Secondary battery electrode plate, method for producing the same, and secondary battery

Abstract

Secondary battery electrode plate, method for manufacturing the same, and secondary battery. This secondary battery electrode plate includes a current collector and a first active material layer. The first active material layer is located on the surface of the current collector and contains first active material particles. The first active material particles have an equivalent sphericity X1 represented by the formula X1 = 3 / (S1R1ρ1), where 0.05 ≤ X1 ≤ 0.8, R1 is the median radius of the first active material particles in units of μm, S1 is the specific surface area of the first active material particles in units of m 2 / g, and ρ1 is the true density of the first active material particles in units of g / cm 3 .

Description

Technical Field

[0001] (Cross - reference to related applications) This disclosure claims priority to Chinese Patent Application No. CN202210752174.8, filed on June 29, 2022. The entire content of the above - mentioned application is incorporated herein by reference.

[0002] This disclosure relates to the field of lithium - ion batteries, and more specifically, to secondary battery electrode plates, their manufacturing methods, and secondary batteries.

Background Art

[0003] Increasing the thickness of the electrode can improve the energy density of the battery core and reduce the cost of the battery core. However, with the increase in thickness, the diffusion path of lithium ions in the electrode becomes longer, the liquid - phase diffusion impedance of the electrode increases, and the electrode reaction rate decreases. In related technologies, in order to improve the kinetic performance of thick electrodes, electrode compression is often reduced, or the content of the conductive agent in the electrode is increased. The former reduces the energy density of the electrode, and the latter often reduces the capacity per gram of the electrode mixture and further increases the cost.

[0004] To ensure both the energy density and the kinetic performance of the electrode, an important research direction is to reduce the tortuosity of the active material layer inside the electrode. There are many methods for reducing the tortuosity of the electrode, such as increasing the porosity, constructing a vertical pore structure of the electrode, and changing the morphology of the material particles. However, the aforementioned methods in related technologies still cannot achieve an excellent effect of reducing the tortuosity of the active material layer inside the electrode.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present disclosure is to provide a secondary battery electrode plate, a method for manufacturing the same, and a secondary battery. Compression of the electrode of the secondary battery electrode plate is ensured, the electrode has a high capacity retention rate, and the liquid-phase diffusion impedance of the electrode is reduced.

Means for Solving the Problems

[0006] To achieve the above object, a first aspect of the present disclosure provides a secondary battery electrode plate. The secondary battery electrode plate includes a current collector and a first active material layer. The first active material layer is located on the surface of the current collector. The first active material layer contains first active material particles. The first active material particles have an equivalent sphericity X1 represented by the following formula (1), X1 = 3 / (S1R1ρ1) Formula (1), where 0.05 ≦ X1 ≦ 0.8, R1 is the median radius of the first active material particles in units of μm, S1 is in units of m 2 / g and is the specific surface area of the first active material particles, and ρ1 is in units of g / cm 3 and is the true density of the first active material particles.

[0007] In one embodiment, when the electrode plate is a positive electrode plate, 0.10 ≦ X1 ≦ 0.8, or when the electrode plate is a negative electrode plate, 0.05 ≦ X1 ≦ 0.8.

[0008] In one embodiment, the secondary battery electrode plate further includes a second active material layer. The second active material layer is located on the surface of the first active material layer away from the surface of the current collector. The second active material layer contains second active material particles. The second active material particles have an equivalent sphericity X2 represented by the following formula (2), X2 = 3 / (S2R2ρ2) Formula (2), where R2 is the median radius of the second active material particles in units of μm, S2 is in units of m 2 / g and is the specific surface area of the second active material particles, and ρ2 is in units of g / cm 3 and is the true density of the second active material particles. The sphericity X2 of the second active material particles is larger than the equivalent sphericity X1 of the first active material particles.

[0009] In one embodiment, 0.05 ≦ X1 ≦ 0.4 and 0.2 ≦ X2 ≦ 0.8.

[0010] In one embodiment, 0.1 ≦ X1 ≦ 0.3 and 0.2 ≦ X2 ≦ 0.5.

[0011] In one embodiment, 0.07 ≦ X2 - X1 ≦ 0.5.

[0012] In one embodiment, 0.2 ≦ X2 - X1 ≦ 0.4.

[0013] In one embodiment, when the electrode plate is a positive electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 0.05 to 5, and S1 and S2 are each and independently any value in the range of 0.5 to 20.

[0014] When the electrode plate is a negative electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 1 to 20, and S1 and S2 are each and independently any value in the range of 0.5 to 5.

[0015] In one embodiment, the surface density of the first active material layer is Y1 = ε × L, and the surface density of the second active material layer is Y2 = (1 - ε) × L, L is in units of m 2 / g is the total surface density of the first active material layer and the second active material layer. One side surface of the current collector is coated with the first active material layer, or each of the two side surfaces of the current collector is coated with the first active material layer, and the surface of each first active material layer away from the current collector is coated with the second active material layer.

[0016] When one side surface of the current collector is coated with the first active material layer, when the electrode plate is a positive electrode plate, 50 ≦ L ≦ 300, or when the electrode plate is a negative electrode plate, 23 ≦ L ≦ 138.

[0017] When each of the two sides of the current collector is coated with the first active material layer, when the electrode plate is a negative electrode plate, 100 ≦ L ≦ 600, or when the electrode plate is a negative electrode plate, 46 ≦ L ≦ 276, and ε is an adjustment parameter, 0.2 ≦ ε ≦ 0.8.

[0018] In one embodiment, 0.1 ≦ (X2 / Y2) / (X1 / Y1) ≦ 6.

[0019] In one embodiment, 0.25 ≦ (X2 / Y2) / (X1 / Y1) ≦ 4.5.

[0020] In one embodiment, when the electrode plate is a positive electrode plate, the compression density is 2.0 to 2.7 g / cm 3 or when the electrode plate is a negative electrode plate, the compression density is 1.0 to 2.0 g / cm 3 is.

[0021] The second aspect of the present disclosure provides a method for manufacturing a secondary battery electrode plate. This method includes the following steps: Coating the current collector with the first slurry to obtain an electrode plate in a state where the current collector is coated with the first slurry layer (S1), and Rolling the electrode plate (S2), including.

