Positive electrode and battery

Abstract

The embodiment of the present application provides a positive electrode and a battery, wherein the positive electrode comprises a current collector layer and an active component layer, wherein the active component layer covers at least one surface of the current collector layer, wherein the active component layer comprises an active material and a conductive component, wherein the conductive component comprises at least one of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material. The active component layer of the positive electrode of the present application comprises a conductive component, wherein the conductive component utilizes a conductive agent that is a combination of one or more of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material, and through different conductive agent size and content parameters and matching with different active materials, an efficient conductive network can be constructed, thereby improving the conductivity and capacity performance of the positive electrode and ensuring the energy density of the positive electrode.

Description

Technical Field

[0001] The present application belongs to the technical field of battery materials, and specifically, the present application relates to a positive electrode and a battery. Background Art

[0002] As a new type of green energy, lithium-ion batteries have developed rapidly in recent years due to their high capacity, high voltage, small size and light weight, long cycle life, wide operating range, good safety, and no memory effect. In the face of large-scale application demand for lithium-ion batteries, improving the performance of lithium-ion batteries and reducing costs are the key, and further improving the power density and energy density of positive and negative electrode materials, and improving cycle performance and safety performance have become the focus of development.

[0003] Taking improving battery performance by increasing the conductivity of lithium-ion battery positive electrode materials as an example, at present, the conductive agents used in the preparation of lithium-ion battery positive electrode slurry are carbon black, acetylene black, conductive graphite, carbon nanotubes, carbon nanofibers, etc., and most of the conductive agents are used alone. The same conductive agent is often used in different electrodes. It is impossible to select the conductive agent according to the type of positive electrode material, which is not conducive to the performance of the conductive agent and limits the energy density and cycle performance of lithium-ion batteries. Summary of the invention

[0004] One purpose of the embodiments of the present application is to provide a new technical solution for a positive electrode and a battery.

[0005] According to a first aspect of an embodiment of the present application, a positive electrode is provided, comprising a current collector layer and an active component layer, wherein the active component layer covers at least one surface of the current collector layer, and the active component layer comprises:

[0006] Active material and conductive component, 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, 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 formula:

[0007] 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)

[0009] 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)

[0010] Among them, d L is the diameter of the active material, ρ 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.

[0011] Optionally, 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.

[0012] Optionally, the diameter of the one-dimensional conductive material is 2-60 nm, and the length of the one-dimensional conductive material is 2-15 μm.

[0013] Optionally, 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.

[0014] Optionally, the diameter of the zero-dimensional conductive material is 20-100 nm.

[0015] Optionally, 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.

[0016] Optionally, the thickness of the two-dimensional conductive material is 1-20 nm, and the length and width of the two-dimensional conductive material are 0.2-10 μm.

[0017] Optionally, the mass fraction of the two-dimensional conductive material in the conductive component is less than or equal to 30%.

[0018] Optionally, the active component layer is a single layer or multiple layers.

[0019] Optionally, the conductive component includes a one-dimensional conductive material, and the number of layers of the active component layer is n, with the active component layer covering the current collector layer as the first layer:

[0020] The mass of the one-dimensional conductive material in the i-th active component layer Mi = M1*(1-i / n);

[0021] Wherein, M1 is the mass of the one-dimensional conductive material in the first active component 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.

[0022] Optionally, the conductive component includes a zero-dimensional conductive material, and the mass of the zero-dimensional conductive material in the first active component layer is N1;

[0023] The mass N of the zero-dimensional conductive material in the i-th active component layer i =N1*i / n.

[0024] Optionally, the active material includes one or more combinations of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide and nickel-cobalt-manganese ternary materials.

[0025] According to a second aspect of an embodiment of the present application, a battery is provided, comprising a negative electrode, a separator, and the positive electrode according to the first aspect;

[0026] The negative electrode and the positive electrode are respectively arranged on both sides of the separator.

[0027] One technical effect of the embodiments of the present application is:

[0028] The embodiment of the present application provides a positive electrode, including a current collector layer and an active component layer. The active component layer of the positive electrode described in the present application includes a conductive component, and the conductive component uses a conductive agent that is a combination of one or more of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material. Through different conductive agent size and content parameters and matching with different active materials, an efficient conductive network can be constructed to improve the conductivity and capacity performance of the positive electrode and ensure the energy density of the positive electrode.

