Positive electrode sheet, battery, battery pack, and electric device

Abstract

The application discloses a positive electrode sheet, a battery, a battery pack and a power utilization device, wherein the positive electrode sheet comprises a positive current collector, a bottom coating layer and an upper coating layer in sequence; the mass fraction of a first binder in the bottom coating layer is P b %, the mass fraction of a second binder in the upper coating layer is P t %, the thickness of the bottom coating layer is h b , the thickness of the upper coating layer is h t , the mass fraction of the first binder on the side surface of the bottom coating layer close to the positive current collector is C b %, the mass fraction of the second binder on the side surface of the upper coating layer away from the bottom coating layer is C t %, P b %>P t %, and 0.8<=A / P t <=1.2 is met. The positive electrode sheet of the application effectively improves the energy density of the battery and reduces the electrode impedance of the electrode sheet on the basis of ensuring that the peeling strength between the positive current collector and the bottom coating layer meets the product requirements.

Description

Technical Field

[0001] This application belongs to the field of batteries, specifically relating to a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Technology

[0002] In the fabrication of the positive electrode sheet for lithium-ion batteries, binders are widely used to improve the bonding strength between the coating layer and the current collector. Decomposition of the peel force in the thickness direction of the positive electrode sheet reveals that the peel force between the coating layers is much greater than the peel force between the coating layer and the current collector. Based on this observation, it can be concluded that the bonding force between the coating layers is strong, but the bonding force between the coating layer and the current collector is weak, causing the coating layer to easily detach from the current collector. To address this issue, existing technologies generally increase the amount of binder in the coating layer. However, this reduces the amount of active material in the coating layer, thereby lowering the battery's energy density and increasing electrode impedance, which is detrimental to ion conduction efficiency. Therefore, it is necessary to improve existing positive electrode sheets. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to provide a positive electrode sheet, a battery, a battery pack, and an electrical device. The positive electrode sheet provided by this application, while ensuring that the peel strength between the positive current collector and the undercoating meets product requirements, also effectively improves the energy density of the battery and reduces the electrode impedance of the electrode sheet.

[0004] A first aspect of this application discloses a positive electrode sheet. According to an embodiment of this application, the positive electrode sheet comprises: a positive current collector, a base coating layer, and an upper coating layer. The base coating layer is disposed on at least a portion of the surface of the positive current collector, and the upper coating layer is disposed on at least a portion of the surface of the base coating layer away from the positive current collector. The base coating layer comprises a first adhesive, and the upper coating layer comprises a second adhesive. The mass fraction of the first adhesive in the base coating layer is P. b The mass fraction of the second adhesive in the upper dressing layer is P. t %, the thickness of the base coating is h b The thickness of the upper dressing layer is h. t The mass fraction of the first binder on the surface of the base coating near the positive current collector is C. b The mass fraction of the second adhesive on the surface of the upper dressing layer away from the base coating layer is C. t %, P b %>P t %;satisfy: 0.8≤A / P t ≤1.2, Wherein, A% represents the optimal mass fraction of the second adhesive in the upper dressing layer.

[0005] The positive electrode sheet according to the above embodiments of this application can not only ensure that the peel strength between the positive current collector and the bottom coating meets the product requirements and avoid delamination or failure caused by insufficient interfacial bonding, but also significantly reduce the amount of adhesive used in the upper coating layer, providing more space for the positive electrode active material, thereby effectively improving the energy density of the battery. At the same time, it also reduces the electrode impedance of the electrode sheet and optimizes the ion transport path of the electrode sheet.

[0006] In addition, the positive electrode sheet according to the above embodiments of this application may also have the following additional technical features:

[0007] In some embodiments of this application, the following condition is satisfied: 0.9 ≤ A / P t ≤1.1.

[0008] In some embodiments of this application, the mass fraction P of the first adhesive in the base coating layer b The value range of % is: 2% ≤ P b % ≤ 10%.

