Positive electrode sheet, method for manufacturing the same, and battery

Abstract

The application relates to a positive electrode sheet, a preparation method thereof and a battery. The positive electrode sheet comprises a current collector, a safety protection layer and an active material layer arranged on at least one surface of the current collector, and the safety protection layer is arranged between the current collector and the active material layer. The safety protection layer comprises an electro-deformation material and a conductive material. The conductive material comprises carbon nanotubes and conductive carbon. The mass proportion of the electro-deformation material in the safety protection layer is 80%-90%. In the case that the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electro-deformation material, the volume of the safety protection layer can expand. In this way, the risk of thermal runaway of the battery under high voltage can be reduced, and the safety performance of the battery can be effectively improved. Meanwhile, when the voltage applied to the safety protection layer is reduced to be lower than the deformation voltage threshold of the electro-deformation material, the volume of the safety protection layer can be restored, and the positive electrode sheet can be restored for use.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a positive electrode sheet, its preparation method, and a battery. Background Technology

[0002] Rechargeable batteries are now widely used in many industries. However, as the complexity of battery application environments increases, the risk of battery abuse also rises. Battery abuse threatens battery safety. Furthermore, as battery energy density increases, heat dissipation efficiency relatively decreases. Under the same abuse conditions, more heat accumulates inside the battery, increasing the risk of thermal runaway.

[0003] Safety concerns surrounding rechargeable batteries have become a major obstacle to their further application in fields such as electric vehicles. Therefore, reducing the risk of thermal runaway and improving the safety of rechargeable batteries are urgent technical challenges that need to be addressed. Summary of the Invention

[0004] In view of this, the present application provides a positive electrode sheet, a method for preparing the same, and a battery to solve at least one problem existing in the prior art.

[0005] In a first aspect, embodiments of this application provide a positive electrode sheet, comprising: a current collector and a safety protection layer and an active material layer disposed on at least one surface of the current collector, wherein the safety protection layer is located between the current collector and the active material layer;

[0006] The safety protection layer comprises an electrodeformable material and a conductive material; the conductive material comprises carbon nanotubes and conductive carbon; the electrodeformable material accounts for 80% to 90% of the mass of the safety protection layer;

[0007] When the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand.

[0008] In conjunction with the first aspect of this application, in an alternative embodiment, the security protection layer satisfies at least one of the following features:

[0009] (1) The conductive material accounts for 10% to 20% of the mass of the safety protection layer;

[0010] (2) The electrodeformation material includes a relaxor ferroelectric material; optionally, the relaxor ferroelectric material includes a multi-component copolymer of vinylidene fluoride and monomer and / or polyvinylidene fluoride, wherein the monomer includes at least one of trifluorochloroethylene, trifluoroethylene, and hexafluoropropylene.

[0011] (3) The conductive material includes carbon nanotubes and conductive carbon; optionally, the mass ratio of the carbon nanotubes to the conductive carbon is 1:20 to 1:1.5.

[0012] (4) The areal density of the safety protection layer is 25 mg / m³. 2 ~35mg / m 2 .

[0013] In conjunction with the first aspect of this application, in an alternative embodiment, the positive electrode sheet satisfies at least one of the following characteristics:

[0014] (1) The active material layer includes a high-nickel ternary material; optionally, the chemical formula of the high-nickel ternary material is LiNi. x Co y M z O2, wherein M is at least one of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1;

[0015] (2) The current collector includes at least one of aluminum foil, porous aluminum foil, and carbon-coated aluminum foil.

[0016] In conjunction with the first aspect of this application, in an alternative embodiment, the positive electrode sheet satisfies at least one of the following characteristics:

[0017] (1) The ratio of the sum of the thicknesses of the safety protection layer and the active material layer to the thickness of the safety protection layer is greater than or equal to 10;

[0018] (2) The thickness of the safety protection layer is 3μm to 10μm;

[0019] (3) The thickness of the active material layer is 110μm to 115μm.

[0020] In conjunction with the first aspect of this application, in an optional embodiment, the active material layer includes a first sub-active layer and a second sub-active layer stacked sequentially in the thickness direction of the current collector, the first sub-active layer being located between the safety protection layer and the second sub-active layer; the first sub-active layer comprises a single-crystal material, and the second sub-active layer comprises a polycrystalline material.

[0021] In conjunction with the first aspect of this application, in an optional embodiment, the active material layer includes a first sub-active layer and a second sub-active layer sequentially stacked in the thickness direction of the current collector, the first sub-active layer being located between the safety protection layer and the second sub-active layer; the first sub-active layer comprises a polycrystalline material, and the second sub-active layer comprises a monocrystalline material.

[0022] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, the method comprising the following steps:

[0023] An electrodeformable material is added to a first solvent and stirred until the electrodeformable material is completely dissolved. Then, a conductive material is added and mixed evenly to obtain a mixed slurry. The conductive material includes carbon nanotubes and conductive carbon.

[0024] The mixed slurry is coated on at least one surface of the current collector and subjected to a first drying treatment to obtain a safety protection layer; the electrodeformable material accounts for 80% to 90% of the mass of the safety protection layer;

[0025] The positive electrode active material, conductive agent and binder are added to the second solvent and mixed evenly to obtain the positive electrode slurry;

[0026] The positive electrode slurry is coated on the surface of the safety protection layer away from the current collector, and after a second drying process, an active material layer is obtained; when the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand.

[0027] In conjunction with the second aspect of this application, in an alternative embodiment, the step of preparing the mixed slurry satisfies at least one of the following characteristics:

[0028] (1) The electrodeformation material includes a relaxor ferroelectric material; optionally, the relaxor ferroelectric material includes a multi-component copolymer of vinylidene fluoride and monomer and / or polyvinylidene fluoride, wherein the monomer includes at least one of trifluorochloroethylene, trifluoroethylene, and hexafluoropropylene.

[0029] (2) The first solvent includes dimethylformamide;

[0030] (3) The mass ratio of the carbon nanotubes to the conductive carbon is 1:20 to 1:1.5;

[0031] (4) In the mixed slurry, the solid-liquid ratio of the electrodeformable material to the first solvent is (1-1.8):(5-12) g / mL;

[0032] (5) The conductive material accounts for 10% to 20% of the mass of the safety protection layer;

[0033] (6) Before the stirring step, a heating treatment is also included; optionally, the temperature of the heating treatment is 60℃~80℃ and the time is 0.5h~1h.

