Winding type electrode assembly and preparation method thereof, secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a winding type electrode assembly and a preparation method thereof, a secondary battery and an electric device. The winding type electrode assembly comprises a main body part and a corner part, and further comprises a positive pole piece, a negative pole piece and an isolating membrane arranged between the positive pole piece and the negative pole piece, the isolating membrane comprises a base membrane and a bonding layer arranged on the base membrane; the adhesive layer in the corner portion includes adhesive particles having an average size of 6 [mu] m to 21 [mu] m, at least part of the adhesive particles having a hollow structure. According to the winding type electrode assembly, the binder particles can enable the distance between the adjacent positive pole piece and negative pole piece in the corner part to be large, sufficient space is provided for expansion and contraction of the negative pole piece, the cycle performance of the secondary battery is improved, and the hollow structure is easy to deform, so that the transmission performance of active ions is improved, and the service life of the secondary battery is prolonged. The preparation of the winding type electrode assembly is facilitated, and the cycle performance of the secondary battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a wound electrode assembly, a preparation method thereof, a secondary battery and an electric device. BACKGROUND

[0002] In the manufacture of secondary batteries, the problem of expansion and contraction of negative electrode sheets has always been an objective difficulty. The expansion and contraction is reversible. During the charging and discharging cycle of a secondary battery, active ions are repeatedly inserted and extracted from a layered material, so that the negative electrode sheet (such as a graphite negative active material or a silicon-based negative active material) will obviously expand and contract. With an increase in the number of cycles, the amplitude of expansion will become larger and larger. This change will cause the spacing between the electrode sheets inside the secondary battery to become smaller and smaller, and the stress distribution inside the secondary battery to become uneven. In particular, in the corner portion of a wound secondary battery, the stress is relatively concentrated, the channel for active ion transmission is relatively difficult, and problems such as active ion precipitation and purple stains often occur in the corner portion, thereby affecting the cycle life of the secondary battery. Therefore, the related technology still needs to be improved. SUMMARY

[0003] In view of the above problems, the present application provides a wound electrode assembly, a preparation method thereof, a secondary battery and an electric device. According to the wound electrode assembly of the embodiments of the present application, the adhesive particles of the bonding layer of the separator in the corner portion have a larger average size and at least partially have a hollow structure, which is beneficial to improve the cycle performance of the secondary battery using the wound electrode assembly.

[0004] In a first aspect, the present application provides a wound electrode assembly. According to the embodiments of the present application, the wound electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the separator comprises a base film and a bonding layer arranged on at least one surface of the base film, and the bonding layer comprises adhesive particles; the wound electrode assembly comprises a main body portion and corner portions located on both sides of the main body portion; the average size of the adhesive particles in the corner portions is 6 μm to 21 μm, and at least part of the adhesive particles have a hollow structure.

[0005] The binder particles with an average size of 6-21 μm in the corner portion of the winding electrode assembly can provide good support, so that the adjacent positive and negative electrode sheets in the corner portion have a larger spacing, thereby providing sufficient space for the expansion and contraction of the negative electrode sheet in the corner portion, effectively improving the active ion precipitation, purple stain and other phenomena in the corner portion, and further improving the cycle performance of the secondary battery using the winding electrode assembly. At least part of the binder particles have a hollow structure, so that the binder layer of the separator in the corner portion can form a certain void, which is beneficial to the adsorption of electrolyte and improves the liquid retention, thereby further improving the cycle performance of the secondary battery.

[0006] According to the embodiments of the present application, the spacing between the adjacent positive and negative electrode sheets in the corner portion is a first spacing, the spacing between the adjacent positive and negative electrode sheets in the main body portion is a second spacing, and the difference between the first spacing and the second spacing is not less than 50 μm and not more than 150 μm. The binder particles in the main body portion can be flattened in the pressing step of the winding electrode assembly preparation, so that the thickness of the binder layer in the main body portion is thinned, so that the winding electrode assembly has a smaller size, which is convenient for assembly, while the corner portion is usually not pressed during preparation. Due to the support of the binder particles with an average size of 6-21 μm in the corner portion, the spacing between the adjacent positive and negative electrode sheets is larger, which can provide more sufficient space for the expansion and contraction of the negative electrode sheet, thereby effectively improving the active ion precipitation, purple stain and other problems in the corner portion, and improving the cycle performance of the secondary battery using the winding electrode assembly.

[0007] According to the embodiments of the present application, the thickness of the binder layer of the single-sided surface of the base film in the corner portion is a first thickness, and the thickness of the binder layer of the single-sided surface of the base film in the main body portion is a second thickness, and the difference between the first thickness and the second thickness is not less than 25 μm and not more than 75 μm. In this way, the first spacing and the second spacing can be effectively adjusted by the thickness of the binder layer, so that the electrode assembly can have a smaller overall size and the corner portion can fully meet the expansion and contraction requirements of the negative electrode sheet, thereby effectively improving the cycle performance of the secondary battery using the winding electrode assembly while maintaining a smaller battery volume.

[0008] According to the embodiments of the present application, the first thickness is 25-45 μm, and the second thickness is 0.1-5 μm. In this thickness range, the size requirement and the expansion and contraction requirement of the corner portion negative electrode sheet can be well met, so that the winding electrode assembly has a smaller volume, and the secondary battery using the electrode assembly has good cycle performance.

[0009] According to embodiments of the present application, the binder particles include non-fluorine binder particles. In this way, the damage of F-containing binder to the environment can be avoided, while the glass transition temperature of the polymer binder is appropriate, and the preparation process of the wound electrode assembly does not need hot pressing, but only needs cold pressing to realize the bonding of the separator and the electrode sheet, which can greatly improve the processing efficiency and reduce the processing cost.

[0010] According to embodiments of the present application, the binder particles include polymer binder particles not containing fluorine elements, and the polymer monomer of the polymer binder particles includes a first monomer shown in Formula 1:

[0011]

[0012] wherein R1 is selected from a hydrogen atom and C 1-12 alkyl, and R2 is selected from C 1-12 alkyl.

[0013] According to embodiments of the present application, the first monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, and lauryl methacrylate.

[0014] The inclusion of the unsaturated ester group in the first monomer is conducive to the preparation of the binder particles, while the anti-swelling ability of the binder particles can be improved, and as a flexible monomer segment in the molecular chain segment, the glass transition temperature of the binder particles can be adjusted, which is helpful to adjust the glass transition temperature of the binder particles to a suitable range, thereby facilitating the preparation, and even cold pressing can be used to replace the original hot pressing in the preparation process of the electrode assembly, which greatly reduces the cost and improves the efficiency.

[0015] According to embodiments of the present application, the polymer binder particles further include a second monomer shown in Formula 2:

[0016]

[0017] wherein R3 includes a hydrogen atom, substituted or unsubstituted C 1-18 alkyl.

[0018] According to embodiments of the present application, the second monomer includes at least one of acrylic acid, methacrylic acid, butenoic acid, or heptoenoic acid. The inclusion of the unsaturated carboxyl group in the second monomer is conducive to the polymerization of the polymer monomer, and the carboxyl group can form a binding force with the functional groups on the electrode sheet and the base film of the separator, thereby improving the bonding effect.

[0019] According to an embodiment of the present application, the polymer binder particles include a third monomer of Formula 3:

[0020]

[0021] wherein R4 is selected from a hydrogen atom and C 1-6 alkyl, R5 is selected from a hydrogen atom, a hydroxyl-substituted C 1-6 alkyl, and C 1-6 alkoxy.

[0022] According to an embodiment of the present application, the third monomer includes at least one of acrylamide and N-methylol acrylamide.

[0023] With the third monomer described above, the cross-linking degree of the polymer binder particles can be improved, the chemical stability can be improved, and the polymer binder particles have better toughness and adhesion, which is beneficial to follow the movement in the expansion and contraction process of the negative electrode sheet, thereby improving the stability of the electrode sheet (positive electrode sheet and / or negative electrode sheet) and the separator film, improving the demolding phenomenon of the positive electrode sheet and / or the negative electrode sheet during the cycle of the secondary battery, and effectively improving the phenomena of active ion precipitation, purple stain, and the like, thereby improving the cycle performance of the secondary battery.

[0024] According to an embodiment of the present application, the binder particles include polymer binder particles, and the polymer binder particles include a first monomer, a second monomer, and a third monomer in a mass ratio of 1:(0.05-0.4):(0.01-0.2). With the polymer binder particles formed by the monomers in the above ratio, the polymer binder particles have a suitable glass transition temperature, better adhesion, and better toughness.

