Secondary battery and electric equipment

Abstract

The invention provides a secondary battery and electric equipment, the secondary battery comprises a pole piece, the pole piece comprises a current collector and a pole piece active layer arranged on at least one surface of the current collector, the pole piece active layer has a pore structure, and in a pore diameter distribution diagram of the pole piece active layer, the pore diameter distribution diagram is larger than the pore diameter distribution diagram. Comprising a first characteristic peak in a range of 0-2 [mu] m, a second characteristic peak in a range of 2-15 [mu] m and a third characteristic peak in a range of 15-500 [mu] m. By constructing a reasonable pore distribution structure, the internal tortuosity of the battery pole piece is reduced, and the dynamic performance of the battery pole piece is improved, so that the low-temperature performance, the quick charge performance and the cycle life of the battery are optimized.

Description

Technical Field

[0001] This application relates to the field of energy storage device technology, specifically to a secondary battery and electrical equipment. Background Technology

[0002] With the increasing demand for low-temperature fast charging technology and high-load, high-performance in the energy storage and electric vehicle sectors, the performance requirements for batteries are also becoming more and more stringent.

[0003] In existing technologies, battery electrodes often possess micro- and nano-sized pore structures. However, these battery electrodes generally suffer from an unreasonable distribution of pore structures within the battery, leading to poor kinetic performance. Summary of the Invention

[0004] This application provides a secondary battery and an electrical device to solve the problems of unreasonable pore structure distribution inside the battery and poor dynamic performance of the battery electrode in the prior art.

[0005] To solve the above problems, this application is implemented as follows: In a first aspect, embodiments of this application provide a secondary battery, including an electrode, the electrode including a current collector and an electrode active layer disposed on at least one side of the current collector, the electrode active layer having a porous structure, and the pore size distribution diagram of the electrode active layer including a first characteristic peak in the range of 0~2μm, a second characteristic peak in the range of 2~15μm and a third characteristic peak in the range of 15~500μm.

[0006] Optionally, in the pore size distribution diagram of the electrode active layer, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak satisfy the following: Q1:Q2=1:(0.2~0.5); And / or Q1:Q3 = 1:(0.015~0.5).

[0007] Optionally, the surface of the electrode active layer is provided with grooves.

[0008] Optionally, the groove satisfies at least one of the following conditions: a. The width of the groove ranges from 10 to 500 μm; b. The ratio of the depth of the groove to the thickness of the electrode active layer is (0.05~0.95):1; c. The spacing between the grooves ranges from 80 to 5000 μm.

[0009] Optionally, the groove may be at least one of a straight line, a mesh, and an S-shape.

[0010] Optionally, the cross-sectional width of the groove decreases along the direction from the surface of the active layer of the electrode to the bottom of the groove.

[0011] Optionally, in the pore size distribution diagram of the electrode active layer, the total pore volume V1 in the range of 0~2μm, the total pore volume V2 in the range of 2~15μm, and the total pore volume V3 in the range of 15~500μm satisfy the following: V1:V2=(5~10):(1~3); And / or, V1:V3=(5~10):(1~5).

[0012] Optionally, the electrode is a positive electrode and / or a negative electrode.

[0013] Optionally, the secondary battery further includes a separator disposed between the positive electrode and the negative electrode, wherein the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode satisfy the following: K2:K3=(2~4):(1~3); And / or, K1:K3=(1~2):(1~3).

[0014] Optionally, the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode satisfy the following: T2:T3 = (1~2):(6~15); And / or, T1:T3=(5~10):(6~15).

[0015] Secondly, embodiments of this application provide an electrical device, which includes the secondary battery described in any of the first aspects above.

[0016] The secondary battery provided in this application embodiment has a three-dimensional pore structure with a first characteristic peak in the range of 0~2μm, a second characteristic peak in the range of 2~15μm, and a third characteristic peak in the range of 15~500μm in the pore size distribution diagram of the active layer of the electrode. Among them, the third characteristic peak in the range of 15~500μm corresponds to a large liquid phase channel, which can significantly accelerate the penetration rate of electrolyte inside the battery electrode and reduce the penetration resistance; the second characteristic peak in the range of 2~15μm and the first characteristic peak in the range of 0~2μm correspond to relatively small channels, which can optimize the uniformity of electrolyte distribution in the battery electrode, avoid local electrolyte enrichment or lack, and at the same time, the electrolyte can be retained in the gaps between the active material particles by strong capillary force, preventing electrolyte loss. The pores with tri-pore size distribution peaks can balance the permeability and capillary force during liquid phase wetting of the electrode, effectively solving the problems of insufficient electrolyte wetting and localized drying caused by the single pore size of traditional battery electrodes. This improves the electrolyte wetting effect and ensures the stability of the battery's initial performance. Furthermore, this tri-pore structure optimizes the ion migration path inside the battery, significantly reducing the tortuosity inside the electrode and minimizing path obstruction during ion migration. This significantly improves ion transport efficiency, optimizes the battery's low-temperature performance, reduces capacity loss caused by ion migration obstruction in low-temperature environments, and maintains stable discharge capacity. Simultaneously, it enhances fast-charging performance, supports high-rate fast charging, and effectively suppresses lithium plating on the electrode surface, ensuring fast-charging safety. In addition, it extends cycle life. During long-term cycling, the optimized pore structure buffers the volume expansion and contraction of active materials, reducing active material shedding and electrode cracking, and minimizing irreversible lithium-ion loss. Furthermore, this structure can expand the upper limit of electrode capacity load, breaking the capacity load limitation caused by insufficient pore design of traditional electrodes. Even with an increase in the active material load, the active material can still be fully utilized through efficient electrolyte wetting and ion transport, providing strong support for the development of high-energy-density secondary batteries and meeting the market demand for high-performance batteries. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a top view of a secondary battery electrode according to an embodiment of this application; Figure 2 This is a top view of a secondary battery electrode with a mesh-like groove according to an embodiment of this application; Figure 3 This is a top view of another secondary battery electrode with a mesh-like groove according to an embodiment of this application; Figure 4 This is a top view of a secondary battery electrode with an S-shaped groove according to an embodiment of this application; Figure 5 This is a cross-sectional view of a secondary battery electrode according to an embodiment of this application; Figure 6 This is a block diagram of an electrical device according to an embodiment of this application.

[0019] Figure label: 1-Current collector; 2-Active layer of electrode; 3-Porous structure formed by pore-forming agent; 4-Linear groove; 5-Mesh groove; 6-S-shaped groove. Detailed Implementation

[0020] 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, 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.

[0021] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0022] The secondary battery and electrical equipment provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0023] Reference Figure 1 This application provides a secondary battery including an electrode, which includes a current collector 1 and an electrode active layer 2 disposed on at least one side of the current collector 1. The electrode active layer 2 has a porous structure 3. In the pore size distribution diagram of the electrode active layer, there are a first characteristic peak in the range of 0~2μm, a second characteristic peak in the range of 2~15μm, and a third characteristic peak in the range of 15~500μm.