[0009] In some embodiments of this application, the mass fraction P of the second adhesive in the upper dressing layer t The value range of % is: 0.6% ≤ P t % ≤ 3.2%.

[0010] In some embodiments of this application, the thickness h of the base coating is... b The value range is: 10μm≤h b ≤30μm.

[0011] In some embodiments of this application, the thickness h of the upper dressing layer t The value range is: 50μm≤h t ≤150μm.

[0012] In some embodiments of this application, the value of k ranges from 0.8 to 1.9.

[0013] In some embodiments of this application, the first adhesive and the second adhesive each independently comprise at least one of polyvinylidene fluoride, polyacrylonitrile, and polyvinyl fluoride.

[0014] A second aspect of this application discloses a battery. According to an embodiment of this application, the battery includes the positive electrode sheet of the first aspect. Therefore, the battery of this application has high energy density and excellent rate performance and cycle life.

[0015] A third aspect of this application discloses a battery pack. According to embodiments of this application, the battery pack includes a positive electrode sheet (first aspect) or a battery (second aspect). Therefore, the battery pack of this application has high energy density and excellent rate performance and cycle life.

[0016] A fourth aspect of this application discloses an electrical device. According to an embodiment of this application, the electrical device includes a positive electrode sheet (first aspect), a battery (second aspect), or a battery pack (third aspect). Therefore, because the electrical device uses the aforementioned battery or battery pack, the battery or battery pack of the electrical device has high energy density and excellent rate performance and cycle life. The features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0019] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application.

[0020] Figure label:

[0021] 100 - Positive current collector, 200 - Base coating layer, 300 - Top dressing layer. Detailed Implementation

[0022] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0024] The first aspect of this application discloses a positive electrode sheet. According to embodiments of this application, refer to the appendix... Figure 1The positive electrode sheet includes: a positive current collector 100, a base coating layer 200, and an upper coating layer 300. The base coating layer 200 is disposed on at least a portion of the surface of the positive current collector 100, and the upper coating layer 300 is disposed on at least a portion of the surface of the base coating layer 200 away from the positive current collector 100. The base coating layer 200 includes a first adhesive, and the upper coating layer 300 includes a second adhesive. The mass fraction of the first adhesive in the base coating layer 200 is P. b The mass fraction of the second adhesive in the upper dressing layer 300 is P. t The thickness of the base coating 200 is h. b The thickness of the upper dressing layer is h (300). t The mass fraction of the first binder on the surface of the base coating 200 near the positive current collector 100 is C. b The mass fraction of the second adhesive on the surface of the upper dressing layer 300 away from the base coating layer 200 is C. t %, P b %>P t % (i.e., the mass fraction of the first adhesive in the base layer 200 is greater than the mass fraction of the second adhesive in the upper dressing layer 300); satisfying: 0.8≤A / P t ≤1.2, Where A% represents the optimal mass fraction of the second adhesive in the upper dressing layer 300, and k represents the adhesive buoyancy unevenness coefficient. This indicates the thickness percentage of the base coating layer (200). This indicates the reduction effect of the primer layer 200 on the adhesive requirement of the dressing layer. Indicates the thickness h of the dressing layer t Compared to a base coating thickness of 200, h b and primer 200 adhesive mass fraction P b The impact.

[0025] It should be noted that during the drying process of preparing the positive electrode sheet, the first binder in the bottom coating layer and the second binder in the upper coating layer may float to the surface. The first binder in the bottom coating layer floats away from the positive current collector, and the second binder in the upper coating layer floats away from the bottom coating layer. Therefore, the mass fraction P of the first binder in the bottom coating layer... b % of the mass fraction C of the first binder on the surface of the base coating near the positive electrode current collector. b The percentage difference is that the mass fraction P of the second adhesive in the upper dressing layer is different. t % of the mass fraction of the second adhesive on the surface of the upper dressing layer away from the base coat layer C t %different.