[0025] In a second aspect, the present application provides a method for preparing a jelly-roll electrode assembly. According to an embodiment of the present application, the method comprises: mixing a polymerization monomer, an emulsifier, an initiator and a solvent, and allowing the obtained raw material mixture to undergo a polymerization reaction to obtain a latex; mixing the latex, a dispersing agent and water to obtain a slurry; performing spray drying on the slurry to obtain binder particles; forming a bonding layer on at least one surface of a base film using the binder particles to obtain a separator film; winding and pressing a positive electrode sheet, the separator film and a negative electrode sheet to obtain a jelly-roll electrode assembly; wherein the jelly-roll electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film arranged between the positive electrode sheet and the negative electrode sheet; the separator film comprises a base film and a bonding layer arranged on at least one surface of the base film, and the bonding layer comprises binder particles; the jelly-roll electrode assembly comprises a main body portion and corner portions located on both sides of the main body portion; in the corner portions, the average size of the binder particles is 6 μm to 21 μm, and at least part of the binder particles have a hollow structure.

[0026] The method can conveniently and quickly obtain a jelly-roll electrode assembly, and has simple steps and easy operation, and is easy to scale up production; the bonding layer of the separator film in the corner portions of the jelly-roll electrode assembly uses binder particles with an average size of 6 μm to 21 μm, and the binder particles with the average size in this range can play a good supporting role, so that the adjacent positive electrode sheet and negative electrode sheet in the corner portions have a larger spacing, thereby providing sufficient space for the expansion and contraction of the negative electrode sheet in the corner portions, effectively improving the phenomena of active ion precipitation, purple stain and the like in the corner portions, and further improving the cycle performance of a secondary battery using the jelly-roll electrode assembly; and at least part of the binder particles have a hollow structure, so that the bonding layer of the separator film in the corner portions can form certain voids, which is beneficial to the adsorption of electrolyte and improves the liquid retention, thereby further improving the cycle performance of the secondary battery.

[0027] According to an embodiment of the present application, in the step of performing spray drying on the slurry to obtain binder particles, the binder particles satisfy at least one of the following conditions: the Dv50 particle size of the binder particles is 10 μm to 30 μm, at least part of the binder particles have a hollow structure; and / or, the tap density of the binder particles is 0.2 g / cm 3 - 0.7 g / cm 3 ; and / or, the storage modulus of the binder particles is 10 MPa to 50 MPa at 25 °C.

[0028] The binder particles with a hollow structure can form certain voids in the binder layer, which is beneficial to adsorbing electrolyte, improving liquid retention, and further improving active ion transmission performance. Meanwhile, the binder particles with a hollow structure have a certain tap density and a relatively low storage modulus, the main part of the wound electrode assembly is easier to be compressed, the wound electrode assembly is easier to be processed, and the rebound amplitude of the binder layer of the compressed main part is small, the expansion amplitude of the binder layer during the cycle process is also small, which is beneficial to improving the dimensional stability of the wound electrode assembly.

[0029] According to the embodiments of the present application, the dispersant includes at least one of sodium polyacrylate, sodium polymethacrylate, polyacryl ether, polyethylene glycol, polyvinylpyrrolidone, and polyacrylic acid. The use of the above dispersant can make the latex fully dispersed and uniform, which is beneficial to obtaining the binder particles with uniform particle size distribution.

[0030] According to the embodiments of the present application, the slurry satisfies at least one of the following conditions: a solid content of 10% to 30%, and a viscosity of 100 mpa.s to 500 mpa.s.

[0031] The slurry satisfying the above parameters is beneficial to obtaining the binder particles with a Dv50 particle size of 10 μm to 30 μm and a hollow structure.

[0032] According to the embodiments of the present application, the spray drying includes at least one of centrifugal spray drying, gas flow spray drying, and pressure spray drying.

[0033] According to the embodiments of the present application, the spray drying is two-fluid spray drying, and satisfies at least one of the following conditions: a gas pressure of 0.1 MPa to 5 MPa, and a liquid pressure of 0.1 MPa to 100 MPa. According to the embodiments of the present application, the liquid pressure of the two-fluid spray drying is 0.5 MPa to 3 MPa. The use of the above spray drying parameters is beneficial to obtaining the binder particles with a Dv50 particle size of 10 μm to 30 μm and a hollow structure.

[0034] In a third aspect, the present application provides a secondary battery. According to the embodiments of the present application, the secondary battery includes all the features and advantages of the wound electrode assembly described above, which will not be repeated here.

[0035] In a fourth aspect of the present application, a power consuming device is provided. According to embodiments of the present application, the power consuming device comprises the secondary battery as described above. It is understood that the power consuming device has all the features and advantages of the secondary battery as described above, which will not be repeated here.

[0036] The above description is merely a summary of the application technical solutions. In order to make the technical means of the present application more clear, the application can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0037] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments, and are not meant to limit the present application. Moreover, the same reference numerals in the attached drawings refer to the same or like components throughout the several drawings. In the drawings:

[0038] Figure 1 is a structural schematic diagram of a wound electrode assembly according to an embodiment of the present application.

[0039] Figure 2 is a partial structural schematic diagram of a separator film in a flattened state according to an embodiment of the present application.

[0040] Figure 3 is a structural schematic diagram of a secondary battery according to an embodiment of the present application.

[0041] Figure 4 is a structural schematic diagram of a power consuming device according to an embodiment of the present application.

[0042] Figure 5 is an ion polishing cross-sectional morphology diagram of the binder particles according to Embodiment 1 of the present application.

[0043] Figure 6 is an ion polishing cross-sectional morphology diagram of the binder particles according to Embodiment 1 of the present application.

[0044] Figure 7 is a CT scan image of a wound electrode assembly according to an embodiment of the present application.

[0045] Figure 8 is an ion polishing cross-sectional morphology diagram of the binder particles according to Comparative Example 1 of the present application.

[0046] Figure 9 is an ion polishing cross-sectional morphology diagram of the binder particles according to Comparative Example 1 of the present application.

[0047] Figure 10is an ion polishing cross-sectional morphology of the binder particle of Comparative Example 2 of the present application.

[0048] The reference signs are as follows:

[0049] 100: electrode assembly 110: separator film 120: positive electrode tab 130: negative electrode tab 101: main body portion 102: corner portion 111: base film 112: adhesive layer 1: battery 200: case 300: cover plate DETAILED DESCRIPTION

[0050] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0052] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly and specifically limited.

[0053] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0054] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of existence of A, existence of A and B, and existence of B. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0055] In the description of the embodiments of the present application, the term "multiple" refers to two or more (including two), and similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0056] During the charge and discharge cycle of the secondary battery, active ions are embedded into the layered material, causing the thickness of the electrode sheet to increase, thereby generating expansion force. This expansion is reversible, and the amplitude of the expansion will become larger and larger as the number of cycles increases. In the related art, the negative electrode sheet will undergo significant expansion and contraction. This change will cause the distance between the adjacent positive electrode sheet and the adjacent negative electrode sheet inside the secondary battery to become smaller and smaller, thereby causing the cell to deform, forming a hollow space between the electrode sheet and the separator, causing the negative active material particles to form micro-cracks, and causing the solid electrolyte interface (SEI) film to break and recombine, consuming electrolyte, and causing the cycle performance of the secondary battery to deteriorate. In particular, in the corner portion of the wound electrode assembly, the stress is relatively concentrated, the channel for the transport of active ions is relatively difficult, and problems such as active ion precipitation and purple stains often occur in the corner portion, thereby affecting the cycle life of the secondary battery.

[0057] To solve the above problems, the present application provides a wound electrode assembly. According to the wound electrode assembly of the embodiments of the present application, the adhesive layer of the separator in the corner portion uses adhesive particles with a larger average size and at least partially having a hollow structure, which is beneficial to improve the cycle performance of the secondary battery using the wound electrode assembly.

[0058] The wound electrode assembly provided by the present application can be used in a secondary battery, and the secondary battery can include but is not limited to a lithium ion battery, a sodium ion battery, etc.; the specific shape of the secondary battery can be square, cylindrical, and other regular or irregular shapes; the outer packaging of the secondary battery can be a hard shell (such as a steel shell, a hard plastic shell, etc.), or a soft shell (such as an aluminum plastic film, a bag-type soft shell, etc.). The above-mentioned secondary battery can exist in the form of a battery monomer, or can be assembled into the form of a battery module, a battery pack, etc. The above-mentioned secondary battery can be used as a power source or an energy storage system for an electric device such as a vehicle, a power tool, a mobile terminal, an aircraft, etc.

[0059] The wound electrode assembly and the preparation method thereof, the secondary battery, and the electric device of the present application will be described in detail below with reference to the accompanying drawings.