[0022] The first slurry contains first active material particles, and the first active material particles have an equivalent sphericity X1 represented by the following formula (1), X1 = 3 / (S1R1ρ1) Formula (1), where 0.05 ≦ X1 ≦ 0.8, R1 is the median radius of the first active material particles in μm, S1 is the specific surface area of the first active material particles in m 2 / g, and ρ1 is the true density of the first active material particles in g / cm 3 is.

[0023] In one embodiment, when the electrode plate is a positive electrode plate, 0.10 ≦ X1 ≦ 0.8, or when the electrode plate is a negative electrode plate, 0.05 ≦ X1 ≦ 0.8.

[0024] In one embodiment, step S1 includes coating a current collector with a first slurry and a second slurry to obtain an electrode plate continuously coated with a first slurry layer and a second slurry layer in a direction away from the current collector.

[0025] The second slurry contains second active material particles, and the second active material particles have an equivalent sphericity X2 represented by the following formula (2). X2 = 3 / (S2R2ρ2) Formula (2) In the formula, R2 is the median radius of the second active material particles in μm, S2 is the specific surface area of the second active material particles in m 2 / g, and ρ2 is the true density of the second active material particles in g / cm 3 The sphericity X2 of the second active material particles is larger than the equivalent sphericity X1 of the first active material particles.

[0026] The third aspect of the present disclosure provides a secondary battery. This secondary battery includes a secondary battery electrode plate according to the first aspect of the present disclosure.

[0027] According to the above technical solution, the first active material layer of the secondary battery electrode plate in the present disclosure uses active material particles having a specific sphericity, reduces the liquid phase impedance of the electrode, and can improve the capacity maintenance while ensuring that the electrode has a high compression density.

[0028] Other features and advantages of the present disclosure will be described in detail in the following embodiments for carrying out the invention.

Embodiments for Carrying Out the Invention

[0029] Specific embodiments of the present disclosure will be described in detail below. It should be noted that the specific embodiments described herein are merely used to explain and illustrate the present disclosure and are not intended to limit the present disclosure.

[0030] A first aspect of the present disclosure provides a secondary battery electrode plate. The secondary battery electrode plate includes a current collector and a first active material layer. The first active material layer is located on the surface of the current collector. The first active material layer includes first active material particles. The first active material particles have an equivalent sphericity X1 represented by the following formula (1), X1 = 3 / (S1R1ρ1) Formula (1), where 0.05 ≤ X1 ≤ 0.8, R1 is the median radius of the first active material particles in μm, S1 is the specific surface area of the first active material particles in m 2 / g, and ρ1 is the true density of the first active material particles in g / cm 3 .

[0031] In the present disclosure, the median radius of the active material particles is 1 / 2 of the median particle size D50 of the quantity distribution of the active material particles. D50 is the average particle size (diameter) of the active material particles in μm. The aforementioned particle size D50 is the corresponding diameter when the cumulative number ratio of the active material particles reaches 50%. The specific surface area S of the active material particles is detected by a nitrogen adsorption / desorption test.

[0032] According to the present disclosure, when randomly selecting electrode active material particles in the electrode plate to determine the particle size D50 of the electrode active material particles, the test method specifically includes the following steps: a) To obtain an electrode plate, disassemble a fully discharged battery to obtain the electrode plate, and then cut an arbitrary position within the coating area with argon ions to obtain an electrode plate cross-section sample. b) Place the aforementioned electrode plate cross-section sample in a scanning electron microscope (SEM) for observation, adjust the voltage and magnification of the SEM according to actual requirements to ensure that a sufficient number of particles in the aforementioned sample are clearly visible and photographed to obtain an SEM image. c) The obtained SEM images may be imported into software for grayscale debugging (e.g., Geodict) to count the particle sizes of the particles, or alternatively, the particle sizes of the particles may be directly identified or counted using an artificial naked eye alternatively. d) Conduct 20 to 30 experiments cumulatively. The amount of particles that can be counted in each experiment is less than 500 pcs. After the above-mentioned results are counted, obtain the particle size D50 of the electrode active material particles in the electrode plate. including.

[0033] The active material particles in the active material layer in the lithium-ion battery in the present disclosure have a specific equivalent sphericity represented by the formula X1 = 3 / (S1R1ρ1), where 0.05 ≤ X1 ≤ 0.8. As a result, the lithium-ion battery in the present disclosure is beneficial for improving the capacity retention rate and liquid-phase diffusion impedance of the electrode based on good compression density.

[0034] In a specific embodiment of the present disclosure, when the electrode plate is a positive electrode plate, 0.10 ≤ X1 ≤ 0.8.

[0035] In a specific embodiment of the present disclosure, when the electrode plate is a negative electrode plate, 0.05 ≤ X1 ≤ 0.8.

[0036] In a specific embodiment of the present disclosure, the secondary battery electrode plate further includes a second active material layer. The second active material layer is located on the surface of the first active material layer away from the surface of the current collector. The second active material layer includes second active material particles. The second active material particles have an equivalent sphericity X2 represented by the following formula (2). X2 = 3 / (S2R2ρ2) Formula (2). wherein, R2 is the median radius of the second active material particles in μm, S2 is the specific surface area of the second active material particles in m 2 / g, and ρ2 is the true density of the second active material particles in g / cm 3 . The sphericity X2 of the second active material particles is larger than the equivalent sphericity X1 of the first active material particles.

[0037] The secondary battery electrode plate of the present disclosure has a double active material layer having different particle sphericities. The equivalent sphericity of the first active material particles closer to the current collector is smaller than that of the second active material particles farther from the current collector. The higher the equivalent sphericity of the active material particles, the higher the degree of isotropy between the particles, and the smaller the total surface area under the same volume, the shorter the path for lithium ions to flow in the electrode, and the lower the overall bendability of the electrode, the lower the resistance to lithium ion diffusion. Active material particles having a high sphericity are used in the second active material layer, and as a result, the degree of isotropy of the surface particles is increased, and physical repulsion and expansion during cycling of the electrode can be reduced. The equivalent sphericity of the active material particles in the first active material layer is low, and as a result, the particle stack can have relatively high compressibility, and the energy density of the electrode can be improved. According to the present disclosure, active material materials having different sphericities are adapted, and as a result, the diffusion path of lithium ions can be optimized, the bendability of the electrode can be effectively reduced while ensuring the compression of the electrode, the capacity retention rate of the electrode can be further improved, and the liquid phase diffusion impedance of the electrode can be reduced.

