Cathode electrode sheet and method for manufacturing the same, and battery and electric device comprising the same

Abstract

The application relates to the technical field of secondary batteries, in particular to a cathode pole piece, a preparation method thereof, a battery containing the cathode pole piece and an electric device. The cathode pole piece comprises a current collector and a coated area arranged on at least one side of the current collector, the coated area comprises at least two active layers; the two adjacent active layers are defined as a first active layer and a second active layer; the first active layer is arranged on the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector; and the mass percentage of a lithium supplement agent in the first active layer is greater than that in the second active layer. In this way, the contact probability of the lithium supplement agent in the first active layer with electrolyte is reduced, and the risk of side reactions caused by the contact of the lithium supplement agent with electrolyte is reduced.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a cathode electrode and its preparation method, as well as a battery and electrical device containing the cathode electrode. Background Technology

[0002] With the rapid growth of portable electronic devices, electric vehicles, and other technologies, the demand for power batteries is also constantly increasing. Among these, the electrochemical performance of batteries is receiving increasing attention.

[0003] There is a problem of lithium loss during the cycling process of lithium secondary batteries. Summary of the Invention

[0004] The main objective of this invention is to provide a cathode electrode to improve the performance of secondary batteries.

[0005] To achieve the above objectives, the present invention provides a cathode electrode, the cathode electrode comprising a current collector and a coating region disposed on at least one side of the current collector, the coating region comprising at least two active layers;

[0006] The two adjacent active layers are defined as the first active layer and the second active layer;

[0007] The first active layer is disposed on the current collector, and the second active layer is disposed on the side of the first active layer away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer.

[0008] Adding a lithium replenishing agent to the active layer improves lithium loss during secondary battery cycling. Considering the potential for side reactions between the lithium replenishing agent and the electrolyte, at least two active layers are formed in the coating area to mitigate these reactions. In two adjacent active layers, the first active layer is located near the current collector, and the second active layer is located on the side of the first active layer facing away from the current collector. The first active layer is closer to the current collector than the second active layer, meaning the second active layer is closer to the surface of the coating (which includes all active layers). This increases the probability of the second active layer contacting the electrolyte, while the first active layer has a lower probability. The mass percentage of the lithium replenishing agent added to the first active layer is greater than that added to the second active layer. This reduces the probability of contact between the lithium replenishing agent in the first active layer and the electrolyte, thus lowering the risk of side reactions.

[0009] Optionally, in the at least two active layers, the total mass percentage of the lithium replenishing agent is defined as x%, the total mass percentage of the lithium replenishing agent = (mass of all lithium replenishing agents in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the lithium replenishing agent x% is 3% to 20%.

[0010] To improve the lithium replenishment effect of secondary batteries, the total mass percentage (x%) of the lithium replenishing agent in at least two active layers ranges from 3% to 20%.

[0011] Optionally, the mass percentage of the lithium replenishing agent in the layer is defined as yi, and the mass percentage of the lithium replenishing agent in the layer is = (mass of lithium replenishing agent in each active layer ÷ total mass of each active layer) * 100%. The mass percentage of the lithium replenishing agent in the second active layer is y(i+1), where i ≥ 1. The mass percentage of the lithium replenishing agent in the first active layer is y(i). Then y(i) - y(i+1) = a, where 3% ≤ a ≤ 40%.

[0012] At least two active layers are arranged sequentially from the current collector to the current collector away. The mass percentage of lithium supplement in each of the sequentially arranged active layers exhibits a gradient distribution; that is, the mass percentage of lithium supplement in each layer decreases from the current collector to the current collector away. This ensures that the mass percentage of lithium supplement in the active layer closer to the current collector is greater than that in the active layer farther away from the current collector, which helps to mitigate the problem of side reactions arising from contact between the lithium supplement and the electrolyte. It is understood that the further the active layer is from the current collector, the closer it is to the surface of the coating, increasing the probability of contact with the electrolyte. Adding different mass percentages of lithium supplement in active layers with varying risks of electrolyte contact improves lithium supplementation performance while reducing the risk of contact between the lithium supplement and the electrolyte, thereby improving battery performance.

[0013] In adjacent active layers, the first active layer is located close to the current collector, and the second active layer is located on the side of the first active layer away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer, and the mass percentage difference between the two active layers is 3% ≤ a ≤ 40%.

[0014] Optionally, the at least two active layers are defined as having an A active layer and a B active layer sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage y1 of the lithium supplement in the A active layer ranges from 4.5% to 40%.

[0015] To improve the lithium replenishment performance of secondary batteries, at least two active layers, namely an A layer and a B layer, are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage y1 of the lithium replenishment agent in the A layer ranges from 4.5% to 40%.

[0016] Optionally, the mass percentage y2 of the lithium supplement in the active layer B ranges from 0% to 18.5%.

[0017] And / or, the at least two active layers are defined as having an A active layer, a B active layer, and a C active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage y3 of the lithium supplement agent in the C active layer ranges from 0% to 17%.

[0018] To improve the lithium replenishment performance of secondary batteries, at least two active layers, namely an A layer and a B layer, are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage y2 of the lithium replenishment agent in the B layer ranges from 0% to 18.5%.

[0019] To improve the lithium replenishment performance of secondary batteries, at least two active layers are provided in sequence from the direction closest to the current collector to the direction furthest from the current collector, namely, active layer A, active layer B, and active layer C. The mass percentage y3 of the lithium replenishment agent in active layer C ranges from 0% to 17%.

[0020] Optionally, the lithium supplement includes at least one of Li5FeO4, Li2M1O2, Li2M2O3, Li6CoO4, Li2S / Fe, Li2S, Li2O / Ni, Li3N, Li2O2, and Li2C4O4, wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr, and Mo, and M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr, and Ru.

[0021] The lithium replenishing agents in this application include, but are not limited to, at least one of Li5FeO4, Li2M1O2, Li2M2O3, Li6CoO4, Li2S / Fe, Li2S, Li2O / Ni, Li3N, Li2O2, and Li2C4O4. M1 includes at least one of Ni, Mn, Cu, Fe, Cr, and Mo, and M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr, and Ru. That is, when selecting a lithium replenishing agent, one can choose one of the lithium replenishing agents listed above in this application, or other types of lithium replenishing agents.

[0022] Optionally, the mass percentage of the conductive agent in the first active layer is greater than the mass percentage of the conductive agent in the second active layer.

