Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a housing, and an electrode assembly and an electrolyte which are arranged in the housing, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a separator arranged between the first electrode sheet and the second electrode sheet. The separator comprises a substrate and a bonding layer arranged on at least one surface of the substrate; the bonding layer is bonded to the first electrode sheet and / or the second electrode sheet; the length direction of the secondary battery is defined as a first direction, and in the first direction, the bonding layer comprises a first edge area, a main body area and a second edge area which are successively arranged; at least one of the first edge area and the second edge area is a continuous coating layer; and the main body area is a discontinuous coating layer.

Description

Secondary batteries and electronic devices Technical Field

[0001] The present application relates to the field of energy storage devices, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries (such as lithium-ion batteries) are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution. Secondary batteries are prone to internal short circuit failure caused by diaphragm shrinkage in hot box and drop conditions, which in turn leads to safety problems such as fire and explosion. Currently, the risk of diaphragm shrinkage can be reduced by coating a ceramic layer with a certain viscosity on the surface of the diaphragm, which can improve the risk of internal short circuit. However, the surface of the ceramic layer is inert and has limited effect on the electrolyte retention performance. Long-term cycling of lithium-ion batteries will increase polarization due to electrolyte consumption, and the cycle performance will drop sharply, thereby greatly shortening the battery life.

[0003] Summary of the Invention

[0004] One purpose of the present application is to provide a secondary battery that can improve the electrolyte retention performance while ensuring internal short-circuit safety performance, thereby improving cycle performance.

[0005] The present application provides a secondary battery, comprising a housing, an electrode assembly and an electrolyte disposed within the housing, the electrode assembly comprising a first electrode piece, a second electrode piece, and a separator disposed between the first electrode piece and the second electrode piece. The separator comprises a substrate and an adhesive layer disposed on at least one surface of the substrate, the adhesive layer being bonded to the first electrode piece and / or the second electrode piece. The longitudinal direction of the secondary battery is defined as a first direction. In the first direction, the adhesive layer comprises a first edge region, a main body region, and a second edge region disposed in sequence. At least one of the first edge region and the second edge region is a continuous coating layer, and the main body region is a discontinuous coating layer.

[0006] In the present application, the adhesive layer of the isolation membrane is configured with a first edge region, a main region, and a second edge region arranged in sequence along the length direction. The first edge region and / or the second edge region are configured as a continuous coating layer, which can effectively reduce the risk of internal short circuits caused by shrinkage of the edges where the first edge region and / or the second edge region of the isolation membrane are located, thereby ensuring safety performance. In addition, the main region is configured as a discontinuous coating layer. The gaps within the discontinuous coating layer reserve space for electrolyte transmission, which can accelerate the transmission of the electrolyte, improve the electrolyte infiltration effect, and increase the storage capacity of the electrolyte, which is conducive to improving the cycle performance. Therefore, the secondary battery of the present application improves the cycle performance while ensuring safety performance.

[0007] In some possible implementations, in the first direction, the width of the separator is a mm, the width of the first edge region is b1 mm, the width of the second edge region is b2 mm, and the width of the main region is b3 mm. b1, b2, and b3 satisfy at least one of the following conditions: 0 < b1 ≤ 0.4a; 0 < b2 ≤ 0.4a; 0 < b1 + b2 ≤ 0.8a; 0.2a ≤ b3 < a. When b1, b2, and b3 are within the above ranges, the adhesion between the first and / or second edge regions and the electrode sheet can be maintained, reducing the risk of shrinkage at the edges of the separator where the first and / or second edge regions are located. The main region 250 also maintains its ability to improve electrolyte wetting and storage, thereby improving safety and cycling performance.

[0008] In some possible implementations, b1, b2, and b3 satisfy at least one of the following conditions: 0.1a≤b1≤0.3a; 0.1a≤b2≤0.3a; 0.2a<b1+b2≤0.6a; 0.4a≤b3≤0.8a. When b1, b2, and b3 are within the above ranges, the effects of improving safety and cycle performance are better.

[0009] In some possible implementations, the difference in length between the first and second pole pieces in the first direction is less than or equal to the sum of b1 and b2. When b1 and b2 meet the above conditions, the first edge region and / or the second edge region can be bonded to the first and second pole pieces simultaneously, further reducing the risk of shrinkage of the edge of the isolation membrane in the first direction X and improving safety.

[0010] In some possible implementations, the main body region includes a plurality of strip-shaped coating layers that are spaced apart.

[0011] In some possible implementations, the direction from one strip of coating to another adjacent strip of coating is defined as a second direction. In the second direction, the width of the strip of coating is c1 mm, the distance between adjacent strips of coating is c2 mm, and c1 and c2 satisfy at least one of the following conditions: 0.1≤c1≤5; 0.1≤c2≤5; 0.2≤c2 / (c1+c2)≤0.8. When c2 / (c1+c2)<0.2, c2 is small, and there is a risk of poor electrolyte infiltration. At the same time, the ability to store electrolyte is limited, and lithium deposition is likely to occur at corners during cycling, and capacity loss is significant in the later stages of cycling. When c2 / (c1+c2)>0.8, c2 is large, and the bonding area between the main body and the electrode is reduced, affecting safety performance. At the same time, excessive electrolyte storage increases electrolyte costs and is prone to electrolyte swelling, affecting the thickness of the electrode assembly.

