Electrode sheet, method for manufacturing electrode sheet, secondary battery, and electronic device

Abstract

The application provides an electrode sheet, a manufacturing method of the electrode sheet, a secondary battery and an electronic device. The electrode sheet comprises a current collector and an active material layer arranged on the surface of the current collector. The porosity of the active material layer is 10-50%, the tortuosity of the active material layer is 1.04-6, the active material layer is provided with a plurality of first holes and a plurality of second holes, the plurality of first holes penetrates the active material layer along the direction perpendicular to the surface of the current collector, the plurality of second holes is arranged in the active material layer in a bent manner, the plurality of second holes communicates with the plurality of first holes, and the ratio of the total volume of the first holes to the total volume of the second holes is 1:3-6:3. The first holes and the second holes in the active material layer can increase the transmission channels of ions and electrons, reduce the transmission resistance, and improve the electrical performance of the electrode sheet.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to electrode sheets, methods for manufacturing electrode sheets, secondary batteries, and electronic devices. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high power, and long cycle life, leading to their widespread use in consumer electronics. As their applications expand, particularly in electric bicycles and electric vehicles, the demands on their energy density are constantly increasing. Improving the energy density of lithium batteries involves both increasing the capacity and voltage of the active materials and increasing the content of active material per unit volume. Current technologies increase the areal density of the battery by increasing electrode thickness. However, increased electrode thickness leads to a greater transport distance between lithium ions and electrons, increasing transport resistance and thus degrading the overall battery performance. Therefore, how to reduce the transport resistance of lithium ions and electrons while increasing areal density has become a crucial issue affecting the future application prospects of lithium-ion batteries. Summary of the Invention

[0003] This application provides an electrode sheet, a method for manufacturing the electrode sheet, a secondary battery, and an electronic device to solve the above-mentioned technical problems.

[0004] The embodiments of this application are implemented as follows:

[0005] An electrode sheet includes a current collector and an active material layer. The active material layer is disposed on the surface of the current collector. The porosity of the active material layer is 10-50%, and the tortuosity of the active material layer is 1.04-6, so that the electrolyte can fully wet the active material layer and allow ions and electrons to be transported smoothly in the pores. The active material layer has a plurality of first pores and a plurality of second pores. The plurality of first pores penetrate the active material layer in a direction perpendicular to the surface of the current collector. Specifically, the first pores extend from the side of the active material layer away from the current collector to the side close to the current collector, forming through holes perpendicular to the surface of the current collector. The pore diameter of the first pores is uniform throughout, reducing energy density loss caused by pore diameter variations. The plurality of second pores are bent within the active material layer and connect to the plurality of first pores. The ratio of the total volume of the first pores to the total volume of the second pores is 1:3 to 6:3.

[0006] Thus, by constraining the porosity and tortuosity of the active material layer 20 and setting the first and second pores in the active material layer, the transport channels for ions and electrons can be increased, transport obstacles can be reduced, and the tortuous second pore connects to the first pore perpendicular to the current collector surface, which is also beneficial to the transport and wetting of electrolyte in the longitudinal and transverse directions, reducing the concentration polarization of the electrode sheet, and thus improving the electrical performance of the electrode sheet.

[0007] In one possible implementation: the electrode is a positive electrode, the porosity of the active material layer is 10-35%, and the tortuosity of the active material layer is 3-6.

[0008] In one possible implementation: the electrode is a negative electrode, the porosity of the active material layer is 20-50%, and the tortuosity of the active material layer is 1.04-3. The porosity of the active material layer of the negative electrode is greater than that of the active material layer of the positive electrode, and the tortuosity is less than that of the active material layer of the positive electrode. This ensures smooth ion flow in the active material layer of the negative electrode during lithium insertion or extraction, improving the internal kinetic performance of the electrode.

[0009] In one possible implementation: the electrode is a positive electrode with a first hole diameter of 3 µm to 22 µm, and / or the electrode is a negative electrode with a first hole diameter of 5 µm to 33 µm.

[0010] In one possible implementation: the depth of the first hole is 80~700 µm, preferably 100 µm~500 µm.

[0011] In one possible implementation: the pore size of the second pore is 2nm~0.5µm.

[0012] In one possible implementation: the spacing between adjacent first holes is 30~100µm.

[0013] In this way, by constraining the relevant dimensions of the first and second holes, we can ensure the smooth transport of ions and electrons on the one hand, and avoid the total volume of the pores being too large, which would affect the energy density of the electrode sheet on the other hand.

[0014] In one possible implementation: along the direction away from the current collector, the difference between the diameter of the first hole on the side away from the current collector and the diameter on the side closer to the current collector is 100 nm to 1 µm. Limiting the diameter fluctuation range of the first hole to a very small interval ensures uniform diameter throughout the first hole, which is beneficial for improving the energy density of the electrode sheet.

[0015] In one possible implementation: the ratio of the total volume of the first hole to the total volume of the second hole is 1:1 to 2:1.

[0016] In one possible implementation: the active material layer includes an active material, a conductive agent and / or a binder, wherein the active material is granular, the conductive agent and / or binder is fibrous, and a plurality of second pores are formed between the active material and the conductive agent and / or binder.

[0017] Fibrous conductive agents or binders can form a three-dimensional conductive network structure in the active material layer. Particulate active materials can be uniformly mixed in the network structure. While connecting the particulate materials, the network fibers can also form capillary channels between the particulate materials, increasing the flexibility and conductive energy of the electrode sheet, improving the dynamic performance, and at the same time improving the adhesion between the active material layer and the current collector inside the electrode sheet and the cohesion between active materials, reducing the risk of mechanical damage to the electrode sheet.