[0029] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0031] Figure 1 A schematic diagram of the structure of a positive electrode provided in an embodiment of the present application;

[0032] Figure 2 A one-dimensional conductive material content in a positive electrode and a resistivity permeation curve of the positive electrode provided in an embodiment of the present application;

[0033] Figure 3 A permeation curve of the content of a zero-dimensional conductive material in a positive electrode and the resistivity of the positive electrode provided in an embodiment of the present application;

[0034] Figure 4 This is a permeation curve of the resistivity of a positive electrode and the content of a two-dimensional conductive material in a positive electrode provided in an embodiment of the present application.

[0035] Among them: 1-current collector layer; 2-active component layer. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0037] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0038] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0039] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0040] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0041] Reference Figure 1 The present embodiment provides a positive electrode, comprising a current collector layer 1 and an active component layer 2, wherein the active component layer 2 covers at least one surface of the current collector layer 1, and the active component layer 2 comprises:

[0042] Active material and conductive component, 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, 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 formula:

[0043] 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)

[0045] 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)

[0046] Among them, d L is the diameter of the active material, ρ 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.

[0047] 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; the two-dimensional conductive material may be at least one of graphene, two-dimensional conductive metal organic frameworks (2D ECMOFs) and conductive two-dimensional molybdenum carbide (MXene).

[0048] Specifically, the size parameters of the one-dimensional conductive material, the zero-dimensional conductive material and the two-dimensional conductive material in Formula 1 and Formula 2 are all size parameters of single one-dimensional conductive material, zero-dimensional conductive material and two-dimensional conductive material particles. The conductive component may include one of the one-dimensional conductive material, the zero-dimensional conductive material and the two-dimensional conductive material, or may include a combination of multiple ones of the one-dimensional conductive material, the zero-dimensional conductive material and the two-dimensional conductive material.

[0049] Formula 1 discloses the content requirements of the conductive components of the one-dimensional conductive material and the zero-dimensional conductive material in the active component layer 2. Since the conductive component is an inactive substance, when the content of the conductive component in the active component layer 2 is too high, the electrode capacity of the positive electrode will be significantly reduced. In order to ensure the conductivity of the positive electrode, the length of the conductive component allocated on 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, thereby constructing a complete conductive network; and the total length of the conductive component is at most 30 times the circumference of the particle. When the total length of the conductive component is too long, the improvement of the conductivity of the positive electrode is already very limited, but it will significantly reduce the electrode capacity of the positive electrode.

[0050] See also Figure 1 The one-dimensional conductive material content and the resistivity penetration curve of the positive electrode shown in the figure show that when the content of the one-dimensional conductive material in the positive electrode increases, the resistivity of the positive electrode will decrease significantly, but when the content of the one-dimensional conductive material increases to a certain extent, such as Figure 1 After the content of one-dimensional conductive material reaches 0.6%, the content of one-dimensional conductive material has little effect on the resistivity of the positive electrode; similarly, see Figure 2 The content of zero-dimensional conductive material and the resistivity penetration curve of the positive electrode shown in the figure show that when the content of zero-dimensional conductive material in the positive electrode increases, the resistivity of the positive electrode will decrease significantly, but when the content of zero-dimensional conductive material increases to a certain extent, such as Figure 2 When the content of zero-dimensional conductive material reaches 2%, the content of zero-dimensional conductive material has little effect on the resistivity of the positive electrode.

[0051] Formula 2 discloses the content requirement of the conductive component of the two-dimensional conductive material in the active component layer 2. In order to ensure that the two-dimensional conductive material can cover the active material particles and form an effective conductive network, the amount of the two-dimensional conductive material added needs to meet the conditions of Formula 2. Figure 3 The content of the two-dimensional conductive material and the resistivity penetration curve of the positive electrode shown in the figure show that when the content of the two-dimensional conductive material in the positive electrode increases, the resistivity of the positive electrode will decrease significantly. However, when the content of the two-dimensional conductive material increases to a certain extent, such as Figure 3 After the content of the two-dimensional conductive material reaches 0.8%, the content of the two-dimensional conductive material has little effect on the resistivity of the positive electrode.