[0023] To improve the conductivity of each active layer, and thus address the poor conductivity of the lithium replenisher, the mass percentage of the conductive agent in the first active layer is greater than that in the second active layer. It is understood that as the mass percentage of the lithium replenisher in the active layer increases, the corresponding mass percentage of the conductive agent in that layer also increases, thereby improving the poor conductivity of the lithium replenisher.

[0024] Optionally, in the at least two active layers, the total mass percentage of the conductive agent is defined as Q%. The total mass percentage of the conductive agent = (mass of all conductive agents in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the conductive agent Q% is 1% to 10%.

[0025] To improve the conductivity of the coating, the total mass percentage Q% of the conductive agent in at least two active layers ranges from 1% to 10%, and it is understood that the coating includes each active layer.

[0026] Optionally, the mass percentage of the conductive agent in the layer is defined as qi, and the mass percentage of the conductive agent in the layer is = (mass of the conductive agent in each active layer ÷ total mass of each active layer) * 100%. The mass percentage of the conductive agent in the second active layer is q(i+1), where i ≥ 1. The mass percentage of the conductive agent in the first active layer is q(i). Then q(i) - q(i+1) = b, where 1% ≤ b ≤ 5%.

[0027] As the mass percentage of lithium replenishing agent in adjacent active layers is gradient-distributed, the mass percentage of conductive agent in adjacent active layers is also gradient-distributed. In adjacent active layers, the first active layer is located closer to the current collector, and the second active layer is located farther away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than that in the second active layer. Therefore, the mass percentage of conductive agent in the first active layer is greater than that in the second active layer. The difference in the mass percentage of conductive agent between two adjacent active layers is 1% ≤ b ≤ 5%.

[0028] Optionally, the at least two active layers are defined to have an active layer A and an active layer B sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector;

[0029] The mass percentage q1 of the conductive agent in the active layer A ranges from 1% to 12.5%.

[0030] To improve the conductivity of the active layer and reduce impedance, at least two active layers are defined, with active layer A and active layer B arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector; the mass percentage q1 of the conductive agent in active layer A ranges from 1% to 12.5%.

[0031] Optionally, the mass percentage q2 of the conductive agent in the active layer B ranges from 0.5% to 9.5%.

[0032] And / or, the at least two active layers are defined as having an A active layer, a B active layer, and a C active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage q3 of the lithium supplement agent in the C active layer ranges from 0.5% to 9.5%.

[0033] To improve the conductivity of the active layer, at least two active layers are defined, with active layer A and active layer B arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector; the mass percentage q2 of the conductive agent in active layer B ranges from 0.5% to 9.5%.

[0034] To improve the conductivity of the active layer, at least two active layers are defined as follows: an active layer A, an active layer B, and an active layer C are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage q3 of the lithium supplement in the active layer C ranges from 0.5% to 9%.

[0035] Optionally, the conductive agent includes at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black, and graphene.

[0036] The conductive agent used in this application includes, but is not limited to, at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black, and graphene. When selecting a conductive agent, one may choose one of the conductive agents described above, or other types of conductive agents.

[0037] Optionally, the volume average particle size Dv50 of the lithium supplement ranges from 100 nm to 20 μm.

[0038] To address the poor conductivity of lithium replenishing agents, the volume average particle size (Dv50) of the lithium replenishing agent ranges from 100 nm to 20 μm. It is understood that a volume average particle size (Dv50) within this range can improve the conductivity of the active layer.

[0039] Optionally, the porosity of the first active layer is less than that of the second active layer.

[0040] The porosity of the active layer closer to the current collector is lower than that of the active layer farther from the current collector. This reduces the probability of electrolyte wetting the active layer closer to the current collector and decreases the risk of side reactions between the electrolyte and the lithium supplement in that layer. Therefore, the porosity of the first active layer is lower than that of the second active layer. It can also be understood that a higher porosity in the active layer farther from the current collector is more conducive to lithium-ion transport and improves the electrode kinetics.

[0041] Optionally, in the at least two active layers, the total porosity of the active layers is defined as p, where the total porosity of the active layers = (the volume of all pores in each active layer ÷ the sum of the volumes of each active layer) * 100%, and the total porosity p of the active layers ranges from 10% to 40%.

[0042] To improve the lithium replenishment effect of the coating, in at least two active layers, the total porosity of the active layer is defined as p, and the total porosity p of the active layer ranges from 10% to 40%.

[0043] Optionally, the porosity of each active layer is defined as n, where the porosity of each active layer = (pore volume in each active layer ÷ volume of each active layer) * 100%, the porosity of the second active layer is n(i+1), where i ≥ 1, and the porosity of the first active layer is n(i). Then, n(i+1) - n(i) = c, where 5% ≤ c ≤ 10%.

[0044] In each active layer, the porosity decreases as it approaches the current collector. This reduces the probability of more lithium supplement in the active layer near the current collector coming into contact with the electrolyte, thus improving battery performance. If the first active layer is close to the current collector and the second active layer is far from the current collector, then the porosity of the first active layer is lower than that of the second active layer, and the porosity difference between adjacent active layers is 5% ≤ c ≤ 10%.

[0045] Optionally, the at least two active layers are defined as having an active layer A and an active layer B arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector, and the porosity n1 of the active layer A ranges from 10% to 35%.

[0046] To improve the lithium replenishment performance of the lithium replenishing agent, at least two active layers, an A layer and a B layer, are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The porosity n1 of the A layer ranges from 10% to 35%. It is understood that the lithium replenishing agent requires the electrolyte to transport lithium ions during the lithium replenishment process; therefore, the porosity n1 of the A layer ranges from 10% to 35%.

[0047] Optionally, the porosity n2 of the active layer B ranges from 15% to 35%.

[0048] And / or, the at least two active layers are defined as having an active layer A, an active layer B, and an active layer C arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector, wherein the porosity n3 of the active layer C ranges from 20% to 40%.

[0049] To improve the lithium replenishment performance of the lithium replenishment agent, at least two active layers are defined, namely an active layer A and an active layer B, which are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The porosity n2 of the active layer B ranges from 15% to 35%.

[0050] To improve the lithium replenishment performance of the lithium replenishment agent, at least two active layers are defined, namely, an active layer A, an active layer B, and an active layer C, which are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The porosity n3 of the active layer C ranges from 20% to 40%.

[0051] Optionally, in the at least two active layers, the total mass percentage of the cathode material is defined as W%. The total mass percentage of the cathode material = (mass of all cathode materials in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the cathode material W% is 70% to 97%.

[0052] To improve the energy density of a secondary battery, in at least two active layers, the total mass percentage of the cathode material is defined as W%, and the range of the total mass percentage of the cathode material W% is 70% to 97%.