[0018] In one possible implementation: the diameter of the conductive agent is 10 nm to 50 nm, and the length of the conductive agent is 30 nm to 50 nm.

[0019] In one possible implementation: the diameter of the adhesive is 10 nm to 100 nm, and the length of the adhesive is 30 nm to 50 nm.

[0020] In one possible implementation: the conductive agent accounts for 0.5-10% of the weight of the active material layer, so that while improving conductivity, the conductive agent avoids affecting other properties of the electrode, such as energy density and cycle performance.

[0021] In one possible implementation: the binder accounts for 0.5-10% of the weight of the active material layer, so that the active material layer has good adhesion and cohesion, while its conductivity and dynamic properties are not reduced.

[0022] Embodiments of this application also provide a method for manufacturing an electrode sheet, which includes: mixing an active material, a fibrous conductive agent, and / or a binder to prepare an active material film, wherein the active material film has a plurality of second pores distributed therein; winding, stacking, or layer-by-layer winding of the active material film, and slicing the wound, stacked, or layer-by-layer winding active material film; coating a slurry with a solid content of 15% to 20% (binder:dispersant:conductive agent = 25 to 35: 5 to 10: 60 to 70) onto a current collector by a gravure process to obtain a current collector with a base coating; bonding the sliced ​​active material film onto the surface of the current collector with the base coating, wherein there is a gap between adjacent single-layer active material films to form a first pore; and obtaining the electrode sheet after drying.

[0023] In one possible implementation, "preparing an active material film" includes: coating a mixture of an active material, a fibrous conductive agent, and / or a binder onto the surface of a support membrane; drying the mixture on the surface of the support membrane; and peeling the dried mixture off the surface of the support membrane to form an active material film.

[0024] Embodiments of this application also provide a method for manufacturing an electrode sheet, which includes: mixing an active material, a fibrous conductive agent, and / or a binder to form an active material substance, wherein a plurality of second pores are distributed in the active material substance; setting a support on the surface of a current collector; coating the active material substance on the surface of the current collector; and surrounding the support with the active material substance; and removing the support to form a first pore.

[0025] An embodiment of this application also provides a secondary battery, including a packaging body and electrode sheets as described in the above embodiment, wherein the electrode sheets are disposed in the packaging body.

[0026] Embodiments of this application also provide an electronic device, including an electrical component and a secondary battery as described in the above embodiments, wherein the electrical component is electrically connected to the secondary battery. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic cross-sectional view of an electrode sheet according to an embodiment of this application.

[0029] Figure 2 This is a top view of the electrode sheet in one embodiment.

[0030] Figure 3 This is a top view of the electrode sheet in another embodiment.

[0031] Figure 4 This is a schematic diagram of the structure of the active material layer in the electrode sheet in one embodiment of this application.

[0032] Figure 5 This is a schematic diagram of the structure of a secondary battery in one embodiment.

[0033] Figure 6 This is a schematic diagram of the structure of an electronic device in one embodiment.

[0034] Explanation of key component symbols:

[0035] Detailed Implementation

[0036] The technical solutions in 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.

[0037] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. When a component is said to be "set on" another component, it can be directly set on the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] Some embodiments of this application are described in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0040] Please see Figure 1 , Figure 2 and Figure 3 This application provides an electrode sheet 100, including a current collector 40 and an active material layer 20. The active material layer 20 is disposed on the surface of the current collector 40. The porosity of the active material layer 20 is 10-50%, and the tortuosity of the active material layer 20 is 1.04-6, so that the electrolyte can fully wet the active material layer 20 and allow ions and electrons to be transported smoothly in the pores. The active material layer 20 is provided with a plurality of first holes 10 and a plurality of second holes 30. The plurality of first holes 10 penetrate the active material layer 20 in a direction perpendicular to the surface of the current collector 40. Specifically, the first holes 10 extend from the side of the active material layer 20 away from the current collector 40 to the side close to the current collector 40, forming through holes perpendicular to the surface of the current collector 40. The pore size of the first holes 10 is uniform at all points, which helps to reduce energy density loss caused by pore size changes. Multiple second holes 30 are bent and disposed within the active material layer 20, and the multiple second holes 30 are connected to multiple first holes 10; the ratio of the total volume of the first holes 10 to the total volume of the second holes 30 is 1:3 to 6:3. It should be noted that... Figure 1 The shape of the second hole 30 shown is only an example. Multiple second holes 30 can present various irregular curved shapes, and this application does not limit them.

[0041] The electrode sheet 100 of this application embodiment increases the transport channels for ions and electrons and reduces transport obstacles by providing a vertical first hole 10 and a curved second hole 30 in the active material layer 20 and constraining the porosity and tortuosity of the active material layer 20. The curved second hole 30 connects to the vertical first hole 10, which also facilitates the transport and wetting of electrolyte in the longitudinal and lateral directions, reduces the concentration polarization of the electrode sheet 100, and thus improves the electrical performance of the electrode sheet 100.

[0042] In one embodiment of this application, the ratio of the total volume of the first hole 10 to the total volume of the second hole 30 is 1:1 to 2:1, which is beneficial to further improve the wettability of the electrolyte to the active material layer and improve the kinetic and cycle performance of the electrode sheet 100.

[0043] To simplify the process, when the electrode sheet 100 is a positive or negative electrode sheet, the ratio of the total volume of the first hole 10 to the total volume of the second hole 30 in the positive electrode sheet can be the same as the ratio of the total volume of the first hole 10 to the total volume of the second hole 30 in the negative electrode sheet. In other embodiments, the ratio of the total volume of the first hole 10 to the total volume of the second hole 30 in the positive electrode sheet can also be different from the ratio of the total volume of the first hole 10 to the total volume of the second hole 30 in the negative electrode sheet, as long as it meets the actual design requirements. This application does not limit this.

