Battery cell, secondary battery, and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a battery monomer, a secondary battery and an electric device. The single battery comprises an electrode assembly, the electrode assembly is provided with a main body part and corner parts located on the two sides of the main body part, the distance between a positive pole piece and a negative pole piece which are adjacent in the corner parts is a first distance, and the distance between the positive pole piece and the negative pole piece which are adjacent in the main body part is a second distance; the difference value between the first spacing and the second spacing is not less than 50 [mu] m and not greater than 150 [mu] m; the isolating membrane comprises a base membrane and a bonding layer, the bonding layer contains polymer binder particles, and the Dv50 particle size of the polymer binder particles is 8 [mu] m-20 [mu] m. The battery monomer has relatively small size and relatively good cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a battery monomer, a secondary battery and a power utilization device. BACKGROUND

[0002] In the manufacturing of secondary batteries, the expansion and contraction of the negative electrode sheet has always been a problem, which is due to the fact that during the charging and discharging cycle of the battery cell, active ions are embedded in the layered material, causing the thickness of the negative electrode sheet to increase, thereby generating the expansion force of the battery cell. This expansion is reversible, because during the charging and discharging cycle of the secondary battery, the negative electrode sheet (such as graphite negative active material, silicon-based negative active material) will undergo obvious expansion and contraction, and with the increase of the number of cycles, the amplitude of the expansion will become larger and larger. This change will cause the spacing between the electrode sheets inside the battery cell to become smaller and smaller, and the stress distribution inside the battery will become uneven, especially at the corner parts of the battery cell, where the stress is more concentrated, and the channel for the transmission of active ions will be relatively difficult, and lithium precipitation, purple stains and other problems often occur at the corner parts of the battery cell, thereby affecting the cycle life and safety performance of the battery. Therefore, the related technology still needs to be improved. SUMMARY

[0003] In view of the above problems, the present application provides a battery monomer, a secondary battery and a power utilization device. In the electrode assembly of the battery monomer, the positive electrode sheet and the negative electrode sheet in the corner part have a larger spacing, which can effectively alleviate the expansion and contraction of the electrode sheet, improve the problem of uneven stress distribution inside the battery, and thereby improve the cycle performance of the battery; at the same time, the spacing between the electrode sheets in the main part is relatively small, and the overall thickness of the electrode assembly is small, which is beneficial to reducing the volume of the battery monomer.

[0004] In a first aspect, the present application provides a battery cell. According to an embodiment of the present application, the battery cell comprises an electrode assembly, the electrode assembly comprising a positive electrode tab, a negative electrode tab and a separator film, the separator film being arranged between the positive electrode tab and the negative electrode tab; the electrode assembly has a main body part and corner parts located on both sides of the main body part, the distance between the adjacent positive electrode tab and negative electrode tab in the corner part is a first distance, the distance between the adjacent positive electrode tab and negative electrode tab in the main body part is a second distance, the difference between the first distance and the second distance is not less than 50 μm and not more than 150 μm; the separator film comprises a base film and a bonding layer, the bonding layer is arranged on at least one surface of the base film, the bonding layer contains polymer binder particles, the Dv50 particle size of the polymer binder particles is 8 μm-20 μm. In the electrode assembly of the battery cell, by adjusting the particle size of the polymer binder particles in the range of 8 μm-20 μm, the main body part can be compressed to a smaller thickness in the pressing step of the electrode assembly preparation process, while the corner part is not pressed, and the bonding layer still maintains a larger thickness, so that the first distance and the second distance have the above difference, the first distance is relatively large, which can provide sufficient space for the expansion and contraction of the negative electrode tab in the corner part, significantly improve the problem of stress concentration in the battery, and further improve the problems of active ion precipitation, purple stain and the like in the corner part of the battery, and improve the cycle performance of the battery; while the second distance is relatively small, which can make the battery cell have a smaller volume, facilitate assembly, and be beneficial to improve the battery capacity.

[0005] According to an embodiment of the present application, the Dv50 particle size of the polymer binder particles is greater than 10 μm and less than or equal to 20 μm. In this particle size range, the first distance can be further increased to better meet the needs of the expansion and contraction of the negative electrode tab, thereby avoiding uneven stress, active ion precipitation, purple stain and the like in the battery, and improving the cycle performance of the battery; at the same time, the second distance does not increase significantly.

[0006] According to an embodiment of the present application, the particle size distribution of the polymer binder particles is less than 2, and the particle size distribution=(Dv90-Dv10) / Dv50. Thus, the particle size distribution of the polymer binder particles is relatively narrow, the particle size of the polymer binder particles is relatively uniform, the uniformity of the distance between the adjacent positive electrode tab and negative electrode tab at different positions in the main body part and / or corner part is good, which can improve the problem of uneven electrode tab distance in the corner part to some extent, thereby significantly improving the problems of active ion precipitation, purple stain and the like in the corner part, and being beneficial to improve the electrochemical performance of the battery.

[0007] According to an embodiment of the present application, the isolation film comprises a base film and a bonding layer, the bonding layer is arranged on at least one surface of the base film, the thickness of the bonding layer on the single surface of the base film in the corner part is a first thickness, the thickness of the bonding layer on the single surface of the base film in the main body part is a second thickness, 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 bonding layer, so that the electrode assembly can meet the requirements of the negative electrode sheet expansion and shrinkage in the corner part, and the overall size of the electrode assembly is small, thereby effectively improving the cycle performance of the battery while keeping a small battery size.