[0024] Specifically, the secondary battery provided in the embodiments of this application can be prepared by the following methods: Step 101: The active material, binder, conductive agent, solvent and pore-forming agent are stirred to prepare a stable homogenized slurry; Step 102: The homogenized slurry is coated onto the current collector, dried, and rolled, and then the electrode sheet is processed to create pores. Step 103: Immerse the processed electrode in the electrolyte.

[0025] In step 101, the active material can be divided into positive electrode active material or negative electrode active material. The positive electrode active material is at least one of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium titanate, and lithium nickel cobalt manganese oxide. The negative electrode active material is at least one of graphite and its derivatives, silicon carbide compounds, and silicon and its derivatives. The binder is polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), sodium alginate (SA), guar gum (GG), chitosan-based binder (CCTS), polyacrylic acid (salt)-based binder (PAA), and polyacrylonitrile-based binder (PAN). The binder is at least one of the following: polyvinyl alcohol-based binder (PVA), polyimide-based binder (PI), polyethylene oxide (PEO), and polymethyl methacrylate (PMMA); the conductive agent is at least one of the following: super P, Ketjen black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and its derivatives, and conductive carbon fibers; the solvent is at least one of the following: deionized water, alcohol, and N-methylpyrrolidone (NMP).The pore-forming agents are lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiC4BO8(LiBOB), lithium difluoro(oxalato)borate (LiC2O4F2B(LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiC2F6NO4S2(LiTFSI)). At least one of Bis(trifluoromethanesulfonyl)imide and its derivatives; the average particle size of the pore-forming agent ranges from 0.05 to 25 μm; the mass ratio of the positive electrode active material, binder, conductive agent, and pore-forming agent in the homogenized slurry is 90-97:1-2:0.5-2:0.5-3, or the mass ratio of the negative electrode active material, binder, conductive agent, and pore-forming agent in the homogenized slurry is 90-97:1-2:0.5-2:0.5-3; the solid content of the homogenized slurry is 45%-62%.

[0026] In step 102, the current collector is aluminum foil or its derivatives, or copper foil or its derivatives, such as carbon-coated aluminum foil, porous aluminum foil, etc.; the drying temperature is 90~105℃, and the drying time is 1~12h; the water content of the electrode is below 500ppm, and the compaction range of the electrode is 1.45~3.45g / cm³. 3 The thickness of the active layer of the electrode ranges from 30 to 1000 μm.

[0027] In step 103, the soaking time is 1~12h, the soaking temperature is 25~45℃, and the soaking reagent is the electrolyte used in the battery.

[0028] The ambient humidity in steps 101, 102 and 103 is 0~1%RH.

[0029] It should be noted that the pore size distribution analysis of the electrode active layer in this embodiment can be performed using mercury intrusion porosimetry (MIP). The core principle of MIP is to inject mercury into the porous structure of the electrode active layer under pressure, utilizing the property that mercury does not wet porous materials, and calculating the pore size distribution based on the intrusion behavior of mercury under different pressures. Pressure and pore size are inversely proportional: the greater the applied pressure, the smaller the pore size that mercury can overcome surface tension to enter; conversely, at lower pressures, mercury can only penetrate larger pores. By precisely controlling pressure changes and monitoring the amount of mercury intrusion in real time, a correlation between pressure, pore size, and intrusion amount can be established, thereby achieving quantitative analysis of the pore structure of the electrode active layer.

[0030] In mercury intrusion porosimetry (MIP), incremental intrusion is a core analytical indicator. Specifically, incremental intrusion refers to the volume increase of mercury penetrating the pores of the active layer of the electrode within a specific pressure range during the test. This volume increase directly corresponds to the total volume of pores of a specific size matched within that pressure range, and is the core foundational data for constructing pore size distribution curves and analyzing characteristic peak intensities. Furthermore, since there is a fixed inverse relationship between pressure and pore size, each pressure range corresponds to a unique pore size range. By correlating the incremental intrusion of different pressure ranges with their corresponding pore size ranges, a pore size distribution curve can be plotted, with pore size on the x-axis and incremental intrusion volume on the y-axis. Each data point on the curve represents the contribution of pores near a certain pore size to the total volume, while the peak value of the curve represents the pore size range corresponding to that peak value, where the pore volume proportion is the largest, indicating the most abundant pores in that range. This peak value is the peak value of the aforementioned characteristic peak. Specifically, in the application scenario of this application, within the pressure range corresponding to pore sizes of 0~2μm, the incremental mercury intrusion measured by mercury porosimetry directly reflects the total pore volume within that 0~2μm size range; within the pressure range corresponding to pore sizes of 2~15μm, the incremental mercury intrusion corresponds to the total pore volume within that range; and within the pressure range corresponding to pore sizes of 15~500μm, the incremental mercury intrusion corresponds to the total pore volume within that range. Through the aforementioned mercury porosimetry, the three-pore size distribution characteristics of the electrode active layer can be quantified, verifying the effectiveness of the electrode preparation technology of this application in pore structure design, and providing reliable test data support for battery performance optimization and technology implementation.

[0031] Furthermore, in the electrode active layer pore size distribution diagram of this application embodiment, the first characteristic peak in the range of 0~2μm, the second characteristic peak in the range of 2~15μm, and the third characteristic peak in the range of 15~500μm correspond to the three types of pores formed during the electrode preparation process: inherent pores, pores formed by pore-forming agents, and pores formed by processing.

[0032] The inherent porosity refers to the pores naturally formed in the electrode material itself during the preparation process, such as the tiny gaps created when active material particles (e.g., graphite particles) are stacked, and the gaps between conductive agent aggregates. Their size is mostly between 0 and 2 μm, constituting the first characteristic peak in the pore size distribution diagram. Subsequently, during electrode fabrication, the electrode needs to be heat-treated. During this process, the pore-forming agent within the electrode decomposes or dissolves in a specific solvent and detaches from the electrode. The space originally occupied by the pore-forming agent then forms a large number of micro / nano-sized micropores, i.e., pores formed by the pore-forming agent. The size of these pores is concentrated in the range of 2–15 μm, corresponding to the second characteristic peak in the pore size distribution diagram. Simultaneously, the pores constructed within the electrode through processing have a size concentrated in the range of 15–500 μm, forming the third characteristic peak in the pore size distribution diagram.

