Pole piece preform, pole piece and battery

Abstract

The application provides a pole piece preform, a pole piece and a battery to improve the technical problem of internal concentration polarization of the pole piece. The pole piece preform comprises a current collector, a first initial active material layer and a second initial active material layer which are sequentially stacked; the first initial active material layer is dispersed with a first pore-forming agent with a mass content of w1, and the average particle size of the first pore-forming agent is d1; the second initial active material layer is dispersed with a second pore-forming agent with a mass content of w2, and the average particle size of the second pore-forming agent is d2; wherein,

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, specifically to an electrode preform, an electrode, and a battery. Background Technology

[0002] With the continuous growth of demand in the power market, higher requirements are being placed on the energy density, fast charging, and cycle performance of lithium-ion batteries. To improve the energy density of lithium-ion batteries, high areal density and high compaction density are commonly used to enhance volume utilization. However, in actual manufacturing, increasing compaction density leads to reduced electrode porosity and poor electrolyte wettability, which is detrimental to the migration and diffusion of lithium ions within the electrode. This results in increased concentration polarization within the electrode and reduces the battery's cycle performance. Summary of the Invention

[0003] The embodiments of this application provide an electrode preform, an electrode, and a battery, which can improve the technical problem of concentration polarization inside the electrode.

[0004] In a first aspect, embodiments of this application provide an electrode preform, comprising a current collector, a first initial active material layer, and a second initial active material layer stacked sequentially; the first initial active material layer disperses a first pore-forming agent with a mass content of w1 and an average particle size of d1; the second initial active material layer disperses a second pore-forming agent with a mass content of w2 and an average particle size of d2.

[0005] in,

[0006] In one embodiment, the first pore-forming agent and the second pore-forming agent have the same composition, and both the first pore-forming agent and the second pore-forming agent contain polymethyl methacrylate.

[0007] In one embodiment, d1 is 1 μm to 50 μm.

[0008] In one embodiment, d2 is 1 μm to 50 μm.

[0009] In one embodiment, the thickness of the first initial active material layer is 10 μm to 300 μm.

[0010] In one embodiment, the thickness of the second initial active material layer is 10 μm to 300 μm.

[0011] In one embodiment, the first initial active material layer further includes a first active material, a first binder, and a first conductive agent; the second initial active material layer further includes a second active material, a second binder, and a second conductive agent.

[0012] In one embodiment, in the first initial active material layer, the content of the first active material is 90wt% to 97wt%, the content of the first binder is 2wt% to 5wt%, the content of the first conductive agent is 0.5wt% to 7.5wt%, and the content of the first pore-forming agent is 0.1wt% to 2wt%.

[0013] In one embodiment, in the second initial active material layer, the content of the second active material is 93wt% to 98wt%, the content of the second binder is 1wt% to 5wt%, the content of the second conductive agent is 0.5wt% to 5wt%, and the content of the second pore-forming agent is 0.1wt% to 2wt%.

[0014] In one embodiment, the content of the first active material in the first initial active material layer is A1, and the content of the second active material in the second initial active material layer is A2, wherein 0.5wt% ≤ A2 - A1 ≤ 5wt%.

[0015] In one embodiment, the content of the first binder in the first initial active material layer is B1, and the content of the second binder in the second initial active material layer is B2, wherein 0.5wt% ≤ B1 - B2 ≤ 3wt%.

[0016] In one embodiment, the content of the first conductive agent in the first initial active material layer is C1, and the content of the second conductive agent in the second initial active material layer is C2, wherein 0.5wt% ≤ C2 - C1 ≤ 3wt%.

[0017] In one embodiment, both the first active material and the second active material comprise lithium manganese iron phosphate, wherein the chemical formula of lithium manganese iron phosphate is: LiFe x Mn y PO4, 0<x<1, 0<y<1.

[0018] In one embodiment, the first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, polyvinylidene fluoride, and polyvinyl alcohol.

[0019] In one embodiment, the first conductive agent and the second conductive agent each independently comprise at least one of conductive carbon black, carbon nanotubes, mesoporous carbon materials, and vapor-grown carbon fibers.

[0020] In one embodiment, the electrode preform further includes an adhesive layer located between the first initial active material layer and the second initial active material layer; the adhesive layer includes a third adhesive and a third conductive agent.

[0021] In one embodiment, the adhesive layer further includes a first lithium supplement agent, and the third adhesive includes a polyurethane adhesive.

[0022] In one embodiment, in the adhesive layer, the content of the third adhesive is 50wt% to 80wt%, the content of the third conductive agent is 15wt% to 40wt%, and the content of the first lithium supplement is 1wt% to 10wt%.

[0023] In one embodiment, the third conductive agent comprises conductive carbon black and vapor-grown carbon fibers, wherein the content of the conductive carbon black in the third conductive agent is 80wt% to 90wt%.

[0024] In one embodiment, the thickness of the adhesive layer is 1 μm to 10 μm.

[0025] In one embodiment, the third binder further includes polyvinylidene fluoride; the content of polyvinylidene fluoride in the third binder is 30 wt% to 70 wt%; and / or, the first lithium supplementer includes lithium oxalate.

[0026] In one embodiment, the current collector includes a stacked metal layer and a lithium replenishment layer, the lithium replenishment layer being located between the metal layer and the first initial active material layer, and the lithium replenishment layer including a fourth conductive agent, a fourth binder, and a second lithium replenishment agent.

[0027] In one embodiment, in the lithium replenishment layer, the content of the fourth conductive agent is 40wt% to 85wt%, the content of the fourth binder is 5wt% to 50wt%, and the content of the second lithium replenishment agent is 0.1wt% to 10wt%.

[0028] In one embodiment, the thickness of the lithium replenishment layer is 1 μm to 20 μm.

[0029] In one embodiment, the second lithium supplement includes at least one of lithium carbonate, lithium squartz, and lithium oxalate.

[0030] In one embodiment, the electrode preform further includes an insulating layer that covers the sides of the current collector, the first initial active material layer, and the second initial active material layer and extends to the edge region of the second initial active material layer on the side surface opposite to the current collector.