[0034] In conjunction with the second aspect of this application, in an optional embodiment, the step of preparing the positive electrode slurry satisfies at least one of the following characteristics:

[0035] (1) The positive electrode active material includes a high-nickel ternary material; optionally, the chemical formula of the high-nickel ternary material is LiNi. x Co y M z O2, where M is one or more of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1;

[0036] (2) The conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0037] (3) The adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose;

[0038] (4) In the positive electrode slurry, the positive electrode active material accounts for 95% to 97% by mass, the conductive agent accounts for 1% to 1.5% by mass, and the binder accounts for 2% to 3.5% by mass.

[0039] Thirdly, embodiments of this application provide a battery comprising a positive electrode sheet as described in any of the first aspects or a positive electrode sheet prepared by a method comprising any of the second aspects.

[0040] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0041] The positive electrode sheet, its preparation method, and battery provided in this application embodiment include a current collector and a safety protection layer and an active material layer disposed on at least one surface of the current collector. The safety protection layer is located between the current collector and the active material layer. The safety protection layer includes an electrodeformable material and a conductive material. The conductive material includes carbon nanotubes and conductive carbon. The mass percentage of the electrodeformable material in the safety protection layer is 80% to 90%. When the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand. In this embodiment, a safety protection layer is provided between the current collector and the active material layer. The safety protection layer includes an electrodeformable material and a conductive material. Carbon nanotubes in the conductive material can form a complete conductive network, and the conductive carbon can act as point-to-point conductive connections. Through the synergistic effect of carbon nanotubes and conductive carbon, the uniform distribution of current in the safety protection layer can be ensured, allowing the electrodeformable material to exhibit excellent electrodeformation performance even at lower voltages. When the battery is overcharged or in other abnormal usage conditions, causing the voltage applied to the safety protection layer to exceed the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand, increasing the spacing between the conductive material particles in the safety protection layer. By increasing the size of the electrodeformation material in the safety protection layer, the conductive network between the active material layer and the current collector is partially or completely blocked. This is achieved by controlling the mass ratio of the electrodeformation material in the safety protection layer to 80%–90%. On the one hand, this ensures that the volume of the safety protection layer expands sufficiently under high voltage, thereby reducing the risk of thermal runaway in the battery under high voltage and effectively improving the battery's safety performance. On the other hand, it avoids the problem of excessive expansion of the safety protection layer leading to a significant loss of battery capacity. As a result, when the voltage applied to the safety protection layer drops below the deformation voltage threshold of the electrodeformation material, the volume of the safety protection layer can recover, restoring the conductive connection between the active material layer and the current collector, and the positive electrode can be reused.

[0042] 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

[0043] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0044] Figure 1 A cross-sectional structural diagram of a positive electrode sheet provided in an embodiment of this application;

[0045] Figure 2 A schematic cross-sectional view of another positive electrode sheet provided in an embodiment of this application;

[0046] Figure 3 This is a schematic flowchart illustrating a method for preparing a positive electrode sheet according to an embodiment of this application. Detailed Implementation

[0047] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0048] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0049] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0050] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0051] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0052] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0053] At lower temperatures and normal voltages, the heat generation rate and total heat from internal side reactions within the battery are relatively low, providing sufficient time for heat dissipation and thus reducing the risk of thermal runaway. However, under abnormal usage conditions, such as overcharging, high voltage can cause rapid electrolyte decomposition or battery short circuits, often generating significant Joule heat and increasing the risk of thermal runaway. Related technologies typically employ three methods to prevent battery thermal runaway: The first is optimizing battery material selection and ratio, for example, using stable cathode, anode, and electrolyte materials; the second is regular battery inspection and maintenance; and the third is installing a thermal management system. These methods are costly in terms of manpower and resources, and their protective effects are limited.

[0054] Based on this, embodiments of this application provide a positive electrode sheet, such as... Figure 1 As shown, the positive electrode includes a current collector 100 and a safety protection layer 200 and an active material layer 300 disposed on at least one surface of the current collector 100. The safety protection layer 200 is located between the current collector 100 and the active material layer 300. The safety protection layer 200 includes an electrodeformable material and a conductive material. The conductive material includes carbon nanotubes (CNTs) and conductive carbon (Super-P). The mass percentage of the electrodeformable material in the safety protection layer 200 is 80% to 90%, for example, it can be 80%, 85%, 90%, or any value between any two of the above ranges. When the voltage applied to the safety protection layer 200 exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer 200 can expand.

[0055] In this embodiment, a safety protection layer 200 is provided between the current collector 100 and the active material layer 300. The safety protection layer 200 includes an electrodeformable material and a conductive material. The carbon nanotubes in the conductive material can form a complete conductive network, and the conductive carbon can play a point-to-point conductive connection role. Through the synergistic effect of carbon nanotubes and conductive carbon, the uniform distribution of current in the safety protection layer 200 can be ensured, so that the electrodeformable material can exhibit excellent electrodeformation performance at a low voltage. When the battery is overcharged or in other abnormal use states, causing the voltage applied to the safety protection layer 200 to exceed the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer 200 can expand, increasing the spacing between the conductive material particles in the safety protection layer 200. By increasing the size of the active material layer 300 and the current collector 100, the conductive network between them is partially or completely blocked. By controlling the mass ratio of the electrodeformable material in the safety protection layer 200 to 80%–90%, on the one hand, it can ensure that the volume of the safety protection layer 200 expands sufficiently under high voltage, thereby effectively reducing the risk of thermal runaway of the battery under high voltage and improving the battery's safety performance; on the other hand, it can avoid the problem of excessive expansion of the safety protection layer leading to a large loss of battery capacity. Thus, when the voltage applied to the safety protection layer 200 drops below the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer 200 can recover, allowing the conductive connection between the active material layer 300 and the current collector 100 to be restored, and the positive electrode can be reused.

[0056] It should be noted that, Figure 1 The fact that the safety protection layer 200 and the active material layer 300 are sequentially stacked on one side surface of the current collector 100 in the thickness direction is only one example. In some specific embodiments, the safety protection layer 200 and the active material layer 300 can be sequentially stacked on two opposite surfaces of the current collector 100 in the thickness direction.

[0057] In this embodiment, the current collector 100 is not particularly limited, and any current collector well known to those skilled in the art that can be used for the positive electrode can be used. For example, the current collector 100 may include at least one of aluminum foil, porous aluminum foil, and carbon-coated aluminum foil.