[0052] The active component layer 2 of the positive electrode described in the present application includes a conductive component, and the conductive component utilizes a conductive agent of one or more combinations of one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials. Through different conductive agent size and content parameters and matching with different active materials, an efficient conductive network can be constructed to improve the conductivity and capacity performance of the positive electrode and ensure the energy density of the positive electrode. Moreover, when the conductive component of the active component layer 2 includes one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials at the same time, the conductive component can construct an efficient conductive network from multiple dimensions of points, lines, and surfaces, and the length, area, and particle size distribution of the conductive component and the active material are combined to achieve a reasonable design of the conductive network of the conductive component.

[0053] Optionally, 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.

[0054] Specifically, the active material may be lithium iron phosphate. Taking 100g of lithium iron phosphate as an example, since the true density of carbon is 2.2g / cm 3 , the true density of lithium iron phosphate is 3.6g / cm 3 , d L Represents the diameter of lithium iron phosphate, where True Density refers to the actual mass of solid matter per unit volume in an absolutely dense state, that is, the density after removing the internal pores or gaps between particles. In order to ensure that the conductive component represented by the one-dimensional conductive material can cover the active material represented by the lithium iron phosphate particles and form an effective conductive network in the positive electrode, combined with Formula 1, the addition amount of the one-dimensional conductive material needs to meet the following conditions:

[0055] 20*3.14*d LFP *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 ]

[0056] The diameter of the one-dimensional conductive material is 2-60nm, preferably 5-15nm; the length of the one-dimensional conductive material is 2-15μm, preferably 5-10μm. Taking the one-dimensional conductive material within the above diameter range and length range as an example, the mass of the one-dimensional conductive material in the active component layer 2 containing 100g of lithium iron phosphate active material can be controlled so that the mass of the one-dimensional conductive material is within the range of 0.5-0.75g. When the mass of the one-dimensional conductive material is too large, such as the one-dimensional conductive material is too thick or too long, the one-dimensional conductive material is not easy to disperse, which easily leads to the agglomeration of the one-dimensional conductive material; and when the mass of the one-dimensional conductive material is too small, it is not conducive to the cross-linking between the one-dimensional conductive materials to form a conductive network.

[0057] Optionally, the conductive component includes the zero-dimensional conductive material, and the mass ratio of the zero-dimensional conductive material to the active material is (0.1-3.0):100, preferably (1.918-2.7):100.

[0058] 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 can cover the active material represented by the lithium iron phosphate particles and form an effective conductive network in the positive electrode, combined with Formula 1, the addition amount of the zero-dimensional conductive material needs to meet the following conditions:

[0059] 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 LFP *100 / [3.6*4 / 3*3.14(d L / 2) 3 ]

[0060] The diameter of the zero-dimensional conductive material is 20-100nm, preferably 30-50nm. Taking the zero-dimensional conductive material within the above diameter range as an example, the mass of the zero-dimensional conductive material in the active component layer 2 containing 100g of lithium iron phosphate active material can be controlled so that the mass of the zero-dimensional conductive material is in the range of 1.918-2.7g. When the mass of the zero-dimensional conductive material is too large, for example, when the diameter of the zero-dimensional conductive material is too large, the conductive efficiency of the conductive component will be reduced because the zero-dimensional conductive material is easy to agglomerate; and when the mass of the zero-dimensional conductive material is too small, it is not conducive to cross-linking between the zero-dimensional conductive materials or between the zero-dimensional conductive material and other conductive agents to form a conductive network.

[0061] Optionally, 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, preferably (0.8-1.2):100.

[0062] 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 can cover the active material represented by the lithium iron phosphate particles and form an effective conductive network in the positive electrode, combined with Formula 2, the addition amount of the two-dimensional conductive material needs to meet the following conditions:

[0063] 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 ]

[0064] The thickness of the two-dimensional conductive material is 1-20nm, and the length and width of the two-dimensional conductive material are both 0.2-10μm. Taking the two-dimensional conductive material within the above-mentioned length, width and thickness range as an example, the mass of the two-dimensional conductive material in the active component layer 2 containing 100g of lithium iron phosphate active material can be controlled so that the mass of the two-dimensional conductive material is in the range of 0.8-1.2g. When the mass of the two-dimensional conductive material is too much, although the impedance of the positive electrode can be reduced, the cost of the active component layer 2 will be increased, and the conductive agent represented by the two-dimensional conductive material is an inactive substance and cannot provide charge and discharge capacity. Therefore, when the amount of the conductive agent represented by the two-dimensional conductive material is too much, the capacity of the positive electrode will be significantly reduced.