[0060] In a first aspect of the present application, a wound electrode assembly is provided. According to the embodiments of the present application, with reference to Figures 2 to 3The jelly-roll electrode assembly 100 includes a positive electrode tab 120, a negative electrode tab 130, and a separator 110 disposed between the positive electrode tab 120 and the negative electrode tab 130; the separator 110 can include a base film 111 and a bonding layer 112 disposed on at least one surface of the base film 111, the bonding layer 112 including binder particles; the jelly-roll electrode assembly 100 includes a main body portion 101 and corner portions 102 located on both sides of the main body portion; in the corner portions 102, the average size of the binder particles is 6 μm to 21 μm, and at least part of the binder particles have a hollow structure. Specifically, the average size of the binder particles can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or any value within a range between any two of the above values.

[0061] It can be understood that the hollow structure refers to the inside of the binder particles being empty, not solid, in other words, the binder particles are hollow.

[0062] The average size described above can be obtained by testing the SEM photograph of the cross section of the bonding layer containing the binder particles, for example, the cross-sectional size (long diameter, i.e., the distance between the two points farthest apart on the cross-sectional profile line of the binder particles) of all the binder particles in multiple fields of view (or fields of view of a predetermined area, or a predetermined number of binder particles) can be tested, and then the average size is calculated.

[0063] It can be understood that the main body portion 101 is a region in which no bending or folding exists in the jelly-roll electrode assembly 100; the corner portion 102 is a region in which bending or folding exists in the jelly-roll electrode assembly 100.

[0064] The binder particles with an average size of 6-21 μm in the adhesive layer of the separator film in the corner portion can provide good support, so that the adjacent positive electrode sheet and negative electrode sheet in the corner portion have a larger spacing, thereby providing sufficient space for the expansion and contraction of the negative electrode sheet in the corner portion, effectively improving the active ion precipitation, purple stain and other phenomena in the corner portion, and further improving the cycle performance of the secondary battery using the wound electrode assembly. At least part of the binder particles have a hollow structure, so that the adhesive layer of the separator film in the corner portion can form certain voids, which is beneficial to the adsorption of electrolyte and improves the liquid retention, thereby further improving the cycle performance of the secondary battery.

[0065] According to the embodiments of the present application, referring to Figure 1 , the spacing between the adjacent positive electrode sheet 120 and negative electrode sheet 130 in the corner portion 102 is a first spacing G1, and the spacing between the adjacent positive electrode sheet 120 and negative electrode sheet 130 in the main body portion 101 is a second spacing G2, and the difference between the first spacing G1 and the second spacing G2 is not less than 50 μm and not more than 150 μm.

[0066] In some embodiments, the difference between the first spacing G1 and the second spacing G2 can be 50-150 μm, 50-100 μm, 50-90 μm, 55-90 μm, 60-80 μm or 50-75 μm, etc. For example, the difference between the first spacing G1 and the second spacing G2 can be 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 62 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 78 μm, 80 μm, 82 μm, 85 μm, 88 μm, 90 μm, 92 μm, 95 μm, 98 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, etc.

[0067] The first distance refers to the distance between the adjacent positive electrode sheet and the negative electrode sheet in the corner portion, measured along a straight line passing through the midpoint of the thickness of the wound electrode assembly (i.e., the midpoint of the dimension of the wound electrode assembly in the direction of stacking of the positive electrode sheet, the separator, and the negative electrode sheet), and parallel to the positive electrode sheet in the main body portion. The second distance can be the distance between the positive electrode sheet and the negative electrode sheet measured at any position in the main body portion. Specifically, the first distance and the second distance can be measured by a CT in-situ characterization technique (Computed Tomography). As an example, a CT device of Model ZEISS METROTOM 1 can be used to non-destructively test the electrode assembly. The CT device can scan to obtain a scanning image of the positive current collector in the wound electrode assembly, and then mark the distance between the adjacent positive current collectors according to the scanning image. Then, the distance between the adjacent positive electrode sheet and the negative electrode sheet can be calculated according to the specific film structure between the adjacent positive current collectors and the thickness of the known film layers.

[0068] It can be understood that the binder particles in the main body portion can be flattened in the pressing step of preparing the wound electrode assembly, so that the thickness of the binder layer in the main body portion is thinned, and the wound electrode assembly has a smaller size, which is convenient for assembly. However, the corner portion is generally not pressed during preparation, and due to the support of the binder particles in the corner portion within the average size range, the distance between the adjacent positive electrode sheet and the negative electrode sheet is larger, which can provide sufficient space for the expansion and contraction of the negative electrode sheet, thereby improving the problems of active ion precipitation, purple discoloration, etc. in the corner portion, and improving the cycle performance of the secondary battery.

[0069] According to the embodiments of the present application, with reference to Figure 2 , the thickness of the binder layer 112 on the single side surface of the base film 111 in the corner portion 102 is a first thickness H1, the thickness of the binder layer 112 on the single side surface of the base film 111 in the main body portion 101 is a second thickness H2, and the difference between the first thickness H1 and the second thickness H2 is not less than 25 μm and not more than 75 μm.

[0070] In some embodiments, the difference can be 25 μm to 75 μm, 25 μm to 50 μm, 25 μm to 45 μm, 30 μm to 40 μm, etc. Specifically, the difference between the first thickness H1 and the second thickness H2 can be 25.1 μm, 25.5 μm, 25.8 μm, 26 μm, 26.2 μm, 26.5 μm, 26.8 μm, 27 μm, 27.2 μm, 27.5 μm, 27.8 μm, 28 μm, 28.5 μm, 29 μm, 29.5 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, etc.

[0071] The first thickness refers to the thickness of the single-side surface adhesive layer of the base film measured in the corner portion along a straight line passing through the midpoint of the thickness of the wound electrode assembly (i.e., the midpoint of the dimension of the wound electrode assembly in the direction of stacking of the positive electrode tab, the separator film, and the negative electrode tab) and parallel to the positive electrode tab in the main body portion. The second thickness can be the thickness of the single-side surface adhesive layer measured at any position in the main body portion. Specifically, the first thickness and the second thickness can be measured by CT in-situ characterization technology (Computed Tomography). As an example, the distance between adjacent positive current collectors can be marked by CT scanning images according to the method described above, and then the first thickness and the second thickness can be obtained by calculation according to the film layer structure between the adjacent positive current collectors and the known film layer thickness.

[0072] Thus, the first distance and the second distance can be effectively adjusted by the thickness of the adhesive layer, so that the wound electrode assembly can have a small overall size and the corner portion can fully meet the space requirement for expansion and contraction of the negative electrode tab, thereby effectively improving the cycle performance of the secondary battery using the wound electrode assembly and reducing the volume of the secondary battery. Moreover, the distance between the tabs is adjusted by the adhesive layer, which has high compatibility with the existing process and does not require additional operation steps, so that the preparation process is simple and easy to implement.

[0073] According to embodiments of the present application, the first thickness H1 is 25 μm to 45 μm, specifically, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, etc.; and the second thickness H2 is 0.1 μm to 5 μm, specifically, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.5 μm, 5 μm, etc. In this thickness range, the size requirement and the space requirement for expansion and contraction of the negative electrode tab in the corner portion can be well met, the wound electrode assembly has a small volume, and the secondary battery using the wound electrode assembly has good cycle performance.

[0074] According to embodiments of the present application, the adhesive particles include non-fluorine adhesive particles. Specifically, the adhesive particles can not contain fluorine elements. Thus, the damage of F-containing adhesive to the environment can be avoided, and the glass transition temperature of the non-fluorine adhesive particles is suitable, so that the wound electrode assembly does not need to be hot-pressed during preparation, but only needs to be cold-pressed to bond the separator film and the tabs, which can greatly improve the processing efficiency and reduce the processing cost.

[0075] It can be understood that the binder particles can include a polymer binder, and the polymer binder particles can be formed by polymerization of one or more polymerizable monomers. In some embodiments, the polymer binder particles include a polymer formed by polymerization of an acrylate monomer.

[0076] According to embodiments of the present application, the polymerizable monomers of the polymer binder particles can include a first monomer represented by Formula 1:

[0077]

[0078] wherein R1 is selected from a hydrogen atom and a C 1-12 alkyl group, and R2 is selected from a C 1-12 alkyl group.

[0079] According to embodiments of the present application, the first monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, and lauryl methacrylate.

[0080] The inclusion of the unsaturated ester group in the first monomer facilitates the preparation of the polymer binder particles, while improving the anti-swelling ability of the polymer binder particles, and as a flexible monomer segment in the molecular chain, can adjust the glass transition temperature of the polymer binder particles, helping to adjust the glass transition temperature of the polymer binder particles to a suitable range, thereby facilitating the preparation, and even replacing the original hot pressing in the electrode assembly preparation process with cold pressing, greatly reducing the cost and improving the efficiency.

[0081] According to embodiments of the present application, the polymerizable monomers of the polymer binder particles further include a second monomer represented by Formula 2:

[0082]

[0083] wherein R3 includes a hydrogen atom, a substituted or unsubstituted C 1-18 alkyl group.

