Cathode pole piece and preparation method thereof, and battery and electric equipment comprising cathode pole piece

Abstract

The invention relates to the technical field of secondary batteries, in particular to a cathode pole piece and a preparation method thereof, and a battery and electric equipment comprising the cathode pole piece. The cathode plate comprises a current collector and a coating area arranged on at least one side surface of the current collector, and the coating area comprises 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 arranged on the current collector, the second active layer is arranged on the side, away from the current collector, of the first active layer, and the mass percent of the lithium supplement agent in the first active layer is larger than that of the lithium supplement agent in the second active layer. Therefore, the contact probability of the lithium supplement agent in the first active layer and the electrolyte is reduced, and the risk of side reaction caused by contact of the lithium supplement agent and the electrolyte is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a cathode electrode piece and a preparation method thereof, as well as a battery and an electrical device comprising the cathode electrode piece. Background Art

[0002] With the rapid growth of portable electronic devices and electric vehicles, the demand for power batteries is also growing. Among them, the electrochemical performance of batteries is also attracting more and more attention.

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

[0004] The main purpose of the present invention is to provide a cathode electrode to improve the performance of a secondary battery.

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

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

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

[0008] A lithium supplement is added to the active layer to improve lithium loss during the cycle of the secondary battery. Considering that side reactions may occur when the lithium supplement contacts the electrolyte, in order to improve the side reactions, at least two active layers are provided in the coating area. Of the two adjacent active layers, the first active layer is provided on the current collector, and the second active layer is provided 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, that is, the second active layer is closer to the surface of the coating layer than the first active layer (it can be understood that the coating layer includes various active layers). The second active layer has a greater probability of contacting the electrolyte, while the first active layer has a lower probability of contacting the electrolyte than the second active layer. The mass percentage of the lithium supplement added to the first active layer is greater than the mass percentage of the lithium supplement added to the second active layer. In this way, the probability of contact between the lithium supplement in the first active layer and the electrolyte is reduced, thereby reducing the risk of side reactions when the lithium supplement contacts the electrolyte.

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

[0010] In order to improve the lithium replenishing effect of the secondary battery, the total mass percentage x% of the lithium replenishing agent in at least two active layers is in a range of 3% to 20%.

[0011] Optionally, the mass percentage of the lithium supplement agent in the layer is defined as yi, the mass percentage of the lithium supplement agent in the layer = (mass of the lithium supplement agent in each active layer ÷ total mass of each active layer) * 100%, the mass percentage of the lithium supplement agent in the second active layer is y(i+1), where i≥1, the mass percentage of the lithium supplement 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 active layer away from the current collector. The mass percentage of the lithium supplement agent in the sequentially arranged active layers is distributed in a gradient, that is, the mass percentage of the lithium supplement agent in each layer decreases from the current collector to the active layer away from the current collector. In this way, the mass percentage of the lithium supplement agent in the active layer close to the current collector is greater than the mass percentage of the lithium supplement agent in the active layer away from the current collector, which helps to alleviate the problem of side reactions caused by contact between the lithium supplement agent and the electrolyte. It can be understood that the farther the active layer is from the current collector, the closer it is to the surface of the coating, and the greater the probability of contact with the electrolyte. Different mass percentages of lithium supplement agent are added to active layers with different risks of electrolyte contact to improve lithium supplement performance while reducing the risk of contact between the lithium supplement agent and the electrolyte, thereby improving battery performance.

[0013] In adjacent active layers, the first active layer is arranged close to the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector. The mass percentage of the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher 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 an A active layer and a B active layer sequentially arranged from close to the current collector to far away from the current collector, and the mass percentage y1 of the lithium supplement agent in the A active layer ranges from 4.5% to 40%.

[0015] In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are defined, including an A layer active layer and a B layer active layer, which are arranged in sequence from close to the current collector to away from the current collector. The mass percentage y1 of the lithium replenisher in the A layer active layer ranges from 4.5% to 40%.

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

[0017] And / or, the at least two active layers are defined as being sequentially arranged from close to the current collector to far away from the current collector, including an A active layer, a B active layer, and a C active layer, and the mass percentage y3 of the lithium supplement agent in the C active layer is in a range of 0% to 17%.

[0018] In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are defined, including an A layer active layer and a B layer active layer, which are arranged in sequence from close to the current collector to away from the current collector. The mass percentage y2 of the lithium replenisher in the B layer active layer ranges from 0% to 18.5%.

[0019] In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are arranged in sequence from the direction close to the current collector to the direction away from the current collector, and the mass percentage y3 of the lithium replenisher in the 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 supplement 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, 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. In other words, when selecting a lithium supplement agent, one can choose the lithium supplement agents listed above or other types.

[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 therefore address the poor conductivity of the lithium supplement, 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. It is understood that as the mass percentage of the lithium supplement in the active layer increases, the mass percentage of the conductive agent in that layer also increases, thereby addressing the poor conductivity of the lithium supplement.

[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 total mass percentage Q% of the conductive agent ranges from 1% to 10%.

