Electrode plate, secondary battery and electric device

Abstract

The invention provides an electrode plate, a secondary battery and an electric device. The electrode pole piece comprises a current collector and a film layer located on at least one surface of the current collector, the film layer is provided with a first surface away from the current collector and a second surface opposite to the first surface, the thickness of the film layer is marked as H, and an area within the thickness range from the second surface of the film layer to 0.3 H is marked as a first area of the film layer, the area from the first surface of the film layer to the thickness range of 0.3 H is marked as the second area of the film layer, the first area and the second area both contain a binder, and the ratio of the mass content of the binder in the second area to the mass content of the binder in the first area is 0.4-1.6; the preparation method of the electrode pole piece comprises the following steps: coating: coating at least one surface of a current collector with electrode slurry, and drying to obtain an initial pole piece; and heating treatment: carrying out laser heating treatment on the surface of the initial pole piece to obtain the electrode pole piece.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to an electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries have advantages such as high energy density, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

[0003] With the rapid development of electric vehicles and mobile electronic devices, the requirements for secondary battery cycle performance are becoming increasingly stringent. Improving battery cycle performance is a pressing scientific and technological problem that needs to be solved in the current application of secondary batteries. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide an electrode plate, a secondary battery and an electrical device, wherein the electrode plate can reduce the DC resistance of the battery and improve the cycle performance and dynamic performance of the battery.

[0005] A first aspect of this application provides an electrode sheet comprising a current collector and a film layer located on at least one surface of the current collector. The film layer has a first surface remote from the current collector and a second surface opposite to the first surface. The thickness of the film layer is denoted as H. A region extending from the second surface of the film layer to a thickness of 0.3H is denoted as a first region of the film layer, and a region extending from the first surface of the film layer to a thickness of 0.3H is denoted as a second region of the film layer. Both the first region and the second region contain an adhesive.

[0006] The ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region is 0.4-1.6.

[0007] The method for preparing the electrode sheet includes:

[0008] Coating: The electrode paste is coated onto at least one surface of the current collector and dried to obtain the initial electrode sheet;

[0009] Heat treatment: The surface of the initial electrode sheet is subjected to laser heating treatment to obtain the electrode sheet.

[0010] This application removes a certain amount of binder from the second region of the initial electrode by laser heating the surface of the initial electrode. The ratio of the mass content of binder in the second region to that in the first region is 0.4-1.6, which can effectively improve the problem of binder enrichment on the film surface, improve the porosity of the electrode surface, increase the wettability of the electrode to the electrolyte, reduce the DC impedance of the battery, and improve the cycle performance and kinetic performance of the battery.

[0011] In any embodiment, the ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region is 0.4-1.3.

[0012] By controlling the ratio of the mass content of the binder in the second region to the mass content of the binder in the first region within a suitable range, the problem of binder enrichment on the film surface can be further improved, the porosity of the electrode surface can be improved, the wettability of the electrode to the electrolyte can be increased, the DC impedance of the battery can be reduced, and the cycle performance and kinetic performance of the battery can be improved.

[0013] In any embodiment, the liquid absorption rate of the electrode sheet is greater than or equal to 2.0 μg / s.

[0014] In any embodiment, the liquid absorption rate of the electrode sheet is 2.4 μg / s to 2.60 μg / s.

[0015] This application utilizes laser heating to improve the uniformity of heating the initial electrode surface, which facilitates uniform heating of the binder in the second region, enhances the connectivity between particles in the second region, and increases the electrolyte absorption rate of the electrode to be greater than or equal to 2.0 μg / s. This improves the electrolyte absorption rate of the electrode, enhances the wettability of the electrode to the electrolyte, reduces the DC impedance of the battery, and improves the cycle performance and kinetic performance of the battery.

[0016] In any embodiment, during the heat treatment process, the initial electrode surface temperature is 300℃-710℃.

[0017] By controlling the initial electrode surface temperature within a suitable range during the heat treatment process, the mass ratio of binder removed from the second region during laser heating can be controlled, so that the mass content of binder in the second region is 0.4-1.6 to the mass content of binder in the first region.

[0018] In any embodiment, the heating treatment time is 0.0030s-0.06s.

