Positive electrode sheet and electrochemical device

Abstract

This invention discloses a positive electrode and an electrochemical device, relating to the field of electrochemical energy storage. The positive electrode includes a first functional region formed by a first base coating and a first active layer, and a second functional region formed by a second base coating and a second active layer; the areal density of the first and second active layers satisfies 1.5 ≤ a ≤ 2.5, and the areal resistivity of the first and second base coatings satisfies 1.0 × 10⁻⁶. 3 ≤β≤1.0×10 6 This application constructs functional regions with differentiated conductivity and areal density on both sides of the current collector. The first functional region, which has a high current carrying capacity, provides high capacity and electronic conduction, while the second functional region, which has a high safety barrier, provides strong mechanical support. This achieves a dynamic response with high rate capability and high conductivity, while also realizing a graded response over thermal abuse time. This effectively prevents the propagation of internal short circuits and the eventual occurrence of thermal runaway, thereby improving safety performance and cycle life.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage, and more particularly to positive electrode plates and electrochemical devices. Background Technology

[0002] Energy density, power density, and safety are the core performance indicators of lithium-ion batteries; however, these indicators often present inherent contradictions. For example, high-rate performance requires extremely low interfacial resistance in the electrodes, which is typically achieved by introducing a highly conductive undercoat or using a thinner coating in electrodes loaded with highly active materials. However, this low-resistance, high-energy-density design is more prone to severe thermal runaway under extreme conditions such as thermal abuse, posing safety hazards. Conversely, if a highly thermally stable ceramic coating is used as an undercoat in the electrodes to enhance safety, it will significantly increase the interfacial resistance, severely sacrificing the battery's rate performance and power characteristics, resulting in low utilization of active materials and a decrease in energy density.

[0003] Currently, most positive electrode materials use a double-sided symmetrical structure, meaning that the coating composition, thickness, and structure on both sides of the current collector are exactly the same. This homogenized design is a compromise in terms of performance and cannot fundamentally solve the aforementioned contradiction. It forces the same coating material to simultaneously bear the almost contradictory functions of "high current carrying capacity" and "ultimate safety barrier" at the physical and chemical levels, resulting in the battery performance still not achieving optimal breakthroughs. Summary of the Invention

[0004] This invention provides a positive electrode sheet and an electrochemical device. By constructing an undercoat layer and an active layer with differentiated conductivity and areal density on both sides of the current collector, a first functional region with high current carrying capacity and a second functional region with strong mechanical support are formed, which synergistically improves the rate performance and safety level of the battery. It can be widely used in the field of electrochemical devices with high requirements for rate performance and safety.

[0005] To solve the above-mentioned technical problems, one of the objectives of the present invention is to provide a positive electrode sheet, including a current collector, a first functional region and a second functional region, wherein the first functional region and the second functional region are respectively disposed on opposite sides of the current collector, the first functional region includes a first base coating layer and a first active layer disposed sequentially along the direction away from the current collector, and the second functional region includes a second base coating layer and a second active layer disposed sequentially along the direction away from the current collector. The areal densities of the first and second active layers satisfy the following relationship: D1 / D2=ɑ, 1.5≤ɑ≤2.5, 180≤D1≤270, where D1 is the areal density of the first active layer, in g / m³. 2 D2 is the areal density of the second active layer, in g / m³. 2 ; The sheet resistivity of the first and second base coatings satisfies the following relationship: R2 / R1 = β, 1.0 × 10⁻⁶. 3 ≤β≤1.0×10 6 1.0×10 4 ≤R2≤1.0×10 8 In the formula, R1 is the surface resistivity of the first base coating layer, in Ω / m. 2 R2 is the surface resistivity of the second base coating, in Ω / m. 2 .

[0006] In some embodiments, the mass retention rate of the first primer coating after heat treatment at 230-270 °C for 40-80 minutes is M1, and the mass retention rate of the second primer coating after heat treatment at 230-270 °C for 40-80 minutes is M2, and M2 / M1=γ, 1.1≤γ≤1.6, 65%≤M1.

[0007] In some implementations, 65%≤M1≤86%, 87%≤M2≤99%.

[0008] In some implementations, 108 ≤ D2 ≤ 150.

[0009] In some implementations, 10 ≤ R1 ≤ 100.

[0010] In some embodiments, the coating width of both the first functional area and the second functional area is perpendicular to the length direction of the current collector, and the coating width of the first functional area and the second functional area satisfy the following relationship: 2 mm ≤ W1 - W2 ≤ 10 mm, where W1 is the coating width of the first functional area in mm, and W2 is the coating width of the second functional area in mm.

[0011] In some embodiments, the ratio of the coating width of the first functional area to the width of the current collector in the same direction is (0.70-0.95):1.

[0012] In some embodiments, the first base layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (10-30):(60-80):(4-16), and the second base layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (0.2-6):(60-95):(5-36).

[0013] In some embodiments, the first functional area is located on the side of the current collector facing the center of the core after winding, and the second functional area is located on the neutral side of the current collector facing away from the core after winding.

[0014] In some embodiments, the conductive agents of the first and second base coatings are each independent and include at least one of conductive carbon black, carbon nanotubes, graphene, graphite flakes, graphite, expanded graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, activated carbon, mesoporous carbon, and carbon fibers.

[0015] In some embodiments, the functional fillers of the first and second base coatings are each independent and include at least one of magnesium oxide, aluminum oxide, boehmite, titanium dioxide, zirconium oxide, magnesium oxide, aluminum nitride, boron nitride, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, and silicates.

[0016] In some embodiments, the adhesives for the first and second primer coatings are each independent and include at least one of polyvinylidene fluoride and its copolymers, styrene-butadiene rubber, polyacrylate, polyimide, polyamide-imide, polyetheretherketone, and fluororubber.