[0026] The positive electrode sheet according to the above embodiments of this application can not only ensure that the peel strength between the positive current collector and the bottom coating meets the product requirements and avoid delamination or failure caused by insufficient interfacial bonding, but also significantly reduce the amount of adhesive used in the upper coating layer, providing more space for the positive electrode active material, thereby effectively improving the energy density of the battery. At the same time, it also reduces the electrode impedance of the electrode sheet and optimizes the ion transport path of the electrode sheet.

[0027] The beneficial effects that the positive electrode sheet proposed in this application can achieve are described in detail below:

[0028] To address the issue of the coating layer easily detaching from the current collector, but increasing the amount of binder in the coating layer reduces the amount of active material, thus lowering the battery's energy density and increasing electrode impedance, this application addresses this problem by sequentially depositing a base layer and an upper coating layer on the surface of the positive electrode current collector. The first binder content in the base layer is greater than the second binder content in the upper coating layer. Therefore, by depositing a base layer with a higher binder content on the surface of the positive electrode current collector, the peel strength between the current collector and the base layer can be ensured to meet product requirements, avoiding delamination or failure due to insufficient interfacial adhesion. By depositing an upper coating layer with a lower binder content on the surface of the base layer, the amount of binder in the upper coating layer is significantly reduced, providing more space for the positive electrode active material, thereby effectively improving the battery's energy density. Simultaneously, it also reduces the electrode impedance of the electrode and optimizes the ion transport path of the electrode.

[0029] However, those skilled in the art do not know the specific method for setting the content P of the first binder in the primer layer. b %, thickness of the primer layer h b The content of the second adhesive in the upper dressing layer, P t % and the thickness h of the upper dressing layer t How can the above problems be solved? The inventors discovered through research that when 0.8 ≤ A / P... t ≤1.2, This not only ensures that the peel strength between the positive electrode current collector and the base coating meets product requirements and avoids delamination or failure caused by insufficient interfacial bonding, but also significantly reduces the amount of adhesive used in the upper coating layer, providing more space for the positive electrode active material, thereby effectively improving the energy density of the battery. At the same time, it also reduces the electrode impedance of the electrode and optimizes the ion transport path of the electrode.

[0030] According to some preferred embodiments of this application, the following condition is met: 0.9 ≤ A / P tWith a strength of ≤1.1, this not only ensures that the peel strength between the positive electrode current collector and the base coating meets product requirements and avoids delamination or failure caused by insufficient interfacial bonding, but also significantly reduces the amount of adhesive used in the upper coating layer, providing more space for the positive electrode active material, thereby effectively improving the energy density of the battery. At the same time, it further reduces the electrode impedance of the electrode and optimizes the ion transport path of the electrode.

[0031] According to some specific embodiments of this application, the mass fraction P of the first adhesive in the base coating layer is... b The value range of % is: 2% ≤ P b % ≤ 10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., by the mass fraction P of the first adhesive in the base layer. b By limiting the percentage within the above range, it can be further ensured that the peel strength between the positive current collector and the base coating meets product requirements, avoiding delamination or failure caused by insufficient interfacial adhesion. In addition, it can also avoid problems caused by the mass fraction P of the first binder in the base coating. b Excessively high P% can increase battery impedance and negatively impact battery performance. Preferably, P% ≤ 4%. b % ≤ 8%.

[0032] According to some further specific embodiments of this application, the mass fraction P of the second adhesive in the upper dressing layer t The value range of % is: 0.6% ≤ P t The percentage is ≤3.2%, for example, it can be 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, etc., by measuring the mass fraction P of the second adhesive in the upper dressing layer. t By limiting the percentage within the aforementioned range, the amount of binder in the upper coating layer can be further reduced, providing more space for the positive electrode active material, thereby further improving the energy density of the battery. Simultaneously, it further reduces the electrode impedance of the electrode sheet and optimizes the ion transport path of the electrode sheet. Additionally, it avoids the problem of the mass fraction P of the second binder in the upper coating layer being affected. t The problem of electrode surface cracking due to excessively low percentage of electrode content, which affects electrode peel strength.