[0019] By controlling the heating treatment time within a suitable range, the mass ratio of the binder removed from the second region during laser heating can be controlled, so that the mass content of the binder in the second region is 0.4-1.6 to the mass content of the binder in the first region.

[0020] In any embodiment, the device for performing the laser heating treatment includes a laser with a power of 1KW-10KW.

[0021] By controlling the power of the laser within a suitable range, the initial electrode surface temperature can be effectively regulated, thereby achieving the purpose of removing a suitable mass content of binder in the second region, so that the mass content of binder in the second region is 0.4-1.6 compared with the mass content of binder in the first region.

[0022] In any embodiment, during the heating process, the initial electrode is passed through the laser at a constant speed of 10 m / min to 150 m / min.

[0023] By controlling the moving speed of the initial electrode, the heating time can be effectively controlled to remove a suitable amount of binder in the second region, so that the ratio of the mass content of binder in the second region to the mass content of binder in the first region is 0.4-1.6.

[0024] In any embodiment, the coating step specifically includes:

[0025] The electrode paste is coated onto at least one surface of the current collector and dried to obtain the first electrode.

[0026] The first electrode is rolled to obtain the initial electrode.

[0027] In any embodiment, the heating step specifically includes:

[0028] The surface of the initial electrode is subjected to laser heating treatment to obtain the second electrode;

[0029] The second electrode is rolled to obtain the electrode sheet.

[0030] A second aspect of this application provides a secondary battery, including the electrode plates described in the first aspect. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of one embodiment of the electrode sheet of this application.

[0032] Figure 2 This is a schematic diagram of another embodiment of the electrode sheet of this application.

[0033] Figure 3 This is a schematic diagram of another embodiment of the electrode sheet of this application.

[0034] Figure 4 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0035] Figure 5 This is an exploded view of one embodiment of the secondary battery of this application.

[0036] Figure 6 This is a schematic diagram of one embodiment of the battery module of this application.

[0037] Figure 7 This is a schematic diagram of one embodiment of the battery pack of this application.

[0038] Figure 8 yes Figure 7 An exploded view of an embodiment of the battery pack shown.

[0039] Figure 9 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0040] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper housing, 3 Lower housing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 10 Electrode electrode, 101 Current collector, 102 Film layer, 102a First surface, 102b Second surface, 1021 First region, 1022 Second region, 1023 Intermediate region. Detailed Implementation

[0041] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrode plates, secondary batteries, and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] The distribution of binder on the electrode directly affects the wetting effect of the electrolyte, thus influencing important battery performance characteristics such as internal resistance, rate performance, and cycle performance. In continuous efforts to improve energy density, increasing the weight of active material per unit area of ​​the electrode (by ≥40%) can achieve this increase. However, this increase in weight of active material per unit area leads to an uneven gradient distribution of the material along the thickness direction of the electrode.

[0049] Extensive research has shown that during the drying process of electrode sheets (especially near the transition point (the junction where the upper layer of the electrode sheet is dried while the lower layer is not), the upper solvent of the active material layer evaporates first, while the lower solvent rises rapidly. Therefore, the solvent carries small-molecule binders during this ascent, causing the binders to float due to the following reasons: (1) surface tension; (2) concentration gradient; (3) capillary action; (4) thermodynamic motion of solid particles; and (5) density difference between particles (particle settling causes density differences between the upper and lower layers). Furthermore, as the coating speed increases, the drying temperature needs to be further increased, which further reduces the surface tension of the solvent, leading to a further increase in the surface tension difference between the upper dried electrode active material layer and the solvent. This makes it easier for the solvent to migrate and spread upwards, and for the binders to float more readily.

[0050] During the drying process of electrode sheets, the binder floats to the surface, leading to binder enrichment on the electrode sheet surface. After cold pressing, the electrode sheet surface tends to become denser. On the one hand, a dense electrode sheet surface makes electrolyte wetting difficult, severely affecting the production efficiency of secondary batteries. On the other hand, the low porosity of the electrode sheet surface makes it difficult for active ions to shuttle within the electrode sheet, reducing rate performance and low-temperature performance. Furthermore, if the electrode sheet has difficulty wetting, the insufficiently wetting areas cannot achieve electrochemical reactions, leading to abnormal battery performance and the risk of metal deposition of active materials (such as lithium plating) at the interface. Therefore, the microstructure of the electrode sheet directly affects the electrolyte wetting effect, thus affecting important battery performance such as internal resistance and lifespan. Additionally, if the electrode sheet surface is rich in binder, during electrode rolling, the binder on the electrode sheet will severely stick to the roller, causing electrode damage and affecting the electrode defect rate.