[0017] In some embodiments, the binder of the first primer layer includes at least one of polyvinylidene fluoride and its copolymers, styrene-butadiene rubber, and polyacrylate.

[0018] In some embodiments, the binder of the second base coating includes at least one of polyimide, polyamide-imide, polyetheretherketone, and fluororubber.

[0019] To address the aforementioned technical problems, a second objective of this invention is to provide an electrochemical device, including a positive electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This application specifies that the areal density of the first active layer and the second active layer satisfies 1.5 ≤ a ≤ 2.5, and the areal resistivity of the first base layer and the second base layer satisfies 1.0 × 10⁻⁶. 3 ≤β≤1.0×10 6 Functional regions with different conductivity and areal density are constructed on both sides of the current collector. The first functional region provides high capacity and electronic conduction, while the second functional region provides strong mechanical support. This enables dynamic response with high rate and high conductivity, and effectively improves safety performance and cycle life.

[0021] 2. This application constructs a high-current-carrying first functional region and a high-safety-barrier second functional region on both sides of the current collector. By limiting the mass retention rate of the first and second base coatings under high-temperature conditions to 1.1≤γ≤1.6, a graded response in thermal abuse time can be achieved. In the early stage of thermal abuse, the first base coating is triggered to absorb a large amount of heat and delay the temperature rise rate. In the middle stage of thermal abuse, the second base coating exerts its intrinsic advantages of high thermal stability and high mechanical strength, passively preventing the current collector from contacting the active material, effectively preventing the spread of internal short circuits and the eventual occurrence of thermal runaway, and improving thermal stability and safety performance.

[0022] 3. This application limits the coating width of the first functional area and the second functional area to 2≤W1-W2≤10. The second base coating, which is more brittle, is prone to micro-burrs being exposed at the edges during the cutting process. The first functional area with a larger coating width can effectively cover the second functional area, reducing the risk of internal short circuit caused by the second base coating being exposed at the edges. At the same time, it optimizes the edge current distribution and improves the reliability and safety of the battery. Meanwhile, it avoids the situation where the width difference is too large, which would result in the active material area of ​​the second functional area being too small. If it is too small, it will affect the overall energy density and aggravate the stress asymmetry on both sides of the electrode, thereby increasing the risk of deformation or wrinkling during winding. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in an embodiment of the present invention; Figure 2 This is a schematic diagram showing the coating width of the first and second functional areas of the positive electrode sheet in an embodiment of the present invention; The accompanying drawings in the instruction manual illustrate: 1. First active layer; 2. First base coating layer; 3. First functional area; 4. Aluminum foil; 5. Second active layer; 6. Second base coating layer; 7. Second functional area. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] As used in this article: In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0028] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0029] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicating orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0030] This application provides a positive electrode sheet, including a current collector, a first functional region and a second functional region, the first functional region and the second functional region being disposed on opposite sides of the current collector, the first functional region including a first base coating and a first active layer disposed sequentially along the direction away from the current collector, and the second functional region including a second base coating and a second active layer disposed sequentially along the direction away from the current collector. The areal densities of the first and second active layers satisfy the following relationship: D1 / D2=ɑ, 1.5≤ɑ≤2.5, 180≤D1≤270, where D1 is the areal density of the first active layer, in g / m³. 2 D2 is the areal density of the second active layer, in g / m³. 2 ; The sheet resistivity of the first and second primer coatings satisfies the following relationship: R2 / R1=β, 1.0×10 3 ≤β≤1.0×10 6 1.0×10 4 ≤R2≤1.0×10 8 In the formula, R1 is the surface resistivity of the first base coating layer, in Ω / m. 2 R2 is the surface resistivity of the second base coating, in Ω / m. 2 .

[0031] This application constructs functional layers with different conductivity and areal density on both sides of the current collector, achieving optimal performance on one side without compromising or even enhancing the performance on the other side. By limiting the areal density of the first and second active layers to 1.5 ≤ a ≤ 2.5, and the areal resistivity of the first and second base coatings to 1.0 × 10⁻⁶, the application achieves this. 3 ≤β≤1.0×10 6 The first functional area provides high capacity and electronic conduction, while the second functional area provides strong mechanical support, enabling dynamic response with high rate and high conductivity, and effectively improving cycle life.

[0032] If α is too low, the loads on both active layers are similar, and the current distribution tends to be balanced, failing to fully utilize the high conductivity advantage of the dynamic response layer, resulting in minimal improvement in high-rate performance. Furthermore, when 1 < α < 1.5, the areal density of the first active layer remains high, and the proportion of active material is large, leading to significant heat generation during thermal abuse. The relatively thin second active layer may not be sufficient to completely block the propagation of thermal runaway, limiting the improvement in safety performance. If α is too high, the thickness of the first active layer becomes excessive, increasing the risk of coating cracking. Moreover, ion transport is restricted, lengthening the solid-state diffusion path of lithium ions in the thick electrode, which actually reduces rate performance and capacity utilization. In this case, the active material layer in the second functional region is too thin, resulting in uneven structure and stress distribution across the entire electrode, affecting cycle life.

[0033] Furthermore, this application ensures that the first base coating has sufficiently low electronic impedance to function as the main current channel, while avoiding the second base coating from having poor conductivity due to excessive differences in properties, avoiding the active material in the second functional area from having insufficient capacity due to blocked electronic pathways, and avoiding mechanical reliability problems caused by structural embrittlement and adhesion degradation due to insufficient conductive agent content.

[0034] In some implementations, the value of α is a range of any one or any two of the following: 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, and 2.5.

[0035] In some implementations, D1 is a range of any one or any two of 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, and 270.