[0008] According to an embodiment of the present application, the first thickness is 25 μm to 45 μm, and the second thickness is 0.1 μm to 5 μm. In this thickness range, the size requirement and the requirement of the negative electrode sheet expansion and shrinkage in the corner part can be well met, the battery using the electrode assembly has a small size and good cycle performance.

[0009] According to an embodiment of the present application, the glass transition temperature of the polymer binder particles is -30 ℃ to 60 ℃, for example, 60 ℃, 55 ℃, 50 ℃, 45 ℃, 40 ℃, 35 ℃, 30 ℃, 25 ℃, 20 ℃, 15 ℃, 10 ℃, 5 ℃, 0 ℃, -5 ℃, -10 ℃, -15 ℃, -20 ℃, -25 ℃, -30 ℃, and the like. In this glass transition temperature range, the cold pressing and hot pressing in the preparation process of the electrode assembly can be considered, the process compatibility is high, the use range is wider, and the adhesion is better.

[0010] According to an embodiment of the present application, the polymer binder particles comprise non-fluorine binder particles. In this way, the damage of F-containing binder to the environment can be avoided, and the glass transition temperature of the polymer binder particles is suitable, the electrode assembly does not need to be hot-pressed in the preparation process, and only needs to be cold-pressed to realize the bonding of the isolation film and the electrode sheet, which can greatly improve the processing efficiency and reduce the processing cost.

[0011] According to an embodiment of the present application, the polymer binder particles comprise a first monomer represented by Formula 1:

[0012]

[0013] wherein R1 is selected from a hydrogen atom and C 1-6 alkyl, R2 is selected from a hydrogen atom, a hydroxyl-substituted C 1-6 alkyl and C 1-6 alkoxy.

[0014] According to an embodiment of the present application, the first monomer comprises at least one of acrylamide, N-hydroxymethyl acrylamide, and N-butoxymethyl acrylamide.

[0015] With the first monomer described above, the cross-linking degree of the polymer binder particles can be improved, the chemical stability can be improved, the polymer binder particles have better toughness, in the pressing step in the preparation of the electrode assembly, the thickness of the adhesive layer of the main body part can be pressed to a smaller thickness, and the polymer binder particles are not easy to break, and also have good adhesion; in the corner part, the appropriate electrode plate spacing can be maintained between the adjacent positive electrode plate and the negative electrode plate, and sufficient space is reserved for the expansion and contraction of the negative electrode plate.

[0016] According to an embodiment of the present application, the polymer binder particles also include a second monomer represented by formula 2:

[0017]

[0018] wherein R3 is selected from a hydrogen atom and a substituted or unsubstituted C 1-6 alkyl group.

[0019] According to an embodiment of the present application, the second monomer includes at least one of acrylic acid and methacrylic acid.

[0020] The inclusion of an unsaturated carboxyl group in the second monomer facilitates the polymerization of the monomer, and during the pressing process of the electrode assembly, the carboxyl group can form a binding force with the functional groups on the electrode plate and the separator material, improving the adhesion effect.

[0021] According to an embodiment of the present application, the polymer binder particles also include a third monomer represented by formula 3:

[0022]

[0023] wherein R4 is selected from a hydrogen atom and a C 1-12 alkyl group, and R2 is selected from a C 1-12 alkyl group.

[0024] According to an embodiment of the present application, the third 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.

[0025] The third monomer includes unsaturated ester groups, which is conducive to the preparation of the polymer binder particles, and can improve 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, and help 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.

[0026] According to the embodiments of the present application, the polymer binder particles include the first monomer, the second monomer and the third monomer in a mass ratio of 10-20:10-30:100. The polymer binder particles formed by the above-mentioned ratio of polymerized monomers can have a suitable glass transition temperature, better adhesion, and better toughness, while meeting the adhesion requirements, the thickness of the adhesive layer of the main part can be thinned in the pressing step of the electrode assembly preparation process, so that the electrode assembly remains small in size, while the adhesive layer of the corner part is still thick, which can keep a suitable distance between the adjacent positive and negative electrode plates, and reserve sufficient space for the expansion and contraction of the negative electrode plate, thereby improving the uneven stress, active ion precipitation, purple stain and other phenomena in the battery, and improving the cycle performance of the battery.

[0027] In a second aspect, the present application provides a secondary battery. According to the embodiments of the present application, the secondary battery includes the electrode assembly described above. The secondary battery has all the features and advantages of the electrode assembly described above, which will not be repeated here.

[0028] In a third aspect, the present application provides a power consuming device. According to the embodiments of the present application, the power consuming device includes the battery cell described above or the secondary battery described above. The power consuming device has all the features and advantages of the battery cell described above or the secondary battery described above, which will not be repeated here.

[0029] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the content of the specification can be implemented, 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

[0030] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered limiting the present application. Moreover, the same reference numerals are used to represent the same components throughout the drawings. In the drawings:

[0031] Figure 1is a structural schematic diagram of an electrode assembly according to an embodiment of the present application.

[0032] Figure 2 is a partial structural schematic diagram of a separator film in a flattened state according to an embodiment of the present application.

[0033] Figure 3 is a structural schematic diagram of a battery according to an embodiment of the present application.

[0034] Figure 4 is a structural schematic diagram of an electrical device according to an embodiment of the present application.

[0035] Figure 5 is a CT scan image of an electrode assembly according to an embodiment of the present application.

