Battery assembly and preparation method thereof, secondary battery and electric equipment

Abstract

The invention relates to the technical field of secondary batteries, in particular to a battery assembly and a preparation method thereof, a secondary battery and electric equipment. The battery assembly comprises a positive plate, a negative plate and a diaphragm; the diaphragm comprises a base film and a coating, the coating comprises a plurality of convex structures and concave structures which are arranged in parallel and alternately distributed, the heights of the convex structures and the concave structures are different, the convex structures and the concave structures are strip-shaped, and the density difference between the convex structures and the concave structures is smaller than 0.01 g / cm < 3 >. The convex structure and the concave structure are arranged in the diaphragm, one end of the convex structure is in contact with the positive plate and / or the negative plate, and the concave structure is not in contact with the positive plate and the negative plate, so that a larger space exists between the diaphragm and the electrode plates (the positive plate and / or the negative plate), and more electrolyte can be stored; and an enough channel is provided for conveying the electrolyte, so that the capacity and the cycle performance of the battery assembly are improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to a battery assembly and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] As a type of mobile power source, batteries can store and release electrical energy, providing convenience for human travel. With the pursuit of a high-quality life, people have higher and higher requirements for battery performance, such as high energy density, high charge and discharge rate, and long battery life. However, these high performances are inseparable from the electrolyte in the battery. The amount of electrolyte stored and its rapid replenishment are prerequisites for the battery cell to exhibit these high performances.

[0003] To achieve electrolyte storage in battery cells, existing technologies have improved the coating membrane by creating high-density and low-density regions. However, when designing the high-density region, the low-density region suffers from poor rigidity. After hot pressing, the low-density region is easily flattened, leaving no effective electrolyte storage space between the coating membrane and the electrode. Simultaneously, during high-rate charging and discharging, the electrolyte is rapidly consumed, and the lack of an effective transfer channel between the membrane and the electrode prevents timely replenishment of the consumed electrolyte in the central region. Consequently, severe lithium analysis occurs in the central region, ultimately leading to reduced battery cycle performance.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a battery assembly that, by incorporating convex and concave structures within a separator, wherein one end of the convex structure contacts the positive and / or negative electrode plates, while the concave structure does not contact either the positive or negative electrode plates, creates a larger space between the separator and the electrode plates (positive and / or negative electrode plates). This allows for the storage of a greater amount of electrolyte and provides sufficient channels for electrolyte transport, thereby improving the battery assembly's capacity and cycle performance. This also solves the problem of severe lithium analysis in the central part of the battery during high-rate charge and discharge.

[0006] A second objective of this invention is to provide a method for preparing a battery assembly.

[0007] A third objective of this invention is to provide a secondary battery.

[0008] The fourth objective of this invention is to provide an electrical device.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention first provides a battery assembly comprising a positive electrode, a negative electrode, and a separator; the separator comprises a base film and a coating disposed on at least one surface of the base film; the coating comprises a plurality of parallel and alternately distributed convex and concave structures, wherein the heights of the convex and concave structures are different, the shapes of the convex and concave structures are strip-shaped, and the density difference between the convex and concave structures is less than 0.01 g / cm³. 3 .

[0011] Furthermore, the height difference ΔH between the convex structure and the concave structure and the width W2 of the convex structure satisfy the following relationship: 1000ΔH / W2≤6.

[0012] Furthermore, the height difference ΔH between the convex structure and the concave structure is ≥1μm.

[0013] Furthermore, the width W1 of the concave structure and the width W2 of the convex structure satisfy W1 / W2≥0.5.

[0014] Furthermore, the width W1 of the concave structure satisfies 0.5mm≤W1≤5.0mm.

[0015] Furthermore, the height H1 of the concave structure satisfies 0.5μm≤H1≤6.0μm.

[0016] Furthermore, the width W2 of the convex structure satisfies 0.5mm≤W2≤5.0mm.

[0017] Furthermore, the height H2 of the convex structure satisfies 1.5μm≤H2≤8.0μm.

[0018] Furthermore, the effective storage space N of the diaphragm satisfies 10% ≤ N ≤ 80%, where N = [W1 × (H2 - H1)] / [H2 × (W1 + W2)] × 100%.

[0019] Furthermore, the effective storage space N of the diaphragm is 20% to 60%.

[0020] Furthermore, the angle θ between the MD direction of the diaphragm and the convex structure or the concave structure satisfies 20°≤θ≤90°.

[0021] Furthermore, the convex structure and / or the concave structure contains filler, the filler including at least one of organic filler and inorganic filler.

[0022] Furthermore, the filler content in the convex structure and / or the concave structure is 75% to 99% by mass.

[0023] Furthermore, the organic filler includes polymer materials.

[0024] Furthermore, the polymer material includes at least one of polyvinylidene fluoride, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer.

[0025] Furthermore, the median particle size of the organic filler is 4–6 μm.

[0026] Furthermore, the inorganic filler includes at least one of alumina, boehmite, silica, titanium dioxide, magnesium oxide, zirconium oxide, LATP, and LLZO.

[0027] Furthermore, the median particle size of the inorganic filler is 0.4–1.0 μm.

[0028] Furthermore, the convex structure and / or the concave structure includes an adhesive.

[0029] Furthermore, the adhesive includes at least one of styrene-butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin.

