Positive electrode and battery

Abstract

A positive electrode and a battery are disclosed, the positive electrode including a current collector layer and an active material layer, the active material layer being coated on at least one surface of the current collector layer, the active material layer including an active material and a conductive component, the conductive component including at least one of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This application claims priority to Chinese Patent Application No. "202110858947.6", filed by BYD Company Limited on July 28, 2021, with the application title "Positive Electrode and Battery".

[0002] This application relates to the technical field of battery materials, and more particularly to positive electrodes and batteries. [Background technology]

[0003] Lithium-ion batteries have been rapidly developing in recent years as a new renewable energy source due to their advantages such as high capacity, high voltage, small size and light weight, long cycle life, wide operating range, superior safety, and absence of memory effect. Faced with the demand for large-scale applications of lithium-ion batteries, improving their performance and reducing costs is crucial. Further improving the power density and energy density of the positive and negative electrode materials, as well as improving cycle performance and safety performance, are key points for development.

[0004] Taking the improvement of lithium-ion battery performance by enhancing the conductivity of the positive electrode material as an example, the conductive agents currently used in the manufacture of lithium-ion battery positive electrode paste include carbon black, acetylene black, conductive graphite, carbon nanotubes, and carbon nanofibers. Conductive agents are often used individually, and the same conductive agent is always applied to different electrodes. This makes it impossible to select a conductive agent according to the type of positive electrode material, which is disadvantageous for the conductive agent's performance and limits the energy density and cycle performance of lithium-ion batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This application aims to solve, at least to some extent, one of the technical problems in related technologies.

[0006] An embodiment of the present application aims to provide new technical means for a positive electrode and a battery.

Means for Solving the Problem

[0007] The positive electrode according to the first aspect of the embodiment of the present application includes a current collector layer and an active material layer, the active material layer is coated on at least one surface of the current collector layer, and the active material layer includes an active material and a conductive component, the mass of the active material is m x + m y (unit: g), the conductive component includes at least one of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material, and the masses of the one-dimensional conductive material, the zero-dimensional conductive material, and the two-dimensional conductive material are m1, m2, and m3 (unit: g) in sequence, m x is the mass of the active material coated with a two-dimensional conductive material on the surface, m y is the mass of the active material coated with a one-dimensional conductive material and / or a zero-dimensional conductive material on the surface, and satisfies the following formula 20 * 3.14 * d L * m y / [ρ L * 4 / 3 * 3.14(d L / 2) 3 ≤ m1 / (2.2 * 3.14 * (d1 / 2) 2 * L1) * L1 + 10 * m2 / (2.2 * 4 / 3 * 3.14 * (d2 / 2) 3 ) * d2 ≤ [30 * 3.14 * d L * m y / [ρ L * 4 / 3 * 3.14(d L / 2) 3 (1) 3.14 * (d L / 2) 2 * m x / [ρ L * 4 / 3 * 3.14(d L / 2) 3 ≤ m3 / [(2.2 * a * b * c)] * a * b ≤ 1.5 * 3.14 * (d L / 2) 2 * m x / [ρ L*4 / 3*3.14*(d L / 2) 3 (2) In the formula, d L (Unit μm) is the diameter of the active material, ρ L is the true density of the active material, d1 (in μm) is the diameter of the one-dimensional conductive material, L1 (in μm) is the length of the one-dimensional conductive material, d2 (in μm) is the diameter of the zero-dimensional conductive material, and a (in μm), b (in μm), and c (in μm) are the width, length, and thickness of the two-dimensional conductive material, respectively.

[0008] Preferably, the conductive component includes the one-dimensional conductive material, and the mass ratio of the one-dimensional conductive material to the active material is (0.1 to 1.0):100.

[0009] Preferably, the diameter of the one-dimensional conductive material is 2 to 60 nm, and the length of the one-dimensional conductive material is 2 to 15 μm.

[0010] Preferably, the conductive component includes the zero-dimensional conductive material, and the mass ratio of the zero-dimensional conductive material to the active material is (0.1~3):100.

[0011] Preferably, the diameter of the zero-dimensional conductive material is 20 to 100 nm.

[0012] Preferably, the conductive component includes the two-dimensional conductive material, and the mass ratio of the two-dimensional conductive material to the active material is (0.1~1.5):100.

[0013] Preferably, the thickness of the two-dimensional conductive material is 1 to 20 nm, and the length and width of the two-dimensional conductive material are 0.2 to 10 μm.

