Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a housing, an electrode assembly disposed in the housing, and a first conductive plate. The electrode assembly is of a stack structure, and comprises first electrode sheets, separators, and second electrode sheets which are sequentially stacked in a first direction. The first conductive plate is connected to the first electrode sheets, and extends out of the housing in a second direction perpendicular to the first direction. The first electrode sheets comprise a first outer electrode sheet located on the outermost layer in the electrode assembly, and when viewed from a third direction perpendicular to both the first direction and the second direction, the first outer electrode sheet comprises a first area and a second area connected in the second direction. When viewed from the third direction, the first area comprises a first end connected to the second area and a second end disposed opposite to the first end in the second direction. The first area extends from the first end in a direction deviating from the second direction, and the second end is farther away from the second electrode sheet in the first direction than the first end. The secondary battery can improve the overcharge resistance.

Description

Secondary batteries and electronic devices Technical Field

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

[0002] With the popularity of consumer electronic products such as laptops, mobile phones, handheld game consoles, tablet computers, mobile power supplies and drones, people's requirements for secondary batteries (eg, lithium-ion secondary batteries) are becoming increasingly stringent.

[0003] However, secondary batteries may experience thermal runaway when overcharged, reducing the reliability and service life of the secondary batteries.

[0004] Summary of the Invention

[0005] In view of the above shortcomings, it is necessary to provide a secondary battery that is beneficial to improving the overcharge resistance performance.

[0006] In addition, the present application also provides an electronic device having the secondary battery.

[0007] In a first aspect, the present application provides a secondary battery comprising a shell, an electrode assembly disposed in the shell, and a first conductive plate. The electrode assembly is a laminated structure comprising a first electrode plate, an isolation membrane, and a second electrode plate stacked in sequence in a first direction. The first conductive plate is connected to the first electrode plate. The first conductive plate extends from the shell in a second direction perpendicular to the first direction. The first electrode plate comprises a first outer electrode plate, which is the outermost layer of the electrode assembly. Observed from a third direction perpendicular to both the first and second directions, the first outer electrode plate comprises a first region and a second region connected in the second direction. Observed from the third direction, the first region comprises a first end connected to the second region and a second end disposed opposite to the first end in the second direction, the first region extending from the first end in a deviation from the second direction, and the second end is further away from the second electrode plate in the first direction than the first end.

[0008] The present application sets the first area to extend away from the second direction. When the secondary battery is overcharged, the first area or the second electrode corresponding to the first area can be used as a sacrificial position during overcharging to preferentially deposit lithium, thereby reducing the probability or degree of lithium deposition at other locations. It is also beneficial to reduce the possibility of contact short circuit caused by the deposited lithium dendrites piercing the isolation membrane, thereby reducing the occurrence of thermal runaway. Furthermore, if gas is produced near the first area when the secondary battery is overcharged, the contact interface of the adjacent first outer electrode sheet, isolation membrane and second electrode sheet can be stretched open by the action of the gas, which is beneficial to further reduce the possibility of contact short circuit caused by the lithium dendrites piercing the isolation membrane, and is also beneficial to the timely dissipation of heat in the electrode assembly. Therefore, the present application can improve the overcharge resistance of the secondary battery, thereby improving reliability and service life.

[0009] In some possible implementations, when viewed from a third direction, the angle α between the line connecting the first end and the second end and the second direction satisfies the following: 1°≤α≤12°. By limiting the lower limit of the angle α, lithium deposition can occur preferentially in the first region or the second electrode corresponding to the first region when the secondary battery is overcharged, and the possibility of the deposited lithium dendrites piercing the isolation membrane and causing a contact short circuit is reduced. By limiting the upper limit of the angle α, the influence of the first region on the energy density and appearance smoothness of the secondary battery is reduced, the possibility of the active material in the first region easily falling off and causing a short circuit is reduced, and the possibility of an increase in the active material in the first region that is difficult to play a capacity role is reduced.

[0010] In some possible implementations, 3°≤α≤10°, thereby further allowing lithium to be deposited preferentially in the first region or the second electrode corresponding to the first region when the secondary battery is overcharged, and reducing the possibility of the deposited lithium dendrites piercing the isolation membrane and causing a contact short circuit; moreover, it further reduces the impact of the first region on the energy density and appearance smoothness of the secondary battery, the possibility of the active material in the first region easily falling off and causing a short circuit, and the possibility of an increase in the active material in the first region that is difficult to play a capacity role.

[0011] In some possible implementations, when viewed from a third direction, the length of the first region extending from the first end to the second end is the first length, the length of the second region in the second direction is the second length, and the ratio of the second length to the first length is greater than or equal to 7 and less than or equal to 29. By limiting the lower limit of L2 / L1, the impact of the first region on the energy density and appearance smoothness of the secondary battery is reduced, and the possibility of an increase in active material in the first region that is difficult to play a capacity role is also reduced. By limiting the upper limit of L2 / L1, the possibility of failing to significantly reduce the probability or degree of lithium deposition in other locations during overcharging is reduced.

[0012] In some possible implementations, the ratio of the second length to the first length is greater than or equal to 11 and less than or equal to 19, thereby further reducing the impact of the first region on the energy density and appearance smoothness of the secondary battery, further reducing the possibility of an increase in active materials in the first region that are difficult to play a capacity role, and further reducing the possibility of failing to significantly reduce the probability or degree of lithium plating in other locations during overcharging.

[0013] In some possible implementations, in the second direction, the first region is farther away from the first conductive plate than the second region, thereby reducing the possibility that when the electrode assembly moves within the shell along the second direction, the first electrode ear connected to the first conductive plate enters the space between the first region and the second electrode sheet adjacent to the first outer electrode sheet, thereby causing a contact short circuit.

[0014] In some possible implementations, the first region is closer to the first conductive plate than the second region in the second direction. Therefore, when the secondary battery is overcharged, gas generated near the first region is facilitated to be released into the space in the housing that accommodates the first conductive plate and the first tab connected to the first conductive plate, thereby reducing the possibility of excessive gas accumulation and causing the first region to further deviate from the second direction.

[0015] In some possible implementations, the first direction has a first side from the second pole piece toward the first outer pole piece. The shell is a packaging bag and includes a main body portion for accommodating the electrode assembly and a packaging portion connected to the main body portion, and the first conductive plate extends from the packaging portion to the shell. The main body portion includes a first end face connected to the packaging portion. When viewed from a third direction, the first end face extends from the packaging portion to the first side. When viewed from the third direction, the first area extends from the first end to the first side. Therefore, the first area of ​​the first outer pole piece is at least partially placed in the recess of the shell formed by the extension of the first end face to the first side, thereby facilitating the reduction of friction on the first outer pole piece when the shell is closed from the other side, thereby reducing the possibility of deformation of the first outer pole piece under friction.

[0016] In some possible implementations, the first direction also has a second side opposite to the first side. The shell is a packaging bag and includes a main body for accommodating the electrode assembly and a packaging part connected to the main body, and the first conductive plate extends out of the shell from the packaging part. The main body includes a first end face connected to the packaging part. When viewed from a third direction, the first end face includes a first part extending from the packaging part to the first side and a second part extending from the packaging part to the second side. The length of the first part in the first direction is greater than the length of the second part in the first direction. When viewed from the third direction, the first area extends from the first end to the first side. Therefore, the first area of ​​the first outer pole piece is at least partially placed in the recess of the shell formed by the extension of the first part to the first side, which is beneficial to reduce the friction on the first outer pole piece when the shell is covered from the other side, thereby reducing the possibility of deformation of the first outer pole piece under friction.

[0017] In some possible implementations, the housing is a packaging bag and includes a main body for accommodating the electrode assembly and an encapsulation portion connected to the main body. The first conductive plate includes a first conductive region and a second conductive region connected to each other. The first conductive region is disposed within the encapsulation portion and extends from the housing. The second conductive region is electrically connected to the first pole piece. The second conductive region includes a first end portion connected to the first conductive region, and the second conductive region extends from the first end portion toward the first side, thereby reducing friction on the first outer pole piece when the housing is closed, thereby reducing the possibility of deformation of the first outer pole piece due to friction.