[0030] Furthermore, the adhesive in the convex structure and / or the concave structure accounts for 2% to 9% by mass.

[0031] Furthermore, the base film includes at least one of PP film, PE film, PE / PP composite film, and PP / PP composite film.

[0032] Furthermore, the thickness of the base film is 5–12 μm.

[0033] The present invention further provides a method for preparing the above-mentioned battery assembly, comprising the following steps: using a micro-gravure roller coating with concave and convex stripes to coat a mixed slurry onto at least one surface of a base film, and drying it to obtain a separator with a convex structure and a concave structure; stacking the separator, the positive electrode sheet and the negative electrode sheet and hot pressing them to obtain the battery assembly.

[0034] The present invention also provides a secondary battery, including the above-mentioned battery assembly.

[0035] The present invention also provides an electrical device, including the aforementioned secondary battery.

[0036] Compared with existing technologies, the beneficial effects of this invention are as follows: By providing convex and concave structures in the separator, wherein one end of the convex structure contacts the positive and / or negative electrode plates, while the concave structure does not contact the positive and negative electrode plates, a larger space is created between the separator and the electrode plates (positive and / or negative electrode plates), enabling the storage of more electrolyte and providing sufficient channels for electrolyte transport, thereby improving the capacity and cycle performance of the battery assembly. This also solves the problem of severe lithium analysis in the central part of the battery during high-rate charge and discharge. Attached Figure Description

[0037] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 A schematic diagram of a battery assembly provided by the present invention;

[0039] Figure 2 Another structural schematic diagram of the battery assembly provided by the present invention;

[0040] Figure 3 A top view of the diaphragm coating provided by the present invention. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0042] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0043] Unless otherwise specified, the terms "comprising" and "including" as used in this invention 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.

[0044] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0045] In a first aspect, the present invention provides a battery assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0046] The separator includes a base membrane and a coating disposed on at least one surface of the base membrane. That is, the coating is disposed on at least one side of the base membrane, which may face the positive electrode or the negative electrode.

[0047] The coating comprises several parallel and alternately distributed convex and concave structures, see [link / reference]. Figure 1 and Figure 2 The diagram shows a cross-sectional view of a battery module, where the convex and concave structures have different heights, with the convex structure being taller than the concave structure. The convex and concave structures are at least partially connected. The other end of the convex structure is in contact with either the positive or negative electrode; while the concave structure is not in contact with either the positive or negative electrode.

[0048] See Figure 1 The diagram shown is a schematic of the structure of a battery assembly when a coating is applied to one surface of the base film. Figure 2 The diagram shows a battery assembly with coatings on both surfaces of the base film.

[0049] Both the convex and concave structures are strip-shaped; see [link / reference]. Figure 3 As shown.

[0050] The density difference between the convex and concave structures is less than 0.01 g / cm³. 3 .

[0051] It is understandable that the capacity and cycle performance of a battery are closely related to the amount of electrolyte in it. After the separator and the electrode are hot-pressed, the larger the space between them, the better for the storage of electrolyte.

[0052] The battery assembly provided by this invention, by setting convex and concave structures in the separator, after the separator and electrode sheets are hot-pressed, one end of the convex structure contacts the positive electrode sheet and / or negative electrode sheet, while the concave structure does not contact the positive electrode sheet and negative electrode sheet. This results in a large space between the separator and the electrode sheets (positive electrode sheet and / or negative electrode sheet), which can store more electrolyte and provide sufficient channels for electrolyte delivery, thereby improving the capacity and cycle performance of the battery assembly.

[0053] Patent CN117438743A discloses a porous aramid coating comprising mutually mixed and connected high-density and low-density regions, ensuring the membrane rupture temperature and thermal shrinkage performance. At the same time, the pits formed by the high-density regions provide better flow and liquid retention channels for the electrolyte, improving the electrolyte absorption rate of the battery cell and reducing the difficulty of liquid injection during battery cell production. However, in actual applications, due to the poor support of the low-density layer, after the membrane and electrode sheets are hot-pressed together, both the high-density and low-density regions are in contact with the electrode sheets, greatly reducing the liquid storage capacity in actual applications and failing to achieve the desired liquid storage effect for the battery cell. Furthermore, in patent CN117438743, the protrusions and depressions formed in the high-density and low-density regions reduce the ionic conductivity of the high-density regions and cause differences in ionic conductivity between the high-density and low-density regions, leading to lithium plating. Moreover, by controlling the compressive stress in different areas during roll coating to create high-density and low-density regions, the excessive pressure applied to the ceramic particles during roll coating can easily damage the separator material, affecting the safety of the lithium-ion battery. The battery assembly provided by this invention solves the technical problems existing in patent CN117438743. This invention uses alternating convex and concave structures, both of which are striped in shape and homogeneous, with a density difference of less than 0.01 g / cm³. 3 It can not only store more electrolyte and has a better electrolyte storage effect, but also solve the lithium plating problem and improve the safety performance of the battery.

[0054] In some specific implementations, the height difference ΔH between the convex and concave structures (ΔH = H2 - H1) and the width W2 of the convex structure satisfy the following relationship: 1000ΔH / W2 ≤ 6. The value of 1000ΔH / W2 includes, but is not limited to, a point value or a range between any two of the following: 0.1, 0.3, 0.5, 0.7, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5. It is understood that the units of ΔH and W2 must be consistent when calculating 1000ΔH / W2.