[0065] Optionally, the mass fraction of the two-dimensional conductive material in the conductive component is less than or equal to 30%.

[0066] Specifically, when the conductive component includes conductive agents such as one-dimensional conductive materials and zero-dimensional conductive materials on the basis of two-dimensional conductive materials, too much two-dimensional conductive material will lead to aggregation between layers of the two-dimensional conductive material, thereby reducing the conductive efficiency of the conductive component; and the flaky two-dimensional conductive material is not conducive to the diffusion of lithium ions in the positive electrode, thereby limiting the energy density and charge and discharge capacity of the positive electrode.

[0067] Optionally, the active component layer 2 is a single layer or multiple layers.

[0068] Specifically, the active component layer 2 can be coated on at least one surface of the current collector layer 1, and the coating of the active component layer 2 can be completed by one coating, that is, forming a single layer coating, which can simplify the preparation process of the positive electrode and reduce the preparation cost of the positive electrode. The coating of the active component layer 2 can also be completed by multiple coatings, that is, forming a multi-layer coating; multi-layer coating can achieve a good match between the energy density and the conductive performance of the positive electrode by controlling the component ratio of the active material and the conductive component in each active component layer.

[0069] Optionally, the conductive component includes a one-dimensional conductive material, the number of layers of the active component layer 2 is n, and n is a natural number greater than or equal to 2, the first layer of the active component layer is in contact with the current collector layer, and the second layer, the third layer, the fourth layer, ... the nth layer are sequentially away from the first layer, that is, the nth layer is the active component layer away from the first layer, so that the nth layer is close to the separator layer;

[0070] Starting from the active component layer covering the current collector layer as the first layer:

[0071] The mass of the one-dimensional conductive material in the i-th active component layer Mi = M1*(1-i / n);

[0072] Wherein, M1 is the mass of the one-dimensional conductive material in the first active component 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.

[0073] Specifically, the mass of the one-dimensional conductive material in the first layer can be determined according to the above formula 1. Since the one-dimensional conductive material has a higher electronic conductivity, the closer to the current collector layer 1, the more one-dimensional conductive material can be in the active component layer 2, so as to enhance the bonding strength and electron transfer efficiency of the active material and conductive component in the active component layer 2 and the current collector layer 1. For example, when the number of layers of the active component layer 2 is four, and the four layers of the active component layer 2 are stacked 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 of the one-dimensional conductive material in the second layer is M2. i =M1*(1-2 / 4)=M1*1 / 2, the mass M of the one-dimensional conductive material in the third layer i =M1*(1-3 / 4)=M1*1 / 4, 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 between the multiple active component layers 2 presents a gradient distribution, thereby ensuring the conductive efficiency of the active component layer 2.

[0074] Optionally, the number of layers of the active component layer 2 is n, the conductive component includes a zero-dimensional conductive material, and the mass of the zero-dimensional conductive material in the first active component layer is N1;

[0075] The mass N of the zero-dimensional conductive material in the i-th active component layer i =N1*i / n, i is an integer greater than or equal to 2.

[0076] Specifically, the mass of the zero-dimensional conductive material in the first layer can be determined according to the above formula 1. Since the zero-dimensional conductive material has a high liquid retention capacity, it is beneficial to the diffusion process of lithium ions in the positive electrode. The farther away from the current collector layer 1, the more zero-dimensional conductive material can be in the active component layer 2. On the basis of ensuring the electrolyte retention rate in the positive electrode, the combination of one-dimensional conductive material and zero-dimensional conductive material is conducive to building a better conductive network in the multi-layer coated active component layer 2 system. For example, when the number of layers of the active component layer 2 is four, and the four layers of the active component layer 2 are stacked and the area and thickness of each layer are the same, 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, so that the mass of the zero-dimensional conductive material between the multiple layers of the active component layer 2 presents a gradient distribution.

[0077] Optionally, the active material includes one or more combinations of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide and nickel-cobalt-manganese ternary materials.

[0078] Specifically, the types of active materials can be various. For example, when lithium iron phosphate (LiFePO4) is selected as the active material, the safety performance and service life of the positive electrode can be guaranteed due to the stable structure of the lithium iron phosphate material during the charge and discharge process; while lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2) and nickel cobalt manganese ternary material (LiNi x Co y Mn 1-x-y The combination of active materials such as O2) can improve the energy density of the positive electrode.