[0018] In some possible implementations, the first external pole piece includes a first current collector and a first active material layer stacked in a first direction. The first current collector includes a first surface facing the second pole piece and a second surface opposite the first surface. The first active material layer is provided on the first surface, while the second surface is free of active material. This reduces energy density waste.

[0019] In some possible implementations, the first pole piece also includes a first inner pole piece, and the first inner pole piece is located on the inner side of the first outer pole piece. The first inner pole piece includes a second current collector. In the first direction, the thickness of the first current collector is the first thickness, the thickness of the second current collector is the second thickness, and the ratio of the first thickness to the second thickness is greater than or equal to 1.2 and less than or equal to 2.5. Therefore, the first outer pole piece located in the outermost layer has a higher strength, so that it can form a protective layer, reducing the possibility of damage to the electrode assembly during mechanical abuse. At the same time, the larger first thickness than the second thickness is also conducive to reducing the possibility of the first current collector being easily curled or warped due to inconsistent tension on the opposite sides of the single-sided coated first current collector. By setting the upper limit value of h1 / h2, the impact of h1 on energy density when it is too large is also reduced.

[0020] In some possible implementations, the secondary battery further includes a first layer disposed on the second surface. The first layer comprises an insulating material. The first layer is configured to dissipate heat generated at the first external electrode sheet when the secondary battery is overcharged, thereby reducing the temperature of the electrode assembly and improving the overcharge resistance of the secondary battery.

[0021] In some possible implementations, in the first direction, the thickness of the first current collector is defined as the first thickness, and the thickness of the first layer is defined as the third thickness, where the third thickness is less than twice the first thickness. This reduces the impact of the first layer on the energy density of the secondary battery when the third thickness is too large, and also reduces the likelihood of the first layer's heat dissipation being reduced and easily pierced by edge burrs of the first current collector when the third thickness is too small.

[0022] In some possible implementations, the first layer is bonded to the second surface and the housing. Therefore, the first layer can also conduct heat generated at the first external electrode sheet when the secondary battery is overcharged to the housing, allowing this heat to be dissipated to the outside through the housing, improving heat dissipation and further enhancing the overcharge resistance of the secondary battery.

[0023] In some possible implementations, the first external pole sheet includes a first active material layer, a first current collector, and a second active material layer stacked in a first direction. The first current collector includes a first surface facing the second pole sheet and a second surface opposite the first surface. The first active material layer is disposed on the first surface, and the second active material layer is disposed on the second surface.

[0024] In some possible implementations, the first electrode is a positive electrode, and the mass of the active material provided on the first current collector per unit area is G, G≤23 mg / cm 2 Therefore, the possibility of active material in the first region falling off can be reduced, and the first region can be easily bent during production (i.e., extended away from the second direction). In addition, by setting an upper limit for the ratio of the first thickness to the second thickness, the possibility of the first thickness being too large is reduced, thereby also making the first region easier to bend during production.

[0025] In some possible implementations, the isolation film adjacent to the first outer pole piece is adhered to the second region, thereby further reducing the possibility of short circuit between the first outer pole piece and the adjacent second pole piece.

[0026] In some possible implementations, a second pole piece adjacent to the first pole piece includes a third region and a fourth region connected in the second direction. When viewed from the first direction, the first region and the third region overlap, and the second region and the fourth region overlap. The isolation film adjacent to the first pole piece is also bonded to the third region, thereby further reducing the possibility of a short circuit between the first pole piece and the adjacent second pole piece.

[0027] In some possible implementations, the third region includes a first partition and a second partition connected in a second direction. When viewed from the third direction, the second partition includes a third end connected to the first partition. The first partition overlaps with the first region in the first direction. When viewed from the first direction, the second partition extends from the third end to beyond the first region. When viewed from the third direction, the second partition extends from the third end in a direction away from the first outer pole piece. By setting the second partition to extend in a direction away from the first outer pole piece, the degree of deviation of the first region can be reduced, thereby reducing the influence of the first region on the energy density and appearance smoothness of the secondary battery, the possibility of the active material in the first region easily falling off and causing a short circuit, and the possibility of an increase in the active material in the first region that is difficult to play a capacity role.

[0028] In some possible implementations, when viewed from the second direction, the isolation membrane includes a plurality of main segments stacked in the first direction and a plurality of connecting segments connecting the ends of two adjacent main segments. The main segments are disposed between adjacent first and second electrode sheets. Due to the provision of the connecting segments, the isolation membrane can restrain at least a portion of the first and second electrode sheets, thereby reducing the possibility of excessive bulging and fracture of the first and second electrode sheets due to the action of high-temperature gas when the secondary battery is overcharged.

[0029] The second aspect of the present application further provides an electronic device comprising the above secondary battery. The electronic device is powered by the above secondary battery, and the secondary battery has high overcharge resistance, thereby improving reliability and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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:

[0031] FIG1 is a schematic structural diagram of a secondary battery provided in one embodiment of the present application when viewed from a first direction.

[0032] FIG. 2 is a cross-sectional view of the secondary battery shown in FIG. 1 along line II-II in some embodiments.

[0033] FIG. 3 is a cross-sectional view of the secondary battery shown in FIG. 1 along line III-III in some embodiments.

[0034] FIG. 4 is a partial enlarged view of the secondary battery at point A shown in FIG. 3 .

[0035] FIG. 5 is a cross-sectional view of the secondary battery shown in FIG. 1 along line IV-IV in some embodiments.

[0036] FIG6 is a cross-sectional view of the secondary battery shown in FIG1 along line II-II in some other embodiments.

[0037] FIG. 7 is a schematic structural diagram of the secondary battery shown in FIG. 1 before packaging in some embodiments.

[0038] FIG8 is a cross-sectional view of the secondary battery shown in FIG1 along line III-III in some other embodiments.

[0039] FIG. 9 is a schematic structural diagram of the secondary battery shown in FIG. 1 before packaging in some other embodiments.

[0040] FIG10 is a cross-sectional view of the first casing of the secondary battery shown in FIG7 or FIG9.

[0041] FIG11 is a cross-sectional view of the second casing of the secondary battery shown in FIG7 or FIG9.

[0042] FIG. 12 is a cross-sectional view of the secondary battery shown in FIG. 1 along line III-III in some other embodiments.

[0043] FIG. 13 is a cross-sectional view of the secondary battery shown in FIG. 1 along line III-III in some other embodiments.

[0044] FIG14 is a partially enlarged view of a secondary battery in some other embodiments.

[0045] FIG15 is a cross-sectional view of a separator of the secondary battery shown in FIG14.

[0046] FIG16 is a partial enlarged view of a secondary battery in some other embodiments.

[0047] FIG17 is a cross-sectional view of a secondary battery provided in another embodiment of the present application.

[0048] FIG18 is a cross-sectional view of a secondary battery provided in another embodiment of the present application.

[0049] FIG19 is a schematic structural diagram of an electronic device provided in one embodiment of the present application.

[0050] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0051] 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.

[0052] 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.

[0053] In addition, for the sake of brevity and clarity, the size or thickness of various components or layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A can be directly connected to element B, or there may be an intermediate element C and element A and element B can be indirectly connected to each other.

[0054] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0055] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of the described features, values, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0056] Spatial related terms, such as "on" etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" can include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, 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 teachings of the exemplary embodiments.

[0057] In this application, the relationship between parameter values ​​that is greater than, less than, or not equal to the design relationship needs to exclude the reasonable error of the measuring equipment.