[0025] In order 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%. It can be understood that the coating includes each active layer.

[0026] Optionally, the mass percentage of the conductive agent in the layer is defined as qi, the mass percentage of the conductive agent in the layer = (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 the lithium replenisher in adjacent active layers is distributed in a gradient, the mass percentage of the conductive agent in adjacent active layers is also distributed in a gradient. In the adjacent active layers, the first active layer is arranged close to the current collector, and the second active layer is arranged away from the current collector. The mass percentage of the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher in the second active layer. Then, 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. The difference in the mass percentage of the conductive agent in the two adjacent active layers is 1%≤b≤5%.

[0028] Optionally, the at least two active layers are defined as an A-layer active layer and a B-layer active layer sequentially arranged from close to the current collector to far away from the current collector;

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

[0030] In order to improve the conductivity of the active layer and reduce the impedance, at least two active layers are defined, including an A layer active layer and a B layer active layer, arranged in sequence from close to the current collector to away from the current collector; the mass percentage q1 of the conductive agent in the A layer active layer ranges from 1% to 12.5%.

[0031] Optionally, the mass percentage q2 of the conductive agent in the active layer B is in a range of 0.5% to 9.5%;

[0032] And / or, the at least two active layers are defined as being sequentially arranged from close to the current collector to far away from the current collector, including an A layer active layer, a B layer active layer, and a C layer active layer, and the mass percentage q3 of the lithium supplement agent in the C layer active layer is in a range of 0.5% to 9.5%.

[0033] In order to improve the conductivity of the active layer, at least two active layers are defined, including an A layer active layer and a B layer active layer, arranged in sequence from close to the current collector to far away from the current collector; the mass percentage q2 of the conductive agent in the B layer active layer ranges from 0.5% to 9.5%.

[0034] In order to improve the conductivity of the active layer, at least two active layers are defined, which are arranged in sequence from close to the current collector to far away from the current collector, and the mass percentage q3 of the lithium supplement agent in the active layer C is in the range of 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 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, the conductive agent mentioned in this application can be selected, or other types of conductive agents can be selected.

[0037] Optionally, the volume average particle size Dv50 of the lithium supplement agent is in the range of 100 nm to 20 μm.

[0038] To improve the poor conductivity of the lithium supplement, the volume average particle size Dv50 of the lithium supplement is in the range of 100 nm to 20 μm. It is understood that the volume average particle size Dv50 of the lithium supplement in the above range can improve the conductivity of the active layer.

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

[0040] The porosity of the active layer closest to the current collector is lower than that of the active layer further away. This reduces the probability of electrolyte infiltration into the active layer near the current collector, minimizing side reactions between the electrolyte and the lithium supplement in this layer. To this end, 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 further away from the current collector facilitates lithium ion transport and improves the dynamics of the electrode.

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

[0042] In order to improve the lithium replenishing effect of the coating, in at least two active layers, the total porosity of the active layer is defined as p, and the range of the total porosity p of the active layer is 10% to 40%.

[0043] Optionally, 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%.

[0044] The porosity of each active layer decreases as it approaches the current collector. This reduces the probability of contact between the lithium supplement and the electrolyte in the active layer near the current collector, improving battery performance. If the first active layer is closer to the current collector and the second active layer is farther away, the porosity of the first active layer is lower than that of the second active layer. The porosity difference between adjacent active layers is 5% ≤ c ≤ 10%.

[0045] Optionally, the at least two active layers are defined as an A-layer active layer and a B-layer active layer sequentially arranged from close to the current collector to far away from the current collector, and the porosity n1 of the A-layer active layer is in a range of 10% to 35%.

[0046] To improve the lithium replenishment performance of the lithium replenisher, at least two active layers are defined, including an active layer A and an active layer B, arranged in order from closest to the current collector to further away from the current collector. The porosity n1 of the active layer A ranges from 10% to 35%. It is understood that the lithium replenisher requires an electrolyte to transport lithium ions during the lithium replenishment process. Therefore, the porosity n1 of the active layer A ranges from 10% to 35%.

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

[0048] And / or, the at least two active layers are defined as being sequentially arranged from close to the current collector to far away from the current collector, including an A-layer active layer, a B-layer active layer, and a C-layer active layer, and the porosity n3 of the C-layer active layer is in a range of 20% to 40%.

[0049] In order to improve the lithium replenishing performance of the lithium replenishing agent, at least two active layers are defined, including an A layer active layer and a B layer active layer, which are arranged in sequence from close to the current collector to far away from the current collector. The porosity n2 of the B layer active layer ranges from 15% to 35%.

[0050] In order to improve the lithium replenishment performance of the lithium replenisher, at least two active layers are defined, including an A layer active layer, a B layer active layer and a C layer active layer, which are arranged in sequence from close to the current collector to far away from the current collector. The porosity n3 of the C layer active layer is in the range of 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 total mass percentage W% of the cathode material ranges from 70% to 97%.