[0036] Reference signs are as follows:

[0037] 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

[0038] Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying 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.

[0039] 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 of the present application, 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.

[0040] In the description of embodiments of the present application, the technical terms "first", "second", and the like 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 embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0041] 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 independent or alternative embodiments 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.

[0042] In the description of the embodiments of the present application, the term "and / or" is merely an 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 " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0043] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0044] The expansion of the negative electrode sheet during the charging and discharging cycle of the secondary battery is mainly caused by the irreversible expansion of the negative active material after the active ion (such as lithium ion, sodium ion, etc.) is inserted. The expansion of the negative electrode sheet causes the deformation of the cell, forms a hollow between the electrode sheet and the separator, forms micro-cracks in the negative active material particles, and causes the rupture and recombination of the solid electrolyte interface (SEI) film, consumes the electrolyte, and makes the cycle performance of the secondary battery worse. The solution in the related art is to use a convex point roller to manufacture convex points on the surface of the positive electrode sheet to increase the spacing between the electrode sheets. The height of such convex points in the battery is consistent, which not only provides space for the expansion of the negative electrode sheet, but also significantly increases the size of the electrode assembly. Moreover, due to the difference between the inner and outer radii of the corner during winding, the tension gradually decreases during the winding process, which causes the corner spacing between the inner and outer layers of the electrode assembly to be inconsistent after heat pressing, thereby causing interface problems due to uneven spacing, and further affecting the cycle life and safety reliability of the battery.

[0045] To solve the above problems, the present application provides a battery monomer, by adjusting the difference between the spacing between the adjacent positive electrode sheet and negative electrode sheet in the corner part and the spacing between the adjacent positive electrode sheet and negative electrode sheet in the main part, the corner part can maintain a larger electrode sheet spacing, providing sufficient space for the expansion and contraction of the negative electrode sheet, greatly reducing the internal stress of the battery and improving the problem of uneven stress; the main part can also maintain a smaller size, facilitating assembly. The battery monomer corner part active ion precipitation, purple spot and other problems are obviously improved, the cycle performance is obviously improved, and at the same time, the battery monomer can have a smaller size, which is beneficial to capacity improvement, and the size of the outer package does not need to be changed.

[0046] The specific type of the battery cell provided in the present application is not subject to any limitation, including but not limited to lithium ion battery, sodium ion battery, etc.; the specific shape of the battery cell can be square, cylindrical, and other regular or irregular shapes; the outer packaging of the battery cell can be hard shell (such as steel shell, hard plastic shell, etc.), or soft shell (such as aluminum plastic film, bag type soft shell, etc.). The above battery cells can be assembled into secondary batteries, and the secondary batteries can be further assembled into battery modules, battery packs, etc. The battery cell can be used as a power source or energy storage system for electric devices such as vehicles, power tools, mobile terminals, aircraft, etc.

[0047] The battery cell, secondary battery and electric device of the present application will be described in detail below with reference to the accompanying drawings.

[0048] In a first aspect of the present application, a battery cell is provided. According to an embodiment of the present application, the battery cell comprises an electrode assembly, referring to Figure 1 The electrode assembly 100 comprises a positive electrode tab 120, a negative electrode tab 130 and a separator film 110, the separator film 130 is arranged between the positive electrode tab 120 and the negative electrode tab 130; the electrode assembly 100 has a main body part 101 and corner parts 102 located on both sides of the main body part 101, the distance between the adjacent positive electrode tab 120 and negative electrode tab 130 in the corner part 102 is a first distance G1, the distance between the adjacent positive electrode tab 120 and negative electrode tab 130 in the main body part 101 is a second distance G2, the difference between the first distance G1 and the second distance G2 is not less than 50 μm and not more than 150 μm; referring to Figure 2 The separator film comprises a base film 111 and a bonding layer 112, the bonding layer 112 is arranged on at least one surface of the base film 111; the bonding layer contains polymer binder particles, the Dv50 particle size of the polymer binder particles is 8 μm-20 μm.

[0049] In some embodiments, the difference between the first distance G1 and the second distance G2 can be 50 μm-150 μm, 50 μm-100 μm, 50 μm-90 μm, 55 μm-90 μm, 60 μm-80 μm or 50 μm-75 μm, etc. For example, the difference between the first distance G1 and the second distance 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.

[0050] In some embodiments, the Dv50 particle size of the polymer binder particles described above can be greater than 10 pm and less than or equal to 20 pm, specifically, 8 pm, 8.5 pm, 9 pm, 9.5 pm, 10 pm, 10.5 pm, 11 pm, 11.5 pm, 12 pm, 12.5 pm, 13 pm, 13.5 pm, 14 pm, 14.5 pm, 15 pm, 15.5 pm, 16 pm, 16.5 pm, 17 pm, 17.5 pm, 18 pm, 18.5 pm, 19 pm, 19.5 pm, 20 pm, and the like.

[0051] It can be understood that the electrode assembly described above is a winding structure formed by winding, that is, the winding structure includes the main body part 101 and the corner part 102. Among them, the main body part 101 is the area where there is no bending or bending in the electrode assembly 100; the corner part 102 is the area where there is bending or bending in the electrode assembly 100.