[0044] In one embodiment of this application, the electrode is a positive electrode, the porosity of the active material layer 20 is 10-35%, and the tortuosity of the active material layer 20 is 3-6.

[0045] In some embodiments, the electrode is a positive electrode, and the porosity of the active material layer 20 is within the range of any two of the following values: 10%, 15%, 20%, 25%, 30%, 35%, preferably 12% to 23%; the tortuosity of the active material layer 20 is within the range of any two of the following values: 3, 3.5, 4, 4.5, 5, 5.5, 6, preferably 3 to 5.

[0046] The electrode is a negative electrode, with the active material layer 20 having a porosity of 20-50% and a tortuosity of 1.04-3. The porosity of the active material layer of the negative electrode is greater than that of the active material layer of the positive electrode, while its tortuosity is less. This ensures smooth ion flow in the active material layer 20 of the negative electrode during lithium insertion or extraction, improving the internal kinetic performance of the electrode sheet 100.

[0047] In some embodiments, the electrode is a negative electrode, and the porosity of the active material layer 20 is within the range of any two of the following values: 20%, 25%, 30%, 35%, 40%, 45%, and 50%, preferably 28% to 50%; the tortuosity of the active material layer 20 is within the range of any two of the following values: 1.04, 1.5, 1.9, 2.0, 2.5, 2.7, 3, 3.5, and 4, preferably 1.04 to 2.5.

[0048] Further, the active material layer 20 includes an active material 21, a conductive agent 22a, and / or a binder 22b. In one embodiment of this application, when the electrode sheet 100 is a positive electrode sheet, the active material layer 20 of the positive electrode sheet may include an active material 21, a conductive agent 22a, and a binder 22b to improve the conductivity and cohesion of the active material in the positive electrode sheet. When the electrode sheet 100 is a negative electrode sheet, the active material layer 20 of the negative electrode sheet may include an active material 21 and a binder 22b. The active material 21 of the negative electrode sheet may include a conductive material, such as graphite, carbon nanotubes, etc., which can replace the role of a conductive agent. If necessary, the active material layer 20 of the negative electrode sheet may also simultaneously include an active material 21, a conductive agent 22a, and a binder 22b to improve the conductivity of the negative electrode sheet.

[0049] In embodiments of this application, the active material 21 is granular, the conductive agent 22a and / or binder 22b are fibrous, and a plurality of second pores 30 are formed between the active material 21 and the conductive agent 22a and / or binder 22b. Figure 4 As shown, the fibrous conductive agent 22a or binder 22b can form a three-dimensional conductive network structure in the active material layer 20, and the particulate active material 21 can be uniformly mixed in the network structure. While connecting the particulate materials, the network fibers can also form capillary channels between the particulate materials, increasing the flexibility and conductive energy of the electrode sheet 100, improving its dynamic performance, and at the same time, improving the adhesion and cohesion within the electrode sheet 100, reducing the risk of mechanical damage to the electrode sheet 100.

[0050] In one embodiment of this application, the conductive agent has a diameter of 10 nm to 50 nm and a length of 30 nm to 50 nm. The binder has a diameter of 10 nm to 100 nm and a length of 30 nm to 50 nm. In the active material layer 20, the conductive agent and binder are fibrous. These fibrous conductive agents and binders are uniformly mixed with and connected to the particulate active material, so that the particulate material is uniformly distributed throughout the network structure, forming an active material layer with uniform material distribution. The diameter of the conductive agent can be the diameter of each conductive agent filament, or the diameter of multiple conductive agent filaments wound together between adjacent particulate materials. The length of the conductive agent can be the length of each conductive agent filament, or the length of a bundle of conductive agents between adjacent particulate materials. Similarly, the diameter of the binder can be the diameter of each binder filament, or the diameter of multiple binder filaments wound together between adjacent particulate materials. The length of the binder can be the length of each binder filament, or the length of a bundle of binders between adjacent particulate materials.

[0051] Furthermore, in one embodiment of this application, the conductive agent 22a accounts for 0.5% to 10% of the weight of the active material layer 20, so that the conductive agent 22a improves conductivity while avoiding affecting other properties of the electrode, such as energy density and cycle performance. In some embodiments, the conductive agent 22a accounts for a weight percentage of the active material layer 20 within the range of any two of the following values: 0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%, preferably 0.5% to 1.5%.

[0052] Furthermore, in one embodiment of this application, the adhesive 22b accounts for 0.5 to 10% of the weight of the active material layer 20, so that the active material layer 20 has good adhesion and cohesion, while its conductivity and dynamic properties are not reduced.

[0053] In some embodiments, the adhesive 22b accounts for a weight percentage of the active material layer 20 of any two of the following values: 0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%, preferably 0.5% to 1.5%.

[0054] In embodiments of this application, when the electrode is a positive electrode, the aperture of the first hole is 3~22 µm, preferably a range of any two of the following values: 3 µm, 5 µm, 10 µm, 15 µm, 17 µm, 19 µm, 20 µm, 21 µm, 22 µm, with a preference for 10 µm~22 µm. And / or, when the electrode is a negative electrode, the aperture of the first hole is 5~33 µm, preferably a range of any two of the following values: 5 µm, 8 µm, 10 µm, 12 µm, 14 µm, 16 µm, 18 µm, 20 µm, 22 µm, 25 µm, 28 µm, 30 µm, 32 µm, 33 µm, with a preference for 16 µm~33 µm. Figure 1 As shown in the diagram, the width of the first hole 10 measured horizontally is the aperture of the first hole 10, and the depth of the first hole 10 measured vertically is the depth of the first hole 10. The depth of the first hole 10 can be equal to the thickness of the active material layer 20. The first hole 10, which penetrates the active material layer 20 along its thickness direction, allows the electrolyte to fully wet the active material layer 20 in the longitudinal direction, reducing the problem of low wettability of the active material near the current collector 40 and reducing the concentration polarization of the electrode sheet 100.