[0012] In some possible implementation manners, the width direction of the secondary battery is defined as the third direction, and the included angle between the strip-shaped coating and the third direction is α, where 25° ≤ α ≤ 90°. When α is within the above range, during the tape running process of the separator, it is not easy to longitudinally contract and wrinkle when subjected to uneven lateral tension, thus achieving stable production.

[0013] In some possible implementation manners, both the first edge area and the second edge area are continuous coating layers.

[0014] In some possible implementation manners, the secondary battery further includes a metal plate, which is connected to the electrode assembly and extends out of the housing from one end of the first edge area deviating from the second edge area in the first direction.

[0015] In some possible implementation manners, the width direction of the secondary battery is defined as the third direction. In the third direction, the adhesive layer includes a third edge area, a main body area, and a fourth edge area that are connected in sequence. Both the third edge area and the fourth edge area are continuous coating layers, and the first edge area, the second edge area, the third edge area, and the fourth edge area are arranged to surround the main body area. When the electrode assembly is in a stacked structure, configuring the first edge area, the second edge area, the third edge area, and the fourth edge area arranged to surround the main body area can reduce the risk of internal short circuit caused by edge shrinkage of the separator in all directions and improve the safety performance.

[0016] In some possible implementation manners, the electrode assembly is in a stacked structure. In the third direction, the width of the third edge area is b4, and the width of the fourth edge area is b5; in the third direction, the length difference between the first electrode sheet and the second electrode sheet is less than or equal to the sum of b4 and b5. When b4 and b5 are within the above range, the third edge area and / or the fourth edge area can bond the first electrode sheet and the second electrode sheet simultaneously, reduce the risk of internal short circuit caused by edge shrinkage of the separator in the width direction, and improve the safety performance.

[0017] In some possible implementation manners, the thickness of the adhesive layer is t μm, where 0 < t ≤ 8. When t is within the above range, it has good high-temperature shrinkage resistance and has little influence on the energy density.

[0018] In some possible implementation manners, the adhesive layer includes an adhesive, and the adhesive includes at least one of polytetrafluoroethylene (PVDF), polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, or epoxy resin derivative.

[0019] In some possible implementations, the bonding layer includes an inorganic filler, and the inorganic filler includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

[0020] In some possible implementations, the substrate includes a polymer film, a multilayer polymer film, or a nonwoven fabric formed from any one of the following polymers or a mixture of two or more thereof: polyolefin, polyvinylidene fluoride, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and polyphenylene phthalamide.

[0021] In some possible implementations, the thickness of the substrate is 3 to 20 mm, which can enable the isolation membrane to have good mechanical properties.

[0022] In some possible implementations, the substrate satisfies at least one of the following conditions: a porosity of 20% to 70%; and an air permeability of 50 to 300 s / 100 cc. When the porosity and air permeability of the substrate are within these ranges, cycling performance is improved.

[0023] The present application also provides an electronic device comprising any of the above-mentioned secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0025] FIG1 is a schematic diagram of a secondary battery provided in one embodiment of the present application, viewed along the thickness direction;

[0026] FIG2 is a schematic diagram of an electrode assembly according to an embodiment of the present application viewed along the thickness direction;

[0027] FIG3 is a schematic diagram of an electrode assembly according to an embodiment of the present application viewed along the length direction;

[0028] FIG4 is a partial cross-sectional view of the electrode assembly shown in FIG3 along line AA;

[0029] FIG5 is a schematic diagram of an isolation film provided by one embodiment of the present application observed along the thickness direction;

[0030] FIG6 is a schematic diagram of an isolation film provided by another embodiment of the present application, viewed along the thickness direction;

[0031] FIG7 is a schematic diagram of an isolation film provided in another embodiment of the present application observed along the thickness direction.

[0032] Description of Main Component Symbols Secondary Battery 100 Housing 10 Electrode Assembly 20 First Pole Sheet 21 Second Pole Sheet 22 Separator 23 First Current Collector 211 First Active Material Layer 212 First Tab 213 Second Current Collector 221 Second Active Material Layer 222 Second Tab 223 Substrate 231 Adhesive Layer 232 First Edge 23a Second Edge 23b First Edge Region 240 Main Body Region 250 Second Edge Region 260 First End 241 Second End 242 Third End 261 Fourth End 262 Fifth End 251 Sixth End 252 Strip Coating 40 Gap G Third Edge 23c Fourth Edge 23d Seventh End 271 Eighth End 272 Ninth End281 Tenth end 282 Eleventh end 253 Twelfth end 254 First direction X Second direction XY Third direction Y Fourth direction Z DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0034] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0035] In addition, for the sake of brevity and clarity, the size or thickness of various components, layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. In addition, it should be understood that when element A is referred to as being "connected to" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0036] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0037] The professional terms used herein are for the purpose of describing specific embodiments and are not intended to limit the application. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. It should be understood that the term "comprising", when used in this specification, refers to the presence of narrated features, numerical values, steps, operations, elements and / or components, but does not exclude the presence or increase of one or more other features, numerical values, steps, operations, elements, components and / or combinations thereof. It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts herein, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teaching of exemplary embodiments.