[0052] The first distance described above refers to the distance between adjacent positive electrode plates and negative electrode plates in the corner part, which is measured along the straight line passing through the midpoint of the thickness of the electrode assembly (i.e., the midpoint of the dimension of the electrode assembly in the stacking direction of the positive electrode plate, the separator, and the negative electrode plate) and parallel to the positive electrode plate in the main body part. The second distance can be the distance between the positive electrode plate and the negative electrode plate measured at any position in the main body part. Specifically, the first distance and the second distance can be measured by CT in-situ characterization technology (Computed Tomography, or computer tomography). As an example, a CT device with 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 electrode assembly, then mark the distance between adjacent positive current collectors at the corresponding positions in the main body part and the corner part according to the scanning image, and then combine the film layer structure between the adjacent positive current collectors and the known film layer thickness to obtain the distance between the adjacent positive electrode plate and the negative electrode plate by calculation.

[0053] The Dv50 particle size described above is also called the median diameter or the 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 a particle size greater than it account for 50% by volume, and the particles with a particle size less than it also account for 50% by volume. The Dv50 particle size of the polymer binder particles can be tested by methods 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 testing, for example, a Malvern Mastersizer-3000 instrument can be used for testing.

[0054] In the battery cell, by adjusting the Dv50 particle size of the polymer binder particles in the range of 8 μm to 20 μm, the main body part can be compressed to a smaller thickness in the compression step of the electrode assembly preparation process, while the corner part is not compressed, and the bonding layer still maintains a larger thickness, so that the first spacing and the second spacing have the above difference, the second spacing is smaller, which can make the overall electrode assembly maintain a smaller size, easy to assemble, without changing the size of the outer package, and conducive to improving the capacity of the battery cell, while the adhesion of the bonding layer is not substantially affected; and the larger first spacing can well meet the expansion and contraction requirements of the negative electrode sheet, effectively improve the stress concentration problem in the battery cell, and significantly improve the problems of active ion precipitation and purple spots in the battery cell, thereby improving the cycle performance of the battery cell. Moreover, when the above polymer binder particles are applied to the separator film, it helps to reduce the resistance of the separator film and improve the ionic conductivity of the separator film, thereby improving the battery performance.

[0055] According to the embodiments of the present application, the particle size distribution of the polymer binder particles is less than 2, and can be 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, etc., and the particle size distribution = (Dv90-Dv10) / Dv50. The particle size distribution represents the uniformity of the polymer binder particles, and the larger the particle size distribution, the more uneven the polymer binder particles; on the contrary, the more uniform the polymer binder particles. The particle size distribution of the polymer binder particles is less than 2, the particle size distribution of the polymer binder particles is relatively narrow, the particle size of the polymer binder particles is relatively uniform, all the polymer binder particles can effectively play a role, the thickness of the bonding layer is relatively uniform, and the spacing uniformity between the adjacent positive electrode sheets and negative electrode sheets at different positions in the main body part and / or the corner part is good, which can partially improve the problem of uneven electrode sheet spacing in the corner part, and is conducive to improving the electrochemical performance of the battery.

[0056] It can be understood that the Dv10 particle size and the Dv90 particle size of the polymer binder particles respectively refer to the particle sizes corresponding to the cumulative volume percentage of 10% and 90% of a sample; the physical meaning of the Dv10 particle size is that the particles with a particle size greater than it account for 90% by volume, and the particles with a particle size less than it account for 10% by volume; the physical meaning of the Dv90 particle size is that the particles with a particle size greater than it account for 10% by volume, and the particles with a particle size less than it account for 90% by volume. The Dv10 particle size, the Dv50 particle size, the Dv90 particle size and the particle size distribution of the polymer binder particles can be adjusted by screening the polymer binder particles, or can be adjusted by the preparation process of the polymer binder particles. As an example, the polymer binder particles are prepared by spray drying, and the particle size and the particle size distribution of the polymer binder particles can be adjusted by adjusting the spray drying process parameters, including but not limited to adjusting the inlet air temperature, the air pressure and the outlet air temperature, the latex solid content and the like.

[0057] According to the embodiments of the present application, with reference to Figure 2 , the isolation film includes a base film 111 and a bonding layer 112, the bonding layer 112 is arranged on at least one surface of the base film 111; the thickness of the bonding layer 112 of the single-sided surface of the base film 111 in the corner portion 102 is a first thickness H1, the thickness of the bonding layer 112 of the single-sided 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.

[0058] In some embodiments, the above 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.

[0059] The first thickness refers to the thickness of the single-sided surface adhesive layer of the base film in the corner portion, measured along a straight line passing through the midpoint of the thickness of the electrode assembly (i.e., the midpoint of the dimension of the electrode assembly in the stacking direction of the positive electrode tab, the separator, 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-sided surface adhesive layer of the base film 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 adjacent positive current collectors and the known film layer thickness.

[0060] Thus, the first distance and the second distance can be effectively adjusted by the thickness of the adhesive layer, so that the battery monomer can have a small overall size and the corner portion can fully meet the space requirement of the negative electrode tab expansion and contraction, thereby effectively improving the cycle performance of the battery monomer and reducing the volume of the battery monomer. Moreover, the tab distance is adjusted by the adhesive layer, which has high compatibility with the existing process, does not need to add additional operation steps, has a simple preparation process, and is easy to implement.

[0061] 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. Within the thickness range, the size requirement and the space requirement of the corner portion negative electrode tab expansion and contraction can be well met, the battery monomer has a small volume, and has good cycle performance.

