Positive pole piece and battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a positive pole piece and a battery. The positive pole piece comprises a base material, a first coating and a second coating, the first coating is arranged on the surface of one side of the base material, and the second coating is arranged on the surface, away from the base material, of the first coating; the positive pole piece meets the following relational expression: A = beta1 * H1 * R (H1 + H2) / (beta1 * H1 + beta2 * H2), wherein 6 < A < 17.5; according to the positive pole piece provided by the embodiment of the invention, the thickness of the first coating, the porosity of the first coating, the resistance of the first coating, the thickness of the second coating and the porosity of the second coating are quantitatively restrained through a formula, and the numerical value of A is controlled within the range, so that the mechanical safety and the electrolyte retention capability can be restrained at the same time; and the passing of the acupuncture test can be ensured, and the liquid retention capacity of the battery cell can be improved, so that the cycle performance of the battery cell is improved, and the battery cell has relatively small energy density loss.

Description

Technical Field

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

[0002] Lithium-ion batteries are prone to thermal runaway when subjected to abnormal conditions such as compression, impact, or puncture. Current research and technical solutions often focus on the impact of parameters such as the hardness, particle size, and formulation of the base coating on battery safety performance, while generally neglecting the influence of the porosity and thickness control of the base coating on cell performance.

[0003] Therefore, there is an urgent need to develop a positive electrode sheet that can construct a structural system that balances safety protection and electrochemical performance by selectively controlling the porosity and thickness of its coating. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a positive electrode sheet and a battery, and to construct a structural system that takes into account both safety protection and electrochemical performance by adjusting the porosity and thickness of its coating.

[0005] To solve the above-mentioned technical problems, on the one hand, embodiments of the present invention provide a positive electrode sheet, including a substrate, a first coating and a second coating, wherein the first coating is disposed on one side surface of the substrate in the thickness direction, and the second coating is disposed on the side surface of the first coating away from the substrate in the thickness direction. The positive electrode sheet satisfies the following relationship: A=β1*H1*R(H1+H2) / (β1*H1+β2*H2), 6<A<17.5; Where A is in Ω·μm, H1 is the thickness of the first coating in μm, β1 is the porosity of the first coating, R is the resistance of the first coating in Ω, H2 is the thickness of the second coating in μm, and β2 is the porosity of the second coating.

[0006] Optionally, the thickness H1 of the first coating is 0.5~3μm, the porosity β1 of the first coating is 15~35%, and the resistance R of the first coating is 1~8Ω.

[0007] Optionally, the thickness H2 of the second coating is 38~55μm, and the porosity β2 of the second coating is 15~35%.

[0008] Optionally, the ratio between the thickness H1 of the first coating and the thickness H2 of the second coating is: H1 / H2 < 0.05.

[0009] Optionally, the substrate includes a first region, a second region, and a third region, wherein the first region is provided with the first coating and the second coating, the second region is provided with only the first coating, and the substrate in the third region is used to connect the electrode tab; The length of the third region is 2~15mm.

[0010] Optionally, the positive electrode further includes a third coating and a fourth coating, wherein the third coating is disposed on the side of the substrate away from the first coating in the thickness direction, and the fourth coating is disposed on the side of the third coating away from the substrate in the thickness direction.

[0011] Optionally, the first coating includes an inorganic filler, a first binder, and a first conductive agent, wherein the inorganic filler accounts for 77-94% of the total mass of the first coating, the first binder accounts for 1-18% of the total mass of the first coating, and the first conductive agent accounts for 0.5-5% of the total mass of the first coating.

[0012] Optionally, the second coating comprises an active substance, a second binder, and a second conductive agent, wherein the active substance accounts for 95-98.7% of the total mass of the second coating, the second binder accounts for 0.7-2% of the total mass of the second coating, and the second conductive agent accounts for 0.3-3% of the total mass of the second coating.