[0053] This application also provides a method for preparing a cathode electrode, comprising the following steps:

[0054] A slurry on which at least two active layers are coated on a current collector, wherein the mass percentage of lithium supplementer in one active layer on the current collector is greater than the mass percentage of lithium supplementer in one active layer on the side opposite to the current collector.

[0055] The cathode electrode is obtained after drying and cold pressing.

[0056] In two adjacent active layers, the mass percentage of lithium replenishing agent in the active layer closer to the current collector is greater than that in the active layer farther from the current collector. This reduces the probability of contact between the lithium replenishing agent in the active layer closer to the current collector and the electrolyte, thereby reducing the risk of side reactions caused by contact between the lithium replenishing agent and the electrolyte.

[0057] This application provides a battery, comprising: a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode is a cathode electrode as described above or a cathode electrode obtained by the method described above for preparing a cathode electrode.

[0058] The battery lifespan is improved by using the above-mentioned cathode electrode.

[0059] This application provides an electrical device, which includes the battery described above.

[0060] Electrical devices using the aforementioned batteries exhibit improved performance.

[0061] The cathode electrode of this application includes a current collector and a coating area disposed on at least one side of the current collector. The coating area includes at least two active layers. Two adjacent active layers are defined as a first active layer and a second active layer. The first active layer is disposed on the current collector, and the second active layer is disposed on the side of the first active layer opposite to the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer. Adding lithium replenishing agent to the active layers improves lithium loss during secondary battery cycling. Considering that side reactions may occur when lithium supplements come into contact with the electrolyte, at least two active layers are provided in the coating area to mitigate these side reactions. Of the two adjacent active layers, the first active layer is located on the current collector, and the second active layer is located on the side of the first active layer away from the current collector. The first active layer is closer to the current collector than the second active layer, meaning the second active layer is closer to the surface of the coating (which includes all active layers). The second active layer has a higher probability of contacting the electrolyte, while the first active layer has a lower probability. The mass percentage of lithium supplement added to the first active layer is greater than that added to the second active layer. This reduces the probability of contact between the lithium supplement in the first active layer and the electrolyte, thus lowering the risk of side reactions. Attached Figure Description

[0062] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0063] Figure 1 This is a schematic flowchart of the method for preparing the cathode electrode of the present invention;

[0064] Figure 2 This is a schematic diagram of the structure of an embodiment of the cathode electrode of the present invention;

[0065] Figure 3 This is a schematic diagram of the structure of an embodiment of the cathode electrode of the present invention;

[0066] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0067] Figure 5 yes Figure 4 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0068] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application;

[0069] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0070] Figure 8 yes Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown;

[0071] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0072] Explanation of icon numbers:

[0073] label name label name 100 Cathode plate 3 Lower box 10 current collector 4 Battery Module 20 A-layer active layer 5 Secondary batteries 30 B-layer active layer 51 case 40 C layer active layer 52 Electrode assembly 1 Battery pack 53 Top cover assembly 2 Upper box

[0074] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0075] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0076] The following detailed description, with appropriate reference to the accompanying drawings, discloses the cathode electrode of this application, its preparation method, and embodiments of batteries and electrical devices incorporating the cathode electrode. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a thorough understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0077] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] During the first charge of a secondary battery, lithium ions are lost, resulting in irreversible capacity loss and a decrease in the energy density of the lithium secondary battery.

[0084] Therefore, this application provides a cathode electrode, which includes a current collector and a coating area disposed on at least one side of the current collector. The coating area includes at least two active layers. Two adjacent active layers are defined as a first active layer and a second active layer. The first active layer is disposed on the current collector, and the second active layer is disposed on the side of the first active layer away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer.

[0085] A current collector is a structure or component that collects electric current. In secondary batteries, it mainly refers to metal foil, such as copper foil or aluminum foil. As a substrate, the current collector is used to attach the positive or negative electrode active material, collecting the current generated by the active material and outputting a large current. Generally, aluminum foil is used as the positive electrode current collector, and copper foil as the negative electrode current collector.

[0086] The coating area is the part of the current collector used to coat the active layer.

[0087] The active layer refers to a layered structure containing active materials, where the active materials refer to the positive electrode active substances involved in the positive electrode.

[0088] Lithium replenishment agent, also known as lithium replenishment material, releases lithium ions during the first charge to compensate for the irreversible capacity loss caused by the formation of the sei film on the negative electrode surface.

[0089] The two adjacent active layers are the first active layer and the second active layer, which means that the two adjacent active layers are the first active layer and the second active layer. It can be understood that the first active layer and the second active layer can be two active layers in contact.

[0090] The first active layer is disposed on the current collector, and the second active layer is disposed on the side of the first active layer away from the current collector. This means that the first active layer is closer to the current collector than the second active layer. It can be understood that, in one embodiment, the first active layer is directly disposed on the current collector. For ease of understanding, as... Figure 2As shown, 20 can be the first active layer, and 30 can be the second active layer. It can also be understood that, in another embodiment, another active layer is disposed between the first active layer and the current collector. For ease of understanding, as shown... Figure 3 As shown, the layer labeled 30 can be the first active layer, and the layer labeled 40 can be the second active layer.

[0091] Adding a lithium replenishing agent to the active layer improves lithium loss during secondary battery cycling. Considering the potential for side reactions between the lithium replenishing agent and the electrolyte, at least two active layers are formed in the coating area to mitigate these reactions. In two adjacent active layers, the first active layer is located near the current collector, and the second active layer is located on the side of the first active layer facing away from the current collector. The first active layer is closer to the current collector than the second active layer, meaning the second active layer is closer to the surface of the coating (which includes all active layers). This increases the probability of the second active layer contacting the electrolyte, while the first active layer has a lower probability. The mass percentage of the lithium replenishing agent added to the first active layer is greater than that added to the second active layer. This reduces the probability of contact between the lithium replenishing agent in the first active layer and the electrolyte, thus lowering the risk of side reactions.

[0092] In one embodiment, in at least two active layers, the total mass percentage of the lithium replenishing agent is defined as x%. The total mass percentage of the lithium replenishing agent is = (mass of all lithium replenishing agents in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the lithium replenishing agent x% is 3% to 20%.

[0093] The mass of all lithium replenishing agents in each active layer refers to the sum of the masses of lithium replenishing agents in each active layer of the cathode electrode. For example, if the cathode electrode has two active layers, active layer A (active layer mass is 100g, lithium replenishing agent is 4g) and active layer B (active layer mass is 100g, lithium replenishing agent is 2g), then the mass of all lithium replenishing agents in each active layer is 4g + 2g = 6g.