[0058] The electrodeformable material in the safety protection layer 200 can be understood as a material capable of deformation under an applied voltage. When the applied voltage reaches the deformation voltage threshold of the electrodeformable material, the material deforms, causing the volume of the safety protection layer 200 to expand. Specifically, the electrodeformable material can be selected based on the type of positive electrode and battery, so that the deformation voltage threshold of the electrodeformable material matches the upper voltage limit of the positive electrode active material and the safe voltage of the battery. In some specific embodiments, the deformation voltage threshold of the electrodeformable material is less than or equal to the maximum safe voltage of the battery.

[0059] In some embodiments, the electrodeformable material may include a relaxor ferroelectric material. Because relaxor ferroelectric materials have a better response to voltage changes, the dielectric constant of the safety protection layer 200 increases significantly under high voltage, which can enhance the voltage's control over the conductive connection between the active material layer 300 and the current collector 100, thereby better preventing thermal runaway.

[0060] Furthermore, the relaxor ferroelectric material may include a multi-component copolymer of vinylidene fluoride (VDF) and monomers, or a mixture of polyvinylidene fluoride (PVDF), wherein the monomers include, for example, at least one of chlorotrifluoroethylene (CTFE), ethylene trifluoroethylene (TrFE), and hexafluoropropylene (HFP). This type of material can be referred to as a PVDF-based relaxor ferroelectric material. PVDF-based relaxor ferroelectric materials exhibit significant deformation at relatively low voltages, providing the safety protection layer 200 with high electro-responsiveness and sensitive electro-deformation properties, enabling faster response to voltage changes and preventing thermal runaway of the battery at high voltages. In one specific example, the electro-deformation material may include poly(vinylidene fluoride-co-chlorotrifluoroethylene), i.e., a binary copolymer of vinylidene fluoride and chlorotrifluoroethylene, which can be abbreviated as P(VDF-CTFE). In another specific example, the electro-deformation material may include poly(vinylidene fluoride-co-hexafluoropropylene), which can be abbreviated as P(VDF-HFP).

[0061] In the safety protection layer 200, conductive materials provide electron transport functionality to ensure the electro-deformation effect of the electro-deformable material. These conductive materials include carbon nanotubes and conductive carbon, significantly improving the dielectric properties of the safety protection layer 200 and further enhancing the electro-deformation effect of the electro-deformable material. Carbon nanotubes facilitate the formation of a relatively complete conductive network, while conductive carbon provides point-to-point conductive connections, ensuring uniform current distribution during electro-deformation and thus improving the overall performance of the safety protection layer 200. Through the synergistic effect of carbon nanotubes and conductive carbon, the electro-deformable material exhibits excellent electro-deformation performance at lower voltages, while minimizing the use of conductive materials, thereby achieving a better balance between the thickness and deformation of the safety protection layer.

[0062] In some specific embodiments, the mass ratio of carbon nanotubes to conductive carbon can be 1:20 to 1:1.5, for example, 1:20, 1:15, 1:10, 1:5, 1:1.5, or any value between any two of the above ranges. Controlling the mass ratio of carbon nanotubes to conductive carbon within the above range is beneficial to further enhance the electrodeformation effect of the electrodeformable material, thereby further improving the overall performance of the safety protection layer 200.

[0063] When the mass proportion of the electrodeformable material in the safety protection layer 200 is too large and the mass proportion of the conductive material is too small, it may affect the conduction and uniform distribution of current during electrodeformation, thus affecting the electrodeformation effect of the electrodeformable material. Conversely, when the mass proportion of the electrodeformable material in the safety protection layer 200 is too small and the mass proportion of the conductive material is too large, it may affect the deformation of the safety protection layer. Therefore, in some specific embodiments, the mass proportion of the conductive material in the safety protection layer can be 10% to 20%, for example, 10%, 15%, 20%, or any value between any two of the above ranges. In this way, the electrodeformation effect of the electrodeformable material and the deformation of the safety protection layer can be better guaranteed.

[0064] When the thickness of the safety protection layer 200 is too small, it may limit the deformation of the safety protection layer 200, thereby affecting the effectiveness of the safety protection layer 200 in blocking the conductive network between the active material layer 300 and the current collector 100 under high voltage. When the thickness of the safety protection layer 200 is too large, it may affect the electro-deformation efficiency of the electro-deformation material and the energy density of the positive electrode. Therefore, in some specific embodiments, the ratio of the sum of the thicknesses of the safety protection layer 200 and the active material layer 300 to the thickness of the safety protection layer 200 can be greater than or equal to 10. In this way, the energy density requirements of the positive electrode can be well considered while effectively preventing thermal runaway of the battery under high voltage through the safety protection layer 200.

[0065] In some specific embodiments, the thickness of the safety protection layer 200 can be 3μm to 10μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any value between any two of the above ranges.

[0066] In some specific embodiments, the thickness of the active material layer 300 can be 110μm to 115μm, for example, it can be 110μm, 111μm, 112μm, 113μm, 114μm, 115μm or any value between any two of the above ranges.

[0067] In some embodiments, the areal density of the safety protection layer 200 may be 25 mg / m³. 2~35mg / m 2 For example, it can be 25mg / m 2 26mg / m 2 27mg / m 2 28mg / m 2 29mg / m 2 30mg / m 2 31mg / m 2 32mg / m 2 33mg / m 2 34mg / m 2 35mg / m 2 Or any value between any two of the above ranges. This is beneficial for balancing the thickness and deformation of the safety protection layer 200, thereby improving the overall performance of the safety protection layer 200.

[0068] In this embodiment, there are no particular limitations on the active material in the active material layer 300; any positive electrode active material well known to those skilled in the art can be used.

[0069] In some embodiments, the active material layer 300 may include a high-nickel ternary material. That is, the active material in the active material layer 300 includes a high-nickel ternary material. For example, the chemical formula of the high-nickel ternary material may be LiNi. x Co y M z O2, wherein M is at least one of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1.

[0070] Specifically, the active material layer 300 may include monocrystalline and / or polycrystalline materials. Monocrystalline materials have advantages such as good cycle performance and high-temperature storage performance, which are beneficial for improving the cycle performance and high-temperature stability of the cathode; while polycrystalline materials have advantages such as good rate performance and high capacity, which are beneficial for improving the energy density and fast-charging performance of the cathode. Therefore, in some embodiments, the active material layer 300 may include two sub-active layers, one of which may be made of monocrystalline material and the other may be made of polycrystalline material. Here, the monocrystalline material may, for example, include a high-nickel ternary monocrystalline material, and the polycrystalline material may, for example, include a high-nickel ternary polycrystalline material.