[0033] In the embodiments of this application, the mass fraction P of the first adhesive in the primer layer can be tested using methods conventional in the art. b %, the mass fraction P of the second adhesive in the upper dressing layer t %, the mass fraction C of the first binder on the surface of the base coating near the positive electrode current collector. b% and the mass fraction C of the second adhesive on the surface of the upper dressing layer away from the base coat layer. t As a specific example, by using infrared spectroscopy to test the characteristic absorption peak intensity of the binder at different thickness locations on the positive electrode sheet, and referring to the binder content standard curve, the binder content P at different thickness locations can be measured. b % and P t %. The PVDF content standard curve was plotted by performing infrared spectroscopy tests on multiple standard samples of positive electrode active material layers with known PVDF content. The standard samples of positive electrode active material layers also included positive electrode active material LFP and conductive agent carbon black, with a mass ratio of positive electrode active material LFP to conductive agent carbon black of 100:2.

[0034] As another concrete example, C t % Test method: The intensity of the characteristic absorption peak of PVDF on the surface of the positive electrode is measured. Referring to the PVDF content standard curve, the PVDF content C on the surface of the positive electrode can be determined. t %. As another concrete example, C b % Test method: Peel off the current collector to expose the bottom surface of the primer coating. Test the intensity of the characteristic absorption peak of the adhesive on the bottom surface of the primer coating. Referring to the standard curve of adhesive content, the adhesive content C of the bottom surface of the primer coating can be determined. b %.

[0035] In the embodiments of this application, the thickness h of the base coating is... b The thickness of the undercoat layer needs to be kept as thin as possible while ensuring good adhesion, so as not to affect the overall conductivity and energy density of the battery. According to some specific embodiments of this application, the thickness h of the undercoat layer... b The value range is: 10μm≤h b ≤30μm, for example, it can be 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, etc., by adjusting the thickness h of the base coating. b The value of h is limited to the above range, which can ensure the bonding strength between the positive electrode current collector and the base coating, avoiding delamination or failure caused by insufficient interfacial bonding, and also avoid problems caused by the thickness h of the base coating. b Excessive thickness can negatively impact the overall conductivity and energy density of the battery. A thickness of 15μm ≤ h is preferred. b ≤25μm.

[0036] In the embodiments of this application, the thickness h of the upper dressing layer t The thickness h of the base coating b It needs to be much larger because the upper coating layer bears the load of the battery's active materials and performs conductive functions. According to some specific embodiments of this application, the thickness h of the upper coating layer... tThe value range is: 50μm≤h t ≤150μm, for example, it can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, etc., by adjusting the thickness h of the upper dressing layer. t The value is limited to the above range to ensure battery capacity while avoiding issues caused by the thickness h of the upper coating layer. t The problem of increased battery impedance due to excessive size. Preferably, 80μm ≤ h. t ≤120μm.

[0037] In the embodiments of this application, the thickness h of the base coating can be tested using methods conventional in the art. b and the thickness h of the upper dressing layer t As a concrete example, the positive electrode sheet undergoes cross-sectional processing (such as ion beam cutting), and the cross-section is then observed using a scanning electron microscope (SEM). The thickness h of the upper dressing layer is directly measured from the surface of the upper dressing layer to the interface between the upper dressing layer and the base layer using the microscope's built-in scale or image analysis software. t The thickness h of the base coat is measured as the vertical distance from the interface between the upper dressing layer and the base coat layer to the surface of the current collector. b .

[0038] According to some specific embodiments of this application, the value range of the adhesive floating unevenness coefficient k is: 0.8 ≤ k ≤ 1.9. For example, k can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, etc. By limiting the value of the adhesive floating unevenness coefficient k to the above range, it can be further ensured that 0.8 ≤ A / P is satisfied. t With a strength of ≤1.2, it can further ensure that the peel strength between the positive electrode current collector and the bottom coating meets the product requirements, avoid delamination or failure caused by insufficient interfacial bonding, and further significantly reduce the amount of binder in the upper coating layer, providing more space for the positive electrode active material, thereby effectively improving the energy density of the battery. At the same time, it also further reduces the electrode impedance of the electrode and optimizes the ion transport path of the electrode.