[0084] According to embodiments of the present application, the second monomer includes at least one of acrylic acid, methacrylic acid, butenoic acid, or heptoenoic acid. The inclusion of the unsaturated carboxyl group in the second monomer facilitates the polymerization of the polymerizable monomers, and the carboxyl group can form a binding force with the functional groups on the pole piece and the base film of the separator film, improving the bonding effect.

[0085] According to embodiments of the present application, the polymer binder particles comprise a third monomer of Formula 3:

[0086]

[0087] wherein R4 is selected from a hydrogen atom and a C 1-6 alkyl group, and R5 is selected from a hydrogen atom, a hydroxyl-substituted C 1-6 alkyl group, and a C 1-6 alkoxy group.

[0088] According to embodiments of the present application, the third monomer comprises at least one of acrylamide and N-methylol acrylamide.

[0089] With the third monomer described above, the cross-linking degree of the polymer binder particles can be improved, the chemical stability can be improved, and the polymer binder particles have better toughness and adhesion, which is beneficial to follow the movement during the expansion and contraction of the negative electrode sheet, thereby improving the stability of the electrode sheet (positive electrode sheet and / or negative electrode sheet) and the separator film, improving the demolding phenomenon of the positive electrode sheet and / or the negative electrode sheet during the cycle of the secondary battery, and effectively improving the phenomena of active ion precipitation and purple stain, thereby improving the cycle performance of the secondary battery.

[0090] According to embodiments of the present application, the polymer binder particles comprise a first monomer, a second monomer, and a third monomer in a mass ratio of 1:(0.05-0.4):(0.01-0.2). Specifically, the mass ratio of the first monomer, the second monomer, and the third monomer can be 1:0.05:0.01, 1:0.1:0.01, 1:0.2:0.01, 1:0.3:0.01, 1:0.4:0.01, 1:0.05:0.05, 1:0.05:0.1, 1:0.05:0.2, 1:0.2:0.1, and the like.

[0091] With the polymer binder particles formed by the above-mentioned ratio of polymer monomers, the polymer binder particles can have a suitable glass transition temperature, better adhesion, and better toughness.

[0092] It can be understood that the binder particles can be secondary particles formed by agglomeration of primary particles, such as secondary particles formed by agglomeration of acrylic polymer primary particles. In some embodiments, the particle size of the primary particles can be 100-200 nm. As an example, the secondary particles can be obtained by granulating the primary particles, and the specific granulation process includes but is not limited to spray drying. For example, secondary particles with a large particle size can be obtained by spray drying acrylic polymer primary particles with a particle size of 100-200 nm.

[0093] It can be understood that, according to actual needs, in addition to the adhesive layer, other coating layers such as ceramic coating layers and the like can also be provided on the base film to improve the heat resistance, ionic conductivity and the like of the separator film. The specific ceramic coating layer can be carried out according to conventional technology, which will not be repeated here. As an example, the ceramic coating layer can be provided between the separator film and the adhesive layer.

[0094] It can be understood that the material of the base film in the above-mentioned separator film can include but is not limited to one or more of glass fiber, non-woven fabric, polyolefin. In some embodiments, the material of the base film can include polyolefin, such as polyethylene, polypropylene, polyvinylidene fluoride, etc. The base film can be a single-layer film or a multi-layer film, such as a polyethylene single-layer film, a polypropylene single-layer film, a polyethylene / polypropylene multi-layer film, etc. The thickness of the base film can be selected according to actual needs, for example, less than or equal to 12 μm, specifically, 3 μm-9 μm, 3 μm-7 μm, 3 μm-5 μm, etc.

[0095] According to embodiments of the present application, the above-mentioned positive electrode tab can include a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is provided on at least one surface of the positive electrode current collector.

[0096] In some embodiments, the positive electrode current collector can be a metal current collector or a composite current collector. For example, the metal current collector includes but is not limited to an aluminum foil current collector; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base film. 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 base film (such as a base film of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0097] In some embodiments, the positive electrode active material layer can include a positive electrode active material, a binder and a conductive agent, and additives with specific functions and effects can also be added according to actual needs, such as lithium supplementing agents, film forming additives, flame retardants, high / low temperature stabilizers, etc.

[0098] Taking a lithium ion battery as an example, the positive electrode active material can include at least one of a layered structure positive electrode active material (such as nickel-cobalt-manganese ternary positive electrode material, nickel-cobalt-aluminum ternary positive electrode material, lithium / sodium nickelate, lithium / sodium cobaltate, lithium / sodium manganate, lithium / sodium-rich layered and rock salt phase layered materials), an olivine-type phosphate active material (such as lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.), a spinel structure positive electrode active material (such as spinel lithium manganate, spinel nickel-manganese lithium manganate, lithium-rich spinel lithium manganate and nickel-manganese lithium manganate, etc.). It can be understood that the above-mentioned positive electrode active material can further include doped elements and coating layers, etc.

[0099] As an example, the binder in the positive electrode active material layer can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate-based resin.

[0100] As an example, the conductive agent in the positive electrode active material layer can include at least one of super P, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] According to an embodiment of the present application, the above-mentioned negative electrode tab can include a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector.

[0102] According to an embodiment of the present application, the negative electrode current collector can be a metal current collector or a composite current collector. For example, the metal current collector includes but is not limited to a copper foil current collector; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base film. 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 base film (such as a base film of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] According to an embodiment of the present application, the negative electrode active material layer can include a negative electrode active material, a binder, and a conductive agent, and additives with specific functions and effects, such as a lithium supplement, a flame retardant, a high / low temperature stabilizer, etc., can also be added according to actual needs.

[0104] According to an embodiment of the present application, the negative electrode active material includes but is not limited to one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based film material, tin-based film material, and lithium titanate. The silicon-based film material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based film material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0105] According to an embodiment of the present application, the binder in the negative electrode active material layer can include but is not limited to 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).

[0106] According to embodiments of the present application, the conductive agent in the negative active material layer can include, but is not limited to, at least one of super-p carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In a second aspect of the present application, a method for preparing a jelly-roll electrode assembly is provided. According to embodiments of the present application, the method includes: mixing a polymerization monomer, an emulsifier, an initiator, and a solvent, and allowing the resulting raw material mixture to undergo a polymerization reaction to obtain a latex; mixing the latex, a dispersing agent, and water to obtain a slurry; performing spray drying on the slurry to obtain binder particles; forming a bonding layer on at least one surface of a base film using the binder particles to obtain a separator film; winding and pressing a positive electrode sheet, the separator film, and a negative electrode sheet to obtain a jelly-roll electrode assembly; wherein the jelly-roll electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator film disposed between the positive electrode sheet and the negative electrode sheet; the separator film includes a base film and a bonding layer disposed on at least one surface of the base film, and the bonding layer includes binder particles; and the jelly-roll electrode assembly includes a main body portion and corner portions located on both sides of the main body portion; in the corner portions, the average size of the binder particles is 6 μm to 21 μm, and at least part of the binder particles have a hollow structure.

[0108] It can be understood that the above polymerization reaction is a process in which the polymerization monomer is dispersed in water to form an emulsion by means of the emulsifier and mechanical stirring, and the polymerization monomer is polymerized under the initiation of the initiator.

[0109] An emulsifier is a substance that can transform mutually incompatible oil and water into an emulsion that is difficult to separate. The emulsifier is usually a surface active agent that has both hydrophilic polar groups and hydrophobic (oleophilic) non-polar groups.

[0110] An initiator is a substance that can initiate the polymerization of a polymerization monomer. For example, a free radical initiator refers to a class of compounds that are easily decomposed into free radicals (i.e., primary free radicals) by heat, and can be used to initiate the free radical polymerization and copolymerization of olefinic and diene polymerization monomers.

[0111] In some embodiments, the solvent (e.g., water), the emulsifier, the initiator, and the polymerization monomer are blended and stirred, and the solvent and the emulsifier are dispersed by stirring to form an emulsion, i.e., micelles of the emulsifier are formed in the solvent, and most of the micelles solubilize the polymerization monomer. Under the condition of heating, the initiator initiates and polymerizes the polymerization monomer inside the micelles to obtain a latex.

[0112] Dispersant is an interfacial active agent with both lipophilic and hydrophilic properties in the molecule. It can uniformly disperse inorganic, organic solids and liquid particles that are difficult to dissolve in liquid, and also prevent the settlement and agglomeration of particles, forming a stable suspension.

[0113] Spray drying is a process that disperses the slurry to be dried into very fine particles like mist (increases the water evaporation area and accelerates the drying process) by mechanical action, and contacts with hot air to remove most of the water in an instant, so that the solid material in the slurry is dried into powder.