[0071] In this embodiment, the active material layer 300 adopts a multi-layer design, which utilizes the combined advantages of single-crystal and polycrystalline materials to effectively improve the dynamic performance and cycle stability of the battery while maintaining high safety performance.

[0072] In some specific embodiments, please refer to Figure 2The active material layer 300 may include a first sub-active layer 301 and a second sub-active layer 302 sequentially stacked in the thickness direction of the current collector 100. The first sub-active layer 301 is located between the safety protection layer 200 and the second sub-active layer 302. The first sub-active layer 301 includes a single crystal material, and the second sub-active layer 302 includes a polycrystalline material.

[0073] In this embodiment, a first sub-active layer 301 comprising monocrystalline material is disposed below a second sub-active layer 302 comprising polycrystalline material. Since monocrystalline material has no internal grain boundaries, it has better structural stability and can reduce the generation of microcracks during charging and discharging, thereby improving the cycle stability of the cathode. Furthermore, the first sub-active layer 301 comprising monocrystalline material in the lower layer can provide better thermal stability, reducing the risk of thermal runaway in the battery. The second sub-active layer 302, located in the upper layer, comprises polycrystalline material, which can provide better electrochemical activity and can avoid side reactions between the first sub-active layer 301 comprising monocrystalline material and the electrolyte, thereby improving the safety and lifespan of the battery.

[0074] Furthermore, the ratio of the thickness of the first sub-active layer 301 to the sum of the thicknesses of the active material layer 300 and the safety protection layer 200 can be greater than 1 / 2; the ratio of the thickness of the second sub-active layer 302 to the sum of the thicknesses of the active material layer 300 and the safety protection layer 200 can be less than 1 / 2. This is beneficial for improving the overall performance of the cathode sheet.

[0075] In some specific embodiments, please refer to [the relevant documentation]. Figure 2 The active material layer 300 may include a first sub-active layer 301 and a second sub-active layer 302 sequentially stacked in the thickness direction of the current collector 100. The first sub-active layer 301 is located between the protective layer and the second sub-active layer 302. The first sub-active layer 301 includes a polycrystalline material, and the second sub-active layer 302 includes a single-crystal material.

[0076] In this embodiment, a first sub-active layer 301 comprising polycrystalline material is disposed below a second sub-active layer 302 comprising monocrystalline material. Polycrystalline materials typically have higher conductivity and larger specific surface area. Placing the first sub-active layer 301 comprising polycrystalline material in the lower layer can improve the conductivity of the positive electrode, thereby improving the rate performance of the battery. Furthermore, placing the first sub-active layer 301 comprising polycrystalline material in the lower layer helps to reduce battery polarization, increase the median voltage during rate discharge, and reduce side reactions during battery storage.

[0077] In some embodiments, the active material layer 300 may include a positive electrode active material, a conductive agent, and a binder. The mass ratio of the positive electrode active material, the conductive agent, and the binder may be (95–97):(1–1.5):(2–3.5). Further, in the active material layer 300, the mass percentage of the positive electrode active material may be 95%–97%, the mass percentage of the conductive agent may be 1%–1.5%, and the mass percentage of the binder may be 2%–3.5%.

[0078] For example, the conductive agent may include at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0079] It should be noted that when the active material layer 300 includes a first sub-active layer 301 and a second sub-active layer 302, the mass ratio of the positive electrode active material (single crystal material or polycrystalline material), conductive agent and binder in the first sub-active layer 301 and the second sub-active layer 302 can be (95~97):(1~1.5):(2~3.5).

[0080] This application also provides a method for preparing a positive electrode sheet. Please refer to... Figure 3 The method for preparing the positive electrode sheet provided in this application includes the following steps:

[0081] S1: Add the electrodeformable material to the first solvent and stir until the electrodeformable material is completely dissolved. Then add the conductive material and mix evenly to obtain a mixed slurry. The conductive material includes carbon nanotubes and conductive carbon.

[0082] S2: The mixed slurry is coated on at least one surface of the current collector and subjected to a first drying treatment to obtain a safety protection layer; the electrodeformable material accounts for 80% to 90% of the mass of the safety protection layer;

[0083] S3: Add the positive electrode active material, conductive agent and binder to the second solvent, mix them evenly to obtain the positive electrode slurry;

[0084] S4: The positive electrode slurry is coated on the surface of the safety protection layer away from the current collector, and after a second drying process, an active material layer is obtained; when the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformation material, the volume of the safety protection layer can expand.

[0085] In this embodiment, a safety protection layer is formed between the current collector and the active material layer. Since the safety protection layer includes an electrodeformable material and a conductive material, the carbon nanotubes in the conductive material can form a complete conductive network, and the conductive carbon can act as a point-to-point conductive connection. Through the synergistic effect of the carbon nanotubes and the conductive carbon, the uniform distribution of current in the safety protection layer can be ensured. This allows the electrodeformable material to exhibit excellent electrodeformation performance even at lower voltages. When the battery is overcharged or in other abnormal usage conditions, causing the voltage applied to the safety protection layer to exceed the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand, allowing the conductive material particles in the safety protection layer to... With increased spacing, the conductive network between the active material layer and the current collector is partially or completely blocked. By controlling the mass ratio of the electrodeformable material in the safety protection layer to 80%–90%, on the one hand, it can ensure that the volume of the safety protection layer expands sufficiently under high voltage, thereby effectively reducing the risk of thermal runaway of the battery under high voltage and improving the battery's safety performance; on the other hand, it can avoid the problem of excessive expansion of the safety protection layer leading to a significant loss of battery capacity. Thus, when the voltage applied to the safety protection layer drops below the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can recover, restoring the conductive connection between the active material layer and the current collector, and the positive electrode can be reused.

[0086] It should be understood that although the steps in the above flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least some of the steps in the above flowchart may include multiple steps or stages, and these steps or stages are not necessarily completed at the same time, nor are they necessarily performed sequentially.

[0087] In the actual preparation process, the specific steps for preparing the mixed slurry in step S1 can be as follows: first, add the electrodeformable material and the first solvent into a container and stir (for example, magnetic stirring and ultrasonic vibration) until the electrodeformable material is completely dissolved. Then, add the conductive material and mix evenly to obtain the mixed slurry.