[0038] Referring to FIG. 1 , one embodiment of the present application provides a secondary battery 100 comprising a housing 10, an electrode assembly 20 (shown in FIG. 2 and FIG. 3 ), an electrolyte, and a metal plate 30. The electrode assembly 20 and the electrolyte are housed in the housing 10. The metal plate 30 is connected to the electrode assembly 20 and extends from one side of the housing 10 along a first direction X for connection to external components. In this application, the first direction X refers to the length of the secondary battery 100. In this embodiment, there are two metal plates 30, serving as a positive terminal and a negative terminal, respectively, and the two metal plates 30 are located on the same side of the secondary battery 100. In some embodiments, the housing 10 is a metal housing, such as a steel or aluminum housing. In other embodiments, the housing 10 is a packaging bag encapsulated with an encapsulation film, i.e., the secondary battery 100 may be a soft-pack battery. FIG. 2 and FIG. 3 illustrate that the secondary battery 100 includes one electrode assembly 20. In other embodiments, to achieve high voltage output, the secondary battery 100 includes multiple electrode assemblies 20.

[0039] As shown in Figures 2 and 3, the electrode assembly 20 includes a first pole piece 21 and a second pole piece 22 and an isolation film 23 disposed between the first pole piece 21 and the second pole piece 22. In this embodiment, the first pole piece 21, the isolation film 23 and the second pole piece 22 are alternately stacked in the fourth direction Z to form a laminated structure. In this application, the fourth direction Z refers to the thickness direction of the secondary battery. The isolation film 23 is used to reduce the risk of short circuit due to direct contact between the first pole piece 21 and the second pole piece 22. In some embodiments, the isolation film 23 includes at least one of the following polymers: polyolefin, polyvinylidene fluoride, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex and polyphenylene phthalate. In other embodiments, the first pole piece 21, the isolation film 23 and the second pole piece 22 are stacked and wound to form a wound structure.

[0040] As shown in Figure 3, the first electrode sheet 21 includes a first current collector 211, a first active material layer 212, and a first electrode tab 213. The first active material layer 212 is disposed on at least one surface of the first current collector 211, and the first electrode tab 213 electrically connects the first current collector 211 and the corresponding metal plate 30. The second electrode sheet 22 includes a second current collector 221, a second active material layer 222, and a second electrode tab 223. The second active material layer 222 is disposed on at least one surface of the second current collector 221, and the second electrode tab 223 electrically connects the second current collector 221 and the corresponding metal plate 30. In this embodiment, the first electrode tab 213 extends outward from one end of the first current collector 211 away from the first active material layer 212, and the second electrode tab 223 extends outward from one end of the second current collector 221 away from the second active material layer 222. The first electrode tab 213 can be welded to the area where the first current collector 211 leaves the second active material layer 222 , and the second electrode tab 223 can be welded to the area where the second current collector 221 leaves the second active material layer 222 , which is not limited in this application.

[0041] In some embodiments, the first electrode sheet 21 is a positive electrode sheet, and the second electrode sheet 22 is a negative electrode sheet. Specifically, the first current collector 211 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The first active material layer 212 includes a positive electrode active material, which may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, and combinations thereof. The second current collector 221 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The second active material layer 222 includes a negative electrode active material, which may be selected from at least one of graphite materials, alloy materials, lithium metal, and alloys thereof. The graphite material may be selected from at least one of artificial graphite and natural graphite; the alloy material may be selected from at least one of silicon, silicon oxide, tin, and titanium sulfide.

[0042] Referring to FIG4 , the isolation film 23 includes a substrate 231 and an adhesive layer 232 disposed on one surface of the substrate 231. The adhesive layer 232 is bonded to the first electrode 21. In another embodiment, the adhesive layer 232 is bonded to the second electrode 22. In yet another embodiment, the adhesive layer 232 is disposed on two opposing surfaces of the substrate 231, and the adhesive layer 232 is bonded to the first electrode 21 and the second electrode 22.

[0043] Referring to Figures 2, 4, and 5, in a first direction X, the substrate 231 includes opposing first and second edges 23a and 23b. The adhesive layer 232 includes a first edge region 240, a main region 250, and a second edge region 260, arranged in sequence. The first edge region 240 overlaps the first edge 23a and extends toward the second edge 23b along the first direction X. The second edge region 260 overlaps the second edge 23b and extends toward the first edge 23a along the first direction X. In the first direction X, the main region 250 is located between the first and second edge regions 240, 260, and is spaced apart from the first and second edges 23a, 23b. The metal plate 30 extends from the electrode assembly 20 at the end of the first edge region 240 facing away from the second edge region 260 in the first direction X. In this embodiment, the first edge region 240, the main region 250, and the second edge region 260 are sequentially connected in the first direction X. In another embodiment, the first edge region 240, the main region 250, and the second edge region 260 are spaced apart in sequence in the first direction X.