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

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

[0054] Coating at least two active layer slurries on a current collector, wherein the mass percentage of the lithium replenisher in one active layer disposed on the current collector is greater than the mass percentage of the lithium replenisher in the active layer on the side away from the current collector;

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

[0056] In two adjacent active layers, the mass percentage of the lithium supplement agent in the active layer close to the current collector is greater than the mass percentage of the lithium supplement agent in the active layer far from the current collector. In this way, the probability of contact between the lithium supplement agent in the active layer close to the current collector and the electrolyte is reduced, and the risk of side reactions caused by the contact between the lithium supplement agent and the electrolyte is reduced.

[0057] The present application provides a battery, comprising: a negative electrode plate, a positive electrode plate, a separator and an electrolyte, wherein the positive electrode plate is the cathode plate as described above or a cathode plate obtained by the preparation method of the cathode plate as described above.

[0058] The service life of the battery using the cathode plate is improved.

[0059] The present application provides an electrical device, which includes the above-mentioned battery.

[0060] The performance of the electrical equipment using the battery is improved.

[0061] The cathode electrode of the present application includes a current collector and a coating region disposed on at least one side of the current collector. The coating region includes 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 disposed on the current collector, and the second active layer is disposed on the side of the first active layer facing away from the current collector. The mass percentage of the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher in the second active layer. The lithium replenisher is added to the active layer to improve lithium loss during the cycling of the secondary battery. Taking into account the side reactions that may occur when the lithium supplement agent contacts the electrolyte, in order to improve the side reactions between the lithium supplement agent and the electrolyte, at least two active layers are arranged in the coating area. Among the two adjacent active layers, 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. The first active layer is closer to the current collector than the second active layer, that is, the second active layer is closer to the surface of the coating than the first active layer (it can be understood that the coating includes various active layers). The second active layer has a greater probability of contacting the electrolyte, and the first active layer has a lower probability of contacting the electrolyte than the second active layer. The mass percentage of the lithium supplement agent added in the first active layer is greater than the mass percentage of the lithium supplement agent added in the second active layer. In this way, the probability of contact between the lithium supplement agent in the first active layer and the electrolyte is reduced, and the risk of side reactions between the lithium supplement agent and the electrolyte is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0063] Figure 1 Schematic diagram of the process of preparing the cathode electrode of the present invention;

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

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

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

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

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

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

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

[0071] Figure 9 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0072] Description of Figure 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 purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0075] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0076] Below, the cathode electrode sheet and its preparation method, as well as the embodiments of the battery and electrical equipment containing the cathode electrode sheet of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0077] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0079] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0080] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

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

[0082] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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, there is a problem of lithium ion loss, which leads to irreversible capacity loss and further reduces the energy density of the lithium secondary battery.

[0084] To this end, the present application provides a cathode electrode sheet, which includes a current collector and a coating area arranged 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 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 the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher in the second active layer.

[0085] A current collector is a structure or component that collects current. In secondary batteries, it primarily refers to metal foil, such as copper or aluminum foil. The current collector serves as a substrate for the positive or negative active material, collecting the current generated by the active material and delivering high current output. Typically, aluminum foil is used as the positive current collector, while copper foil is used for the negative current collector.

[0086] Coating area: The area on the current collector used to coat the active layer.

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

[0088] Lithium replenisher, also known as lithium replenishing material, will release lithium ions during the first charging process to compensate for the irreversible capacity loss caused by the formation of sei film on the negative electrode surface.

[0089] The two adjacent active layers are respectively the first active layer and the second active layer, which refers to two adjacent active layers, namely 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, which 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 shown in FIG. Figure 2As shown, the first active layer is labeled 20, and the second active layer is labeled 30. It can also be understood that in another embodiment, other active layers are provided between the first active layer and the current collector. Figure 3 As shown, the element numbered 30 may be the first active layer, and the element numbered 40 may be the second active layer.

[0091] A lithium supplement is added to the active layer to improve lithium loss during the cycle of the secondary battery. Considering that side reactions may occur when the lithium supplement contacts the electrolyte, in order to improve the side reactions, at least two active layers are provided in the coating area. Of the two adjacent active layers, the first active layer is provided on the current collector, and the second active layer is provided 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, that is, the second active layer is closer to the surface of the coating layer than the first active layer (it can be understood that the coating layer includes various active layers). The second active layer has a greater probability of contacting the electrolyte, while the first active layer has a lower probability of contacting the electrolyte than the second active layer. The mass percentage of the lithium supplement added to the first active layer is greater than the mass percentage of the lithium supplement added to the second active layer. In this way, the probability of contact between the lithium supplement in the first active layer and the electrolyte is reduced, thereby reducing the risk of side reactions when the lithium supplement contacts the electrolyte.

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

[0093] The mass of all lithium supplements in each active layer refers to the sum of the masses of the lithium supplements 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 supplement 4g) and active layer B (active layer mass is 100g, lithium supplement 2g), the mass of all lithium supplements in each active layer is 4g + 2g = 6g.

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

[0095] In order to improve the lithium replenishing effect of the secondary battery, the total mass percentage x% of the lithium replenishing agent in at least two active layers is in a range of 3% to 20%.