[0013] Optionally, the inorganic filler includes one or more of boehmite, barium titanate, aluminum oxide, silicon dioxide, lithium iron phosphate, barium sulfate, talc, and kaolin; and / or, The first adhesive comprises one or more of polyacrylic acid, polyacrylate, polyurethane, polystyrene-butadiene, polyvinyl alcohol, carboxymethyl cellulose, epoxy resin, and ethylene-vinyl acetate copolymer; and / or, The first conductive agent includes one or more of furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene; and / or, The active material includes one or more of lithium cobalt oxide, ternary materials, and lithium iron phosphate; and / or, The second adhesive comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylate, and polyimide; and / or, The second conductive agent includes one or more of the following: furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene.

[0014] On the other hand, embodiments of the present invention provide a battery including a negative electrode, a separator, an electrolyte, and a positive electrode as described in any of the preceding claims, wherein the separator is disposed between the positive electrode and the negative electrode.

[0015] The positive electrode sheet provided in this embodiment of the invention uses formulas to quantitatively constrain the thickness, porosity, and resistance of the first coating, as well as the thickness and porosity of the second coating, so that the matching between the parameters reaches an optimized state. By controlling the value of A within the above range, it can simultaneously constrain mechanical safety and electrolyte retention capacity. This not only ensures the passing of the needle penetration test but also increases the electrolyte retention of the cell, thereby improving the cycle performance of the cell and resulting in a smaller energy density loss in the cell. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a positive electrode sheet provided in an embodiment of the present invention.

[0017] The reference numerals in the accompanying drawings are as follows: 1. Substrate; 1a. First region; 1b. Second region; 1c. Third region; 2. First coating; 3. Second coating; 4. Third coating; 5. Fourth coating. Detailed Implementation

[0018] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] like Figure 1 As shown, an embodiment of the present invention provides a positive electrode sheet, including a substrate 1, a first coating 2 and a second coating 3. The first coating 2 is disposed on one side surface of the substrate 1 in the thickness direction, and the second coating 3 is disposed on the side surface of the first coating 2 away from the substrate 1 in the thickness direction.

[0020] The first coating 2 is a functional coating, and the second coating 3 is an active material layer. The first coating 2 serves to prevent thermal runaway caused by mechanical abuse (such as collision, squeezing, puncture, vibration, etc.). The first coating 2 can cover the substrate 1. By setting the first coating 2, the substrate 1 is protected, preventing the electrode from being punctured, so that the positive electrode cannot come into contact with the negative electrode, avoiding thermal runaway, thereby improving safety performance.

[0021] The positive electrode has the following characteristics: A=β1*H1*R(H1+H2) / (β1*H1+β2*H2), 6<A<17.5; Where A is in Ω·μm, H1 is the thickness of the first coating 2 in μm, β1 is the porosity of the first coating 2, R is the resistance of the first coating 2 in Ω, H2 is the thickness of the second coating 3 in μm, and β2 is the porosity of the second coating 3.

[0022] The thickness and porosity of the coating are closely related to the electrolyte storage capacity of the battery cell. Specifically, when the porosity is too high, the coating has more space to hold electrolyte, resulting in a higher electrolyte storage capacity. During battery cycling, the surface of the active material can be continuously wetted by the electrolyte. However, excessively high porosity leads to a loose pore structure within the coating, and even the formation of ineffective pores. While these pores can store electrolyte, they cannot form effective ion transport channels, instead increasing ion migration resistance and causing a decrease in battery rate performance. Conversely, when the porosity is too low, the space within the coating that can hold electrolyte decreases, resulting in a reduced electrolyte storage capacity and causing battery capacity decay.

[0023] Coating thickness and electrolyte storage space are linearly positively correlated. Excessive coating thickness increases the electrolyte volume per unit area, reducing electrolyte consumption during cycling and thus improving battery cycle life. However, excessive thickness may decrease coating structural stability, reducing adhesion and making the coating more susceptible to structural damage from external impacts. Conversely, insufficient coating thickness reduces electrolyte storage capacity, leading to a deterioration in cycle life. Therefore, it is necessary to design appropriate porosity and coating thickness to ensure sufficient electrolyte storage, adequate electrolyte wetting, sufficient particle contact without affecting ion movement channels, and simultaneously maintain coating structural stability.