[0031] In one embodiment, the insulating layer comprises 5 wt% to 65 wt% of a fifth adhesive and 35 wt% to 95 wt% of an insulating material.

[0032] In one embodiment, the thickness of the insulating layer is 1 μm to 40 μm.

[0033] In one embodiment, the insulating layer extends to a length of 1 mm to 10 mm, and the width of the insulating layer overlapping the second initial active material layer on the side of the second initial active material layer opposite to the current collector is 1 mm to 3 mm.

[0034] Secondly, embodiments of this application provide an electrode sheet, which is obtained by removing the first pore-forming agent and the second pore-forming agent from the aforementioned electrode sheet preform, wherein the first initial active material layer is formed as a first active material layer, the second initial active material layer is formed as a second active material layer, and the porosity of the first active material layer is greater than that of the second active material layer.

[0035] Thirdly, embodiments of this application provide a battery including the aforementioned electrode.

[0036] The beneficial effects of the embodiments of this application are as follows:

[0037] In the embodiments of this application, since a first pore-forming agent is dispersed in the first initial active material layer and a second pore-forming agent is dispersed in the second initial active material layer, pores are formed in both the first active material layer obtained after removing the first pore-forming agent from the first initial active material layer and the second active material layer obtained after removing the second pore-forming agent from the second initial active material layer. These pores can reduce the resistance to lithium ion insertion / extraction and transport in the first and second active material layers, thereby improving the lithium ion transport efficiency and kinetic performance.

[0038] Furthermore, since the first initial active material layer is closer to the current collector than the second initial active material layer, by making the product of the mass content of the first pore-forming agent and the average particle size of the first pore-forming agent in the first initial active material layer greater than the product of the mass content of the second pore-forming agent and the average particle size of the second pore-forming agent in the second initial active material layer, the porosity of the first active material layer is greater than that of the second active material layer. This reduces the resistance to electrolyte transport in the second active material layer, improves the wetting effect of the electrolyte on the second active material layer, reduces the polarization effect in the electrode, optimizes the interfacial reaction between the electrolyte and the active material in the electrode, and improves the energy density and cycle stability of the battery. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a cross-sectional structural schematic diagram of the electrode preform provided in an embodiment of this application;

[0041] Figure 2 This is a cross-sectional structural diagram of the electrode provided in an embodiment of this application;

[0042] Figure 3 This is a schematic diagram of the electrode structure provided in an embodiment of this application.

[0043] Figure label:

[0044] 1. Electrode preform;

[0045] 11. Current collector; 111. Metal layer; 112. Lithium replenishment layer;

[0046] 12. First initial active material layer;

[0047] 13. Adhesive layer;

[0048] 14. Second initial active material layer;

[0049] 15. Insulation layer;

[0050] 10. Electrode; 101. First active material layer; 102. Second active material layer;

[0051] 100. Battery. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] Furthermore, it should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operation, specifically the directions shown in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0054] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0055] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0056] The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0057] In the description of the embodiments of this application, the words "example" or "for example" are used to indicate exemplification, illustration, or description. Any embodiment or design described as "example" or "for example" in the embodiments of this application is not to be construed as being more preferred or having more advantages than another embodiment or design. The use of the words "example" or "for example" is intended to present relative concepts in a clear manner.

[0058] To facilitate understanding of the present application, the spline curves and arrows used in the reference numerals in the accompanying drawings are explained below: spline curves without arrows indicate solid parts, that is, parts with solid structures; spline curves with arrows indicate virtual parts, that is, parts without solid structures.

[0059] Firstly, please see Figure 1 and Figure 2 This application provides an electrode preform 1, which can be made into an electrode 10, and the electrode 10 can be directly applied to a battery 100.

[0060] Specifically, the electrode preform 1 includes a current collector 11, a first initial active material layer 12, and a second initial active material layer 14, which are stacked sequentially. Figure 1As can be seen, the first initial active material layer 12 is disposed on one side of the current collector 11, and the second initial active material layer 14 is disposed on the side of the first initial active material layer 12 away from the current collector 11. That is, the first initial active material layer 12 is closer to the current collector 11 than the second initial active material layer 14. It should be noted that the first initial active material layer 12 and the second initial active material layer 14 can be disposed on one side of the current collector 11, or the first initial active material layer 12 and the second initial active material layer 14 can be disposed on both opposite sides of the current collector 11.

[0061] Specifically, a first pore-forming agent is dispersed in the first initial active material layer 12, and a second pore-forming agent is dispersed in the second initial active material layer 14. The first and second pore-forming agents are added to the first and second initial active material layers 12 and 14, respectively. The first and second initial active material layers 12 and 14 can usually be post-processed to decompose the first and second pore-forming agents, thereby leaving pores inside the first and second initial active material layers 12 and 14. That is, the first initial active material layer 12 is formed into a first active material layer 101 with pores inside, and the second initial active material layer 14 is formed into a second active material layer 102 with pores inside. Then, the electrode preform 1 is formed into an electrode 10 that can be directly applied to the battery 100.

[0062] In the first initial active material layer 12, the mass content of the first pore-forming agent is w1, and the average particle size of the first pore-forming agent is d1. In the second initial active material layer 14, the mass content of the second pore-forming agent is w2, and the average particle size of the second pore-forming agent is d2. The mass content and average particle size of the first pore-forming agent in the first initial active material layer 12 and the mass content and average particle size of the second pore-forming agent in the second initial active material layer 14 satisfy the following relationship:

[0063]

[0064] As can be seen from the above relationship, the product of the mass content of the first pore-forming agent and the average particle size of the first pore-forming agent in the first initial active material layer 12 (i.e., w1d1) is 1 to 1.5 times the product of the mass content of the second pore-forming agent and the average particle size of the second pore-forming agent in the second initial active material layer 14 (i.e., w2d2). For example, the ratio of w1d1 to w2d2 can be 1, 1.1, 1.2, 1.3, 1.4, or 1.5. Generally, the difference between w1d1 and w2d2 should not be too large, otherwise it will lead to insufficient strength of the first active material layer 101 and a decrease in the energy density of the battery 100. For example, w1 = w2, d1 > d2; or w1 > w2, d1 = d2; or w1 > w2, d1 > d2.