[0039] In the embodiments of this application, the specific types of the first and second adhesives are not particularly limited, and those skilled in the art can choose them according to actual needs. As some preferred embodiments, the first and second adhesives each independently include at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyvinyl fluoride (PVF), and other polymeric materials resistant to electrolyte corrosion can also be selected. It should be noted that the types of the first and second adhesives can be the same or different.

[0040] In some embodiments of this application, the aforementioned base coating layer and upper dressing layer may further include a positive electrode active material and an optional positive electrode conductive agent, respectively. As examples, the positive electrode active material includes lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate (LiFe). 1-x M x At least one of PO4, M includes at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, and B, 0 ≤ x ≤ 0.6, for example, x is 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.3, 0.4, 0.5, 0.6, etc. As an example, the positive electrode 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 types of positive electrode active materials in the base coating layer and the upper coating layer can be the same or different. Similarly, the types of positive electrode conductive agents in the base coating layer and the upper coating layer can be the same or different.

[0041] In some embodiments of this application, the positive current collector may include a metal foil or a composite positive current collector. For example, the metal foil may be aluminum foil. The composite positive current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. For example, the composite negative current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0042] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the undercoating is disposed on either or both of the two opposite surfaces of the positive current collector.

[0043] In the embodiments of this application, the method for preparing the above-mentioned positive electrode sheet is not particularly limited. As some specific embodiments, the above method includes:

[0044] S100: First, the positive electrode active material, a first binder, an optional conductive agent, and a solvent are mixed to form a first slurry. Then, the first slurry is coated onto at least a portion of the surface of the positive electrode current collector and dried to form a base coating.

[0045] S200: First, the positive electrode active material, the second binder, an optional conductive agent, and a solvent are mixed to form a second slurry. Then, the second slurry is coated onto at least a portion of the surface of the base coating layer and dried to form the upper coating layer.

[0046] A second aspect of this application discloses a battery. According to an embodiment of this application, the battery includes the positive electrode sheet of the first aspect. Therefore, the battery of this application has high energy density and excellent rate performance and cycle life.

[0047] The aforementioned battery also includes a positive electrode, a negative electrode, and an electrolyte, with a composite separator disposed between the positive and negative electrodes. The specific type of battery is not particularly limited, and includes, but is not limited to, lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries.

[0048] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer including a negative active material.

[0049] In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0050] In some embodiments of this application, 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 substrate 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 (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0051] In some embodiments of this application, the negative electrode active material layer may optionally include a binder. The binder may include at least one 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).

[0052] In some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0053] This application does not impose any particular limitation on the aforementioned diaphragm; any known porous diaphragm with electrochemical and chemical stability can be selected, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The diaphragm can be single-layered or multi-layered.

[0054] In embodiments of this application, the battery further includes an electrolyte comprising an organic solvent and an electrolyte salt. The organic solvent serves as a medium for ion transport in the electrochemical reaction and can be any organic solvent known in the art for use in battery electrolytes. Exemplarily, the organic solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). In specific embodiments, two or more of the above-mentioned organic solvents can be selected.

[0055] The electrolyte salt serves as the ion source and can be any electrolyte salt known in the art for use in battery electrolytes. Exemplarily, the electrolyte salt can be at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium nitrate (LiNO3), and lithium fluoride (LiF).

[0056] As an example, the electrolyte formulation is EC:DMC:EMC:LiPF6 = 2:3:5:1.

[0057] A third aspect of this application discloses a battery pack. According to embodiments of this application, the battery pack includes a positive electrode sheet (first aspect) or a battery (second aspect). Therefore, the battery pack of this application has high energy density and excellent rate performance and cycle life.

[0058] In some embodiments, the battery pack can be a battery module, and the number of battery cells 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.