[0024] The positive electrode sheet provided in this application embodiment has a first coating 2 and a second coating 3 on a substrate 1. Both the first coating 2 and the second coating 3 can store electrolyte. By adding the first coating 2, the electrolyte retention of the battery cell can be increased based on the active material layer. The thickness, porosity, and resistance of the first coating 2, as well as the thickness and porosity of the second coating 3, are quantitatively constrained by formulas to optimize the matching between the parameters. By controlling the value of A within the above range, both mechanical safety and electrolyte retention capacity can be constrained simultaneously. This not only ensures the passing of the needle penetration test but also increases the electrolyte retention of the battery cell, thereby improving the cycle performance of the battery cell and resulting in a smaller energy density loss.

[0025] In one embodiment, the thickness H1 of the first coating 2 is 0.5~3μm, the porosity β1 of the first coating 2 is 15~35%, and the resistance R of the first coating 2 is 1~8Ω. Further, the porosity β1 of the first coating 2 is 15~30%.

[0026] Within the aforementioned thickness range, the first coating 2 can store sufficient electrolyte, and the greater the coating thickness, the greater the electrolyte storage volume per unit area, preventing electrolyte drying during battery cycling and ensuring battery cycle capacity. Within the aforementioned porosity range, the first coating 2 can accommodate sufficient electrolyte, resulting in good battery cycle performance without affecting ion migration, thus providing good rate performance. Within the aforementioned resistance range, ions exhibit good transport efficiency.

[0027] In one embodiment, the thickness H2 of the second coating 3 is 38~55μm, and the porosity β2 of the second coating 3 is 15~35%.

[0028] Within the aforementioned thickness range, the second coating 3 can store sufficient electrolyte. A greater coating thickness increases the electrolyte storage volume per unit area, ensuring continuous electrolyte wetting of the active material surface during battery cycling and guaranteeing the battery's cycle capacity. Within the aforementioned porosity range, the second coating 3 can accommodate sufficient electrolyte, resulting in good battery cycle performance without affecting ion migration, thus providing good rate performance.

[0029] In one embodiment, the ratio between the thickness H1 of the first coating 2 and the thickness H2 of the second coating 3 must satisfy: H1 / H2 < 0.05.

[0030] In the embodiments of this application, the first coating 2 has a protective and liquid-retaining function, but its protective function does not increase with the increase of thickness. On the contrary, it may cause the first coating 2 to become more brittle and prone to detachment and cracking.

[0031] By controlling the ratio between the thickness H1 of the first coating 2 and the thickness H2 of the second coating 3 to be less than 0.05, the thickness H1 of the first coating 2 is less than the thickness H2 of the second coating 3. The first coating 2 is thin and uniform, which can not only adhere tightly to the substrate 1 to form a barrier, but also avoid the brittleness problem caused by excessive thickness, thus having a good protective effect.

[0032] On the other hand, the thinner first coating 2 does not hinder the migration of ions to the active material, thus achieving a balance between liquid storage and ion conduction.

[0033] In one embodiment, the substrate 1 includes a first region 1a, a second region 1b and a third region 1c. The first region 1a is provided with a first coating 2 and a second coating 3. The second region 1b is only provided with the first coating 2. The substrate 1 in the third region 1c is used to connect the electrode tab. The length of the third region 1c in the longitudinal direction of the substrate is 2-15 mm. Preferably, the length of the third region 1c in the longitudinal direction of the substrate is 5-10 mm.

[0034] A first coating 2 and a second coating 3 are sequentially disposed on the substrate 1 in the first region 1a. The first region 1a is the core region for the electrochemical reaction of the positive electrode. The first coating 2 has the functions of protection and electrolyte retention, protecting the substrate 1 from mechanical impact (such as extrusion). On the other hand, it stores electrolyte through a porous structure, replenishing the ion conduction medium for long-term cycling. The second coating 3 is the active material layer, which is the coating for lithium ion insertion / extraction. Its presence directly determines the energy density and capacity of the battery.

[0035] The second region 1b is located on the outermost layer of the core, and the substrate 1 of the second region 1b is protected by the first coating 2.

[0036] The third region 1c is an empty foil region. The substrate 1 in the third region 1c is not covered with the first coating 2 and the second coating 3. The substrate 1 is exposed, and the electrode tab can be soldered to the substrate 1.