[0065] In this embodiment, since a first pore-forming agent is dispersed in the first initial active material layer 12 and a second pore-forming agent is dispersed in the second initial active material layer 14, pores are formed in both the first active material layer 101 obtained after removing the first pore-forming agent from the first initial active material layer 12 and the second active material layer 102 obtained after removing the second pore-forming agent from the second initial active material layer 14. These pores can reduce the resistance to lithium ion insertion / extraction and transport in the first active material layer 101 and the second active material layer 102, thereby improving the lithium ion transport efficiency and kinetic performance.

[0066] Furthermore, since the first initial active material layer 12 is closer to the current collector 11 than the second initial active material layer 14, by making the product of the mass content of the first pore-forming agent in the first initial active material layer 12 and the average particle size of the first pore-forming agent greater than the product of the mass content of the second pore-forming agent in the second initial active material layer 14 and the average particle size of the second pore-forming agent, the porosity of the first active material layer 101 is greater than that of the second active material layer 102. This reduces the resistance of electrolyte transport in the second active material layer 102, improves the wetting effect of the electrolyte on the second active material layer 102, reduces the polarization effect in the electrode 10, optimizes the interfacial reaction between the electrolyte and the active material in the electrode 10, and improves the energy density and cycle stability of the battery 100.

[0067] Typically, the thickness of the first initial active material layer 12 of the electrode preform 1 determines the thickness of the first active material layer 101 of the electrode 10, and the thickness of the second initial active material layer 14 of the electrode preform 1 determines the thickness of the second active material layer 102 of the electrode 10.

[0068] In conventional electrodes, the thickness of the active material layer should not be too large, otherwise it will lead to an increase in concentration polarization inside the electrode. However, in the embodiments of this application, by adjusting the content and particle size of the first pore-forming agent in the first initial active material layer 12, and the content and particle size of the second pore-forming agent in the second initial active material layer 14, the porosity of the first active material layer 101 can be made greater than that of the second active material layer 102. This allows for a further increase in the thickness of the first initial active material layer 12 and the second initial active material layer 14, thereby increasing the thickness of the first active material layer 101 and the second active material layer 102 and improving the energy density of the battery 100.

[0069] In some embodiments, the thickness of the first initial active material layer 12 is 10 μm to 300 μm. As examples, the thickness of the first initial active material layer 12 is 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, or 300 μm. Optionally, the thickness of the first initial active material layer 12 is 100 μm to 300 μm. Increasing the thickness of the first initial active material layer 12 is beneficial to increasing the energy density of the battery 100.

[0070] In some embodiments, the thickness of the second initial active material layer 14 is 10 μm to 300 μm. As examples, the thickness of the second initial active material layer 14 is 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, or 300 μm. Optionally, the thickness of the second initial active material layer 14 is 100 μm to 300 μm. Increasing the thickness of the second initial active material layer 14 is beneficial to increasing the energy density of the battery 100.

[0071] In some embodiments, the thickness of the first initial active material layer 12 is not equal to the thickness of the second initial active material layer 14. Of course, in other embodiments, the thickness of the first initial active material layer 12 and the thickness of the second initial active material layer 14 may also be equal.

[0072] In some embodiments, the first pore-forming agent and the second pore-forming agent have the same composition. This facilitates the removal of the first pore-forming agent in the first initial active material layer 12 and the second pore-forming agent in the second initial active material layer 14 through the same post-processing to obtain the first active material layer 101 and the second active material layer 102, reducing the manufacturing difficulty of the electrode 10, and also facilitating the control of the porosity in the first active material layer 101 and the second active material layer 102. Of course, in other embodiments, the compositions of the first pore-forming agent and the second pore-forming agent may be different.

[0073] In some embodiments, the first pore-forming agent and the second pore-forming agent each independently comprise at least one of paraffin microspheres, refined naphthalene, polyethylene oxide, and polymethyl methacrylate (PMMA). Different pore-forming agents typically require different post-treatment processes. For example, some pore-forming agents can be removed by heat treatment to melt or decompose them into gas; while others can be removed by extraction. As an example, the first and second pore-forming agents are the same, and both contain PMMA. PMMA can be removed by extraction.

[0074] In some embodiments, d1 is 1 μm to 50 μm, meaning the average particle size of the first pore-forming agent is 1 μm to 50 μm. The average particle size of the first pore-forming agent affects the distribution and size of pores in the first active material layer 101. With the same content of the first pore-forming agent, a larger average particle size results in larger pore sizes, fewer pores, and increased distance between pores in the first active material layer 101, thus decreasing continuity. Conversely, a smaller average particle size results in smaller pore sizes, more pores, and decreased distance between pores in the first active material layer 101, thus increasing continuity. For example, d1 can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm.

[0075] In some embodiments, d2 is 1 μm to 50 μm, meaning the average particle size of the second pore-forming agent is 1 μm to 50 μm. The average particle size of the second pore-forming agent affects the distribution and size of pores in the second active material layer 102. With the same content of the second pore-forming agent, a larger average particle size results in larger pore sizes, fewer pores, and increased distance between pores in the second active material layer 102, thus reducing continuity. Conversely, a smaller average particle size results in smaller pore sizes, more pores, and decreased distance between pores in the second active material layer 102, thus increasing continuity. As an example, d2 can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm.

[0076] In some embodiments, the first initial active material layer 12 further includes a first active material, a first binder, and a first conductive agent; the second initial active material layer 14 further includes a second active material, a second binder, and a second conductive agent. It is understood that the first pore-forming agent is dispersed in the first active material, the first binder, and the first conductive agent, and the first pore-forming agent is dispersed in the second active material, the second binder, and the second conductive agent. It should be noted that the first active material and the second active material can be the same or different; the first binder and the second binder can be the same or different; the first conductive agent and the second conductive agent can be the same or different. However, the first active material and the second active material are of the same type; for example, both the first active material and the second active material are positive electrode active materials, or both the first active material and the second active material are negative electrode active materials.