[0079] The embodiment of the present application also provides a battery, including a negative electrode, a separator and a positive electrode;

[0080] The negative electrode and the positive electrode are respectively arranged on both sides of the separator.

[0081] Specifically, the positive electrode active component layer 2 of the battery includes a conductive component, and the conductive component uses a conductive agent of one or more combinations of one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials. Through different conductive agent size and content parameters and matching with different active materials, it is possible to construct an efficient conductive network, improve the conductivity and capacity performance of the positive electrode, and ensure the energy density of the battery. Moreover, when the conductive component of the active component layer 2 includes one-dimensional conductive materials, zero-dimensional conductive materials, and two-dimensional conductive materials at the same time, the conductive component can construct an efficient conductive network from multiple dimensions of points, lines, and surfaces, and combine the length and area of ​​the conductive component with the particle size distribution of the active material to achieve a reasonable design of the conductive network of the conductive component and ensure the capacity of the battery.

[0082] The positive electrode provided in the present application is described in detail below through examples and comparative examples.

[0083] The positive electrode in the following embodiments and comparative examples includes a current collector layer and an active component layer, the current collector layer is aluminum foil, and the active component layer includes lithium iron phosphate, a binder, nitrogen methyl pyrrolidone, and one or more of a one-dimensional conductive material, a zero-dimensional conductive material, and a two-dimensional conductive material;

[0084] The preparation methods of the positive electrode in the embodiment and the comparative example both include:

[0085] The components of the active component layer are mixed to prepare a slurry, the slurry is coated on an aluminum foil, and then baked and rolled to prepare a positive electrode.

[0086] The positive electrode and the corresponding negative electrode are assembled into a battery with a designed capacity of 1.8Ah.

[0087] Example 1

[0088] Active materials include: lithium iron phosphate;

[0089] The conductive components include: carbon nanotubes.

[0090] 100g of lithium iron phosphate was selected, the average particle size of lithium iron phosphate D50=1.30μm, the average diameter of carbon nanotubes was 11nm, and the average length of carbon nanotubes was 8μm. According to the above formulas 1 and 2, the amount of carbon nanotubes added was 0.6g.

[0091] Example 2

[0092] Active materials include: lithium iron phosphate;

[0093] The conductive component includes: carbon black.

[0094] 100g of lithium iron phosphate is selected, the average particle size of lithium iron phosphate D50=1.30μm, the average diameter of carbon black is 60nm, and according to the above formula 1 and formula 2, the amount of carbon black added is 2.2g.

[0095] Example 3

[0096] Active materials include: lithium iron phosphate;

[0097] The conductive components include: graphene.

[0098] 100g of lithium iron phosphate was selected, the average particle size of lithium iron phosphate was D50=1.30μm, the average length of graphene was 4.2μm, the average width of graphene was 2.45μm, and the average thickness of graphene was 14nm. According to the above formulas 1 and 2, the amount of graphene added was 1.0g.

[0099] Example 4

[0100] Active materials include: lithium iron phosphate;

[0101] The conductive components include carbon nanotubes and carbon black.

[0102] 100g of lithium iron phosphate was selected, the average particle size of lithium iron phosphate was D50=1.30μm, the average diameter of carbon nanotubes was 11nm, the average length of carbon nanotubes was 8μm, and the average diameter of carbon black was 60nm. According to the above formula 1 and formula 2, the amount of carbon nanotubes added was 0.3g and the amount of carbon black added was 0.9g.

[0103] Comparative Example 1

[0104] The material selection was the same as in Example 1, except that the amount of carbon tube added was changed to 0.3 g.

[0105] Comparative Example 2

[0106] The material selection was the same as in Example 1, except that the amount of carbon tube added was changed to 1.0 g.

[0107] Comparative Example 3

[0108] The material selection was the same as in Example 2, except that the amount of carbon black added was changed to 1.4 g.

[0109] Comparative Example 4

[0110] The material selection was the same as in Example 2, except that the amount of carbon black added was changed to 3 g.

[0111] Comparative Example 5

[0112] The material selection was the same as in Example 3, except that the amount of graphene added was changed to 0.5 g.

[0113] Comparative Example 6

[0114] The material selection is the same as in Example 3, except that the amount of graphene added is changed to 1.6 g.