[0036] It should be noted that the areal density of the active layer can be controlled by adjusting the solid content, slurry flow rate, roller pressure, and roller gap width of the active layer slurry during the preparation of the positive electrode sheet. For example, increasing the solid content and slurry flow rate can increase the areal density of the active layer of the positive electrode sheet.

[0037] It should be noted that the areal density test method for the first and second active layers includes the following steps: Taking the first active layer as an example, a current collector sample containing only the first active layer is punched out using a circular stamping die, and the sample area S is recorded; the initial mass of the sample is weighed using an analytical balance and recorded as W1; the active layer is wiped with lint-free paper soaked in an appropriate amount of solvent until it is completely removed, and the mass of the sample is weighed again and recorded as W2. Then the areal density of the first active layer is: D1 = (W1-W2) / S (g / m²); at least 3 data points are tested and their average value is taken. The areal density test method for the second active layer is the same.

[0038] In some implementations, the value of β is 1.0 × 10⁻⁶. 3 5.0×10 3 1.0×10 4 5.0×10 4 1.0×10 5 5.0×10 5 1.0×10 6 5.0×10 6 The range of values ​​between any one of them or any two of them.

[0039] In some implementations, R2 is 1.0 × 10⁻⁶. 4 5.0×10 4 1.0×10 5 5.0×10 5 1.0×10 6 5.0×10 6 1.0×10 7 5.0×10 7 1.0×10 8 The range of values ​​between any one of them or any two of them.

[0040] It should be noted that the surface resistance of the base coating can be controlled by adjusting the content and composition of the conductive agent in the base coating slurry during the preparation of the positive electrode sheet; for example, increasing the content of the conductive agent can increase the surface resistance of the base coating of the positive electrode sheet.

[0041] It should be noted that the sheet resistance test method for the first and second primer coatings includes the following steps: Taking the first primer coating as an example, the four probes of the four-probe tester are pressed in a straight line at equal intervals onto the current collector surface coated only with the first primer coating, ensuring good contact between the probes and the coating. The instrument will apply a known small current (I) to the two outer probes and measure the voltage drop (V) between the two inner probes. The internal program will automatically calculate and display the sheet resistance value according to the formula R = k × (V / I), where k is the probe spacing coefficient. The sheet resistance of the first primer coating is obtained by testing. The sheet resistance test method for the second primer coating is the same.

[0042] In some embodiments, the mass retention rate of the first primer coating after heat treatment at 230-270 °C for 40-80 minutes is M1, and the mass retention rate of the second primer coating after heat treatment at 230-270 °C for 40-80 minutes is M2, and M2 / M1=γ, 1.1≤γ≤1.6, 65%≤M1.

[0043] This application constructs a first functional region with high current carrying capacity and a second functional region with high safety barrier on opposite sides of the current collector. By limiting the mass retention rates of the first and second base coatings under high-temperature conditions to 1.1 ≤ γ ≤ 1.6, a graded response over thermal abuse time can be achieved. In the initial stage of thermal abuse, the temperature rise first triggers the endothermic decomposition or phase change of the multifunctional filler in the first base coating, absorbing a large amount of heat to actively inhibit the combustion chain reaction and slow down the temperature rise rate. As thermal abuse continues and the temperature rises further, the second base coating leverages its inherent advantages of high thermal stability and high mechanical strength, acting as a robust firewall to passively prevent the current collector from contacting the active material layer, effectively preventing the propagation of internal short circuits and the eventual occurrence of thermal runaway. If the γ value is less than 1.1, the mass retention rate of the second base coating at high temperature is almost the same as that of the first base coating, and the thermal stability advantage is not prominent. If the γ value is greater than 1.6, the thermal stability of the first base coating is poor, and it will undergo a large amount of decomposition or failure at lower temperatures. All thermal shocks will be borne by the second base coating alone, greatly increasing its probability of breakdown and reducing the safety performance of the battery.

[0044] In some implementations, the value of γ is a range of any one of 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6, or any two of them.

[0045] In some implementations, 65%≤M1≤86%, 87%≤M2≤99%.

[0046] In some implementations, M1 is a range of any one or any two of 65%, 70%, 75%, 80%, 85%, and 86%.

[0047] In some implementations, M2 is a range of any one of 87%, 90%, 95%, 99%, or any two of them.

[0048] It should be noted that by controlling the content, type, content, type, binder content, and type of functional filler, as well as the binder content and type in the base coating slurry during the preparation of the positive electrode sheet, the quality retention rate of the base coating after heat treatment at 230-270 °C for 40-80 minutes can be controlled. For example, using high-temperature resistant binders such as PI and PAI can increase the quality retention rate of the positive electrode sheet base coating compared to using PVDF binders.

[0049] It should be noted that the test method for the quality retention rate of the first and second primer coatings after heat treatment at 230-270 °C for 40-80 minutes, taking 250 °C heat treatment for 60 minutes as an example, includes the following steps: (1) Place the blank current collector in a TGA crucible and heat it from room temperature to 250 ℃ at a rate of 10 ℃ / min in an air atmosphere. Hold the temperature at 250 ℃ for 60 minutes, then cool it. Record the mass of the blank current collector at the beginning and end of the 250 ℃ holding period. Calculate the mass change rate of the blank current collector: ΔM0 = (M 0结束 - M 0开始 ) / M 0开始 ; (2) Place the current collector containing only the first base coating into the TGA crucible. Under the same test conditions as the blank current collector, calculate the mass of the sample at the beginning and end of the heat preservation at 250 ℃. Calculate the mass change rate of the current collector containing the first base coating: ΔM1 = (M 1结束 – M 1开始 ) / M 1开始 The final quality retention rate of the first base coat is M1 = [1 + (ΔM1 – ΔM0)] × 100%, and the quality retention rate of the second base coat is tested in the same way.