[0077] In some embodiments, the first active material and the second active material are the same, and both the first active material and the second active material are positive electrode active materials. In this way, the obtained electrode preform 1 is a positive electrode preform, and the positive electrode preform can be made into a positive electrode.

[0078] In some embodiments, both the first and second active materials comprise lithium manganese iron phosphate. Lithium manganese iron phosphate has the characteristics of high energy density, good stability, and low cost, which is beneficial for improving the overall performance of battery 100. Specifically, the chemical formula of lithium manganese iron phosphate is: LiFe... x Mn y PO4, 0 < x < 1, 0 < y < 1. For example, x is 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.999; y is 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.999.

[0079] In some embodiments, the first binder includes at least one selected from polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA). Independently, the second binder includes at least one selected from polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA).

[0080] In some embodiments, the first conductive agent includes at least one selected from conductive carbon black, carbon nanotubes (CNTs), mesoporous carbon materials, and vapor-grown carbon fibers (VGCF). Independently, the second conductive agent includes at least one selected from conductive carbon black, carbon nanotubes, mesoporous carbon materials, and vapor-grown carbon fibers. As an example, the conductive carbon black includes at least one selected from acetylene black, Super P (SP), and Ketjen black. As an example, the carbon nanotubes include at least one selected from single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). As an example, the mesoporous carbon material includes the ordered mesoporous carbon material CMK-3.

[0081] In some embodiments, in the first initial active material layer 12, the content of the first active material is 90wt% to 97wt%, the content of the first binder is 2wt% to 5wt%, the content of the first conductive agent is 0.5wt% to 7.5wt%, and the content of the first pore-forming agent (i.e., w1) is 0.1wt% to 2wt%. As an example, the content of the first active material is 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, or 97wt%; the content of the first binder is 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%; and the content of the first conductive agent is 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2 ... 0.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, or 7.5wt%; the content of the first pore-forming agent is 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, or 2wt%.

[0082] In some embodiments, in the second initial active material layer 14, the content of the second active material is 93wt% to 98wt%, the content of the second binder is 1wt% to 5wt%, the content of the second conductive agent is 0.5wt% to 5wt%, and the content of the second pore-forming agent (i.e., w2) is 0.1wt% to 2wt%. As an example, the content of the second active material is 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, or 98wt%; the content of the second binder is 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%; the content of the second conductive agent is 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%; and the content of the second pore-forming agent is 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, or 2wt%.

[0083] In some embodiments, the content of the first active material in the first initial active material layer 12 is A1, and the content of the second active material in the second initial active material layer 14 is A2, wherein 0.5wt% ≤ A2 - A1 ≤ 5wt%. That is, the content of the second active material in the second initial active material layer 14 is higher than that in the first initial active material layer 12, which facilitates improving the energy density of the battery 100. As an example, the difference between A2 and A1 is 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5wt%.

[0084] In some embodiments, the content of the first binder in the first initial active material layer 12 is B1, and the content of the second binder in the second initial active material layer 14 is B2, wherein 0.5 wt% ≤ B1 - B2 ≤ 3 wt%. That is, the content of the second binder in the second initial active material layer 14 is lower than that in the first initial active material layer 12. As an example, the difference between B1 and B2 is 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3 wt%.

[0085] In some embodiments, the content of the first conductive agent in the first initial active material layer 12 is C1, and the content of the second conductive agent in the second initial active material layer 14 is C2, wherein 0.5wt% ≤ C2 - C1 ≤ 3wt%. That is, the content of the second conductive agent in the second initial active material layer 14 is higher than that in the first initial active material layer 12. This facilitates the improvement of the conductivity of the second active material layer 102, especially when the content of the second active material in the second initial active material layer 14 is also higher than the content of the first active material in the first initial active material layer 12. The second conductive agent and the second active material work together to improve the cycle performance of the battery 100. As an example, the difference between C2 and C1 is 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, or 3wt%.

[0086] In some embodiments, the electrode preform 1 further includes an adhesive layer 13 located between the first initial active material layer 12 and the second initial active material layer 14; the adhesive layer 13 includes a third adhesive and a third conductive agent. It is understood that since the electrode preform 1 includes the adhesive layer 13, the electrode 10 also includes the adhesive layer 13, located between the first active material layer 101 and the second active material layer 102 in the electrode 10.

[0087] Normally, during battery cycling, the electrolyte in battery 100 is consumed, leading to insufficient electrolyte and subsequent cycle failure. However, by providing an adhesive layer 13, which includes a third binder and a third conductive agent, the adhesive layer 13 not only has conductivity but also electrolyte absorption properties. This allows the adhesive layer 13 to absorb and store a portion of the electrolyte during battery manufacturing. Thus, in the later stages of battery cycling, the adhesive layer 13 can act as a secondary electrolyte supply source to continue replenishing the electrolyte to the first active material layer 101 and the second active material layer 102, delaying the occurrence of cycle failure in battery 100.

[0088] In some embodiments, the adhesive layer 13 further includes a first lithium replenishing agent, and the third adhesive includes a polyurethane-based adhesive. By adding the first lithium replenishing agent to the adhesive layer 13, the ion transport performance of the adhesive layer 13 can be effectively improved. Furthermore, the third adhesive includes a polyurethane-based adhesive, whose functional groups such as -C=O, -NH, and -COC- facilitate lithium-ion transport. This allows the first lithium replenishing agent in the adhesive layer 13 to replenish lithium ions to the first active material layer 101 and the second active material layer 102 on both sides of the adhesive layer 13, thereby improving the quality of the interface film between the active material and the electrolyte and enhancing the cycle performance of the battery 100. Additionally, by adding the first lithium replenishing agent to the adhesive layer 13, the lithium ions provided by the first lithium replenishing agent can be transported to the first active material layer 101 and the second active material layer 102 through the polyurethane-based adhesive. However, the gas generated by the decomposition of the first lithium replenishing agent does not easily escape from the adhesive layer 13, thus reducing the risk of the battery 100 bulging due to gas generation from the first lithium replenishing agent. In addition, the electrolyte usually contains ester solvents. Polyurethane binders have good affinity with ester solvents, which helps to improve the wettability of the electrolyte and promote the transport of the electrolyte within the electrode 10. Especially when the porosity of the second active material layer 102 is less than that of the first active material layer 101, the binder layer 13 can promote the rapid passage of the electrolyte through the second active material layer 102 and its migration to the first active material layer 101, thereby reducing concentration polarization within the electrode 10.