[0055] like Figure 2 and Figure 3 As shown, the plurality of first holes 10 can be multiple coaxially arranged annular holes, and the shape of the annular holes can be circular, rectangular, triangular, or polygonal. In this way, the active material layer 20 can be formed by winding the active material film layer by layer, thereby improving the thickness and material uniformity of the active material layer 20, and the pore size of the first holes 10 can be stably controlled. In other embodiments, the plurality of first holes 10 can also be spiral holes or elongated holes arranged in an array, with each turn of the spiral hole constituting one first hole 10. This facilitates the formation of a thicker active material layer 20 through continuous winding, and the formation of first holes 10 with uniform pore size during the winding process, which is beneficial for improving the energy density of the electrode sheet 100. Among the plurality of first holes 10, the spacing between adjacent first holes 10 is 30~150µm, and the spacing between adjacent first holes 10 is a range of any two of the following values: 30 µm, 40 µm, 50 µm, 60 µm, 70 µm, 80 µm, 90 µm, 100 µm, 110 µm, 120 µm, 130 µm, 140 µm, and 150 µm, preferably 30 µm~100 µm.

[0056] In the embodiments of this application, the pore size of the second pore 30 is 2 nm to 4 µm. The pore size of the second pore 30 is within the range of any two values ​​from 2 nm, 5 nm, 10 nm, 50 nm, 0.1 µm, 0.2 µm, 0.3 µm, 0.5 µm, 0.7 µm, 0.9 µm, 1 µm, 2 µm, 3 µm, and 4 µm, preferably 2 nm to 0.5 µm. The plurality of second pores 30 are capillaries distributed throughout the active material layer 20. Each capillary connects to two adjacent first pores 10, allowing the electrolyte to wet the active material layer 20 in the lateral direction, enabling rapid transport of ions and electrons within the active material layer 20. Along the direction perpendicular to the surface of the current collector 40, i.e. Figure 1 In the vertical direction of the viewing angle, the width of the second hole 30 is measured as the diameter of the second hole 30. Along the direction parallel to the surface of the current collector 40, i.e. Figure 1 The dimension of the second hole 30 measured in the horizontal direction of the viewing angle is the depth of the second hole 30. When the second hole 30 connects two adjacent first holes 10, the depth of the second hole 30 can be the same as the distance between the adjacent first holes 10.

[0057] In this way, by constraining the relevant dimensions of the first hole 10 and the second hole 30, on the one hand, the smooth transport of ions and electrons can be ensured, and on the other hand, the total volume of the pores can be avoided from being too large and affecting the energy density of the electrode sheet 100.

[0058] Furthermore, along the direction away from the current collector 40, the difference between the diameter of the first hole 10 on the side away from the current collector 40 and the diameter of the first hole 10 on the side closer to the current collector 40 is 100 nm to 1 µm. Limiting the diameter fluctuation range of the first hole 10 to a very small range makes the diameter of the first hole 10 uniform at all points, which is beneficial to improving the energy density of the electrode sheet 100.

[0059] like Figure 5 As shown, an embodiment of this application also provides a secondary battery 200, including a packaging body 201 and electrode sheets 100 as described in the above embodiment, with the electrode sheets 100 disposed within the packaging body 201. The secondary battery 200 includes, but is not limited to, a stacked battery. Specifically, the positive electrode sheet 100 and the negative electrode sheet 100 are stacked within the packaging body 201, and a separator 202 is disposed between the positive and negative electrode sheets to prevent internal short circuits. The secondary battery 200 also includes connection terminals (not shown) respectively connecting the positive and negative electrode sheets for electrical connection to an external circuit.

[0060] The beneficial effects of the electrode sheet of this application will be explained below with reference to specific embodiments and test data.

[0061] After fabricating a stacked battery using electrode sheet 100, the battery needs to be tested to verify the improvement in its electrical performance. The test items are as follows:

[0062] 1. Test of the total volume of the first and second wells: ① The total volume of the first well is determined by the total length L of all single-layer active material membranes, the thickness T of the active material layer, and the spacing d between adjacent single-layer active material membranes according to the formula V. 第一孔 =L×T×d, where d is the diameter of the first hole and T is the depth of the first hole; ② The total volume of the second hole is determined by testing the porosity α of the self-supporting membrane using the gas displacement method, and then by calculating the apparent volume V1 of the self-supporting membrane according to the formula V 第二孔 =V1×ɛ.

[0063] 2. Testing the difference in aperture at different depths of the first hole.

[0064] Cut a section along the thickness direction of the electrode sheet, and then measure the diameter of the first hole on the side away from the current collector and the side close to the current collector under a scanning electron microscope. Divide the active material layer into three equal parts along the thickness direction of the active material layer. The position on the side away from the current collector is the position at 2 / 3 of the thickness from the surface of the current collector, and the position on the side close to the current collector is the position at 1 / 3 of the thickness from the surface of the current collector.