[0096] In the above 3% to 20%, the values ​​include the minimum and maximum values ​​of the range, and 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 supplement agent in the layer is defined as yi, the mass percentage of the lithium supplement agent in the layer = (mass of the lithium supplement agent in each active layer ÷ total mass of each active layer) * 100%, the mass percentage of the lithium supplement agent in the second active layer is y(i+1), where i ≥ 1, the mass percentage of the lithium supplement 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 the lithium supplement agent in the layer refers to the mass percentage of the lithium supplement agent in each active layer of the cathode electrode. For example, the cathode electrode has two active layers, active layer A (active layer mass is 100g, lithium supplement agent 6g) and active layer B (active layer mass is 100g, lithium supplement agent 3g), then the mass percentage y1 of the lithium supplement agent in the active layer A is (6g / 100g)*100%=6%; then the mass percentage y2 of the lithium supplement agent in the active layer B is (3g / 100g)*100%=3%.

[0099] At least two active layers are arranged sequentially from the current collector to the active layer away from the current collector. The mass percentage of the lithium supplement agent in the sequentially arranged active layers is distributed in a gradient, that is, the mass percentage of the lithium supplement agent in each layer decreases from the current collector to the active layer away from the current collector. In this way, the mass percentage of the lithium supplement agent in the active layer close to the current collector is greater than the mass percentage of the lithium supplement agent in the active layer away from the current collector, which helps to alleviate the problem of side reactions caused by contact between the lithium supplement agent and the electrolyte. It can be understood that the farther the active layer is from the current collector, the closer it is to the surface of the coating, and the greater the probability of contact with the electrolyte. Different lithium supplement agents are added to active layers with different risks of electrolyte contact to improve lithium supplement performance while reducing the risk of contact between the lithium supplement agent and the electrolyte, thereby improving battery performance.

[0100] In adjacent active layers, the first active layer is arranged close to the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector. The mass percentage of the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher 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 replenisher in the first active layer and the mass percentage y(i+1) of the lithium replenisher in the second active layer is 3% to 40%, where i ≥ 1. This indicates that the mass percentages of the lithium replenisher in the two adjacent active layers are different. The mass percentage difference between the two adjacent active layers can be 3% to 40%, for example, 3%, 5%, 7%, 10%, 15%, 18%, 20%, 25%, 27%, 30%, 35%, 40%, etc., and ranges between any two of the above values.

[0102] In one embodiment, at least two active layers are defined, including active layer A and active layer B, arranged in sequence from close to the current collector to far away from the current collector, and 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 that are arranged on the current collector 10. In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are defined, and the A-layer active layer and the B-layer active layer are sequentially arranged from close to the current collector to away from the current collector. The mass percentage y1 of the lithium replenisher in the A-layer active layer ranges from 4.5% to 40%.

[0104] In the above 4.5% to 40%, the values ​​include the minimum and maximum values ​​of the range, as well as every value between such 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 replenisher in the B active layer ranges from 0% to 18.5%; and / or, at least two active layers are defined as being sequentially arranged from close to the current collector to far away from the current collector, including an A active layer, a B active layer, and a C active layer, and the mass percentage y3 of the lithium replenisher in the C active layer ranges from 0% to 17%.

[0106] In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are defined, including an A layer active layer and a B layer active layer, which are arranged in sequence from close to the current collector to far away from the current collector. The mass percentage y2 of the lithium replenisher in the B layer active layer ranges from 0% to 18.5%.

[0107] In order to improve the lithium replenishment performance of the secondary battery, at least two active layers are arranged in sequence from the direction close to the current collector to the direction away from the current collector, and the mass percentage y3 of the lithium replenisher in the active layer C ranges from 0% to 17%.

[0108] like Figure 3 As shown, at least two active layers are defined, with active layer A 20, active layer B 30, and active layer C 40 arranged in order from closest to the current collector to furthest from the current collector. Active layer A is closest to the current collector, and the mass percentage y1 of the lithium replenisher in active layer A is higher than that in the other active layers. The mass percentage y1 of the lithium replenisher in active layer A ranges from 4.5% to 40%, for example, 4.5%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, and the like, as well as values ​​ranging between any two of the above values. The mass percentage y2 of the lithium replenisher in active layer B ranges from 0% to 18.5%, for example, 0%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 16%, 17%, 18%, 18.5%, and the like, as well as values ​​ranging between any two of the above values. The mass percentage y3 of the lithium supplement in the active layer C ranges from 0% to 17%, for example, and can be 0%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 16%, 17%, and the like, as well as values ​​between any two of the aforementioned 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 supplement 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, 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. In other words, when selecting a lithium supplement agent, one can choose the lithium supplement agents listed above or other types.

[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 agent is used to ensure that the electrode has good charge and discharge performance. A certain amount of conductive material is usually added during the production of the electrode. It collects microcurrents between the active materials and between the active materials and the current collector to reduce the contact resistance of the electrode and accelerate the movement rate of electrons. At the same time, it can also effectively increase 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 therefore address the poor conductivity of the lithium supplement, 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. It is understood that as the mass percentage of the lithium supplement in the active layer increases, the mass percentage of the conductive agent in that layer also increases, thereby addressing the poor conductivity of the lithium supplement.

