coating amounts of the first active material layer and the second active material layer satisfy CW1 and CW2, respectively.

[0094] Preparation of positive electrode sheet The positive electrode active material LiFePO4, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2. The solvent N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet was obtained.

[0095] Preparation of electrolyte Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0096] Preparation of the separating membrane Polyethylene film is used as the separation membrane.

[0097] Preparation of secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0098] Comparative Examples 1-3 The preparation methods of the secondary batteries in Comparative Examples 1-3 are similar to those in Examples 1-13, except that the preparation process of the negative electrode sheet is detailed in Table 1.

[0099] Test section Energy density: At 25℃, a lithium-ion battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at 0.1C to 2.8V, yielding the discharge energy Q. The mass of the battery is M, then the energy density = Q / M.

[0100] Charging time: The time taken to charge from 85% SOC to 85% SOC at a constant current rate within the lithium plating window at 25°C is the charging time described in this application.

[0101]

[0102] This application achieves a battery negative electrode with both higher energy density and better charge-discharge kinetics by employing double or multiple active material layers in the negative electrode and controlling the relationship between the interlayer spacing and coating weight of each active material layer.

[0103] According to Table 1, a comparison between Examples 1-9 and Comparative Examples 1-3 shows that by employing a double-layer active material layer on the negative electrode and controlling the relationship between the interlayer spacing and coating weight of each active material layer, the resulting secondary battery exhibits both higher energy density and better charge-discharge kinetics performance. In short, the negative electrode materials prepared by the method of this invention all meet the requirements of charging time ≤ 75 min and 0.3C energy density ≥ 170 Wh / kg.

[0104] Comparative Examples 1-3 do not conform to the relationship between the interlayer spacing and coating weight of the active material layers in this application. Specifically, compared with Example 1 of this application, Comparative Example 1 uses hard carbon with a larger interlayer spacing as the second active material, resulting in a much lower capacity density than Example 1. That is, a larger interlayer spacing in the second active material layer leads to stronger charging capability but lower capacity, clearly failing to balance energy density and charge-discharge kinetics performance. Compared with Example 1, in Comparative Example 2, the interlayer spacing relative factor α is outside the range of this application (1≤α≤1.12), also failing to balance energy density and charge-discharge kinetics performance. Compared with Example 1, Comparative Example 3 uses a single-layer coating, demonstrating that under the same coating weight, a single-layer coating cannot balance energy density and charge-discharge kinetics performance.

[0105] Furthermore, compared with Examples 1-3, the CW2 / (CW2+CW1) of Example 5 exceeds the scope of this application, resulting in good charge-discharge kinetic performance but failing to achieve good energy density. Conversely, the CW2 / (CW2+CW1) of Example 4 exceeds the scope of this application, resulting in good energy density but failing to achieve good charge-discharge kinetic performance.

[0106] Furthermore, compared with Examples 1, 6, and 7, the Db50 / Da50 of Examples 8 and 9 are outside the scope of this application and cannot simultaneously achieve energy density and charge / discharge kinetic performance.

[0107] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0108] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and an active material layer disposed on at least one surface of the negative electrode current collector, wherein, The active material layer includes a first active material layer and a second active material layer disposed on the surface of the first active material layer. The first active material layer includes a first active material, and the second active material layer includes a second active material. The active material layer satisfies: α CW2≤CW1, where α: Interlayer spacing relative factor, α= And 1≤α≤1.12; d1: Interlayer spacing corresponding to the d002 peak of the first active material, in nm; d2: The interlayer spacing corresponding to the d002 peak of the second active material, in nm; CW1: The mass of the first active material layer disposed on the negative electrode current collector per unit area, in g / m². 2 ; CW2: The mass of the second active material layer disposed on the negative electrode current collector per unit area, in g / m². 2 ; The interlayer spacing d1 corresponding to the d002 peak of the first active material ranges from 0.335 to 0.3362 nm, and the interlayer spacing d2 corresponding to the d002 peak of the second active material ranges from 0.3356 to 0.38 nm. The volume average particle size Da50 of the first active material ranges from 8 to 20 μm, and the volume average particle size Db50 of the second active material ranges from 4 to 12 μm. The mass CW1 of the first active material layer disposed on the negative electrode current collector per unit area ranges from 80 to 200 g / m. 2 The mass CW2 of the second active material layer disposed on the negative electrode current collector per unit area ranges from 10 to 110 g / m². 2 .

2. The negative electrode sheet according to claim 1, wherein, The active material layer satisfies: CW2 ≥ α CW1.

3. The negative electrode sheet according to claim 1 or 2, wherein, and Inversely proportional, and 0.2 ≤ ≤0.45, in Da50: Volume average particle size of the first active material, in μm; Db50: Volume average particle size of the second active material, in μm.

4. The negative electrode sheet according to claim 3, wherein, The volume average particle size Da50 of the first active material and the volume average particle size Db50 of the second active material satisfy 0.2 ≤ ≤0.

8.

5. The negative electrode sheet according to claim 1, wherein, The first active material is natural graphite or artificial graphite, and / or, The second active material is artificial graphite.

6. The negative electrode sheet according to claim 1, wherein, The first active material layer and / or the second active material layer contain soft carbon or hard carbon.

7. A secondary battery, wherein, The secondary battery includes a negative electrode sheet according to any one of claims 1-6.

8. A battery module, wherein, Includes the secondary battery according to claim 7.

9. A battery pack, wherein, This includes the secondary battery according to claim 7 or the battery module according to claim 8.

10. An electrical device comprising at least one of the secondary battery according to claim 7, the battery module according to claim 8, and the battery pack according to claim 9.

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