[0062] According to embodiments of the present application, the glass transition temperature of the polymer binder particles is -30°C to 60°C, for example, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C, 0°C, -5°C, -10°C, -15°C, -20°C, -25°C, -30°C, etc. Within the glass transition temperature range, the cold pressing and hot pressing during the preparation of the electrode assembly can be considered, which has high compatibility with the processing technology, wider application range, and better adhesion.

[0063] According to embodiments of the present application, the polymer binder particles include non-fluorine binder particles. Specifically, the polymer binder particles can not contain fluorine elements. In this way, the damage of F-containing binder to the environment can be avoided, while the glass transition temperature of the polymer binder particles is suitable, and the electrode assembly does not need to be hot-pressed in the preparation process, but only needs to be cold-pressed to realize the bonding of the isolation film and the electrode sheet, which can greatly improve the processing efficiency and reduce the processing cost.

[0064] According to embodiments of the present application, the polymer binder particles include a first monomer represented by Formula 1:

[0065]

[0066] wherein R1 is selected from a hydrogen atom and C 1-6 alkyl, R2 is selected from a hydrogen atom, a hydroxyl-substituted C 1-6 alkyl and C 1-6 alkoxy.

[0067] Herein, "alkyl" refers to a saturated straight-chain or branched-chain monovalent hydrocarbon group; "hydroxyl-substituted alkyl" refers to an alkyl group in which at least one hydrogen atom is replaced by a hydroxyl group; "alkoxy" refers to an alkyl group connected to the rest of the molecule through an oxygen atom; C 1～6 refers to a group containing 1-6 carbon atoms, and the number of carbon atoms can be specifically 1, 2, 3, 4, 5, or 6; for example, C 1～6 alkyl refers to an alkyl group with 1-6 carbon atoms, and specifically includes but is not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, etc.; a hydroxyl-substituted C 1-6 alkyl and C 1-6 alkoxy is similar, and will not be repeated here.

[0068] According to embodiments of the present application, the first monomer includes at least one of acrylamide, N-hydroxymethyl acrylamide, and N-butoxymethyl acrylamide.

[0069] By using the above-mentioned first monomer, the cross-linking degree of the polymer binder particles can be improved, the chemical stability can be improved, the polymer binder particles have better toughness, in the pressing step in the battery preparation, the bonding layer of the main part can be pressed thin, so that the second distance is smaller, the size of the battery is kept smaller, and the polymer binder particles are not easy to break, and also have good bonding property; while the corner part is not pressed, the first distance is larger, so as to reserve sufficient space for the expansion of the negative electrode sheet, and improve the cycle performance of the battery.

[0070] It can be understood that the polymer binder particles can be formed by polymerization of one or more polymer monomers.

[0071] According to an embodiment of the present application, the polymer binder particles further comprise a second monomer of Formula 2:

[0072]

[0073] wherein R3 is selected from a hydrogen atom and a substituted or unsubstituted C 1-6 alkyl group.

[0074] According to an embodiment of the present application, the second monomer can comprise at least one of acrylic acid and methacrylic acid.

[0075] The inclusion of the unsaturated carboxyl group in the second monomer facilitates the polymerization of the monomer, and during the pressing process of the separator film and the pole piece, the carboxyl group can form a binding force with the functional groups on the pole piece and the separator film material, improving the bonding effect.

[0076] According to an embodiment of the present application, the polymer binder particles further comprise a third monomer of Formula 3:

[0077]

[0078] wherein R4 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 an embodiment of the present application, the third monomer can comprise 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 third 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, it can adjust the glass transition temperature of the polymer binder particles, helping to adjust the glass transition temperature of the polymer binder particles to an appropriate range, and thus effectively bonding the separator film and the pole piece during the preparation of the electrode assembly by cold pressing only.

[0081] It can be understood that the above-mentioned polymer binder particles can be a polymer formed by polymerization of any one, any two, or all three of the above-mentioned first monomer, second monomer, and third monomer.

[0082] It can be understood that, according to actual needs, other coating layers, such as ceramic coating layers, etc., can be provided on the base film in addition to the adhesive layer, so as to improve the heat resistance, ionic conductivity, etc. 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.

[0083] It can be understood that the polymer binder particles can be secondary particles formed by agglomeration of primary particles, such as secondary particles formed by agglomeration of acrylic polymer primary particles, the particle size of the primary particles can be 100 nm-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 large particle size can be obtained by spray drying acrylic polymer primary particles with a particle size of 100 nm-200 nm.

[0084] By using secondary particles, polymer binder particles with larger particle size can be obtained, which is beneficial to make the thickness of the adhesive layer in the main part of the electrode assembly after pressing thinner, and the thickness of the adhesive layer in the corner part thicker, and keep a predetermined difference, so as to balance the size of the battery and the expansion space of the corner negative electrode sheet, thereby improving the electrochemical performance of the battery.

[0085] In some embodiments, the polymer binder particles can be prepared by the following steps: weighing the first monomer, the second monomer and the third monomer according to a mass ratio of 100:10-30:10-20, blending water, emulsifier, initiator and the above polymerized monomers to obtain a polymer emulsion; and then preparing large-particle-size polymer binder particles with a Dv50 particle size of 8 μm-20 μm by spray drying.

[0086] 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.