[0051] [Electrode Plate]

[0052] Based on this, this application provides an electrode sheet, such as... Figures 1 to 3 As shown, the electrode sheet 10 includes a current collector 101 and a film layer 102 formed on at least one surface of the current collector 101. The film layer 102 has a first surface 102a away from the current collector 101 and a second surface 102b opposite to the first surface 102a. The thickness of the film layer 102 is denoted as H. The region from the second surface 102b to a thickness of 0.3H is denoted as the first region 1021 of the film layer, and the region from the first surface 102a to a thickness of 0.3H is denoted as the second region 1022 of the film layer. The thickness H of the film layer refers to the thickness of the film layer located on one side of the current collector. Both the first region 1021 and the second region 1022 contain an adhesive.

[0053] The ratio of the mass content of the adhesive in the second region 1022 to the mass content of the adhesive in the first region 1021 is 0.4-1.6.

[0054] The method for preparing the electrode sheet includes:

[0055] Coating: The electrode paste is coated onto at least one surface of the current collector and dried to obtain the initial electrode sheet;

[0056] Heat treatment: The surface of the initial electrode sheet is subjected to laser heating treatment to obtain the electrode sheet.

[0057] In some implementations, the electrode is a positive electrode.

[0058] In some implementations, the electrode is a negative electrode.

[0059] In some embodiments, the ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region can be selected as 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or any value range between the two.

[0060] The mass content of binder in different regions of the electrode sheet can be tested using any method known in the art. As an example, the electrode sheet to be tested is cut into 20cm × 10cm pieces. A clean blade is prepared; the electrode sheet is held down with the left hand, and the blade is held in the right hand, with the blade at a 45° angle to the electrode sheet. Powder is scraped from left to right along the middle of the electrode sheet, with a scraping length of 10cm and a width of 5cm. If a total of 10 scrapings are performed from the start of powder scraping until the current collector of the electrode sheet leaks out, the first 3 scrapings are taken as the sample for the second region, and the last 3 scrapings are taken as the sample for the first region. The collected samples are stored in a sealed bottle. 50mg of the collected sample is weighed and placed in an alumina crucible and leveled. The binder content in the sample is detected using a thermogravimetric analyzer (atmosphere: nitrogen, flow rate: 20mL / min). The sample is heated from 25℃ to 600℃ at a rate of 10℃ / min. The percentage of mass lost in different regions is the mass percentage of binder in each region.

[0061] The inventors discovered that in electrode sheets prepared by traditional processes, the binder exhibits a significantly uneven gradient distribution along the thickness direction of the film layer, resulting in a large accumulation of binder on the electrode sheet surface. The ratio of the mass content of binder in the second region to the mass content of binder in the first region is much greater than 1.6, which affects the electrochemical performance of the electrode sheet.

[0062] This application utilizes laser heating to remove a certain amount of binder from the second region of the initial electrode, resulting in a binder mass content in the second region that is 0.4-1.6 compared to the first region. This effectively addresses the issue of binder accumulation on the film surface, improves the surface porosity of the electrode, enhances the wettability of the electrode to the electrolyte, reduces the DC impedance of the battery, and improves the battery's cycle performance and kinetic performance. Simultaneously, controlling the binder mass content in the second region to the first region within a suitable range ensures excellent bonding between the binders in both regions, effectively binding the components in the film together and reducing the likelihood of powder shedding during cycling, thus improving the battery's cycle performance and safety. Furthermore, compared to direct flame heating of the initial electrode, this application utilizes laser heating, which facilitates the uniform removal of binder in the second region, improves particle connectivity in the second region, enhances the electrode's wettability to the electrolyte, improves the kinetic performance of the electrode during cycling, and ultimately improves the battery's cycle performance and rate performance.

[0063] In some embodiments, the electrode sheet is a positive electrode sheet, and the binder includes at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. Further, the binder includes polyvinylidene fluoride (PVDF).