[0037] In this embodiment, the battery cell is a wound battery cell. After the positive electrode, negative electrode and separator are wound, the second region 1b is located at the outermost ring of the winding.

[0038] In one embodiment, the third region 1c is located between the first region 1a and the second region 1b.

[0039] It is understandable that the location of the third region 1c is not limited to the middle between the first region 1a and the second region 1b. The location of the third region 1c can also be set on the side of the first region 1a away from the second region 1b, or on the side of the second region 1b away from the first region 1a.

[0040] In one embodiment, the positive electrode further includes a third coating 4 and a fourth coating 5. The third coating 4 is disposed on the surface of the substrate 1 away from the first coating 2 in the thickness direction, and the fourth coating 5 is disposed on the surface of the third coating 4 away from the substrate 1 in the thickness direction. That is, the second coating 3, the first coating 2, the substrate 1, the third coating 4, and the fourth coating 5 are stacked sequentially. The third coating 4 is a functional coating, and its function is the same as that of the first coating 2. The fourth coating 5 is an active material layer, and its function is the same as that of the second coating 3. The third coating 4 serves to prevent thermal runaway caused by mechanical abuse (such as collision, extrusion, puncture, vibration, etc.) and can protect the surface of the substrate 1 away from the first coating 2.

[0041] By applying a coating to both sides of the substrate 1, the total amount of active material per unit area increases while keeping the thickness of the substrate 1 constant, thereby improving the energy density of the battery cell.

[0042] In one embodiment, the first coating 2 includes an inorganic filler, a first binder, and a first conductive agent. The inorganic filler accounts for 77-94% of the total mass of the first coating 2, the first binder accounts for 1-18% of the total mass of the first coating 2, and the first conductive agent accounts for 0.5-5% of the total mass of the first coating 2. The inorganic filler is typically a high-hardness ceramic or inorganic particles. Its 77-94% proportion allows for the formation of a rigid framework structure within the first coating 2, effectively resisting the impact of needle puncture. The first binder facilitates the bonding between the inorganic particles and the first conductive agent, and helps the first coating 2 adhere tightly to the substrate 1 and the second coating 3, reducing detachment during charge-discharge cycles and processing. The first conductive agent assists in ion / electron conduction, preventing the first coating 2 from hindering electron conduction between the second coating 3 and the substrate 1.

[0043] In one embodiment, the inorganic filler includes one or more of boehmite, barium titanate, aluminum oxide, silicon dioxide, lithium iron phosphate, barium sulfate, talc, and kaolin.

[0044] In one embodiment, the first adhesive includes one or more of polyacrylic acid, polyacrylate, polyurethane, polystyrene-butadiene, polyvinyl alcohol, carboxymethyl cellulose, epoxy resin, and ethylene-vinyl acetate copolymer.

[0045] In one embodiment, the first conductive agent includes one or more of furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene.

[0046] In one embodiment, the second coating 3 includes an active substance, a second binder, and a second conductive agent. The active substance accounts for 95-98.7% of the total mass of the second coating 3, the second binder accounts for 0.7-2% of the total mass of the second coating 3, and the second conductive agent accounts for 0.3-3% of the total mass of the second coating 3.

[0047] The active material serves as the core carrier for lithium-ion insertion / extraction. A high proportion of active material enables the battery cell to achieve greater capacity and energy density. The second binder facilitates the bonding between the active material and the second conductive agent, and also helps the second coating 3 adhere tightly to the first coating 2, reducing detachment during charge-discharge cycles and processing. The second conductive agent establishes electronic conduction pathways between the active material particles, enabling electron conduction between the second coating 3 and the substrate 1.

[0048] In one embodiment, the active material includes one or more of lithium cobalt oxide, ternary materials, and lithium iron phosphate (LiFePO4). The ternary material can be lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0049] In one embodiment, the second adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylate, and polyimide.

[0050] In one embodiment, the second conductive agent includes one or more of furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene.

[0051] On the other hand, the present invention provides a battery including a negative electrode, a separator, an electrolyte, and a positive electrode as described in any of the above embodiments, wherein the separator is disposed between the positive electrode and the negative electrode.

