Secondary battery and electric device

Abstract

A secondary battery (100) and an electric device. The secondary battery (100) comprises a casing (10), an electrode assembly (20), and a first filler (30). The casing (10) comprises a first wall (11), a second wall (12), a third wall (13), a fourth wall (14), and a surrounding wall (15), and encloses a first space; in a first direction (X), the distance between the first wall (11) and the second wall (12) is less than the distance between the first wall (11) and the third wall (13). The electrode assembly (20) is accommodated in the first space; the electrode assembly (20) comprises a first portion (201) and a second portion (202), wherein the second portion (202) is located on the side of the first portion (201) facing the third wall (13), the projection of the second portion (202) in the first direction (X) being located within the range of the third wall (13); the second portion (202) is separated from the fourth wall (14), and a first gap is formed between the first portion (201) and the fourth wall (14). The first filler (30) is arranged in the first gap; in the first direction (X), the first filler (30) is located between the first portion (201) and the third wall (13), and in a second direction (Y), the first filler (30) is located between the fourth wall (14) and the second portion (202). In the secondary battery (100), the provision of the first filler (30) can reduce the possibility of lithium plating occurring in the secondary battery (100).

Description

Secondary batteries and electrical equipment Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] Currently, to adapt to different application scenarios, secondary batteries are processed into different shapes, resulting in irregularly shaped secondary batteries. The casing of irregularly shaped secondary batteries has different depths in different areas, forming steps in the transition regions at different depths. The electrodes lack support at these step locations. During the secondary battery formation process, the portion of the electrode corresponding to the step region is not sufficiently compressed, resulting in low interface yield and a high risk of lithium plating after formation. Summary of the Invention

[0003] In view of the above situation, it is necessary to provide a secondary battery and an electrical device to improve the pressure on the stepped area of ​​the electrode assembly corresponding to the housing, thereby improving the interface yield of the electrode assembly after formation.

[0004] A first aspect of the embodiments of this application provides a secondary battery, including a housing, an electrode assembly, and a first filler. The housing includes a first wall, a second wall, a third wall, a fourth wall, and a surrounding wall. The first wall and the second wall are disposed opposite each other along a first direction, and the first wall and the third wall are disposed opposite each other along the first direction. The third wall is located on the side of the second wall along the second direction. The fourth wall connects the second wall and the third wall. The surrounding wall connects the first wall, the second wall, the third wall, and the fourth wall, and together with the first wall, the second wall, the third wall, and the fourth wall, encloses a first space. Along the first direction, the distance between the first wall and the second wall is less than the distance between the first wall and the third wall. An electrode assembly is housed in a first space. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a first positive electrode and a second positive electrode. Along a second direction, the size of the first positive electrode is larger than that of the second positive electrode. The negative electrode includes a first negative electrode and a second negative electrode. Along the second direction, the size of the first negative electrode is larger than that of the second negative electrode. A plurality of first positive electrodes, a plurality of separators, and a plurality of first negative electrodes are alternately stacked along a first direction to form a first part of the electrode assembly. A plurality of second positive electrodes, a plurality of separators, and a plurality of second negative electrodes are alternately stacked along a first direction to form a second part of the electrode assembly. The first part and the second part are stacked along the first direction. The second part is located on the side of the first part facing the third wall, and the projection of the second part along the first direction is within the range of the third wall. The second part is separated from the fourth wall, and a first gap is formed between the first part and the fourth wall. The first direction is the thickness direction of the positive electrode, and the second direction is perpendicular to the first direction. The first filler is disposed in the first gap. Along the first direction, the first filler is located between the first part and the third wall. Along the second direction, the first filler is located between the fourth wall and the second part.

[0005] In this secondary battery, the second, third, and fourth walls together form a stepped structure to adapt to the needs of the application scenario; the shape of the electrode assembly adapts to the shape of the casing, which is conducive to making full use of the internal space of the casing and improving the energy density of the secondary battery; and by setting the first filler, the electrode assembly can be supported at the step of the casing to improve the pressure resistance of the electrode assembly during the formation process. On the one hand, it improves the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, and on the other hand, it improves the interface yield after formation, thereby reducing the possibility of lithium plating in the secondary battery during long-term cycling.