[0050] In some implementations, 108 ≤ D2 ≤ 150.

[0051] In some implementations, D2 is a range of any one or any two of 108, 110, 115, 120, 125, 130, 135, 140, 145, and 150.

[0052] In some implementations, 10 ≤ R1 ≤ 100.

[0053] In some implementations, R1 is a range of any one or any two of the following: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100.

[0054] In some embodiments, the coating widths of the first functional area and the second functional area are both perpendicular to the length direction of the current collector. The coating widths of the first functional area and the second functional area satisfy the following relationship: 2 mm ≤ W1 - W2 ≤ 10 mm, where W1 is the coating width of the first functional area in mm and W2 is the coating width of the second functional area in mm.

[0055] This application specifies that the coating width of the first functional area and the second functional area must satisfy 2 mm ≤ W1 - W2 ≤ 10 mm. The coating width of different functional areas is different. Since the second undercoat has low conductivity and high brittleness, micro-burrs are easily generated and exposed at the edges during the slitting process. The first functional area with a larger coating width can effectively cover the micro-burrs generated during the slitting process of the second functional area, reduce the risk of internal short circuit caused by the micro-burrs of the second undercoat exposed at the edges, and optimize the edge current distribution. At the same time, it avoids that the area ratio of active material in the second functional area is too small due to the excessive width difference. If it is too small, it will affect the overall energy density and aggravate the stress asymmetry on both sides of the electrode, increasing the risk of deformation or wrinkling during winding. Therefore, the coating width of the first and second functional areas can improve the reliability and safety of the battery.

[0056] In some embodiments, the ratio of the coating width of the first functional area to the width of the current collector in the same direction is (0.70-0.95):1.

[0057] It should be noted that the coating width test method for the first and second functional areas includes the following steps: (1) Lay the coated electrode flat on the measuring table with the first functional coating side facing up. Align the zero mark of the film ruler with the edge of one side of the electrode. Ensure that the direction of the film ruler is completely parallel to the coating transverse direction of the electrode (i.e., perpendicular to the length direction of the current collector). Gently press the film ruler flat so that it fits tightly against the surface of the electrode. Keep the film ruler still and visually find the boundary between the coating of the first functional area and the blank area of ​​the current collector. Read the scale value corresponding to the boundary line on the film ruler and record it as W1. (2) Using the same method, find the boundary of the second functional area coating on the other side of the electrode (or measure the back side after flipping the electrode), read the corresponding scale value, and record it as W2.

[0058] In some implementations, the first functional area is located on the side of the current collector facing the center of the core after winding, and the second functional area is located on the neutral side of the current collector facing away from the core after winding.

[0059] In some embodiments, the first primer layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (10-30):(60-80):(4-16), and the second primer layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (0.2-6):(60-95):(5-36).

[0060] In some embodiments, the conductive agents of the first and second base coatings are each independent and include at least one of conductive carbon black, carbon nanotubes, graphene, graphite flakes, graphite, expanded graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, activated carbon, mesoporous carbon, and carbon fibers.

[0061] In some embodiments, the functional fillers of the first and second primer coatings are each independent and include at least one of magnesium oxide, aluminum oxide, boehmite, titanium dioxide, zirconium oxide, magnesium oxide, aluminum nitride, boron nitride, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, and silicates.

[0062] In some embodiments, the adhesives for the first and second primer coatings are each independent and include at least one of polyvinylidene fluoride and its copolymers, styrene-butadiene rubber, polyacrylate, polyimide, polyamide-imide, polyetheretherketone, and fluororubber.

[0063] In some embodiments, the binder for the first primer layer includes at least one of polyvinylidene fluoride and its copolymers, styrene-butadiene rubber, and polyacrylate.

[0064] In some embodiments, the binder for the second base coating includes at least one of polyimide, polyamide-imide, polyetheretherketone, and fluororubber.

[0065] In some embodiments, the first active layer and the second active layer are independent and include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0066] In some embodiments, the positive electrode active material includes LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al zAt least one of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, and LiMnPO4, wherein each x is independent and has a value of 0.2-0.9; each y is independent and has a value of 0.1-0.45; and each z is independent and has a value of 0-0.2.

[0067] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer.

[0068] In some embodiments, the positive electrode conductive agent includes at least one of conductive carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanofibers, carbon nanotubes, activated carbon, and mesoporous carbon.

[0069] In some embodiments, the current collector is a metal foil or a composite metal foil.

[0070] In some implementations, the current collector is aluminum foil.

[0071] This application also provides a method for preparing a positive electrode sheet, including the following steps: S1. The conductive agent, functional filler and binder of the first base layer are mixed and uniformly dispersed in a solvent to prepare the first base layer slurry; the conductive agent, functional filler and binder of the second base layer are mixed and uniformly dispersed in a solvent to prepare the second base layer slurry; the positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed and uniformly dispersed in a solvent to prepare the active layer slurry. S2. A first base coat slurry is applied to the first surface of the current collector with a width of W1, and dried to form a first base coat. A second base coat slurry is applied to the second surface of the current collector with a width of W2, and dried to form a second base coat. S3. Double-sided synchronous extrusion coating is performed on the dried base coating surface. The active layer slurry is coated on the first base coating surface with a width of W1 and the areal density is controlled to be D1. After drying, the first active layer is formed. The active layer slurry is coated on the second base coating surface with a width of W2 and the areal density is controlled to be D2. After drying, the second active layer is formed. After rolling, the positive electrode sheet is prepared.