[0058] When a secondary battery is overcharged, the positive electrode material releases excessive lithium ions, causing the charging voltage to exceed the charge cut-off voltage. On the one hand, the positive electrode material and the electrolyte easily undergo redox reactions under high voltage, generating a large amount of heat and causing the secondary battery to experience thermal runaway. At the same time, the occurrence of side reactions will also release a large amount of oxygen and other flammable gases, causing the shell to swell and aggravate thermal runaway. On the other hand, the excess lithium ions that are released may accumulate on the surface of the negative electrode and precipitate lithium dendrites. The lithium dendrites may pierce the separator and cause the positive and negative electrodes to short-circuit, further accelerating heat generation. Therefore, overcharging a secondary battery will reduce the reliability and service life of the secondary battery.

[0059] Referring to Figures 1 to 5 , one embodiment of the present application provides a secondary battery 100 comprising a housing 10, an electrode assembly 20 and an electrolyte (not shown) disposed within the housing 10, a first conductive plate 30, and a second conductive plate 40. As shown in Figures 2 and 3 , the electrode assembly 20 is a laminated structure comprising a plurality of first electrode sheets 21, a plurality of second electrode sheets 22, and a plurality of separators 23. In the laminated structure, the first electrode sheets 21 and the second electrode sheets 22 are alternately stacked, with one second electrode sheet 22 provided between each pair of adjacent first electrode sheets 21, and one first electrode sheet 21 provided between each pair of adjacent second electrode sheets 22. The separator 23 is disposed between adjacent first electrode sheets 21 and second electrode sheets 22 to prevent direct contact between the first electrode sheets 21 and second electrode sheets 22, thereby reducing the possibility of a contact short between the first electrode sheets 21 and second electrode sheets 22. As shown in Figures 1 and 3 , the first conductive plate 30 is electrically connected to the first electrode sheet 21. As shown in Figures 1 and 5 , the second conductive plate 40 is electrically connected to the second electrode sheet 22. The first conductive plate 30 and the second conductive plate 40 both extend from one end of the housing 10 . The first conductive plate 30 and the second conductive plate 40 are used to connect to an external device (not shown).

[0060] A three-dimensional coordinate system is established based on mutually perpendicular first direction X, second direction Y, and third direction Z. In the description of the embodiments of the present application, the first direction X is the stacking direction of the first electrode 21, the isolation membrane 23, and the second electrode 22. As shown in Figures 2 and 3, the first direction X has a first side X1 and a second side X2 opposite to the first side X1. The second direction Y is the direction in which the first conductive plate 30 or the second conductive plate 40 extends out of the housing 10, and is also the direction in which the first conductive plate 30 or the second conductive plate 40 protrudes from the electrode assembly 20. The third direction Z is the direction from the second conductive plate 40 to the first conductive plate 30.

[0061] As shown in Figures 2 and 3, the outermost pole pieces of the plurality of first pole pieces 21 are defined as the first outer pole piece 21a and the second outer pole piece 21b, respectively, and the inner pole piece of the plurality of first pole pieces 21 is defined as the first inner pole piece 21c. In the first direction X, the first inner pole piece 21c is disposed between the first outer pole piece 21a and the second outer pole piece 21b, and the first inner pole piece 21c is located on the inner side of the first outer pole piece 21a. In the first direction X, the second pole piece 22 and the isolation film 23 may also be located between the first outer pole piece 21a and the second outer pole piece 21b. The first outer pole piece 21a and the second outer pole piece 21b are located at the outermost layer of the electrode assembly 20. The first side X1 is the direction from the second pole piece 22 toward the first outer pole piece 21a, or the direction from the second outer pole piece 21b toward the first outer pole piece 21a. The second side X2 is a direction from the first outer pole piece 21 a toward the second outer pole piece 22 , or a direction from the first outer pole piece 21 a toward the second outer pole piece 21 b .

[0062] In some embodiments, the first outer pole sheet 21a and the second outer pole sheet 21b are each single-sided coated pole sheets. The first outer pole sheet 21a includes a first current collector 210 and a first active material layer 211 stacked in a first direction X. The first current collector 210 includes a first surface 210a facing the second pole sheet 22 and a second surface 210b opposite the first surface 210a. The first active material layer 211 is provided on the first surface 210a, while the second surface 210b is not provided with active material. The first inner pole sheet 21c is a double-sided coated pole sheet. The first inner pole sheet 21c includes a first active material layer 211, a second current collector 213, and a second active material layer 212 stacked in the first direction X. The second outer pole sheet 21b includes a fourth current collector 214 and a first active material layer 211 stacked in the first direction X. The first active material layer 211 of the second outer pole sheet 21b is provided on the surface of the fourth current collector 214 facing the second pole sheet 22. The first pole sheet 21 may be a positive electrode. Correspondingly, the first current collector 210, the second current collector 213, and the fourth current collector 214 can all be positive electrode current collectors, and the first active material layer 211 and the second active material layer 212 can all be positive electrode active material layers. The active material contained in the first active material layer 211 of the second outer pole piece 21b can be the same as or different from the active material contained in the first active material layer 211 of the first outer pole piece 21a. The active material contained in the first active material layer 211 or the second active material layer 212 of the first inner pole piece 21c can be the same as or different from the active material contained in the first active material layer 211 of the first outer pole piece 21a. By providing the first outer pole piece 21a and the second outer pole piece 21b as single-sided coated pole pieces, energy density waste is reduced. When the first pole piece 21 is a positive electrode pole piece, the possibility of excessive lithium ion accumulation and lithium precipitation due to the failure of the second pole piece 22 to embed the corresponding lithium ions (e.g., lithium ions released from the active material when the second surface 210b is provided with active material) can also be reduced.

[0063] Referring further to FIG. 4 , in some embodiments, in the first direction X, the thickness of the first current collector 210 is a first thickness h1, and the thickness of the second current collector 213 is a second thickness h2, where 1.2 ≤ h1 / h2 ≤ 2.5. By setting a lower limit for h1 / h2, the thickness h1 of the first current collector 210 is increased. This increases the strength of the outermost first pole piece 21a, thereby forming a protective layer that reduces the likelihood of damage to the electrode assembly 20 from mechanical abuse (such as extrusion, needle puncture, etc.) and improves the electrode assembly 20's ability to withstand mechanical impact. Furthermore, the greater thickness h1 of the first current collector 210 compared to the thickness h2 of the second current collector 213 reduces the likelihood of curling or warping of the first current collector 210 due to inconsistent tension on opposite sides of the single-sided coating. Furthermore, by setting an upper limit for h1 / h2, the impact of excessively large thickness h1 on energy density is reduced. Furthermore, the thickness of the fourth current collector 214 of the second outer pole piece 21 b may be set to be greater than the thickness of the second current collector 213 .

[0064] The second electrode sheet 22 may be a double-sided coated electrode sheet. The second electrode sheet 22 includes a stacked third active material layer 221, a third current collector 220, and a fourth active material layer 222. The third active material layer 221 is disposed across the separator 23 toward the first active material layer 211, and the fourth active material layer 222 is disposed across the separator 23 toward the second active material layer 212. The second electrode sheet 22 may be a negative electrode electrode sheet. Correspondingly, the third current collector 220 may be a negative electrode current collector, and the third active material layer 221 and the fourth active material layer 222 may both be negative electrode active material layers. To reduce the possibility of lithium plating on the second electrode sheet 22, the edge of the second electrode sheet 22 in the second direction Y may extend beyond the edge of the first electrode sheet 21 in the second direction Y, so that the second electrode sheet 22 forms an overhang area 2200 (indicated in FIG. 3 ). The electrode assembly 20 may be provided with a plurality of first electrode tabs 51 and a plurality of second electrode tabs 52. Multiple first electrode tabs 51 are integrally connected to the first current collector 210 and the second current collector 213. Multiple second electrode tabs 52 are integrally connected to the third current collector 220. The first electrode tabs 51 are welded to the first conductive plate 30 by transfer welding, and the second electrode tabs 52 are welded to the second conductive plate 40 by transfer welding.

[0065] The positive electrode current collector may be made of aluminum foil or nickel foil, and the negative electrode current collector may be made of at least one of copper foil, nickel foil or carbon-based current collector. The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly embed and deintercalate lithium ions (lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material is selected from lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4). The negative electrode active material layer contains a negative electrode active material, and adopts a negative electrode active material known in the art that can perform reversible deintercalation of active ions, which is not limited in this application. For example, it can be a combination of one or more including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium. Among them, graphite can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys.