[0014] Preferably, the mass fraction of the conductive component in the two-dimensional conductive material is 30% or less.

[0015] Preferably, the active material layer is a single layer or a multilayer.

[0016] Preferably, the conductive component includes a one-dimensional conductive material, the active material layer is an n-layer, and the active material layer covering the current collector layer is the first layer. Mass M of the one-dimensional conductive material in the active material layer of layer i i =M1*(1-i / n), In the formula, M1 is the mass of the one-dimensional conductive material in the first active material layer, n is a natural number greater than or equal to 2, and i is a natural number greater than or equal to 2 and less than or equal to n.

[0017] Preferably, the conductive component includes a zero-dimensional conductive material, and the mass of the zero-dimensional conductive material in the first layer of the active material is N1. Mass N of the zero-dimensional conductive material in the active material layer of the i-th layer i = N1*i / n

[0018] Preferably, the active material includes a combination of one or more materials selected from lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and nickel-cobalt-manganese ternary materials.

[0019] The battery according to the second embodiment of the present invention includes a negative electrode, a separator, and the positive electrode described in the first embodiment. The negative electrode and the positive electrode are provided on both sides of the separator, respectively. [Effects of the Invention]

[0020] The technical effects of the embodiment of the present application are as follows:

[0021] The positive electrode according to the embodiment of the present application includes a current collector layer and an active material layer. The active material layer of the positive electrode of the present application includes a conductive component, and by using a conductive agent that combines one or more of one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials, and by combining conductive agents with different dimensions and content parameters with different active materials, an efficient conductive network can be constructed, improving the conductive performance and capacitance performance of the positive electrode and guaranteeing the energy density of the positive electrode.

[0022] Some additional aspects and advantages of the present application are shown in the following description, some become apparent in the following description, or are understood through the practice of the present application. [Brief explanation of the drawing]

[0023] The above and / or additional aspects and advantages of the present application will become clearer and easier to understand by describing the embodiments with reference to the following drawings.

[0024] [Figure 1] This is a schematic diagram of the positive electrode according to an embodiment of the present invention. [Figure 2] This shows the penetration curve of the resistivity of the positive electrode and the content of the one-dimensional conductive material in the positive electrode according to the embodiment of the present application. [Figure 3] This shows the content of the zero-dimensional conductive material in the positive electrode according to the embodiment of the present application and the penetration curve of the resistivity of the positive electrode. [Figure 4] This shows the penetration curve of the resistivity of the positive electrode and the content of the two-dimensional conductive material in the positive electrode according to the embodiment of the present application. [Modes for carrying out the invention]

[0025] Hereinafter, various exemplary embodiments of the present application will be described in detail with reference to the drawings. Unless otherwise specified, the relative arrangements of the components and steps, numerical expressions, and numerical values ​​described in these embodiments do not limit the scope of the present application.

[0026] The following description of at least one exemplary embodiment is illustrative in nature and is not intended to limit the Application or its application or use.

[0027] Although the author has not described in detail any techniques, methods, and apparatus known to those skilled in the art, such techniques, methods, and apparatus should be considered as part of the specification where appropriate.

[0028] In all the examples presented and discussed herein, any specific values ​​should be interpreted as illustrative only and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0029] Furthermore, since similar symbols and letters represent similar items in the following drawings, if something is defined in one drawing, it does not need to be considered further in subsequent drawings.

[0030] As shown in Figure 1, the positive electrode according to the embodiment of the present invention includes a current collector layer 1 and an active material layer 2, wherein the active material layer 2 is coated on at least one surface of the current collector layer 1, and the active material layer 2 is It comprises an active material and a conductive component, and the mass of the active material is m x +m y The conductive component includes at least one of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material, and the masses of the one-dimensional conductive material, the zero-dimensional conductive material, and the two-dimensional conductive material are m1, m2, and m3, respectively, and satisfy the following equation. 20*3.14*d L *m y / [ρ L *4 / 3*3.14(d L / 2) 3 ]≦m1 / (2.2*3.14*(d1 / 2) 2 *L1)*L1+10*m2 / (2.2*4 / 3*3.14*(d2 / 2) 3 )*d2≦[30*3.14*d L ]*m y / [ρ L *4 / 3*3.14(d L / 2) 3 (1) 3.14*(d L / 2) 2 *m x / [ρ L *4 / 3*3.14(d L / 2) 3 ]≦m3 / [(2.2*a*b*c)]*a*b≦1.5*3.14*(d L / 2) 2 *m x / [ρ L *4 / 3*3.14*(d L / 2) 3 (2) In the formula, d L ρ is the diameter of the active material mentioned above. L is the true density of the active material, d1 is the diameter of the one-dimensional conductive material, L1 is the length of the one-dimensional conductive material, d2 is the diameter of the zero-dimensional conductive material, and a, b, and c are the width, length, and thickness of the two-dimensional conductive material, respectively.