[0044] Referring to Figures 4 and 5 , the first edge region 240 and the second edge region 260 are both continuous coating layers, while the main body region 250 is a discontinuous coating layer. A continuous coating layer is a continuous film layer that can be formed using a continuous coating method. A discontinuous coating layer has multiple isolated coating regions and can be formed using a discontinuous coating method. As continuous coating layers, the first and second edge regions 240 and 260 can effectively reduce the risk of internal short circuits caused by shrinkage of the separator 23 at one end at the first edge 23a and one end at the second edge 23b, thereby ensuring safety. Furthermore, as the main body region 250 is a discontinuous coating layer, the gaps within the discontinuous coating layer reserve space for electrolyte transmission, which can accelerate electrolyte transmission, improve electrolyte infiltration, and increase electrolyte storage capacity, thereby improving cycle performance. Therefore, the secondary battery 100 of the present application improves cycle performance while ensuring safety. In another embodiment, one of the first edge region 240 and the second edge region 260 is a continuous coating layer, and the other is a discontinuous coating layer.

[0045] Referring to Figure 5, in the first direction X, the first edge region 240 includes a first end 241 and a second end 242 opposite to each other, and the first end 241 overlaps with the first edge 23a. In the first direction X, the distance between the first edge 23a and the second edge 23b is defined as a mm, and the distance between the first end 241 and the second end 242 is defined as b1 mm. In other words, in the first direction X, the width of the isolation film 23 is a mm, and the width of the first edge region 240 is b1 mm. In some embodiments, 0<b1≤0.4a. When b1 is within the above range, the adhesion between the first edge region 240 and the electrode can be maintained, reducing the risk of shrinkage at one end of the isolation film 23 located in the first edge region 240, thereby ensuring safety performance. Preferably, 0.1a≤b1≤0.3a, which has higher safety performance.

[0046] In the first direction X, the second edge region 260 includes a third end 261 and a fourth end 262 that are opposite to each other, and the fourth end 262 overlaps with the second edge 23b. In the first direction X, the distance between the third end 261 and the fourth end 262 is defined as b2 mm. In other words, in the first direction X, the width of the second edge region 260 is b2 mm. In some embodiments, 0<b2≤0.4a. When b2 is within the above range, the adhesion between the second edge region 260 and the pole piece can be maintained, reducing the risk of shrinkage of the isolation film 23 at one end of the second edge region 260, thereby ensuring safety performance. Preferably, 0.1a≤b2≤0.3a, which has higher safety performance.

[0047] In some embodiments, 0<b1+b2≤0.8a. When b1 and b2 are within the above ranges, the adhesion between the first edge region 240 and / or the second edge region 260 and the electrode can be maintained, reducing the risk of shrinkage of the isolation film 23 at one end of the first edge region 240 and / or at one end of the second edge region 260, thereby ensuring safety performance. In addition, the main body region 250 is made to have a sufficient size to maintain the main body region 250's effect of improving electrolyte wetting and electrolyte storage capabilities, thereby improving cycle performance. Preferably, 0.2a<b1+b2≤0.6a, which has a better effect of improving safety performance and cycle performance.

[0048] In the first direction X, the main body region 250 includes a fifth end 251 and a sixth end 252 that are opposite each other, with the fifth end 251 being closer to the first end 241 than the sixth end 252. In the first direction X, the distance between the fifth end 251 and the sixth end 252 is defined as b3 mm. In other words, in the first direction X, the width of the main body region 250 is b3 mm. In some embodiments, 0.2a ≤ b3 < a. When b3 is within the above range, it is beneficial to balance cycle performance and safety performance. Preferably, 0.4a ≤ b3 ≤ 0.8a, which has a better effect of improving safety performance and cycle performance.

[0049] Referring to Figure 2 , in the first direction X, the length of the first electrode 21 is defined as L1, and the length of the second electrode 22 is defined as L2. In some embodiments, L2-L1 ≤ b1+b2. When b1 and b2 are within the above ranges, the first edge region 240 and / or the second edge region 260 can simultaneously bond the first electrode 21 and the second electrode 22, thereby increasing the bonding strength, further reducing the risk of shrinkage at the edge of the isolation film 23 in the first direction X, and improving safety.

[0050] Referring to Figure 5 , the main body region 250 includes a plurality of spaced-apart strip coatings 40, each parallel to the other. A gap G is defined between adjacent strip coatings 40. The gap G between the plurality of strip coatings 40 provides space for electrolyte transfer. After electrolyte injection, the electrolyte flows through the gap G and fully soaks the electrode. In other embodiments, the main body region 250 may include a plurality of spaced-apart dot coatings, a plurality of spaced-apart block coatings, or a plurality of spaced-apart curved coatings.