[0066] The separator 23 has a porous structure and includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in improving short circuits and can improve the stability of the secondary battery 100 through a shutdown effect.

[0067] Please refer to Figure 6. In some other embodiments, the electrode assembly 20 may also include an isolation membrane 23. The isolation membrane 23 is an integrated structure and is formed into a Z-shaped structure by alternating forward and reverse bending and folding. The isolation membrane 23 includes a plurality of main body segments 233 stacked and a connecting segment 234 connecting the ends of two adjacent main body segments 233. Each main body segment 233 is arranged between adjacent first pole pieces 21 and second pole pieces 22. Due to the provision of the connecting segment 234, the isolation membrane 23 can restrain at least a portion of the first pole piece 21 and at least a portion of the second pole piece 22, thereby reducing the possibility of the first pole piece 21 and the second pole piece 22 being excessively bulged and broken under the action of high-temperature gas when the secondary battery 100 is overcharged.

[0068] In some embodiments, the housing 10 may be a packaging bag encapsulated with an encapsulating film, and the secondary battery 100 is a soft-pack battery. As shown in Figures 1 and 3, the housing 10 includes a main body 11 for accommodating the electrode assembly 20 and an encapsulating portion 12 connected to the main body 11. Both the first conductive plate 30 and the second conductive plate 40 extend from the encapsulating portion 12. The main body 11 includes a first end surface 110 connected to the encapsulating portion 12. In some embodiments, when viewed from a third direction Z, the first end surface 110 extends from the encapsulating portion 12 toward a first side X1. Figure 7 is a schematic diagram of the structure of the secondary battery 100 before encapsulation. As shown in Figure 7, the housing 10 includes a first housing 101 and a second housing 102 arranged opposite each other in the first direction X. The first housing 101 includes a first housing section 101a and a second housing section 101b connected to each other. The second housing section 101b is surrounded on three sides by the first housing section 101a. The second housing 102 includes a third housing section 102a and a fourth housing section 102b connected to each other. The third housing section 102a surrounds the fourth housing section 102b on three sides. The housing 10 is enclosed by a first housing 101 and a second housing 102. The second housing section 101b of the first housing 101 is provided with a first recess R1, while the second housing 102 is a flat plate. During fabrication, the electrode assembly 20 can be placed in the first recess R1 of the first housing 101, and the second housing 102 is placed over the first housing 101. Once the first and second housings 101, 102 are enclosed, the first recess R1 is sealed by the second housing section 101b of the first housing 101, and the first and third housing sections 101a, 102a, are connected to enclose the main body 11.

[0069] As shown in FIG3 , in some embodiments, the first conductive plate 30 is bent as a whole. The first conductive plate 30 includes a first conductive region 31 and a second conductive region 32 connected to each other. The first conductive region 31 is provided in the packaging portion 12 and extends from the packaging portion 12 to the housing 10 along the second direction Y. The second conductive region 32 is electrically connected to the first electrode 21 (e.g., the second conductive region 32 is connected to the first electrode 21 through the first electrode tab 51). The second conductive region 32 is bent relative to the first conductive region 31. The second conductive region 32 includes a first end 321 connected to the first conductive region 31 and a second end 322 arranged opposite to the first end 321. The second conductive region 32 extends from the first end 321 to the first side X1. Therefore, when viewed from the second direction Y, the second conductive region 32 overlaps with the first end face 110. The second conductive region 32 can extend along the first direction X or can be arranged tilted relative to the first direction X.

[0070] As shown in FIG8 , in other embodiments, when viewed from the third direction Z, the first end surface 110 may further include a first portion 111 extending from the packaging portion 12 toward the first side X1 and a second portion 112 extending from the packaging portion 12 toward the second side X2. The packaging portion 12 is located at the junction of the first portion 111 and the second portion 112 in the first direction X. The length W1 of the first portion 111 in the first direction X is less than the length W2 of the second portion 112 in the first direction X. For example, the first portion 111 is the deep groove surface of the housing 10, and the second portion 112 is the shallow groove surface of the housing 10. FIG9 is a schematic diagram of the structure of the secondary battery 100 before packaging. As shown in FIG9 , the fourth housing region 102b of the second housing 102 is provided with a second recess R2. When the first and second housings 101 and 102 are packaged, the second housing region 101b and the fourth housing region 102b together form the main body 11 for accommodating the electrode assembly 20.

[0071] As shown in Figures 10 and 11, in some embodiments, the materials of the first shell 101 and the second shell 102 can both be multilayer sheets. As shown in Figure 10, the first shell 101 may include a first protective layer 1011, a first metal layer 1012, and a first polymer layer 1013 stacked in sequence. Compared to the first protective layer 1011, the first polymer layer 1013 is closer to the electrode assembly 20. The material of the first protective layer 1011 can be a polymer resin, which can be used to protect the first metal layer 1012 and reduce the possibility of damage to the first metal layer 1012 due to external forces. It can also delay the infiltration of air from the external environment, maintaining a normal operating environment inside the secondary battery 100. In some embodiments, the material of the first protective layer 1011 can be selected from at least one of polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyamide, and polyimide. The first metal layer 1012 can be used to delay the infiltration of moisture from the external environment and reduce damage to the electrode assembly 20 caused by external forces. In some embodiments, the first metal layer 1012 may be an aluminum foil layer or a steel foil layer. The first polymer layer 1013 has the property of melting upon heating, can be used for packaging, and can reduce the possibility of the multilayer sheet being dissolved or swollen by the organic solvent in the electrolyte. The first polymer layer 1013 can also be used to reduce the possibility of corrosion of the metal layer caused by contact between the electrolyte in the electrolyte and the first metal layer 1012. In some embodiments, the first polymer layer 1013 comprises a polymer material, which can be selected from at least one of polypropylene, propylene copolymer, polyethylene, and polymethyl methacrylate. As shown in Figure 11, the second housing 102 may include a second protective layer 1021, a second metal layer 1022, and a second polymer layer 1023 stacked in sequence. It will be understood that when the first housing 101 and the second housing 102 are formed by folding a single packaging film, the materials of the second protective layer 1021, the second metal layer 1022, and the second polymer layer 1023 are identical to those of the first protective layer 1011, the first metal layer 1012, and the first polymer layer 1013, respectively, and are not described again here. When preparing the shell 10 , a certain temperature and pressure can be applied to the first shell area 101a and the third shell area 102a by using the sealing head of the packaging equipment to melt and bond the first polymer layer 1013 and the second polymer layer 1023 to form the packaging part 12 .

[0072] In other embodiments, the housing 10 may also be a metal housing, such as a steel housing or an aluminum housing.

[0073] As shown in FIG4 , when viewed from the third direction Z, the first outer pole piece 21a includes a first region 2101 and a second region 2102 connected in the second direction Y. When viewed from the third direction Z, the first region 2101 includes a first end 2101a connected to the second region 2102 and a second end 2101b disposed opposite the first end 2101a in the second direction Y. The first region 2101 extends away from the first end 2101a in the second direction Y, and the second end 2101b is further away from the second pole piece 22 in the first direction X than the first end 2101a. In the present application, an extension line S1 can be formed by extending outward along the outline of the first region 2101, and an extension line S2 can be formed along the second direction Y for the second region 2102. The intersection of the extension lines S1 and S2 is the first end 2101a. The first end 2101a can be regarded as the dividing point between the first region 2101 and the second region 2102 when viewed from the third direction Z. The fact that the second end 2101b is positioned opposite the first end 2101a in the second direction Y does not necessarily mean that the line S3 connecting the first end 2101a and the second end 2101b must extend along the second direction Y. In the description of the embodiments of the present application, when the second end 2101b is described as being positioned opposite the first end 2101a in the second direction Y, it means that the line S3 connecting the first end 2101a and the second end 2101b may deviate from the second direction Y while ensuring that the objectives of the present invention are achieved. The second region 2102 may include a curved portion when viewed from the third direction Z. With reference to Figures 3 and 4 , in some embodiments, the first region 2101 is further away from the first conductive plate 30 than the second region 2102 in the second direction Y. This reduces the possibility of the first tab 51 entering the space between the first region 2101 and the second electrode sheet 22 adjacent to the first outer electrode sheet 21a when the electrode assembly 20 moves within the housing 10 along the second direction Y (e.g., if the secondary battery 100 is dropped or vibrated), thereby reducing the possibility of a contact short circuit.