[0055] Satisfying the above relationship 1000ΔH / W2≤6 ensures the rigidity of the convex structure. During hot pressing of the cell, the convex structure is not easy to collapse, leaving liquid storage space, thereby improving the cycle performance of the cell.

[0056] In some specific implementations, the height difference ΔH between the convex and concave structures is ≥1μm, including but not limited to a point value or a range between any one of 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm, and 10μm. When the height difference between the convex and concave structures is within the above range, a larger liquid storage space between the convex and concave structures can be ensured, thereby improving the cycle performance of the battery cell.

[0057] In some specific embodiments, the width W1 of the concave structure and the width W2 of the convex structure satisfy W1 / W2≥0.5, where W1 / W2 includes, but is not limited to, any one of the values ​​of 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, and 8, or a range between any two. The widths of the concave and convex structures satisfying this relationship ensure that the coating has a large liquid storage space, guaranteeing the cycle performance of the battery cell.

[0058] In some specific implementations, the width W1 of the concave structure satisfies 0.5mm≤W1≤5.0mm, where W1 includes, but is not limited to, any one of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, and 5.0mm, or a range between any two.

[0059] In some specific implementations, the height H1 of the concave structure satisfies 0.5μm≤H1≤6.0μm, where H1 includes, but is not limited to, any one of 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5.0μm, 5.5μm, and 6μm, or a range between any two.

[0060] In some specific implementations, the width W2 of the convex structure satisfies 0.5mm≤W2≤5.0mm, where W2 includes, but is not limited to, any one of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, and 5.0mm, or a range between any two.

[0061] In some specific implementations, the height H2 of the convex structure satisfies 1.5μm≤H2≤8.0μm, where H2 includes, but is not limited to, any one of 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5.0μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, or a range between any two.

[0062] In some specific embodiments, the effective storage space N of the separator satisfies 10% ≤ N ≤ 80%, including but not limited to any one of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%, or a range between any two. Wherein, N = [W1 × (H2 - H1)] / [H2 × (W1 + W2)] × 100%. The units of all parameters must be consistent when calculating N. The effective liquid storage space N of the separator directly affects the liquid storage space of the battery cell. Controlling N within the above range ensures a larger liquid storage space, and is easy to manufacture and has low cost.

[0063] In some specific implementations, the effective storage space N of the diaphragm is 20% to 60%.

[0064] For some specific implementation methods, see Figure 3 As shown, the angle θ between the MD direction of the separator and the convex or concave structure satisfies 20°≤θ≤90°, including but not limited to any one of 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°, or any range between two; preferably 45°~90°. The concave structure is at a certain angle to the electrolyte injection direction of the cell, which is beneficial for electrolyte injection. By controlling the angle θ, the electrolyte can be quickly replenished to the central region of the battery through the space of the concave structure, solving the problem of severe lithium analysis in the central part of the battery during high-rate charge and discharge, thereby improving the cycle performance of the battery.

[0065] Among them, the MD direction (Machine Direction) refers to the longitudinal direction of mechanical stretching or movement of materials on the production line, which is the opposite of the transverse direction (TD). The MD direction is the main direction of mechanical traction in the diaphragm manufacturing process.

[0066] It is understandable that the convex and concave structures are parallel to each other, so the angle between the MD direction of the diaphragm and the convex structure is equal to the angle between the MD direction of the diaphragm and the concave structure.

[0067] It is understandable that the width and height parameters of the convex and concave structures mentioned above are parameters after hot pressing.

[0068] In some specific embodiments, the convex and / or concave structures contain fillers, including at least one of organic and inorganic fillers.

[0069] In some specific embodiments, the mass fraction of the filler in the convex structure and / or concave structure is 75% to 99%, including but not limited to the point value of any one of 75%, 80%, 85%, 90%, 95%, and 99%, or the range between any two.

[0070] In some specific embodiments, the organic filler includes polymer materials. These polymer materials serve to bond with the positive and negative electrodes, thereby improving the rigidity of the battery cell.

[0071] In some specific embodiments, the polymer material includes at least one of polyvinylidene fluoride, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer.

[0072] In some specific embodiments, the polymer material is a secondary agglomerate particle.

[0073] In some specific embodiments, the median particle size of the organic filler is 4 to 6 μm, including but not limited to point values ​​of any one of 4 μm, 4.5 μm, 5 μm, 5.5 μm, and 6 μm, or a range between any two.

[0074] In some specific embodiments, the inorganic filler includes at least one of alumina, boehmite, silica, titanium dioxide, magnesium oxide, zirconium oxide, LATP, and LLZO.

[0075] On the one hand, inorganic materials can improve the rigidity of the coating and the heat resistance of the separator, thus ensuring the safety of the battery cell. On the other hand, inorganic materials can improve the affinity of the electrolyte, thereby indirectly improving the cycle performance of the battery cell.

[0076] In some specific embodiments, the median particle size of the inorganic filler is 0.4 to 1.0 μm, including but not limited to point values ​​or ranges between any one of 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1.0 μm.