[0114] For example, in one embodiment, the lithium supplement agent in the active layer close to the current collector has poor conductivity and larger particles. Increasing the mass percentage of the conductive agent in this layer is beneficial to reducing the cathode impedance and improving the performance of the battery.

[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 = (mass of all conductive agents in each active layer ÷ total mass of each active layer) * 100%, and the total mass percentage of the conductive agent Q% ranges from 1% to 10%.

[0116] The mass of all conductive agents in each active layer refers to the sum of the masses of the conductive agents in each active layer of the cathode plate. For example, if the cathode plate has two active layers, active layer A (active layer mass is 100g, conductive agent is 3g) and active layer B (active layer mass is 100g, conductive agent is 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. For example, for the above-mentioned 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] In order 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%. It can be understood that the coating includes each active layer.

[0119] In the above 1% to 10%, the values ​​include the minimum and maximum values ​​of the range, as well as every value between such 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, the mass percentage of the conductive agent in the layer = (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 the layer refers to the mass percentage of the conductive agent in each active layer of the cathode electrode. For example, 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 q1 of the conductive agent in the active layer A is (4g / 100g)*100%=4%; then the mass percentage q2 of the conductive agent in the active layer B is (2g / 100g)*100%=2%.

[0122] As the mass percentage of the lithium replenisher in adjacent active layers is distributed in a gradient, the mass percentage of the conductive agent in adjacent active layers is also distributed in a gradient. In the adjacent active layers, the first active layer is arranged close to the current collector, and the second active layer is arranged away from the current collector. The mass percentage of the lithium replenisher in the first active layer is greater than the mass percentage of the lithium replenisher in the second active layer. Then, 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. The difference in the mass percentage of the conductive agent in the two adjacent active layers is 1%≤b≤5%.

[0123] In the above 1%-5%, the values ​​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%, etc., as well as the range values ​​between any two of the above point values.

[0124] In one embodiment, at least two active layers are defined, including an A active layer and a B active layer arranged in sequence from close to the current collector to far away from the current collector; the mass percentage q1 of the conductive agent in the A active layer ranges from 1% to 12.5%.

[0125] In order to improve the conductivity of the active layer and reduce the impedance, at least two active layers are defined, including an A layer active layer and a B layer active layer, arranged in sequence from close to the current collector to away from the current collector; the mass percentage q1 of the conductive agent in the A layer active layer ranges from 1% to 12.5%.

[0126] In the above-mentioned 1% to 12.5%, the values ​​include the minimum and maximum values ​​of the range, as well as every value between such 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-mentioned point values.

[0127] In one embodiment, the mass percentage q2 of the conductive agent in the B active layer is in a range of 0.5% to 9.5%; and / or, at least two active layers are defined, which are sequentially arranged from close to the current collector to far away from the current collector, including the A active layer, the B active layer and the C active layer, and the mass percentage q3 of the lithium replenisher in the C active layer is in a range of 0.5% to 9%.

[0128] In order to improve the conductivity of the active layer, at least two active layers are defined, including an A layer active layer and a B layer active layer, arranged in sequence from close to the current collector to far away from the current collector; the mass percentage q2 of the conductive agent in the B layer active layer ranges from 0.5% to 9.5%.

[0129] In order to improve the conductivity of the active layer, at least two active layers are defined, which are arranged in sequence from close to the current collector to far away from the current collector, and the mass percentage q3 of the lithium supplement agent in the active layer C is in the range of 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 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, the conductive agent mentioned in this application can be selected, or other types of conductive agents can be selected.

[0132] In one embodiment, the volume average particle size Dv50 of the lithium supplement is in a range of 100 nm to 20 μm.

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

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

[0135] To improve the poor conductivity of the lithium supplement, the volume average particle size Dv50 of the lithium supplement is in the range of 100 nm to 20 μm. It is understood that the volume average particle size Dv50 of the lithium supplement in the above range can improve the conductivity of the active layer.

[0136] In the above-mentioned 100nm to 20μm, the values ​​include the minimum and maximum values ​​of the range, as well as every value between such 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-mentioned point values.

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

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

[0139] Porosity test: prepare mercury liquid and a pressure gauge, pour a certain amount of mercury liquid into the material; use the pressure gauge to measure the pressure of the mercury liquid, calculate the volume of the mercury liquid, use the density of mercury and the pressure measured by the pressure gauge to calculate the volume of the mercury liquid, calculate the porosity, and use the ratio of the volume of the mercury liquid to the volume of the material to calculate the porosity.

[0140] The porosity of the active layer closest to the current collector is lower than that of the active layer further away. This reduces the probability of electrolyte infiltration into the active layer near the current collector, minimizing side reactions between the electrolyte and the lithium supplement in this layer. To this end, 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 further away from the current collector facilitates lithium ion transport and improves electrode dynamics.