[0088] In some embodiments, after the electrodeformable material and the first solvent are added to the container, a heat treatment may be performed before the stirring step. This facilitates the complete and rapid dissolution of the electrodeformable material. Specifically, the heat treatment temperature can be 60°C to 80°C, and the time can be 0.5 h to 1 h.

[0089] In some embodiments, the electrodeformable material may include a relaxor ferroelectric material. Because relaxor ferroelectric materials have a better response to voltage changes, the dielectric constant of the safety protection layer increases significantly under high voltage, which enhances the voltage's control over the conductive connection between the active material layer and the current collector, thereby better preventing thermal runaway.

[0090] Furthermore, relaxor ferroelectric materials may include one or a mixture of polyvinylidene fluoride (PVDF) and monomers, or polyvinylidene fluoride (PVDF), where the monomers include, for example, at least one of chlorotrifluoroethylene, trifluoroethylene, and hexafluoropropylene. This type of material can be called a PVDF-based relaxor ferroelectric material. PVDF-based relaxor ferroelectric materials can exhibit significant deformation at relatively low voltages, providing a high electro-responsiveness for the safety protection layer. They possess sensitive electro-deformation properties, enabling faster response to voltage changes and preventing thermal runaway of the battery at high voltages. In one specific example, the electro-deformation material may include poly(vinylidene fluoride-co-chlorotrifluoroethylene). In another specific example, the electro-deformation material may include poly(vinylidene fluoride-co-hexafluoropropylene).

[0091] In step S1, the solid-liquid ratio of the electrodeformable material to the first solvent can be (1-1.8):(5-12) g / mL. Controlling the solid-liquid ratio of the electrodeformable material to the first solvent within the above range is beneficial for the complete dissolution of the electrodeformable material and the formation of a gel with a suitable mass concentration, which facilitates the uniform dispersion of the conductive material in the gel. For example, the first solvent may include dimethylformamide (DMF).

[0092] Conductive materials in the safety protection layer provide electron transport functionality to ensure the electro-deformation effect of the electro-deformation material. Conductive materials, including carbon nanotubes and conductive carbon, significantly improve the dielectric properties of the safety protection layer, further enhancing the electro-deformation effect of the electro-deformation material. Carbon nanotubes facilitate the formation of a relatively complete conductive network, while conductive carbon provides point-to-point conductive connections, ensuring a uniform current distribution during electro-deformation and thus improving the overall performance of the safety protection layer. Through the synergistic effect of carbon nanotubes and conductive carbon, the electro-deformation material can exhibit excellent electro-deformation performance at lower voltages, while minimizing the use of conductive materials, thereby achieving a better balance between the thickness and deformation of the safety protection layer.

[0093] In some specific embodiments, the mass ratio of carbon nanotubes to conductive carbon can be 1:20 to 1:1.5, for example, 1:20, 1:15, 1:10, 1:5, 1:1.5, or any value between any two of the above ranges. Controlling the mass ratio of carbon nanotubes to conductive carbon within the above range is beneficial to further enhance the electrodeformation effect of the electrodeformation material, thereby further improving the overall performance of the safety protection layer.

[0094] In some specific embodiments, the mass percentage of conductive material in the safety protection layer can be 10% to 20%, for example, 10%, 15%, 20%, or any value between any two of the above ranges. Thus, in the formed safety protection layer, the mass percentage of electrodeformable material corresponds to 80% to 90%, and the mass percentage of conductive material corresponds to 10% to 20%, thereby better ensuring the electrodeformation effect of the electrodeformable material and the deformation of the safety protection layer.

[0095] In step S2, the mixed slurry can be coated onto at least one surface of the current collector using a coating process well known to those skilled in the art. The coating process is not limited here. The current collector can be, for example, at least one of aluminum foil, porous aluminum foil, or carbon-coated aluminum foil. Exemplarily, the mixed slurry can be coated onto the aluminum foil surface using a doctor blade, the blade thickness of which can be 10 μm to 20 μm.

[0096] In step S2, the temperature of the first drying treatment can be 50℃ to 80℃, and the drying time can be 4h to 7h. This effectively removes residual solvent, ensuring the quality and performance of the resulting protective layer.

[0097] In step S3, the positive electrode slurry preparation step, the positive electrode active material may include a high-nickel ternary material. For example, the chemical formula of the high-nickel ternary material may be LiNi. x Co y M z O2, wherein M is one or more of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1. The conductive agent may include at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose. The second solvent may include N-methylpyrrolidone (NMP).

[0098] In some embodiments, the positive electrode slurry may contain 95% to 97% by mass of the positive electrode active material, 1% to 1.5% by mass of the conductive agent, and 2% to 3.5% by mass of the binder.

[0099] In some embodiments, step S3, preparing the positive electrode slurry, may include preparing a first positive electrode slurry and a second positive electrode slurry, respectively. Specifically, preparing the first positive electrode slurry may include: adding a first positive electrode active material, a first conductive agent, and a first binder to a solvent, mixing them evenly, and then obtaining the first positive electrode slurry. Preparing the second positive electrode slurry may include: adding a second positive electrode active material, a second conductive agent, and a second binder to a solvent, mixing them evenly, and then obtaining the second positive electrode slurry.

[0100] The first positive electrode active material includes a single crystal material (specifically, for example, a high-nickel ternary single crystal material); the second positive electrode active material includes a polycrystalline material (specifically, for example, a high-nickel ternary polycrystalline material). The types of the first conductive agent, the first binder, the second conductive agent, and the second binder can be understood with reference to the types of conductive agents and binders in the above embodiments.

[0101] In some embodiments, in the first positive electrode slurry, the mass percentage of the first positive electrode active material can be 95% to 97%, the mass percentage of the first conductive agent can be 1% to 1.5%, and the mass percentage of the first binder can be 2% to 3.5%.

[0102] In some embodiments, the second positive electrode slurry may contain 95% to 97% by mass of the second positive electrode active material, 1% to 1.5% by mass of the second conductive agent, and 2% to 3.5% by mass of the second binder.

[0103] Step S4 may include coating the first positive electrode slurry and the second positive electrode slurry onto the surface of the safety protection layer away from the current collector, followed by a second drying process to obtain the active material layer.

[0104] In this embodiment, the active material layer adopts a multi-layer design, which utilizes the combined advantages of single-crystal and polycrystalline materials to effectively improve the dynamic performance and cycle stability of the battery while maintaining high safety performance.