[0065] 3. Dynamic performance testing. The test data will be displayed as follows:

[0066] DC-rate@02C (discharge rate test under 0.2C conditions, DC refers to discharge): Specifically, it is the ratio of the full-charged battery's capacity at 0.2C DC to its capacity at 0.1C DC under 0.2C CC + 0.05C CV conditions. That is, the battery is charged at a constant current at 0.2C, then switched to constant voltage charging at 0.05C, and the ratio of the discharged capacity at 0.2C to that at 0.1C. 0.2C represents the charging rate, and nC charge / discharge means the battery is fully charged or fully discharged in 1 / n hours.

[0067] The higher the DC-rate@02C test result, the better the battery's power performance.

[0068] 4. Cyclic performance test. The test data is displayed as follows:

[0069] 25℃ capacity retention@02C 500cls: This refers to the ratio of the 02C DC capacity after 500 cycles to the 02C DC capacity after 1 cycle, when the battery is charged at 0.2C CC + 0.05C CV and discharged at 02C DC. A higher ratio indicates better cycle performance.

[0070] 5. Nail test.

[0071] In a test environment of 20±5℃, the sample is placed on the test platform and tested from the center of the sample with a 4mm diameter steel nail at a speed of 150mm / s. The sample is completely pierced. Judgment criteria: The sample does not catch fire or explode.

[0072] 6. Impact test.

[0073] In a test environment of 20±5℃, the sample is placed on the test platform, and a 15.8mm diameter round bar is placed at the center of the wide side of the sample, with the round bar perpendicular to the long axis of the sample. A 9.1±0.1kg weight is dropped vertically from a height of 610±25mm into the sample, landing at the intersection of the round bar and the sample. Judgment criteria: The sample does not ignite or explode.

[0074] The following specific embodiments and comparative examples are provided to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0075] Example 1

[0076] The preparation process of electrode sheet 100 is as follows:

[0077] Preparation of the positive electrode sheet:

[0078] Lithium cobalt oxide (CCO) as the positive electrode active material, polytetrafluoroethylene (PTFE) as the binder, and carbon nanotubes (50 nm in diameter and 30 µm in length) as the conductive agent are added to a mixer in a mass ratio of 97:1.5:1.5 and dry-mixed. The mixture is then processed by an air jet mill to transform the granular binder into fibrous strands with a diameter of 100 nm and a length of 30 µm, maintaining the fibrous morphology within the mixture. This fibrous binder forms a three-dimensional network structure within the mixture, facilitating the formation of curved secondary pores in subsequent active material layers. The mixture is then hot-pressed and extruded, stretched, and hot-pressed to thin the film, forming a self-supporting membrane (100 µm thick, PD 4.15 g / cc, porosity 12.7%, secondary pore diameter 0.5 µm) of the positive electrode active material. By controlling the winding tension to maintain a layer spacing of 12.7 ± 0.5 µm, the self-supporting membrane is wound into a circular shape, forming an active material roll. Then, slices (200µm thick) are made, and a slurry with a solid content of 17% (styrene-butadiene rubber binder: sodium carboxymethyl cellulose dispersant: conductive carbon black = 40:5:55) is coated onto the current collector using a gravure process to obtain a current collector with a base coating. The sliced ​​active material film is then laminated onto the surface of the current collector with the base coating. There is a gap between adjacent single-layer active material films to form the first pore. After drying, a positive electrode is obtained (first pore: second pore = 3:3, porosity 22.5%, active material layer tortuosity 4.5, McMallin number 20).

[0079] Preparation of negative electrode sheet:

[0080] Graphite (anode active material), PTFE (binder), and CNTs (conductive material, 50 nm in diameter, 30 µm in length) were added to a mixer in a mass ratio of 97:1.5:1.5 and dry-mixed. The mixture was then processed using an air jet mill to form fibers with a diameter of 100 nm and a length of 30 µm. The mixture was then hot-pressed and extruded, stretched, and hot-pressed to thin the film, forming a self-supporting membrane for the anode active material (100 µm thickness, PD 1.80 g / cc, porosity 16%, second pore diameter 0.5 µm). The layer spacing was controlled to 16 ± 0.5 µm by controlling the winding tension. The self-supporting membrane is wound into a circle and then sliced ​​(200µm thick). A slurry with a solid content of 17% (styrene-butadiene rubber binder: sodium carboxymethyl cellulose dispersant: conductive carbon black = 30:5:65) is coated onto the current collector using a gravure process to obtain a current collector with a base coating. The sliced ​​active material membrane is then laminated onto the surface of the current collector with the base coating. There is a gap between adjacent single-layer active material membranes to form the first pore. After drying, the negative electrode is obtained. (First pore: second pore = 3:3, porosity 28%, active material layer tortuosity 2.5, McMallin number 8.9).

[0081] Examples 2 to 7 and Comparative Examples 1 to 2 are provided only on the positive electrode sheet, and only the second hole is provided on the negative electrode sheet; Examples 8 to 11 and Comparative Examples 3 to 4 are provided only on the negative electrode sheet, and only the second hole is provided on the positive electrode sheet; The ratio of the total volume of the first hole to the total volume of the second hole and the diameter of the first hole are adjusted by controlling the compaction density and porosity of the self-supporting membrane, the winding spacing (i.e., the diameter of the first hole), etc.

[0082] Comparative Example 5

[0083] Preparation of the positive electrode sheet:

[0084] Lithium cobalt oxide (CCO), polytetrafluoroethylene (PTFE), and carbon nanotubes (50 nm in diameter and 30 µm in length) were mixed at a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred uniformly under vacuum to obtain a CCO slurry with a solid content of 70 wt%. The CCO slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil current collector. The aluminum foil was then dried at 85 °C to obtain a single-sided CCO electrode with a 50 µm thick CCO material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided CCO electrode.