[0031] Specifically, the zero-dimensional conductive material may be carbon black, the one-dimensional conductive material may be at least one of carbon nanotubes, metal nanowires, and one-dimensional conductive polymers, and the two-dimensional conductive material may be at least one of graphene, two-dimensional conductive metal-organic skeletons (2DECMOFs), and conductive two-dimensional molybdenum carbide (MXene). Specifically, the dimensional parameters of the one-dimensional conductive material, zero-dimensional conductive material, and two-dimensional conductive material in Equations 1 and 2 are all dimensional parameters of a single particle of the one-dimensional conductive material, zero-dimensional conductive material, and two-dimensional conductive material. The conductive component may include one of the one-dimensional conductive material, zero-dimensional conductive material, and two-dimensional conductive material, or it may include a combination of multiple types of the one-dimensional conductive material, zero-dimensional conductive material, and two-dimensional conductive material.

[0032] Equation 1 discloses the requirements for the content of conductive components in the one-dimensional conductive material and the zero-dimensional conductive material in the active material layer 2. Since the conductive components are inert substances, if the content of the conductive components in the active material layer 2 is too high, it will significantly reduce the electrode capacitance of the positive electrode. To ensure the conductivity of the positive electrode, the length of the conductive components distributed to a single active material particle is at least 20 times the circumference of the active material particle. That is, a single active material particle can be covered by 20 conductive components to construct a complete conductive network, and the total length of the conductive components is at most 30 times the particle circumference. If the total length of the conductive components is too long, there is a limit to the improvement in the conductivity of the positive electrode, but it will significantly reduce the electrode capacitance of the positive electrode.

[0033] As can be seen from the penetration curve of the one-dimensional conductive material content and electrode resistivity shown in Figure 2, when the content of one-dimensional conductive material in the positive electrode increases, the resistivity of the positive electrode clearly decreases. However, after the content of one-dimensional conductive material increases to a certain extent, for example, after the content of one-dimensional conductive material in Figure 2 reaches 0.6%, the effect of the content of one-dimensional conductive material on the resistivity of the positive electrode becomes smaller. Similarly, as can be seen from the penetration curve of the zero-dimensional conductive material content and positive electrode resistivity shown in Figure 3, when the content of zero-dimensional conductive material in the positive electrode increases, the resistivity of the positive electrode clearly decreases. However, after the content of zero-dimensional conductive material increases to a certain extent, for example, after the content of zero-dimensional conductive material in Figure 3 reaches 2%, the effect of the content of zero-dimensional conductive material on the resistivity of the positive electrode becomes smaller.

[0034] Equation 2 discloses the requirements for the content of conductive components in the two-dimensional conductive material in the active material layer 2. In order to ensure that the two-dimensional conductive material coats the active material particles and forms an effective conductive network, the amount of two-dimensional conductive material added must satisfy the conditions of Equation 2. As can be seen from the penetration curve of the two-dimensional conductive material content and the resistivity of the positive electrode shown in Figure 4, the resistivity of the positive electrode clearly decreases as the content of the two-dimensional conductive material in the positive electrode increases. However, after the content of the two-dimensional conductive material increases to a certain extent, for example, after the content of the two-dimensional conductive material in Figure 4 reaches 0.8%, the effect of the content of the two-dimensional conductive material on the resistivity of the positive electrode becomes small.

[0035] The active material layer 2 of the positive electrode in this application contains a conductive component, and the conductive component utilizes a conductive agent that combines one or more of one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials. By combining conductive agents with different dimensions and content parameters with different active materials, an efficient conductive network can be constructed, improving the conductivity and capacitance performance of the positive electrode and guaranteeing the energy density of the positive electrode. When the conductive component of the active material layer 2 includes all three—one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials—the conductive component constructs an efficient multidimensional conductive network of points, lines, and planes. By combining the length, area, and particle size distribution of the conductive component and the active material, a rational design of the conductive network of the conductive component can be achieved. Preferably, the conductive component includes the one-dimensional conductive material, and the mass ratio of the one-dimensional conductive material to the active material is (0.1~1.0):100, preferably (0.5~0.75):100.