[0094] The total mass percentage of lithium replenishing agent refers to the total mass percentage of lithium replenishing agent in the cathode electrode. As mentioned above, for active layer A (active layer mass is 100g, lithium replenishing agent 4g) and active layer B (active layer mass is 100g, lithium replenishing agent 2g), the total mass percentage of lithium replenishing agent is (6g / 200g)*100%=3%.

[0095] To improve the lithium replenishment effect of secondary batteries, the total mass percentage (x%) of the lithium replenishing agent in at least two active layers ranges from 3% to 20%.

[0096] The values ​​in the range of 3% to 20% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., as well as the range values ​​between any two of the above point values.

[0097] In one embodiment, the mass percentage of the lithium replenishing agent in the layer is defined as yi, and the mass percentage of the lithium replenishing agent in the layer is = (mass of lithium replenishing agent in each active layer ÷ total mass of each active layer) * 100%. The mass percentage of the lithium replenishing agent in the second active layer is y(i+1), where i≥1. The mass percentage of the lithium replenishing agent in the first active layer is y(i). Then y(i)-y(i+1)=a, where 3%≤a≤40%.

[0098] The mass percentage of lithium replenishing agent in each layer refers to the mass percentage of lithium replenishing agent in each active layer of the cathode electrode. For example, if the cathode electrode has two active layers, active layer A (active layer mass is 100g, lithium replenishing agent 6g) and active layer B (active layer mass is 100g, lithium replenishing agent 3g), then the mass percentage of lithium replenishing agent in active layer A, y1, is (6g / 100g)*100% = 6%; and the mass percentage of lithium replenishing agent in active layer B, y2, is (3g / 100g)*100% = 3%.

[0099] At least two active layers are arranged sequentially from the current collector to the layer furthest away from it. The mass percentage of lithium supplementer in each of the sequentially arranged active layers exhibits a gradient distribution; that is, the mass percentage of lithium supplementer in each layer decreases from the current collector to the layer furthest away from it. This ensures that the mass percentage of lithium supplementer in the active layer closer to the current collector is greater than that in the active layer farther away from the current collector, which helps to mitigate the problem of side reactions arising from contact between the lithium supplementer and the electrolyte. It is understood that the further the active layer is from the current collector, the closer it is to the surface of the coating, increasing the probability of contact with the electrolyte. Adding different lithium supplementers to active layers with varying risks of electrolyte contact improves lithium supplementation performance while reducing the risk of contact between the lithium supplementer and the electrolyte, thereby improving battery performance.

[0100] In adjacent active layers, the first active layer is located close to the current collector, and the second active layer is located on the side of the first active layer away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer, and the mass percentage difference between the two active layers is 3% ≤ a ≤ 40%.

[0101] The difference between the mass percentage y(i) of the lithium supplement in the first active layer and the mass percentage y(i+1) of the lithium supplement in the second active layer is 3% to 40%, where i ≥ 1. This indicates that the mass percentage of the lithium supplement in adjacent active layers is different. The difference of 3% to 40% can be, for example, 3%, 5%, 7%, 10%, 15%, 18%, 20%, 25%, 27%, 30%, 35%, 40%, etc., or any range between any two of the above values.

[0102] In one embodiment, at least two active layers are defined, with active layer A and active layer B sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage y1 of the lithium supplement in active layer A ranges from 4.5% to 40%.

[0103] like Figure 2 As shown, the cathode electrode 100 includes a current collector 10 and an A-layer active layer 20 and a B-layer active layer 30 disposed in the current collector 10. In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are defined to be disposed in sequence from the direction closer to the current collector to the direction farther away from the current collector, with the A-layer active layer and the B-layer active layer being disposed in sequence. The mass percentage y1 of the lithium replenishment agent in the A-layer active layer ranges from 4.5% to 40%.

[0104] The values ​​in the range of 4.5% to 40% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 4.5%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc., as well as the range values ​​between any two of the above point values.

[0105] In one embodiment, the mass percentage y2 of the lithium replenishing agent in the B active layer ranges from 0% to 18.5%; and / or, at least two active layers are defined to be sequentially disposed in the direction from near the current collector to away from the current collector, wherein the mass percentage y3 of the lithium replenishing agent in the C active layer ranges from 0% to 17%.

[0106] To improve the lithium replenishment performance of secondary batteries, at least two active layers are defined, with an A layer and a B layer arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage y2 of the lithium replenishment agent in the B layer ranges from 0% to 18.5%.

[0107] To improve the lithium replenishment performance of secondary batteries, at least two active layers are provided in sequence from the direction closest to the current collector to the direction furthest from the current collector, namely, active layer A, active layer B, and active layer C. The mass percentage y3 of the lithium replenishment agent in active layer C ranges from 0% to 17%.

[0108] like Figure 3 As shown, at least two active layers are defined, arranged sequentially from the direction closest to the current collector to the direction furthest away from the current collector: active layer A 20, active layer B 30, and active layer C 40. Active layer A is closest to the current collector, and therefore, the mass percentage y1 of the lithium supplement agent in active layer A is higher than that in other active layers. The mass percentage y1 of the lithium supplement agent in active layer A ranges from 4.5% to 40%, for example, it can be 4.5%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc., as well as any range between any two of the above values. The mass percentage y2 of the lithium supplement agent in active layer B ranges from 0% to 18.5%, for example, it can be 0%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 16%, 17%, 18%, 18.5%, etc., as well as any range between any two of the above values. The mass percentage y3 of the lithium supplement in the C-layer active layer ranges from 0% to 17%, for example, it can be 0%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 16%, 17%, etc., or any range between any two of the above values. Furthermore, a mass percentage difference is formed in each active layer.

[0109] In one embodiment, the lithium supplement includes at least one of Li5FeO4, Li2M1O2, Li2M2O3, Li6CoO4, Li2S / Fe, Li2S, Li2O / Ni, Li3N, Li2O2, and Li2C4O4, wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr, and Mo, and M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr, and Ru.

[0110] The lithium replenishing agents in this application include, but are not limited to, at least one of Li5FeO4, Li2M1O2, Li2M2O3, Li6CoO4, Li2S / Fe, Li2S, Li2O / Ni, Li3N, Li2O2, and Li2C4O4. M1 includes at least one of Ni, Mn, Cu, Fe, Cr, and Mo, and M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr, and Ru. That is, when selecting a lithium replenishing agent, one can choose one of the lithium replenishing agents listed above in this application, or other types of lithium replenishing agents.