[0087] The preparation method of the isolation film is not particularly limited. As an example, a mixture of polymer binder particles and glue can be stirred and mixed uniformly in deionized water to obtain an isolation film slurry; the isolation film slurry is uniformly sprayed on one or both surfaces of the base film, and the solvent is removed by drying to obtain the isolation film. Among them, the main function of using glue is to bond the polymer binder particles to the base film to prevent powder loss. The glue that can be used includes but is not limited to PVDF (polyvinylidene fluoride), polyacrylic acid, polyacrylate, butadiene-styrene rubber, sodium carboxymethyl cellulose, etc.

[0088] According to the embodiments of the present application, the 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 arranged on at least one surface of the positive electrode current collector.

[0089] 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.).

[0090] 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 supplement, film forming additive, flame retardant, high / low temperature stabilizer, etc.

[0091] For example, in a lithium ion battery, 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.

[0092] As an example, the binder in the positive electrode active material layer can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic ester resin.

[0093] 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.

[0094] According to an embodiment of the present application, the 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.

[0095] 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.).

[0096] 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 agent, a flame retardant, a high / low temperature stabilizer, etc., can also be added according to actual needs.

[0097] 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.

[0098] 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).

[0099] According to an embodiment of the present application, the conductive agent in the negative electrode active material layer can include, but is not limited to, at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In a second aspect, the present application provides a secondary battery. According to an embodiment of the present application, the secondary battery includes the battery cell described above. The secondary battery has all the features and advantages of the battery cell described above, which will not be repeated here.

[0101] 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, cylindrical battery, etc., all of which are not particularly limited by the present application.

[0102] Figure 3 is a square structure secondary battery 1 as an example. In some embodiments, referring to Figure 3 , the outer package can include a shell 200 and a cover plate 300. Among them, the shell 200 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a containing cavity. The shell 200 has an opening communicating with the containing cavity, and the cover plate 300 can be provided on the opening to close the containing cavity. The electrode assembly 100 is packaged in the containing cavity. The electrolyte is infiltrated in the electrode assembly 100. The number of electrode assemblies 100 contained in the battery 1 can be one or more, which can be selected by those skilled in the art according to the specific actual needs.

[0103] In a third aspect of the present application, a power consuming device is provided. According to embodiments of the present application, the power consuming device includes the battery cell or the secondary battery as described above. The power consuming device has all the features and advantages of the battery cell or the secondary battery as described above, which will not be repeated here.

[0104] According to embodiments of the present application, the specific type of the power consuming device is not particularly limited, which can be any device that uses the battery cell or the secondary battery as a power source or energy storage unit. As an example, the power consuming device includes but is not limited to electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (such as mobile phones, notebook computers, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc. It can be understood that in addition to the battery as described above, the power consuming device also includes necessary structures and components, which can be referred to conventional technology, for example, the 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 repeated here.

[0105] 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.

[0106] The specific embodiments of the present application will be described in detail below.

[0107] Embodiment 1

[0108] ① Preparation of polymer binder particles:

[0109] The polymer emulsion is prepared by emulsifying 1500 g of deionized water, 32 g of sodium dodecyl sulfate emulsifier, 10 g of sodium persulfate initiator, and 1000 g of the above-mentioned mixed monomers in a 5000 mL four-necked flask equipped with mechanical stirring, a thermometer, and a condenser tube at a high speed for 30 min, and then the temperature is raised to 80°C for 4 h of reaction. After adjusting the pH to 6-8, the temperature is lowered to below 40°C to obtain the polymer emulsion (Dv10: 132 nm, Dv50: 156 nm, Dv90: 178 nm).

[0110] The polymer emulsion is prepared by emulsifying 1500 g of deionized water, 32 g of sodium dodecyl sulfate emulsifier, 10 g of sodium persulfate initiator, and 1000 g of the above-mentioned mixed monomers in a 5000 mL four-necked flask equipped with mechanical stirring, a thermometer, and a condenser tube at a high speed for 30 min, and then the temperature is raised to 80°C for 4 h of reaction. After adjusting the pH to 6-8, the temperature is lowered to below 40°C to obtain the polymer emulsion (Dv10: 132 nm, Dv50: 156 nm, Dv90: 178 nm).

[0111] The polymer emulsion is prepared by emulsifying 1500 g of deionized water, 32 g of sodium dodecyl sulfate emulsifier, 10 g of sodium persulfate initiator, and 1000 g of the above-mentioned mixed monomers in a 5000 mL four-necked flask equipped with mechanical stirring, a thermometer, and a condenser tube at a high speed for 30 min, and then the temperature is raised to 80°C for 4 h of reaction. After adjusting the pH to 6-8, the temperature is lowered to below 40°C to obtain the polymer emulsion (Dv10: 132 nm, Dv50: 156 nm, Dv90: 178 nm).

[0112] ②Preparation of the isolation film:

[0113] A PE microporous film (from Zhuogao Electronics Technology Co., Ltd.) with a thickness of 7 μm and an average pore size of 80 nm is used as the base film. The polymer binder particles and the glue PVDF are mixed uniformly in deionized water at a solid mass ratio of 100:15 to obtain the isolation film slurry (solid content of 20%); the isolation film slurry is uniformly coated on the two opposite surfaces of the base film, and the solvent is removed by drying, and the thickness of the adhesive layer on the single surface of the base film is 35.7 μm.