[0077] In one embodiment, the filler is an inorganic filler, and the mass fraction of the inorganic filler in the convex structure and / or concave structure is 90% to 99%, including but not limited to any one of 90%, 92%, 94%, 96%, 98%, and 99%, or any range between two of them.

[0078] In one embodiment, the filler is an organic filler, and the mass fraction of the organic filler in the convex structure and / or concave structure is 90% to 99%, including but not limited to the point value of any one of 90%, 92%, 94%, 96%, 98%, and 99%, or the range between any two.

[0079] In one embodiment, the filler is a combination of organic and inorganic fillers. In the convex and / or concave structures, the organic filler accounts for 10% to 31% by mass (e.g., 12%, 15%, 18%, 20%, 23%, 25%, 27%, or 30%), and the inorganic filler accounts for 66% to 89% by mass (e.g., 66%, 70%, 75%, 80%, 85%, or 89%).

[0080] In some specific embodiments, the material of the convex and / or concave structures includes an adhesive.

[0081] In some specific embodiments, the adhesive includes at least one of styrene-butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin.

[0082] In some specific embodiments, the adhesive in the convex structure and / or concave structure accounts for 1% to 9% by mass, including but not limited to point values ​​of any one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, and 9%, or range values ​​between any two.

[0083] In some specific embodiments, the base film includes at least one of PP film, PE film, PE / PP composite film, and PP / PP composite film.

[0084] In some specific embodiments, the thickness of the base film is 5 to 12 μm, including but not limited to point values ​​or ranges between any two of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, and 12 μm.

[0085] In some specific embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector, wherein the positive active layer is mainly composed of a positive active material, a first binder and a first conductive agent.

[0086] As an example, the positive electrode active material may be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, sodium iron composite oxide, sodium cobalt composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium manganese phosphate compound, etc., and the mass fraction of the positive electrode active material in the positive electrode active layer is 90% to 95%; the first binder may be at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, etc., and the mass fraction of the first binder in the positive electrode active layer is 3% to 8%; the first conductive agent may be at least one of acetylene black, carbon black, carbon nanotubes, superconducting carbon, graphene, carbon nanofibers, etc., and the mass fraction of the first conductive agent in the positive electrode active layer is 0.5% to 3.0%, but is not limited thereto.

[0087] As an example, the positive current collector can be made of aluminum foil or a composite current collector, and the present invention does not limit this.

[0088] In some specific embodiments, the negative electrode sheet includes a negative current collector and a negative active layer disposed on the surface of the negative current collector, wherein the negative active layer is mainly composed of a negative active material, a second binder, a second conductive agent and a thickener.

[0089] As an example, the negative electrode active material may be at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, etc., and the mass fraction of the negative electrode active material in the negative electrode active layer is 90% to 95%; the second binder may be at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, polymethacrylic acid, polyacrylonitrile, etc., and the mass fraction of the second binder in the negative electrode active layer is 3% to 8%; the second conductive agent may be at least one of acetylene black, carbon black, carbon nanotubes, superconducting carbon, graphene, and carbon nanofibers, and the mass fraction of the second conductive agent in the negative electrode active layer is 0.5% to 3.0%; the thickener may be at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium carboxymethyl acrylate, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, etc., and the mass fraction of the thickener in the negative electrode active layer is 0.5% to 3.0%, but is not limited thereto.

[0090] As an example, the negative electrode current collector can be made of copper foil or a composite current collector, and the present invention does not limit this.

[0091] Secondly, the present invention further provides a method for preparing the above-mentioned battery assembly, specifically including the following steps:

[0092] A micro-gravure roller coating with embossed stripes is used to coat the mixed slurry onto at least one surface of the base film, and after drying, a diaphragm with convex and concave structures is obtained.

[0093] The separator, positive electrode, and negative electrode are stacked (wound / stacked) and then hot-pressed to obtain a battery assembly.

[0094] The use of a micro-gravure roller coating with embossed stripes creates a coating with parallel, spaced embossed patterns. After the electrode sheets (positive and negative electrodes) are hot-pressed to the separator, the separator retains its embossed structure, increasing the electrolyte storage space between the separator and the electrode sheets, thereby improving the battery's cycle performance. Simultaneously, the concave structure provides a channel for the electrolyte to enter the central region of the battery, effectively preventing lithium plating caused by electrolyte consumption in the central area during high-rate charging and discharging.

[0095] In some specific embodiments, the mixed slurry mainly consists of at least one of fillers and binders.

[0096] In some specific implementations, the mixed slurry also includes a wetting agent.

[0097] In some specific embodiments, the wetting agent includes at least one of alkyl sulfate, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, alkylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether.

[0098] In some specific embodiments, the mass fraction of the wetting agent in the mixed slurry is 0.2% to 1%, including but not limited to any one of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%, or a range between any two.

[0099] Thirdly, the present invention also provides a secondary battery, including the above-mentioned battery assembly.

[0100] The central part of this secondary battery hardly deposits lithium, has a low cell expansion rate, and excellent cycle performance.

[0101] In some specific implementations, the secondary battery includes lithium-ion batteries and sodium-ion batteries.

[0102] In some specific embodiments, the secondary battery also includes an electrolyte, but this invention does not limit this.

[0103] Fourthly, the present invention also provides an electrical device including the aforementioned secondary battery.