[0006] In an optional embodiment of this application, the thickness of the second portion along the first direction is H1, the distance between the second wall and the third wall along the first direction is H2, H1 > H2, and the thickness of the first filler along the first direction is H3, H2 ≤ H3 ≤ H1. Setting H3 ≥ H2 ensures that the thickness of the first filler along the first direction is not too small, which is beneficial to improving the support effect of the first filler on the electrode assembly; setting H3 ≤ H1 ensures that the thickness of the first filler along the first direction is not too large, which is beneficial to improving the pressure consistency of the electrode assembly during the formation process.

[0007] In an optional embodiment of this application, H2+0.7(H1-H2)≤H3≤H2+0.9(H1-H2). Setting H3≥H2+0.7(H1-H2) ensures that the thickness of the first filler along the first direction is not too small, which is beneficial for further improving the support effect of the first filler on the electrode assembly; setting H3≤H2+0.9(H1-H2) ensures that the thickness of the first filler along the first direction is not too large, which is beneficial for balancing the pressure resistance of the electrode assembly during the formation process and material cost.

[0008] In an optional embodiment of this application, the first filler is separated from the second portion. This helps to reduce the possibility of the first filler compressing the second portion of the electrode assembly, thereby maintaining the laminated structure of the electrode assembly.

[0009] In one optional embodiment of this application, the distance between the fourth wall and the second part along the second direction is W1, and the dimension of the first filler along the second direction is W, where 0.6W1≤W≤0.9W1. Setting W≥0.6W1 prevents the dimension of the first filler along the second direction from being too small, which is beneficial to increasing the dimension of the part of the electrode assembly supported by the first filler along the second direction and improving the supporting effect of the first filler on the electrode assembly. Setting W≤0.9W1 prevents the dimension of the first filler along the second direction from being too large, which is beneficial to reducing the possibility that the first filler supports the first part and affects the pressure effect of the first part during the formation process.

[0010] In an optional embodiment of this application, 0.8W1≤W≤0.9W1. Setting W≥0.8W1 ensures that the dimension of the first filler along the second direction is not too small, which is beneficial to further improve the dimension of the portion of the electrode assembly supported by the first filler along the second direction, thereby improving the supporting effect of the first filler on the electrode assembly.

[0011] In one optional embodiment of this application, the dimension of the electrode assembly along the third direction is L1, and the dimension of the first filler along the third direction is L. The third direction is perpendicular to the first and second directions, and 0.9L1≤L≤L1. Setting L≥0.9L1 prevents the dimension of the first filler along the third direction from being too small, which is beneficial to increasing the dimension of the portion of the electrode assembly supported by the first filler along the third direction and improving the support effect of the first filler on the electrode assembly. Setting L≤L1 prevents the dimension of the first filler along the second direction from being too large, which is beneficial to reducing the possibility of the first filler encroaching on the internal space of the housing.

[0012] In an optional embodiment of this application, 0.95L1≤L≤L1. Setting L≥0.95L1 prevents the dimension of the first filler along the third direction from becoming too small, which is beneficial to further improve the dimension of the portion of the electrode assembly supported by the first filler along the third direction, thereby improving the support effect of the first filler on the electrode assembly.

[0013] In one alternative embodiment of this application, the first filler is a hot melt pressure-sensitive adhesive or an expanding adhesive.

[0014] In one optional embodiment of this application, the dimension of the first positive electrode along the second direction is D1, and the dimension of the second positive electrode is D2, where 0.1D1≤D2≤0.9D1.

[0015] In one optional embodiment of this application, the dimension of the first negative electrode sheet along the second direction is D3, and the dimension of the second negative electrode sheet is D4, where 0.1D3≤D4≤0.9D3.

[0016] A second aspect of the embodiments of this application provides an electrical device including a secondary battery as described in any of the foregoing embodiments. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the structure of a secondary battery in one embodiment of this application.

[0018] Figure 2 is a schematic diagram of the cross-sectional structure at point II-II in Figure 1.

[0019] Figure 3 is a partial structural schematic diagram of the secondary battery in one embodiment of this application.

[0020] Figure 4 is a schematic diagram of the structure of the electrical equipment in one embodiment of this application.