[0111] In one embodiment, the mass percentage of the conductive agent in the first active layer is greater than the mass percentage of the conductive agent in the second active layer.

[0112] Conductive agents are used to ensure that the electrodes have good charge and discharge performance. A certain amount of conductive material is usually added during the electrode manufacturing process. It plays a role in collecting micro-currents between active materials and between active materials and current collectors, so as to reduce the contact resistance of the electrode and accelerate the movement rate of electrons. At the same time, it can also effectively improve the migration rate of lithium ions in the electrode material, thereby improving the charge and discharge efficiency of the electrode.

[0113] To improve the conductivity of each active layer, and thus address the poor conductivity of the lithium replenisher, the mass percentage of the conductive agent in the first active layer is greater than that in the second active layer. It is understood that as the mass percentage of the lithium replenisher in the active layer increases, the corresponding mass percentage of the conductive agent in that layer also increases, thereby improving the poor conductivity of the lithium replenisher.

[0114] For example, in one embodiment, the lithium replenishing agent in the active layer near the current collector has poor conductivity and large particles. Increasing the mass percentage of the conductive agent in this layer helps to reduce cathode impedance and improve battery performance.

[0115] In one embodiment, in at least two active layers, the total mass percentage of the conductive agent is defined as Q%. The total mass percentage of the conductive agent is = (mass of all conductive agents in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the conductive agent Q% is 1% to 10%.

[0116] The mass of all conductive agents in each active layer refers to the sum of the masses of conductive agents in each active layer of the cathode electrode. For example, if the cathode electrode has two active layers, active layer A (active layer mass is 100g, conductive agent 3g) and active layer B (active layer mass is 100g, conductive agent 2g), then the mass of all conductive agents in each active layer is 3g + 2g = 5g.

[0117] The total mass percentage of the conductive agent refers to the total mass percentage of the conductive agent in the cathode electrode. As mentioned above, for active layer A (active layer mass is 100g, conductive agent 4g) and active layer B (active layer mass is 100g, conductive agent 2g), the total mass percentage of the conductive agent is (5g / 200g)*100% = 2.5%.

[0118] To improve the conductivity of the coating, the total mass percentage Q% of the conductive agent in at least two active layers ranges from 1% to 10%, and it is understood that the coating includes each active layer.

[0119] The values ​​in the range of 1% to 10% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., as well as the range values ​​between any two of the above point values.

[0120] In one embodiment, the mass percentage of the conductive agent in the layer is defined as qi, and the mass percentage of the conductive agent in the layer is = (mass of the conductive agent in each active layer ÷ total mass of each active layer) * 100%. The mass percentage of the conductive agent in the second active layer is q(i+1), where i ≥ 1. The mass percentage of the conductive agent in the first active layer is q(i). Then q(i) - q(i+1) = b, where 1% ≤ b ≤ 5%.

[0121] The mass percentage of the conductive agent in each layer refers to the mass percentage of the conductive agent in each active layer of the cathode electrode. For example, if the cathode electrode has two active layers, active layer A (active layer mass is 100g, conductive agent 4g) and active layer B (active layer mass is 100g, conductive agent 2g), then the mass percentage of the conductive agent in active layer A, q1, is (4g / 100g)*100% = 4%; and the mass percentage of the conductive agent in active layer B, q2, is (2g / 100g)*100% = 2%.

[0122] As the mass percentage of lithium replenishing agent in adjacent active layers is gradient-distributed, the mass percentage of conductive agent in adjacent active layers is also gradient-distributed. In adjacent active layers, the first active layer is located closer to the current collector, and the second active layer is located farther away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than that in the second active layer. Therefore, the mass percentage of conductive agent in the first active layer is greater than that in the second active layer. The difference in the mass percentage of conductive agent between two adjacent active layers is 1% ≤ b ≤ 5%.

[0123] The values ​​in the range of 1%-5% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 1%, 2%, 3%, 4%, 5%, etc., and the range values ​​between any two of the above point values.

[0124] In one embodiment, at least two active layers are defined, with active layer A and active layer B sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector; the mass percentage q1 of the conductive agent in active layer A ranges from 1% to 12.5%.

[0125] To improve the conductivity of the active layer and reduce impedance, at least two active layers are defined, with active layer A and active layer B arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector; the mass percentage q1 of the conductive agent in active layer A ranges from 1% to 12.5%.

[0126] The values ​​from 1% to 12.5% ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 12.5%, etc., as well as the range values ​​between any two of the above point values.

[0127] In one embodiment, the mass percentage q2 of the conductive agent in the B active layer ranges from 0.5% to 9.5%; and / or, at least two active layers are defined as having an A active layer, a B active layer, and a C active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage q3 of the lithium supplement agent in the C active layer ranges from 0.5% to 9%.

[0128] To improve the conductivity of the active layer, at least two active layers are defined, with active layer A and active layer B arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector; the mass percentage q2 of the conductive agent in active layer B ranges from 0.5% to 9.5%.

[0129] To improve the conductivity of the active layer, at least two active layers are defined as follows: an active layer A, an active layer B, and an active layer C are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The mass percentage q3 of the lithium supplement in the active layer C ranges from 0.5% to 9%.

[0130] In one embodiment, the conductive agent includes at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black, and graphene.

[0131] The conductive agent used in this application includes, but is not limited to, at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black, and graphene. When selecting a conductive agent, one may choose one of the conductive agents described above, or other types of conductive agents.

[0132] In one embodiment, the volume average particle size Dv50 of the lithium supplement ranges from 100 nm to 20 μm.

[0133] The volume average particle size Dv50 is the value of the particle size of 50% of the total volume of particles in a sample, and the particle size of another 50% of the total volume of particles is smaller than this value; Dv50 can represent the median particle size of the sample.

[0134] The volume average particle size Dv50 can be tested using methods known in the art. As an example, GB / T 19077-2016 can be referenced for characterization testing using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000.

[0135] To address the poor conductivity of lithium replenishing agents, the volume average particle size (Dv50) of the lithium replenishing agent ranges from 100 nm to 20 μm. It is understood that a volume average particle size (Dv50) within this range can improve the conductivity of the active layer.

[0136] The values ​​in the range of 100nm to 20μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 100nm, 150nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 2μm, 5μm, 7μm, 10μm, 12μm, 15μm, 18μm, 20μm, etc., as well as the range values ​​between any two of the above point values.

[0137] In one embodiment, the porosity of the first active layer is less than that of the second active layer.