[0059] In some embodiments, the battery pack can be a battery module, and the number of battery modules 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.

[0060] A fourth aspect of this application discloses an electrical device. According to an embodiment of this application, the electrical device includes a positive electrode sheet (first aspect), a battery (second aspect), or a battery pack (third aspect). Therefore, because the electrical device uses the aforementioned battery or battery pack, the battery or battery pack of the electrical device has high energy density and excellent rate performance and cycle life. The features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0061] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, 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.

[0062] As electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0063] As one example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device, a battery pack or battery module can be used.

[0064] Another example of the device could be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a single battery cell as its power source.

[0065] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0066] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Furthermore, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art. 10μm

[0067] Example 1

[0068] This embodiment provides a battery, the preparation method of which includes:

[0069] (1) Preparation of positive electrode sheet

[0070] 1) Weigh out the positive electrode active material LFP, binder PVDF, and conductive agent carbon black, wherein the mass ratio of positive electrode active material LFP, binder PVDF, and conductive agent carbon black is 92:6:2. Add NMP solvent, stir evenly, and adjust the viscosity of the slurry to obtain the first slurry. Coat the first slurry evenly on both sides of the aluminum foil, control the coating thickness, dry the thin coating to ensure no residual solvent, and form a base coating with a thickness of 20μm.

[0071] 2) Weigh out the positive electrode active material LFP, binder PVDF, and conductive agent carbon black, wherein the mass ratio of positive electrode active material LFP, binder PVDF, and conductive agent carbon black is 97.46:1.04:1.5. Add NMP solvent, stir evenly, and adjust the slurry viscosity to obtain the second slurry. Coat the second slurry evenly on the surface of the base layer, control the coating thickness, dry the thin coating to ensure no residual solvent, and form the upper coating layer with a thickness of 100μm.

[0072] (2) Preparation of negative electrode sheet

[0073] A negative electrode slurry was prepared by mixing graphite material, conductive carbon black, SBR binder, CMC dispersant, NMP, and H2O, with the mass ratio of graphite material, conductive carbon black, SBR, CMC, NMP, and H2O being 100:2:2:2:5:100. The slurry was then coated, baked, and rolled (compacted to 1.5 g / cm³). 3 After that, the negative electrode sheet is obtained.

[0074] (3) Electrolyte

[0075] The electrolyte formulation is EC:DMC:EMC:LiPF6 = 2:3:5:1.

[0076] (4) Diaphragm

[0077] A polyethylene film with a thickness of 16 micrometers was selected as the diaphragm.

[0078] (5) Battery manufacturing

[0079] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. This is then wound to obtain a bare cell. Tabs are welded onto the cells, and the bare cell is placed in outer packaging. Each battery consists of one core, which comprises 7 positive electrode sheets, 8 negative electrode sheets, and 16 separator sheets, with a negative electrode excess of 15%. The prepared electrolyte is injected into the dried cell, followed by encapsulation, settling, formation, and shaping to complete the preparation of the lithium-ion battery.

[0080] Examples 2-10

[0081] The preparation method of this embodiment is basically the same as that of Example 1, except for the preparation of the positive electrode sheet, as shown in Table 1.

[0082] Comparative Examples 1-5

[0083] The preparation methods of Comparative Examples 1 to 5 are basically the same as those of Example 1, except for the preparation of the positive electrode sheet, as shown in Table 1.

[0084] The parameter testing methods in Table 1 are as follows.

[0085] 1. Adhesive content test method:

[0086] (1) The intensity of the characteristic absorption peak of PVDF at different thickness positions of the positive electrode sheet was measured by infrared spectroscopy. With reference to the PVDF content standard curve, the PVDF content P at different thickness positions could be measured. b % and P t %. The PVDF content standard curve was plotted by performing infrared spectroscopy tests on multiple standard samples of positive electrode active material layers with known PVDF content. The standard samples of positive electrode active material layers also included positive electrode active material LFP and conductive agent carbon black, with a mass ratio of positive electrode active material LFP to conductive agent carbon black of 100:2.