[0052] The negative electrode sheet can be prepared by coating a negative electrode active material layer onto the current collector of the negative electrode. The negative electrode active material layer can be formed by coating a negative electrode slurry, including a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a solvent, onto the negative electrode current collector, and then drying and rolling the coated negative electrode current collector.

[0053] There are no restrictions on the aforementioned negative electrode active materials, negative electrode conductive agents, negative electrode binders, and solvents; they can be selected based on existing technical requirements in this field.

[0054] The present invention will be further illustrated by the following examples.

[0055] Example 1 1. Preparation of positive electrode sheet Boehmite, conductive carbon black, and polyacrylic acid (PAA) were mixed according to the specified mass ratio, then dispersed in pure water and stirred until homogeneous. The slurry was then applied to the front surface of the aggregate to obtain the first coating 2. The resistance of the first coating 2 was measured to be 1.5Ω.

[0056] Lithium cobalt oxide, conductive graphite, and polyvinylidene fluoride (PVDF) are mixed in a specific mass ratio, then dispersed in the solvent N-methyl-2-pyrrolidone (NMP). After stirring until homogeneous, the slurry is coated onto the first coating layer 2 to obtain the second coating layer 3. After drying, rolling, and vacuum drying, the positive electrode sheet is obtained.

[0057] The thickness H1 of the first coating 2 is 2.5 μm, and the porosity β1 of the first coating 2 is 35%. The thickness H2 of the second coating 3 is 55 μm, and the porosity β2 of the second coating 3 is 16%.

[0058] 2. Preparation of negative electrode sheet Artificial graphite, conductive carbon black Super-P, binder, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in a specific mass ratio and then dispersed in deionized water to obtain a negative electrode slurry. The slurry is coated on both sides of a copper foil, and after drying, calendering, and vacuum drying, a negative electrode sheet is obtained.

[0059] 3. Cell fabrication The above-mentioned positive electrode, negative electrode and polypropylene separator are wound together to obtain the battery cell.

[0060] Example 2 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 5Ω, the thickness H1 of the first coating 2 is 1μm, the porosity β1 of the first coating 2 is 35%, the thickness H2 of the second coating 3 is 38μm, and the porosity β2 of the second coating 3 is 25%.

[0061] Example 3 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 3Ω, the thickness H1 of the first coating 2 is 1.5μm, the porosity β1 of the first coating 2 is 30%, the thickness H2 of the second coating 3 is 38μm, and the porosity β2 of the second coating 3 is 20%.

[0062] Example 4 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 3Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 20%, the thickness H2 of the second coating 3 is 50μm, and the porosity β2 of the second coating 3 is 20%.

[0063] Example 5 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 8Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 54μm, and the porosity β2 of the second coating 3 is 25%.

[0064] Example 6 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 1μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 16%.

[0065] Example 7 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 54μm, and the porosity β2 of the second coating 3 is 25%.

[0066] Example 8 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 34%.

[0067] Example 9 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 29%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0068] Example 10 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 16%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0069] Example 11 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 6Ω, the thickness H1 of the first coating 2 is 1μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 39μm, and the porosity β2 of the second coating 3 is 25%.

[0070] Example 12 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 5Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 16%.

[0071] Comparative Example 1 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 5Ω, the thickness H1 of the first coating 2 is 3μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 34%.

[0072] Comparative Example 2 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 1Ω, the thickness H1 of the first coating 2 is 3μm, the porosity β1 of the first coating 2 is 29%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0073] Comparative Example 3 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 3Ω, the thickness H1 of the first coating 2 is 1μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0074] Comparative Example 4 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 6Ω, the thickness H1 of the first coating 2 is 3μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 54μm, and the porosity β2 of the second coating 3 is 25%.

[0075] Comparative Example 5 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 7Ω, the thickness H1 of the first coating 2 is 3μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 39μm, and the porosity β2 of the second coating 3 is 25%.

[0076] Comparative Example 6 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 15Ω, the thickness H1 of the first coating 2 is 1μm, the porosity β1 of the first coating 2 is 16%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0077] Comparative Example 7 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 0.4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0078] Comparative Example 8 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 0.4μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0079] Comparative Example 9 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 4μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0080] Comparative Example 10 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 14%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0081] Comparative Example 11 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 36%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 25%.