[0051] The direction from one strip coating 40 to another adjacent strip coating 40 is defined as the second direction XY. Observed along the fourth direction Z, in the second direction XY, the width of the strip coating 40 is c1 mm, and the distance between adjacent strip coatings 40 is c2 mm. Among them, 0.2≤c2 / (c1+c2)≤0.8. When c2 / (c1+c2)<0.2, c2 is small, and there is a risk of poor electrolyte infiltration. At the same time, the ability to store electrolyte is limited. Lithium deposition is prone to occur at the corners during the cycle, and the capacity loss in the later stage of the cycle is large. When c2 / (c1+c2)>0.8, c2 is large, and the bonding area between the main area 250 and the electrode is reduced, affecting safety performance. At the same time, excessive electrolyte storage increases the cost of the electrolyte, and it is easy to swell, affecting the thickness of the electrode assembly 20.

[0052] The angle between the strip coating 40 and the third direction Y is α. In the present application, the third direction Y is the width direction of the secondary battery 100. The strip coating 40 is inclined, parallel or perpendicular to the third direction Y, that is, 0°≤α≤90°. As shown in Figure 5, the strip coating 40 is inclined relative to the third direction Y, that is, 0°<α<90°. As shown in Figure 6, the strip coating 40 is perpendicular to the third direction Y, that is, α=90°. In some embodiments, 25°≤α≤90°. When α is within the above range, the isolation film 23 is not prone to longitudinal shrinkage and wrinkling when subjected to uneven lateral tension during the tape running process, thereby achieving stable production.

[0053] Referring to Figure 7, the substrate 231 further includes a third edge 23c and a fourth edge 23d that are opposite to each other in the third direction Y. The adhesive layer 232 further includes a third edge region 270 and a fourth edge region 280. In the third direction Y, the third edge region 270, the main body region 250, and the fourth edge region 280 are sequentially arranged. The third edge region 270 overlaps with the third edge 23c and extends along the third direction Y toward the fourth edge 23d. The fourth edge region 280 overlaps with the fourth edge 23d and extends along the third direction Y toward the third edge 23c. The first edge region 240, the second edge region 260, the third edge region 270, and the fourth edge region 280 are arranged around the main body region 250. In this embodiment, in the third direction Y, the third edge region 270, the main body region 250, and the fourth edge region 280 are sequentially connected. In another embodiment, in the third direction Y, the third edge region 270, the main body region 250, and the fourth edge region 280 are sequentially spaced apart. The third edge region 270 and the fourth edge region 280 are both continuous coating layers, which is beneficial to increasing the adhesion between the third edge region 270 and the pole piece and the adhesion between the fourth edge region 280 and the pole piece, reducing the risk of internal short circuit caused by shrinkage of the isolation membrane 23 at one end of the third edge 23c and one end of the fourth edge 23d, thereby improving safety performance.

[0054] In the third direction Y, the third edge region 270 includes a seventh end 271 and an eighth end 272 that are opposite to each other, with the seventh end 271 overlapping the third edge 23c. In the third direction Y, the distance between the third edge 23c and the fourth edge 23d is defined as d mm, and the distance between the seventh end 271 and the eighth end 272 is defined as b4. In some embodiments, 0 < b4 ≤ 0.4d. When b4 is within the above range, the adhesion between the third edge region 270 and the electrode can be maintained, reducing the risk of shrinkage of the isolation film 23 at the end located in the third edge region 270, thereby improving safety performance. Preferably, 0.1d ≤ b4 ≤ 0.3d, which is more effective in improving safety performance.

[0055] In the third direction Y, the fourth edge region 280 includes a ninth end 281 and a tenth end 282 opposite to each other, and the tenth end 282 overlaps with the fourth edge 23d. In the third direction Y, the distance between the ninth end 281 and the tenth end 282 is defined as b5 mm. In some embodiments, 0<b5≤0.4d. When b5 is within the above range, the adhesion between the fourth edge region 280 and the pole piece can be maintained, reducing the risk of shrinkage of the isolation film 23 at one end of the fourth edge region 280, thereby improving safety performance. Preferably, 0.1d≤b4≤0.3d, which has a better effect on improving safety performance.

[0056] In the third direction Y, the main body region 250 further includes an eleventh end 253 and a twelfth end 254, with the eleventh end 253 being closer to the seventh end 271 than the twelfth end 254. The distance between the eleventh end 253 and the twelfth end 254 is defined as b6 mm. In some embodiments, 0.2d ≤ b6 < d. When b6 is within the above range, it is beneficial to balance cycle performance and safety performance. Preferably, 0.4d ≤ b6 ≤ 0.8d, which further improves safety and cycle performance.

[0057] Referring to Figure 2 , in the third direction Y, the length of the first pole piece 21 is defined as L3, and the length of the second pole piece 22 is defined as L4. In some embodiments, L4 - L1 ≤ b4 + b5. When b4 and b5 are within the above ranges, the third edge region 270 and / or the fourth edge region 280 can simultaneously bond the first pole piece 21 and the second pole piece 22, thereby increasing the bonding strength, further reducing the risk of shrinkage of the isolation film 23 in the third direction Y, and improving safety performance.