[0104] Among them, electrical equipment includes any equipment, device or system containing the aforementioned secondary batteries, including but not limited to laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, and large household batteries, etc.

[0105] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0106] Example 1

[0107] The battery assembly provided in this embodiment includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The separator comprises a base film and a coating, with the coating disposed on one side of the base film and facing the positive electrode (see [reference]). Figure 1 As shown), the coating includes multiple parallel and alternating concave and convex structures. After hot pressing, the height H1 of the concave structure is 0.6 μm, the width W1 is 0.6 mm, the height H2 of the convex structure is 1.6 μm, the width W2 is 0.6 mm, the angle θ between the convex or concave structure and the MD direction of the separator is 65°, the ratio of the width W1 of the concave structure to the width W2 of the convex structure is W1 / W2 = 1, the height difference ΔH between the convex and concave structures is ΔH = H2 - H1 = 1.0 μm, 1000ΔH / W2 = 1.7, and the effective storage space N = 31% (N = [W1 × (H2 - H1)] / [H2 × (W1 + W2)] × 100%).

[0108] The method for preparing the battery module provided in this embodiment includes the following steps:

[0109] (1) Take 95 parts of alumina (inorganic material) with a median particle size of 0.5 μm, 200 parts of deionized water, and 4.5 parts of polyacrylate (adhesive), mix them, stir at high speed and sonicate, then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a embossed microgravure roller coating to coat the mixed slurry on one side of a PE film with a thickness of 7 μm, and dry to obtain a separator.

[0110] (2) Take 93 parts of lithium iron phosphate, 5 parts of polyvinylidene fluoride, 2 parts of acetylene black, and 300 parts of NMP (N-methylpyrrolidone), mix and stir evenly to obtain a positive electrode slurry. Coat the positive electrode slurry onto both sides of an aluminum foil with a thickness of 12 μm, dry it, and obtain a total thickness of 98 μm and a compaction density of 1.53 g / cm³. 3 The positive electrode plate.

[0111] (3) Take 92 parts of artificial graphite, 4.5 parts of styrene-butadiene rubber, 2.5 parts of acetylene black, 1 part of carboxymethyl cellulose, and 200 parts of deionized water, and mix them evenly to obtain a negative electrode slurry. Coat the negative electrode slurry onto both sides of a copper foil with a thickness of 8 μm, and dry it to obtain a total thickness of 108 μm and a compaction density of 1.54 g / cm³. 3 The negative electrode.

[0112] (4) The separator, positive electrode and negative electrode are wound and then hot-pressed, wherein the hot pressing temperature is 75℃ and the pressure is 1.5MPa, to obtain the battery assembly.

[0113] Examples 2 to 10

[0114] The battery modules and their preparation methods in Examples 2 to 10 are basically the same as those in Example 1, except that the height H1 and width W1 of the concave structure and the height H2 and width W2 of the convex structure are different (the values ​​of W1 / W2, ΔH, 1000ΔH / W2 and the effective storage space N are also different), as shown in Table 1.

[0115] Examples 11-12

[0116] The battery modules and their preparation methods in Examples 11 and 12 are basically the same as those in Example 1, except that the included angle θ between the convex or concave structure and the MD direction of the separator is different, being 90° and 20° respectively (see Table 1).

[0117] Example 13

[0118] The battery assembly and its preparation method provided in this embodiment are basically the same as those in Embodiment 1, except that: in step (1) of the preparation method, the mixed slurry is coated on both sides (that is, the mixed slurry is coated on both sides of a PE film with a thickness of 7μm), that is, the coatings in the separator obtained in this embodiment are respectively set on both sides of the base film, see Figure 2 As shown.

[0119] Example 14

[0120] The battery assembly provided in this embodiment includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The separator comprises a base film and a coating, with the coating disposed on one side of the base film and facing the positive electrode (see [reference]). Figure 1As shown), the coating includes multiple parallel and alternating concave and convex structures. After hot pressing, the height H1 of the concave structure is 3.5 μm, the width W1 is 4.5 mm, the height H2 of the convex structure is 6.5 μm, the width W2 is 1.0 mm, the angle θ between the convex or concave structure and the MD direction of the separator is 65°, the ratio of the width W1 of the concave structure to the width W2 of the convex structure is W1 / W2 = 4.5, the height difference ΔH between the convex and concave structures is ΔH = H2 - H1 = 3.0 μm, 1000ΔH / W2 = 3.0, and the effective storage space N = 38%.

[0121] The method for preparing the battery module provided in this embodiment includes the following steps:

[0122] (1) Take 75 parts of alumina (inorganic material) with a median particle size of 0.5 μm, 20 parts of polyvinylidene fluoride (polymer material) with a median particle size of 4.5 μm, 300 parts of deionized water, and 4.5 parts of polyacrylate (adhesive) and mix them. Stir at high speed and sonicate. Then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a embossed microgravure roller coating to coat the mixed slurry onto one side of a PE film with a thickness of 7 μm. Dry to obtain a separator.

[0123] (2)~(4): Same as steps (2)~(4) of Example 1.

[0124] Examples 15 to 17

[0125] The battery modules and their preparation methods in Examples 15 to 17 are basically the same as those in Example 14, except that the height H1 and width W1 of the concave structure and the height H2 and width W2 of the convex structure are different (the values ​​of W1 / W2, ΔH, 1000ΔH / W2 and the effective storage space N are also different), as shown in Table 1.