[0021] Explanation of main component symbols

[0022] Secondary battery 100

[0023] Casing 10

[0024] First Wall 11

[0025] Second Wall 12

[0026] Third Wall 13

[0027] Fourth Wall 14

[0028] Wall 15

[0029] First Space 16

[0030] First gap 16a

[0031] Electrode assembly 20

[0032] Part 1 201

[0033] Part Two 202

[0034] Positive electrode 21

[0035] Positive current collector 21a

[0036] Positive electrode active material layer 21b

[0037] First positive electrode plate 211

[0038] Second positive electrode plate 212

[0039] Negative electrode 22

[0040] Negative current collector 22a

[0041] Negative electrode active material layer 22b

[0042] First negative electrode 221

[0043] Second negative electrode 222

[0044] Separator 23

[0045] First filler 30

[0046] 1000 electrical appliances

[0047] First direction X

[0048] Second direction Y

[0049] Third direction Z

[0050] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0052] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0054] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0055] In the description of the embodiments of this application, the term "perpendicular" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately perpendicular. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be approximately straight lines or planes. From a macroscopic perspective, if the overall extension direction is a straight line or plane, the component can be considered as a "straight line" or "plane".

[0056] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other.

[0057] Embodiments of this application provide a secondary battery, including a casing, an electrode assembly, and a first filler.

[0058] The shell includes a first wall, a second wall, a third wall, a fourth wall, and a surrounding wall. The first wall and the second wall are arranged opposite each other along a first direction, and the first wall and the third wall are arranged opposite each other along the first direction. The third wall is located on the side of the second wall along the second direction. The fourth wall connects the second wall and the third wall. The surrounding wall connects the first wall, the second wall, the third wall, and the fourth wall, and together with the first wall, the second wall, the third wall, and the fourth wall, it encloses a first space. Along the first direction, the distance between the first wall and the second wall is less than the distance between the first wall and the third wall.

[0059] An electrode assembly is housed in a first space. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a first positive electrode and a second positive electrode. Along a second direction, the size of the first positive electrode is larger than that of the second positive electrode. The negative electrode includes a first negative electrode and a second negative electrode. Along the second direction, the size of the first negative electrode is larger than that of the second negative electrode. A plurality of first positive electrodes, a plurality of separators, and a plurality of first negative electrodes are alternately stacked along a first direction to form a first part of the electrode assembly. A plurality of second positive electrodes, a plurality of separators, and a plurality of second negative electrodes are alternately stacked along a first direction to form a second part of the electrode assembly. The first part and the second part are stacked along the first direction. The second part is located on the side of the first part facing the third wall, and the projection of the second part along the first direction is within the range of the third wall. The second part is separated from the fourth wall, and a first gap is formed between the first part and the fourth wall. The first direction is the thickness direction of the positive electrode, and the second direction is perpendicular to the first direction.

[0060] The first filler is disposed in the first gap. Along the first direction, the first filler is located between the first part and the third wall. Along the second direction, the first filler is located between the fourth wall and the second part.

[0061] In this secondary battery, the second, third, and fourth walls together form a stepped structure to adapt to the needs of the application scenario; the shape of the electrode assembly adapts to the shape of the casing, which is conducive to making full use of the internal space of the casing and improving the energy density of the secondary battery; and, by setting the first filler, the electrode assembly can be supported at the step of the casing to improve the pressure resistance of the electrode assembly during the formation process. On the one hand, this improves the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, and on the other hand, it improves the interface yield after formation and reduces the possibility of lithium plating in the secondary battery during long cycles.

[0062] The embodiments of this application will be further described below with reference to the accompanying drawings. For ease of explanation, in the following text, the thickness direction of the positive electrode sheet of the secondary battery is taken as the first direction X, and the first direction X, the second direction Y, and the third direction Z are perpendicular to each other.

[0063] As shown in Figures 1 and 2, an embodiment of this application provides a secondary battery 100, which includes a housing 10 and an electrode assembly 20. The housing 10 has a first space 16, and the electrode assembly 20 is housed in the first space 16.

[0064] In some embodiments, the housing 10 is a rigid outer shell, such as a plastic shell, or a metal shell including at least one of steel alloy, aluminum alloy, and copper alloy.

[0065] In some embodiments, as shown in FIG2, the electrode assembly 20 includes a positive electrode 21, a negative electrode 22, and a separator 23.