[0089] In some embodiments, the third binder further includes polyvinylidene fluoride (PVDF), and the PVDF content in the third binder is 30 wt% to 70 wt%. PVDF has good adhesion properties, providing strong adhesion and cohesion to the adhesive layer 13, allowing the first active material layer 101 and the second active material layer 102 to better bond with the adhesive layer 13, thereby improving the structural stability and integrity of the electrode 10. As an example, the PVDF content in the third binder is 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%.

[0090] In some embodiments, polyurethane adhesives include waterborne polyurethane adhesives (WUP).

[0091] In some embodiments, the third conductive agent includes conductive carbon black and vapor-grown carbon fibers, wherein the content of conductive carbon black in the third conductive agent is 80wt% to 90wt%. Conductive carbon black has good electron conduction and liquid retention capabilities, while vapor-grown carbon fibers facilitate lithium-ion transport. The two work together to ensure the transport of ions and electrons within the adhesive layer 13; simultaneously, increasing the content of conductive carbon black in the third conductive agent enhances the liquid storage capacity of the adhesive layer 13. As an example, the content of conductive carbon black in the third conductive agent is 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, or 90wt%.

[0092] In some embodiments, the first lithium supplement includes at least one of lithium carbonate, lithium squaric acid, and lithium oxalate. Optionally, the first lithium supplement includes lithium oxalate.

[0093] In some embodiments, the content of the third binder in the adhesive layer 13 is 50wt% to 80wt%, the content of the third conductive agent is 15wt% to 40wt%, and the content of the first lithium supplement is 1wt% to 10wt%. Typically, the third conductive agent can improve the conductivity of the adhesive layer 13, while the first lithium supplement can improve the ion transport capability of the adhesive layer 13. By controlling the content of the third binder, the third conductive agent, and the first lithium supplement in the adhesive layer 13, the adhesive layer 13 can possess both good ion and electron transport properties. As an example, in the adhesive layer 13, the content of the third adhesive is 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, or 80 wt%, the content of the third conductive agent is 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, and the content of the first lithium supplement is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0094] In some embodiments, the thickness of the adhesive layer 13 is 1 μm to 10 μm. The adhesive layer 13 should not be too thin, otherwise its liquid retention capacity will be insufficient; however, the adhesive layer 13 should not be too thick either, otherwise it will lead to a decrease in the energy density of the battery 100. As an example, the thickness of the adhesive layer 13 is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0095] In some embodiments, the current collector 11 includes a stacked metal layer 111 and a lithium replenishment layer 112. The lithium replenishment layer 112 is located between the metal layer 111 and the first initial active material layer 12. The lithium replenishment layer 112 includes a fourth conductive agent, a fourth binder, and a second lithium replenishing agent. The lithium replenishment layer 112 not only improves the bonding effect between the metal layer 111 and the first initial active material layer 12, but the second lithium replenishing agent in the lithium replenishment layer 112 can also replenish the lithium ions consumed by the formation of the interface film between the active material and the electrolyte.

[0096] In some embodiments, in the lithium replenishment layer 112, the content of the fourth conductive agent is 40wt% to 85wt%, the content of the fourth binder is 5wt% to 50wt%, and the content of the second lithium replenishment agent is 0.1wt% to 10wt%. As an example, the content of the fourth conductive agent is 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, or 85wt%, the content of the fourth binder is 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, or 50wt%, and the content of the second lithium replenishment agent is 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%.

[0097] In some embodiments, the thickness of the lithium replenishment layer 112 is 1 μm to 20 μm. As an example, the thickness of the lithium replenishment layer 112 is 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm.

[0098] In some embodiments, the fourth adhesive includes at least one of polyacrylic acid (PAA) and waterborne polyurethane adhesive (WUP).

[0099] In some embodiments, the second lithium supplement includes at least one of lithium carbonate, lithium squaric acid, and lithium oxalate.

[0100] In some embodiments, the fourth conductive agent includes at least one of conductive carbon black, carbon nanotubes (CNTs), mesoporous carbon materials, and vapor-grown carbon fibers (VGCF).

[0101] In some embodiments, the electrode preform 1 further includes an insulating layer 15 that covers the sides of the current collector 11, the first initial active material layer 12, and the second initial active material layer 14, and extends to the edge region of the second initial active material layer 14 facing away from the current collector 11. When the electrode preform 1 also includes an adhesive layer 13, the insulating layer 15 also covers the sides of the adhesive layer 13. That is, the insulating layer 15 covers the side region from the current collector 11 to the second initial active material layer 14, and the insulating layer 15 also covers a portion of the surface of the second initial active material layer 14, specifically the edge region of the second initial active material layer 14 facing away from the current collector 11, which is close to the side of the second initial active material layer 14.

[0102] Typically, the sides of the first initial active material layer 12 and the second initial active material layer 14 are looser than the middle structure of the first initial active material layer 12 and the second initial active material layer 14, which is prone to problems such as burrs and dust shedding. By setting an insulating layer 15, the burrs and dust on the sides of the first initial active material layer 12 and the second initial active material layer 14 can be covered, thereby improving the safety performance of the battery 100.

[0103] In some embodiments, the insulating layer 15 comprises 5 wt% to 65 wt% of a fifth adhesive and 35 wt% to 95 wt% of an insulating material. As an example, the content of the fifth adhesive in the insulating layer 15 is 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or 65 wt%. Optionally, the fifth adhesive comprises polyvinylidene fluoride, and the insulating material comprises a ceramic material.

[0104] In some embodiments, the thickness of the insulating layer 15 is 1 μm to 40 μm. As an example, the thickness of the insulating layer 15 is 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm.