[0126] Example 18

[0127] The battery assembly and its preparation method provided in this embodiment are basically the same as those in Embodiment 14, except that: in step (1) of the preparation method, the mixed slurry is coated on both sides (that is, the mixed slurry is coated on both sides of a PE film with a thickness of 7μm), that is, the coatings in the separator prepared in this embodiment are respectively set on both sides of the base film, see Figure 2 As shown.

[0128] Example 19

[0129] The battery assembly and its preparation method provided in this embodiment are basically the same as those in Embodiment 14, except that in step (1), polyvinylidene fluoride is replaced with polymethyl methacrylate in equal mass fractions and with equal median particle size.

[0130] Example 20

[0131] The battery assembly provided in this embodiment includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The separator comprises a base film and a coating, with the coating disposed on one side of the base film and facing the positive electrode (see [reference]). Figure 1 As shown), the coating includes multiple parallel and alternating concave and convex structures. After hot pressing, the height H1 of the concave structure is 5.5 μm, the width W1 is 4.5 mm, the height H2 of the convex structure is 7.5 μm, the width W2 is 0.8 mm, the angle θ between the convex or concave structure and the MD direction of the separator is 65°, the ratio of the width W1 of the concave structure to the width W2 of the convex structure is W1 / W2 = 5.6, the height difference ΔH between the convex and concave structures is ΔH = H2 - H1 = 2.0 μm, 1000ΔH / W2 = 2.5, and the effective storage space N = 23%.

[0132] The method for preparing the battery module provided in this embodiment includes the following steps:

[0133] (1) Take 92 parts of polyvinylidene fluoride (polymer material) with a median particle size of 4.5 μm, 400 parts of deionized water, and 7.5 parts of polyacrylate (adhesive), mix them, stir at high speed and sonicate, then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a embossed microgravure roller coating to coat the mixed slurry on one side of a PE film with a thickness of 7 μm, and dry to obtain a separator.

[0134] (2)~(4): Same as steps (2)~(4) of Example 1.

[0135] Example 21

[0136] The battery component and its preparation method provided in this embodiment are basically the same as those in Embodiment 20, except that in step (1), polyvinylidene fluoride is replaced with polymethyl methacrylate in equal mass fractions and with equal median particle size.

[0137] Comparative Example 1

[0138] The method for preparing the battery module provided in this comparative example includes the following steps:

[0139] (1) Take 95 parts of alumina (inorganic material) with a median particle size of 0.5 μm, 200 parts of deionized water, and 4.5 parts of polyacrylate (adhesive), mix them, stir at high speed and sonicate, then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a micro-gravure roller coating to coat the mixed slurry onto one side of a PE film with a thickness of 7 μm, and dry it to obtain a separator. The coating in the separator is full coating and its thickness is 1.6 μm.

[0140] (2)~(4): Same as steps (2)~(4) of Example 1.

[0141] Comparative Example 2

[0142] The method for preparing the battery module provided in this comparative example includes the following steps:

[0143] (1) Take 75 parts of alumina (inorganic material) with a median particle size of 0.5 μm, 20 parts of polyvinylidene fluoride (polymer material) with a median particle size of 4.5 μm, 300 parts of deionized water, and 4.5 parts of polyacrylate (adhesive), mix them, stir at high speed and sonicate, then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a micro-gravure roller coating to coat the mixed slurry onto one side of a PE film with a thickness of 7 μm, and dry it to obtain a separator. The coating in the separator is full coating and its thickness is 6.5 μm.

[0144] (2)~(4): Same as steps (2)~(4) of Example 1.

[0145] Comparative Example 3

[0146] The method for preparing the battery module provided in this comparative example includes the following steps:

[0147] (1) Take 92 parts of polyvinylidene fluoride (polymer material) with a median particle size of 4.5 μm, 400 parts of deionized water, and 7.5 parts of polyacrylate (adhesive), mix them, stir at high speed and sonicate, then add 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and stir to disperse evenly to obtain a mixed slurry. Use a micro-gravure roller coating to coat the mixed slurry onto one side of a PE film with a thickness of 7 μm, and dry it to obtain a separator. The coating in the separator is full coating and its thickness is 7.5 μm.

[0148] (2)~(4): Same as steps (2)~(4) of Example 1.

[0149] Comparative Example 4

[0150] The method for preparing the battery module provided in this comparative example is basically the same as that in Example 1, except that the height H1 of the concave structure and the height H2 of the convex structure are different (the values ​​of ΔH, 1000ΔH / W2 and the effective storage space N are also different, where 1000ΔH / W2 = 12.5, which does not satisfy the relationship 1000ΔH / W2≤6), as shown in Table 1.

[0151] Comparative Example 5

[0152] The preparation method of the battery module provided in this comparative example is basically the same as that in Example 1, except that the width W2 of the convex structure is different (the values ​​of W1 / W2, 1000ΔH / W2 and the effective storage space N are also different, where W1 / W2=0.2, which does not satisfy W1 / W2≥0.5), as shown in Table 1.