[0066] In some embodiments, as shown in FIG2, the positive electrode 21 includes a positive current collector 21a and a positive active material layer 21b, wherein the positive active material layer 21b is disposed on at least one surface of the positive current collector 21a along the thickness direction of the positive electrode 21.

[0067] In some embodiments, the positive current collector 21a is a metal layer. As an example, the positive current collector 21a may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0068] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0069] In some embodiments, as shown in FIG2, the negative electrode 22 includes a negative electrode current collector 22a and a negative electrode active material layer 22b, wherein the negative electrode active material layer 22b is disposed on at least one surface of the negative electrode current collector 22a along the thickness direction of the negative electrode 22.

[0070] In some embodiments, the negative electrode current collector 22a is a metal layer. The negative electrode current collector 22a may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0071] In some embodiments, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.

[0072] In some embodiments, the separator 23 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0073] In some embodiments, the secondary battery 100 further includes an electrolyte contained in a first space 16.

[0074] In some embodiments, the electrolyte comprises an electrolyte salt. The electrolyte salt comprises at least one of an organic lithium salt or an inorganic lithium salt.

[0075] In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluoromethanesulfonyl)imide (LiN(CF3SO2)2(LiTFSI)), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2)(LiFSI)), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0076] In some embodiments, as shown in Figures 1 and 2, the housing 10 includes a first wall 11, a second wall 12, a third wall 13, a fourth wall 14, and a surrounding wall 15. The first wall 11 and the second wall 12 are arranged opposite each other along a first direction X, and the first wall 11 and the third wall 13 are also arranged opposite each other along the first direction X. The third wall 13 is located on the side of the second wall 12 along a second direction Y. The fourth wall 14 connects the second wall 12 and the third wall 13. The surrounding wall 15 connects the first wall 11, the second wall 12, the third wall 13, and the fourth wall 14, and together with the first wall 11, the second wall 12, the third wall 13, and the fourth wall 14, it encloses a first space 16. Along the first direction X, the distance between the first wall 11 and the second wall 12 is less than the distance between the first wall 11 and the third wall 13. Thus, the second wall 12, the third wall 13, and the fourth wall 14 together form a stepped structure to adapt to the needs of the application scenario.

[0077] In some embodiments, as shown in Figures 1 and 2, the positive electrode 21 includes a first positive electrode 211 and a second positive electrode 212. Along the second direction Y, the size of the first positive electrode 211 is larger than the size of the second positive electrode 212. The negative electrode 22 includes a first negative electrode 221 and a second negative electrode 222. Along the second direction Y, the size of the first negative electrode 221 is larger than the size of the second negative electrode 222. A plurality of first positive electrode 211, a plurality of separators 23, and a plurality of first negative electrode 221 are alternately stacked along the first direction X to form a first portion 201 of the electrode assembly 20; a plurality of second positive electrode 212, a plurality of separators 23, and a plurality of second negative electrode 222 are alternately stacked along the first direction X to form a second portion 202 of the electrode assembly 20. The first portion 201 and the second portion 202 are stacked along the first direction X, with the second portion 202 located on the side of the first portion 201 facing the third wall 13, and the projection of the second portion 202 along the first direction X falling within the area of ​​the third wall 13. Thus, the shape of the electrode assembly 20 is adapted to the shape of the housing 10, which helps to make full use of the internal space of the housing 10 and improve the energy density of the secondary battery 100.

[0078] Figure 3 shows a schematic diagram of the secondary battery 100 when viewed along the first direction after omitting the second wall 12, the third wall 13 and the fourth wall 14.

[0079] In some embodiments, the first positive electrode 211 has a dimension of D1 along the second direction Y, and the second positive electrode 212 has a dimension of D2, where 0.1D1≤D2≤0.9D1.

[0080] In some embodiments, the first negative electrode 221 has a dimension of D3 along the second direction Y, and the second negative electrode 222 has a dimension of D4, where 0.1D3≤D4≤0.9D3.