[0085] Preparation of negative electrode sheet:

[0086] Graphite (anode active material), PTFE (binder), and CNTs (50 nm in diameter, 30 µm in length) (conductive agent) were mixed in a mass ratio of 97:1.5:1.5. Deionized water was added, and the mixture was stirred under vacuum to obtain a cathode slurry with a solid content of 75 wt%. The cathode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector. The copper foil was dried at 85 °C to obtain a cathode sheet with a single-sided cathode material layer, the thickness of which was 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a cathode sheet with a double-sided cathode material layer. The obtained cathode sheet was then cold-pressed, cut, and slit, and dried under vacuum at 85 °C for 12 h to obtain a cathode sheet with a double-sided cathode material layer, measuring 74 mm × 867 mm and with a thickness of 0.113 mm.

[0087] The electrodes from the above embodiments and comparative examples were fabricated into stacked cells and then tested. The specific parameters and test performance are shown in Table 1.

[0088] Table 1. Changes in the ratio of the total volume of the first hole to the total volume of the second hole and test results.

[0089]

[0090] Among them, the McMalline number N of the active material layer m The ratio of the tortuosity τ of the active material layer to the porosity ε of the active material layer is calculated using the following formula:

[0091]

[0092] R ion The ionic impedance of the electrode active material layer was measured by the symmetrical cell method.

[0093] A represents the electrode area in the symmetrical cell method;

[0094] κ represents the conductivity of the electrolyte in the symmetrical cell method;

[0095] d represents the thickness of the active material layer of the electrode in the symmetrical cell method.

[0096] The above four parameters are all measured values. The porosity ε of the active material layer can also be measured by the gas displacement method. Therefore, the tortuosity τ of the active material layer can be calculated according to the above formula, and then the McMalline number of the active material layer can be calculated.

[0097] The McMulline number of an electrode reflects the ease of ion and electron transport. A higher McMulline number indicates a more tortuous pore structure within the electrode, resulting in less smooth transport of ions and electrons within the pores. Conversely, a lower McMulline number indicates smoother transport of ions and electrons within the pores.

[0098] Table 1 shows the effect of the ratio of the total volume of the first pore 10 to the total volume of the second pore 30 and the change in tortuosity on the improvement of electrical performance when the porosity of the active material layer is in the range of 10% to 50%. The data in Table 1 show that when the ratio of the total volume of the first pore 10 to the total volume of the second pore 30 is in the range of 1:3 to 6:3, and the tortuosity is in the range of 1 to 6, the kinetic and cycling performance of the electrode sheet is better. When the ratio of the total volume of the first pore 10 to the total volume of the second pore 30 is in the range of 1:3 to 3:3, the tortuosity of the positive electrode active material layer is in the range of 4 to 5, and the tortuosity of the negative electrode active material layer is in the range of 1 to 2, the kinetic and cycling performance of the electrode sheet is even better.

[0099] The data in Table 1 show that the porosity of the positive electrode active material layer is in the range of 10% to 35%, and the tortuosity τ is in the range of 3 to 6. The smaller the tortuosity τ, the better the kinetic and cycle performance. The porosity of the negative electrode active material layer is in the range of 20% to 50%, and the tortuosity τ is in the range of 1.04 to 3. The smaller the tortuosity τ of the negative electrode active material layer, the better the kinetic and cycle performance.

[0100] As can be seen from the data in Table 1, when the ratio of the total volume of the first pore to the total volume of the second pore is constant, the larger the pore diameter of the first pore, the greater the porosity of the active material layer of the electrode where the first pore is located, and the better the kinetics and cycle performance of the battery.

[0101] Table 2. Parameter variations and test results for the depth of the first hole.

[0102]

[0103] Apart from the parameters shown in Table 2, such as the ratio of the total volume of the first hole to the total volume of the second hole, the hole depth of the first hole, and the thickness of the electrode active material layer, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 12 and 17 are the same as those in Example 1.

[0104] Table 2 shows the effect of varying the depth of the first pore on improving electrical performance. The data in Table 2 indicate that, within the range of 80-700 µm, a thicker electrode active material layer results in poorer kinetic and cycling performance.

[0105] The kinetic performance test results of Example 12 in Table 2 are better than those of Comparative Example 1, while the puncture test and impact test data are worse than those of Comparative Example 1. This is because the electrode thickness in Example 12 is 80µm, while the electrode thickness in Comparative Example 1 is 200µm. The thinner the electrode, the more layers are required for the same capacity, and the higher the probability of contact between the aluminum foil and the fully charged anode in the puncture and impact tests, making it more prone to failure.

[0106] Table 3. Variation of pore diameter parameters and test results for the first pore on the side furthest from or near the current collector.

[0107]

[0108] Except for the pore size difference parameters of the first pore on the side far from or near the current collector shown in Table 3, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 18 and 19 are the same as those in Example 1.

[0109] Table 3 illustrates the effect of varying pore size differences on the electrical performance of the first pore on the side furthest from or near the current collector. The data in Table 3 shows that, within the range of 100 nm to 1 µm, the smaller the pore size difference between the furthest and near-current collector sides of the first pore, the more similar the pore size of a single first pore is at different depths, resulting in better kinetic and cycling performance. In other words, the more uniform the pore size of the first pore, the better the kinetic and cycling performance of the electrode sheet.

[0110] Table 4. Variation of spacing parameters and test results between adjacent first holes.

[0111]

[0112] Apart from the spacing parameters between adjacent first holes shown in Table 4, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 20 and 21 are the same as those in Example 3.