[0033] For example, ions can achieve rapid long-distance migration through the main channel of 15~500μm (corresponding to the pores of the third characteristic peak), cover the middle region of the electrode active layer through the branch channels of the pore-forming agent of 2~15μm (corresponding to the pores of the second characteristic peak), and then reach the surface of each active material particle through the inherent pores of 0~2μm (corresponding to the pores of the first characteristic peak). Finally, they complete the efficient migration from the positive electrode to the negative electrode (or vice versa) during charging and discharging. The presence of the three characteristic peaks in the pore size distribution diagram directly proves that the size and quantity distribution of the three types of pores in the electrode meet the design expectations. The first characteristic peak reflects the abundance of inherent pores, which can ensure the retention of electrolyte and short-distance ion transport. The second characteristic peak reflects the effectiveness of the pore-forming agent, ensuring comprehensive coverage of ion transport. The third characteristic peak verifies the processing and preparation effect, supporting the rapid long-distance migration of ions. The precise correspondence between the three types of pores and the three characteristic peaks jointly ensures the structural rationality and functional integrity of the electrode active layer, providing core structural support for the optimization of battery low-temperature performance, fast-charging performance and cycle life.

[0034] In summary, in the embodiments of this application, the pore size distribution diagram of the active layer of the secondary battery electrode exhibits a three-pore size distribution pore structure with a first characteristic peak in the range of 0~2μm, a second characteristic peak in the range of 2~15μm, and a third characteristic peak in the range of 15~500μm. The third characteristic peak in the range of 15~500μm corresponds to a large liquid phase channel, which can significantly accelerate the penetration rate of the electrolyte inside the battery electrode and reduce penetration resistance. The second characteristic peak in the range of 2~15μm and the first characteristic peak in the range of 0~2μm correspond to relatively small channels, which can optimize the uniformity of electrolyte distribution within the battery electrode, avoid local electrolyte enrichment or deficiency, and simultaneously retain the electrolyte in the gaps between active material particles due to strong capillary force, preventing electrolyte loss. The pores with tri-pore size distribution peaks can balance the permeability and capillary force during liquid phase wetting of the electrode, effectively solving the problems of insufficient electrolyte wetting and localized drying caused by the single pore size of traditional battery electrodes. This improves the electrolyte wetting effect and ensures the stability of the battery's initial performance. Furthermore, this tri-pore structure optimizes the ion migration path inside the battery, significantly reducing the tortuosity inside the electrode and minimizing path obstruction during ion migration. This significantly improves ion transport efficiency, optimizes the battery's low-temperature performance, reduces capacity loss caused by ion migration obstruction in low-temperature environments, and maintains stable discharge capacity. Simultaneously, it enhances fast-charging performance, supports high-rate fast charging, and effectively suppresses lithium plating on the electrode surface, ensuring fast-charging safety. In addition, it extends cycle life. During long-term cycling, the optimized pore structure buffers the volume expansion and contraction of active materials, reducing active material shedding and electrode cracking, and minimizing irreversible lithium-ion loss. Furthermore, this structure can expand the upper limit of electrode capacity load, breaking the capacity load limitation caused by insufficient pore design of traditional electrodes. Even with an increase in the active material load, the active material can still be fully utilized through efficient electrolyte wetting and ion transport, providing strong support for the development of high-energy-density secondary batteries and meeting the market demand for high-performance batteries.

[0035] Optionally, in the pore size distribution diagram of the electrode active layer, the peak values ​​of the first characteristic peak (Q1), the second characteristic peak (Q2), and the third characteristic peak (Q3) satisfy: Q1:Q2 = 1:(0.2~0.5); and / or, Q1:Q3 = 1:(0.015~0.5). For example, Q1:Q2 can be a range of one or both of 1:0.2, 1:0.35, and 1:0.5, and Q1:Q3 can be a range of one or both of 1:0.015, 1:0.35, and 1:0.5. Specifically, on the generated pore size distribution curve, the pore size range of 0~2μm is located. The highest point of the curve within this range, which corresponds to the maximum value of the incremental intrusion volume on the ordinate, is the peak value Q1 of the first characteristic peak. The physical meaning of the peak value Q1 of the first characteristic peak is the maximum incremental intrusion volume of mercury within the 0~2μm inherent porosity range, directly reflecting the total volume contribution capacity of the inherent porosity in this range. Similarly, on the pore size distribution curve, the pore size range of 2~15μm is found. The maximum value of the incremental intrusion volume on the ordinate corresponding to the highest point of the curve within this range is the second characteristic peak. The peak value Q2 represents the maximum incremental intrusion volume of mercury within the pore-forming range of 2-15 μm, reflecting the overall volume contribution level of micropores in this range and the effectiveness of the pore-forming process. Finally, the maximum value of the incremental intrusion volume on the vertical axis corresponding to the highest point of the pore size distribution curve within this range is the peak value Q3 of the third characteristic peak. The peak value Q3 of the third characteristic peak corresponds to the maximum incremental intrusion volume of mercury within the pore size range of 15-500 μm, which can intuitively reflect the macroscopic pore volume contribution after processing.

[0036] In this embodiment, the ratio of the aforementioned peak values ​​is based on the pore function requirements corresponding to each characteristic peak: the peak value Q1 of the first characteristic peak serves as the peak value of the inherent pores, providing the electrode with basic ion retention and contact space for the active material; the peak value Q2 of the second characteristic peak corresponds to the micropores created by the pore-forming agent, which can cover the active material particles, ensuring that the active material can contact the electrolyte more fully; the peak value Q3 of the third characteristic peak corresponds to the processed pores, which need to balance the rapid penetration of the electrolyte and the stability of the electrode structure. This ratio ensures that the electrode simultaneously meets the functional requirements of sufficient electrolyte wetting and efficient ion transport, providing structural support for optimizing the battery's low-temperature performance, fast-charging performance, and cycle life, and ensuring that the electrode transforms from a simple physical framework into an electrochemically active structure with ion transport capabilities.

[0037] Optional, refer to Figure 1 The surface of the active layer 2 of the electrode is provided with grooves.

[0038] In this embodiment, grooves are provided on the surface of the electrode active layer 2, which can improve the wetting efficiency of the electrolyte, shorten the wetting time, avoid local liquid shortage, improve the utilization rate of active materials, and ultimately improve the low temperature performance, fast charging performance and cycle life of the secondary battery, thereby achieving a comprehensive performance upgrade.

[0039] Optionally, the groove satisfies at least one of the following conditions: a. The width of the groove ranges from 10 to 500 μm; b. The ratio of the groove depth to the electrode active layer thickness is (0.05~0.95):1; c. The spacing between grooves ranges from 80 to 5000 μm.

[0040] Specifically, the groove can be formed on the surface of the electrode active layer using a specific processing technique. This technique can be at least one of ion beam etching (IBE), reactive ion etching, inductively coupled plasma etching, focused electron beam etching, focused ion beam (FIB), and embossing, or it can be combined with traditional techniques such as laser grooving, molding, and milling. The resulting groove, in the pore size distribution diagram of the electrode active layer, corresponds to a pore size within the range of 15–500 μm. Several grooves formed by the above processing can be selectively formed on the surface of the electrode active layer, and the grooves must meet at least one of the following conditions, each condition being set based on a comprehensive consideration of the feasibility of the electrode fabrication process and the battery performance requirements.