[0081] In some embodiments, as shown in FIG2, the second portion 202 is separated from the fourth wall 14, and a first gap 16a is formed between the first portion 201 and the fourth wall 14. The secondary battery 100 also includes a first filler 30, which is disposed in the first gap 16a. Along the first direction X, the first filler 30 is located between the first portion 201 and the third wall 13, and along the second direction Y, the first filler 30 is located between the fourth wall 14 and the second portion 202.

[0082] In this secondary battery 100, by providing the first filler 30, the electrode assembly 20 can be supported at the step of the housing 10, thereby increasing the pressure resistance of the electrode assembly 20 during the formation process. This improves the adhesion between the positive electrode 21 and the separator 23, as well as between the negative electrode 22 and the separator 23, and also improves the interface yield after formation, reducing the possibility of lithium plating in the secondary battery 100 during long cycles.

[0083] In some embodiments, as shown in FIG2, the thickness of the second portion 202 along the first direction X is H1, the distance between the second wall 12 and the third wall 13 along the first direction X is H2, H1 > H2, and the thickness of the first filler 30 along the first direction X is H3, H2 ≤ H3 ≤ H1. Setting H3 ≥ H2 ensures that the thickness of the first filler 30 along the first direction X is not too small, which is beneficial to improving the support effect of the first filler 30 on the electrode assembly 20. When H3 > H1, the first portion 201 is supported by the first filler 30, which may result in insufficient pressure on a portion of the first portion 201 during the formation process. Therefore, setting H3 ≤ H1 ensures that the thickness of the first filler 30 along the first direction X is not too large, which is beneficial to improving the pressure consistency of the electrode assembly 20 during the formation process. Here, the first filler 30 supporting the first portion 201 refers to the situation where a portion of the first portion 201 is separated from the second wall 12 due to the support of the first filler 30.

[0084] When measuring the thickness H1 of the second part 202 along the first direction X, the second part 202 can be detached from the electrode assembly, and the distance between the surfaces of the electrode plates at both ends of the second part 202 along the first direction X can be measured with a micrometer. When measuring the distance between the second wall 12 and the third wall 13, the distance between the first wall 11 and the third wall 13 along the first direction X can be measured with a micrometer, and then the distance between the first wall 11 and the second wall 12 along the first direction X can be measured. By subtracting the two measurements, the distance H2 between the second wall 12 and the third wall 13 along the first direction X can be obtained.

[0085] In some embodiments, H2+0.7(H1-H2)≤H3≤H2+0.9(H1-H2). Setting H3≥H2+0.7(H1-H2) ensures that the thickness of the first filler 30 along the first direction X is not too small, which is beneficial to further improve the support effect of the first filler 30 on the electrode assembly 20; setting H3≤H2+0.9(H1-H2) ensures that the thickness of the first filler 30 along the first direction X is not too large, which is beneficial to balance the pressure resistance of the electrode assembly during the formation process and material cost.

[0086] In some embodiments, as shown in FIG2, the first filler 30 is separated from the second portion 202. This helps to reduce the possibility that the first filler 30 may compress the second portion 202 of the electrode assembly 20, thereby maintaining the laminated structure of the electrode assembly 20.

[0087] In some embodiments, as shown in FIG2, the distance between the fourth wall 14 and the second portion 202 along the second direction Y is W1, and the dimension of the first filler 30 along the second direction Y is W, where 0.6W1≤W≤0.9W1. Setting W≥0.6W1 prevents the dimension of the first filler 30 along the second direction Y from being too small, which is beneficial for increasing the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the second direction Y, thereby improving the supporting effect of the first filler 30 on the electrode assembly 20. Setting W≤0.9W1 prevents the dimension of the first filler 30 along the second direction Y from being too large, which is beneficial for reducing the possibility that the first filler 30 supporting the first portion 201 might affect the pressure resistance of the first portion 201 during the formation process.

[0088] The distance W1 between the fourth wall 14 and the second part 202 is the minimum distance between them, which can be measured using computed tomography (CT). The dimension W of the first filler 30 along the second direction Y can be measured using a micrometer.

[0089] In some embodiments, 0.8W1≤W≤0.9W1. Setting W≥0.8W1 ensures that the dimension of the first filler 30 along the second direction Y is not too small, which is beneficial to further increase the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the second direction Y, thereby improving the support effect of the first filler 30 on the electrode assembly 20.