[0082] Comparative Example 12 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 37μm, and the porosity β2 of the second coating 3 is 25%.

[0083] Comparative Example 13 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 56μm, and the porosity β2 of the second coating 3 is 25%.

[0084] Comparative Example 14 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 14%.

[0085] Comparative Example 15 The preparation process is basically the same as in Example 1, except that the resistance of the first coating 2 is 4Ω, the thickness H1 of the first coating 2 is 2μm, the porosity β1 of the first coating 2 is 25.6%, the thickness H2 of the second coating 3 is 47μm, and the porosity β2 of the second coating 3 is 37%.

[0086] Performance testing The lithium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-15 were subjected to the following performance tests: 1) Needle prick test At room temperature, the formed battery was charged to 4.53V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.01C, and then left to stand for 2 hours. A 3mm steel needle was then used to pierce the center of the battery surface at a speed of 30mm / s, and the cell condition was observed after 10 minutes of standing.

[0087] 2) Cyclic performance test At room temperature, the formed battery was charged to 4.53V using a 1C constant current and constant voltage method, with a cutoff current of 0.01C, and then discharged to 3.0V using a 1C constant current method. After 1000 charge / discharge cycles, the capacity retention rate after the 1000th cycle was calculated to evaluate its cycle performance.

[0088] The formula for calculating the capacity retention rate after 1000 cycles at room temperature (1°C) is as follows: Capacity retention rate after 1000 cycles (%) = (Discharge capacity after 1000 cycles / Discharge capacity after the first cycle) × 100%.

[0089] 3) Energy density loss test At room temperature, the formed battery was charged to 4.53V using a 1C constant current and constant voltage method, with a cutoff current of 0.01C. Then, it was discharged to 3.0V using a 1C constant current method to obtain the battery energy (Wh). The thickness of each cell was measured using a thickness gauge, and the energy density (Wh / L) was calculated based on the formula: thickness * length * width = volume, energy / volume = energy density (Wh / L).

[0090] 4) Resistance test Cut the electrode sample to 5*5cm and place it in a vacuum drying oven (60℃, 2h); clean the upper and lower probes of the diaphragm resistance tester with a lint-free cloth, set the test pressure to 25Mpa, the test time to 1h, place the electrode sample between the upper and lower probes and control the probes to press down, and obtain the electrode resistance data.

[0091] 5) Porosity test Cut 100 mg of electrode material and place it in a vacuum drying oven (60℃, 2 h). Place the sample in the sample cell of a mercury porosimeter and evacuate to below 1 Pa. Apply low pressure (0.01-0.1 MPa) and record the initial intrusion volume. Gradually increase the pressure to 400 MPa, allowing mercury to gradually penetrate the small-diameter pores. Record the relationship between pressure and mercury intrusion volume in real time. Obtain the electrode porosity after the test.

[0092] The test results are entered into Table 1.

[0093] Table 1. Test results of Examples 1-12 and Comparative Examples 1-15 As can be seen from the test results of Examples 1 to 12 and Comparative Examples 1 to 15 in Table 1, when the values ​​of R, H1, β1, H2, and β2 are within the range, and the relationship A = β1 * H1 * R (H1 + H2) / (β1 * H1 + β2 * H2) is satisfied, and 6 < A < 17.5, the battery can pass the nail penetration test and has good cycle performance with small energy density loss.

[0094] A comparison between Comparative Example 1 and the embodiment reveals that the ratio of the thickness H1 of the first coating 2 to the thickness H2 of the second coating 3 is greater than 0.05, failing to satisfy the relationship H1 / H2 < 0.05, which increases the energy density loss of the battery. This may be due to the brittleness caused by the excessive thickness of the first coating 2, leading to its detachment, or the insufficient thickness of the second coating 3, reducing the amount of active material in the positive electrode, thus causing a loss in energy density.