[0036] Specifically, the active material may be lithium iron phosphate. For example, 100g of lithium iron phosphate has a true carbon density of 2.2g / cm³. 3 Therefore, the true density of lithium iron phosphate is 3.6 g / cm³. 3 and d Lrepresents the diameter of lithium iron phosphate, and true density is the actual mass of solid material per unit volume when the material is in an absolutely dense state, i.e., the density after removing internal voids or interparticle voids. In order to ensure that the conductive component, represented by a one-dimensional conductive material, coats the active material, represented by lithium iron phosphate particles, and forms an effective conductive network at the positive electrode, the amount of the above one-dimensional conductive material added, in combination with Equation 1, is: 20*3.14*d L *100 / [3.6*4 / 3*3.14*(d L / 2) 3 ]≦m1 / (2.2*3.14*(d1 / 2) 2 *L1)*L1≦30*3.14*d L *100 / [3.6*4 / 3*3.14*(d L / 2) 3 It must satisfy the following conditions.

[0037] The diameter of the above-mentioned one-dimensional conductive material is 2 to 60 nm, preferably 5 to 15 nm, and the length of the above-mentioned one-dimensional conductive material is 2 to 15 μm, preferably 5 to 10 μm. Taking the above-mentioned one-dimensional conductive material within the above-mentioned diameter and length range as an example, the mass of the one-dimensional conductive material in the active material layer 2 containing 100 g of lithium iron phosphate active material is controlled to be in the range of 0.5 to 0.75 g. If the mass of the one-dimensional conductive material is too large, for example, if the one-dimensional conductive material is too thick or too long, the one-dimensional conductive material is difficult to disperse and tends to aggregate. If the mass of the one-dimensional conductive material is too small, it is disadvantageous for the one-dimensional conductive material to cross-link and form a conductive network.

[0038] Preferably, the conductive component includes the zero-dimensional conductive material, and the mass ratio of the zero-dimensional conductive material to the active material is (0.1 to 3.0):100, preferably (1.918 to 2.7):100.

[0039] Specifically, the active material may be lithium iron phosphate. Taking 100g of lithium iron phosphate as an example, in order to ensure that the conductive component, represented by the zero-dimensional conductive material, coats the active material, represented by the lithium iron phosphate particles, and that an effective conductive network is formed at the positive electrode, the amount of the zero-dimensional conductive material added, in combination with Equation 1, is 20*3.14*d L *100 / [3.6*4 / 3*3.14(d L / 2) 3 ]≦10*m2 / [(2.2*4 / 3*3.14*(d2 / 2) 3 )]*d2≦30*3.14*d L *100 / [3.6*4 / 3*3.14(d L / 2) 3 It must satisfy the following conditions.

[0040] The diameter of the above zero-dimensional conductive material is 20 to 100 nm, preferably 30 to 50 nm. Taking the above zero-dimensional conductive material within the above diameter range as an example, the mass of the zero-dimensional conductive material in the active material layer 2 containing 100 g of lithium iron phosphate active material can be controlled to a range of 1.918 to 2.7 g. If the mass of the zero-dimensional conductive material is too large, for example, if the diameter of the zero-dimensional conductive material is too large, the zero-dimensional conductive material is prone to aggregation, which reduces the conductivity efficiency of the conductive component. If the mass of the zero-dimensional conductive material is too small, it becomes unfavorable for the zero-dimensional conductive material to crosslink with each other or for the zero-dimensional conductive material to crosslink with other conductive agents to form a conductive network.

[0041] Preferably, the conductive component includes the two-dimensional conductive material, and the mass ratio of the two-dimensional conductive material to the active material is (0.1 to 1.5):100, preferably (0.8 to 1.2):100.

[0042] Specifically, the active material may be lithium iron phosphate. Taking 100g of lithium iron phosphate as an example, in order to ensure that the conductive component, represented by the two-dimensional conductive material, coats the active material, represented by the lithium iron phosphate particles, and that an effective conductive network is formed at the positive electrode, the amount of the two-dimensional conductive material added, in combination with Equation 2, is 3.14*(d L / 2) 2 *100 / [3.6*4 / 3*3.14(d L / 2) 3 ]≦m3 / [(2.2*a*b*c)]*a*b≦1.5*3.14*(d L / 2) 2 *100 / [3.6*4 / 3*3.14*(d L / 2) 3 The following conditions must be met.