[0038] In a specific embodiment of the present disclosure, 0.05 ≦ X1 ≦ 0.4, preferably 0.1 ≦ X1 ≦ 0.3. Within this range, the first active material layer of the secondary battery electrode plate can be ensured to have a relatively low sphericity and a relatively high compression density, and as a result, the electrode has a higher capacity retention rate and a lower liquid phase diffusion impedance, thereby further optimizing the electrochemical performance of the electrode.

[0039] In a specific embodiment of the present disclosure, 0.2 ≦ X2 ≦ 0.8, preferably 0.2 ≦ X2 ≦ 0.5. Within this range, the second active material layer of the secondary battery electrode plate can be ensured to have a relatively low sphericity and a relatively high lithium ion diffusion capacity.

[0040] In certain embodiments of the present disclosure, 0.07 ≦ X2 - X1 ≦ 0.5, preferably, 0.1 ≦ X2 - X1 ≦ 0.5, preferably, 0.2 ≦ X2 - X1 ≦ 0.4. When the difference between the equivalent sphericity X2 of the second active material particles and the equivalent sphericity X1 of the first active material particles is within the above range, the particle sphericity matching of the two active material layers is further optimized, and the electrochemical performance of the secondary battery electrode plate can be further improved.

[0041] In certain embodiments of the present disclosure, the surface density of the first active material layer is Y1 = ε × L, and the surface density of the second active material layer is Y2 = (1 - ε) × L, where L is the total surface density of the first active material layer and the second active material layer in m 2 / g. One side of the current collector is coated with the first active material layer, or each of the two sides of the current collector is coated with the first active material layer, and the surface of each first active material layer away from the current collector is coated with the second active material layer. When one side of the current collector is coated with the first active material layer, when the electrode plate is a positive electrode plate, 50 ≦ L ≦ 300, and when the electrode plate is a negative electrode plate, 23 ≦ L ≦ 138. When each of the two sides of the current collector is coated with the first active material layer, when the electrode plate is a negative electrode plate, 100 ≦ L ≦ 600, and when the electrode plate is a negative electrode plate, 46 ≦ L ≦ 276. ε is an adjustment parameter, and 0.2 ≦ ε ≦ 0.8. It should be understood that when the thickness of the secondary battery electrode plate is within the above range, the capacity retention rate of the electrode can be further improved, and the liquid phase diffusion impedance of the electrode can be reduced.

[0042] According to the present disclosure, the relationship between the surface density of the active material layer of the secondary battery electrode plate and the equivalent sphericity of the active material particles affects the electrochemical performance of the electrode. In a specific embodiment of the present disclosure, 0.1 ≦ (X2 / Y2) / (X1 / Y1) ≦ 6, preferably, 0.25 ≦ (X2 / Y2) / (X1 / Y1) ≦ 4.5, more preferably, 3 ≦ (X2 / Y2) / (X1 / Y1) ≦ 4.5. The higher the surface density of the active material layer with high sphericity, the lower the overall flexibility of the electrode. At the same time, the lower the compression ability of the electrode, the lower the liquid-phase diffusion impedance of the electrode. The lower the surface density of the active material layer with high sphericity, the higher the flexibility of the electrode. At the same time, the higher the compression ability of the electrode, the higher the liquid-phase diffusion impedance of the electrode. When the relationship between the parameters of the secondary battery electrode plate is within the above range, the liquid-phase diffusion and energy density of the secondary battery electrode plate can be balanced. As a result, the energy density and liquid-phase diffusion impedance of the electrode can be maintained within an appropriate range.

[0043] In a specific embodiment of the present disclosure, when the electrode plate is a positive electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 0.05 to 5.0, and S1 and S2 are each and independently any value in the range of 0.5 to 20. When the electrode plate is a negative electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 1 to 20, and S1 and S2 are each and independently any value in the range of 0.5 to 5. ρ1ρ2 are the true densities of the second active material particles and the first active material particles, respectively. For example, the true density of lithium cobaltate is 5.1 g / cm 3 and the true density of the ternary material is 4.8 g / cm 3 and the true density of lithium manganate is 4.2 g / cm 3 and the true density of lithium iron phosphate is 3.6 g / cm 3 and the true density of graphite is 2.26 g / cm 3 is.

[0044] In certain embodiments of the present disclosure, when the electrode plate is a positive electrode plate, the total surface density of the first active material layer and the second active material layer is 50 to 300 g / m 2 and the compression density is 2.0 to 2.7 g / m 3 When the electrode plate is a negative electrode plate, the total surface density of the first active material layer and the second active material layer is 23 to 138 g / m 2 and the compression density is 1.0 to 2.0 g / m 3 The total surface density refers to the total density of the first active material layer and the second active material layer on a single side of the current collector, and is obtained by cutting an electrode plate having a specific surface density and measuring its weight. In the present disclosure, the total surface density is measured by a method for measuring the weight of a specific region of the electrode plate excluding the current collector, and the compression density is obtained by measuring the thickness of the electrode plate after rolling and the surface density of the electrode plate, and the compression density = surface density / (the thickness of the electrode plate after rolling minus the thickness of the current collector).

[0045] In certain embodiments of the present disclosure, based on the total weight of the first active material layer, the content of the first active material particles is 90% to 99% by weight, preferably 94% to 97% by weight. Based on the total weight of the second active material layer, the content of the second active material particles is 90% to 99% by weight, preferably 94% to 97% by weight.

[0046] In certain embodiments of the present disclosure, the secondary battery electrode plate is a positive electrode, and the first active material particles and the second active material particles can use various active materials for positive electrodes known to those skilled in the art. For example, the first active material particles and the second active material particles may each, and independently, be selected from one or more of LiFePO4, Li3V2(PO4)3, LiMn2O4, LiMnO2, LiNiO2, LiCoO2, LiVPO4F, and LiFeO2. The first active material layer and the second active material layer further each, and independently, contain a conductive agent and a binder. The conductive agent and the binder may alternatively be known to those skilled in the art. Preferably, the conductive agent may be selected from one or more of carbon nanotubes, carbon black, graphite, graphene, and carbon nanofibers, and the binder may be selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, and polyacrylate.