[0058] In some embodiments, the bonding layer 232 has a uniform thickness. Uniform thickness means that the difference between the thickness of different regions of the bonding layer 232 and the maximum thickness is less than or equal to 5%. The thickness of the bonding layer 232 is defined as t μm, where 0 < t ≤ 8. When t is within the above range, the bonding layer has good high-temperature shrinkage resistance and has a minimal impact on energy density.

[0059] The bonding layer 232 includes a bonding material. In some embodiments, the bonding material includes at least one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, or epoxy resin derivatives. These bonding materials have a strong bonding effect, bonding the isolation membrane 23 and the electrode together.

[0060] In some embodiments, the bonding layer 232 further includes an inorganic filler. The inorganic filler includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite. The inorganic filler serves to increase the strength of the bonding layer 232 and reduce the risk of thermal shrinkage of the separator.

[0061] In some embodiments, substrate 231 comprises a polymer film, multilayer polymer film, or nonwoven fabric formed from any one of the following polymers, or a mixture of two or more thereof: polyolefin, polyvinylidene fluoride, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and polyphenylene phthalamide. These polymers have high thermal stability and are easily surface treated, making it easier to coat adhesive layer 232 on substrate 231. Furthermore, these polymers have good toughness and are easily bendable.

[0062] In some embodiments, the thickness of the substrate is 3 to 20 mm, which can enable the isolation film 23 to have good mechanical properties.

[0063] In some embodiments, the porosity of the substrate 231 is 20% to 70%. For example, the porosity of the substrate 231 is 20%, 30%, 40%, 50%, 60%, 70%, or a range consisting of any two of these values. When the porosity of the substrate 231 is within the above range, it facilitates the transport of active metal ions in the separator 23, thereby improving cycle performance.

[0064] In some embodiments, the air permeability of the substrate 231 is between 50 and 300 s / 100 cc. For example, the air permeability of the substrate 231 is 50 s / 100 cc, 100 s / 100 cc, 150 s / cc, 200 s / cc, 250 s / cc, 300 s / cc, or a range consisting of any two of these values. When the air permeability of the substrate 231 is within the above range, it helps reduce the ionic resistance of the separator 23, improves the wettability of the separator 23, and improves the cycle performance.

[0065] One embodiment of the present application further provides an electronic device, comprising the secondary battery 100 described above. The electronic device of the present application may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup electronic power source, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0066] The present application is described in detail below through specific examples and comparative examples. A soft-pack lithium-ion battery is used as an example to illustrate the present application in conjunction with a specific preparation process and testing methods. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0067] Example 1-1

[0068] Preparation of the positive electrode: The cathode active material (lithium cobalt oxide), conductive agent (conductive carbon black), and binder (polyvinylidene fluoride) are dissolved in N-methylpyrrolidone solution at a weight ratio of 97.5:1:1.5 to form a slurry with a solid content of 75%. Aluminum foil is used as the current collector, and the slurry is applied to the current collector surface to form the active layer. The positive electrode is then cold pressed and cut to form the positive electrode.

[0069] Preparation of the negative electrode sheet: The negative electrode active material (graphite), conductive agent (conductive carbon black), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) are mixed in a mass ratio of 97.5:1:0.5:1. Deionized water is then added as a solvent and stirred to obtain a negative electrode slurry with a solid content of 50 wt%. Using copper foil as a current collector, the negative electrode slurry is applied to the surface of the negative electrode current collector to form the negative electrode active layer. The negative electrode sheet is then cold pressed and cut into pieces.

[0070] Preparation of the separator: A polyethylene film was used as the substrate. A slurry consisting of an inorganic filler (Al2O3) and a binder (PVDF) was applied to two opposing surfaces of the substrate to form a bonding layer. The separator structure is shown in Figure 6. The binder content in the bonding layer was 9 wt%.

[0071] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 and the organic solvent are mixed in a weight ratio of 8:92 to obtain an electrolyte.

[0072] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to obtain an electrode assembly; place the electrode assembly in an aluminum-plastic film packaging bag, perform hot-pressing bonding at a preset pressure, and obtain a lithium-ion battery after liquid injection and formation.

[0073] Examples 1-2 to 1-10

[0074] The difference from Example 1-1 is that at least one of the ratio b1 / a of the width b1 of the first edge area to the width a of the isolation membrane, the ratio b2 / a of the width b2 of the second edge area to the width a of the isolation membrane, and the ratio b3 / a of the width b3 of the main area to the width a of the isolation membrane is different, wherein the width a of the isolation membrane remains unchanged.

[0075] Comparative Example 1

[0076] The difference from Example 1-1 is that the slurry is continuously coated on the surface of the substrate to form a bonding layer, and the entire bonding layer is a continuous coating layer.