[0115] The resistivity test was conducted on the positive electrodes of the above-mentioned embodiments and comparative examples, and the mixed material gram capacity and DC internal resistance test were conducted on the batteries composed of the positive electrodes.

[0116] The test results of the positive electrodes of the embodiments and comparative examples are shown in Table 1:

[0117] Table 1

[0118]

[0119] It can be seen from the longitudinal resistivity of the positive electrode in Table 1 that the positive electrodes provided in the embodiments of the present application all have relatively low resistivity, and the resistivity of the positive electrode in each embodiment is less than 32Ω*cm; and by comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 3, and Example 3 and Comparative Example 5, it can be seen that when the amount of the conductive component used is too low, the resistivity of the positive electrode increases significantly, and the resistivity of the positive electrode in Comparative Example 1, Comparative Example 3 and Comparative Example 5 is greater than 50Ω*cm.

[0120] From the 0.33C mixed material gram capacity in Table 1 (i.e., the capacity contributed by each gram of electrode active component layer at a 0.33C discharge rate), the battery mixed material gram capacity of the positive electrode composition provided in the embodiments of the present application is greater than 137.0 mAh / g. By comparing Examples 1, 2, 3 and Comparative Examples 1, 3, and 5, it can be seen that when the content of the conductive component is too low, the mixed material gram capacity of the battery will be significantly reduced, all lower than 135.2 mAh / g; and in the case of Comparative Examples 1, 2, 3 and Comparative Examples 2, 4, and 6, although the resistivity of the positive electrode will be slightly reduced after the content of the conductive component is increased, the excessive conductive component leads to an increase in the content of inactive substances, which reduces the mixed material gram capacity of the battery of the positive electrode composition. The mixed material gram capacity of the battery of the positive electrode composition of Comparative Examples 2, 4, and 6 is less than 136.7 mAh / g, which ultimately leads to a reduction in the energy density of the battery.

[0121] It can be seen from the 50% SOC DC internal resistance in Table 1 that the DC internal resistance of the battery composed of the positive electrode provided in the embodiments of the present application is less than 56.5mΩ; while the conductive component content of the positive electrode in Comparative Example 1, Comparative Example 3 and Comparative Example 5 is insufficient, resulting in an increase in the resistivity of the positive electrode, and the DC internal resistance (DCIR) of the battery is greater than 58.9mΩ, which seriously affects the battery's kinetic performance.

[0122] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A positive electrode, comprising a current collector layer and an active component layer, wherein the active component layer covers at least one surface of the current collector layer, characterized in that: The active component layer comprises: Active material and conductive component, 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, 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 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) Among them, d L is the diameter of the active material, ρ 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, a, b, c are the width, length and thickness of the two-dimensional conductive material respectively; m x is the mass of active material covered by the two-dimensional conductive material, m y is the mass of active material covered by zero-dimensional conducting material and one-dimensional conducting material.

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 (0.1-1.0):

100.

3. The positive electrode according to claim 2, characterized in that The diameter of the one-dimensional conductive material is 2-60 nm, and the length of the one-dimensional conductive material is 2-15 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 (0.1-3.0):

100.

5. The positive electrode according to claim 4, characterized in that The diameter of the zero-dimensional conductive material is 20-100 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 (0.1-1.5):

100.

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

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

9. The positive electrode according to claim 1, characterized in that The active component layer is a single layer or multiple layers.

10. The positive electrode according to claim 9, characterized in that The conductive component includes a one-dimensional conductive material, and the number of layers of the active component layer is n, starting from the active component layer covering the current collector layer as the first layer: The mass of the one-dimensional conductive material in the i-th active component layer Mi = M1*(1-i / n); Wherein, M1 is the mass of the one-dimensional conductive material in the first active component 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.

11. The positive electrode according to claim 10, characterized in that The conductive component includes a zero-dimensional conductive material, and the mass of the zero-dimensional conductive material in the first active component layer is N1; The mass N of the zero-dimensional conductive material in the i-th active component layer i =N1*i / n.

12. The positive electrode according to claim 1, characterized in that The active material includes one or more combinations of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide and nickel-cobalt-manganese ternary materials.

13. A battery, characterized in that: A method comprising: comprising a negative electrode, a separator and a positive electrode according to any one of claims 1 to 12; The negative electrode and the positive electrode are respectively arranged on both sides of the separator.

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