[0114] ③Preparation of the positive electrode sheet

[0115] Polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive agent carbon black, and N-methyl pyrrolidone (NMP) are mixed uniformly at a mass ratio of 1.2:60.38:0.42:38 to prepare a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil (thickness 13 μm) at a loading of 197 g / m 2 After drying, cold pressing, and cutting, the positive electrode sheet is obtained, and the thickness of the positive electrode film layer formed by the positive electrode slurry coating on the single surface of the positive electrode current collector is 83.5 μm.

[0116] ④Preparation of the negative electrode sheet

[0117] Natural graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC-Na) were added into deionized water according to the mass ratio of 95.5:1.2:1.6:1.7, and a negative electrode slurry (solid content of 64%) was prepared after fully stirring and mixing uniformly. The negative electrode slurry was coated on the negative electrode current collector copper foil (thickness of 6 μm) at a loading of 102 g / m 2 Afterwards, the negative electrode slurry was dried, cold-pressed, and cut to obtain a negative electrode sheet, and the thickness of the negative electrode film layer formed by the negative electrode slurry on the single side surface of the negative electrode current collector was 67 μm.

[0118] Preparation of electrolyte

[0119] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed according to 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.

[0120] Preparation of secondary battery

[0121] The above negative electrode sheet, separator, and positive electrode sheet were stacked in sequence and wound and cold-pressed (25°C-5 MPa-10 s) to obtain an electrode assembly; the electrode assembly was placed in an outer package, and the above-prepared electrolyte was added, and after processes such as packaging, standing, formation, and aging, a secondary battery was obtained.

[0122] Examples 2-16

[0123] The same as Example 1, except for the differences shown in Table 1.

[0124] Comparative Example 1

[0125] The same as Example 1, except that the Dv50 particle size of the polymer binder particles was 7 μm.

[0126] Comparative Example 2

[0127] The same as Comparative Example 1, except that the positive electrode sheet surface was pressed by a bump roller to form bumps, and the height of the bumps was 7 μm.

[0128] Table 1

[0129]

[0130]

[0131] Performance test

[0132] 1. Particle size test

[0133] The laser particle size analyzer (MasterSizer 3000) is used for testing, and the main light source uses a helium-neon red light source. A clean small beaker is taken and 1 g of the sample to be tested is added, 20 ml of deionized water is added, and ultrasonic treatment is performed at 53 KHz / 120 W for 5 min to ensure that the sample is completely dispersed. Turn on the laser particle size analyzer, clean the light path system, and then automatically test the background. Stir the ultrasonically treated sample solution to make it uniformly dispersed, place it in the sample cell as required, and start measuring the particle size. The measurement results can be read from the instrument.

[0134] 2. Width and thickness of the electrode assembly

[0135] The width of the electrode assembly is measured using a vernier caliper. The horizontal widths of the upper half, middle, and lower half of the electrode assembly are measured, and the average value is calculated to obtain the width data of the electrode assembly.

[0136] Thickness test: The thickness of the electrode assembly is measured using a vernier caliper. The thicknesses of the upper, middle, and lower parts of the electrode assembly are measured, and the average value is calculated to obtain the thickness data of the electrode assembly.

[0137] 3. Thickness of the bonding layer

[0138] 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 5 ). Then, according to the scanning image, the distance between adjacent positive current collectors in the corner part is marked as D1, and the distance between adjacent positive current collectors in the main part is marked as D2. According to the description in the examples, the distance between adjacent positive current collectors includes two single-sided positive film layers, a negative current collector, two single-sided negative film layers, and two separator films (including a base film and bonding layers on both sides), the first thickness = (D1-2*single-sided positive film layer thickness-2*separator base film thickness-negative current collector thickness-2*single-sided negative film layer thickness) / 4; the second thickness = (D2-2*single-sided positive film layer thickness-2*separator base film thickness-negative current collector thickness-2*single-sided negative film layer thickness) / 4.

[0139] It should be noted that the thicknesses of the positive and negative electrode plates and the separator base film remain unchanged before and after cold pressing, and only the bonding layer changes in thickness. Because the pressure during the preparation of the positive and negative electrode plates is 20-40 MPa, which is much greater than the pressure during the shaping of the electrode assembly (i.e., the cold pressing pressure), it can be considered that all changes in the electrode assembly before and after cold pressing are caused by the bonding layer. In addition, the first distance, the second distance, the first thickness, and the second thickness obtained by testing Comparative Example 2 include the height of the protrusions.

[0140] 4. The distance between adjacent positive and negative electrode sheets (i.e. the electrode sheet distance) test

[0141] D1, D2, the first thickness and the second thickness are obtained according to the method described in the above 3, then the first distance = the single-sided positive film layer thickness + the single-sided negative film layer thickness + the separator base film thickness + the first thickness x 2; the second distance = the single-sided positive film layer thickness + the single-sided negative film layer thickness + the separator base film thickness + the second thickness x 2.

[0142] 5. Adhesion test:

[0143] The battery electrode sheet (negative electrode sheet or positive electrode sheet) is overlapped with the separator film together and placed on a hot press, and the hot press parameters are set as follows: temperature 65℃, pressure 5MPa, time 10s, and the bonded separator film / electrode sheet sample is prepared by pressing. The separator film / electrode sheet sample is cut into a rectangular sample of 150x20mm. The electrode sheet of the above rectangular sample is pasted on a steel plate by double-sided tape, and the separator film and the electrode sheet are separated by 2cm in length at one end of the rectangular sample in the length direction, and the test sample is prepared.