[0105] In one embodiment, a first positive electrode slurry and a second positive electrode slurry can be stacked on the surface of the safety protection layer away from the current collector, with the first positive electrode slurry being closer to the safety protection layer than the second positive electrode slurry. After a second drying process, a first sub-active layer and a second sub-active layer are obtained, with the first sub-active layer located between the safety protection layer and the second sub-active layer.

[0106] In this embodiment, a first sub-active layer comprising monocrystalline material is formed below a second sub-active layer comprising polycrystalline material. Since monocrystalline material has no internal grain boundaries, it has better structural stability and can reduce the generation of microcracks during charging and discharging, thereby improving the cycle stability of the cathode. Furthermore, the first sub-active layer comprising monocrystalline material in the lower layer can provide better thermal stability, reducing the risk of thermal runaway in the battery. The second sub-active layer, located in the upper layer, comprises polycrystalline material, which can provide better electrochemical activity and can avoid side reactions between the first sub-active layer comprising monocrystalline material and the electrolyte, thereby improving the safety and lifespan of the battery.

[0107] Furthermore, the ratio of the thickness of the first sub-active layer to the sum of the thicknesses of the active material layer and the safety protection layer can be greater than 1 / 2; the ratio of the thickness of the second sub-active layer to the sum of the thicknesses of the active material layer and the safety protection layer can be less than 1 / 2. This is beneficial for improving the overall performance of the cathode.

[0108] In another embodiment, the first positive electrode slurry and the second positive electrode slurry can be stacked on the surface of the safety protection layer away from the current collector, with the second positive electrode slurry being closer to the safety protection layer than the first positive electrode slurry. After a second drying process, a first sub-active layer and a second sub-active layer are obtained, with the first sub-active layer located between the safety protection layer and the second sub-active layer.

[0109] In this embodiment, a first sub-active layer comprising polycrystalline material is formed below a second sub-active layer comprising monocrystalline material. Polycrystalline materials typically have higher conductivity and a larger specific surface area. Forming the first sub-active layer comprising polycrystalline material in the lower layer can improve the conductivity of the positive electrode, thereby improving the rate performance of the battery. Furthermore, forming the first sub-active layer comprising polycrystalline material in the lower layer helps to reduce battery polarization, increase the median voltage during rate discharge, and reduce side reactions during battery storage.

[0110] In step S4, a coating process well known to those skilled in the art can be used to coat the positive electrode slurry onto the surface of the safety protection layer away from the current collector. No limitations are imposed on the coating process here.

[0111] In step S4, the temperature of the second drying process can be between 50°C and 80°C. This allows for better removal of residual solvent, ensuring the quality and performance of the resulting protective layer and active material layer.

[0112] Furthermore, in the final cathode sheet, the ratio of the sum of the thicknesses of the safety protection layer and the active material layer to the thickness of the safety protection layer can be greater than or equal to 10. This allows for effective prevention of thermal runaway at high voltages through the safety protection layer while also meeting the energy density requirements of the cathode sheet.

[0113] In some specific embodiments, the thickness of the safety protection layer can be 3μm to 10μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any value between any two of the above ranges.

[0114] In some specific embodiments, the thickness of the active material layer can be 110 μm to 115 μm, for example, it can be 110 μm, 111 μm, 112 μm, 113 μm, 114 μm, 115 μm or any value between any two of the above ranges.

[0115] In some embodiments, the areal density of the safety protection layer may be 25 mg / m³. 2 ~35mg / m 2 For example, it can be 25mg / m 2 26mg / m 2 27mg / m 2 28mg / m 2 29mg / m 2 30mg / m 2 31mg / m 2 32mg / m 2 33mg / m 2 34mg / m 2 35mg / m 2 Or any value between any two of the above ranges. This approach helps to balance the thickness and deformation of the safety protection layer, thereby improving its overall performance.

[0116] This application also provides a battery comprising a positive electrode sheet as described in any of the above embodiments or a positive electrode sheet prepared by a method comprising a positive electrode sheet as described in any of the above embodiments.

[0117] The battery in this application is a secondary battery. Further, the secondary battery may include a lithium-ion battery.

[0118] It should be understood that since the battery in this application embodiment includes the positive electrode sheet described in any of the above embodiments or the positive electrode sheet prepared by the method described in any of the above embodiments, the beneficial effects of the positive electrode sheet in the above embodiments are all applicable to this battery. The battery in this application embodiment has high safety performance.

[0119] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0120] Example 1

[0121] The preparation of the positive electrode in this embodiment includes the following steps:

[0122] Step S101: Add 1.5g of P(VDF-CTFE) particles (electrodeformable material) to 8mL of DMF (first solvent), heat at 70℃ for 1h, then magnetically stir and ultrasonically vibrate for more than 30min until the P(VDF-CTFE) particles are completely dissolved. Then add 0.357g of conductive carbon and 0.018g of carbon nanotubes (conductive material), mix evenly to obtain a mixed slurry.

[0123] Step S102: The mixed slurry prepared in step S101 is coated on one surface of the aluminum foil (current collector) along the thickness direction, with a scraper thickness of 10 μm; next, it is dried in an oven at 70°C (first drying treatment) to obtain a safety protective layer;

[0124] Step S103: Add high-nickel ternary single crystal material (first positive electrode active material), conductive carbon and oily carbon nanotubes (first conductive agent), and PVDF (first binder) to NMP in a mass ratio of 97:2:1, mix evenly, and obtain the first positive electrode slurry;

[0125] Step S104: Add high-nickel ternary polycrystalline material (second positive electrode active material), conductive carbon and oily carbon nanotubes (second conductive agent) and PVDF (second binder) to NMP in a mass ratio of 97:2:1, mix evenly, and obtain the second positive electrode slurry;

[0126] Step S105: Using a double-layer coating die, the first positive electrode slurry and the second positive electrode slurry are simultaneously coated on the surface of the safety protection layer away from the aluminum foil, with the first positive electrode slurry closer to the safety protection layer than the second positive electrode slurry. The coating is then dried in a 70°C oven (second drying process) to obtain a first sub-active layer and a second sub-active layer (active material layer). The first sub-active layer is located between the safety protection layer and the second sub-active layer. After cold pressing, a positive electrode sheet is obtained. The coating surface density of the first and second positive electrode slurries is 155 g / m³. 2 The compaction density of the positive electrode is 3.45 g / cm³. 3 .

[0127] Example 2

[0128] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, with the main difference being:

[0129] In step S101, the amount of conductive carbon added is 0.2g, and the amount of carbon nanotubes added is 0.1g.