[0043] The thickness of the above-mentioned two-dimensional conductive material is 1 to 20 nm, and the length and width of the above-mentioned two-dimensional conductive material are both 0.2 to 10 μm. Taking the above-mentioned two-dimensional conductive material within the above length, width, and thickness ranges as an example, the mass of the two-dimensional conductive material in the active material layer 2 containing 100 g of lithium iron phosphate active material can be controlled to a range of 0.8 to 1.2 g. If the mass of the above-mentioned two-dimensional conductive material is too large, the impedance of the above-mentioned positive electrode can be reduced, but the cost of the above-mentioned active material layer 2 will increase, and since conductive agents, such as the two-dimensional conductive material, are inert substances and cannot provide charge / discharge capacity, if the amount of conductive agent, such as the two-dimensional conductive material, added is too large, the capacity of the above-mentioned positive electrode will be significantly reduced.

[0044] Preferably, the mass fraction of the conductive component in the two-dimensional conductive material is 30% or less.

[0045] Specifically, based on the fact that the above conductive component includes a two-dimensional conductive material, if it further includes conductive agents such as a one-dimensional conductive material or a zero-dimensional conductive material, too much of the two-dimensional conductive material can cause aggregation between the layers of the two-dimensional conductive material, reducing the conductivity efficiency of the above conductive component. Furthermore, sheet-like two-dimensional conductive material is unfavorable for the diffusion of lithium ions in the positive electrode, limiting the energy density and charge / discharge capacity of the positive electrode.

[0046] Preferably, the active material layer 2 is a single layer or a multilayer.

[0047] Specifically, the active material layer 2 is coated onto at least one surface of the current collector layer 1 by coating, and the coating of the active material layer 2 can be completed in a single coating, that is, coated in a single layer, which simplifies the manufacturing process of the positive electrode and reduces the manufacturing cost of the positive electrode. The coating of the active material layer 2 can be completed in multiple coatings, that is, coated in multiple layers, which allows for the achievement of an excellent combination of energy density and conductivity performance of the positive electrode by controlling the ratio of active material and conductive components in the active material layer of each layer.

[0048] Preferably, the conductive component includes a one-dimensional conductive material, the active material layer 2 is n layers, where n is a natural number of 2 or more, the layer bonded to the current collector layer is the first layer, and the layers are sequentially the second layer, third layer, fourth layer...nth layer away from the first layer, that is, the nth layer is an active material layer away from the first layer, and the nth layer is brought close to the separator layer. The active material layer covering the current collector layer is designated as the first layer. Mass M of the one-dimensional conductive material in the active material layer of layer i i =M1*(1-i / n), In the formula, M1 is the mass of the one-dimensional conductive material in the first active material layer, n is a natural number greater than or equal to 2, and i is a natural number greater than or equal to 2 and less than or equal to n.

[0049] Specifically, the mass of the one-dimensional conductive material in the first layer can be determined based on the above formula (1). Since the one-dimensional conductive material has a high electron conductivity, the closer it is to the current collector layer 1, the more one-dimensional conductive material can be added to the active material layer 2 to improve the bonding strength and electron transfer efficiency between the active material and the conductive component in the active material layer 2 and the current collector layer 1. For example, when the active material layer 2 has 4 layers, and the 4 layers of the active material layer 2 are laminated, and the area and thickness of each layer are the same, the mass of the one-dimensional conductive material in the first layer is M1, and the mass M of the one-dimensional conductive material in the second layer i = M1*(1 - 2 / 4) = M1*1 / 2, and the mass M of the one-dimensional conductive material in the third layer i = M1*(1 - 3 / 4) = M1*1 / 4, and the mass M of the one-dimensional conductive material in the fourth layer i = M1*(1 - 4 / 4) = 0. The mass of the one-dimensional conductive material in the multi-layer active material layer 2 is distributed step by step to ensure the conductive efficiency of the active material layer 2.

[0050] Preferably, the active material layer 2 has n layers, the conductive component includes a zero-dimensional conductive material, the mass of the zero-dimensional conductive material in the first layer of the active material layer is N1, the mass N of the zero-dimensional conductive material in the i-th layer of the active material layer i = N1*i / n, where i is an integer greater than or equal to 2.