[0095] By comparing Comparative Examples 2-5 with the embodiment, it can be found that the resistance R of the first coating 2 is in the range of 1~8Ω, the thickness H1 of the first coating 2 is in the range of 0.5~3μm, and the porosity β1 of the first coating 2 is in the range of 15~35%. The thickness H2 of the second coating 3 is in the range of 38~55μm, and the porosity β2 of the second coating 3 is in the range of 15~35%. However, when the calculated result of the relationship is not in the range of 6<A<17.5, the cycle performance of the battery is significantly reduced.

[0096] By comparing Comparative Examples 6-15 with the Examples, it can be found that when any one of the resistance R of the first coating 2, the thickness H1 of the first coating 2, the porosity β1 of the first coating 2, the thickness H2 of the second coating 3, and the porosity β2 of the second coating 3 exceeds the range, even if the calculated result of the relational formula is within the range of 6 < A < 17.5, the cycle performance of the battery will still deteriorate and the energy density loss will increase.

[0097] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a substrate, a first coating, and a second coating. The first coating is disposed on one side surface of the substrate in the thickness direction, and the second coating is disposed on the side surface of the first coating away from the substrate in the thickness direction. The positive electrode sheet has the following characteristics: A=β1*H1*R(H1+H2) / (β1*H1+β2*H2), 6<A<17.5; Where A is in Ω·μm, H1 is the thickness of the first coating in μm, β1 is the porosity of the first coating, R is the resistance of the first coating in Ω, H2 is the thickness of the second coating in μm, and β2 is the porosity of the second coating.

2. The positive electrode sheet as described in claim 1, characterized in that, The thickness H1 of the first coating is 0.5~3μm, the porosity β1 of the first coating is 15~35%, and the resistance R of the first coating is 1~8Ω.

3. The positive electrode sheet as described in claim 1, characterized in that, The thickness H2 of the second coating is 38~55μm, and the porosity β2 of the second coating is 15~35%.

4. The positive electrode sheet as described in any one of claims 1-3, characterized in that, The ratio between the thickness H1 of the first coating and the thickness H2 of the second coating is: H1 / H2 < 0.

05.

5. The positive electrode sheet as described in claim 1, characterized in that, The substrate includes a first region, a second region, and a third region. The first region is provided with the first coating and the second coating, the second region is provided with only the first coating, and the substrate in the third region is used to connect the electrode tab. The length of the third region in the longitudinal direction of the substrate is 2~15mm.

6. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode sheet further includes a third coating and a fourth coating. The third coating is disposed on the side of the substrate away from the first coating in the thickness direction, and the fourth coating is disposed on the side of the third coating away from the substrate in the thickness direction.

7. The positive electrode sheet as described in claim 1, characterized in that, The first coating comprises an inorganic filler, a first binder, and a first conductive agent. The inorganic filler accounts for 77-94% of the total mass of the first coating, the first binder accounts for 1-18% of the total mass of the first coating, and the first conductive agent accounts for 0.5-5% of the total mass of the first coating.

8. The positive electrode sheet as described in claim 7, characterized in that, The second coating comprises an active substance, a second binder, and a second conductive agent. The active substance accounts for 95-98.7% of the total mass of the second coating, the second binder accounts for 0.7-2% of the total mass of the second coating, and the second conductive agent accounts for 0.3-3% of the total mass of the second coating.

9. The positive electrode sheet as described in claim 8, characterized in that, The inorganic filler includes one or more of boehmite, barium titanate, aluminum oxide, silicon dioxide, lithium iron phosphate, barium sulfate, talc, and kaolin; and / or, The first adhesive comprises one or more of polyacrylic acid, polyacrylate, polyurethane, polystyrene-butadiene, polyvinyl alcohol, carboxymethyl cellulose, epoxy resin, and ethylene-vinyl acetate copolymer; and / or, The first conductive agent includes one or more of furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene; and / or, The active material includes one or more of lithium cobalt oxide, ternary materials, and lithium iron phosphate; and / or, The second adhesive comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylate, and polyimide; and / or, The second conductive agent includes one or more of the following: furnace black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene.

10. A battery, characterized in that, It includes a negative electrode, a separator, an electrolyte, and a positive electrode as described in any one of claims 1-9, wherein the separator is disposed between the positive electrode and the negative electrode.

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