[0064] In some embodiments, the electrode sheet is a negative electrode sheet, and the binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0065] In some embodiments, the electrode is a positive electrode, and the current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0066] In some embodiments, the electrode sheet is a negative electrode sheet, and the current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In some embodiments, the ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region is 0.4-1.3. In some embodiments, the ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region may be selected as 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.3, or any value range between the two.

[0068] By controlling the ratio of the mass content of the binder in the second region to the mass content of the binder in the first region within a suitable range, the problem of binder enrichment on the film surface can be further improved, the porosity of the electrode surface can be improved, the wettability of the electrode to the electrolyte can be increased, the DC impedance of the battery can be reduced, and the cycle performance and kinetic performance of the battery can be improved.

[0069] In some embodiments, the liquid absorption rate of the electrode sheet is greater than or equal to 2.0 μg / s, and can be selected as 2.4 μg / s-2.6 μg / s.

[0070] In some embodiments, the liquid absorption rate of the electrode sheet can be selected as 2.0 μg / s, 2.1 μg / s, 2.2 μg / s, 2.3 μg / s, 2.4 μg / s, 2.5 μg / s, 2.6 μg / s, or any value range between the two.

[0071] The liquid absorption rate of the electrode sheet can be tested using any method known in the art. As an example, 1) the electrode sheet is dried at 80°C for 4 hours; 2) an electrode sheet of appropriate size is cut, its thickness is tested, and it is fixed on the sample stage; 3) a capillary tube with an inner diameter d of 200 μm is selected and polished with 5000-grit sandpaper until the end is clean; 4) the microscope is turned on, the lens magnification is adjusted to 20-30x, and the height of the sample stage and the angle between the lens and the sample stage are adjusted until the image is clear; 5) the capillary tube draws up the electrolyte (in an environment with a water content of less than 10 ppm, the non-aqueous organic solvent ethylene carbonate EC and diethyl carbonate are added). Ester DMC was mixed at a volume ratio of 1:1 to obtain the electrolyte solvent. Then, lithium salt was mixed with the solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L and an electrolyte density of p). The electrolyte height h was controlled at 3 mm. The capillary was clamped onto the support clip. After further adjusting the image clarity, the capillary was lowered to contact the electrode. A stopwatch was used to time the descent of the capillary liquid level. 6) After the liquid level had completely descended, the absorption time t was read and recorded. 7) The average absorption rate v of the electrode was calculated using the formula: v = π × (d / 2). 2 ×h×p / t.

[0072] This application utilizes laser heating to improve the uniformity of heating the initial electrode surface, which facilitates the uniform removal of the binder in the second region, enhances the connectivity between particles in the second region, and increases the electrolyte absorption rate of the electrode to be greater than or equal to 2.0 μg / s. This improves the electrolyte absorption rate of the electrode, enhances the wettability of the electrode to the electrolyte, reduces the DC impedance of the battery, and improves the cycle performance and kinetic performance of the battery.

[0073] In some embodiments, the initial electrode surface temperature during the heat treatment process is 300℃-710℃. In some embodiments, the initial electrode surface temperature during the heat treatment process can be selected as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 710℃, or any value range between two of these.

[0074] By controlling the initial electrode surface temperature within a suitable range during the heat treatment process, the mass ratio of binder removed from the second region during laser heating can be controlled, so that the mass content of binder in the second region is 0.4-1.6 to the mass content of binder in the first region.

[0075] In some embodiments, the heating treatment time is 0.0030s-0.06s. In some embodiments, the heating treatment time can be selected from 0.0030s, 0.0050s, 0.0100s, 0.0150s, 0.0200s, 0.0250s, 0.030s, 0.040s, 0.050s, 0.060s, or any value range between the two.

[0076] By controlling the heating treatment time within a suitable range, the mass ratio of the binder removed from the second region during laser heating can be controlled, so that the mass content of the binder in the second region is 0.4-1.6 to the mass content of the binder in the first region.

[0077] In some embodiments, the apparatus for performing the laser heating treatment includes a laser with a power of 1KW-10KW. In some embodiments, the power of the laser can be selected from 1KW, 2KW, 3KW, 4KW, 5KW, 6KW, 7KW, 8KW, 9KW, 10KW, or any value range between two of these.