[0041] The width of the groove can be set in the range of 10~500μm to balance the electrolyte flow space and the stability of the electrode structure. If the groove width is less than 10μm, although it can reduce the space loss of the active material in the electrode, the narrow channel can easily lead to increased electrolyte flow resistance, which will reduce the wetting rate. In addition, during the electrode preparation process, the forming accuracy of the groove that is too narrow needs to be strictly controlled to avoid the collapse of the groove wall due to uneven etching depth. When using the concave-convex roll pressing process, the groove that is too narrow is prone to problems such as incomplete filling of the roll pattern and groove blockage. If the groove width is greater than 500μm, although it can reduce the electrolyte flow resistance, it will excessively squeeze the distribution space of the active material in the active layer of the electrode, resulting in a decrease in the capacity load per unit area of ​​the electrode and affecting the battery energy density. Therefore, limiting the groove width to 10~500μm can balance the content of active material and structural stability of the electrode while ensuring efficient electrolyte flow, ensuring that the electrode has both high wetting efficiency and high capacity potential.

[0042] The ratio of the groove depth to the electrode active layer thickness can be set to (0.05~0.95):1. By cooperating with the electrode active layer, the electrolyte can be fully penetrated in the electrode thickness direction. If the depth ratio is less than 0.05, meaning the groove depth is too shallow, it can only act on the surface area of ​​the electrode active layer and cannot effectively penetrate the core area in the electrode thickness direction. The electrolyte still needs to slowly penetrate to the deeper layers through the internal pores of the active layer, making it difficult to significantly improve the overall wetting efficiency. If the depth ratio is greater than 0.95, meaning the groove depth is too deep, close to or equal to the thickness of the electrode active layer, although it can shorten the electrolyte penetration path to the greatest extent, the excessively deep groove will weaken the structural strength of the electrode active layer. When using dry etching processes such as reactive ion etching and inductively coupled plasma etching, excessively deep grooves are prone to insufficient verticality of the etched sidewalls, exacerbating structural fragility. When using concave-convex roll forming, excessively deep grooves are prone to making the local thickness of the electrode active layer too thin. In subsequent battery assembly, such as winding, stacking, or cyclic use, the electrode active layer is prone to cracking and falling off, and may even lead to exposure of the current collector, causing the risk of internal short circuit in the battery. Therefore, limiting the depth ratio to (0.05~0.95):1 ensures that the groove can effectively assist the electrolyte in penetrating deep into the electrode while maintaining the structural integrity of the electrode active layer, thus avoiding structural defects from affecting battery safety and cycle life.

[0043] The spacing between grooves can be set in the range of 80~5000μm to balance the coverage of the grooves with the uniformity of the electrode active layer. If the groove spacing is less than 80μm, i.e. the grooves are too densely distributed, it will result in too many groove areas on the surface of the electrode active layer. This not only increases the complexity of the electrode manufacturing process, but also makes it more difficult to position the dense grooves when using high-precision processes such as focused electron beam etching and focused ion beam etching, requiring multiple calibrations of the etching position. When using concave-convex roll forming, the dense texture can easily lead to uneven distribution of roll pressure. At the same time, it may also cause uneven stress on the electrode surface, which can easily lead to local stress concentration during molding, resulting in the delamination of the electrode active layer. If the groove spacing is greater than 5000μm, i.e. the grooves are too sparsely distributed, the area of ​​the electrode surface not covered by the grooves will be too large. The electrolyte in these areas still needs to rely on the pores inside the active layer to penetrate, resulting in significant differences in the wetting rate of different areas of the electrode, causing local insufficient wetting. This affects the uniform migration of lithium ions in the electrode, and consequently leads to local overheating or uneven capacity decay during battery charging and discharging. Therefore, limiting the groove spacing to 80~5000μm can achieve a reasonable distribution of grooves on the electrode surface, ensuring that the electrolyte can uniformly cover the surface of the electrode active layer, while reducing the difficulty of the preparation process and maintaining the uniformity and stability of the electrode surface structure.

[0044] Optionally, the groove shape can be at least one of straight, mesh, and S-shaped.

[0045] Specifically, refer to Figure 1 The grooves are straight in shape. The straight grooves 4 are distributed continuously in a straight line on the surface of the active layer of the electrode. The extension direction of the grooves can be set according to the application scenario of the electrode and the electrolyte flow requirements, such as along the length direction, width direction or a specific inclined direction of the electrode. The processing difficulty of straight grooves is low. They can be quickly formed by processes such as concave-convex roller pressing and laser straight groove engraving. They can also provide a smooth flow path for the electrolyte in a straight direction, reducing the turning resistance of the electrolyte during the transmission process.

[0046] Reference Figure 2 and Figure 3 The grooves are mesh-like in shape. The mesh-like groove 5 consists of several intersecting grooves, such as transverse and longitudinal grooves, or oblique and transverse grooves. These grooves can be interconnected or disconnected, forming a mesh-like structure covering the surface of the electrode active layer. Figure 2 The transverse grooves are interconnected. Figure 3 The transverse grooves in the mesh are disconnected from each other. The mesh-like grooves allow for omnidirectional diffusion of the electrolyte on the electrode surface, avoiding the limitation of linear grooves that can only guide the electrolyte in one direction. This allows the electrolyte to quickly cover all areas of the electrode surface through the mesh channels, making it particularly suitable for larger electrodes and effectively solving the problem of uneven electrolyte wetting between the electrode edges and the center.

[0047] Reference Figure 4 The grooves are S-shaped. The S-shaped grooves 6 are distributed in a continuous S-curve pattern on the surface of the electrode active layer. The curvature of the curve can be adjusted according to the electrode structure and process precision requirements. This allows for an increase in the total extension length of the grooves within the same electrode length or width range, thereby expanding the contact area between the electrolyte and the electrode active layer. Simultaneously, the curved structure can buffer the stress on the electrode during winding and stacking to a certain extent, reducing the risk of localized breakage caused by the rigid straight-line structure of the grooves. This design is suitable for secondary battery electrodes with high requirements for electrolyte contact area and electrode flexibility.

[0048] In the embodiments of this application, grooves of different shapes can improve the wetting efficiency of electrolyte, shorten the wetting time, avoid local liquid shortage, improve the utilization rate of active materials, and ultimately improve the low-temperature performance, fast charging performance and cycle life of secondary batteries, thereby achieving a comprehensive performance upgrade.

[0049] Optional, refer to Figure 5 Along the surface of the active layer 2 of the electrode, pointing towards the bottom of the groove, the cross-sectional width of the groove decreases.

[0050] Specifically, the cross-sectional width of the groove starts from the surface of the active layer of the electrode and gradually narrows with increasing depth. At the electrode surface, the cross-sectional width is the largest, consistent with the opening width of the groove on the surface. As it extends towards the bottom of the groove, the width decreases until it reaches its minimum at the bottom. For example, the cross-section may be wider at the top and narrower at the bottom, such as a trapezoid or V-shape. The specific shape can be adjusted according to the processing precision and electrode structure requirements.