[0105] In some embodiments, the insulating layer 15 extends to a length of 1 mm to 10 mm, and the width of the overlap between the insulating layer 15 and the second initial active material layer 14 on the side of the second initial active material layer 14 away from the current collector 11 is 1 mm to 3 mm. If the first side of the insulating layer 15 is located on the current collector 11, and the second side of the insulating layer 15 opposite to the first side is located on the second initial active material layer 14, then the length of the insulating layer 15 from the first side to the second side is the length of the insulating layer 15. As an example, the length of the insulating layer 15 is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm. A portion of the insulating layer 15 extends to the side of the second initial active material layer 14 away from the current collector 11, and this portion overlaps with the second initial active material layer 14. The width of this portion is the width of the overlap. As an example, the width of the overlap can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, or 3 mm.

[0106] Secondly, please see Figure 2 This application embodiment also provides an electrode 10, which is obtained by removing the first pore-forming agent and the second pore-forming agent from the aforementioned electrode preform 1. The first initial active material layer 12 is formed as the first active material layer 101, and the second initial active material layer 14 is formed as the second active material layer 102. The porosity of the first active material layer 101 is greater than that of the second active material layer 102. It can be understood that the electrode 10 includes a current collector 11, the first active material layer 101, and the second active material layer 102 stacked sequentially. That is, the difference between the electrode 10 and the aforementioned electrode preform 1 is that the electrode 10 does not contain or substantially does not contain the first pore-forming agent and the second pore-forming agent, and the original positions where the first pore-forming agent and the second pore-forming agent were present are formed into pores.

[0107] In some embodiments, when the electrode preform 1 further includes an adhesive layer 13, the electrode 10 also includes an adhesive layer 13, which is located between the first active material layer 101 and the second active material layer 102.

[0108] In some embodiments, where the electrode preform 1 further includes an insulating layer 15, the electrode 10 also includes an insulating layer 15, which covers the sides of the current collector 11, the first active material layer 101 and the second active material layer 102 and extends to the edge region of the second active material layer 102 on the side surface opposite to the current collector 11.

[0109] In some embodiments, when the current collector 11 includes a stacked metal layer 111 and a lithium replenishment layer 112, the electrode 10 also includes a metal layer 111 and a lithium replenishment layer 112, with the lithium replenishment layer 112 located between the metal layer 111 and the first active material layer 101.

[0110] Thirdly, please see Figure 2 This application embodiment also provides a battery 100, including the above-mentioned electrode 10.

[0111] In some embodiments, the battery 100 further includes an electrolyte that wets the electrode 10. The electrolyte includes a solute and a solvent, with the solute dissolved in the solvent, which includes ester solvents. As an example, ester solvents include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0112] The following description is based on specific embodiments.

[0113] Example 1

[0114] S1, please refer to Figure 1 A first coating layer (corresponding to lithium replenishment layer 112), a second coating layer (corresponding to first initial active material layer 12), a third coating layer (corresponding to adhesive layer 13), a fourth coating layer (corresponding to second initial active material layer 14), and a fifth coating layer (corresponding to insulating layer 15) are sequentially applied to an aluminum foil using a coating method to obtain an electrode preform, wherein:

[0115] The composition of the first coating is:

[0116] Conductive agent (including SP and CMK-3 in a mass ratio of 8:2): binder (PAA): lithium supplement (lithium squartz oxide) = 70wt%: 25wt%: 5wt%; the coating thickness of the first coating is 10μm.

[0117] The composition of the second coating is:

[0118] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 5wt%: 2wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 2μm, and the coating thickness of the second coating is 100μm.

[0119] The third coating consists of:

[0120] The adhesive (including PVDF and WPU in a mass ratio of 1:1): conductive agent (including SP and VGCF in a mass ratio of 8:2): lithium supplement (lithium oxalate) = 60wt%: 35wt%: 5wt%, and the thickness of the third coating is 5μm.

[0121] The fourth coating consists of:

[0122] Active materials (LiFe) 0.5 Mn0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 94wt%: 3wt%: 2.5wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 1.5μm, and the coating thickness of the fourth coating is 100μm.

[0123] The fifth coating consists of:

[0124] Adhesive (PVDF): Insulating material (ceramic) = 20wt%: 80wt%, the coating thickness of the fifth coating is 5μm.

[0125] S2. After cold pressing, the electrode preform is extracted in a dichloromethane extraction tank for 3 minutes. After extraction, it is dried in an oven at 45°C to obtain the electrode.

[0126] Example 2

[0127] The difference from Example 1 lies in the composition of the first coating:

[0128] Conductive agent (SP+CMK-3): Adhesive (PAA): Lithium supplement (lithium squartz oxide) = 68wt%: 25wt%: 7wt%.

[0129] Everything else is the same as in Example 1.

[0130] Example 3

[0131] The difference from Example 1 lies in the composition of the fourth coating:

[0132] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 94.5wt%: 2wt%: 2.5wt%: 1wt%, and the D50 particle size of the pore-forming agent is 1μm.

[0133] Everything else is the same as in Example 1.

[0134] Example 4

[0135] The difference from Example 1 lies in the composition of the second coating:

[0136] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 4.5wt%: 2wt%: 1wt%, and the D50 particle size of the pore-forming agent is 2μm.

[0137] The fourth coating consists of: active material (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 94wt%: 2.5wt%: 2.5wt%: 1wt%, the D50 particle size of the pore-forming agent is 1.5μm.

[0138] Everything else is the same as in Example 1.

[0139] Example 5

[0140] The difference from Example 1 lies in the composition of the second coating:

[0141] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and SWCNT in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 5wt%: 2wt%: 0.5wt%, and the D50 particle size of the pore-forming agent is 2μm.

[0142] The fourth coating consists of:

[0143] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and SWCNT in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 94wt%: 3wt%: 2.5wt%: 0.5wt%, and the D50 particle size of the pore-forming agent is 1.5μm.

[0144] Everything else is the same as in Example 1.

[0145] Example 6

[0146] The difference from Example 1 lies in the composition of the fifth coating:

[0147] Adhesive (PVDF): Insulating material (ceramic) = 15wt%: 85wt%.

[0148] Everything else is the same as in Example 1.

[0149] Example 7

[0150] The difference from Example 1 lies in the composition of the second coating:

[0151] Active materials (LiFe) 0.5 Mn 0.5PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 5wt%: 2wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 1.5μm, and the coating thickness of the second coating is 100μm.