[0072] In some embodiments, when the active layer slurry is applied to the first base coating surface with a width W1, the flow rate of the first precision metering pump is adjusted to 200-450 mL / min; when the active layer slurry is applied to the second base coating surface with a width W2, the flow rate of the second precision metering pump is adjusted to 80-220 mL / min.

[0073] This application controls the flow rate of precision metering pumps on both sides while maintaining a constant coating conveyor speed and basically consistent solid content of slurry on both sides. After coating, the slurry enters an oven for drying, forming a first active layer and a second active layer respectively. By adjusting the flow rate of the aforementioned precision metering pumps, the density of the first active layer after drying is D1, and the density of the second active layer is D2.

[0074] In some implementations, the pressure of the roller pressing line is controlled at 2.5-4.0 t / cm.

[0075] In some embodiments, the solid content of the first primer slurry is 42%-48%.

[0076] In some embodiments, the solid content of the second primer slurry is 35%-41%.

[0077] In some embodiments, the solid content of the active layer slurry is 67%-73%.

[0078] This application also provides an electrochemical device, including a positive electrode.

[0079] In some embodiments, the electrochemical device includes any apparatus in which an electrochemical reaction occurs to interconvert chemical energy into electrical energy, and specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0080] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0081] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available, and the same raw materials were used in parallel experiments.

[0082] Table 1 - Abbreviations for Raw Materials in Examples and Comparative Examples of this Application Example 1 Positive electrode sheet, such as Figure 1 As shown, it includes a current collector, a first functional region, and a second functional region. The current collector is an aluminum foil. The first and second functional regions are respectively coated and disposed on opposite sides of the current collector. The first functional region is located on the inner side of the wound positive electrode sheet, and the second functional region is located on the outer side of the wound positive electrode sheet. Figure 2 As shown, the coating width of the first functional area and the second functional area are both perpendicular to the length direction of the current collector. The coating width of the first functional area is 0.9 times the width of the current collector. The coating width of the first functional area is W1, and the coating width of the second functional area is W2. The value of W1-W2 is 4 mm. In this embodiment, W1 is specifically 116 mm and W2 is specifically 112 mm.

[0083] The first functional region includes a first base layer and a first active layer arranged sequentially along the direction away from the current collector. The thickness of the first base layer is 5 μm. The first base layer includes a conductive agent, a functional filler, and a binder in a mass ratio of 20:72:8. The conductive agent is SP, the functional filler is boehmite, and the binder is PVDF. The first active layer includes NCM811, SP, and PVDF in a mass ratio of 96.5:1.5:2. The second functional region includes a second base layer and a second active layer arranged sequentially along the direction away from the current collector. The thickness of the second base layer is 8 μm. The second base layer includes a functional filler, a conductive agent, and a binder in a mass ratio of 92:1.5:6.5. The functional filler is alumina, the conductive agent is SP, and the binder is PAI. The second active layer includes NCM811, SP, and PVDF in a mass ratio of 96.5:1.5:2.

[0084] The areal density of the first active layer is D1, and the areal density of the second active layer is D2, satisfying the following relationship: D1 / D2=a, 1.5≤a≤2.5. In this embodiment, D1 is specifically 240 g / m³. 2 D2 is specifically 120 g / m 2 , ɑ specifically means 2.

[0085] The sheet resistivity of the first base coat is R1, and the sheet resistivity of the second base coat is R2, satisfying the following relationship: R2 / R1=β, 1×10 3≤β≤1×10 6 In this embodiment, R1 is specifically 25Ω / m 2 R² is specifically 2.5 × 10⁻⁶. 6 Ω / m 2 β is specifically 1.0 × 10 5 .

[0086] The mass retention rate of the first base coating after heat treatment at 250 °C for 1 h is M1, and the mass retention rate of the second base coating after heat treatment at 250 °C for 1 h is M2, satisfying the following relationship: M2 / M1=γ, 1.1≤γ≤1.8. In this embodiment, M1 is specifically 78%, M2 is specifically 95%, and γ is specifically 1.22.

[0087] The above-mentioned method for preparing the positive electrode sheet includes the following steps: S1. The conductive agent, functional filler, and binder of the first primer layer are mixed and uniformly dispersed in NMP to prepare a first primer layer slurry with a solid content of 45%; the conductive agent, functional filler, and binder of the second primer layer are mixed and uniformly dispersed in NMP to prepare a second primer layer slurry with a solid content of 40%; NCM811, conductive agent SP, and binder PVDF are mixed at a mass ratio of 96.5:1.5:2 and uniformly dispersed in NMP to prepare an active layer slurry with a solid content of 70%. S2. Select a 12 μm thick aluminum foil as the current collector. Use a precision double-sided coating machine to coat the first surface of the aluminum foil with a width of W1 and dry it in an oven at 120 ℃ to form the first base coating. Coat the second surface of the current collector with a width of W2 and dry it in an oven at 120 ℃ to form the second base coating. S3. After drying, the first and second base coating layers are simultaneously coated with an active layer slurry on both sides. While keeping the conveyor belt speed of the coating machine constant at 40 m / min, the flow rate of the precision metering pumps of the upper and lower dies is independently controlled by the double-sided coating machine. When the active layer slurry is coated on the first base coating layer with a width W1, the flow rate of the first precision metering pump is adjusted to Q1, which is 280 mL / min in this embodiment. At the same time, when the active layer slurry is coated on the second base coating layer with a width W2, the flow rate of the second precision metering pump is adjusted to Q2, which is 140 mL / min in this embodiment. The coated electrode sheet is dried in a 120 ℃ oven to form the first active layer and the second active layer, respectively. Then, it is cold-pressed, and the linear pressure of the roller press is controlled at 3.2 t / cm to prepare the positive electrode sheet.