[0047] In another embodiment of the present disclosure, the secondary battery electrode plate is a negative electrode, and the first active material particles and the second active material particles may use various active materials for negative electrodes known to those skilled in the art. For example, the first active material particles and the second active material particles may each, and independently, be selected from one or more of graphite, petroleum coke, organic decomposed carbon, mesophase carbon microspheres, carbon fibers, tin alloys, and silicon alloys.

[0048] The second aspect of the present disclosure provides a method for manufacturing a secondary battery electrode plate. The method includes the following steps. In S1, the current collector is coated with a first slurry to obtain an electrode plate in a state where the current collector is coated with the first slurry layer. In S2, the electrode plate is rolled.

[0049] The first slurry contains first active material particles. The first active material particles have an equivalent sphericity X1 represented by the following formula (1): X1 = 3 / (S1R1ρ1) Formula (1), where 0.05 ≦ X1 ≦ 0.8, R1 is the median radius of the first active material particles in units of μm, S1 is the specific surface area of the first active material particles in units of m 2 / g, and ρ1 is the true density of the first active material particles in units of g / cm 3 In the method according to the present disclosure, a secondary battery electrode plate having an electrode with a high capacity retention rate and an electrode with a low liquid-phase diffusion impedance can be produced.

[0050] In a specific embodiment of the present disclosure, when the electrode plate is a positive electrode plate, 0.10 ≦ X1 ≦ 0.8.

[0051] In a specific embodiment of the present disclosure, when the electrode plate is a negative electrode plate, 0.05 ≦ X1 ≦ 0.8.

[0052] In a specific embodiment of the present disclosure, step S1 includes the following steps. The current collector is coated with the first slurry and the second slurry to obtain an electrode plate that is continuously coated with the first slurry layer and the second slurry layer in a direction away from the current collector. The second slurry contains second active material particles. The second active material particles have an equivalent sphericity X2 represented by the following formula (2): X2 = 3 / (S2R2ρ2) Formula (2), where R2 is the median radius of the second active material particles in units of μm, S2 is the specific surface area of the second active material particles in units of m 2 / g, and ρ2 is the true density of the second active material particles in units of g / cm 3 The sphericity X2 of the second active material particles is greater than the equivalent sphericity X1 of the first active material particles.

[0053] The method for coating the current collector with the first slurry and the second slurry is not specifically limited in the present disclosure. In a specific embodiment of the present disclosure, in step S1, the current collector may be coated with the first slurry and the second slurry by a two-layer coating die head. In a specific embodiment of the present disclosure, in step S1, the current collector is coated with the first slurry to obtain an electrode plate coated with the first slurry layer, and then the first slurry layer is coated with the second slurry.

[0054] In a specific embodiment of the present disclosure, in step S1, 20 °C and 50 s -1 the viscosity of the first slurry at is 2000~3000 mPa·s, and 20 °C and 50 s -1 the viscosity of the second slurry at is 2000~3000 mPa·s. The surface density of the first slurry layer is 50~150 g / m 2 and the surface density of the second slurry layer is 50~150 g / m 2 is.

[0055] According to the present disclosure, rolling is a conventional method for fabricating electrodes by those skilled in the art. Rolling is carried out according to the target compression density of the electrode, and may be, for example, single-pass rolling, multi-pass rolling, cold rolling, and hot rolling.

[0056] According to the present disclosure, the first slurry and the second slurry further contain a solvent. The solvents contained in the first slurry and the second slurry in the present disclosure are not specifically limited in the present disclosure, and may be, for example, water, N-methylpyrrolidone (NMP), and ethyl alcohol, but are not limited thereto.

[0057] In a specific embodiment of the present disclosure, the content of the first active material particles in the first slurry is 40% to 70% by weight, preferably 50% to 70% by weight. The content of the second active material particles in the second slurry is 30% to 70% by weight, preferably 50% to 70% by weight.

[0058] In certain embodiments of the present disclosure, the positive electrode is fabricated by the method in the present disclosure. In step S1, the first active material particles and the second active material particles may use various active materials for positive electrodes known to those skilled in the art. For example, the first active material particles and the second active material particles may each, and independently, be selected from one or more of LiFePO4, Li3V2(PO4)3, LiMn2O4, LiMnO2, LiNiO2, LiCoO2, LiVPO4F, and LiFeO2. The first active material layer and the second active material layer further each, and independently, contain a conductive agent and a binder. The conductive agent and the binder may alternatively be known to those skilled in the art. Preferably, the conductive agent may be selected from one or more of carbon nanotubes, carbon black, graphite, graphene, and carbon nanofibers, and the binder may be selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, butadiene styrene rubber, and polyacrylate. In certain embodiments of the present disclosure, the first slurry and the second slurry further each, and independently, contain a conductive agent and a binder. Preferably, the conductive agent may be known to those skilled in the art. For example, the conductive agent may be selected from one or more of carbon nanotubes, carbon black, graphite, graphene, and carbon nanofibers, and the binder may be selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, and polyacrylate.

[0059] In another embodiment of the present disclosure, the negative electrode is fabricated according to the present disclosure. In step S1, the first active material particles and the second active material particles may use various active materials for negative electrodes known to those skilled in the art. For example, the first active material particles and the second active material particles may each, and independently, be selected from one or more of graphite, petroleum coke, organic decomposed carbon, mesophase carbon microspheres, carbon fibers, tin alloys, and silicon alloys.

[0060] In certain embodiments of the present disclosure, 0.05 ≦ X1 ≦ 0.4, and more preferably, 0.1 ≦ X1 ≦ 0.3.

[0061] In certain embodiments of the present disclosure, 0.2 ≦ X2 ≦ 0.8, and more preferably, 0.2 ≦ X2 ≦ 0.5.

[0062] In certain embodiments of the present disclosure, 0.07 ≦ X2 - X1 ≦ 0.5, and more preferably, 0.2 ≦ X2 - X1 ≦ 0.4.

[0063] In certain embodiments of the present disclosure, when the electrode plate is a positive electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 0.05 to 5, and S1 and S2 are each and independently any value in the range of 0.5 to 20. When the electrode plate is a negative electrode plate, R1 and R2 of the first active material particles are each and independently any value in the range of 1 to 20, and S1 and S2 are each and independently any value in the range of 0.5 to 5. ρ1 and ρ2 are the true densities of the first active material particles and the second active material particles, respectively. For example, the true density of lithium cobaltate is 5.1 g / cm 3 and the true density of the ternary material is 4.8 g / cm 3 and the true density of lithium manganate is 4.2 g / cm 3 and the true density of lithium iron phosphate is 3.6 g / cm 3 and the true density of graphite is 2.26 g / cm 3 is.