[0114] The method can conveniently and quickly obtain the wound electrode assembly, and the steps are simple, easy to operate, and easy to scale production; the adhesive layer of the separator film at the corner portion of the wound electrode assembly adopts adhesive particles with an average size of 6-21 μm, the adhesive particles with the average size can play a good supporting role, so that the adjacent positive electrode sheet and negative electrode sheet in the corner portion have a larger spacing, thereby providing sufficient space for the expansion and contraction of the negative electrode sheet in the corner portion, effectively improving the active ion precipitation, purple stain and other phenomena at the corner portion, and further improving the cycle performance of the secondary battery using the wound electrode assembly. At least part of the adhesive particles have a hollow structure, so that the adhesive layer of the separator film at the corner portion can form a certain gap, which is beneficial to the adsorption of electrolyte and improves the liquid retention, thereby further improving the cycle performance of the secondary battery.

[0115] According to the embodiments of the present application, the emulsifier can include at least one of sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium dodecyl benzene sulfate, sodium laurate, sodium stearate, and sodium palmitoleate; the initiator can include at least one of potassium persulfate, ammonium persulfate, benzoyl peroxide, di-n-octyl peroxide, azobis isobutyronitrile, and dimethyl azobis isobutyrate; and the solvent can include deionized water. The use of the above emulsifier, initiator and solvent facilitates the polymerization reaction, promotes the complete reaction, and is suitable for the reaction conditions and easy to control.

[0116] According to the embodiments of the present application, the mass ratio of the polymerization monomer, the emulsifier and the initiator can be 100:(0.5-10):(0.1-1.2). Specifically, it can be 100:0.5:0.1, 100:01:01, 100:5:0.1, 100:10:0.1, 100:0.5:0.5, 100:0.5:1.2, 100:5:0.5, 100:5:1, 100:8:1.2, etc. Within the above ratio range, the latex with a suitable particle size can be obtained, which is beneficial to subsequent spray drying, and the obtained latex has better adhesive performance.

[0117] According to the embodiments of the present application, the solid content of the mixture of the polymerized monomers, the emulsifier, the initiator and the solvent can be 20% to 60%. Specifically, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value within the range between any two of the above values. Within the above solid content range, the latex with suitable particle size can be obtained, which is beneficial for subsequent spray drying, and the obtained latex has better bonding performance.

[0118] According to the embodiments of the present application, the dispersant includes at least one of sodium polyacrylate, sodium polymethacrylate, polyacrylic ether, polyethylene glycol, polyvinylpyrrolidone and polyacrylic acid. The use of the above dispersant can make the latex fully dispersed and uniform, which is beneficial for preparing the binder particles with uniform particle size distribution and hollow structure.

[0119] According to the embodiments of the present application, the mass ratio of the latex and the dispersant can be 100:(1-20), specifically, 100:1, 100:5, 100:8, 100:10, 100:12, 100:15, 100:18, 100:20 or any value within the range between any two of the above values. The use of the above proportioned materials can further uniformly disperse the latex, obtain the binder particles with particle size of 10-30 microns, and the particle size distribution of the binder particles is more uniform.

[0120] According to the embodiments of the present application, in the step of spray drying the slurry to obtain the binder particles, the Dv50 particle size of the binder particles is 10-30 microns, and at least part of the binder particles have a hollow structure.

[0121] The above Dv50 particle size is also called median diameter or median particle size, which refers to the particle size corresponding to the cumulative volume percentage of 50% of a sample; its physical meaning is that the particles with particle size greater than it account for 50% by volume, and the particles with particle size less than it also account for 50% by volume. The Dv50 particle size of the binder particles can be tested by the method known in the art. As an example, GB / T 19077-2016 can be referred to, and a Malvern laser particle size analyzer can be used for characterization test, for example, a Malvern Mastersizer-3000 instrument can be used for test.

[0122] The binder particles with a Dv50 particle size of 10 μm to 30 μm and at least partially having a hollow structure form the binder layer of the separator of the wound electrode assembly, which can provide sufficient expansion space for the negative electrode sheet in the corner portion, relieve the local stress concentration problem caused by expansion obstruction, improve the demolding phenomenon of the positive electrode sheet and / or the negative electrode sheet of the secondary battery using the wound electrode assembly during the cycle process, and also significantly relieve the local stress concentration problem caused by expansion obstruction; at the same time, effectively improve the active ion precipitation, purple stain and other phenomena, and thus improve the cycle performance of the secondary battery using the wound electrode assembly; and the partial binder particles having a hollow structure can form certain voids in the binder layer, which is beneficial to adsorb electrolyte, improve the liquid retention, and thus improve the active ion transmission performance; at the same time, the binder particles with a hollow structure have a certain tap density and a lower storage modulus, the main body portion of the wound electrode assembly is more easily compressed, the wound electrode assembly is more easily processed, and the rebound amplitude of the binder layer of the compressed main body portion is small, the expansion amplitude of the binder layer during the cycle process is also small, which is beneficial to improve the dimensional stability of the wound electrode assembly.

[0123] According to the embodiments of the present application, in the step of spray drying the slurry to obtain the binder particles, the tap density of the binder particles can be 0.2 g / cm 3 ~ 0.7 g / cm 3 , specifically 0.2 g / cm 3 , 0.25 g / cm 3 , 0.3 g / cm 3 , 0.35 g / cm 3 , 0.4 g / cm 3 , 0.45 g / cm 3 , 0.5 g / cm 3 , 0.55 g / cm 3 , 0.6 g / cm 3 , 0.65 g / cm 3 , 0.7 g / cm 3 , or any value within a range between any two of the above values.

[0124] The tap density refers to the mass per unit volume measured after the powder in the container is vibrated under specified conditions. The tap density can be tested by a method known in the art. As an example, the test can be performed according to GB / T21354-2008 General Method for Determination of Tap Density of Powder Products.

[0125] The binder particles have the above tap density, which is beneficial to improve the energy density of the secondary battery.

[0126] According to the embodiments of the present application, in the step of spray drying the slurry to obtain the binder particles, the binder particles have a storage modulus of 10 MPa to 50 MPa at 25°C, specifically 10 MPa, 12 MPa, 15 MPa, 18 MPa, 20 MPa, 22 MPa, 25 MPa, 28 MPa, 30 MPa, 32 MPa, 35 MPa, 38 MPa, 40 MPa, 42 MPa, 45 MPa, 48 MPa, 50 MPa, or any value within a range between any two of the above values.

[0127] The storage modulus refers to the ability of a solid material to store elastic potential energy, and is used to describe the energy stored by a material during elastic and plastic deformation. The storage modulus can be tested by methods known in the art. As an example, the storage modulus of a sample can be tested by a DMA 8000 of Perkin Elmer.

[0128] With the above storage modulus, the binder particles can be flattened but not easily broken during the preparation of the jelly-roll type electrode assembly, and can also form certain gaps in the binder layer, which is beneficial for adsorbing electrolyte, improving liquid retention, and further improving the active ion transmission performance. A lower storage modulus makes the rebound amplitude of the binder layer of the flattened main body small, and the expansion amplitude of the binder layer during the cycle process is also small, which is beneficial for improving the dimensional stability of the jelly-roll type electrode assembly, and further improves the cycle performance of the secondary battery using the jelly-roll type electrode assembly.

[0129] It can be understood that the main steps of preparing the binder particles with hollow structure by the spray drying process include droplet formation, drying process, shell formation, hollow structure formation, cooling and collection. The main reason for obtaining the binder particles with hollow structure during spray drying can be that:

[0130] 1. Droplet drying speed: If the droplet drying speed is too fast, the outer layer solidifies while the inner part is moist, which can cause the hollow structure of the particles.

[0131] 2. Solubility of solute: The solubility of the solute in the droplet also affects the formation of the hollow structure. If the solute precipitates during the drying process, hollow structure particles can be formed.

[0132] 3. Internal pressure of droplet: Uneven distribution of internal pressure or the presence of small cavities in the droplet can also lead to the formation of hollow structure particles.

[0133] 4. Surface tension of droplet: Uneven surface tension of the droplet can cause the droplet to tear or break, which can form hollow structure particles during the drying process.

[0134] 5. Pe number: The Pe number is determined by the properties of the solute and solvent, and the process parameters of the evaporation rate. When the Pe number is greater than 1, the surface moves faster than the dissolving or precipitating component, which results in the enrichment of the high component on the surface, and can lead to the formation of hollow structures.

[0135] As an example, the process of spray drying to prepare binder particles with hollow structures can be as follows: the slurry is atomized into tiny droplets, and then these tiny droplets are sent into a drying chamber to contact with hot air, and the water is rapidly evaporated, leaving solid material; during the drying process, due to the very fast evaporation rate, the water on the surface of the tiny droplets is rapidly evaporated, forming a hard shell (which can be single-layered or multi-layered), and as the water inside the droplet continues to evaporate, the internal pressure increases due to the hard shell formed on the outside hindering the escape of the internal water, eventually leading to the collapse of the central part of the droplet and the formation of a hollow structure; finally, the dried binder particles with hollow structures are cooled in a cooling zone and then collected. In practical applications, the size, shape and structure of the binder particles with hollow structures can be optimized by adjusting the relevant parameters of the slurry and spray drying.