[0153] Table 1 Summary of diaphragm parameters in each embodiment and comparative example

[0154]

[0155]

[0156] In Table 1, the measurement methods for the heights of the convex and concave structures are as follows: Take the battery assembly, disassemble the battery assembly to obtain the separator, clean the separator with anhydrous ethanol and dry it, place the separator on a two-dimensional image measuring instrument (JTVMA-3020), turn on the transmitted light, and control the light intensity at 300 microcandela. Utilizing the transmissivity of light, the image of the convex structure is dark black, while the image of the concave structure appears bright white relative to the image of the convex structure. Mark the midpoints of the dark black and bright white areas. Using SEM-CP technology, measure the distances from the midpoints of the dark black and bright white areas to the base film, which are H2 and H1, respectively. Perform 10 parallel tests and take the final average value to obtain the height H2 of the convex structure and the height H1 of the concave structure.

[0157] In Table 1, the measurement methods for the widths of the convex and concave structures are as follows: Take the battery assembly, disassemble the battery assembly to obtain the separator, clean the separator with anhydrous ethanol and dry it, place the separator on a two-dimensional image measuring instrument (JTVMA-3020), turn on the transmitted light, and control the light intensity at 300 microcandela. Utilizing the transmissivity of light, the image of the convex structure is dark black, while the image of the concave structure appears bright white relative to the image of the convex structure. Taking the middle of the junction between the dark black and bright white as the dividing line, measure the width of the dark black and the width of the bright white along the direction perpendicular to the concave and convex structures, which are W2 and W1 respectively. Perform 10 parallel tests and take the final average value to obtain the width W2 of the convex structure and the width W1 of the concave structure.

[0158] In Table 1, the measurement method for the angle θ between the MD direction of the separator and the convex or concave structure is as follows: Take the battery assembly, disassemble the battery assembly to obtain the separator, clean the separator with anhydrous ethanol and dry it, place the separator on a two-dimensional image testing instrument (JTVMA-3020), turn on the transmitted light, and control the light intensity at 300 microcandela. The concave and convex structures appear as bright white and dark black, respectively. With the separator winding direction as the MD direction, align the separator MD direction with the X-axis of the two-dimensional image, and measure the angle between the strip-shaped dark black structure and the strip-shaped bright white structure and the X-axis. This is the angle θ between the separator concave and convex structure and the separator MD. Perform 10 parallel tests and take the final average value, which is the angle θ between the separator concave and convex structure and the separator MD direction.

[0159] Experimental Example

[0160] The battery modules prepared in each embodiment and comparative example were fabricated into bare cells. The bare cells were then hot-pressed. One end of the hot-pressed bare cell (non-winding direction) was immersed 5 mm into an electrolyte solution (EC:EP:DEC volume ratio = 2:2:3, 0.5 mol / L lithium hexafluorophosphate). The time taken for the electrolyte to seep out from the other end was recorded. Ten parallel tests were conducted, and the final value was taken as the electrolyte immersion rate of the battery module. The results are shown in Table 2. A shorter time indicates a faster immersion rate, which is more conducive to electrolyte injection; a longer time indicates a slower immersion rate, which is less conducive to electrolyte injection.

[0161] Meanwhile, the battery modules prepared in each embodiment and comparative example were fabricated into cells and charged at a constant current of 2C to 3.6V, then charged at a constant voltage of 3.6V to a current of 0.02C, charging was terminated, and the cells were allowed to stand for 20 minutes. Next, they were discharged at a constant current of 2C to 2.0V, discharging was terminated, and the cells were allowed to stand for 20 minutes. The first discharge capacity was recorded. This cycle was repeated 500 times, and the discharge capacity on the 500th cycle was recorded. The discharge capacity on the 500th cycle was divided by the discharge capacity on the first cycle to obtain the capacity retention rate of the cell after 500 cycles. The results are shown in Table 2. The cells after 500 cycles were disassembled, and the lithium plating in the central part of the cell was observed. The results are shown in Table 2.

[0162] The battery modules prepared in each embodiment and each comparative example were respectively fabricated into cells, and the overall thickness h1 of the cells was recorded. The cells were cycled 100 times at 2C, and the cell thickness h2 after 100 cycles was recorded. The cell expansion rate = h2 / h1×100%, and the results are shown in Table 2.

[0163] Table 2 Performance data of the battery cells assembled in each embodiment and comparative example.

[0164]

[0165]

[0166] As can be seen from Tables 1 and 2, the cells of each embodiment all exhibit good electrochemical performance.

[0167] Specifically, comparing Examples 1, 11 and 12, it can be seen that the angle θ between the convex or concave structure and the MD direction of the separator has a certain influence on the liquid injection speed of the cell. Therefore, it is preferable that the angle θ satisfies 20°≤θ≤90°, and more preferably 45°~90°.

[0168] In Example 9, the effective storage space of the separator reaches 69%. The cycle performance of the battery cell does not show a significant improvement compared to Example 5, where the effective storage space is 59%. However, the ratio of the height difference between the concave and convex structures to the width of the convex structure is relatively large in Example 9. This means that when the height difference between the concave and convex structures is high, the width of the convex structure is too narrow. Higher process technology is required when manufacturing the separator, and the required production cost is greater. In Example 10, the effective storage space of the separator is 10%. Although the cycle performance of the battery cell remains at a high level, the capacity retention rate decreases relatively significantly compared to other examples. Therefore, the preferred effective storage space N of the separator is 10%–80%, more preferably 20%–60%.