[0090] In some embodiments, as shown in FIG3, the dimension of the electrode assembly 20 along the third direction Z is L1, and the dimension of the first filler 30 along the third direction Z is L, where 0.9L1≤L≤L1. Setting L≥0.9L1 prevents the dimension of the first filler 30 along the third direction Z from being too small, which helps to increase the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the third direction Z, thereby improving the support effect of the first filler 30 on the electrode assembly 20. Setting L≤L1 prevents the dimension of the first filler 30 along the second direction Y from being too large, which helps to reduce the possibility of the first filler 30 encroaching on the internal space of the housing 10.

[0091] The values ​​of L1 and L can be measured using a micrometer.

[0092] In some embodiments, 0.95L1≤L≤L1. Setting L≥0.95L1 ensures that the dimension of the first filler 30 along the third direction Z is not too small, which is beneficial to further improve the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the third direction Z, thereby improving the support effect of the first filler 30 on the electrode assembly 20.

[0093] In some embodiments, the first filler 30 is a hot melt pressure-sensitive adhesive or an expanding adhesive.

[0094] In some embodiments, the hot-melt pressure-sensitive adhesive includes a first adhesive layer, a first substrate layer, and a second adhesive layer. The first adhesive layer bonds the housing 10 to the first substrate layer, and the second adhesive layer bonds the electrode assembly 20 to the first substrate layer. Thus, the first filler 30 provides support for the electrode assembly 20 while also bonding the electrode assembly 20 to the housing 10, thereby improving the stability of the electrode assembly 20 within the housing 10.

[0095] In some embodiments, the material of the first adhesive layer includes styrene-isoprene-styrene block copolymer; the material of the first substrate layer includes at least one of polyethylene terephthalate, polyimide, or polypropylene; and the material of the second adhesive layer includes at least one of polymethyl methacrylate (PMMA, commonly known as acrylic), polypropylene (PP), polyethylene (PE), or polyamide.

[0096] In some embodiments, the expanding adhesive is a liquid-absorbing expanding adhesive or a heat-expanding adhesive.

[0097] In some embodiments, the liquid-absorbing and expanding adhesive includes a liquid-absorbing and expanding material that expands after absorbing liquid, thereby providing support for the electrode assembly 20.

[0098] In some embodiments, the liquid-absorbing and swelling adhesive includes a second substrate layer and a third adhesive layer disposed on the second substrate layer. The liquid-absorbing and swelling material can be added to the second substrate layer or to the third adhesive layer. Of course, the liquid-absorbing and swelling material can also be added to both the second substrate layer and the third adhesive layer.

[0099] In some embodiments, the liquid-absorbing and swelling material includes at least one of polycaprolactam, sodium polyacrylate, and lithium polyacrylate. Polymer materials such as polycaprolactam, sodium polyacrylate, and lithium polyacrylate utilize the polyanionic properties within their crystal structures to absorb small-molecule solvents into the crystal structure. By adding the aforementioned polymer material to the liquid-absorbing and swelling adhesive paper, when electrolyte is injected, small-molecule solvents such as ethylene carbonate (EC) can be absorbed by the polymer material. The polymer expands in volume after absorbing the liquid, thus filling the gap between the electrode assembly 20 and the housing 10.

[0100] In some embodiments, the heat-expanding adhesive includes a heat-expanding material that expands when heated, thereby providing support for the electrode assembly 20.

[0101] The heat-expanding adhesive paper includes a third substrate layer and a fourth adhesive layer disposed on the third substrate layer. The heat-expanding material can be added to the third substrate layer or the fourth adhesive layer. Of course, the heat-expanding material can also be added to both the third substrate layer and the fourth adhesive layer.

[0102] In some embodiments, the thermal expansion material may be at least one of polycaprolactam, ethylene-ethyl acrylate, and cellulose acetate.

[0103] As shown in Figure 4, an embodiment of this application also provides an electrical device 1000, which includes a secondary battery 100 as described in any of the foregoing embodiments.

[0104] To verify the impact of the technical solutions provided in the embodiments of this application on the interface yield of the secondary battery 100 after formation, the inventors conducted an experimental investigation. The experiment included one set of comparative examples and 15 sets of specific examples, each set of comparative examples and each set of specific examples including 30 secondary batteries 100.