[0078] By controlling the power of the laser within a suitable range, the initial electrode surface temperature can be effectively regulated, thereby achieving the purpose of removing a suitable mass content of binder in the second region, so that the mass content of binder in the second region is 0.4-1.6 compared with the mass content of binder in the first region.

[0079] In some embodiments, during the heat treatment step, the initial electrode is passed through the laser at a constant speed of 10 m / min to 150 m / min.

[0080] In some embodiments, during the heating process, the initial electrode is passed through the laser at a constant speed, which can be selected as 10 m / min, 20 m / min, 50 m / min, 100 m / min, 120 m / min, 150 m / min or any range between the two.

[0081] By controlling the moving speed of the initial electrode, the heating time can be effectively controlled to remove a suitable amount of binder in the second region, so that the ratio of the mass content of binder in the second region to the mass content of binder in the first region is 0.4-1.6.

[0082] In some embodiments, the coating step specifically includes:

[0083] The electrode paste is coated onto at least one surface of the current collector and dried to obtain the first electrode.

[0084] The first electrode is rolled to obtain the initial electrode.

[0085] In some embodiments, the heating step specifically includes:

[0086] The surface of the initial electrode is subjected to laser heating treatment to obtain the second electrode;

[0087] The second electrode is rolled to obtain the electrode sheet.

[0088] In some embodiments, the electrode paste is a positive electrode active paste, comprising one or more of a positive electrode active material, a conductive agent, a binder, and a solvent.

[0089] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0090] In some embodiments, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the solvent is selected from one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, water, and ethanol.

[0092] In any embodiment of this application, the positive electrode active slurry further includes a dispersant selected from one or more of sodium polyacrylate, polybutadiene acrylonitrile, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, polyvinylpyrrolidone, polyethylene glycol, octylphenol polyoxyethylene, or sulfonate fluorinated dispersants.

[0093] In some embodiments, the electrode paste is a negative electrode active paste, comprising one or more of a negative electrode active material, a conductive agent, a binder, and a solvent.

[0094] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0095] In some embodiments, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative electrode active slurry may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0097] In some embodiments, the solvent is selected from one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, water, and ethanol.

[0098] [Electrolytes]

[0099] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0100] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0101] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0102] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0103] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0104] [Isolation membrane]

[0105] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0106] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0107] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0108] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0109] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0110] [Rechargeable Battery]

[0111] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the binder in the active material layer of the positive electrode includes polymers according to any embodiment of this application.

[0112] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0113] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0114] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0115] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0116] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 5.

[0117] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0118] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0119] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0120] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0121] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0122] Figure 7 and Figure 8This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0123] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0124] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0125] Figure 9 This is one example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used. Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a secondary battery as their power source.

[0126] Example

[0127] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0128] I. Preparation Method

[0129] Example 1

[0130] 1) Preparation of positive electrode sheet

[0131] Lithium nickel cobalt manganese oxide (NCM523), conductive carbon black, polyvinylidene fluoride (PVDF), and polyvinylpyrrolidone (PVP) were added to a mixer in a ratio of 96.9%:1%:2%:0.1%. Then, nitrogen-methylpyrrolidone (NMC) was added to bring the solid content of the slurry to 65%. The mixture was stirred evenly to prepare the electrode slurry.

[0132] The prepared electrode paste was uniformly coated on both sides of a 12μm aluminum foil, with a single-sided coating weight of 250mg / 1540.25mm. 2 And dry it to form the first electrode sheet;

[0133] The first electrode is rolled to obtain the initial electrode.

[0134] The front and back surfaces of the first electrode are heated by a laser. The initial electrode passes through the laser at a speed of 20 m / min, and the power of the laser is controlled at 3 KW, so that the surface temperature of the initial electrode reaches 700.3℃. The heating treatment time of the initial electrode is 0.58 s.

[0135] The initial electrode sheet after heat treatment is punched into a fixed shape to obtain the positive electrode sheet.

[0136] 2) Preparation of negative electrode sheet

[0137] A negative electrode slurry was prepared by dissolving graphite (anode active material), styrene-butadiene rubber (SBR) (binder), sodium carboxymethyl cellulose (CMC-Na) (thickener), and carbon black (SuperP) (conductive agent) in deionized water at a weight ratio of 96.2:1.8:1.2:0.8 and mixing thoroughly. The negative electrode slurry was then uniformly coated onto both sides of the copper foil used as the negative electrode current collector, with a coating density of 8.6 mg / cm³. 2 The negative electrode sheet is obtained by drying, cold pressing, and slitting.