[0051] In this embodiment, the decreasing cross-sectional width reduces the resistance of the electrolyte entering the groove from the electrode surface. The wide opening on the surface allows for rapid electrolyte intake, while the gradual narrowing along the depth direction creates a guiding effect, directing the electrolyte towards the bottom of the groove and the surrounding pores of the active layer, thus preventing electrolyte accumulation on the groove surface. Simultaneously, the narrowed groove walls enhance structural stability. When using processes such as ion beam etching or focused ion beam etching, the inclined or arc-shaped groove walls reduce stress concentration, lowering the risk of the active layer detaching from the groove walls during subsequent assembly and cycling.

[0052] Optionally, in the pore size distribution diagram of the electrode active layer, the total pore volume V1 in the range of 0~2μm, the total pore volume V2 in the range of 2~15μm, and the total pore volume V3 in the range of 15~500μm satisfy: V1:V2=(5~10):(1~3); and / or, V1:V3=(5~10):(1~5).

[0053] Specifically, the total volume of pores in the 0~2μm range is denoted as V1. This pore size is inherent to the electrode, primarily originating from naturally formed gaps during the stacking of active material particles and tiny voids between conductive agent aggregates. It represents the naturally occurring basic pore structure during electrode fabrication. The total volume of pores in the 2~15μm range is denoted as V2, corresponding to pores formed by the pore-forming agent. Heat treatment of the electrode is required; when the pore-forming agent decomposes into gas and detaches from the electrode, the space originally occupied by the agent can form micron-sized micropores. The total volume of pores in the 15~500μm range is denoted as V3, corresponding to the processed groove pores. These are relatively large liquid-phase channels constructed through processes such as ion beam etching and concave-convex roll forming, used to accelerate electrolyte penetration along the length or width of the electrode. The total volume of these three types of pores must satisfy the following ratio: V1:V2 = (5~10):(1~3); and / or, V1:V3 = (5~10):(1~5).

[0054] It should be noted that the values ​​of V1, V2, and V3 mentioned above were all obtained through the mercury intrusion porosimetry test. During the test, mercury was injected into the pores of the active layer of the electrode under progressively increasing pressure. Taking advantage of the inverse relationship between pressure and pore size, the amount of mercury intrusion under different pressures was recorded. Subsequently, the pressure data was converted into corresponding pore size data, and the amount of mercury intrusion under each pressure was divided into incremental intrusion volumes for different pore size intervals. Finally, all incremental intrusion volumes within the three target pore size intervals of 0~2μm, 2~15μm, and 15~500μm were accumulated respectively to obtain the total pore volume V1, V2, and V3 for each interval, which can reflect the actual volume ratio of each type of pore.

[0055] In the embodiments of this application, the total volumes V1, V2, and V3 of the pores in each interval can reflect the actual volume ratio of each type of pore, avoiding performance defects caused by excessive or insufficient single pore type. For the total volume V1 of the pores in the range of 0~2μm, the electrolyte can be efficiently retained by capillary force, providing sufficient carriers for ions and preventing the electrolyte from being lost rapidly due to excessively large pores; for the total volume V2 of the pores in the range of 2~15μm, the electrolyte can be guided to the spaces between active material particles, while avoiding excessive crowding of the active material space by micropores, allowing the electrolyte to diffuse evenly to the deep layers of the electrode and improving the utilization rate of the active material; for the total volume V3 of the pores in the range of 15~500μm, the externally injected electrolyte can be quickly received, shortening the diffusion time of the electrolyte on the electrode surface.

[0056] Optionally, the electrode can be a positive electrode and / or a negative electrode.

[0057] Specifically, the structural design can be adjusted based on the characteristics of the positive and negative electrode materials and the performance requirements of the secondary battery to adapt to the electrolyte wetting and ion transport needs of the two types of electrodes. The active materials of the positive electrode are typically ternary materials, lithium iron phosphate materials, or lithium manganese iron phosphate materials, which can release lithium ions during battery charging and accept lithium ions during discharge, providing the electrochemical activity basis for battery energy output. The active materials of the negative electrode are mostly silicon-based materials, whose main function is to store lithium ions during charging and release lithium ions during discharge, forming a lithium ion cycle migration path with the positive electrode.

[0058] Optionally, the secondary battery also includes a separator, which is disposed between the positive electrode and the negative electrode. The porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode satisfy: K2:K3=(2~4):(1~3); and / or, K1:K3=(1~2):(1~3).

[0059] The separator plays a role in physically isolating the positive and negative electrodes to prevent short circuits inside the battery. The separator needs to have good ion permeability to provide a stable channel for the migration of ions between the positive and negative electrodes, thereby ensuring the normal charge and discharge cycle of the battery.

[0060] It should be noted that porosity refers to the proportion of the volume of pores inside a material to the total volume of the material. The formula for calculating porosity is: Porosity = Total pore volume / Total volume of electrode or diaphragm. Here, the total pore volume refers to the sum of the volumes of all pores inside the electrode or diaphragm, and the total volume of the electrode or diaphragm refers to the overall apparent volume of the electrode or diaphragm itself. This formula can quantify the porosity ratio of the electrode and diaphragm.

[0061] Specifically, the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode satisfy the ratio K2:K3=(2~4):(1~3); and / or K1:K3=(1~2):(1~3). A higher separator porosity reduces the transport resistance of ions crossing the separator, avoiding a decrease in charge / discharge efficiency due to separator obstruction. Matching the porosity of the positive and negative electrodes creates a reasonable porosity gradient with the separator. This ensures uniform distribution of the electrolyte among the three, providing sufficient carriers for ion migration, and avoids structural problems caused by excessively high porosity. Excessively high electrode porosity can reduce the density of active materials, thus affecting the battery's energy density.

[0062] Optionally, the average pore size T1 of the negative electrode, the average pore size T2 of the diaphragm, and the average pore size T3 of the positive electrode satisfy: T2:T3=(1~2):(6~15); and / or, T1:T3=(5~10):(6~15).

[0063] The average pore size refers to the statistical average of the pore sizes of all pores within the material. When using the mercury intrusion porosimetry method, the pore size distribution curve is obtained by testing the volume of mercury intrusion under different pressures. Then, the volume-weighted average of all pore sizes is calculated using the pore volume as the weight. That is, the proportion of the pore volume corresponding to a certain pore size to the total pore volume is multiplied by the pore size and summed to obtain the average pore size.