[0088] Examples 2-5 The positive electrode differs from that in Example 1 in that the components and mass ratios in the first and second base coatings are different. By adjusting the flow rates of the first and second precision metering pumps, the areal densities of the first and second active layers are made different, thereby changing D1, D2, R1, R2, M1, M2, α, β, and γ.

[0089] Examples 6-7 The positive electrode differs from that in Example 1 in that the areal densities of the first active layer and the second active layer are different by adjusting the flow rates of the first precision metering pump and the second precision metering pump, so as to change D1, D2, and α.

[0090] Examples 8-12 The positive electrode differs from that in Example 1 in that the components and mass ratios in the first and second base coatings are different, so as to achieve changes in R1, R2, M1, M2, β, and γ.

[0091] Examples 13-16 The positive electrode differs from that in Example 1 in that the coating width W1 of the first functional area and the coating width W2 of the second functional area are different, so as to achieve a change in the value of W1-W2.

[0092] Comparative Example 1 The positive electrode sheet differs from that in Example 1 in that the thickness of the first and second base coatings is 0, that is, there are no first and second base coatings. Furthermore, by adjusting the flow rates of the first and second precision metering pumps, the areal densities of the first and second active layers are made different, thereby changing D1, D2, and α.

[0093] Comparative Example 2 The positive electrode differs from that in Example 1 in that the combination and mass ratio of the second base coating are different, and the areal density of the second active layer is different by adjusting the flow rate of the second precision metering pump, so as to change D2, R2, M2, α, β, γ.

[0094] Comparative Example 3 The positive electrode differs from that in Example 1 in that the components and mass ratios in the first base coating are different, and the areal density of the first active layer is different by adjusting the flow rate of the first precision metering pump, so as to change D1, R1, M1, α, β, γ.

[0095] Comparative Examples 4-6 The positive electrode differs from that in Example 1 in that the areal densities of the first active layer and the second active layer are different by adjusting the flow rates of the first precision metering pump and the second precision metering pump, so as to change D1, D2, and α.

[0096] Comparative Examples 7-9 The positive electrode differs from that in Example 1 in that the components and mass ratios in the first and second base coatings are different, so as to achieve changes in R1, R2, M1, M2, β, and γ.

[0097] The flow rates Q1 and Q2 of the first precision metering pump, the areal density D1 of the first active layer, the areal density D2 of the second active layer, the coating width W1 of the first functional area, the coating width W2 of the second functional area, and the W1-W2 values ​​in the above embodiments and comparative examples are all shown in Table 2.

[0098] The components and their mass ratios in the first base coating, the components and their mass ratios in the second base coating, the areal density D1 of the first active layer, the areal density D2 of the second active layer, α, the sheet resistance R1 of the first base coating, the sheet resistance R2 of the second base coating, β, the mass retention rate M1 of the first base coating after heat treatment at 250 °C for 1 h, and the mass retention rate M2 of the second base coating after heat treatment at 250 °C for 1 h, γ are all shown in Table 3 below.

[0099] Table 2 - Parameter settings for the positive electrode sheets of the embodiments and comparative examples of this application Table 3 - Parameter settings for the positive electrode sheets of the embodiments and comparative examples of this application The positive electrode sheets prepared according to the above embodiments and comparative examples are used to assemble battery cells, including the following steps: A bare battery cell is formed by overlapping and winding a positive electrode sheet, an artificial graphite negative electrode, and a 12 μm thick PE separator. The first functional region is located on the inner side of the winding, and the second functional region is located on the outer side of the winding. The areal density of the artificial graphite negative electrode is 145 g / m³. 2 After pre-sealing with aluminum-plastic film, an electrolyte is injected into a glove box. The electrolyte includes 1 mol / L LiPF6 and the remainder organic solvent, which includes ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1. After vacuuming and resealing, the cells are formed and aged to obtain a soft-pack battery.

[0100] Performance testing 1. Areal density test: Measure the areal density of the first and second active layers in the examples and comparative examples. Use a circular stamping die to punch out the current collector sample containing only the first active layer and record the sample area S. Weigh the initial mass of the sample using an analytical balance and record it as W1. Wipe the active layer with lint-free paper soaked in an appropriate amount of solvent until it is completely removed and weigh the sample again, recording it as W2. The areal density of the active layer is: D1 = (W1-W2) / S (g / m²). Take the average of at least 3 data points. The method for testing the areal density of the second active layer is the same. The test results D1 and D2 are shown in Table 2-3 above.

[0101] 2. Sheet resistance test: The four probes of the four-probe tester are pressed in a straight line at equal intervals onto the current collector surface of the first primer coating of the embodiment or comparative example, ensuring good contact between the probes and the coating. The instrument will apply a known small current (I) to the two outer probes and measure the voltage drop (V) between the two inner probes. The internal program will automatically calculate and display the sheet resistance value according to the formula R = k × (V / I), where k is the probe spacing coefficient. The sheet resistance of the first primer coating is obtained by testing. The sheet resistance test method of the second primer coating is the same. The test results R1 and R2 are shown in Table 3 above.

[0102] 3. 250℃ Heat Treatment Mass Retention Rate Test: Blank aluminum foil was placed in a TGA crucible and heated from room temperature to 250℃ at a rate of 10℃ / min in air. The temperature was then held at 250℃ for 60 minutes, followed by cooling. The mass of the blank aluminum foil was recorded at the beginning and end of the 250℃ holding period. The mass change rate of the blank aluminum foil was calculated as follows: ΔM0 = (M... 0结束 - M 0开始 ) / M 0开始 Subsequently, aluminum foil containing only the first base coating of the examples or comparative examples was placed in a TGA crucible. Under the same test conditions as the blank aluminum foil, the mass of the sample at the beginning and end of the heat treatment at 250 °C was calculated, and the mass change rate of the aluminum foil containing the first base coating was calculated: ΔM1 = (M 1结束 – M 1开始 ) / M 1开始 The final quality retention rate of the first base coat is M1 = [1 + (ΔM1 – ΔM0)] × 100%. The quality retention rate of the second base coat is tested in the same way. The test results M1 and M2 are shown in Table 3 above.