[0074] As shown in Figure 3 , when the first end surface 110 extends from the packaging portion 12 toward the first side X1, the first region 2101 extends from the first end 2101a toward the first side X1. When viewed from the second direction Y, the first region 2101 may overlap with the first end surface 110. The first region 2101 of the first outer pole piece 21a is at least partially located within the first recess R1 formed by the extension of the first end surface 110. This reduces friction on the first outer pole piece 21a when the second housing 102 is placed over the first housing 101, thereby reducing the possibility of deformation of the first outer pole piece 21a due to friction. As shown in Figure 8 , when the first end surface 110 includes a first portion 111 extending from the packaging portion 12 toward the first side X1 and a second portion 112 extending from the packaging portion 12 toward the second side X2, the first region 2101 extends from the first end 2101a toward the first side X1. When viewed from the second direction Y, the first region 2101 may overlap with the first portion 111. This can also reduce the friction on the first outer pole piece 21 a when the second housing 102 is covered on the first housing 101 , thereby reducing the possibility of deformation of the first outer pole piece 21 a due to friction.

[0075] As shown in Figure 4, the second electrode sheet 22, adjacent to the first outer electrode sheet 21a, includes a third region 2201 and a fourth region 2202 connected in the second direction Y. When viewed from the first direction X, the first region 2101 and the third region 2201 are disposed opposite each other, and the first and third regions 2101 and 2201 overlap. When viewed from the first direction X, the second region 2102 and the fourth region 2202 are disposed opposite each other, and the second and fourth regions 2102 and 2202 overlap. Therefore, when the secondary battery 100 is charged, lithium ions deposited from the first region 2101 can be embedded in the third region 2201, and lithium ions deposited from the second region 2102 can be embedded in the fourth region 2202. In the present application, a dotted line S4 can be drawn through the first end 2101a and parallel to the first direction X. When viewed from the third direction Z, the intersection of the dotted line S4 and the second electrode sheet 22 is the boundary between the third and fourth regions 2201 and 2202. Because the first region 2101 of the first outer pole piece 21a extends away from the second direction Y, the distance between the first region 2101 and the third region 2201 in the first direction X is greater than the distance between the second region 2102 and the fourth region 2202, thereby extending the ion transmission path between the first region 2101 and the third region 2201. The distance between the first region 2101 and the third region 2201 is not constant; the distance between the first end 2101a of the first region 2101 and the third region 2201 is less than the distance between the second end 2101b and the third region 2201. In some embodiments, the third region 2201 includes a first subregion 2203 and a second subregion 2204, connected in the second direction Y. When viewed from the third direction Z, the second subregion 2204 includes a third end 2204a connected to the first subregion 2203 and a fourth end 2204b opposite the third end 2204a. The first subregion 2203 overlaps with the first region 2101 in the first direction X. When viewed from the first direction X, the second subarea 2204 extends from the third end 2204a to beyond the first region 2101. The second subarea 2204 is the extended region 2200 of the second pole piece 22 adjacent to the first outer pole piece 21a. In the present application, a dotted line S5 can be drawn along the first direction X at the second end 2101b. When viewed from the third direction Z, the intersection of the dotted line S5 and the second pole piece 22 is the third end 2204a. The third end 2204a is also the dividing point between the first subarea 2203 and the second subarea 2204 when viewed from the third direction Z.

[0076] The present invention extends outwardly by setting the first region 2101 of the first external pole piece 21a to deviate from the second direction Y, thereby extending the ion transmission path between the first region 2101 and the third region 2201 and increasing the transmission impedance. When the secondary battery 100 is overcharged, the third region 2201 can be used as a sacrificial position during overcharging to preferentially deposit lithium, thereby reducing the probability or degree of lithium deposition at other locations in the second pole piece 22 adjacent to the first external pole piece 21a, and also reducing the probability or degree of lithium deposition at other second pole pieces 22, thereby reducing the occurrence of thermal runaway. Moreover, since the distance between the first region 2101 and the third region 2201 is large, the possibility of lithium dendrites deposited in the third region 2201 contacting the first region 2101 is reduced even after piercing the isolation membrane 23, thereby reducing the possibility of lithium dendrites contacting and short-circuiting the first external pole piece 21a. In addition, when the secondary battery 100 is overcharged and gas is generated near the first region 2101, the contact interface of the adjacent first external pole piece 21a, the isolation membrane 23 and the second pole piece 22 can be stretched open by the action of the gas, which is conducive to further reducing the possibility of lithium dendrites precipitated in the third region 2201 and the first external pole piece 21a contacting and short-circuiting, and is also conducive to the timely dissipation of heat in the electrode assembly 20. Therefore, the present application can improve the overcharge resistance of the secondary battery 100, thereby improving the reliability and service life of the secondary battery 100. Referring to Figure 13, in some embodiments, in order to further improve the overcharge resistance of the secondary battery 100, the second external pole piece 21b can also be provided with the same structure as the first external pole piece 21a, such as providing a region extending outward from the second direction Y on the second external pole piece 21b.

[0077] Referring to FIG. 12 , in other embodiments, the first region 2101 may be positioned closer to the first conductive plate 30 than the second region 2102 in the second direction Y. Because there is a certain space between the first end surface 110 and the electrode assembly 20 to accommodate the first tab 51 and a portion of the first conductive plate 30, positioning the first region 2101 closer to the first conductive plate 30 facilitates the release of gas generated near the first region 2101 into the space when the secondary battery 100 is overcharged, thereby reducing the possibility of excessive gas accumulation and causing the first region 2101 to further deviate from the second direction Y. This reduces the impact of a significant deviation of the first region 2101 on the energy density and surface smoothness of the secondary battery 100, reduces the possibility of active material in the first region 2101 easily falling off and causing a short circuit, and also reduces the possibility of an increase in active material in the first region 2101 that is unable to fully utilize its capacity.

[0078] In some embodiments, the mass of the active material provided on the first current collector 210 per unit area is G (ie, the weight of the first active material layer 211 per unit area is G), and G≤23 mg / cm 2. Therefore, the possibility of the active material in the first region 2101 falling off can be reduced, and the first region 2101 of the first outer pole sheet 21a can be easily bent during preparation (i.e., extending away from the second direction Y). In addition, it can be understood that when the upper limit value of h1 / h2 is set, the possibility of the thickness h1 being too large can be reduced, thereby also making the first region 2101 of the first outer pole sheet 21a easily bent during preparation. Among them, the measurement steps of G can be: (1) discharging the secondary battery 100 to 2.75V at 0.2C, disassembling the secondary battery 100, cleaning and drying; (2) using a balance to weigh the first outer pole sheet 21a of a certain area A, and the weight is recorded as G1; (3) using a solvent to wash off the active material on the first current collector 210 of the first outer pole sheet 21a, drying, and measuring the weight of the first current collector 210, and recording it as G2; (4) calculating G by the following formula: G = (G1-G2) / A.