[0077] Comparative Example 2

[0078] The difference from Example 1-1 is that the slurry is intermittently coated on the surface of the substrate to form a bonding layer, and the bonding layer as a whole is a discontinuous coating layer.

[0079] The test methods for various parameters of this application are described below.

[0080] 1. Drop test:

[0081] The lithium-ion battery was pre-conditioned at 25°C and allowed to stand at room temperature for 60 minutes. The voltage of the lithium-ion battery before the drop test was measured. The lithium-ion battery was placed in a fixture and freely dropped from a height of 1.5m from the ground using a drop device in the following order: head-tail-right corner of the head-right corner of the tail-left corner of the head-left corner of the tail (angle: 45±15°), and repeated 6 times. After the drop, the battery was allowed to stand at room temperature for 24 hours, and the voltage of the lithium-ion battery was measured and recorded. The appearance of the lithium-ion battery was inspected and photographed before and after the test. The pass criteria for the drop test were: no smoke, no leakage, and a voltage drop of <30mV. 100 lithium-ion batteries were tested, and the number of batteries that passed the test was X, with a test pass rate of X / 100.

[0082] 2. High temperature short circuit test:

[0083] At 25°C, let it rest for 5 minutes. Charge the lithium-ion battery to 4.50V at a constant current of 0.2C. Then, charge it to 0.025C at a constant voltage of 4.50V and let it rest for 30 minutes. Perform a short-circuit test using a 60±20mΩ resistor at a test temperature of 57±2°C. The test stops when the voltage falls below 0.1V or the temperature drops to ±10°C below the test ambient temperature. The pass criteria are that the sample does not ignite or explode, and the temperature does not exceed 150°C. If 100 batteries are tested and X number of batteries pass the test, the test pass rate is X / 100.

[0084] 3. Cycle capacity retention test:

[0085] Cycle capacity retention rate: For lithium-ion batteries, first, perform the first charge and discharge in an environment of 25°C, and perform constant current charging at a charging current of 0.7C until the voltage reaches 4.50V, then switch to constant voltage charging, and charge at constant voltage until the current is 0.025C. Then, perform constant current discharge at a discharge current of 0.7C until the voltage reaches 3.0V, and record the discharge capacity of the first cycle; then, perform multiple charge and discharge cycles according to the above charging and discharging process, and record the discharge capacity of each cycle. The nth capacity retention rate (%) = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%. When the capacity retention rate = 80%, record the total number of cycles.

[0086] Table 1 lists the parameters and evaluation results of various embodiments and comparative examples.

[0087] Table 1

[0088] Comparing Examples 1-1 to 1-10 with Comparative Examples 1 and 2, it can be seen that configuring the first edge region / second edge region of the adhesive layer as a continuous coating layer and configuring the main region of the adhesive layer as a discontinuous coating layer simultaneously achieves a high drop test pass rate, high-temperature short-circuit pass rate, and a high number of cycles, thereby improving cycling performance while ensuring safety. In Comparative Example 1, the adhesive layer is entirely a continuous coating layer. Despite achieving a high drop test pass rate and high-temperature short-circuit pass rate, the number of cycles required to reach 80% of the battery capacity is low. This is because the adhesive layer, which is an entirely continuous coating layer, has limited improvement in electrolyte retention, shortening the cycle life. In Comparative Example 2, the adhesive layer is entirely a discontinuous coating layer. Despite a high number of cycles, the drop test pass rate and high-temperature short-circuit pass rate are low. This is because the adhesive layer, which is an entirely discontinuous coating layer, has weak adhesion to the electrode, limiting its effectiveness in improving the risk of internal short circuits caused by separator shrinkage.

[0089] As can be seen from Examples 1-1 to 1-10, when 0 < b1 ≤ 0.4a, 0 < b2 ≤ 0.4a, 0 < b1 + b2 ≤ 0.8a, and 0.2a ≤ b3 < a, a certain drop test pass rate and high-temperature short-circuit pass rate, a higher number of cycles, and better cycling performance are achieved. In Example 1-10, b1 > 0.4a, b2 > 0.4a, and b3 < 0.2a, although the drop test pass rate and high-temperature short-circuit pass rate are high, the number of cycles is the lowest. This is because the size of the discontinuous coating layer is too small, which limits the amount of electrolyte that can be stored, resulting in a limited effect on improving cycling performance. It can be seen from Examples 1-1, 1-4, and 1-5 that when 0.1a≤b1≤0.3a, 0.1a≤b2≤0.3a, 0.2a<b1+b2≤0.6a, and 0.4a≤b3≤0.8a, the drop test pass rate and the high-temperature short-circuit pass rate reach more than 90%, and the number of cycles reaches more than 1100, taking into account both safety performance and cycle performance.

[0090] Examples 2-1 to 2-13

[0091] The difference from Example 1-1 is that at least one of the width c1 of the stripe coating and the distance c2 between adjacent stripe coatings is different.