[0169] Compared to Examples 1-18, Examples 14-19 contain polymer materials in their diaphragms. Therefore, under the same storage space, the effective storage space at the application end decreases due to the swelling of the polymer materials by absorbing electrolyte. Compared to Examples 1-18, the cycle performance is slightly lower, but the decrease is not significant.

[0170] In Examples 20-21, the diaphragm's concave-convex structure is mainly composed of polymer materials. After the cell is injected with electrolyte, the polymer materials absorb the electrolyte and swell, resulting in a decrease in the effective storage space at the application end, but the cycle performance still remains at a high level.

[0171] In contrast, the separators in Comparative Examples 1 to 3 use a full-coat coating instead of a textured coating. When the separator is made into a battery cell, the polymer absorbs electrolyte and expands. Also, because the coating is full-coat, lithium plating is severe in the center of the battery cell, resulting in a high cell expansion rate and poor cycle performance.

[0172] In Comparative Example 4, 1000ΔH / W2 = 12.5, which does not satisfy the relationship 1000ΔH / W2≤6. The ratio of the height difference to the width of the convex structure is too large. During the hot pressing formation of the diaphragm and electrode sheet, the convex structure is prone to collapse, resulting in a decrease in the liquid storage performance and affecting the liquid injection and cycling performance of the cell. In addition, this high ratio convex structure design requires higher technical support at the coating end, which will greatly increase the cost of coating.

[0173] In Comparative Example 5, W1 / W2 = 0.2, which does not satisfy the relationship W1 / W2 ≥ 0.5. The liquid storage space provided by the concave structure is greatly reduced. After the diaphragm and electrode sheet are hot-pressed, the liquid storage space is seriously insufficient, which not only affects the liquid injection rate, but also easily leads to lithium plating in the cell, ultimately deteriorating the cycle performance of the cell.

[0174] In summary, by setting convex and concave structures in the separator and satisfying the relationship 1000ΔH / W2≤6, the present invention can improve the capacity and cycle performance of the battery assembly, and the secondary battery produced by it has almost no lithium deposition in the central part and low expansion rate.

[0175] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A battery assembly, characterized in that, Includes positive electrode, negative electrode, and separator; The diaphragm includes a base membrane and a coating disposed on at least one surface of the base membrane; The coating comprises a plurality of parallel and alternately distributed convex and concave structures, wherein the convex and concave structures have different heights, are strip-shaped, and have a density difference of less than 0.01 g / cm³. 3 .

2. The battery assembly according to claim 1, characterized in that, The height difference ΔH between the convex structure and the concave structure and the width W2 of the convex structure satisfy the following relationship: 1000ΔH / W2≤6.

3. The battery assembly according to claim 1, characterized in that, The height difference ΔH between the convex structure and the concave structure is ≥1μm.

4. The battery assembly according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The width W1 of the concave structure and the width W2 of the convex structure satisfy W1 / W2≥0.5; (2) The width W1 of the concave structure satisfies 0.5mm≤W1≤5.0mm; (3) The height H1 of the concave structure satisfies 0.5μm≤H1≤6.0μm; (4) The width W2 of the convex structure satisfies 0.5mm≤W2≤5.0mm; (5) The height H2 of the convex structure satisfies 1.5μm≤H2≤8.0μm.

5. The battery assembly according to claim 4, characterized in that, The effective storage space N of the diaphragm satisfies 10% ≤ N ≤ 80%, where N = [W1 × (H2 - H1)] / [H2 × (W1 + W2)] × 100%; Preferably, the effective storage space N of the diaphragm is 20% to 60%.

6. The battery assembly according to claim 1, characterized in that, The angle θ between the MD direction of the diaphragm and the convex structure or the concave structure satisfies 20°≤θ≤90°.

7. The battery assembly according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The convex structure and / or the concave structure contains filler, the filler including at least one of organic filler and inorganic filler; the mass fraction of the filler in the convex structure and / or the concave structure is 75% to 99%; preferably, the organic filler includes polymer material; preferably, the polymer material includes at least one of polyvinylidene fluoride, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer; preferably, the median particle size of the organic filler is 4 to 6 μm; preferably, the inorganic filler includes at least one of alumina, boehmite, silica, titanium dioxide, magnesium oxide, zirconium oxide, LATP, and LLZO; preferably, the median particle size of the inorganic filler is 0.4 to 1.0 μm; (2) The convex structure and / or the concave structure includes an adhesive; preferably, the adhesive includes at least one of styrene-butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile and epoxy resin; preferably, the adhesive in the convex structure and / or the concave structure accounts for 1% to 9% by mass. (3) The base film includes at least one of PP film, PE film, PE / PP composite film and PP / PP composite film; preferably, the thickness of the base film is 5 to 12 μm.

8. The method for preparing the battery assembly according to any one of claims 1 to 7, characterized in that, Includes the following steps: A micro-gravure roller coating with convex and concave stripes is used to coat the mixed slurry onto at least one surface of the base film, and after drying, a diaphragm with convex and concave structures is obtained. The separator, positive electrode, and negative electrode are stacked and then hot-pressed to obtain the battery assembly.

9. A secondary battery, characterized in that, Includes the battery assembly as described in any one of claims 1 to 7.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

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