[0138] The formula for calculating porosity is P = [V / V0] * 100%. V0 is the volume of the material in its natural state, and V is the volume of all pores in the material.

[0139] Porosity test: Prepare a mercury solution and a pressure gauge. Pour a certain amount of mercury solution into the material. Use the pressure gauge to measure the pressure of the mercury solution, calculate the volume of the mercury solution, use the density of mercury and the pressure measured by the pressure gauge to determine the volume of the mercury solution, calculate the porosity, and use the ratio of the volume of the mercury solution to the volume of the material to determine the porosity.

[0140] The porosity of the active layer closer to the current collector is lower than that of the active layer farther from the current collector. This reduces the probability of electrolyte wetting the active layer closer to the current collector and decreases the risk of side reactions between the electrolyte and the lithium supplement in that layer. Therefore, the porosity of the first active layer is lower than that of the second active layer. It can also be understood that a higher porosity in the active layer farther from the current collector is more conducive to lithium-ion transport and improves the electrode kinetics.

[0141] In one embodiment, in at least two active layers, the total porosity of the active layers is defined as p, where the total porosity of the active layers = (the total volume of all pores in each active layer ÷ the sum of the volumes of each active layer) * 100%, and the total porosity p of the active layers ranges from 10% to 40%.

[0142] The total porosity of the active layer refers to the volume of all pores in the active layers of the cathode electrode divided by the sum of the volumes of all active layers in the cathode electrode. The total porosity of the active layer ranges from 10% to 40%, for example, it can be 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, etc., as well as the range between any two of the above values. It can be understood that porosity is related not only to the mass percentage of lithium supplementation agent but also to the compaction density.

[0143] To improve the lithium replenishment effect of the coating, in at least two active layers, the total porosity of the active layer is defined as p, and the total porosity p of the active layer ranges from 10% to 40%.

[0144] In one embodiment, the porosity of each active layer is defined as n, the porosity of each active layer = (pore volume in each active layer ÷ volume of each active layer) * 100%, the porosity of the second active layer is n(i+1), where i ≥ 1, the porosity of the first active layer is n(i), then n(i+1) - n(i) = c, where 5% ≤ c ≤ 10%.

[0145] The porosity of each active layer refers to the pore volume in each active layer of the cathode electrode divided by the volume of each active layer. The difference between the porosity of the second active layer and the porosity of the first active layer is 5% ≤ c ≤ 10%, for example, the difference between the porosity of the second active layer and the porosity of the first active layer is 5%, 6%, 7%, 8%, 9%, 10%, etc., as well as the range between any two of the above values.

[0146] In each active layer, the porosity decreases as it approaches the current collector. This reduces the probability of more lithium supplement in the active layer near the current collector coming into contact with the electrolyte, thus improving battery performance. If the first active layer is close to the current collector and the second active layer is far from the current collector, then the porosity of the first active layer is lower than that of the second active layer, and the porosity difference between adjacent active layers is 5% ≤ c ≤ 10%.

[0147] In one embodiment, at least two active layers are defined, with active layer A and active layer B sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, and the porosity n1 of active layer A ranges from 10% to 35%.

[0148] The active layer A is closest to the current collector. The porosity of the active layer A is lower than that of other active layers. The porosity of the active layer A is 10% to 35%, for example, it can be 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, etc., as well as the range between any two of the above values.

[0149] To improve the lithium replenishment performance of the lithium replenishing agent, at least two active layers, namely an A layer and a B layer, are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The porosity n1 of the A layer ranges from 10% to 35%. It is understood that the lithium replenishing agent requires the electrolyte to transport lithium ions during the lithium replenishment process; therefore, the porosity n1 of the A layer ranges from 10% to 35%.

[0150] In one embodiment, the porosity n2 of the B active layer ranges from 15% to 35%; and / or, at least two active layers are defined as having an A active layer, a B active layer, and a C active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the porosity n3 of the C active layer ranges from 20% to 40%.

[0151] To improve the lithium replenishment performance of the lithium replenishment agent, at least two active layers are defined, namely an active layer A and an active layer B, which are sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector. The porosity n2 of the active layer B ranges from 15% to 35%.

[0152] To improve the lithium replenishment performance of the lithium replenishment agent, at least two active layers are defined, namely, active layer A, active layer B and active layer C, which are arranged sequentially from the direction closer to the current collector to the direction farther away from the current collector. The porosity n3 of active layer C ranges from 20% to 40%.

[0153] In one embodiment, in at least two active layers, the total mass percentage of the cathode material is defined as W%. The total mass percentage of the cathode material = (mass of all cathode materials in each active layer ÷ total mass of each active layer) * 100%, and the range of the total mass percentage of the cathode material W% is 70% to 97%.

[0154] The total mass percentage of the cathode material is equal to the sum of the masses of all cathodes in each active layer divided by the total mass of each active layer.

[0155] To improve the energy density of secondary batteries, in at least two active layers, the total mass percentage of cathode material is defined as W%, and the range of the total mass percentage of cathode material W% is 70% to 97%.

[0156] The values ​​in the range of 70% to 97% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 97%, etc., as well as the range values ​​between any two of the above point values.

[0157] like Figure 1As shown, this application also provides a method for preparing a cathode electrode, comprising the following steps: coating a slurry with at least two active layers on a current collector, wherein the mass percentage of lithium replenishing agent in one active layer on the current collector is greater than the mass percentage of lithium replenishing agent in one active layer on the side away from the current collector; and obtaining a cathode electrode after drying and cold pressing.

[0158] In two adjacent active layers, the mass percentage of lithium replenishing agent in the active layer closer to the current collector is greater than that in the active layer farther from the current collector. This reduces the probability of contact between the lithium replenishing agent in the active layer closer to the current collector and the electrolyte, thereby reducing the risk of side reactions caused by contact between the lithium replenishing agent and the electrolyte.

[0159] This application provides a battery, comprising: a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode is a cathode electrode as described above or a cathode electrode obtained by the method described above for preparing a cathode electrode. Since the cathode electrode employs all the technical solutions of all the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated further here.

[0160] The battery life is improved by using the above-described cathode electrode. It is understood that a battery includes individual cells, battery modules, and battery packs. When the battery is an individual cell, the individual cell includes the cathode electrode as described above; when the battery is a battery module, the battery module includes the cathode electrode as described above; and when the battery is a battery pack, the battery pack includes the cathode electrode as described above.

[0161] This application provides an electrical device, which includes the battery described above. Since the battery employs all the technical solutions of all the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here.

[0162] Electrical devices using the aforementioned batteries exhibit improved performance.