[0113] Table 4 shows the effect of varying the spacing between adjacent first holes on improving electrical performance. The data in Table 4 indicates that, within the range of 30µm to 150µm, a smaller spacing between adjacent first holes indicates a thinner self-supporting membrane, resulting in better kinetic and cycling performance.

[0114] Table 5. Variation of aperture parameters and test results of the second hole.

[0115]

[0116] Apart from the parameters such as the pore size and conductive agent content of the second pore shown in Table 5, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 22 and 23 are the same as those in Example 3. The pore size of the second pore is positively correlated with the conductive agent content.

[0117] Within the range of 2nm to 4µm, the larger the pore size of the second pore, the better the kinetic and cycling performance.

[0118] Table 6. Variation of pore diameter parameters of the second hole and adhesive and test results.

[0119]

[0120] Apart from the parameters such as the pore size and binder content of the second pore shown in Table 6, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 24 and 25 are the same as those in Example 3. The pore size of the second pore is also positively correlated with the binder content.

[0121] As shown in Tables 5 and 6, the pore size of the second pore can be controlled by changing the content of the conductive agent or the binder. Of course, depending on the actual needs, the pore size of the second pore can also be controlled by changing the content of both the conductive agent and the binder.

[0122] Table 7. Variation of conductive agent diameter and length parameters and test results.

[0123]

[0124] Except for the conductive agent diameter and length parameters shown in Table 7, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 26 to 29 are the same as in Example 3. The length and diameter of the conductive agent are related to the preparation method of the conductive agent and can be set independently, unaffected by the lithium battery preparation process in the embodiments of this application.

[0125] As can be seen from the data in Table 7, within the range of 10~100nm in diameter of the conductive agent, the larger the ratio of the length to the diameter of the conductive agent, the better the kinetic and cycling performance, and the better the results of the puncture test and impact test.

[0126] Table 8. Variation of adhesive diameter parameters and test results

[0127]

[0128] Except for the binder content parameters shown in Table 8, the other parameters of the electrode sheet 100 used to prepare the battery in Examples 30 and 31 are the same as in Example 3. The length and diameter of the binder are related to the binder fiberization process during electrode preparation, and the length and diameter of the binder are interrelated.

[0129] As can be seen from the data in Table 8, for adhesives with diameters ranging from 10 nm to 200 nm, the larger the ratio of the adhesive length to its diameter, the better the kinetic and cycling performance, and the better the results of puncture and impact tests.

[0130] This application also provides a method for manufacturing an electrode sheet 100, used to manufacture the electrode sheet 100 described in the above embodiments. The method for manufacturing the electrode sheet 100 includes:

[0131] An active material membrane is prepared by mixing an active material, a fibrous conductive agent, and / or a binder, wherein a plurality of second pores 30 are distributed within the active material membrane;

[0132] The active material film is wound, stacked, or wound layer by layer to form multiple layers of first holes 10, and the active material film after being wound, stacked, or wound layer by layer is sliced.

[0133] A slurry with a solid content of 15%~20% (binder:dispersant:conductive agent = 25~40:5~10:60~65) is coated onto a current collector using a gravure process to obtain a current collector 40 with a base coating. A sliced ​​active material film is then laminated onto the surface of the current collector 40 with the base coating. There is a gap between adjacent single-layer active material films to form a first pore. After drying, the electrode sheet is obtained.

[0134] Furthermore, in one embodiment of this application, the "preparation of active material film" includes: coating a mixture of active material, fibrous conductive agent, and / or binder onto the surface of a support film;

[0135] The mixed material on the surface of the support membrane is dried, and the dried mixed material is peeled off from the surface of the support membrane to form an active material film.

[0136] The thickness of the active material film is the spacing between adjacent first holes 10. According to the aforementioned test results, within the allowable range, the thinner the active material film, the better the kinetic and cycling performance of the final electrode sheet. The content range, diameter, and length of the conductive agent and binder are roughly the same as in the aforementioned embodiments, and will not be repeated here.

[0137] In the manufacturing method of this embodiment, the first hole in the obtained positive and negative electrode sheets is a spiral hole. In other embodiments, the active material film can also be intermittently wound layer by layer, so that the first hole is a plurality of concentric annular holes. Alternatively, the active material film can be formed into an active material column or active material block by layer-by-layer stacking or Z-shaped stacking, and then sliced ​​and laminated onto the surface of the current collector to obtain an electrode sheet. In this case, the plurality of first holes in the active material layer are approximately arrayed strip holes.

[0138] In another embodiment of this application, the method for manufacturing the electrode sheet 100 includes:

[0139] An active material is formed by mixing an active material, a fibrous conductive agent, and / or a binder, and a plurality of second pores 30 are distributed in the active material.

[0140] A support is provided on the surface of the current collector 40, and the active material is coated on the surface of the current collector 40, with the support being surrounded by the active material.

[0141] Remove the support to form the first hole 10.

[0142] The support includes, but is not limited to, easily shaped and decomposed materials such as paraffin wax. Paraffin wax can be applied to the surface of the current collector 40 by means of 3D printing, casting, etc., and the shape and size of the paraffin wax application form the shape and size of the first pore. After the active material is coated on the surface of the current collector 40, the paraffin wax in the active material can be removed by chemical or physical means, thereby forming the first pore 10 in the active material layer.

[0143] Please see Figure 6 The embodiments of this application also provide an electronic device 300, including an electrical component 301 and a secondary battery 200 as described in the above embodiments, wherein the electrical component 301 is electrically connected to the secondary battery 200.