[0051] Specifically, the mass of the zero-dimensional conductive material in the first layer can be determined based on Equation 1 above. Since the zero-dimensional conductive material has high liquid retention properties, it is advantageous for the diffusion process of lithium ions in the positive electrode. The further away from the current collector layer 1, the more zero-dimensional conductive material may be present in the active material layer 2. Based on the guarantee of electrolyte retention in the positive electrode, the bonding of the one-dimensional conductive material and the zero-dimensional conductive material is advantageous for constructing a good conductive network in the multilayer coated active material layer 2 system. For example, if the active material layer 2 consists of four layers, and these four layers are stacked together, and the area and thickness of each layer are the same, then the mass of the zero-dimensional conductive material in the first layer is N1, the mass of the zero-dimensional conductive material in the second layer is N1*2 / 4=N1*1 / 2, the mass of the zero-dimensional conductive material in the third layer is N1*3 / 4, and the mass of the zero-dimensional conductive material in the fourth layer is N1*4 / 4=N1, thus distributing the mass of the zero-dimensional conductive material in the multilayer active material layer 2 in a stepwise manner.

[0052] Preferably, the active material includes a combination of one or more materials selected from lithium iron phosphate, lithium cobalt oxide, lithium nickelate, and nickel-cobalt-manganese ternary materials.

[0053] Specifically, the type of active material can vary. For example, when lithium iron phosphate (LiFePO4) is selected as the active material, the lithium iron phosphate material maintains a stable structure during the charge-discharge process, thus guaranteeing the safety performance and service life of the positive electrode. Other options include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and nickel-cobalt manganese ternary materials (LiNi x Co y Mn 1-x-y Combinations of active materials such as O2 can improve the energy density of the positive electrode.

[0054] The battery according to the embodiment of the present application includes a negative electrode, a separator, and a positive electrode. The negative electrode and positive electrode are provided on both sides of the separator, respectively.

[0055] Specifically, the active material layer 2 of the positive electrode of the battery contains a conductive component. This conductive component utilizes a conductive agent that combines one or more of one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials. By combining conductive agents with different dimensions and content parameters with different active materials, an efficient conductive network can be constructed, improving the conductivity and capacity performance of the positive electrode and guaranteeing the energy density of the battery. When the conductive component of the active material layer 2 includes all three—one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials—the conductive component can construct an efficient multi-dimensional conductive network of points, lines, and surfaces. By combining the length, area, and particle size distribution of the conductive component and the active material, a rational design of the conductive network of the conductive component can be achieved, guaranteeing the battery's capacity.

[0056] The positive electrode according to this application will be described in detail below with reference to the examples and comparative examples.

[0057] The positive electrode in the following examples and comparative examples comprises a current collector layer and an active material layer, the current collector layer being aluminum foil, and the active material layer comprising one or more of lithium iron phosphate, a binder, N-methylpyrrolidone, a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material. The methods for manufacturing the positive electrode in the examples and comparative examples are all the same. The process includes the steps of mixing the components of the active material layer to produce a paste, applying the paste to aluminum foil, baking it, and then roll-pressing it to obtain a positive electrode.

[0058] Assemble the positive electrode and the corresponding negative electrode to obtain a battery, and set the design capacity of the battery to 1.8 Ah. [Examples]

[0059] The active material contains lithium iron phosphate. The conductive component includes carbon nanotubes.

[0060] Select 100 g of lithium iron phosphate, and set the average particle size of lithium iron phosphate to D50 = 1.30 μm (d L ), set the average diameter of the carbon nanotubes to 11 nm, set the average length of the carbon nanotubes to 8 μm, and according to the above formula 1, the addition amount of the carbon nanotubes is 0.6 g.

Example

[0061] The active material contains lithium iron phosphate, The conductive component contains carbon black.

[0062] Select 100 g of lithium iron phosphate, and set the average particle size of lithium iron phosphate to D50 = 1.30 μm (d L ), set the average diameter of the carbon black to 60 nm, and according to the above formula 1, the addition amount of the carbon black is 2.2 g.

Example

[0063] The active material contains lithium iron phosphate, The conductive component contains graphene.

[0064] Select 100 g of lithium iron phosphate, and set the average particle size of lithium iron phosphate to D50 = 1.30 μm (d L ), set the average length of the graphene to 4.2 μm, set the average width of the graphene to 2.45 μm, set the average thickness of the graphene to 14 nm, and according to the above formula 2, the addition amount of the graphene is 1.0 g.