[0163] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0164] In one embodiment of this application, a secondary battery is provided.

[0165] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through. The separator described above is the improved separator of this application.

[0166] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0167] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0168] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0170] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0171] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0172] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0173] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0174] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0175] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0176] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0177] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0178] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0179] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0180] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0181] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0182] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0183] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0184] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0185] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0186] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0187] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0188] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0189] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0190] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0191] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 5.

[0192] In some implementations, refer to Figure 5The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0193] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0194] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0195] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0196] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0197] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0198] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0199] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0200] Figure 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0201] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0202] Example

[0203] Cathode electrode preparation

[0204] Cathode material, lithium supplement, conductive agent, and binder are mixed uniformly in different mass ratios. Then, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous to obtain a cathode active slurry. Different cathode active slurries are then uniformly coated onto a current collector, dried, and cold-pressed to obtain the cathode electrode.

[0205] Anode preparation

[0206] The active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a certain weight ratio (e.g., 96.5:0.7:1.8:1). The mixture is then coated onto a current collector (e.g., copper foil), dried, and cold-pressed to obtain the anode electrode.

[0207] The diaphragm is a commercially available PE microporous film with a thickness of 7μm and an average pore size of 80nm (from Zhuogao Electronic Technology Co., Ltd.).

[0208] Preparation of electrolyte

[0209] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 1 / 1. LiPF6 lithium salt was added and dissolved in the organic solvent and stirred until homogeneous to obtain 1 M LiPF6, thus obtaining the electrolyte.

[0210] Preparation of lithium-ion batteries

[0211] The cathode electrode, separator, and anode electrode of the embodiment are wound in sequence to obtain a bare cell, wherein the separator is located between the positive and negative electrodes to isolate them. After shaping, the cells are vacuum baked for 24 hours to remove water, and then the electrolyte is injected and sealed to obtain a battery without charge. The cells are then subjected to a series of processes such as settling, formation, and capacity testing to obtain a lithium-ion battery product.

[0212] Example 1

[0213] Preparation of the first layer of slurry

[0214] The nickel-cobalt-manganese (NCM) ternary material NCM523, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), and lithium supplementer Li5FeO4 were mixed evenly in a mass ratio of 86:3:1:60:10 to obtain the first layer of positive electrode slurry.

[0215] Preparation of the second layer of slurry

[0216] The nickel-cobalt-manganese (NCM) ternary material NCM523, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), and lithium supplementer Li5FeO4 were mixed evenly in a mass ratio of 98:1:1:60:0 to obtain the second layer of positive electrode slurry.

[0217] The first layer of slurry is uniformly coated onto the current collector and dried at 95℃-115℃ to obtain the first active layer. Then, the second layer of slurry is coated onto the first active layer. After drying at 95℃-115℃, cold pressing (at 5T pressure), and slitting, the cathode electrode is obtained. The first active layer of the cathode electrode contains 10% lithium supplementer Li5FeO4 and 3% conductive carbon. The second active layer contains 0% lithium supplementer Li5FeO4 and 1% conductive carbon black, with a weight ratio of 5:5 between the two coatings.

[0218] Example 2

[0219] Based on Example 1, the proportions of each raw material were adjusted to obtain a first active layer with a lithium replenishing agent Li5FeO4 content of 10% and a conductive carbon black content of 1wt%, and a second active layer with a lithium replenishing agent Li5FeO4 content of 0% and a conductive carbon black content of 1%, with a two-layer coating weight ratio of 5:5.

[0220] Example 3

[0221] Based on Example 1, the proportions of each raw material were adjusted to obtain a first active layer with a lithium supplement Li5FeO4 content of 10% and a conductive carbon black content of 3wt%, and a second active layer with a lithium supplement Li5FeO4 content of 5% and a conductive carbon black content of 2%.

[0222] Example 4

[0223] Based on Example 3, the types of lithium replenishing agent and conductive agent were changed.

[0224] Example 5

[0225] Based on Example 3, a three-layer active layer was prepared. The first active layer contained 10% lithium replenishing agent Li5FeO4 and 3 wt% conductive carbon black. The second active layer contained 5% lithium replenishing agent Li5FeO4 and 2% conductive carbon black. The third active layer contained 3% lithium replenishing agent Li5FeO4 and 1% conductive carbon black.

[0226] Example 6

[0227] Based on Example 1, the proportions of each raw material were adjusted to obtain a first active layer with a lithium supplement Li5FeO4 content of 4.5% and a conductive carbon black content of 1 wt%, and a second active layer with a lithium supplement Li5FeO4 content of 1.5% and a conductive carbon black content of 0.5%.

[0228] Example 7

[0229] Based on Example 3, a three-layer active layer was prepared. The first active layer contained 40% lithium supplement Li5FeO4 and 12.5 wt% conductive carbon black. The second active layer contained 18.5% lithium supplement Li5FeO4 and 9.5% conductive carbon black. The third active layer contained 17% lithium supplement Li5FeO4 and 9% conductive carbon black.

[0230] Comparative Example 1

[0231] Based on Example 1, a single-layer coating is applied, with 5% lithium supplementing agent Li5FeO4 and 2% conductive agent.

[0232] Table 1 List of experimental parameters

[0233]

[0234] Table 2 List of Experimental Parameters

[0235]

[0236] Performance testing

[0237] Cycle life tests were conducted in parallel using five battery cells from each of the above embodiments and comparative examples. Each battery cell was charged at room temperature at a rate of 0.33C to a voltage of 4.3V, and then discharged at a rate of 0.33C to a voltage of 2.5V. The reversible capacity was measured as C0. This charging and discharging process was repeated until the discharge capacity Cn / C0 ≤ 80% in a certain cycle. The total number of cycles is denoted as X-Cycle, where Cn is the capacity at the nth cycle.

[0238] Battery first efficiency test: First coulombic efficiency = first discharge capacity / first charge capacity. During the cycle life test, the first discharge capacity and the first charge capacity are calculated to calculate the first coulombic efficiency.

[0239] Table 3 Battery Performance Data

[0240] Serial Number First effect 80% of the cycle count Comparative Example 1 81.7％ 454 Example 1 89.5％ 771 Example 2 86.1％ 685 Example 3 87.0％ 727 Example 4 92％ 660 Example 5 93.5％ 673 Example 6 85.6％ 655 Example 7 95％ 710

[0241] As can be seen from the table above, the mass percentage of lithium replenishing agent in the active layer closer to the current collector is greater than that in the active layer farther from the current collector. This can improve the contact between the lithium replenishing agent and the electrolyte, thereby improving the battery performance.