[0144] The steel plate is kept horizontal and fixed with the lower clamp of a universal testing machine (Shanghai Cetech Instrument Manufacturing Co., Ltd., model CTM2100), and the peeling end of the separator film as described above is fixed with the upper clamp of the universal testing machine and connected to the tension machine. The test conditions are set as follows: tensile speed 20mm / min, and horizontal pulling 10cm. After the tension is stable, the tension value is recorded, and the adhesion of the separator film and the electrode sheet is obtained by the ratio of the tension value to the sample width.

[0145] 6. Capacity retention rate test

[0146] The test steps are as follows: at 25℃, the battery prepared in the above examples and comparative examples is charged at 1 / 3C to 3.8V, then charged at 3.8V constant voltage to a current of 0.05C, left for 5min, then discharged at 1 / 3C to 2.0V, and the obtained discharge capacity is recorded as the initial capacity CO. The above steps are repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle is recorded at the same time, then the battery capacity retention rate Pn after each cycle = (Cn / CO) x 100%. The battery capacity retention rate after 500 cycles can be used to reflect the difference in cycle performance.

[0147] Table 2: Performance test results

[0148]

[0149]

[0150]

[0151]

[0152] From the above test results, it can be seen that the performance of the batteries of Examples 1-16 is significantly better than that of Comparative Examples 1-2. Specifically, compared with Comparative Example 1, the cycle capacity retention of the battery of Example 1 is improved by 5%, indicating that by setting large-particle-size polymer binder particles on the separator and optimizing the polymer binder particles, the inter-tab spacing can be effectively improved, sufficient expansion space is reserved for the negative tab, thereby reducing the battery and internal stress, and improving the cycle performance of the battery. At the same time, the increase in the width and thickness of the electrode assembly is almost negligible, and the battery maintains a small size, so the size parameters of the battery outer package do not need to be changed, and the compatibility with the prior art is higher.

[0153] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the description of the specification

[0154] The specific embodiments disclosed herein are intended to be illustrative only and not limiting of the true scope of the present application, which is set forth in the following claims.

Claims

1. A battery cell, characterized by, An electrode assembly including a positive electrode tab, a negative electrode tab, and a separator disposed between the positive electrode tab and the negative electrode tab; The electrode assembly has a main portion and corner portions on both sides of the main portion, the distance between adjacent positive and negative electrode tabs in the corner portions is a first distance, the distance between adjacent positive and negative electrode tabs in the main portion is a second distance, the difference between the first distance and the second distance is not less than 50 µm and not more than 150 µm; The separator includes a base film and a bonding layer disposed on at least one surface of the base film, the bonding layer contains polymer binder particles, and the Dv50 particle size of the polymer binder particles is 8 µm to 20 µm.

2. The battery cell of claim 1, wherein, The difference between the first distance and the second distance is not less than 50 µm and not more than 90 µm.

3. The battery cell according to claim 1 or 2, characterized in that, The Dv50 particle size of the polymer binder particles is greater than 10 µm and not more than 20 µm.

4. The battery cell according to any one of claims 1 to 3, the particle size distribution of the polymer binder particles is less than 2, the particle size distribution = (Dv90 - Dv10) / Dv50.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The thickness of the bonding layer of the single-sided surface of the base film in the corner portion is a first thickness, the thickness of the bonding layer of the single-sided surface of the base film in the main portion is a second thickness, the difference between the first thickness and the second thickness is not less than 25 µm and not more than 75 µm.

6. The battery cell according to any one of claims 1 to 5, characterized in that The first thickness is 25 µm to 45 µm; and / or, The second thickness is 0.1 µm to 5 µm.

7. The battery cell according to any one of claims 1 to 6, characterized in that The glass transition temperature of the polymer binder particles is less than 60 degrees Celsius.

8. The battery cell according to any one of claims 1 to 7, characterized in that The polymer binder particles include non-fluorine binder particles.

9. The battery cell according to any one of claims 1 to 8, characterized in that, The polymer monomers of the polymer binder particles include a first monomer represented by Formula 1: wherein R1is selected from the group consisting of a hydrogen atom and C 1-6 alkyl, R2is selected from the group consisting of a hydrogen atom, a hydroxy-substituted C 1-6 alkyl, and C 1-6 alkoxy.

10. The battery cell of claim 9, wherein, The first monomer includes at least one of acrylamide, N-hydroxymethyl acrylamide, and N-butoxymethyl acrylamide.

11. The battery cell according to any one of claims 1 to 10, characterized in that The polymer monomers of the polymer binder particles further include a second monomer represented by Formula 2: wherein R3is selected from the group consisting of a hydrogen atom and a substituted or unsubstituted C 1-6 alkyl group.

12. The battery cell of claim 11, wherein, The second monomer includes at least one of acrylic acid and methacrylic acid.

13. The battery cell of any one of claims 1-12, wherein, The polymer monomers of the polymer binder particles further include a third monomer represented by Formula 3: wherein R4is selected from the group consisting of a hydrogen atom and C 1-12 alkyl, R2is selected from the group consisting of C 1-12 alkyl.

14. The battery cell of claim 13, wherein, The third 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.

15. The battery cell of any one of claims 1-14, wherein, The polymer monomers of the polymer binder particles include the first monomer, the second monomer, and the third monomer in a mass ratio of 10 to 20:10 to 30:

100.

16. A secondary battery characterized by comprising: The battery cell of any one of claims 1 to 15.

17. An electrical device, comprising: The secondary battery of claim 16.

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