[0138] 3) Separating membrane

[0139] Polyethylene film is used as the separation membrane.

[0140] 4) Preparation of electrolyte

[0141] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC) and diethyl carbonate (DMC) are mixed at a volume ratio of 1:1 to obtain an electrolyte solvent. Then, lithium salt is mixed with the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0142] 5) Battery manufacturing

[0143] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a wound battery cell. The wound battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0144] Implementation 2-15

[0145] Compared with Example 1, Examples 2-15 adjusted the surface temperature and heating time of the initial electrode by adjusting the movement speed of the initial electrode or the power of the laser. Specific parameters are shown in Table 1.

[0146] Comparative Example 1

[0147] The difference compared to Example 1 lies in the preparation method of the positive electrode sheet, as detailed below:

[0148] Lithium nickel cobalt manganese oxide (NCM523), conductive carbon black, polyvinylidene fluoride (PVDF), and polyvinylpyrrolidone (PVP) were added to a mixer in a ratio of 96.9%:1%:2%:0.1%. Then, nitrogen-methylpyrrolidone (NMC) was added to bring the solid content of the slurry to 65%. The mixture was stirred evenly to prepare the electrode slurry.

[0149] The prepared electrode paste was uniformly coated on both sides of a 12μm aluminum foil, with a single-sided coating weight of 250mg / 1540.25mm. 2 And dry it to form the first electrode sheet;

[0150] The first electrode is rolled to obtain the initial electrode.

[0151] The initial electrode sheet is punched into a fixed shape to obtain the positive electrode sheet.

[0152] Comparative Examples 2-5

[0153] Compared with Example 1, Comparative Examples 2-5 adjusted the surface temperature of the initial electrode and the heating time by adjusting the movement speed of the initial electrode or the power of the laser. Specific parameters are shown in Table 1.

[0154] II. Testing Methods

[0155] 1. DC internal resistance of a secondary battery

[0156] At 25℃, the battery is charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage until the current is 0.05C. The battery is then discharged at a constant current of 0.5C for 30 minutes to adjust the battery to 50% SOC. The voltage of the battery at this time is recorded as U1. The battery is then discharged at a constant current of 4C for 30 seconds, with a sampling time of 0.1 seconds. The voltage at the end of the discharge is recorded as U2. The initial DC internal resistance DCR of the battery is represented by the discharge DCR at 50% SOC. The initial DC internal resistance DCR of the battery is calculated as (U1-U2) / 4C.

[0157] 2. Capacity retention rate of secondary batteries during room temperature cycling

[0158] At 25°C, the secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 1C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 1C to the discharge cutoff voltage of 3.0V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method. Using the capacity of the first discharge as 100%, the capacity retention rate after 800 cycles was calculated. The capacity retention rate (%) after 800 cycles = (Discharge capacity of the 800th cycle / Capacity of the first discharge) × 100%.

[0159] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0160] Electrode sheets and secondary batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0161] Table 1

[0162]

[0163]

[0164] Table 2

[0165]

[0166] The preparation methods of the electrode sheets in Examples 1-15, as shown in Tables 1 and 2, are as follows:

[0167] Coating: The electrode paste is coated onto at least one surface of the current collector and dried to obtain the initial electrode sheet;

[0168] Heat treatment: The surface of the initial electrode sheet is subjected to laser heat treatment to obtain the electrode sheet.

[0169] The electrode includes a current collector and a film layer located on at least one surface of the current collector. The film layer has a first surface away from the current collector and a second surface opposite to the first surface. The thickness of the film layer is denoted as H. The region from the second surface of the film layer to a thickness of 0.3H is denoted as the first region of the film layer, and the region from the first surface of the film layer to a thickness of 0.3H is denoted as the second region of the film layer. Both the first region and the second region contain an adhesive.

[0170] The ratio of the mass content of adhesive in the second region to the mass content of adhesive in the first region is 0.4-1.6.