[0103] 4. 500-cycle capacity retention test: The pouch batteries prepared in the examples and comparative examples were subjected to an initial capacity test at an ambient temperature of 25 ℃ ± 2 ℃. The batteries were charged at a constant current of 0.5 C to 4.2 V, then switched to constant voltage charging until the current dropped to 0.05 C. After resting for 5 minutes, they were discharged at a constant current of 0.5 C to 2.8 V. This discharge capacity was recorded as the initial capacity C0. Subsequently, the batteries were charged at a constant current of 1 C to 4.2 V, then switched to constant voltage charging until the current ≤ 0.05 C. After resting for 5 minutes, they were discharged at a constant current of 1 C to 2.8 V. This constituted one complete cycle. This charge-discharge cycle was repeated 500 times, and the battery capacity C was then tested. 500 Capacity retention rate = (Discharge capacity at 500th cycle C) 500 The test results are shown in Table 4 below, calculated as (initial capacity C0) × 100%.

[0104] 5. 3C Capacity Retention Test: The pouch batteries prepared in the examples and comparative examples were first charged at a constant current of 0.5 C to 4.2 V at an ambient temperature of 25 ℃ ± 2 ℃, then switched to constant voltage charging until the current dropped to 0.05 C. After standing for 5 minutes, they were discharged at a constant current of 0.5 C to 2.8 V. This capacity was recorded as the baseline capacity C0. Subsequently, the batteries were charged under the same conditions and then discharged at a constant current of 3 C to 2.8 V. The discharge capacity C at this point was recorded. 3C 3C capacity retention rate = (C 3C The test results are shown in Table 4 below, calculated as (C0) × 100%.

[0105] 6. Hot Chamber Test: The fully charged batteries prepared in the examples and comparative examples were placed in an explosion-proof high-temperature test chamber. The temperature of the test chamber was increased from room temperature to 130±1℃ at a rate of 5±2℃ / min, and maintained at this temperature for 30 minutes. If the battery did not catch fire, explode, or leak during or after the test, the sample was considered to have passed the test. If the battery caught fire, exploded, or leaked severely, the test was considered to have failed. Twenty batteries were tested in each group, and the pass rate of the hot chamber test was calculated. The test results are shown in Table 4 below.

[0106] Table 4 - Performance test results of the positive electrode assembly cells of the embodiments and comparative examples of this application As shown in Table 4, embodiments 1-16 of this application construct a first functional region with high current carrying capacity and a second functional region with high safety barrier on opposite sides of the current collector. Functional layers with different conductivity, thermal stability, and areal density are constructed on both sides of the current collector. The areal density of the first active layer and the second active layer is limited to satisfy 1.5≤a≤2.5, and the areal resistivity of the first base layer and the second base layer is satisfied to be 1.0×10⁻⁶. 3≤β≤1.0×10 6 The mass retention rates of the first and second base coatings under high temperature conditions satisfy 1.1≤γ≤1.8. The first functional area provides high capacity and electronic conductivity, while the second functional area provides strong mechanical support. This enables dynamic response with high rate and high conductivity, as well as graded response over thermal abuse time. In the early stages of thermal abuse, the first base coating absorbs a large amount of heat to slow down the rate of temperature rise. When thermal abuse continues, the second base coating leverages its inherent advantages of high thermal stability and high mechanical strength to passively prevent the current collector from contacting the active layer material, effectively preventing the propagation of internal short circuits and the eventual occurrence of thermal runaway. This effectively improves safety performance and cycle life while ensuring high rate and high conductivity.

[0107] Compared to Example 1, Comparative Example 1 did not have a first and second base coating. Due to the high areal density of active material on the first active layer, the lack of a highly conductive first base coating resulted in increased interfacial resistance, severely sacrificing the rate performance and power characteristics of the cell, reducing the utilization rate of the active material, and consequently reducing the cycle capacity retention rate. Furthermore, without the first base coating, it was impossible to absorb heat significantly in the early stages of thermal abuse to slow the temperature rise rate. Without the second base coating, it was impossible to prevent contact between the current collector and the active material layer. The lack of heat absorption buffering from the first base coating and high-temperature support from the second base coating caused the aluminum foil to rapidly melt and shrink at high temperatures, resulting in large-area collapse contact between the positive and negative electrodes, triggering uncontrollable thermal runaway, and reducing thermal stability and safety performance.

[0108] Compared to Example 1, Comparative Example 2 has the same surface density, surface resistivity, and thermal stability in the first and second functional areas on both sides of the current collector, which cannot achieve graded response to thermal abuse time. Furthermore, the high surface density of the active layers on both sides results in a high loading of active materials. The interface resistance of the first and second undercoat layers is low, but the thermal stability is poor. This low-resistance, high-energy-density design is more likely to cause severe thermal runaway under extreme conditions in the hot chamber test, resulting in a reduction in safety performance.

[0109] Compared to Example 1, Comparative Example 3 has the same surface density, surface resistance, and thermal stability in the first and second functional regions on both sides of the current collector. The current distribution on both sides tends to be balanced. However, the low surface density of the active layers on both sides results in a low loading of active material, which cannot fully utilize the high conductivity advantage of the dynamic response layer. The low surface density on both sides leads to an excessively low total loading of active material. Under the same rate test, the actual current density is too high and it is easy to over-discharge, causing severe polarization and structural damage. It cannot meet the high rate performance requirements and results in a low cycle capacity retention rate of the cell.