[0087] (2)C t % Test method: The intensity of the characteristic absorption peak of PVDF on the surface of the positive electrode is measured. Referring to the PVDF content standard curve, the PVDF content C on the surface of the positive electrode can be determined. t %.

[0088] (3)C b % Test method: The current collector is peeled off to expose the bottom surface of the primer coating. The intensity of the characteristic absorption peak of PVDF on the bottom surface of the primer coating is tested. Referring to the PVDF content standard curve, the PVDF content (C) on the bottom surface of the primer coating can be determined. b %.

[0089] 2. Thickness testing method:

[0090] The positive electrode sheet was subjected to ion beam cutting for cross-section analysis, followed by observation of the cross-section using a scanning electron microscope (SEM). The thickness h of the upper dressing layer was directly measured using the microscope's built-in scale, from the surface of the upper dressing layer to the interface between the upper dressing layer and the base layer. t The thickness h of the base coat is measured as the vertical distance from the interface between the upper dressing layer and the base coat layer to the surface of the current collector. b .

[0091] Table 1

[0092] <![CDATA[P b %]]> <![CDATA[P t %]]> <![CDATA[h b (μm)]]> <![CDATA[h t (μm)]]> k A <![CDATA[A / P t ]]> Example 1 2 3.125 20 100 1.5 3.13 1.002 Example 2 10 0.625 20 100 1.5 0.63 1.008 Example 3 6 1.89 10 100 1.5 1.89 1.000 Example 4 6 0.75 30 100 1.5 0.75 1.000 Example 5 6 0.60 20 50 1.5 0.60 1.000 Example 6 6 1.47 20 150 1.5 1.47 1.000 Example 7 6 0.940 20 100 0.8 0.94 1.000 Example 8 6 1.100 20 100 1.9 1.10 1.000 Example 9 6 0.938 20 100 1.5 1.04 1.109 Example 10 6 1.25 20 100 1.5 1.04 0.832 Comparative Example 1 6 1.49 20 152 1.5 2.01 1.349 Comparative Example 2 6 1.125 20 100 1.5 1.61 1.431 Comparative Example 3 6 2.767 20 100 1.5 2.13 0.770 Comparative Example 4 6 2.6838 20 100 1.5 2.13 0.794 Comparative Example 5 2.5 2.5 50 50 1.5 0.7 0.28

[0093] The peeling force of the positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-5 was tested. The DC internal resistance at 50% SOC, the mixed specific capacity, and the energy density of the batteries prepared in Examples 1-10 and Comparative Examples 1-5 were also tested. The test methods are as follows, and the test results are shown in Table 2.

[0094] Peel strength test method: Adhere pressure-sensitive tape to a stainless steel plate, then fix the area (40×100mm) 2The positive electrode active material layer of the positive electrode sheet is bonded to a pressure-sensitive adhesive tape on one side. The tensile testing machine clamps the positive electrode sheet and peels it off at 180°. The force that peels the positive electrode active material layer off the aluminum foil is called the peeling force.

[0095] 50% SOC DC internal resistance test method: At room temperature (25±5℃), discharge the battery at 1 / 3C constant current to 2.0V, charge it at 1 / 3C constant current to 50% SOC, and let it rest for 30 minutes; discharge it at 1.5C constant current for 30 seconds, and then test the 50% SOC DC internal resistance.

[0096] Mixed material specific capacity test method: At room temperature (25±5℃), the battery is discharged at 1 / 3C constant current to 2.0V, and then charged at 1 / 3C constant current and constant voltage to 3.8V. The cutoff current is 0.05C, and the cycle is repeated 3 times. The discharge capacity of the third cycle is the battery capacity. Mixed material specific capacity = battery capacity / positive electrode coating amount.