[0171] As can be seen from the comparison between Examples 1-15 and Comparative Examples 1-5, controlling the ratio of the mass content of the binder in the second region to the mass content of the binder in the first region in the electrode sheet to be 0.4-1.6 can reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0172] As can be seen from the comparison between Examples 1-7, 9-15 and Example 8, the ratio of the mass content of the binder in the second region to the mass content of the binder in the first region is 0.4-1.3, which can further improve the liquid absorption rate of the electrode sheet, reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0173] As can be seen from Examples 1-15, the liquid absorption rate of the electrode sheet is greater than or equal to 2.0 μg / s, the electrolyte has excellent wetting properties on the electrode sheet, the battery has low DC resistance and excellent cycle capacity retention, and the battery has excellent electrochemical performance.

[0174] As can be seen from Examples 1-15, the surface temperature of the initial electrode sheet during the heat treatment process is 300℃-710℃, which makes the mass content of the binder in the second region of the electrode sheet to the mass content of the binder in the first region 0.4-1.6, which can reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0175] As can be seen from Examples 1-15, the heat treatment time is 0.0030s-0.06s, so that the mass content of the binder in the second region of the electrode sheet is 0.4-1.6 to the mass content of the binder in the first region, which can reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0176] As can be seen from Examples 1-15, the power of the laser is 1KW-10KW, which makes the surface of the initial electrode have a suitable heating temperature, and the ratio of the mass content of the binder in the second region to the mass content of the binder in the first region is 0.4-1.6, which can reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0177] As can be seen from Examples 1-15, the initial electrode passes through the laser at a constant speed of 10m / min-150m / min, and the electrode has a suitable heating treatment time, so that the mass content of the binder in the second region to the mass content of the binder in the first region is 0.4-1.6, which can reduce the DC internal resistance of the battery, improve the cycle capacity retention rate of the battery, and improve the cycle performance of the battery.

[0178] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrode sheet, characterized in that, The electrode sheet includes a current collector and a film layer located on at least one surface of the current collector. The film layer has a first surface away from the current collector and a second surface opposite to the first surface. The thickness of the film layer is denoted as H. The region from the second surface of the film layer to a thickness of 0.3H is denoted as a first region of the film layer, and the region from the first surface of the film layer to a thickness of 0.3H is denoted as a second region of the film layer. Both the first region and the second region contain an adhesive. The ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region is 0.4-1.

6. The method for preparing the electrode sheet includes: Coating: The electrode paste is coated onto at least one surface of the current collector and dried to obtain the initial electrode sheet; Heat treatment: The surface of the initial electrode sheet is subjected to laser heating treatment to obtain the electrode sheet.

2. The electrode sheet according to claim 1, characterized in that, The ratio of the mass content of the adhesive in the second region to the mass content of the adhesive in the first region is 0.4-1.

3.

3. The electrode sheet according to claim 1 or 2, characterized in that, The liquid absorption rate of the electrode sheet is greater than or equal to 2.0 μg / s.

4. The electrode sheet according to claim 1 or 2, characterized in that, The liquid absorption rate of the electrode sheet is 2.4 μg / s-2.6 μg / s.

5. The electrode sheet according to any one of claims 1 to 4, characterized in that, During the heat treatment process, the initial electrode surface temperature is 300℃-710℃.

6. The electrode sheet according to any one of claims 1 to 5, characterized in that, The heating treatment time is 0.0030s-0.06s.

7. The electrode sheet according to any one of claims 1 to 6, characterized in that, The equipment for performing the laser heating treatment includes a laser with a power of 1KW-10KW.

8. The electrode sheet according to claim 7, characterized in that, In the heat treatment step, the initial electrode is passed through the laser at a constant speed of 10m / min-150m / min.

9. The electrode sheet according to any one of claims 1 to 8, characterized in that, The coating step specifically includes: The electrode paste is coated onto at least one surface of the current collector and dried to obtain the first electrode. The first electrode is rolled to obtain the initial electrode.

10. The electrode sheet according to any one of claims 1 to 9, characterized in that, The heating step specifically includes: The surface of the initial electrode is subjected to laser heating treatment to obtain the second electrode; The second electrode is rolled to obtain the electrode sheet.

11. A secondary battery, characterized in that, Includes the electrode sheet according to any one of claims 1 to 10.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

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