[0064] The third aspect of the present disclosure provides a secondary battery. This secondary battery includes the secondary battery electrode plate according to the first aspect of the present disclosure. The secondary battery of the present disclosure has electrodes with a relatively high capacity retention rate and a relatively low liquid phase diffusion impedance.

[0065] The present disclosure will be further described below through examples, but the present disclosure is not limited in any way thereby.

[0066] (Example 1) One side of the positive current collector was coated with a first slurry and a second slurry by a die head for double-layer coating to obtain an electrode plate coated with a first slurry layer and a second slurry layer (S1). The positive current collector was coated with the first slurry layer, and the first slurry layer was coated with the second slurry layer. Both the first slurry and the second slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The content of lithium iron phosphate in the first slurry layer was 60.1% by weight, and the viscosity of the first slurry at 20 °C and 50 s -1 was 2560 mPa·s, and the surface density of the first slurry layer was 125 g / m 2 . The content of lithium iron phosphate in the second slurry layer was 60.3% by weight, and the viscosity of the second slurry at 20 °C and 50 s -1 was 2600 mPa·s, and the surface density of the second slurry layer was 125 g / m 2 , and the total surface density of the first slurry layer and the second slurry layer was 250 g / m 2 .

[0067] The electrode plate was dried and rolled. The first slurry layer formed a first active material layer, the second slurry layer formed a second active material layer, and a positive electrode of a lithium-ion battery was obtained (S2). The compression density of the positive electrode of the lithium-ion battery was 2.50 g / cm 3 .

[0068] The median radius R1 of lithium iron phosphate in the first active material layer was 0.34 μm, the specific surface area S1 was 15 m 2 / g, the true density ρ1 was 3.6 g / cm 3 . The equivalent sphericity X1 was 0.163. The median radius R2 of lithium iron phosphate in the second active material layer was 0.34 μm, the specific surface area S2 was 10 m 2 / g, the true density ρ2 was 3.6 g / cm 3and the equivalent sphericity X2 was 0.245. An overview of various parameters of the positive electrode of the lithium-ion battery is shown in Table 1.

[0069] (Example 2) The positive electrode was fabricated in the same manner as in Example 1. The difference was that in step S1, the median radius R2 of lithium iron phosphate in the second active material layer was 0.34 μm, the specific surface area S2 was 7.2 m 2 / g, and the true density ρ2 was 3.6 g / cm 3 and the equivalent sphericity X2 was only 0.34.

[0070] (Example 3) The positive electrode was fabricated in the same manner as in Example 1. The difference was that in step S1, the median radius R2 of lithium iron phosphate in the second active material layer was 0.25 μm, the specific surface area S2 was 6.6 m 2 / g, and the true density ρ2 was 3.6 g / cm 3 and the equivalent sphericity X2 was only 0.505.

[0071] (Example 4) The positive electrode was fabricated in the same manner as in Example 2. The difference was that in step S1, the median radius R1 of lithium iron phosphate in the first active material layer was 0.38 μm, the specific surface area S1 was 25 m 2 / g, and the true density ρ1 was 3.6 g / cm 3 and the equivalent sphericity X1 was only 0.088.

[0072] (Example 5) The positive electrode was fabricated in the same manner as in Example 2. The difference was that in step S1, the median radius R1 of lithium iron phosphate in the first active material layer was 0.34 μm, the specific surface area S1 was 12 m 2 / g, and the true density ρ1 was 3.6 g / cm 3 and the equivalent sphericity X1 was only 0.204.

[0073] (Example 6) The positive electrode was fabricated by the same method as in Example 2. The difference was that in step S1, the surface density of the first active material layer was 145 g / m 2 and the surface density of the second active material layer was 105 g / m 2 only.

[0074] (Example 7) The positive electrode was fabricated by the same method as in Example 2. The difference was that in step S1, the surface density of the first active material layer was 165 g / m 2 and the surface density of the second active material layer was 85 g / m 2 only.

[0075] (Example 8) The positive electrode was fabricated by the same method as in Example 3. The difference was that in step S1, the surface density of the first active material layer was 100 g / m 2 and the surface density of the second active material layer was 150 g / m 2 only.

[0076] (Example 9) The positive electrode was fabricated by the same method as in Example 3. The difference was that in step S1, the surface density of the first active material layer was 70 g / m 2 and the surface density of the second active material layer was 180 g / m 2 only.

[0077] (Example 10) The positive electrode was fabricated by the same method as in Example 3. The difference was that in step S1, the specific surface area S1 of lithium iron phosphate in the first active material layer was 9.5 m 2 / g, the median radius R1 was 0.22 μm, the true density was 3.6 g / cm 3 and the surface density of the first active material layer was 70 g / m 2 only. The specific surface area S2 of lithium iron phosphate in the second active material layer was 5.2 m 2 / g, the median radius R2 was 0.22 μm, the true density was 3.6 g / cm3 and the surface density of the second active material layer was 180 g / m 2 .

[0078] (Example 11) The positive electrode was fabricated in the same manner as in Example 3. The difference was that in step S1, the specific surface area S1 of lithium iron phosphate in the first active material layer was 12 m 2 / g, the median radius R1 was 0.34 μm, the true density was 3.6 g / cm 3 , and the surface density of the first active material layer was only 70 g / m 2 . The specific surface area S2 of lithium iron phosphate in the second active material layer was 6.6 m 2 / g, the median radius R2 was 0.25 μm, the true density was 3.6 g / cm 3 , and the surface density of the second active material layer was 180 g / m 2 .

[0079] (Example 12) One side of the negative current collector was coated with the first slurry and the second slurry using a two-layer coating die head to obtain an electrode plate coated with the first slurry layer and the second slurry layer (S1). The negative current collector was coated with the first slurry layer, and the first slurry layer was coated with the second slurry layer. The surface density of the first slurry layer was 58 g / m 2 , and the surface density of the second slurry layer was 58 g / m 2 , and the total surface density was 116 g / m 2 .

[0080] The electrode plate was dried and rolled to obtain the negative electrode of the lithium-ion battery (S2). The compression density of the negative electrode of the lithium-ion battery was 1.50 g / cm 3 .