[0097] Energy density test method: At room temperature (25±5℃), the battery is discharged at 1 / 3C constant current to 2.0V, charged at 1 / 3C constant current and constant voltage to 3.8V, and the cut-off current is 0.05C. The cycle is repeated 3 times. The energy of the third discharge is the battery energy. The battery volume is tested by the water displacement method. Energy density = battery energy / battery volume.

[0098] Table 2

[0099]

[0100] As shown in Table 2, compared with Comparative Examples 1-5, the positive electrode sheets of Examples 1-10, while ensuring that the peel force meets product requirements (peel force ≥ 1.0 N / 40 mm), also reduced the battery's SOC DC internal resistance by 50%, and improved the battery's mixed-material specific capacity and energy density. This demonstrates that by setting a base coating with a high binder content on the surface of the positive electrode current collector, and simultaneously setting a top coating layer with a low binder content on the surface of the base coating, while satisfying 0.8 ≤ A / P... t When the value is ≤1.2, it can effectively reduce the DC internal resistance of the battery by 50% and improve the mixed capacity and energy density of the battery, while ensuring that the peeling force of the positive electrode meets the product requirements (peeling force ≥1.0N / 40mm).

[0101] Compared to Examples 9 and 10, the 50% SOC DC internal resistance of the batteries in Examples 1-8 is further reduced, and the mixed-material specific capacity and energy density of the batteries in Examples 1-8 are further improved. It can be seen that when 0.9 ≤ A / P is satisfied... t When the value is ≤1.1, the DC internal resistance of the battery can be further reduced by 50% of the SOC, and the mixed capacity and energy density of the battery can be further improved.

[0102] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0103] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode plate, characterized in that, include: A positive current collector, a base coating layer, and an upper dressing layer, wherein the base coating layer is disposed on at least a portion of the surface of the positive current collector, and the upper dressing layer is disposed on at least a portion of the surface of the base coating layer away from the positive current collector, the base coating layer comprising a first adhesive, and the upper dressing layer comprising a second adhesive; The mass fraction of the first adhesive in the base coating is P. b The mass fraction of the second adhesive in the upper dressing layer is P. t %, the thickness of the base coating is h b The thickness of the upper dressing layer is h. t The mass fraction of the first binder on the surface of the base coating near the positive current collector is C. b The mass fraction of the second adhesive on the surface of the upper dressing layer away from the base coating layer is C. t %, P b %>P t %; satisfy: 0.8≤A / P t ≤1.2, Wherein, A% represents the optimal mass fraction of the second adhesive in the upper dressing layer.

2. The positive electrode sheet according to claim 1, characterized in that, Satisfies: 0.9 ≤ A / P t ≤1.

1.

3. The positive electrode sheet according to claim 1, characterized in that, The mass fraction P of the first adhesive in the base coating b The value range of % is: 2% ≤ P b % ≤ 10%.

4. The positive electrode sheet according to claim 1, characterized in that, The mass fraction P of the second adhesive in the upper dressing layer t The value range of % is: 0.6% ≤ P t % ≤ 3.2%.

5. The positive electrode sheet according to claim 1, characterized in that, The thickness h of the base coating b The value range is: 10μm≤h b ≤30μm.

6. The positive electrode sheet according to claim 1, characterized in that, The thickness h of the upper dressing layer t The value range is: 50μm≤h t ≤150μm.

7. The positive electrode sheet according to claim 1, characterized in that, The range of values ​​for k is: 0.8≤k≤1.

9.

8. The positive electrode sheet according to claim 1, characterized in that, The first adhesive and the second adhesive each independently comprise at least one of polyvinylidene fluoride, polyacrylonitrile, and polyvinyl fluoride.

9. A battery, characterized in that, The positive electrode sheet includes any one of claims 1 to 8.

10. A battery pack, characterized in that, It includes the positive electrode sheet according to any one of claims 1 to 8 or the battery according to claim 9.

11. An electrical appliance, characterized in that, It includes the positive electrode sheet according to any one of claims 1 to 8, the battery according to claim 9, or the battery pack according to claim 10.

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