[0144] The electrode sheet 100, secondary battery 200, and electronic device 300 of this application, by providing a vertical first hole 10 and a curved second hole 30 in the active material layer 20, with the curved second hole 30 connecting to the vertical first hole 10, increase the transport channels for ions and electrons, reduce transport obstacles, and also facilitate the transport and wetting of electrolyte in the longitudinal and lateral directions, reduce the concentration polarization of the electrode sheet 100, and thus improve the electrical performance of the electrode sheet 100.

[0145] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrode sheet, characterized in that, include: current collector; and An active material layer is disposed on the surface of the current collector. The porosity of the active material layer is 10-50%, and the tortuosity of the active material layer is 1.04-6. The active material layer has a plurality of first pores and a plurality of second pores. The plurality of first pores penetrate the active material layer in a direction perpendicular to the surface of the current collector, and the plurality of second pores are bent and disposed within the active material layer, and the plurality of second pores are connected to the plurality of first pores. The ratio of the total volume of the first pores to the total volume of the second pores is 1:3 to 6:

3. The first hole has single-layer active material films on both sides; The total volume of the first pore is calculated by the total length L of all monolayer active material films, the thickness T of the active material layer, and the spacing d between adjacent monolayer active material films according to formula V. 第一孔 =Calculated as L×T×d; The total volume of the second pore was determined by testing the porosity α of the self-supporting membrane using the gas displacement method, and then calculated according to the formula V1 based on the apparent volume V of the self-supporting membrane. 第二孔 = V1×ɛ.

2. The electrode sheet according to claim 1, characterized in that: The electrode is a positive electrode, the porosity of the active material layer is 10~35%, and the tortuosity of the active material layer is 3~6.

3. The electrode sheet according to claim 1, characterized in that: The electrode is a negative electrode, the porosity of the active material layer is 20-50%, and the tortuosity of the active material layer is 1.04-3.

4. The electrode sheet according to claim 1, characterized in that: The electrode is a positive electrode with a first hole diameter of 3 µm to 22 µm, and / or the electrode is a negative electrode with a first hole diameter of 5 µm to 33 µm.

5. The electrode sheet according to claim 4, characterized in that: The depth of the first hole is 100 µm to 500 µm.

6. The electrode sheet according to claim 1, characterized in that: The pore size of the second pore is 2nm~0.5µm.

7. The electrode sheet according to claim 1, characterized in that: In the plurality of first holes, the spacing between adjacent first holes is 30 µm to 100 µm.

8. The electrode sheet according to claim 1, characterized in that: Along the direction away from the current collector, the difference between the diameter of the first hole on the side away from the current collector and the diameter of the first hole on the side closer to the current collector is 100 nm to 1 µm.

9. The electrode sheet according to claim 1, characterized in that: The ratio of the total volume of the first hole to the total volume of the second hole is 1:1 to 2:

1.

10. The electrode sheet according to claim 1, characterized in that: The active material layer includes an active material, a conductive agent, and / or a binder, wherein the conductive agent and / or the binder are fibrous, and a plurality of second pores are formed between the active material and the conductive agent and / or the binder.

11. The electrode sheet according to claim 10, characterized in that: The conductive agent has a diameter of 10 nm to 50 nm and a length of 30 nm to 50 nm.

12. The electrode sheet according to claim 10, characterized in that: The diameter of the adhesive is 10 nm to 100 nm, and the length of the adhesive is 30 nm to 50 nm.

13. The electrode sheet according to claim 10, characterized in that: The conductive agent accounts for 0.5-10% of the weight of the active material layer.

14. The electrode sheet according to claim 10, characterized in that: The adhesive accounts for 0.5-10% of the weight of the active material layer.

15. A method for manufacturing an electrode sheet, used to manufacture the electrode sheet according to any one of claims 1-14, characterized in that, The method for manufacturing the electrode sheet includes: An active material membrane is prepared by mixing an active material, a fibrous conductive agent, and / or a fibrous binder, wherein the active material membrane has a plurality of second pores distributed therein; The active material film is wound, stacked, or wound layer by layer, and the wound, stacked, or wound layer by layer active material film is sliced. A slurry with a solid content of 15% to 20% is coated onto a current collector using a gravure process to obtain a current collector with a base coating. The sliced ​​active material film is then laminated onto the surface of the current collector with the base coating. There is a gap between adjacent single-layer active material films to form a first pore. After drying, the electrode sheet is obtained. In the slurry with a solid content of 15% to 20%, the ratio of binder:dispersant:conductive agent is 25 to 35: 5 to 10: 60 to 70.

16. The method for manufacturing the electrode sheet according to claim 15, characterized in that: The "preparation of active material membranes" includes: A mixture of active materials, fibrous conductive agents, and / or fibrous binders is coated onto the surface of the support membrane. The mixed material on the surface of the support membrane is dried, and the dried mixed material is peeled off from the surface of the support membrane to form an active material film.

17. A method for manufacturing an electrode sheet, used to manufacture the electrode sheet according to any one of claims 1-14, characterized in that, The method for manufacturing the electrode sheet includes: An active material is formed by mixing an active material, a fibrous conductive agent, and / or a fibrous binder, with multiple second pores distributed within the active material. A support is provided on the surface of the current collector, and the active material is coated on the surface of the current collector, with the support being surrounded by the active material. Remove the support to form the first hole.

18. A secondary battery, characterized in that, It includes a packaging body and an electrode sheet as described in any one of claims 1-14, wherein the electrode sheet is disposed in the packaging body.

19. An electronic device, characterized in that, It includes an electrical component and the secondary battery of claim 18, wherein the electrical component is electrically connected to the secondary battery.

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