[0136] According to embodiments of the present application, the solid content of the slurry can be 10% to 30%, specifically, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any value within the range between any two of the above values.

[0137] The solid content refers to the percentage or weight percentage of solid components contained in a substance, and the solid content reflects the content of solid components in the substance. Specifically, in the present application, the solid content is the total mass of solids in the slurry divided by the mass of all components that make up the slurry. It can be calculated or tested by conventional methods in the art. As an example, the solid content can be calculated by the amount of solid materials and non-solid materials added.

[0138] If the solid content is greater, the viscosity of the slurry is greater, the probability of agglomeration between particles increases, the risk of nozzle clogging increases, and wall sticking phenomenon can occur, the rate of coarse particles increases, and thus the size distribution of the binder particles is relatively uneven, and there can be a small amount of large-sized spherical particles and / or non-spherical particles; if the solid content is smaller, the probability of fine powder formation increases, which can affect the particle size distribution and shape of the product, in addition, too low solid content can lead to the aggregation and instability of the particles during the spray drying process, thereby affecting the quality and performance of the product. It can be understood that the solid content also has a certain influence on the formation of hollow structures during the spray drying process. Within the above-mentioned solid content range, the droplets can shrink due to the evaporation of internal water during the drying process, and the material inside which has not been completely dried forms a hollow structure; at the same time, the particle size of the obtained binder particles is appropriate, the particle size distribution is uniform, the sphericity is good, and the morphology is stable.

[0139] According to embodiments of the present application, the viscosity of the slurry can be 100 mpa.s to 500 mpa.s, specifically, 100 mpa.s, 150 mpa.s, 200 mpa.s, 250 mpa.s, 300 mpa.s, 350 mpa.s, 400 mpa.s, 450 mpa.s, 500 mpa.s, or any value within a range between any two of the above values.

[0140] Viscosity can also be referred to as viscosity, which refers to the resistance of a fluid to flow. In the present application, the viscosity of the slurry can be tested by using a rotational Brookfield viscometer, specifically, a 62# rotor can be used, and the test is carried out at 25°C.

[0141] As the viscosity of the slurry increases, the likelihood of the material adhering to the inner wall of the drying tower during the drying process increases, and the so-called "wall sticking" phenomenon is more likely to occur. If the "wall sticking" phenomenon is serious, it can cause the material to stay on the hot wall for too long and be scorched or deteriorated, affecting the product quality. In addition, the "wall sticking" phenomenon can also cause the product yield to decrease, or the spray drying process needs to be interrupted to clean the wall-stuck material, thereby prolonging the operation cycle and reducing the production capacity. As the viscosity of the slurry decreases, the risk of the material being unable to form stable droplets during the spray drying process increases, which can affect the drying effect. A proper viscosity of the slurry helps to ensure that the material forms good droplets during the spray drying process, thereby improving the drying efficiency and product quality. The viscosity of the slurry also has an impact on the formation of hollow structures during the spray drying process. The slurry that meets the above viscosity range can be beneficial for the formation of hollow structures due to insufficient drying or uneven internal pressure, and at the same time, it is beneficial to obtain binder particles with a Dv50 particle size of 10 μm to 30 μm and at least partially having hollow structures, and has a high processing efficiency.

[0142] According to embodiments of the present application, the spray drying includes at least one of centrifugal spray drying, air flow spray drying, and pressure spray drying.

[0143] It can be understood that the centrifugal spray drying method uses a disc rotating at high speed in the horizontal direction to give the solution a centrifugal force, so that it is thrown out at high speed to form a film, a filament or a droplet. Due to the friction, resistance and tearing of the air, the tangential acceleration generated by the disc rotation and the radial acceleration generated by the centrifugal force, the liquid moves on the disc at a combined speed, and its trajectory is a spiral. The liquid is thrown off from the disc along the spiral line and moves along the tangential direction of the disc at an average speed, and is dried in the dryer.

[0144] Airflow spray drying refers to that wet material and heated natural air enter the dryer at the same time through a conveyor, the two are fully mixed, and are evaporated and dried in a very short time through a large heat mass exchange area.

[0145] Pressure spray drying is to use a high-pressure pump to spray the material through an atomizer (such as a spray gun) at a high pressure, and the mist particles are directly contacted with hot air for heat exchange, and the drying is completed in a short time.

[0146] According to the embodiments of the present application, the spray drying is two-fluid spray drying (belongs to airflow spray drying). Specifically, two-fluid spray drying refers to spraying liquid into a drying chamber by using multiphase jet technology, so that the sprayed droplets evaporate rapidly and a large number of small particles are generated, which are dried into fine powder particles under the action of air flow. As an example, granular or liquid substances can be made into a slurry suitable for spraying, and the prepared slurry is sprayed into a two-fluid spray drying chamber, and the sprayed droplets are evaporated into small particles under the high temperature and high humidity conditions in the drying chamber, and are quickly dried in the air to produce powder particles. According to needs, the produced powder can be further screened, sealed, dried, etc.

[0147] According to the embodiments of the present application, the air pressure of the above-mentioned spray drying can be 0.1-5 MPa, specifically 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, or any value within the range between any two of the above values; the liquid pressure is 0.1-100 MPa, such as 0.5-3 MPa, specifically 0.1 MPa, 0.5 MPa, 1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, 75 MPa, 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa, etc.

[0148] In the two-fluid spray drying process, the role of air pressure in spray drying is mainly to maintain the stability of the pressure in the drying chamber. During the drying process, positive pressure can prevent external air from entering the drying chamber, avoid contaminating the material, and help quickly exhaust the water vapor generated during the drying process, maintaining the stability of the temperature and humidity in the drying chamber. The role of hydraulic pressure in spray drying is mainly to provide energy for spraying. In the spray drying tower, the hydraulic system usually lifts the liquid to a certain height through the pump, and then atomizes it into small particles through the nozzle, so that it can contact with hot air at high temperature to evaporate the water, thus completing the drying process. In addition, the size of the liquid droplet and the distribution of the liquid droplet are affected by the size of the hydraulic pressure and the air pressure, which in turn affects the drying process. As mentioned earlier, larger particles and faster drying speed can promote the formation of hollow structures.

[0149] By using the above-mentioned spray drying air pressure and hydraulic pressure, liquid droplets with suitable particle size can be formed, and the water evaporation speed is suitable, thereby facilitating the obtaining of binder particles with Dv50 particle size of 10 μm-30 μm and having hollow structures.

[0150] According to the embodiments of the present application, the specific method for forming the adhesive layer on at least one surface of the base film using the binder particles is not particularly limited. As an example, a mixture of the binder particle powder and glue can be stirred and mixed uniformly in deionized water to obtain a separator film slurry; the separator film slurry is uniformly sprayed on one or both surfaces of the base film, and the solvent is removed by drying, thereby obtaining a separator film. The main function of using glue is to bond the binder particles to the base film to avoid powder falling. The glue that can be used includes but is not limited to polyacrylic acid, polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, etc.

[0151] According to the embodiments of the present application, the winding and pressing of the positive electrode sheet, the separator film, and the negative electrode sheet can be carried out according to conventional technology, which is not particularly limited in the present application. As an example, the positive electrode sheet, the separator film, and the negative electrode sheet can be sequentially stacked and arranged to form a wound electrode assembly through the winding process and the pressing process.

[0152] In a third aspect, the present application provides a secondary battery. According to embodiments of the present application, the secondary battery comprises the jelly-roll electrode assembly described above or the jelly-roll electrode assembly prepared by the method described above. The secondary battery uses binder particles with an average size of 6-21 μm in the adhesive layer of the separator film at the corner portion of the jelly-roll electrode assembly. Binder particles with the average size can provide better support, so that the adjacent positive electrode sheet and negative electrode sheet in the corner portion have a larger spacing, thereby providing sufficient space for the expansion and contraction of the negative electrode sheet in the corner portion, effectively improving the phenomena of active ion precipitation, purple stain, etc. at the corner portion, and further improving the cycle performance of the secondary battery. At least part of the binder particles have a hollow structure, so that the adhesive layer of the separator film at the corner portion can form certain voids, which is beneficial to the adsorption of electrolyte and improves the liquid retention, thereby further improving the cycle performance of the secondary battery.

[0153] According to embodiments of the present application, the specific type of the secondary battery is not particularly limited, for example, including but not limited to prismatic battery, pouch battery and cylindrical battery, etc., which are not particularly limited in the present application.