[0081] Both the first slurry and the second slurry contained graphite, SBR, CMC, carbon black, and water. The median radius R1 of graphite in the first active material layer was 3 μm, and the specific surface area S1 was 3 m2 / g, and the true density ρ1 is 2.1 g / cm 3 and the equivalent sphericity X1 was 0.16. The viscosity of the first slurry at 20 °C and 50 s -1 was 2560 mPa·s, and the content of graphite in the first slurry was 45% by weight. The median radius R2 of graphite in the second active material layer was 3 μm, and the specific surface area S2 was 1.4 m 2 / g, and the true density ρ2 is 2.1 g / cm 3 and the equivalent sphericity X2 was 0.340. The viscosity of the second slurry at 20 °C and 50 s -1 was 2660 mPa·s, and the content of graphite in the second slurry was 45% by weight. A summary of various parameters of the negative electrode of the lithium-ion battery is shown in Table 1.

[0082] (Example 13) One side of the positive current collector was coated with the first slurry by a coating die head to obtain an electrode plate coated with the first slurry layer (S1). The first slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The content of lithium iron phosphate in the first slurry layer was 60.1% by weight, and at 20 °C and 50 s -1 the viscosity of the first slurry was 2450 mPa·s, and the surface density of the first slurry layer was 250 g / m 2 was.

[0083] The electrode plate was dried and rolled, and the first slurry layer formed the first active material layer to obtain a positive electrode of the lithium-ion battery (S2). The compression density of the positive electrode of the lithium-ion battery was 2.50 g / cm 3 was.

[0084] The median radius R1 of lithium iron phosphate in the first active material layer was 0.30 μm, and the specific surface area S1 was 8 m 2 / g, and the true density ρ1 is 3.6 g / cm 3and the equivalent sphericity X1 was 0.347. An overview of various parameters of the positive electrode of the lithium-ion battery is shown in Table 1.

[0085] (Example 14) One side surface of the positive current collector was coated with a first slurry by a coating die head to obtain an electrode plate coated with a first slurry layer (S1). The first slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The content of lithium iron phosphate in the first slurry layer was 59.3% by weight, and the viscosity of the first slurry at 20 °C and 50 s -1 was 2570 mPa·s. The surface density of the first slurry layer was 250 g / m 2 .

[0086] The electrode plate was dried and rolled, and the first slurry layer formed a first active material layer to obtain the positive electrode of the lithium-ion battery (S2). The compression density of the positive electrode of the lithium-ion battery was 2.50 g / cm 3 .

[0087] The median radius R1 of lithium iron phosphate in the first active material layer was 0.2 μm, the specific surface area S1 was 8 m 2 / g, the true density ρ1 was 3.6 g / cm 3 , and the equivalent sphericity X1 was 0.520. An overview of various parameters of the positive electrode of the lithium-ion battery is shown in Table 1.

[0088] (Example 15) One side surface of the positive current collector was coated with a first slurry by a coating die head to obtain an electrode plate coated with a first slurry layer (S1). The first slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The content of lithium iron phosphate in the first slurry layer was 58.9% by weight, and the viscosity of the first slurry at 20 °C and 50 s -1The viscosity of the first slurry was 2,670 mPa·s. The surface density of the first slurry layer was 250 g / m 2 was.

[0089] The electrode plate was dried and rolled, and the first slurry layer formed the first active material layer, obtaining the positive electrode of the lithium-ion battery (S2). The compression density of the positive electrode of the lithium-ion battery was 2.50 g / cm 3 was.

[0090] The median radius R1 of lithium iron phosphate in the first active material layer was 0.30 μm, the specific surface area S1 was 18 m 2 / g, the true density ρ1 was 3.6 g / cm 3 was, and the equivalent sphericity X1 was 0.154. A summary of various parameters of the positive electrode of the lithium-ion battery is shown in Table 1.

[0091] (Example 16) One side of the negative current collector was coated with the first slurry using a coating die head, obtaining an electrode plate coated with the first slurry layer (S1). The first slurry contained graphite, SBR, CMC, carbon black, and water. The content of graphite on the first slurry layer was 46.3% by weight, the surface density was 116 g / m 2 was, and the compression density was 1.60 g / cm 3 was.

[0092] The electrode plate was dried and rolled, obtaining the negative electrode of the lithium-ion battery (S2). The compression density of the negative electrode of the lithium-ion battery was 1.60 g / cm 3 was.

[0093] The median radius R1 of graphite in the first active material layer was 4.0 μm, the specific surface area S1 was 1.0 m 2 / g, the true density ρ1 was 2.1 g / cm 3 was, and the equivalent sphericity X1 was 0.357. At 20 °C and 50 s -1The viscosity of the first slurry was 2,750 mPa·s. An overview of various parameters of the negative electrode of the lithium-ion battery is shown in Table 1.

[0094] (Example 17) One side of the positive current collector was coated with the first slurry in Example 1, and the electrode plate coated with the obtained first slurry layer was rolled under the condition of a compression density of 2.50 g / cm 3 to obtain the positive electrode of the lithium-ion battery.

[0095] The first slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The median radius R of lithium iron phosphate was 0.34 μm, the specific surface area S was 15 m 2 / g, the true density ρ1 was 3.6 g / cm 3 , and the equivalent sphericity X1 was 0.163. The viscosity of the first slurry at 20 °C and 50 s -1 was 2,560 mPa·s, and the content of lithium iron phosphate in the first slurry was 60.1% by weight. The total surface density of the positive electrode of the lithium-ion battery was 250 g / m 2 .

[0096] (Example 18) One side of the positive current collector was coated with the second slurry in Example 1, and the electrode plate coated with the obtained second slurry layer was rolled under the condition of a compression density of 2.50 g / cm 3 to obtain the positive electrode of the lithium-ion battery.

[0097] The second slurry contained lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The median radius R of lithium iron phosphate was 0.34 μm, the specific surface area S was 10 m 2 / g, the true density ρ was 3.6 g / cm 3 , and the equivalent sphericity X2 was 0.245. At 20 °C and 50 s -1The viscosity of the second slurry was 2,600 mPa·s, and the content of lithium iron phosphate in the second slurry was 60.3% by weight. The total surface density of the positive electrode of the lithium-ion battery was 250 g / m 2 It was.