Example

[0065] The active material contains lithium iron phosphate, The conductive component contains carbon nanotubes and carbon black.

[0066] Select 100 g of lithium iron phosphate, and set the average particle size of lithium iron phosphate to D50 = 1.30 μm (d LAssuming the average diameter of the carbon nanotubes is 11 nm, the average length of the carbon nanotubes is 8 μm, and the average diameter of the carbon black is 60 nm, according to Equation 1 above, the amount of carbon nanotubes to be added is 0.3 g, and the amount of carbon black to be added is 0.9 g. (Comparative Example 1)

[0067] The materials were selected in the same way as in Example 1, but the amount of carbon nanotubes added was changed to 0.3 g. (Comparative Example 2)

[0068] The materials were selected in the same way as in Example 1, but the amount of carbon nanotubes added was changed to 1.0 g. (Comparative Example 3)

[0069] The materials were selected in the same way as in Example 2, but the amount of carbon black added was changed to 1.4g. (Comparative Example 4)

[0070] The materials were selected in the same way as in Example 2, but the amount of carbon black added was changed to 3g. (Comparative Example 5)

[0071] The materials were selected in the same way as in Example 3, but the amount of graphene added was changed to 0.5g. (Comparative Example 6)

[0072] The materials were selected in the same way as in Example 3, but the amount of graphene added was changed to 1.6g.

[0073] Resistivity measurements were performed on the positive electrodes of the above examples and comparative examples, and the capacity per unit mass of the mixed paste and the DC internal resistance were measured for the batteries manufactured using the positive electrodes.

[0074] Table 1 shows the measurement results of the positive electrodes in the examples and comparative examples. [Table 1]

[0075] As can be seen from the longitudinal resistivity of the positive electrode in Table 1, the positive electrodes in the embodiments of this application all have low resistivity, and the resistivity of the positive electrode in each embodiment is 32 Ω*cm. Comparing Example 1 with Comparative Example 1, Example 2 with Comparative Example 3, and Example 3 with Comparative Example 5, when the amount of conductive component used is too low, the resistivity of the positive electrode clearly improves, and the resistivity of the positive electrode in Comparative Example 1, Comparative Example 3, and Comparative Example 5 is all greater than 50 Ω*cm.

[0076] Table 1 shows the capacity per unit mass of the mixed paste at 0.33C (i.e., the capacity per gram of the electrode's active material layer at a discharge rate of 0.33C). In all cases, the capacity per unit mass of the mixed paste of batteries manufactured with the positive electrodes according to the embodiments of this application is greater than 137.0 mAh / g. Comparing Examples 1, 2, and 3 with Comparative Examples 1, 3, and 5, when the content of conductive components is too low, the capacity per unit mass of the mixed paste of the batteries clearly decreases, all being lower than 135.2 mAh / g. Comparing Examples 1, 2, and 3 with Comparative Examples 2, 4, and 6, after increasing the content of conductive components, the resistivity of the positive electrode decreases slightly. However, because there are too many conductive components, the content of inert material increases, which reduces the capacity per unit mass of the mixed paste of batteries manufactured with the positive electrodes. In all cases, the capacity per unit mass of the mixed paste of batteries manufactured with the positive electrodes of Comparative Examples 2, 4, and 6 is 136.7 mAh / g, which ultimately reduces the energy density of the battery.

[0077] As can be seen from the 50% SOC DC internal resistance in Table 1, the DC internal resistance of the batteries manufactured with the positive electrode according to the embodiment of this application was all less than 56.5 mΩ. This indicates that the content of conductive components in the positive electrode in Comparative Examples 1, 3, and 5 was insufficient, resulting in an increased resistivity of the positive electrode. Consequently, the DC internal resistance (DCIR) of the batteries was all greater than 58.9 mΩ, which seriously affected the dynamic performance of the batteries.