[0130] Example 3

[0131] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, with the main difference being:

[0132] In step S101, the amount of conductive carbon added is 0.16g, and the amount of carbon nanotubes added is 0.07g.

[0133] Example 4

[0134] In step S101, the amount of conductive carbon added is 0.13g, and the amount of carbon nanotubes added is 0.04g.

[0135] Example 5

[0136] In step S101, the amount of conductive carbon added is 0.1g, and the amount of carbon nanotubes added is 0.066g.

[0137] Comparative Example 1

[0138] The preparation method of the positive electrode in this comparative example is basically the same as that in Example 1, with the main difference being:

[0139] In step S101, no conductive carbon is added. Only 0.1g of carbon nanotubes are added as a conductive material.

[0140] Comparative Example 2

[0141] The preparation method of the positive electrode in this comparative example is basically the same as that in Example 1, with the main difference being:

[0142] In step S101, no carbon nanotubes are added. Only 0.2g of conductive carbon is added as a conductive material.

[0143] Comparative Example 3

[0144] The preparation method of the positive electrode in this comparative example is basically the same as that in Example 1, with the main difference being:

[0145] In step S101, the amount of P(VDF-CTFE) particles added is 3g.

[0146] The performance of the positive electrode sheets prepared in the above embodiments and comparative examples was tested.

[0147] (1) Electrodeformation test of positive electrode: The positive electrode prepared above is clamped with a glass plate and placed on a CCD (Charge-Coupled Device) detection device. First, the thickness of the positive electrode is measured with a ruler and recorded as D1. Then, a constant current of 4.4V is applied to both ends of the positive electrode, and the thickness of the positive electrode is measured with a ruler when the current is applied and recorded as D2. Electrodeformation = ((D2-D1) / D1)*100%.

[0148] The positive electrode sheets obtained in the above embodiments and comparative examples were used to prepare batteries for performance testing. The battery preparation steps are as follows:

[0149] Preparation of the negative electrode: Graphite, conductive carbon and carbon nanotubes, polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 97:1:2, then added to deionized water and stirred to form a uniform and stable negative electrode slurry. The negative electrode slurry was then uniformly coated onto copper foil with a coating density of 110 g / m². 2 After drying and cold pressing, a negative electrode sheet is obtained, with a compaction density of 1.60 g / cm³. 3 ;

[0150] Electrolyte preparation: LiPF6 was dissolved in a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 to prepare an electrolyte with a concentration of 1.2 mol / L.

[0151] Battery assembly: The positive electrode, separator, negative electrode, and separator are stacked and arranged in sequence, and then wound to obtain the battery cell; the separator is a PP film with a thickness of 13μm; the electrolyte is injected into the dry battery cell, and after soaking for 10 hours, it is formed at 45℃. The formation process is as follows: charge to 3.4V at 0.05C, and then charge to 3.75V at 0.2C; after aging at room temperature for 24 hours, it is resealed, and finally the battery is completed by capacity testing.

[0152] Battery discharge current test: The battery with a designed capacity of 4.4Ah was tested using a charge-discharge instrument. The battery was charged to 50% SOC, and an electric field of 3.8kV / mm to 3.95kV / mm (i.e., 4.5V voltage) was applied. Constant voltage charging was performed, and the current value after the electric field was applied and the capacity displayed on the charge-discharge instrument after 30 minutes of charging were observed.

[0153] The test results are shown in Table 1.

[0154] Table 1

[0155]

[0156]

[0157] As can be seen from the data in Table 1, compared with Comparative Examples 1 and 2, the positive electrode sheets prepared in Examples 1 to 5 all exhibited significant electroinduced deformation when an electric field was applied. Consequently, the current value of the corresponding batteries decreased to a lower value after the electric field was applied. This indicates that the conductive network between the active material layer and the current collector in the positive electrode sheet was effectively blocked. In contrast, in Comparative Examples 1 and 2, the conductive material only contained one of carbon nanotubes and conductive carbon. Without the synergistic effect of carbon nanotubes and conductive carbon, it was difficult to ensure a uniform current distribution in the safety protection layer, leading to a decrease in the electroinduced deformation performance of the electrodeformation material. Under the same voltage, the electroinduced deformation of the positive electrode sheet was lower than that in Examples 1 to 5, resulting in a significant increase in the current value of the corresponding batteries after the electric field was applied compared to Examples 1 to 5. This indicates that the conductive network between the active material layer and the current collector was not effectively blocked, thus failing to effectively reduce the risk of thermal runaway of the battery under high voltage. In Comparative Example 3, due to the excessive amount of electrodeformable material added to the safety protection layer, the mass ratio of electrodeformable material in the safety protection layer is greater than 90%. As can be seen from the data in Table 1, under the same voltage, the electrodeformation of the positive electrode in Comparative Example 3 is significantly increased compared to Examples 1 to 5. Although this reduces the current value of the corresponding battery after applying an electric field to a very low value, which can effectively reduce the risk of thermal runaway of the battery under high voltage, the 30-minute charging capacity of the battery in Comparative Example 3 after applying an electric field at 50% SOC is significantly lower than that of Examples 1 to 5. This indicates that excessive volume expansion of the positive electrode will lead to a significant loss of battery capacity, making it difficult to ensure that the battery can be restored to use after the voltage drops.As can be seen from the above, in this application, by setting a safety protection layer between the current collector and the active material layer, since the safety protection layer includes electrodeformable materials and conductive materials, the carbon nanotubes in the conductive material can form a complete conductive network, and the conductive carbon can play a point-to-point conductive connection role. Through the synergistic effect of carbon nanotubes and conductive carbon, the uniform distribution of current in the safety protection layer can be ensured, thereby enabling the electrodeformable material to exhibit excellent electrodeformation performance at a low voltage. When the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand, increasing the spacing between the conductive material particles in the safety protection layer, and the active material layer and the current collector... The conductive network between them is partially or even completely blocked. By controlling the mass ratio of electrodeformable material in the safety protection layer to 80% to 90%, on the one hand, it can ensure that the volume of the safety protection layer expands sufficiently under high voltage, thereby effectively reducing the risk of thermal runaway of the battery under high voltage and improving the battery's safety performance; on the other hand, it can avoid the problem of excessive expansion of the safety protection layer leading to a large loss of battery capacity. Thus, when the voltage applied to the safety protection layer drops below the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can recover, allowing the conductive connection between the active material layer and the current collector to be restored, and the positive electrode sheet can be reused, that is, the battery can be reused.