[0152] Everything else is the same as in Example 1.

[0153] Example 8

[0154] The difference from Example 1 lies in the composition of the second coating:

[0155] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 5wt%: 2wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 2.25μm, and the coating thickness of the second coating is 100μm.

[0156] Everything else is the same as in Example 1.

[0157] Example 9

[0158] The difference from Example 1 is that no lithium supplement is added to the third coating (i.e., the third coating only contains PVDF+WPU).

[0159] Example 10

[0160] The difference from Example 1 is that WPU is not added to the third coating (i.e., the third coating only contains PVDF + lithium supplement).

[0161] Comparative Example 1

[0162] The difference from Example 1 lies in the composition of the second coating:

[0163] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1) = 92.96wt%: 5.03wt%: 2.01wt%, and the coating thickness of the second coating is 100μm.

[0164] Everything else is the same as in Example 1.

[0165] Comparative Example 2

[0166] The difference from Example 1 lies in the composition of the second coating:

[0167] Active materials (LiFe)05 Mn 05 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 94.5wt%: 2.5wt%: 2.5wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 1μm, and the coating thickness of the second coating is 100μm.

[0168] Everything else is the same as in Example 1.

[0169] Comparative Example 3

[0170] The difference from Example 1 lies in the composition of the second coating:

[0171] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1): Pore-forming agent (PMMA) = 92.5wt%: 5wt%: 2wt%: 0.5wt%, the D50 particle size of the pore-forming agent is 2.5μm, and the coating thickness of the second coating is 100μm.

[0172] Everything else is the same as in Example 1.

[0173] Comparative Example 4

[0174] The difference from Example 1 is that the third coating is omitted; otherwise, it is the same as Example 1.

[0175] Comparative Example 5

[0176] The difference from Example 1 lies in the composition of the second coating:

[0177] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1) = 92.96wt%: 5.03wt%: 2.01wt%, and the coating thickness of the second coating is 100μm.

[0178] The fourth coating consists of:

[0179] Active materials (LiFe) 0.5 Mn 0.5 PO4): Adhesive (PVDF): Conductive agent (including CNT, SP and VGCF in a mass ratio of 3:6:1) = 94.47wt%: 3.02wt%: 2.51wt%, and the coating thickness of the fourth coating is 100μm.

[0180] Everything else is the same as in Example 1.

[0181] The following performance characteristics were performed:

[0182] 1. Electrode tortuosity test.

[0183] The electrodes prepared in the above examples and comparative examples were assembled into symmetrical cells, and electrochemical impedance spectroscopy (EIS) was measured using an electrochemical workstation with a frequency range of 100,000 Hz to 0.1 Hz and an amplitude of 5 mV. The measured Nyquist plot was fitted with an equivalent circuit to obtain the ionic impedance Rion.

[0184] The degree of curvature is determined by the formula The calculation is performed, where Rion is the liquid phase transport impedance of ions in the electrode pores, A is the apparent area of ​​the electrode, ε is the electrode porosity, κ is the ionic conductivity of the electrolyte, and t is the total thickness of the two electrodes. The tortuosity test results of the electrode sheets are recorded in Table 1.

[0185] 2. Battery cycle performance test.

[0186] 2.1 The positive electrode is prepared by slitting and die-cutting the electrode sheets prepared in the above examples and comparative examples. Artificial graphite is used as the negative electrode and 1M LiPF6 (EC:DEC:DMC=1:1:1, volume ratio) is used as the electrolyte. The electrode sheets are stacked, injected with electrolyte, packaged and vacuum sealed to obtain a lithium-ion battery (specifically a soft pack battery).

[0187] 2.2 Testing the cycle capacity retention rate of lithium-ion batteries at 25℃: At 25℃, the lithium-ion batteries were subjected to 1C / 1C cycle tests with a voltage range of 2.5 to 3.65V. The capacity retention rate was calculated by dividing the capacity after 500 cycles by the initial capacity. The test results are recorded in Table 1.

[0188] 2.3 Testing the capacity retention rate of lithium-ion batteries at 45℃: At 45℃, the lithium-ion batteries were subjected to 1C / 1C cycle tests with a voltage range of 2.5 to 3.65V. The capacity retention rate was calculated by dividing the capacity after 500 cycles by the initial capacity. The test results are recorded in Table 1.

[0189] Table 1

[0190]

[0191]

[0192] As can be seen from Table 1, compared with Comparative Examples 1 and 5, the results of Examples 1 to 10 show that adding a pore-forming agent to both the second and fourth coatings can effectively reduce the tortuosity of the channels in the electrode, making it easier for lithium ions to be transported in the electrode and improving the cycle capacity retention rate of the battery.

[0193] Further comparison of Comparative Example 1, Comparative Example 2, Example 7, Example 1, Example 8, and Comparative Example 3 shows that, with... As the value increases from 0 to 1.6, the tortuosity of the channels in the electrode decreases from 3.54 to 1.72. However, the cycle capacity retention rate of the battery first increases and then decreases. This is because... As the value increases, the tortuosity decreases, the transport difficulty of lithium ions in the electrode decreases, and the concentration polarization inside the electrode decreases, thereby increasing the cycle capacity retention of the battery; however, Excessive strength (see Comparative Example 3) leads to a decrease in the strength of the second coating, which in turn reduces the battery's cycle capacity retention.

[0194] Further comparison of Examples 1, 9, 10, and 4 reveals that although the tortuosity of the four examples is similar, the cycle capacity retention rates of the batteries corresponding to Examples 9, 10, and 4 all decrease. This is because no lithium replenishing agent was added to the third coating in Example 9, resulting in a decrease in the ion transport performance of the third coating and an increase in the volume resistivity and interfacial resistance of the electrode, thus reducing the cycle capacity retention rate of the battery. In Example 10, although a lithium replenishing agent was added, no WPU was added, making it difficult for lithium ions in the lithium replenishing agent to transfer. Therefore, the lithium replenishing agent could not effectively perform its function, leading to a decrease in the cycle capacity retention rate of the battery. In other words, the lithium replenishing agent and WPU can work together to reduce the volume resistivity and interfacial resistance of the electrode, thereby improving the cycle performance of the battery. Comparative Example 4, which omits the third coating, shows a cycle capacity retention rate close to that of the batteries corresponding to Examples 9 and 10, further demonstrating that only by adding a lithium replenishing agent to the third coating, and ensuring that the lithium ions in the lithium replenishing agent can be effectively transferred, can the cycle performance of the battery be effectively improved.