[0098] (Example 19) One side of the positive current collector was coated with a third slurry, and the electrode plate coated with the obtained third slurry layer was dried and rolled to obtain a positive electrode of a lithium-ion battery. The compression density of the positive electrode of the lithium-ion battery was 2.50 g / cm 3 It was.

[0099] The surface density of the third slurry layer was 250 g / m 2 It was, and at 20 °C and 50 s -1 The viscosity of the third slurry was 2,700 mPa·s. The third slurry contained two types of lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon nanotubes, carbon black, and NMP. The first type of lithium iron phosphate was the same as the lithium iron phosphate in the first slurry in Example 1. The second type of lithium iron phosphate was the same as the lithium iron phosphate in the second slurry in Example 1. The content of lithium iron phosphate in the third slurry was 60.2%.

[0100] (Example 20) The positive electrode was produced by the same method as that in Example 1. The only difference was that in step S1, one side of the positive current collector was coated with a second slurry layer, and the second slurry layer was coated with a first slurry layer.

[0101] (Example 21) The positive electrode was produced by the same method as in Example 13. The difference was that in step S1, the median radius R1 of lithium iron phosphate in the first active material layer was 0.2 μm, the specific surface area S1 was 5.3 m 2 / g, and the true density ρ1 was 3.6 g / cm 3and the equivalent sphericity X1 was 0.786.

[0102] (Comparative Example 1) The positive electrode was fabricated in the same manner as in Example 14. The difference was that the median radius R1 of lithium iron phosphate in the first active material layer was 0.16 μm, the specific surface area S1 was 6.1 m 2 / g, and the true density ρ1 was 3.6 g / cm 3 and the equivalent sphericity X1 was 0.853.

[0103] (Comparative Example 2) The positive electrode was fabricated in the same manner as in Example 14. The difference was that the median radius R1 of lithium iron phosphate in the first active material layer was 0.8 μm, the specific surface area S1 was 22 m 2 / g, and the true density ρ1 was 3.6 g / cm 3 and the equivalent sphericity X1 was 0.047.

[0104] (Comparative Example 3) The negative electrode was fabricated in the same manner as in Example 16. The difference was that the median radius R1 of lithium iron phosphate in the first active material layer was 3.5 μm, the specific surface area S1 was 0.5 m 2 / g, and the true density ρ1 was 2.1 g / cm 3 and the equivalent sphericity X1 was 0.816.

[0105] (Comparative Example 4) The negative electrode was fabricated in the same manner as in Example 16. The difference was that the median radius R1 of lithium iron phosphate in the first active material layer was 7 μm, the specific surface area S1 was 4.2 m 2 / g, and the true density ρ1 was 2.1 g / cm 3 and the equivalent sphericity X1 was 0.0485.

[0106] [Table 1]

[0107] (Test Example) (1) The electrode plates fabricated in the examples and comparative examples were assembled into symmetrical cells. For example, when testing the liquid-phase impedance of the positive electrode plate fabricated in Example 1, two positive electrode plates fabricated in Example 1 were assembled into a symmetrical cell and the liquid-phase impedance was tested. When testing the liquid-phase impedance of the negative electrode plate fabricated in Example 12, two negative electrode plates fabricated in Example 12 were assembled into a symmetrical cell and the liquid-phase impedance was tested. When testing the liquid-phase impedance of the positive electrode plate fabricated in Example 1, two positive electrode plates fabricated in Example 1 were assembled into a symmetrical cell and the liquid-phase impedance was tested. The dimensions of the electrode plates were 62 cm × 72 cm and they were tested by electrochemical impedance spectroscopy. The test was carried out within a frequency range of 100 kHz to 0.01 Hz, and the test results were fitted and calculated to obtain the liquid-phase diffusion impedance of the electrodes.

[0108] (2) The positive electrode plates fabricated in Examples 1 to 11, 13 to 15, and 17 to 21, the negative electrode plate fabricated in Example 12, and the electrolytes were combined to obtain Cells A1 to A11, A13 to A15, and A17 to A21 in sequence. The positive electrode plates fabricated in Examples 1 and 2, the negative electrode plate fabricated in Example 12, and the electrolyte were combined to obtain Cells A22 and A23. The negative electrode plates fabricated in Examples 12 and 16, the positive electrode plate fabricated in Example 1, and the electrolyte were combined to obtain Cells A1 and A16. The negative electrode plates fabricated in Comparative Examples 3 and 4, the positive electrode plate fabricated in Example 1, and the electrolyte were combined to obtain Cells A24 and A25. The positive electrode plate fabricated in Example 1, the negative electrode plate fabricated in Comparative Example 3, and the electrolyte were combined to obtain Cell A26. The capacity retention rate of the above-fabricated cells for 2C discharge with respect to 0.2C discharge was tested.

[0109] (3) The unrolled electrode plates having a width of 5 cm in the examples and comparative examples were passed through a roller. After applying a predetermined pressure of 5 t by the roller to roll the electrode plates, the compression density was measured.

[0110] The above test results are shown in Table 2.

[0111]

Table 2

[0112] Analyzing the data in Table 2 and comparing Test Examples 13 to 15, it can be seen that in the case of single-layer coating, materials with high sphericity have weak compression ability. However, under the same electrode plate compression, the liquid-phase diffusion impedance of the electrode plate is lower and the movement performance is better. Electrodes manufactured from materials within the sphericity range limited by the present disclosure can achieve both energy density (compression density) and movement performance (low degree of bending and liquid-phase diffusion impedance).

[0113] Test Examples 1 to 11 show the results of designs using upper and lower layers with different sphericities and different surface densities in the case of two-layer coating. Comparing Test Example 1, as well as Test Example 17 (electrode made of the upper layer material in Test Example 1), Test Example 18 (electrode made of the lower layer material in Character Example 1), Test Example 19 (mixing two types of materials in Test Example 1), and Test Example 20 (exchanging the upper layer material and the lower layer material in Test Example 1), it can be seen that with the two-layer coating design, the upper layer uses a material with high sphericity and the lower layer uses a material with low sphericity, and as a result, both the compression performance and the movement performance of the electrode can be achieved.

[0114] It can be further seen from Table 2 that the compression density of the secondary battery electrode plate manufactured by the method according to the present disclosure can reach a level similar to that of an electrode having a single-layer active material layer with low sphericity.