[0079] As shown in FIG4 , in some embodiments, when viewed from the third direction Z, the angle α between the line S3 connecting the first end 2101a and the second end 2101b and the second direction Y satisfies the following: 1°≤α≤12°. By limiting the lower limit of the angle α, the first region 2101 can be deviated from the second direction Y by a certain range, thereby extending the ion transmission path between the first region 2101 and the third region 2201. When the secondary battery 100 is overcharged, the third region 2201 can serve as a sacrificial location for preferential lithium deposition. Furthermore, the deviation of the first region 2101 from the second direction Y by a certain range also reduces the possibility of lithium dendrites deposited in the third region 2201 contacting the first region 2101. By limiting the upper limit value of the angle α, the impact of the first region 2101 on the energy density and appearance smoothness of the secondary battery 100 when the deviation degree of the first region 2101 is large is reduced. The possibility that the active material in the first region 2101 will easily fall off and cause a short circuit when the deviation degree of the first region 2101 is large is also reduced. The possibility that the active material in the first region 2101 will be difficult to play a capacity role when the deviation degree of the first region 2101 is large is also reduced.

[0080] Furthermore, in some embodiments, 3°≤α≤10°. By further limiting the lower limit of the angle α, the ion transmission path between the first region 2101 and the third region 2201 is further extended, so that when the secondary battery 100 is overcharged, the third region 2201 can serve as a sacrificial location for preferential lithium deposition during overcharge, and the possibility of lithium dendrites deposited in the third region 2201 contacting the first region 2101 is further reduced. By further limiting the upper limit of the angle α, the impact of the first region 2101 on the energy density and appearance smoothness of the secondary battery 100 is further reduced, and the possibility of active materials in the first region 2101 easily falling off and causing a short circuit is further reduced. The possibility of an increase in active materials in the first region 2101 that are unable to exert their capacity is further reduced.

[0081] The steps for measuring α may be: (1) performing two-dimensional projection and scanning testing on the secondary battery 100 from a third direction Z using X-rays. The instrument may be an instrument or device known to those skilled in the art (e.g., GE Phoenix vtomex S device) to obtain a CT image; and (2) directly measuring the value of α using a caliper or other suitable measuring tool.

[0082] The measurement steps of α can also be as follows: (1) discharge the secondary battery 100 at 0.2C to 2.75V; (2) prepare a resin composition, which is prepared by mixing a crystal glue resin matrix (such as epoxy resin), a catalyst and a curing agent in a certain proportion; (3) pour the resin composition into a mold, and cut the shell 10 of the secondary battery 100 and place it in the mold at an angle to reduce the bubbles that may remain at the bottom of the secondary battery 100, and then continue to slowly pour the resin composition so that the secondary battery 100 is completely immersed in the resin composition. The resin composition slowly flows into the shell 10 through the cutout of the shell 10; (4) the secondary battery 100 is adjusted to a horizontal position, excess bubbles are discharged, and then the secondary battery 100 is allowed to stand until the resin composition solidifies; (5) the secondary battery 100 is cut along a cross section perpendicular to the third direction Z and the cut surface is polished to obtain a cross section of the secondary battery 100; (6) the angle α between the line S3 connecting the first end 2101a and the second end 2101b and the second direction Y is marked on the cross section, and the value of α is directly measured using a caliper or other suitable measuring tool.

[0083] In some embodiments, as shown in FIG4 , when viewed from the third direction Z, the length of the first region 2101 extending from the first end 2101a to the second end 2101b is a first length L1 (when the first region 2101 includes a curved portion, L1 refers to the arc length of the first region 2101). As shown in FIG3 , the length of the second region 2102 in the second direction Y is a second length L2, and 7≤L2 / L1≤29. By limiting the lower limit of L2 / L1, the impact of the first region 2101 on the energy density and appearance smoothness of the secondary battery 100 when the above ratio is too small (e.g., the length L1 is too large, resulting in a large deviation of the first region 2101) is reduced, and the possibility of an increase in active material in the first region 2101 that makes it difficult to play a capacity role is also reduced. By limiting the upper limit of L2 / L1, the possibility of the third region 2201 failing to significantly reduce the probability or degree of lithium deposition in other locations during overcharging when the above ratio is too large (e.g., the length L1 is too small, the area of ​​the first region 2101 is too small) is reduced.

[0084] Furthermore, in some embodiments, 11≤L2 / L1≤19, thereby further reducing the impact of the first region 2101 on the energy density and appearance smoothness of the secondary battery 100, further reducing the possibility of an increase in active material in the first region 2101 that is unable to exert its capacity, and further reducing the possibility that the third region 2201 fails to significantly reduce the probability or extent of lithium deposition in other locations during overcharging. The lengths L1 and L2 can be measured using a similar measurement procedure as for the angle α.

[0085] As shown in FIG14 , in some other embodiments, the secondary battery 100 may further include a first layer 60 comprising an insulating material disposed on the second surface 210 b. The first layer 60 is used to dissipate heat generated at the first external pole piece 21 a during overcharging of the secondary battery 100, thereby reducing the temperature of the electrode assembly 20 and improving the overcharge resistance of the secondary battery 100. When the first pole piece 21 is a negative electrode and the metal layer of the housing 10 is an aluminum foil layer, the first layer 60 can also insulate the first current collector 210 from the housing 10, thereby reducing the possibility of burrs on the edge of the first current collector 210 (such burrs may be generated during cutting of the first current collector 210, but this is not a limitation in this application) piercing the polymer layer of the housing 10 and short-circuiting with the aluminum foil layer, thereby causing excessive heat generation in the secondary battery 100. It can also reduce the possibility of lithium ions released from the first external pole piece 21 a during charging reacting at the contact point between the first current collector 210 and the aluminum foil layer to form an aluminum-lithium alloy (AlLi), thereby causing corrosion of the aluminum foil layer. The insulating material of the first layer 60 can be selected from at least one of an inorganic ceramic material and a binder. Inorganic ceramic materials include at least one of hafnium dioxide, strontium titanate, tin dioxide, cesium oxide, magnesium oxide, nickel oxide, calcium oxide, barium oxide, zinc oxide, zirconium oxide, yttrium oxide, aluminum oxide, titanium oxide, silicon dioxide, boehmite, magnesium hydroxide, or aluminum hydroxide. The binder can be selected from at least one of styrene-butadiene rubber, polypropylene, polyacrylic acid, acrylates and their derivatives, polyvinyl alcohol, natural rubber, or modified rubber. Specifically, the first layer 60 can be a single-sided tape, a double-sided tape, or a hot melt adhesive. The first layer 60 can be bonded to the second surface 210b and cover the entire second surface 210b. In other embodiments, the first layer 60 can be distributed on the second surface 210b in the form of dots, strips, or other irregular shapes.

[0086] In some embodiments, the thickness of the first current collector 210 is defined as a first thickness h1, and the thickness of the first layer 60 is defined as a third thickness h3 in the first direction X, where h3 < 2h1. Therefore, when the thickness h3 is too large, the impact of the first layer 60 on the energy density of the secondary battery 100 is reduced. When the thickness h3 is too small, the first layer 60 is also less likely to be pierced by burrs on the edge of the first current collector 210 due to reduced heat dissipation.

[0087] In some embodiments, the first layer 60 can be a double-sided adhesive or hot melt adhesive, which bonds the second surface 210b to the housing 10. Therefore, the first layer 60 can also conduct the heat generated at the first external electrode sheet 21a when the secondary battery 100 is overcharged to the housing 10, so that this heat is dissipated to the outside through the housing 10, improving the heat dissipation effect, thereby further improving the overcharge resistance of the secondary battery 100.

[0088] As shown in FIG4 or FIG14, in some embodiments, the isolation film 23 adjacent to the first external pole piece 21a is bonded to the second region 2102, thereby further reducing the possibility of a short circuit between the first external pole piece 21a and the adjacent second pole piece 22. Referring to FIG15, in some specific embodiments, the isolation film 23 may include a first adhesive layer 231, a base layer 230, and a second adhesive layer 232 stacked in the first direction X. The first adhesive layer 231, the base layer 230, and the second adhesive layer 232 all have a porous structure. The isolation film 23 is bonded to the second region 2102 via the first adhesive layer 231. The base layer 230 may be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. The first adhesive layer 231 and the second adhesive layer 232 respectively include an adhesive, and the adhesive includes a homopolymer or a copolymer formed by a polymer monomer, and the polymer monomer includes at least one of vinylidene fluoride, hexafluoropropylene, acrylic acid, acrylic ester, butadiene, styrene, acrylonitrile, ethylene, chlorostyrene, fluorostyrene or propylene.