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

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

[0143] In order to improve the lithium replenishing effect of the coating, in at least two active layers, the total porosity of the active layer is defined as p, and the range of the total porosity p of the active layer is 10% to 40%.

[0144] In one embodiment, 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. The porosity of the first active layer is n(i), where 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 plate 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., and the range between any two of the above points.

[0146] The porosity of each active layer decreases as it approaches the current collector. This reduces the probability of contact between the lithium supplement and the electrolyte in the active layer near the current collector, improving battery performance. If the first active layer is closer to the current collector and the second active layer is farther away, the porosity of the first active layer is lower than that of the second active layer. The porosity difference between adjacent active layers is 5% ≤ c ≤ 10%.

[0147] In one embodiment, at least two active layers are defined, including an A active layer and a B active layer, arranged in sequence from close to the current collector to far away from the current collector. The porosity n1 of the A active layer ranges from 10% to 35%.

[0148] The active layer A is closest to the current collector, and 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., and the range value between any two of the above point values.

[0149] To improve the lithium replenishment performance of the lithium replenisher, at least two active layers are defined, including an active layer A and an active layer B, arranged in order from closest to the current collector to further away from the current collector. The porosity n1 of the active layer A ranges from 10% to 35%. It is understood that the lithium replenisher requires an electrolyte to transport lithium ions during the lithium replenishment process. Therefore, the porosity n1 of the active layer A ranges from 10% to 35%.

[0150] In one embodiment, the porosity n2 of the B-layer active layer is in a range of 15% to 35%; and / or, at least two active layers are defined as being sequentially arranged from close to the current collector to far away from the current collector, including an A-layer active layer, a B-layer active layer and a C-layer active layer, and the porosity n3 of the C-layer active layer is in a range of 20% to 40%.

[0151] In order to improve the lithium replenishing performance of the lithium replenishing agent, at least two active layers are defined, including an A layer active layer and a B layer active layer, which are arranged in sequence from close to the current collector to far away from the current collector. The porosity n2 of the B layer active layer ranges from 15% to 35%.

[0152] In order to improve the lithium replenishment performance of the lithium replenisher, at least two active layers are defined, including an A layer active layer, a B layer active layer and a C layer active layer, which are arranged in sequence from close to the current collector to far away from the current collector. The porosity n3 of the C layer active layer 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%, and the total mass percentage of the cathode material = (the mass of all cathode materials in each active layer ÷ the total mass of each active layer) * 100%. The total mass percentage of the cathode material W% ranges from 70% to 97%.

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

[0155] In order to improve the energy density of the secondary battery, in at least two active layers, the total mass percentage of the cathode material is defined as W%, and the total mass percentage W% of the cathode material ranges from 70% to 97%.

[0156] In the above-mentioned 70% to 97%, the values ​​include the minimum and maximum values ​​of the range, and every value between such 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-mentioned point values.

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

[0158] In two adjacent active layers, the mass percentage of the lithium supplement agent in the active layer close to the current collector is greater than the mass percentage of the lithium supplement agent in the active layer far from the current collector. In this way, the probability of contact between the lithium supplement agent in the active layer close to the current collector and the electrolyte is reduced, and the risk of side reactions caused by the contact between the lithium supplement agent and the electrolyte is reduced.

[0159] The present application provides a battery comprising: a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet is a cathode sheet as described above or a cathode sheet obtained by the method for preparing a cathode sheet as described above. Because the cathode sheet employs all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and no further description is given here.

[0160] Batteries using the aforementioned cathode plate have improved service life. It is understood that batteries include battery cells, battery modules, and battery packs. When the battery is a single cell, the single cell includes the aforementioned cathode plate; when the battery is a battery module, the module includes the aforementioned cathode plate; and when the battery is a battery pack, the pack includes the aforementioned cathode plate.

[0161] The present application provides an electrical device including the above-mentioned battery. Since the battery adopts all the technical solutions of all the above-mentioned embodiments, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be described in detail here.

[0162] The performance of the electrical equipment using the battery is improved.

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

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

[0165] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery's charge and discharge process, active ions are embedded in and released from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is located between the positive and negative electrodes, primarily preventing a short circuit between the positive and negative electrodes while allowing ions to pass through. The separator is the separator described above in this application.

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

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

[0168] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material 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 adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

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

[0171] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of 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 the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

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

[0174] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material 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 for a battery that is well known in the art. 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional 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 further 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 layer may further include a conductive agent, which 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 layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0180] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0181] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0182] In some embodiments, the electrolyte is an electrolyte solution, which 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

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

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

[0186] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

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

[0188] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0189] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0191] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 4 The secondary battery 5 is a square structure as an example.

[0192] In some embodiments, reference Figure 5, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

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

[0194] Figure 6 4 is an example of a battery module. Figure 6 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

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

[0196] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0197] Figure 7 and Figure 8 The battery pack 1 is used as an example. Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0198] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but is not limited thereto.

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

[0200] Figure 9 This is an example of an electric device. This device is 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, a battery pack or battery module can be used.