[0064] In this embodiment, the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode satisfy the ratio T2:T3=(1~2):(6~15); and / or, T1:T3=(5~10):(6~15). This ensures smooth ion passage while effectively intercepting active material particles, such as ternary material particles in the positive electrode and graphite particles in the negative electrode, preventing particles from penetrating the separator and causing internal short circuits. The average pore size of the negative electrode can accommodate the volume expansion characteristics of active materials such as graphite and silicon. When the volume of the active material changes during charging and discharging, this pore size can reduce the risk of pore blockage and ensure continuous unobstructed ion transport channels. The slightly larger average pore size of the positive electrode can accelerate the penetration rate of the electrolyte in the positive electrode active layer, reduce ion transport lag, and improve charging and discharging efficiency.

[0065] The performance of the secondary battery provided in the embodiments of this application will be further illustrated below with specific examples.

[0066] Example 1 This application provides a secondary battery, including a positive electrode, a negative electrode, and a separator. The preparation method includes the following steps: stacking the positive electrode, negative electrode, and separator in sequence, with the separator positioned between the positive and negative electrodes, and then winding them to obtain a bare cell; then placing the bare cell in an outer packaging, baking to remove moisture, injecting electrolyte, and vacuum packaging to obtain a secondary battery (full cell).

[0067] The above-mentioned positive electrode sheet is prepared by the following method: Step 201: The positive electrode active material (lithium manganese iron phosphate), binder (polyvinylidene fluoride), conductive agent (carbon nanotubes), and pore-forming agent (lithium tetrafluoroborate) are added to a solvent (N-methylpyrrolidone) in a ratio of 96.7:0.8:0.4:1.3. After stirring, a stable homogenized slurry is prepared with a solid content of 58.8% and a viscosity of 9000 mPa·s. The particle size of the lithium tetrafluoroborate (LiBF4) solid particles is 3 μm.

[0068] Step 202: The slurry is coated onto the current collector (aluminum foil, 14 μm), dried, and rolled to obtain an electrode with a coating (active layer) and a compaction density of 2.4 g / cm³. 3 The single-sided thickness of the active layer is 232 μm, and the porosity of the electrode is 25%. Then, the electrode is processed with long straight grooves. The width of the grooves is 200 μm, the depth of the grooves is 116 μm, the spacing between the grooves is 1000 μm, and the ratio of the groove depth to the single-sided thickness of the active layer of the electrode is 0.5:1.

[0069] Step 203: The processed electrode sheet is immersed in the electrolyte for 2 hours at a temperature of 45°C. The pore-forming agent particles dissolve in the electrolyte to obtain the positive electrode sheet. The electrolyte solution is a 0.8 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent of the electrolyte is a mixture of ethyl methyl carbonate (C4H8O3, EMC), dimethyl carbonate (C3H6O3, DMC), and ethylene carbonate (C3H4O3, EC) in a ratio of 4:4:2. At this time, the porosity of the positive electrode sheet is 36.5%.

[0070] The above-mentioned negative electrode sheet is prepared by the following method: Step 301: The negative electrode active material (graphite), binder (styrene-butadiene rubber and sodium carboxymethylcellulose, SBR & CMC), conductive agent (carbon nanotubes), and pore-forming agent (lithium tetrafluoroborate) are added to a solvent (deionized water) in a ratio of 95.2:0.8:0.4:0. After stirring, a stable homogenized slurry is prepared with a solid content of 48.6% and a viscosity of 5000 mPa·s. The particle size of the lithium tetrafluoroborate (LiBF4) solid particles is 3 μm.

[0071] Step 302: The slurry is coated onto the current collector (copper foil, 6 μm), dried, and rolled to obtain a coated electrode with a compaction of 1.65 g / cm³. 3 The thickness on one side is 192μm, and the porosity of the electrode is 28%.

[0072] The aforementioned diaphragm is made of 10μm porous membrane material such as polypropylene (PP) or polyethylene (PE).

[0073] The secondary battery prepared above has the following measurement parameters: In the active layer of the positive electrode, the ratio of the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak is: Q1:Q2:Q3 = 1:0.31:0.22.

[0074] In the active layer of the positive electrode, the ratio of the total pore volume V1 in the range of 0~2μm, the total pore volume V2 in the range of 2~15μm, and the total pore volume V3 in the range of 15~500μm is as follows: V1:V2:V3 = 5:1:2.5.

[0075] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2:3:1.8.

[0076] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 10:1.5:6.

[0077] The specific values ​​of Q1, Q2, and Q3 are 0.0275 mL / g, 0.0085 mL / g, and 0.0061 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1031 mm. 3 0.0206mm 3 0.0515mm 3 The specific values ​​of K3, K2, and K1 are 36.50%, 54.75%, and 32.85%, respectively; the specific values ​​of T3, T2, and T1 are 1.00μm, 0.15μm, and 0.60μm, respectively.

[0078] Example 2: Example 2 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the groove width is reduced to 20 μm, so that in the pore size distribution diagram of the active layer of the positive electrode sheet, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are: Q1:Q2:Q3=1:0.31:0.1.

[0079] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1.2:2.

[0080] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 1.5:2.5:1.8.

[0081] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 8:1.5:6.

[0082] The specific values ​​of Q1, Q2, and Q3 are 0.0300 mL / g, 0.0093 mL / g, and 0.0030 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1001 mm. 3 0.0240mm 3 0.0400mm 3 The specific values ​​of K3, K2, and K1 are 34.20%, 57.00%, and 41.04%, respectively; the specific values ​​of T3, T2, and T1 are 0.43μm, 0.08μm, and 0.32μm, respectively.

[0083] Example 3: Example 3 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the width of the groove is increased to 500 μm, so that in the pore size distribution diagram of the active layer of the positive electrode sheet, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are: Q1:Q2:Q3 = 1:0.31:0.5.

[0084] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:5.

[0085] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.5:3.4:1.8.

[0086] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 15:1.5:6.

[0087] The specific values ​​of Q1, Q2, and Q3 are 0.0281 mL / g, 0.0087 mL / g, and 0.0141 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.0833 mm. 3 0.0167mm 3 0.0833mm 3 The specific values ​​of K3, K2, and K1 are 38.20%, 51.95%, and 27.50%, respectively; the specific values ​​of T3, T2, and T1 are 0.90μm, 0.09μm, and 0.36μm, respectively.

[0088] Example 4: Example 4 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode, the groove depth is adjusted so that the ratio of groove depth to the thickness of the active layer is 0.05:1. This results in the following values ​​in the pore size distribution diagram of the positive electrode active layer: the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak. Q1:Q2:Q3 = 1:0.31:0.15.

[0089] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:1.

[0090] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 1.2:2:1.8.

[0091] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 8:1.5:6.

[0092] The specific values ​​of Q1, Q2, and Q3 are 0.0282 mL / g, 0.0087 mL / g, and 0.0042 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1159 mm. 3 0.0232mm 3 0.0232mm 3 The specific values ​​of K3, K2, and K1 are 33.80%, 56.33%, and 50.70%, respectively; the specific values ​​of T3, T2, and T1 are 0.58μm, 0.13μm, and 0.43μm, respectively.