[0110] Compared to Example 1, in Comparative Example 4, the ratio α of the first active layer to the second active layer is too large. This results in an excessively high areal density of the first active layer, leading to an increased risk of coating cracking due to its excessive thickness. Furthermore, it restricts ion transport, lengthening the solid-state diffusion path of lithium ions in the thick electrode, thus reducing rate performance and capacity utilization. Conversely, the areal density of the second active layer is too small compared to the first, resulting in an excessively thin layer and uneven structure and stress distribution across the entire electrode, affecting cycle life and thermal stability. In Comparative Example 5, the ratio α of the first active layer to the second active layer is too small, leading to similar loads on both active layers and a more balanced current distribution. This prevents the full utilization of the high conductivity of the dynamic response layer, resulting in minimal improvement in high-rate performance. In Comparative Example 6, the ratio α of the first active layer to the second active layer is too small and greater than 1. In this case, the areal density of the first active layer remains high, resulting in a large proportion of active material. This leads to significant heat generation during thermal abuse, while the relatively thin second active layer may not be sufficient to completely block thermal runaway propagation, limiting the improvement in safety performance and maintaining insufficient thermal stability.

[0111] Compared to Example 1, the surface resistivity ratio β of the second base coating and the first base coating in Comparative Example 7 is too large. At this time, the conductivity of the second base coating is too poor compared to the first base coating. The second base coating is prone to electronic pathway obstruction, resulting in a serious underperformance of capacity. In addition, the low content of conductive agent may lead to structural embrittlement and mechanical reliability problems caused by poor adhesion, resulting in a decrease in cycle capacity and 3C discharge capacity. Furthermore, the adhesion of the second base coating is insufficient.

[0112] Compared to Example 1, the surface resistivity ratio β of the second base coating and the first base coating in Comparative Examples 8-9 is too small. At this time, the conductivity of the second base coating is not much different from that of the first base coating. Moreover, the amount of conductive agent added to the second base coating is too large, which leads to a decrease in thermal stability. In the later stage of thermal abuse, it is not possible to effectively suppress the spread of internal short circuits and thermal runaway, resulting in insufficient thermal stability.

[0113] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A positive electrode sheet, characterized in that, It includes a current collector, a first functional area and a second functional area, which are respectively disposed on opposite sides of the current collector. The first functional area includes a first base layer and a first active layer disposed sequentially in the direction away from the current collector, and the second functional area includes a second base layer and a second active layer disposed sequentially in the direction away from the current collector. The areal densities of the first and second active layers satisfy the following relationship: D1 / D2=ɑ, 1.5≤ɑ≤2.5, 180≤D1≤270, where D1 is the areal density of the first active layer, in g / m³. 2 D2 is the areal density of the second active layer, in g / m³. 2 ; The sheet resistivity of the first and second base coatings satisfies the following relationship: R2 / R1 = β, 1.0 × 10⁻⁶. 3 ≤β≤1.0×10 6 1.0×10 4 ≤R2≤1.0×10 8 In the formula, R1 is the surface resistivity of the first base coating layer, in Ω / m. 2 R2 is the surface resistivity of the second base coating, in Ω / m. 2 .

2. The positive electrode sheet as described in claim 1, characterized in that, The mass retention rate of the first primer coating after heat treatment at 230-270 ℃ for 40-80 minutes is M1, and the mass retention rate of the second primer coating after heat treatment at 230-270 ℃ for 40-80 minutes is M2, and M2 / M1=γ, 1.1≤γ≤1.6, 65%≤M1.

3. The positive electrode sheet as described in claim 2, characterized in that, 65%≤M1≤86%, 87%≤M2≤99%.

4. The positive electrode sheet as described in claim 1, characterized in that, 108≤D2≤150； And / or, 10≤R1≤100.

5. The positive electrode sheet as described in claim 1, characterized in that, The coating width of the first functional area and the second functional area are both perpendicular to the length direction of the current collector. The coating width of the first functional area and the second functional area satisfy the following relationship: 2 mm ≤ W1 - W2 ≤ 10 mm, where W1 is the coating width of the first functional area in mm and W2 is the coating width of the second functional area in mm.

6. The positive electrode sheet as described in claim 5, characterized in that, The ratio of the coating width of the first functional area to the width of the current collector in the same direction is (0.70-0.95):

1.

7. The positive electrode sheet as described in claim 1, characterized in that, The first functional area is located on the side facing the center of the winding core after the current collector is wound, and the second functional area is located on the neutral side facing away from the winding core after the current collector is wound.

8. The positive electrode sheet as described in claim 1, characterized in that, The first base layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (10-30):(60-80):(4-16), and the second base layer comprises a conductive agent, a functional filler, and a binder in a mass ratio of (0.2-6):(60-95):(5-36).

9. The positive electrode sheet as described in claim 8, characterized in that, The conductive agents of the first and second base coatings are independent and include at least one of conductive carbon black, carbon nanotubes, graphene, graphite flakes, graphite, expanded graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, activated carbon, mesoporous carbon, and carbon fibers. And / or, the functional fillers of the first and second base coatings are each independent and include at least one of magnesium oxide, aluminum oxide, boehmite, titanium dioxide, zirconium oxide, magnesium oxide, aluminum nitride, boron nitride, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, and silicates; And / or, the adhesives for the first and second primer coatings are each independent and include at least one of polyvinylidene fluoride and its copolymers, styrene-butadiene rubber, polyacrylate, polyimide, polyamide-imide, polyetheretherketone, and fluororubber.

10. An electrochemical device, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-9.

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