[0092] Table 2

[0093] It can be seen from Examples 2-1 to 2-13 that when at least one of the three conditions of 0.1≤c1≤5, 0.1≤c2≤5, and 0.2≤c2 / (c1+c2)≤0.8 is met, the drop test pass rate and the high-temperature short-circuit pass rate reach more than 34%, and the number of cycles reaches more than 998, thereby improving the cycle performance while ensuring safety performance.

[0094] In Examples 2-2 to 2-7 and 2-9 to 2-13, at least two of the above three conditions are met, the drop test pass rate and the high-temperature short-circuit pass rate reach more than 60%, and the number of cycles reaches more than 1010, which is a better effect.

[0095] In Examples 2-3 to 2-6 and 2-10 to 2-12, the above three conditions are met, the drop test pass rate and the high-temperature short-circuit pass rate reach more than 90%, and the number of cycles reaches more than 1083, which is a better effect.

[0096] The above disclosure is only a preferred embodiment of the present application and certainly cannot be used to limit the present application. Therefore, equivalent changes made based on the present application are still within the scope covered by the present application.

Claims

1. A secondary battery comprising a housing, an electrode assembly disposed within the housing, and an electrolyte, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a separator disposed between the first electrode sheet and the second electrode sheet, wherein: The isolation film includes a substrate and an adhesive layer arranged on at least one surface of the substrate, the adhesive layer is bonded to the first pole piece and / or the second pole piece, and the longitudinal direction of the secondary battery is defined as a first direction. In the first direction, the adhesive layer includes a first edge area, a main area and a second edge area arranged in sequence, at least one of the first edge area and the second edge area is a continuous coating layer, and the main area is a discontinuous coating layer.

2. The secondary battery according to claim 1, wherein In the first direction, the width of the isolation film is a mm, the width of the first edge region is b1 mm, the width of the second edge region is b2 mm, and the width of the main region is b3 mm. b1, b2, and b3 satisfy at least one of the following conditions: 0<b1≤0.4a; 0<b2≤0.4a; 0<b1+b2≤0.8a; 0.2a≤b3<a.

3. The secondary battery according to claim 2, wherein b1, b2, b3 meet at least one of the following conditions: 0.1a≤b1≤0.3a; 0.1a≤b2≤0.3a; 0.2a<b1+b2≤0.6a; 0.4a≤b3≤0.8a.

4. The secondary battery according to claim 2, wherein In the first direction, the length difference between the first pole piece and the second pole piece is less than or equal to the sum of b1 and b2.

5. The secondary battery according to any one of claims 1 to 4, wherein: The main body area includes a plurality of strip coatings arranged at intervals.

6. The secondary battery according to claim 5, wherein The direction from one stripe coating to another adjacent stripe coating is defined as a second direction. In the second direction, the width of the stripe coating is c1 mm, and the distance between adjacent stripe coatings is c2 mm. c1 and c2 satisfy at least one of the following conditions: 0.1≤c1≤5； 0.1≤c2≤5； 0.2≤c2 / (c1+c2)≤0.

8.

7. The secondary battery according to claim 5, wherein The width direction of the secondary battery is defined as a third direction, and the angle between the strip coating and the third direction is α, where 25°≤α≤90°.

8. The secondary battery according to claim 1, wherein The first edge region and the second edge region are both continuous coating layers.

9. The secondary battery according to claim 1, wherein The secondary battery further includes a metal plate connected to the electrode assembly and extending out of the housing from one end of the first edge region facing away from the second edge region in the first direction.

10. The secondary battery according to claim 1 or 8, wherein The width direction of the secondary battery is defined as a third direction. In the third direction, the bonding layer includes a third edge area, the main body area and a fourth edge area connected in sequence. The third edge area and the fourth edge area are both continuous coating layers. The first edge area, the second edge area, the third edge area and the fourth edge area are arranged around the main body area.

11. The secondary battery according to claim 10, wherein The electrode assembly is a laminated structure. In the third direction, the width of the third edge region is b4, and the width of the fourth edge region is b5. In the third direction, the length difference between the first pole piece and the second pole piece is less than or equal to the sum of b4 and b5.

12. The secondary battery according to claim 1, wherein The thickness of the bonding layer is t μm, 0 <t≤8。 13. The secondary battery according to claim 1, wherein The bonding layer includes a bonding material, and the bonding material includes at least one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin or epoxy resin derivative.

14. The secondary battery according to claim 1, wherein The bonding layer includes an inorganic filler, and the inorganic filler includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

15. The secondary battery according to claim 1, wherein The substrate comprises a polymer film, a multilayer polymer film, or a non-woven fabric formed by any one of the following polymers or a mixture of two or more thereof: polyolefin, polyvinylidene fluoride, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and polyphenylene phthalamide.

16. The secondary battery according to claim 1, wherein The thickness of the substrate is 3 to 20 mm.

17. The secondary battery according to claim 1, wherein The substrate satisfies at least one of the following conditions: The porosity of the substrate is 20% to 70%; The air permeability of the substrate is 50 to 300 s / 100 cc.

18. An electronic device, wherein: The invention comprises the secondary battery according to any one of claims 1 to 17.

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