[0158] This invention proposes a novel voltage-sensitive positive electrode. Utilizing the characteristic of electrodeformable materials to exhibit significant electrodeformation at low voltages, a safety protection layer comprising both electrodeformable and conductive materials is placed between the current collector and the active material layer. This safety protection layer exhibits sensitive electrodeformation properties at low voltages; for example, it undergoes significant deformation under an electric field of 4.4 kV / mm, causing the electrical contact between the active material layer and the current collector to disengage. This prevents thermal runaway when the battery voltage exceeds its operating limit, providing overvoltage protection and enhancing battery safety. The cell can be reused after the battery voltage is reduced. This safety protection layer achieves excellent dielectric properties and electrodeformation efficiency, possesses high-voltage self-blocking functionality, and is particularly suitable for scenarios preventing thermal failure due to overcharging.

[0159] It should be noted that the positive electrode sheet embodiments, positive electrode sheet preparation method embodiments, and battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0160] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations of this application. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A positive electrode plate, characterized in that, include: A current collector and a safety protection layer and an active material layer disposed on at least one surface of the current collector, wherein the safety protection layer is located between the current collector and the active material layer; The safety protection layer comprises an electrodeformable material and a conductive material; the electrodeformable material comprises a relaxor ferroelectric material, which comprises a multi-component copolymer of vinylidene fluoride and monomers and / or polyvinylidene fluoride, wherein the monomers comprise at least one of chlorotrifluoroethylene, trifluoroethylene, and hexafluoropropylene; the conductive material comprises carbon nanotubes and conductive carbon; the electrodeformable material comprises 80% to 90% of the mass of the safety protection layer; and the thickness of the safety protection layer is 3 μm to 10 μm. When the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand.

2. The positive electrode sheet according to claim 1, characterized in that, The security protection layer satisfies at least one of the following characteristics: (1) The conductive material accounts for 10% to 20% of the mass of the safety protection layer; (2) The mass ratio of the carbon nanotubes to the conductive carbon is 1:20 to 1:1.5; (3) The areal density of the safety protection layer is 25 mg / m³. 2 ~35mg / m 2 .

3. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet satisfies at least one of the following characteristics: (1) The active material layer includes a high-nickel ternary material; (2) The current collector includes at least one of aluminum foil, porous aluminum foil, and carbon-coated aluminum foil.

4. The positive electrode sheet according to claim 1, characterized in that, The active material layer includes a high-nickel ternary material; the chemical formula of the high-nickel ternary material is LiNi. x Co y M z O2, wherein M is at least one of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1.

5. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet satisfies at least one of the following characteristics: (1) The ratio of the sum of the thicknesses of the safety protection layer and the active material layer to the thickness of the safety protection layer is greater than or equal to 10; (2) The thickness of the active material layer is 110μm~115μm.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that, The active material layer includes a first sub-active layer and a second sub-active layer stacked sequentially in the thickness direction of the current collector, wherein the first sub-active layer is located between the safety protection layer and the second sub-active layer; the first sub-active layer includes a single crystal material and the second sub-active layer includes a polycrystalline material.

7. The positive electrode sheet according to any one of claims 1 to 5, characterized in that, The active material layer includes a first sub-active layer and a second sub-active layer stacked sequentially in the thickness direction of the current collector, wherein the first sub-active layer is located between the safety protection layer and the second sub-active layer; the first sub-active layer includes a polycrystalline material and the second sub-active layer includes a monocrystalline material.

8. A method for preparing a positive electrode sheet, characterized in that, The method includes the following steps: An electrodeformable material is added to a first solvent and stirred until it is completely dissolved. Then, a conductive material is added and mixed evenly to obtain a slurry. The electrodeformable material includes a relaxor ferroelectric material, which includes a multi-component copolymer of vinylidene fluoride and monomers and / or polyvinylidene fluoride. The monomers include at least one of trifluorochloroethylene, trifluoroethylene, and hexafluoropropylene. The conductive material includes carbon nanotubes and conductive carbon. The mixed slurry is coated on at least one surface of the current collector and subjected to a first drying treatment to obtain a safety protection layer; the electrodeformable material accounts for 80% to 90% of the mass of the safety protection layer; the thickness of the safety protection layer is 3 μm to 10 μm. The positive electrode active material, conductive agent and binder are added to the second solvent and mixed evenly to obtain the positive electrode slurry; The positive electrode slurry is coated on the surface of the safety protection layer away from the current collector, and after a second drying process, an active material layer is obtained; when the voltage applied to the safety protection layer exceeds the deformation voltage threshold of the electrodeformable material, the volume of the safety protection layer can expand.

9. The method for preparing the positive electrode sheet according to claim 8, characterized in that, The steps for preparing the mixed slurry satisfy at least one of the following characteristics: (1) The first solvent includes dimethylformamide; (2) The mass ratio of the carbon nanotubes to the conductive carbon is 1:20 to 1:1.5; (3) In the mixed slurry, the solid-liquid ratio of the electrodeformable material to the first solvent is (1~1.8):(5~12) g / mL; (4) The conductive material accounts for 10% to 20% of the mass of the safety protection layer; (5) Before the stirring step, a heating treatment is also included.

10. The method for preparing the positive electrode sheet according to claim 8, characterized in that, Before the stirring step, a heating treatment is also included; the temperature of the heating treatment is 60℃~80℃, and the time is 0.5h~1h.

11. The method for preparing the positive electrode sheet according to claim 8, characterized in that, The steps for preparing the positive electrode slurry satisfy at least one of the following characteristics: (1) The positive electrode active material includes a high-nickel ternary material; (2) The conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (3) The adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; (4) In the positive electrode slurry, the positive electrode active material accounts for 95% to 97% by mass, the conductive agent accounts for 1% to 1.5% by mass, and the binder accounts for 2% to 3.5% by mass.

12. The method for preparing the positive electrode sheet according to claim 8, characterized in that, The positive electrode active material includes a high-nickel ternary material; the chemical formula of the high-nickel ternary material is LiNi. x Co y M z O2, where M is one or more of Mn, Al, Mg, Zr, Ti, W, and B, x ≥ 0.8, and x + y + z = 1.

13. A battery, characterized in that, The positive electrode includes the positive electrode sheet according to any one of claims 1 to 7, or the positive electrode sheet prepared by any one of claims 8 to 12.

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