[0195] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrode sheet, characterized in that, The electrode is prepared from an electrode preform, which includes a current collector, a first initial active material layer, and a second initial active material layer stacked sequentially. The first initial active material layer contains a first pore-forming agent with a mass content of w1 and an average particle size of d1. The second initial active material layer contains a second pore-forming agent with a mass content of w2 and an average particle size of d2. in, ; The electrode preform further includes an adhesive layer located between the first initial active material layer and the second initial active material layer; the adhesive layer includes a third adhesive and a third conductive agent; the adhesive layer further includes a first lithium supplement agent, and the third adhesive includes a polyurethane adhesive; The electrode is obtained by removing the first pore-forming agent and the second pore-forming agent from the electrode preform. The first initial active material layer is formed into a first active material layer, and the second initial active material layer is formed into a second active material layer. The porosity of the first active material layer is greater than that of the second active material layer. The electrode further includes the adhesive layer, which comprises the first lithium supplement agent and the polyurethane adhesive, and is located between the first active material layer and the second active material layer.

2. The electrode sheet according to claim 1, characterized in that, The first pore-forming agent and the second pore-forming agent have the same composition, and both the first pore-forming agent and the second pore-forming agent contain polymethyl methacrylate; and / or, The d1 is 1 μm ~ 50 μm; and / or, The d2 is 1 μm ~ 50 μm; and / or, The thickness of the first initial active material layer is 10 μm to 300 μm; and / or, The thickness of the second initial active material layer is 10 μm to 300 μm.

3. The electrode sheet according to claim 1, characterized in that, The first initial active material layer further includes a first active material, a first binder, and a first conductive agent; the second initial active material layer further includes a second active material, a second binder, and a second conductive agent.

4. The electrode sheet according to claim 3, characterized in that, In the first initial active material layer, the content of the first active material is 90wt%~97wt%, the content of the first binder is 2wt%~5wt%, the content of the first conductive agent is 0.5wt%~7.5wt%, and the content of the first pore-forming agent is 0.1wt%~2wt%; and / or, In the second initial active material layer, the content of the second active material is 93wt%~98wt%, the content of the second binder is 1wt%~5wt%, the content of the second conductive agent is 0.5wt%~5wt%, and the content of the second pore-forming agent is 0.1wt%~2wt%.

5. The electrode sheet according to claim 3, characterized in that, The content of the first active material in the first initial active material layer is A1, and the content of the second active material in the second initial active material layer is A2, wherein 0.5wt%≤A2-A1≤5wt%; and / or, The content of the first binder in the first initial active material layer is B1, and the content of the second binder in the second initial active material layer is B2, wherein 0.5wt%≤B1-B2≤3wt%; and / or, The content of the first conductive agent in the first initial active material layer is C1, and the content of the second conductive agent in the second initial active material layer is C2, wherein 0.5wt%≤C2-C1≤3wt%.

6. The electrode sheet according to claim 3, characterized in that, Both the first active material and the second active material contain lithium manganese iron phosphate, the chemical formula of which is: LiFe x Mn y PO4, 0 < x < 1, 0 < y < 1; and / or, The first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, polyvinylidene fluoride, and polyvinyl alcohol; and / or, The first conductive agent and the second conductive agent each independently include at least one of conductive carbon black, carbon nanotubes, mesoporous carbon materials and vapor-grown carbon fibers.

7. The electrode sheet according to claim 1, characterized in that, In the adhesive layer, the content of the third adhesive is 50wt%~80wt%, the content of the third conductive agent is 15wt%~40wt%, and the content of the first lithium supplement agent is 1wt%~10wt%; and / or, The third conductive agent comprises conductive carbon black and vapor-grown carbon fibers, wherein the content of the conductive carbon black in the third conductive agent is 80wt%~90wt%; and / or, The thickness of the adhesive layer is 1μm to 10μm.

8. The electrode sheet according to claim 1, characterized in that, The third binder further includes polyvinylidene fluoride; the content of polyvinylidene fluoride in the third binder is 30wt%~70wt%; and / or, the first lithium supplementer includes lithium oxalate.

9. The electrode sheet according to any one of claims 1 to 6, characterized in that, The current collector includes a stacked metal layer and a lithium replenishment layer, wherein the lithium replenishment layer is located between the metal layer and the first initial active material layer, and the lithium replenishment layer includes a fourth conductive agent, a fourth binder, and a second lithium replenishment agent.

10. The electrode sheet according to claim 9, characterized in that, In the lithium replenishment layer, the content of the fourth conductive agent is 40wt%~85wt%, the content of the fourth binder is 5wt%~50wt%, and the content of the second lithium replenishment agent is 0.1wt%~10wt%; and / or, The thickness of the lithium replenishment layer is 1μm~20μm; and / or, The second lithium supplement includes at least one of lithium carbonate, lithium squaric acid, and lithium oxalate.

11. The electrode sheet according to any one of claims 1 to 6, characterized in that, The electrode preform also includes an insulating layer that covers the sides of the current collector, the first initial active material layer, and the second initial active material layer and extends to the edge region of the second initial active material layer on the side surface opposite to the current collector.

12. The electrode sheet according to claim 11, characterized in that, The insulating layer comprises a fifth adhesive of 5wt% to 65wt% and an insulating material of 35wt% to 95wt%; and / or, The thickness of the insulating layer is 1μm~40μm; And / or, The length of the insulating layer is 1mm to 10mm, and the width of the overlap between the insulating layer and the second initial active material layer on the side of the second initial active material layer away from the current collector is 1mm to 3mm.

13. A battery, characterized in that, Includes the electrode sheet according to any one of claims 1 to 12.

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