[0089] In some embodiments, the separator 23 adjacent to the first external pole piece 21a may also be bonded to the third region 2201. For example, the separator 23 adjacent to the first external pole piece 21a may be bonded to the third region 2201 via a second adhesive layer 232, thereby further reducing the possibility of a short circuit between the first external pole piece 21a and the adjacent second pole piece 22. It is understood that when the secondary battery 100 is overcharged and gas is generated near the first region 2101, since the separator 23 has a porous structure, the gas may pass through the separator 23 and expand the contact interface between the adjacent first external pole piece 21a, the separator 23, and the second pole piece 22, thereby reducing the possibility of a short circuit between lithium dendrites precipitated in the third region 2201 and the first external pole piece 21a, and also facilitating the timely dissipation of heat within the electrode assembly 20.

[0090] Referring to FIG. 16 , in some other embodiments, when viewed from the third direction Z, the second partition 2204 extends from the third end 2204a in a direction away from the first external pole piece 21a. The extension direction of the second partition 2204 is inclined relative to the second direction Y. By extending the second partition 2204 from the third end 2204a in a direction away from the first external pole piece 21a, the ion transmission path between the third region 2201 and the first region 2101 is extended, thereby reducing the degree of deviation of the first region 2101. This reduces the impact of a large deviation of the first region 2101 on the energy density and appearance smoothness of the secondary battery 100. This also reduces the possibility of active material in the first region 2101 easily falling off and causing a short circuit when the first region 2101 is significantly deviated. It also reduces the possibility of an increase in active material in the first region 2101 that hinders its capacity function when the first region 2101 is significantly deviated.

[0091] Please refer to Figure 17. In other embodiments, the first electrode 21 can also be set as a negative electrode and the second electrode 22 can be set as a positive electrode. In this case, since the ion transmission path between the first region 2101 and the third region 2201 is extended, when the secondary battery 100 is overcharged, the first region 2101 can be used as a sacrificial position during overcharging to preferentially deposit lithium, thereby reducing the possibility or degree of lithium deposition at other locations of the first external electrode 21a, and also reducing the possibility or degree of lithium deposition at other first electrode 21 outside the first external electrode 21a. Moreover, since the distance between the first region 2101 and the third region 2201 is large, the possibility of lithium dendrites deposited in the first region 2101 contacting the third region 2201 is reduced even after piercing the isolation membrane 23, thereby reducing the possibility of lithium dendrites contacting the third region 2201 and short-circuiting.

[0092] Please refer to Figure 18. In some other embodiments, the first outer pole piece 21a can also be a double-sided coated pole piece. The first outer pole piece 21a includes a first active material layer 211, a first current collector 210, and a second active material layer 212 stacked in the first direction X. The first current collector 210 includes a first surface 210a facing the second pole piece 22 and a second surface 210b opposite to the first surface 210a. The first active material layer 211 is provided on the first surface 210a, and the second active material layer 212 is provided on the second surface 210b. At this time, the mass of the active material provided on the first current collector 210 per unit area is G, and G≤23 mg / cm 2 Specifically, the total mass of the first active material layer 211 and the second active material layer 212 provided on the first current collector 210 per unit area is less than 23 mg / cm 2 .

[0093] The secondary battery 100 of the present application may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0094] Referring to FIG. 19 , one embodiment of the present application further provides an electronic device 1 comprising the aforementioned secondary battery 100. The electronic device 1 is powered by the aforementioned secondary battery 100, and the secondary battery 100 has a high overcharge resistance. In one embodiment, the electronic device 1 of the present application may be, 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 power supply, a motor, a car, 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, etc.

[0095] The present application is described in detail below through specific examples and comparative examples. A soft-pack lithium-ion secondary battery 100 is used as an example and described in conjunction with specific testing methods. Those skilled in the art will understand that the preparation methods described herein are merely examples, and any other suitable preparation methods are within the scope of this application.

[0096] Examples 1-14

[0097] Preparation of the first pole piece 21: The active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of an aluminum foil with a thickness of 12μm, and an empty foil area is reserved at the edge of the aluminum foil. Drying at 90°C obtains an active material layer with a thickness of 100μm. The single-sided coated first pole piece 21 is subsequently used as the first outer pole piece 21a and the second outer pole piece 21b. When preparing other double-sided coated first pole pieces 21, repeat the above steps on the other surface of the aluminum foil. Then, the excess empty foil area is removed by laser die-cutting to obtain the first pole piece 51.

[0098] Preparation of the second electrode sheet 22: Mix the negative electrode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, prepare a slurry with a solid content of 70wt%, and stir evenly. The slurry is evenly coated on one surface of a copper foil with a thickness of 10μm, leaving an empty foil area at the edge of the copper foil. Dry at 110°C to obtain an active material layer with a thickness of 150μm. Repeat the above steps on the other surface of the foil. Then, the excess empty foil area is removed by laser die-cutting to obtain the second electrode tab 52.

[0099] Preparation of electrolyte: In a dry argon atmosphere, first mix the organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) in a mass ratio of 1:1, then add 5% by mass of fluoroethylene carbonate (FEC), 5% by mass of 1,3-propane sultone (PS), and lithium salt lithium hexafluorophosphate (LiPF6) to the organic solvent, dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0100] Preparation of the electrode assembly 20: The first electrode sheet 21, separator 23, and second electrode sheet 22, excluding the first external electrode sheet 21a, are stacked in sequence. The separator 23 is a 15μm thick polyethylene (PE) film. The resulting structure is then hot-pressed at 60°C and 1 MPa for 10 seconds. The first and second external electrode sheets 21a and 21b are then stacked on opposite sides of the structure. The first external electrode sheet 21a is then heated at 150°C for 60 seconds at the location where it is to be bent, causing the first region 2101 to bend outward, away from the second direction Y. Bend-related parameters are reported in Tables 1 and 2. The angle α, L2 / L1, and other values ​​can be controlled by adjusting the temperature and heating time of the curved rollers. The second region 2102 of the first external electrode sheet 21a is then hot-pressed at 60°C and 1 MPa for 10 seconds, bonding the second region 2102 to the separator 23. The second outer pole piece 21 b is subjected to a hot pressing process through similar steps.

[0101] Assembly of the secondary battery 100: The first and second tabs 51, 52 are respectively welded to the first and second conductive plates 30, 40 via transfer welding. The first conductive plate 30 is made of aluminum, and the second conductive plate 40 is made of nickel. A 150μm thick aluminum-plastic film with cavities punched and formed is placed in an assembly fixture, with the cavities facing upward. The electrode assembly 20 is placed in the cavities, and electrolyte is injected into the cavities of the aluminum-plastic film. The first and second conductive plates 30, 40 are then extended out of the film. A special-shaped sealing head is used to apply pressure to the edges of the aluminum-plastic film to form the encapsulation portion 12. The film is then filled with electrolyte, formed, and encapsulated to complete the battery.

[0102] Comparative Example

[0103] The difference from the first embodiment is that the outermost first pole piece 21 is not bent outward.

[0104] 20 batteries of each embodiment and comparative example were taken for overcharge test and energy density test respectively.

[0105] The overcharge test steps include: 1) charging the battery at a constant current of 0.5C to 4.48V at 25°C, and then charging it at a constant voltage to 0.05C; 2) after covering the battery with 10mm thick white foam (the foam must cover the entire surface of the battery), placing the battery in an overcharge and overdischarge tester (manufacturer: Arbin, model: BT-ML-30V15A), and then charging the battery at a constant current of 1C to 18.5V, and then charging it at a constant voltage for 2 hours; 3) monitoring the battery's open circuit voltage and temperature during overcharge. After the overcharge is completed, measure the battery weight and observe whether the battery smokes or catches fire. If not, the battery passes the test. The number of batteries that pass the test is then counted, and the results are recorded in Table 1.