[0154] Figure 3 is a secondary battery 1 with a square structure as an example. In some embodiments, referring to Figure 3 , the outer package can comprise a shell 200 and a cover plate 300. The shell 200 can comprise a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a containing cavity. The shell 200 has an opening communicating with the containing cavity, and the cover plate 300 can be arranged on the opening to close the containing cavity. The jelly-roll electrode assembly 100 described above is packaged in the containing cavity. The electrolyte is infiltrated in the jelly-roll electrode assembly 100. The number of jelly-roll electrode assemblies 100 contained in the secondary battery 1 can be one or more, which can be selected by those skilled in the art according to the specific actual needs.

[0155] In a fourth aspect, the present application provides a power consuming device. According to embodiments of the present application, the power consuming device comprises the jelly-roll electrode assembly described above or the secondary battery described above. It can be understood that the power consuming device has all the features and advantages of the jelly-roll electrode assembly described above or the secondary battery described above, which will not be repeated here.

[0156] According to embodiments of the present application, the specific type of the power consuming device is not particularly limited, and can be any device that employs a battery as a power source or energy storage unit. As examples, the power consuming device includes, but is not limited to, an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a mobile terminal (e.g., a cell phone, a laptop, a game console, a wearable device, etc.), a drone, an aerospace device, a satellite, a ship, an energy storage system, etc. It can be understood that, in addition to the battery as described above, the power consuming device also includes necessary structures and components, all of which can be implemented with reference to conventional technology, e.g., an electric vehicle can include a vehicle body, a chassis, tires, a navigation system, a radar system, a steering system, a braking system, a lubrication system, a cooling system, a driving system, etc., which will not be described in detail herein.

[0157] Figure 4 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0158] The specific embodiments of the present application are described in detail below.

[0159] Embodiment 1

[0160] Preparation of binder particles:

[0161] ① Preparation of binder particles:

[0162] All emulsifiers, 30% of the total mass of the mixed monomers, and 30% of the total mass of the initiator were added to the reaction kettle, and water was stirred. After stirring at room temperature for 1 h, the temperature was raised to 60°C within 1 h. The remaining monomers and initiator were uniformly fed into the reaction kettle within 3 h. After the feeding was completed, the temperature was maintained for 4 hours, the pH was adjusted to 7, and the temperature was lowered to below 40°C. An acrylate latex (Dv50: 182 nm) was obtained.

[0163] In the mixed monomers, the mass ratio of n-butyl acrylate, methacrylic acid, and N-hydroxymethyl acrylamide was 100:20:5. The mass ratio of the mixed monomers, emulsifiers, and initiators was 100:5:1.

[0164] The acrylate latex and the dispersant polyacrylic acid were weighed according to a mass ratio of 90:10, and then water was added and stirred to prepare a slurry with a solid content of 30% and a viscosity of 800 mpa.s. Two fluids were selected for spray drying, with an air pressure of 0.3 MPa and a liquid pressure of 0.2 MPa. The binder particles were prepared, and the ion polishing cross-sectional morphology of the binder particles is shown in Figure 5 and Figure 6 from Figure 5 and Figure 6As can be seen, the binder particles have a good spherical morphology and have a hollow structure.

[0165] ② Preparation of the isolation film:

[0166] A PE microporous film (from Zhuogao Electronics Technology Co., Ltd.) with a thickness of 7 pm and an average pore size of 80 nm was used as the base film. The above binder particles and acrylate glue were mixed in deionized water at a solid mass ratio of 100:15 to obtain an isolation film slurry (solid content of 20%). The isolation film slurry was uniformly coated on both surfaces of the base film, and the solvent was removed by drying. The single-layer coating thickness of the bonding layer was 32 pm.

[0167] ③ Preparation of the positive electrode sheet

[0168] Polyvinylidene fluoride (PVDF), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), conductive agent carbon black, N-methyl pyrrolidone (NMP) were mixed at a mass ratio of 0.8:74.6:1.6:23 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil at a loading of 165 g / m 2 , and then dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0169] ④ Preparation of the negative electrode sheet

[0170] Natural graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickening agent carboxymethyl cellulose sodium (CMC-Na) were added to deionized water at a mass ratio of 96.5:1.2:0.8:1.5, and then fully stirred and mixed to prepare a negative electrode slurry (solid content of 64%). The negative electrode slurry was coated on the negative electrode current collector copper foil at a loading of 100 g / m 2 , and then dried, cold-pressed, and cut to obtain the negative electrode sheet.

[0171] ⑤ Preparation of the electrolyte

[0172] At 25°C, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 was dissolved in the mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0173] ⑥ Preparation of the secondary battery

[0174] The above negative electrode sheet, separator, and positive electrode sheet are stacked in order and wound and cold-pressed (25°C-5MPa-10s) to obtain a wound electrode assembly; the wound electrode assembly is placed in an outer package, the above prepared electrolyte is added, and after processes such as packaging, standing, formation, and aging, a secondary battery is obtained.

[0175] Example 2-8

[0176] The same as Example 1, except for the differences shown in Table 1 below.

[0177] Comparative Example 1

[0178] The same as Example 1, except for the differences that the binder particles have a solid structure and a Dv50 particle size of 6.8 μm, and the ion polishing cross-sectional morphology is shown in Figure 8 and Figure 9 .

[0179] Comparative Example 2

[0180] The same as Example 1, except for the differences that the binder particles have a solid structure, and the ion polishing cross-sectional morphology is shown in Figure 10 .

[0181] Comparative Example 3

[0182] The same as Example 1, except for the differences that the binder particles have a hollow structure and a Dv50 particle size of 7 μm.

[0183] Performance Test

[0184] 1. Particle size test

[0185] Dv50 particle size: tested using a laser particle size analyzer (Malvern 3000, MasterSizer 3000), with a helium-neon red light source used as the main light source. A clean small beaker was taken and 1 g of the sample to be tested was added, 20 ml of deionized water was added, and ultrasonic treatment was performed at 53 KHz / 120 W for 5 min to ensure complete dispersion of the sample. After cleaning the light path system, the laser particle size analyzer was turned on and the background was automatically tested. The measured solution was stirred to ensure uniform dispersion, and then placed in the sample cell as required, and the particle size measurement was started. The measurement results can be read from the instrument.

[0186] Average size: according to the ion polishing cross-sectional morphology test method, the test sample was prepared, 5 cross-sectional morphology images at 2000 times magnification were randomly taken by SEM (see Figure 6 , Figure 8 ), and the size of the cross section of all the binder particles in the field of view (both hollow spheres and solid spheres were counted as the size of the outermost circle, i.e. the size between the two points with the largest distance on the cross-sectional profile line of the binder particles) was counted. The average size of the binder particles was obtained by dividing the sum of all sizes by the number of binder particles.

[0187] 2. Width and thickness test of electrode assembly

[0188] The width of the electrode assembly is measured by using a vernier caliper. The horizontal width of the upper, middle and lower parts of the electrode assembly is measured and the average value is calculated to obtain the width data of the electrode assembly.

[0189] Thickness test: The thickness of the electrode assembly is measured by using a vernier caliper. The thickness of the upper, middle and lower parts of the electrode assembly is measured and the average value is calculated to obtain the thickness data of the electrode assembly.

[0190] 3. Test of the distance between adjacent positive and negative electrode plates (i.e. the distance between electrode plates)

[0191] A CT device of model ZEISS METROTOM 1 is used to non-destructively test the electrode assembly to obtain a scanning image of the positive current collector in the electrode assembly (see Figure 7 , where the white part is the positive current collector), and then the distance between the two adjacent positive current collectors is measured according to the scanning image. Then, according to the film structure between the two adjacent positive current collectors and the known thickness of each film, the first distance and the second distance are calculated. It should be noted that the thickness of the positive electrode plate, the negative electrode plate and the separator base film remains unchanged before and after cold pressing, and only the adhesive layer changes. Because the pressure during the preparation of the positive electrode plate and the negative electrode plate is 20-40 MPa, which is much greater than the pressure during the shaping of the electrode assembly (i.e. the pressure during cold pressing), it can be considered that the changes before and after cold pressing of the electrode assembly are entirely due to the adhesive layer.

[0192] Specifically, as described in Example 1, the distance between the two adjacent positive electrode plates includes two layers of separator and one negative electrode plate, i.e. the distance between the two adjacent positive current collectors includes the single-sided positive film layer, the separator base film and the adhesive layer on both sides of its surface, the negative current collector and the negative film layer on both sides of its surface, the separator base film and the adhesive layer on both sides of its surface, and the single-sided positive film layer. Therefore, after measuring the distance D between the two adjacent positive current collectors, the sum of the thicknesses of the adhesive layers on the single-sided surface of the separator is equal to (D-2x single-sided positive film layer thickness-2x separator base film thickness-negative current collector thickness-2x single-sided negative film layer thickness) / 4; the distance between the adjacent positive electrode plate and the negative electrode plate is equal to the single-sided positive film layer thickness + the single-sided negative film layer thickness + the separator base film thickness + 2x the adhesive layer thickness on the single-sided surface of the separator.