[0242] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A cathode electrode, characterized in that, The cathode electrode includes a current collector and a coating area disposed on at least one side of the current collector, the coating area including at least two active layers; The two adjacent active layers are defined as the first active layer and the second active layer; The first active layer is positioned closer to the current collector than the second active layer, and the second active layer is positioned on the side of the first active layer that is away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than the mass percentage of lithium replenishing agent in the second active layer, the mass percentage of conductive agent in the first active layer is greater than the mass percentage of conductive agent in the second active layer, and the porosity of the first active layer is less than the porosity of the second active layer.

2. The cathode electrode as described in claim 1, characterized in that, In the at least two active layers, the total mass percentage of the lithium replenishing agent is defined as x%. The total mass percentage of the lithium replenishing agent is = (mass of all lithium replenishing agents in each active layer ÷ total mass of each active layer) × 100%, and the range of the total mass percentage of the lithium replenishing agent x% is 3% to 20%.

3. The cathode electrode as described in claim 1, characterized in that, The mass percentage of the lithium replenishing agent in the layer is defined as yi, and the mass percentage of the lithium replenishing agent in the layer is = (mass of lithium replenishing agent in each active layer ÷ total mass of each active layer) × 100%. The mass percentage of the lithium replenishing agent in the second active layer is y(i+1), where i≥1. The mass percentage of the lithium replenishing agent in the first active layer is y(i). Then y(i)-y(i+1)=a, where 3%≤a≤40%.

4. The cathode electrode sheet according to any one of claims 1 to 3, characterized in that, The at least two active layers are defined as having a first active layer and a second active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage y1 of the lithium supplement in the first active layer ranges from 4.5% to 40%.

5. The cathode electrode as described in claim 4, characterized in that, The mass percentage y2 of the lithium supplement in the second active layer ranges from 0% to 18.5%. And / or, the at least two active layers are defined as having a first active layer, a second active layer and a third active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage y3 of the lithium supplement in the third active layer ranges from 0% to 17%.

6. The cathode electrode sheet according to any one of claims 1 to 3, characterized in that, The lithium replenishing agent includes at least one of Li5FeO4, Li2M1O2, Li2M2O3, Li6CoO4, Li2S / Fe, Li2S, Li2O / Ni, Li3N, Li2O2, and Li2C4O4, wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr, and Mo, and M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr, and Ru.

7. The cathode electrode as described in claim 1, characterized in that, In the at least two active layers, the total mass percentage of the conductive agent is defined as Q%. The total mass percentage of the conductive agent is = (mass of all conductive agents in each active layer ÷ total mass of each active layer) × 100%, and the range of the total mass percentage of the conductive agent Q% is 1% to 10%.

8. The cathode electrode as described in claim 7, characterized in that, The mass percentage of the conductive agent in the layer is defined as qi, and the mass percentage of the conductive agent in the layer is = (mass of the conductive agent in each active layer ÷ total mass of each active layer) × 100%. The mass percentage of the conductive agent in the second active layer is q(i+1), where i≥1. The mass percentage of the conductive agent in the first active layer is q(i). Then q(i)-q(i+1)=b, where 1%≤b≤5%.

9. The cathode electrode as described in claim 7 or 8, characterized in that, The at least two active layers are defined to have a first active layer and a second active layer sequentially disposed from the direction closest to the current collector to the direction far from the current collector; The mass percentage q1 of the conductive agent in the first active layer ranges from 1% to 12.5%.

10. The cathode electrode as described in claim 9, characterized in that, The mass percentage q2 of the conductive agent in the second active layer ranges from 0.5% to 9.5%. And / or, the at least two active layers are defined as having a first active layer, a second active layer and a third active layer sequentially disposed from the direction closest to the current collector to the direction furthest from the current collector, wherein the mass percentage q3 of the lithium supplement in the third active layer ranges from 0.5% to 9%.

11. The cathode electrode as described in claim 7 or 8, characterized in that, The conductive agent includes at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black, and graphene.

12. The cathode electrode sheet according to any one of claims 1 to 3, characterized in that, The volume average particle size Dv50 of the lithium supplement ranges from 100 nm to 20 μm.

13. The cathode electrode sheet according to any one of claims 1 to 3, characterized in that, In the at least two active layers, the total porosity of the active layers is defined as p, where the total porosity of the active layers = (the volume of all pores in each active layer ÷ the sum of the volumes of each active layer) × 100%, and the total porosity p of the active layers ranges from 10% to 40%.

14. The cathode electrode as described in claim 13, characterized in that, Define the porosity of each active layer as n, the porosity of each active layer = (pore volume in each active layer ÷ volume of each active layer) × 100%, the porosity of the second active layer is n(i+1), where i≥1, the porosity of the first active layer is n(i), then n(i+1)-n(i)=c, where 5%≤c≤10%.

15. The cathode electrode as described in claim 14, characterized in that, The at least two active layers are defined as having a first active layer and a second active layer arranged sequentially from the direction closest to the current collector to the direction furthest from the current collector, wherein the porosity n1 of the first active layer ranges from 10% to 35%.

16. The cathode electrode as described in claim 15, characterized in that, The porosity n2 of the second active layer ranges from 15% to 35%. And / or, the at least two active layers are defined as having a first active layer, a second active layer and a third active layer sequentially arranged from the direction closest to the current collector to the direction furthest from the current collector, wherein the porosity n3 of the third active layer ranges from 20% to 40%.

17. The cathode electrode sheet according to any one of claims 1 to 3, characterized in that, In the at least two active layers, the total mass percentage of the cathode material is defined as W%. The total mass percentage of the cathode material = (mass of all cathode materials in each active layer ÷ total mass of each active layer) × 100%, and the range of the total mass percentage of the cathode material W% is 70% to 97%.

18. A method for preparing a cathode electrode, characterized in that, Includes the following steps: A slurry with at least two active layers coated on a current collector is defined as a first active layer and a second active layer, with the first active layer being positioned closer to the current collector than the second active layer, and the second active layer being positioned on the side of the first active layer away from the current collector. The mass percentage of lithium replenishing agent in the first active layer is greater than that in the second active layer, the mass percentage of conductive agent in the first active layer is greater than that in the second active layer, and the porosity of the first active layer is less than that of the second active layer. The cathode electrode is obtained after drying and cold pressing.

19. A battery, characterized in that, include: A negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode is a cathode electrode as described in any one of claims 1 to 17 or a cathode electrode prepared by the method described in claim 18.

20. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 19.

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