[0201] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0202] Example

[0203] Cathode electrode preparation

[0204] The cathode material, lithium supplement, conductive agent, and binder are mixed uniformly in different mass ratios. N-methylpyrrolidone (NMP) is then added as a solvent and stirred in a vacuum mixer until the mixture is uniform, thereby obtaining a cathode active slurry. The different cathode active slurries are then uniformly coated on the current collector, dried, and cold-pressed to obtain the cathode electrode sheet.

[0205] Anode plate preparation

[0206] The active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener carbon methyl cellulose sodium (CMC) are fully stirred and mixed in a deionized water solvent system in a certain weight ratio (such as 96.5:0.7:1.8:1), and then coated on a current collector (such as copper foil), dried, and cold pressed to obtain an anode electrode.

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

[0208] Preparation of electrolyte

[0209] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvent ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1 / 1, LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain 1M LiPF6 to obtain an 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 battery cell, wherein the separator is located between the positive and negative electrode sheets to serve as an isolation. After shaping, the battery cell is vacuum-baked for 24 hours to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The battery cell undergoes the following steps: standing, 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, the conductive agent carbon black, the binder polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), and the lithium supplement Li5FeO4 were stirred and mixed 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 slurry

[0216] The nickel-cobalt-manganese (NCM) ternary material NCM523, the conductive agent carbon black, the binder polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), and the lithium supplement Li5FeO4 are stirred and mixed 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 evenly coated on the current collector and dried at 95°C-115°C to form the first active layer. The second layer of slurry is then coated on top of the first active layer, dried at 95°C-115°C, cold pressed (at 5T pressure), and slit to form the cathode electrode. The first active layer of the cathode electrode comprises 10% lithium supplement Li5FeO4 and 3% conductive carbon. The second active layer comprises 0% lithium supplement Li5FeO4 and 1% conductive carbon black, with a coating weight ratio of 5:5.

[0218] Example 2

[0219] On the basis of Example 1, the ratio of each raw material was adjusted to obtain that the lithium replenisher Li5FeO4 accounted for 10% and the conductive carbon black accounted for 1wt% in the first active layer, the lithium replenisher Li5FeO4 accounted for 0% and the conductive carbon black accounted for 1% in the second active layer, and the coating weight ratio of the two layers was 5:5.

[0220] Example 3

[0221] Based on Example 1, the ratio of each raw material was adjusted to obtain a lithium supplement agent Li5FeO4 accounting for 10% and a conductive carbon black accounting for 3wt% in the first active layer, and a lithium supplement agent Li5FeO4 accounting for 5% and a conductive carbon black accounting for 2% in the second active layer.

[0222] Example 4

[0223] On the basis of Example 3, the types of lithium supplement agent and conductive agent were changed.

[0224] Example 5

[0225] On the basis of Example 3, three active layers were prepared, in which the lithium replenisher Li5FeO4 accounted for 10% in the first active layer and the conductive carbon black accounted for 3wt%, the lithium replenisher Li5FeO4 accounted for 5% in the second active layer and the conductive carbon black accounted for 2%, and the lithium replenisher Li5FeO4 accounted for 3% in the third active layer and the conductive carbon black accounted for 1%.

[0226] Example 6

[0227] On the basis of Example 1, the ratio of each raw material was adjusted to obtain that the lithium supplement agent Li5FeO4 accounted for 4.5% and the conductive carbon black accounted for 1wt% in the first active layer, and the lithium supplement agent Li5FeO4 accounted for 1.5% and the conductive carbon black accounted for 0.5% in the second active layer.

[0228] Example 7

[0229] On the basis of Example 3, three active layers were prepared, in which the lithium replenisher Li5FeO4 accounted for 40% in the first active layer and the conductive carbon black accounted for 12.5wt%; the lithium replenisher Li5FeO4 accounted for 18.5% in the second active layer and the conductive carbon black accounted for 9.5%; and the lithium replenisher Li5FeO4 accounted for 17% in the third active layer and the conductive carbon black accounted for 9%.

[0230] Comparative Example 1

[0231] Based on Example 1, a single layer coating was performed, in which the lithium supplement Li5FeO4 accounted for 5% and the conductive agent accounted for 2%.

[0232] Table 1 Experimental parameters

[0233]

[0234] Table 2 Experimental parameters

[0235]

[0236] Performance Testing

[0237] Cycle life testing involved parallel testing of five battery cells from each of the aforementioned examples and comparative examples. Each cell was charged at room temperature at a 0.33C rate to a voltage of 4.3V, then discharged at a 0.33C rate to a voltage of 2.5V. The reversible capacity, C0, was measured. This charge and discharge cycle was repeated until the discharge capacity, Cn / C0, at a specific cycle, reached ≤80%. The total number of cycles was recorded as X-Cycle. 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 first charge capacity are calculated to calculate the first coulombic efficiency.