[0093] Example 5: Example 5 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode, the groove depth is adjusted so that the ratio of groove depth to the thickness of the active layer is 0.95:1. This results in the following values ​​in the pore size distribution diagram of the positive electrode active layer: the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are: Q1:Q2:Q3 = 1:0.31:0.3.

[0094] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:3.5.

[0095] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.2:3:1.8.

[0096] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 13:1.5:6.

[0097] The specific values ​​of Q1, Q2, and Q3 are 0.0264 mL / g, 0.0082 mL / g, and 0.0079 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.0993 mm. 3 0.0199mm 3 0.0695mm 3 The specific values ​​of K3, K2, and K1 are 39.30%, 53.59%, and 32.15%, respectively; the specific values ​​of T3, T2, and T1 are 1.13μm, 0.13μm, and 0.43μm, respectively.

[0098] Example 6: Example 6 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the spacing between the grooves is increased to 5000 μm, so that in the pore size distribution diagram of the active layer of the positive electrode sheet, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are: Q1:Q2:Q3 = 1:0.31:0.18.

[0099] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:1.5.

[0100] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 1.6:2.5:1.8.

[0101] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 9:1.5:6.

[0102] The specific values ​​of Q1, Q2, and Q3 are 0.0266 mL / g, 0.0082 mL / g, and 0.0048 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1104 mm. 3 0.0221mm 3 0.0331mm 3 The specific values ​​of K3, K2, and K1 are 34.50%, 53.91%, and 38.81%, respectively; the specific values ​​of T3, T2, and T1 are 1.08μm, 0.18μm, and 0.72μm, respectively.

[0103] Example 7: Example 7 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the spacing between the grooves is adjusted to 80 μm, so that in the pore size distribution diagram of the active layer of the positive electrode sheet, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are: Q1:Q2:Q3 = 1:0.31:0.4. The ratio of the total pore volume V1 (0~2μm), V2 (2~15μm), and V3 (15~500μm) in the pore size distribution diagram of the positive electrode active layer is: V1:V2:V3 = 5:1:4.

[0104] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 3:3.8:1.8.

[0105] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 14:1.5:6.

[0106] The specific values ​​of Q1, Q2, and Q3 are 0.0282 mL / g, 0.0087 mL / g, and 0.0113 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1013 mm. 3 0.0203mm 3 0.0810mm 3The specific values ​​of K3, K2, and K1 are 42.20%, 53.45%, and 25.32%, respectively; the specific values ​​of T3, T2, and T1 are 1.40μm, 0.15μm, and 0.60μm, respectively.

[0107] Example 8: Example 8 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the shape of the processed groove is set as follows: Figure 4 As shown in the S-shape, the peak values ​​of the first characteristic peak (Q1), the second characteristic peak (Q2), and the third characteristic peak (Q3) in the pore size distribution diagram of the active layer of the positive electrode are: Q1:Q2:Q3 = 1:0.31:0.27.

[0108] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:2.6.

[0109] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.3:3.5:1.8.

[0110] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 10.5:1.5:6.

[0111] The specific values ​​of Q1, Q2, and Q3 are 0.0276 mL / g, 0.0086 mL / g, and 0.0075 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1047 mm. 3 0.0209mm 3 0.0544mm 3 The specific values ​​of K3, K2, and K1 are 37.50%, 57.07%, and 29.35%, respectively; the specific values ​​of T3, T2, and T1 are 1.12 μm, 0.16 μm, and 0.64 μm, respectively.

[0112] Example 9: Example 9 provides a secondary battery, which differs from Example 1 in that, in the preparation process of the positive electrode sheet, in step 202, the shape of the processed groove is set as follows: Figure 2 The mesh-like structure shown results in the following: in the pore size distribution diagram of the positive electrode active layer, the peak values ​​of the first characteristic peak (Q1), the second characteristic peak (Q2), and the third characteristic peak (Q3) are: Q1:Q2:Q3 = 1:0.31:0.31.

[0113] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1:2.9.

[0114] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.6:3.4:1.8.

[0115] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 12:1.5:6.

[0116] The specific values ​​of Q1, Q2, and Q3 are 0.0271 mL / g, 0.0084 mL / g, and 0.0084 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1060 mm. 3 0.0212mm 3 0.0615mm 3 The specific values ​​of K3, K2, and K1 are 39.30%, 51.39%, and 27.21%, respectively; the specific values ​​of T3, T2, and T1 are 0.72μm, 0.09μm, and 0.36μm, respectively.

[0117] Example 10: Example 10 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the shape of the processed groove is set as follows: Figure 3 The mesh-like structure shown results in the following: in the pore size distribution diagram of the positive electrode active layer, the peak values ​​of the first characteristic peak (Q1), the second characteristic peak (Q2), and the third characteristic peak (Q3) are: Q1:Q2:Q3 = 1:0.31:0.29.

[0118] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3=5:1:2.8.

[0119] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.5:3.4:1.8.

[0120] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 11:1.5:6.

[0121] The specific values ​​of Q1, Q2, and Q3 are 0.0290 mL / g, 0.0090 mL / g, and 0.0084 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.1039 mm. 3 0.0208mm 3 0.0582mm 3 The specific values ​​of K3, K2, and K1 are 38.10%, 51.82%, and 27.43%, respectively; the specific values ​​of T3, T2, and T1 are 0.88μm, 0.12μm, and 0.48μm, respectively.

[0122] Example 11: Example 11 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode, the particle size of the pore-forming agent LiBF4 solid particles is increased to 10 μm, so that in the pore size distribution diagram of the active layer of the positive electrode, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak are as follows: Q1:Q2:Q3 = 1:0.4:0.22.

[0123] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:1.5:2.5.

[0124] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.1:3:1.8.

[0125] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 9:1.5:6.

[0126] The specific values ​​of Q1, Q2, and Q3 are 0.0280 mL / g, 0.0112 mL / g, and 0.0062 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.0973 mm. 3 0.0292mm 3 0.0487mm 3 The specific values ​​of K3, K2, and K1 are 36.50%, 52.14%, and 31.29%, respectively; the specific values ​​of T3, T2, and T1 are 1.02μm, 0.17μm, and 0.68μm, respectively.

[0127] Example 12: Example 12 provides a secondary battery, which differs from Example 1 in that, during the preparation of the positive electrode sheet, the proportion of the pore-forming agent is increased, so that the ratio of active material, binder, conductive agent, and pore-forming agent is 96.7:0.8:0.4:3, thereby making the peak values ​​of the first characteristic peak Q1, the second characteristic peak Q2, and the third characteristic peak Q3 in the pore size distribution diagram of the active layer of the positive electrode sheet as follows: Q1:Q2:Q3 = 1:0.5:0.22.

[0128] The proportions of the total pore volume V1 in the pore size distribution diagram of the positive electrode active layer, the total pore volume V2 in the pore size distribution diagram of the pore size distribution diagram of the positive electrode active layer are as follows: V1:V2:V3 = 5:3:2.5.