[0193] 4. Storage modulus test

[0194] The adhesive is pressed into a sample block with dimensions of 10 mm x 10 mm x 4 mm using a mold. The test conditions are: single cantilever mode, frequency 1 Hz, amplitude 0.5 mm, temperature 25°C. The storage modulus of the sample is tested by using the DMA 8000 of Perkin Elmer company.

[0195] 5. Tapped density

[0196] Determined according to GB / T 21354-2008 Powder Products - Determination of Tapped Density - General Method.

[0197] 6. Viscosity test

[0198] The test is performed using a rotational Brookfield viscometer, specifically, a 62# rotor can be used, and the test is performed at 25°C.

[0199] 7. Capacity retention test

[0200] The test procedure is as follows: at 25°C, the battery prepared in the above examples and comparative examples is charged at 1 / 3C constant current to 4.2V, then charged at 4.2V constant voltage to a current of 0.05C, left for 5 min, then discharged at 1 / 3C to 2.8V, and the obtained discharge capacity is recorded as initial capacity Co. The above procedure is repeated for the same battery, and the discharge capacity of the battery after the nth cycle is recorded as Cn. The capacity retention Pn of the battery after each cycle is (Cn / Co) x 100%. The capacity retention of the battery after 500 cycles can be used to reflect the difference in cycle performance.

[0201] 8. Ion polishing section morphology analysis

[0202] The binder particles are mixed with a small amount of acrylic glue, diluted with water to a suitable solid content, coated on the base film, and dried to obtain the sample used for testing; the sample is cut into a size of 6mm x 6mm, attached to the sample stage, and slightly protruding (<1mm) from the edge of the sample stage; the cross section of the material sample is bombarded using argon ion polishing technology (CP cross section polishing technology), which removes a layer of material from the surface, exposing the internal structure, and obtaining a smooth polished section; the polished section morphology is observed using a scanning electron microscope (SEM).

[0203] Table 1: Binder particle related parameters

[0204]

[0205]

[0206]

[0207] Table 2: Secondary battery performance test results

[0208]

[0209]

[0210] The test results above show that, compared to the comparative example, the adhesive layer of the separator at the corner of the wound electrode assembly in each embodiment uses adhesive particles with an average size of 6μm-21μm. Adhesive particles within this average size range provide better support, resulting in a larger gap between adjacent positive and negative electrode plates at the corner. This provides sufficient space for the expansion and contraction of the negative electrode plate at the corner, effectively reducing active ion deposition and purple spots at the corner, thereby improving the cycle performance of the secondary battery using this wound electrode assembly. Furthermore, at least some of the adhesive particles have a hollow structure, allowing the adhesive layer of the separator at the corner to form certain voids, which is beneficial for electrolyte adsorption and improves electrolyte retention, further improving the cycle performance of the secondary battery. Specifically, compared to Comparative Example 1, the cycle capacity retention rate of the battery in Example 1 is improved by 4%, indicating that using adhesive particles with an average size of 6μm-21μm can reduce internal stress problems, thereby improving the battery's cycle performance.

[0211] According to the data in the table above, compared with Comparative Example 2, the energy storage modulus of the binder in each embodiment is smaller, which means that the binder particles with hollow structure can store less energy under the same degree of deformation, and have lower elastic potential. As a result, the possibility and degree of thickness rebound of the battery cell after pressing are smaller during storage, and the stability of the battery cell is higher.

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still 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. 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 this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A wound electrode assembly, characterized in that, It includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; The isolation membrane includes a base membrane and an adhesive layer disposed on at least one surface of the base membrane, the adhesive layer including adhesive particles; The wound electrode assembly includes a main body and corner portions located on both sides of the main body; In the corner portion, the average size of the adhesive particles is 6μm to 21μm, and at least some of the adhesive particles have a hollow structure.

2. The wound electrode assembly according to claim 1, characterized in that, The distance between adjacent positive and negative electrode plates in the corner portion is the first distance, and the distance between adjacent positive and negative electrode plates in the main body portion is the second distance. The difference between the first distance and the second distance is not less than 50 μm and not greater than 150 μm.

3. The wound electrode assembly according to any one of claims 1 to 2, characterized in that, The thickness of the adhesive layer on one side of the base film in the corner portion is a first thickness, and the thickness of the adhesive layer on one side of the base film in the main body portion is a second thickness. The difference between the first thickness and the second thickness is not less than 25 μm and not greater than 75 μm.

4. The wound electrode assembly according to claim 3, characterized in that, The first thickness is 25 μm to 45 μm; and / or, The second thickness is 0.1 μm to 5 μm.

5. The wound electrode assembly according to any one of claims 1 to 4, characterized in that, The binder particles include non-fluorinated binder particles.

6. The wound electrode assembly according to any one of claims 1 to 5, characterized in that, The binder particles comprise polymer binder particles, and the polymeric monomers of the polymer binder particles comprise a first monomer shown in Formula 1: R1 is selected from hydrogen atoms and C atoms. 1-12 Alkyl group, R2 is selected from C 1-12 alkyl.

7. The wound electrode assembly according to claim 6, characterized in that, The first monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, and lauryl methacrylate.

8. The wound electrode assembly according to any one of claims 6 to 7, characterized in that, The polymer binder particles also include a second monomer as shown in Formula 2: R3 includes hydrogen atoms, substituted or unsubstituted carbon atoms. 1-18 alkyl.

9. The wound electrode assembly according to claim 8, characterized in that, The second monomer includes at least one of acrylic acid, methacrylic acid, butenoic acid, or heptenoic acid.

10. The wound electrode assembly according to any one of claims 6 to 9, characterized in that, The polymer binder particles include a third monomer as shown in Formula 3: R4 is selected from hydrogen and C atoms. 1-6 Alkyl group, R5 is selected from C atoms substituted with hydrogen atoms or hydroxyl groups. 1-6 Alkyl and C 1-6 Alkyl group.

11. The wound electrode assembly according to claim 10, characterized in that, The third monomer includes at least one of acrylamide and N-hydroxymethylacrylamide.

12. The wound electrode assembly according to any one of claims 6 to 11, characterized in that, The polymer binder particles comprise a first monomer, a second monomer, and a third monomer in a mass ratio of 1:(0.05~0.4):(0.01~0.2).

13. A method for preparing a wound electrode assembly, characterized in that, include: Polymer monomers, emulsifiers, initiators, and solvents are mixed, and the resulting raw material mixture is subjected to a polymerization reaction to obtain latex; The latex, dispersant, and water are mixed to obtain a slurry; The slurry is spray-dried to obtain binder particles; An adhesive layer is formed on at least one surface of the base film using the adhesive particles to obtain a release film; The positive electrode sheet, the separator, and the negative electrode sheet are wound and pressed together to obtain a wound electrode assembly. The wound electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The isolation membrane includes a base membrane and an adhesive layer disposed on at least one surface of the base membrane, the adhesive layer including the adhesive particles; The wound electrode assembly includes a main body and corner portions located on both sides of the main body; In the corner portion, the average size of the adhesive particles is 6μm to 21μm, and at least some of the adhesive particles have a hollow structure.

14. The method according to claim 13, characterized in that, In the step of spray drying the slurry to obtain binder particles: The binder particles have a Dv50 particle size of 10μm-30μm, and at least a portion of the binder particles have a hollow structure; and / or, The tap density of the binder particles is 0.2 g / cm³. 3 ~0.9g / cm 3 ; and / or, At 25°C, the storage modulus of the binder particles is 10 MPa to 50 MPa.

15. The method according to claim 13 or 14, characterized in that, The dispersant includes at least one of sodium polyacrylate, sodium polymethacrylate, polypropylene ether, polyethylene glycol, polyvinylpyrrolidone, and polyacrylic acid.

16. The method according to any one of claims 13 to 15, characterized in that, The slurry has a solid content of 10% to 30%; and / or The viscosity of the slurry is 100 mPa·s to 500 mPa·s.

17. The method according to any one of claims 13 to 16, characterized in that, The spray drying includes at least one of centrifugal spray drying, airflow spray drying, and pressure spray drying.

18. The method according to any one of claims 13 to 17, characterized in that, The spray drying is a two-fluid spray drying, and The spray drying pressure is 0.1 MPa-5 MPa; and / or The hydraulic pressure for spray drying is 0.1 MPa-100 MPa.

19. The method according to claim 18, characterized in that, The hydraulic pressure for the two-fluid spray dryer is 0.5MPa-3MPa.

20. A secondary battery, characterized in that, The winding electrode assembly includes any one of claims 1 to 12 or any one of claims 13 to 19.

21. An electrical appliance, characterized in that, The invention includes the wound electrode assembly according to any one of claims 1 to 12, the wound electrode assembly prepared by the method according to any one of claims 13 to 19, or the secondary battery according to claim 20.

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