[0106] The energy density test procedure includes the following: 1) Charge the battery at a constant current of 0.5C to 4.4V at 25°C, then charge it at a constant voltage of 4.4V to 0.025C, let it rest for 5 minutes, and then discharge it at a discharge rate of 0.1C to 3.0V. Let it rest for 5 minutes, and measure the 0.1C discharge capacity C. After the charge and discharge steps are completed, measure the length (L), width (W), and thickness (H) of the battery. Battery energy density = C / (L × W × H). The test results are recorded in Table 2.

[0107] Table 1

[0108] Note: Overcharge pass rate X / 20 means that among the 20 samples tested, the number of samples that passed the test is X.

[0109] It can be seen from the data in Table 1 that, compared with the comparative example, in Example 1, the first region 2101 of the first outer electrode sheet 21 a is bent outwardly away from the second direction Y, thereby improving the overcharge pass rate.

[0110] Table 2

[0111] It can be seen from the data in Table 2 that among Examples 1-8, Examples 1 and 4-6 satisfy 3°≤α≤10°, so the overcharge pass rate and energy density are both high; the angle α of Example 2 is smaller, so when the secondary battery 100 is overcharged, lithium deposition does not occur preferentially in the third region 2201, and the possibility of lithium dendrites deposited in the third region 2201 contacting the first region 2101 is increased, so the overcharge pass rate is relatively reduced; the angle α of Examples 7-8 is larger, so the energy density is reduced.

[0112] In Examples 4, 9-14, Examples 4 and 10-13 satisfy 7≤L2 / L1≤29, so the overcharge pass rate and energy density are both high; the L2 / L1 ratio of Example 14 is large, so lithium deposition does not preferentially occur in the third region 2201 when the secondary battery 100 is overcharged, so the overcharge pass rate is relatively reduced; the L2 / L1 ratio of Example 9 is small, so the energy density is reduced.

[0113] 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 in the housing, and a first conductive plate, wherein the electrode assembly is a laminated structure, the electrode assembly comprises a first electrode sheet, a separator, and a second electrode sheet stacked in sequence in a first direction, the first conductive plate is connected to the first electrode sheet, and the first conductive plate extends from the housing along a second direction perpendicular to the first direction, characterized in that: The first pole piece includes a first outer pole piece, which is the outermost layer of the electrode assembly. When viewed from a third direction perpendicular to both the first direction and the second direction, the first outer pole piece includes a first region and a second region connected in the second direction; Observed from the third direction, the first region includes a first end connected to the second region and a second end arranged opposite to the first end in the second direction, the first region extends from the first end away from the second direction, and the second end is farther away from the second pole piece in the first direction than the first end.

2. The secondary battery according to claim 1, wherein: When viewed from the third direction, an angle α between a line connecting the first end and the second end and the second direction satisfies: 1°≤α≤12°.

3. The secondary battery according to claim 2, characterized in that: 3°≤α≤10°。 4. The secondary battery according to claim 1, wherein: Observed from the third direction, the length of the first region extending from the first end to the second end is a first length, the length of the second region in the second direction is a second length, and the ratio of the second length to the first length is greater than or equal to 7 and less than or equal to 29.

5. The secondary battery according to claim 4, characterized in that: A ratio of the second length to the first length is greater than or equal to 11 and less than or equal to 19.

6. The secondary battery according to claim 1, wherein: In the second direction, the first region is farther away from the first conductive plate than the second region.

7. The secondary battery according to claim 1, wherein: In the second direction, the first region is closer to the first conductive plate than the second region.

8. The secondary battery according to claim 1, wherein: The first direction has a first side from the second pole piece toward the first outer pole piece; the shell is a packaging bag and includes a main body portion for accommodating the electrode assembly and a packaging portion connected to the main body portion, and the first conductive plate extends from the packaging portion to the shell; the main body portion includes a first end face connected to the packaging portion, and when observed from the third direction, the first end face extends from the packaging portion to the first side; when observed from the third direction, the first region extends from the first end to the first side.

9. The secondary battery according to claim 1, wherein: The first direction has a first side from the second pole piece toward the first outer pole piece and a second side opposite to the first side; the shell is a packaging bag and includes a main body for accommodating the electrode assembly and a packaging part connected to the main body, and the first conductive plate extends from the packaging part to the shell; the main body includes a first end surface connected to the packaging part, and when viewed from the third direction, the first end surface includes a first part extending from the packaging part to the first side and a second part extending from the packaging part to the second side, and the length of the first part in the first direction is greater than the length of the second part in the first direction; When viewed from the third direction, the first region extends from the first end to the first side.

10. The secondary battery according to claim 1, wherein: The first direction has a first side from the second pole piece toward the first outer pole piece; the shell is a packaging bag and includes a main body for accommodating the electrode assembly and a packaging part connected to the main body; the first conductive plate includes a first conductive area and a second conductive area connected to each other, the first conductive area is arranged in the packaging part and extends from the packaging part to the shell, the second conductive area is electrically connected to the first pole piece, the second conductive area includes a first end connected to the first conductive area, and the second conductive area extends from the first end to the first side.

11. The secondary battery according to claim 1, wherein The first outer pole piece includes a first current collector and a first active material layer stacked in the first direction, the first current collector includes a first surface facing the second pole piece and a second surface opposite to the first surface, the first active material layer is arranged on the first surface, and no active material is arranged on the second surface.

12. The secondary battery according to claim 11, wherein: The first pole piece also includes a first inner pole piece, which is located on the inner side of the first outer pole piece. The first inner pole piece includes a second current collector. In the first direction, the thickness of the first current collector is a first thickness, and the thickness of the second current collector is a second thickness. The ratio of the first thickness to the second thickness is greater than or equal to 1.2 and less than or equal to 2.

5.

13. The secondary battery according to claim 11, wherein: The secondary battery further includes a first layer disposed on the second surface, wherein the first layer includes an insulating material.

14. The secondary battery according to claim 13, characterized in that: In the first direction, the thickness of the first current collector is defined as a first thickness, the thickness of the first layer is defined as a third thickness, and the third thickness is less than twice the first thickness.

15. The secondary battery according to claim 13, wherein: The first layer bonds the second surface and the housing.

16. The secondary battery according to claim 1, wherein: The first outer pole sheet includes a first active material layer, a first current collector and a second active material layer stacked in the first direction, the first current collector includes a first surface facing the second pole sheet and a second surface opposite to the first surface, the first active material layer is arranged on the first surface, and the second active material layer is arranged on the second surface.

17. The secondary battery according to claim 11 or 16, characterized in that: The first electrode sheet is a positive electrode sheet, and the mass of the active material provided on the first current collector per unit area is G, G≤23 mg / cm 2 .

18. The secondary battery according to claim 1, wherein: The isolation film adjacent to the first outer pole piece is bonded to the second region.

19. The secondary battery according to claim 18, wherein: The second pole piece adjacent to the first outer pole piece includes a third region and a fourth region connected in the second direction, and when viewed from the first direction, the first region and the third region overlap, and the second region and the fourth region overlap; The isolation film adjacent to the first outer pole piece is also bonded to the third region.

20. The secondary battery according to claim 19, wherein: The third area includes a first partition and a second partition connected in the second direction, and when viewed from the third direction, the second partition includes a third end connected to the first partition; the first partition overlaps with the first area in the first direction, and when viewed from the first direction, the second partition extends from the third end to beyond the first area; When viewed from the third direction, the second partition extends from the third end in a direction away from the first outer pole piece.

21. The secondary battery according to claim 1, characterized in that: Observed from the second direction, the isolation membrane includes a plurality of main body segments stacked in the first direction and a plurality of connecting segments connecting ends of two adjacent main body segments, and the main body segment is arranged between adjacent first pole pieces and second pole pieces.

22. An electronic device, characterized in that: Includes the secondary battery according to any one of claims 1 to 21.

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