[0129] The ratio of the porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode is: K3:K2:K1 = 2.4:3.5:1.8.

[0130] The ratio of the average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode is: T3:T2:T1 = 7:1.5:6.

[0131] The specific values ​​of Q1, Q2, and Q3 are 0.0269 mL / g, 0.0135 mL / g, and 0.0059 mL / g, respectively; in a space of 0.2 mm × 1.2 mm × 2 mm = 0.48 mm 3 In the positive electrode sample, the specific values ​​of V1, V2, and V3 are 0.0859 mm. 3 0.0516mm 3 0.0430mm 3 The specific values ​​of K3, K2, and K1 are 37.60%, 54.83%, and 28.20%, respectively; the specific values ​​of T3, T2, and T1 are 0.75μm, 0.16μm, and 0.64μm, respectively.

[0132] Comparative Example 1 The preparation process differs from that in Example 1. No pore-forming agent was added to the positive electrode during the preparation process, and the positive electrode was not grooved.

[0133] Performance testing: Half-cell electrochemical impedance spectroscopy (EIS) was performed on the positive electrode to determine the ion transport resistance (Rion). After assembling the positive electrode, separator, and negative electrode into a full cell, low-temperature cycling and room-temperature cycling tests were conducted, and the results are presented in the table. Furthermore, mercury intrusion porosimetry was used to determine the pore size distribution of the positive electrode.

[0134] It should be noted that in the above embodiments, the object of the half-cell electrochemical impedance spectroscopy experiment is a two-electrode test system constructed by using the prepared positive electrode as the working electrode and another existing electrode (which can be lithium metal) as the counter electrode and reference electrode; the test frequency is set to high frequency fi=100kHz, low frequency ff=10mHz; and the voltage perturbation amplitude is set to Va=5mV.

[0135] The room temperature cycle performance test involves charging and discharging the battery at 25°C for 1000 cycles. The cycle capacity retention is obtained by dividing the discharge capacity of the 1000th cycle by the discharge capacity calibrated in the 1st cycle. The charge / discharge steps are as follows: 3C constant current / constant voltage charging to the upper limit cutoff voltage, with a cutoff current of 0.05C; and 3C constant current discharging to the lower limit cutoff voltage. The low temperature cycle performance test involves charging the battery at 0°C for 1000 cycles. The cycle capacity retention is obtained by dividing the discharge capacity of the 1000th cycle by the discharge capacity calibrated in the 1st cycle. The charge / discharge steps are as follows: 0.5C constant current / constant voltage charging to the upper limit cutoff voltage, with a cutoff current of 0.05C; and 0.5C constant current discharging to the lower limit cutoff voltage. For lithium iron phosphate batteries, the upper limit cutoff voltage is 3.7V and the lower limit cutoff voltage is 2.5V. For ternary lithium batteries, the upper limit cutoff voltage is 4.25V and the lower limit cutoff voltage is 2.8V.

[0136] After testing, the porosity, the ratio between the peak value of the first characteristic peak Q1, the peak value of the second characteristic peak Q2, and the peak value of the third characteristic peak Q3 of the above embodiments, the ion transport resistance (Rion), the low temperature cycle retention rate, and the room temperature cycle retention rate were obtained.

[0137] The parameter settings for each embodiment and comparative example are shown in Table 1, and the corresponding test results are shown in Table 2.

[0138] Table 1

[0139] Table 2

[0140] Combining the data in Tables 1 and 2, it can be concluded that in the process of preparing the above-mentioned positive electrode sheet, adding a pore-forming agent and opening grooves on the electrode sheet can adjust the ratio between the peak values ​​of the first characteristic peak, the second characteristic peak, and the third characteristic peak in the pore size distribution diagram of the pore structure in the active layer of the electrode sheet. This is beneficial to improving the room temperature cycle retention rate and low temperature cycle retention rate of the secondary battery and reducing the ion transport resistance (Rion) of the electrode sheet.

[0141] The above embodiments illustrate the influence of the pore structure of the positive electrode on the performance of the secondary battery. The pore structure can also be applied to the negative electrode. Those skilled in the art can refer to the above preparation process of the positive electrode to obtain a negative electrode and a secondary battery that meet the conditions defined in this application, which will not be repeated here.

[0142] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more.

[0143] 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 or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0144] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that, The electrode includes a current collector and an active electrode layer disposed on at least one side of the current collector. The active electrode layer has a porous structure and includes a first characteristic peak in the range of 0 to 2 μm, a second characteristic peak in the range of 2 to 15 μm, and a third characteristic peak in the range of 15 to 500 μm in the pore size distribution diagram of the active electrode layer.

2. The secondary battery according to claim 1, characterized in that, In the pore size distribution diagram of the active layer of the electrode, the peak value Q1 of the first characteristic peak, the peak value Q2 of the second characteristic peak, and the peak value Q3 of the third characteristic peak satisfy the following: Q1:Q2 = 1:(0.2~0.5); And / or, Q1:Q3=1:(0.015~0.5).

3. The secondary battery according to claim 1, characterized in that, The surface of the active layer of the electrode is provided with grooves.

4. The secondary battery according to claim 3, characterized in that, The groove satisfies at least one of the following conditions: a. The width of the groove ranges from 10 to 500 μm; b. The ratio of the depth of the groove to the thickness of the electrode active layer is (0.05~0.95):1; c. The spacing between the grooves ranges from 80 to 5000 μm.

5. The secondary battery according to claim 3, characterized in that, The groove is at least one of the following shapes: straight, mesh, and S-shaped.

6. The secondary battery according to claim 3, characterized in that, The cross-sectional width of the groove decreases along the direction from the surface of the active layer of the electrode to the bottom of the groove.

7. The secondary battery according to claim 1, characterized in that, In the pore size distribution diagram of the active layer of the electrode, the total pore volume V1 in the range of 0~2μm, the total pore volume V2 in the range of 2~15μm, and the total pore volume V3 in the range of 15~500μm satisfy the following: V1:V2=(5~10):(1~3); And / or, V1:V3=(5~10):(1~5).

8. The secondary battery according to claim 1, characterized in that, The electrode is a positive electrode and / or a negative electrode.

9. The secondary battery according to claim 8, characterized in that, The secondary battery further includes a separator disposed between the positive electrode and the negative electrode. The porosity K1 of the negative electrode, the porosity K2 of the separator, and the porosity K3 of the positive electrode satisfy the following: K2:K3=(2~4):(1~3); And / or, K1:K3=(1~2):(1~3).

10. The secondary battery according to claim 9, characterized in that, The average pore size T1 of the negative electrode, the average pore size T2 of the separator, and the average pore size T3 of the positive electrode satisfy the following: T2:T3 =(1~2):(6~15); And / or, T1:T3=(5~10):(6~15).

11. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in any one of claims 1 to 10.

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