[0239] Table 3 Battery performance data

[0240] Serial number First effect 80% cycle number 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 above table, the mass percentage of the lithium supplement agent in the active layer close to the current collector is greater than the mass percentage of the lithium supplement agent in the active layer far from the current collector, which can improve the contact between the lithium supplement agent and the electrolyte, thereby improving the performance of the battery.

[0242] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's description and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A cathode electrode, characterized in that: The cathode electrode sheet comprises a current collector (10) and a coating region arranged on at least one side of the current collector (10), wherein the coating region comprises at least two active layers; The two adjacent active layers are defined as a first active layer (20) and a second active layer (30); The first active layer (20) is arranged on the current collector (10), the second active layer (30) is arranged on a side of the first active layer (20) away from the current collector (10), and the mass percentage of the lithium replenisher in the first active layer (20) is greater than the mass percentage of the lithium replenisher in the second active layer (30).

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

3. The cathode electrode according to claim 1 or 2, characterized in that: The mass percentage of the lithium supplement in the layer is defined as yi, the mass percentage of the lithium supplement in the layer = (mass of the lithium supplement in each active layer ÷ total mass of each active layer) * 100%, the mass percentage of the lithium supplement in the second active layer is y(i+1), where i≥1, the mass percentage of the lithium supplement in the first active layer is y(i), then y(i)-y(i+1)=a, where 3%≤a≤40%.

4. The cathode electrode according to any one of claims 1 to 3, characterized in that: The at least two active layers are defined as an A layer active layer and a B layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the mass percentage y1 of the lithium supplement in the A layer active layer ranges from 4.5% to 40%.

5. The cathode electrode according to claim 4, characterized in that: The mass percentage y2 of the lithium supplement in the B active layer ranges from 0% to 18.5%; And / or, the at least two active layers are defined as an A layer active layer, a B layer active layer and a C layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the mass percentage y3 of the lithium supplement agent in the C layer active layer ranges from 0% to 17%.

6. The cathode electrode according to any one of claims 1 to 5, characterized in that: 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.

7. The cathode electrode according to any one of claims 1 to 6, characterized in that: 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.

8. The cathode electrode according to claim 7, 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 = (mass of all conductive agents in each active layer ÷ total mass of each active layer) * 100%, and the total mass percentage Q% of the conductive agent ranges from 1% to 10%.

9. The cathode electrode according to claim 8, characterized in that: The mass percentage of the conductive agent in the layer is defined as qi, the mass percentage of the conductive agent in the layer = (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%.

10. The cathode electrode according to claim 8 or 9, characterized in that: The at least two active layers are defined as an A-layer active layer and a B-layer active layer arranged in sequence from the direction close to the current collector to the direction far away from the current collector; The mass percentage q1 of the conductive agent in the A-layer active layer is in the range of 1% to 12.5%.

11. The cathode electrode according to claim 10, characterized in that: The mass percentage q2 of the conductive agent in the B active layer ranges from 0.5% to 9.5%; And / or, the at least two active layers are defined as an A-layer active layer, a B-layer active layer and a C-layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the mass percentage q3 of the lithium supplement agent in the C-layer active layer is in the range of 0.5% to 9%.

12. The cathode electrode according to any one of claims 7 to 11, characterized in that: The conductive agent includes at least one of graphite, carbon nanotubes, carbon nanofibers, carbon black and graphene.

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

14. The cathode electrode according to any one of claims 1 to 13, characterized in that: The porosity of the first active layer is smaller than the porosity of the second active layer.

15. The cathode electrode according to any one of claims 1 to 14, characterized in that: In the at least two active layers, the total porosity of the active layer is defined as p, the total porosity of the active layer = (volume of all pores in each active layer ÷ sum of volumes of each active layer) * 100%, and the range of the total porosity p of the active layer is 10% to 40%.

16. The cathode electrode according to claim 15, characterized in that: 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%.

17. The cathode electrode according to claim 16, characterized in that: The at least two active layers are defined as an A-layer active layer and a B-layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the porosity n1 of the A-layer active layer is in a range of 10% to 35%.

18. The cathode electrode according to claim 17, characterized in that: The porosity n2 of the B layer active layer ranges from 15% to 35%; And / or, the at least two active layers are defined as an A-layer active layer, a B-layer active layer and a C-layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the porosity n3 of the C-layer active layer is in a range of 20% to 40%.

19. The cathode electrode according to any one of claims 1 to 18, 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 total mass percentage W% of the cathode material ranges from 70% to 97%.

20. A method for preparing a cathode electrode, characterized in that: The following steps are involved: Coating at least two active layer slurries on a current collector, wherein the mass percentage of the lithium replenisher in one active layer disposed on the current collector is greater than the mass percentage of the lithium replenisher in one active layer disposed on a side away from the current collector; The cathode electrode is obtained after drying and cold pressing.

21. A battery, characterized in that: include: A negative electrode sheet, a positive electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet is a cathode electrode sheet as described in any one of claims 1 to 19 or a cathode electrode sheet obtained by the method for preparing a cathode electrode sheet as described in claim 20.

22. An electrical equipment, characterized in that: The electrical device comprises the battery according to claim 21.

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