[0115] Preferred embodiments of the present disclosure are described in detail above. However, the present disclosure is not limited to the specific details in the foregoing embodiments. A plurality of simple modifications can be made to the technical solutions of the present disclosure within the scope of the technical concept of the present disclosure, and these simple modifications fall within the protection scope of the present disclosure.

[0116] Additionally, the various specific technical features described in the foregoing specific embodiments can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the various possible combination manners are not separately described in the present disclosure.

[0117] In addition, the various different embodiments of the present disclosure can alternatively be arbitrarily combined, and these combinations shall still be regarded as the content disclosed in the present disclosure as long as they do not deviate from the concept of the present disclosure.

Claims

1. A secondary battery electrode plate, comprising: a current collector, and A first active material layer located on the surface of the current collector, wherein the first active material layer contains first active material particles, and the first active material particles have an equivalent sphericity X represented by the following formula (1). １ has X １ = 3 / (S １ R １ ρ １ ) Equation (1), where 0.05 ≦ X １ ≦ 0.8, R １ is the median radius of the first active material particles in units of µm, S １ is the specific surface area of the first active material particles in units of m ２ / g, ρ １ is the true density of the first active material particles in units of g / cm ３ A secondary battery electrode plate which is

2. When the electrode plate is a positive electrode plate, 0.10 ≤ X １ ≤ 0.8, or when the electrode plate is a negative electrode plate, 0.05 ≤ X １ ≤ 0.8, The secondary battery electrode plate according to claim 1.

3. Further comprising a second active material layer, the second active material layer is located on a surface of the first active material layer that is away from the surface of the current collector, the second active material layer contains second active material particles, and the second active material particles have an equivalent sphericity X represented by the following formula (2). ２ have X ２ = 3 / (S ２ R ２ ρ ２ ) Equation (2), wherein R ２ is the median radius of the second active material particles in units of μm, S ２ is the specific surface area of the second active material particles in units of m ２ / g, ρ ２ is the true density of the second active material particles in units of g / cm ３ , and the sphericity X ２ of the second active material particles is larger than the equivalent sphericity X １ of the first active material particles. The secondary battery electrode plate according to claim 1 or 2.

4. 0.05 ≤ X １ ≤ 0.4, and 0.2 ≤ X ２ ≤ 0.8, The secondary battery electrode plate according to claim 3.

5. 0.1 ≤ X １ ≤ 0.3, and 0.2 ≤ X ２ ≤ 0.5, The secondary battery electrode plate according to claim 3.

6. 0.07 ≤ X ２ -X １ ≤ 0.5, the secondary battery electrode plate according to any one of claims 3 to 5.

7. 0.2 ≤ X ２ -X １ ≤ 0.4, the secondary battery electrode plate according to any one of claims 3 to 5.

8. When the electrode plate is a positive electrode plate, R of the first active material particles １ and R ２ are each and independently any value in the range of 0.05 to 5, and S １ and S ２ are each and independently any value in the range of 0.5 to 20, When the electrode plate is a negative electrode plate, R of the first active material particles １ and R ２ are each and independently any value in the range of 1 to 20, and S １ and S ２ are each and independently any value in the range of 0.5 to 5. The secondary battery electrode plate according to any one of claims 3 to 7.

9. The surface density of the first active material layer is Y １ = ε × L, and the surface density of the second active material layer is Y ２ = (1 - ε) × L L is the total surface density of the first active material layer and the second active material layer in g / m ２ One side surface of the current collector is coated with the first active material layer, or each of the two side surfaces of the current collector is coated with the first active material layer, and the surface of each first active material layer away from the current collector is coated with the second active material layer, When one side surface of the current collector is coated with the first active material layer, when the electrode plate is a positive electrode plate, 50 ≦ L ≦ 300, or when the electrode plate is a negative electrode plate, 23 ≦ L ≦ 138, or When each of the two side surfaces of the current collector is coated with the first active material layer, when the electrode plate is the negative electrode plate, 100 ≦ L ≦ 600, or when the electrode plate is the negative electrode plate, 46 ≦ L ≦ 276, ε is an adjustment parameter, and 0.2 ≦ ε ≦ 0.

8. The secondary battery electrode plate according to any one of Claims 3 to 8.

10. 0.1 ≤ (X ２ / Y ２ ) / (X １ / Y １ ) ≤ 6, the secondary battery electrode plate according to claim 9.

11. 0.25 ≤ (X ２ / Y ２ ) / (X １ / Y １ ) ≤ 4.5, the secondary battery electrode plate according to claim 9.

12. When the electrode plate is a positive electrode plate, the compression density is 2.0 to 2.7 g / cm ３ or when the electrode plate is a negative electrode plate, the compression density is 1.0 to 2.0 g / cm ３ The secondary battery electrode plate according to any one of claims 3 to 11.

13. A method for manufacturing a secondary battery electrode plate, comprising: coating a current collector with a first slurry to obtain an electrode plate having the current collector coated with a first slurry layer (S1); and rolling the electrode plate (S2). The first slurry contains first active material particles, and the first active material particles have an equivalent sphericity X represented by the following formula (1). １ and have X １ = 3 / (S １ R １ ρ １ ) Equation (1), wherein 0.05 ≦ X １ ≦ 0.8, R １ is the median radius of the first active material particles in units of μm, S １ is the specific surface area of the first active material particles in units of m ２ / g, and ρ １ is the true density of the first active material particles in units of g / cm ３ , method.

14. When the electrode plate is a positive electrode plate, 0.10 ≤ X １ ≤ 0.8, or when the electrode plate is a negative electrode plate, 0.05 ≤ X １ ≤ 0.8, the method according to claim 13.

15. Step S1 includes coating the current collector with the first slurry and a second slurry to obtain an electrode plate continuously coated with the first slurry layer and the second slurry layer in a direction away from the current collector. The second slurry contains second active material particles, and the second active material particles have an equivalent sphericity X represented by the following formula (2). ２ and have X ２ = 3 / (S ２ R ２ ρ ２ ) Equation (2), wherein R ２ is the median radius of the second active material particles in units of μm, S ２ is the specific surface area of the second active material particles in units of m ２ / g, ρ ２ is the true density of the second active material particles in units of g / cm ３ , and the sphericity X ２ of the second active material particles is greater than the equivalent sphericity X １ of the first active material particles, the method according to claim 13 or 14.

16. A secondary battery comprising the secondary battery electrode plate according to any one of Claims 1 to 12.

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