[0078] While several specific embodiments of this application have been described in detail with examples, those skilled in the art should understand that these examples are for illustrative purposes only and do not limit the scope of this application. Those skilled in the art should also understand that these embodiments can be modified without departing from the scope and spirit of this application. The scope of this application is limited by the attached claims. [Explanation of symbols]

[0079] 1 Current collector layer 2 Active material layer

Claims

1. A positive electrode comprising a current collector layer (1) and an active material layer (2), wherein the active material layer (2) is coated on at least one surface of the current collector layer (1), and the active material layer (2) comprises an active material and a conductive component, and the mass of the active material is m ｘ +m ｙ (Unit: g), and the conductive component includes at least one of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material, and the masses of the one-dimensional conductive material, the zero-dimensional conductive material, and the two-dimensional conductive material are, in order, m １ , m ２ and m ３ (Unit: g), m ｘ m is the mass of the active material whose surface is coated with a two-dimensional conductive material. ｙ is the mass of the active material coated on its surface with a one-dimensional conductive material or a zero-dimensional conductive material, satisfying the following equation, 20*3.14*d Ｌ *m ｙ / [ρ Ｌ *4 / 3*3.14(d Ｌ / 2) ３ ]≦m １ / (2.2*3.14*(d １ / 2) ２ *L １ )*L １ +10*m ２ / (2.2*4 / 3*3.14*(d ２ / 2) ３ )*d ２ ≦[30*3.14*d Ｌ ]*m ｙ / [ρ Ｌ *4 / 3*3.14(d Ｌ / 2) ３ ](1) 3.14*(d) Ｌ / 2) ２ *m ｘ / [p Ｌ *4 / 3*3.14(d Ｌ / 2) ３ ]≦m ３ / [(2.2**1*3.14*3.4*1�*4)]***********� Ｌ / 2) ２ *m ｘ / [p Ｌ *4 / 3*3.14*(d Ｌ / 2) ３ ](2) In the formula, d Ｌ (Unit: μm) is the diameter of the active material, ρ Ｌ (Unit: g / cm) ３ ) is the true density of the active material, and d １ (Unit: μm) is the diameter of the one-dimensional conductive material, L １ (Unit: μm) is the length of the one-dimensional conductive material, and d ２ (Unit: μm) is the diameter of the zero-dimensional conductive material, and a (unit: μm), b (unit: μm), and c (unit: μm) are the width, length, and thickness of the two-dimensional conductive material, respectively. The active material layer (2) is multilayered, The conductive component includes a one-dimensional conductive material, the positive electrode includes an n-layer active material (2), and the active material (2) covering the current collector layer (1) is the first layer. Mass M of the one-dimensional conductive material in the i-th layer active material layer (2) ｉ = M １ * (1 - i / n) In the formula, M １ n is the mass of the one-dimensional conductive material in the first layer of the active material layer (2), n is a natural number greater than or equal to 2, and i is a natural number greater than or equal to 2 and less than or equal to n. The conductive component includes a zero-dimensional conductive material, and the mass of the zero-dimensional conductive material in the first layer of the active material layer (2) is N = 1. A positive electrode characterized in that the mass N i of the zero-dimensional conductive material in the i-th layer active material layer (2) is N 1 * i / n.

2. The positive electrode according to claim 1, characterized in that the conductive component includes the one-dimensional conductive material, and the mass ratio of the one-dimensional conductive material to the active material is (0.1 to 1.0):

100.

3. The positive electrode according to claim 2, characterized in that the diameter of the one-dimensional conductive material is 2 to 60 nm, and the length of the one-dimensional conductive material is 2 to 15 μm.

4. The positive electrode according to claim 1, characterized in that the conductive component includes the zero-dimensional conductive material, and the mass ratio of the zero-dimensional conductive material to the active material is (0.1 to 3.0):

100.

5. The positive electrode according to claim 4, characterized in that the diameter of the zero-dimensional conductive material is 20 to 100 nm.

6. The positive electrode according to claim 1, characterized in that the conductive component includes the two-dimensional conductive material, and the mass ratio of the two-dimensional conductive material to the active material is (0.1 to 1.5):

100.

7. The positive electrode according to claim 6, characterized in that the thickness of the two-dimensional conductive material is 1 to 20 nm, and the length and width of the two-dimensional conductive material are 0.2 to 10 μm.

8. The positive electrode according to claim 6, characterized in that the mass fraction of the conductive component in the two-dimensional conductive material is 30% or less.

9. The positive electrode according to claim 1, characterized in that the active material includes one or a combination of two or more materials selected from lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and nickel-cobalt manganese ternary materials.

10. A negative electrode, a separator, and a positive electrode according to any one of claims 1 to 9, A battery characterized in that the negative electrode and the positive electrode are provided on both sides of the separator, respectively.

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