[0105] The preparation process of the secondary battery 100 in Example 1 includes the following steps:

[0106] (1) Preparation of positive electrode 21: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNTs (carbon nanotubes), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material with a solid content of 75 wt%, which was then stirred evenly for later use. A 10 μm thick aluminum foil was used as the positive electrode current collector 21a. The above active material was uniformly coated on one surface of the positive electrode current collector 21a along its thickness direction using a slit coater, and then dried at 90°C to obtain a positive electrode 21 with a single-sided coating of positive electrode active material. At this time, the thickness of the positive electrode active material layer 21b along the thickness direction of the positive electrode current collector 21a was 50 μm. The coating process is then repeated on the other surface of the positive current collector 21a along its thickness direction to obtain a positive electrode sheet 21 coated with a positive active material layer 21b on both sides. The coated positive electrode sheet 21 is then cold-pressed, resulting in a positive active material layer 21b thickness of 35 μm. The area of ​​the positive current collector 21a not covered by the positive active material layer 21b is the empty foil area, which is cut to obtain the positive electrode tab. Multiple positive electrode sheets 21 are fabricated through the aforementioned steps, a portion of which is the first positive electrode sheet 211, and the remainder is the second positive electrode sheet 212. Two of the first positive electrode sheets 211 have a positive active material layer 21b coated only on one side of the positive current collector 21a, while the rest have a positive active material layer 21b coated on both sides of the positive current collector 21a; two of the second positive electrode sheets 212 have a positive active material layer 21b coated only on one side of the positive current collector 21a, while the rest have a positive active material layer 21b coated on both sides of the positive current collector 21a.

[0107] (2) Preparation of negative electrode 22: Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2. Deionized water was added as a solvent to prepare a negative electrode active material with a weight percentage of 50 wt%, and the mixture was stirred evenly for later use. A copper foil with a thickness of 10 μm was used as the negative electrode current collector 22a. The above negative electrode active material was uniformly coated onto one surface of the negative electrode current collector 22a along its thickness direction using a slot coater, and then dried at 110°C to obtain a negative electrode 22 with a single-sided coating of negative electrode active material layer 22b. At this time, the thickness of the negative electrode active material layer 22b along the thickness direction of the negative electrode current collector 22a was 55 μm. The above steps were then repeated on the other surface of the negative electrode current collector 22a along its thickness direction to obtain a negative electrode 22 with negative electrode active material layers 22b coated on both sides. The coated negative electrode sheet 22 is then cold-pressed, resulting in a negative electrode active material layer 22b thickness of 45 μm. The area of ​​the negative electrode current collector 22a not covered by the negative electrode active material layer 22b is the empty foil area, which is then cut to obtain the negative electrode tab. Multiple negative electrode sheets 22 are fabricated through the aforementioned steps, some of which are first negative electrode sheets 221, and the remainder are second negative electrode sheets 222. Two of the first negative electrode sheets 221 have the negative electrode active material layer 22b coated only on one side of the negative electrode current collector 22a, while the rest have the negative electrode active material layer 22b coated on both sides of the negative electrode current collector 22a. Similarly, two of the second negative electrode sheets 222 have the negative electrode active material layer 22b coated only on one side of the negative electrode current collector 22a, while the rest have the negative electrode active material layer 22b coated on both sides of the negative electrode current collector 22a.

[0108] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0109] (4) Preparation of the isolation membrane 23: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane 23.

[0110] (5) Fabrication of electrode assembly 20: A first part 201 of electrode assembly 20 is obtained by alternately stacking a first positive electrode 211, a separator 23, and a first negative electrode 221 along a first direction X. The two outermost electrodes of the first part 201 along the first direction X are both first positive electrode 211 with a positive active material layer 21b only on one side of the positive current collector 21a. A second part 202 of electrode assembly 20 is obtained by alternately stacking a second positive electrode 212, a separator 23, and a second negative electrode 222 along the first direction X. The two outermost electrodes of the second part 202 along the first direction X are both second positive electrode 212 with a positive active material layer 21b only on one side of the positive current collector 21a. The first part 201 and the second part 202 are stacked along the first direction X and separated by the separator 23.

[0111] (6) Assembly of secondary battery 100: Take a first filler 30, put the first filler 30 and electrode assembly 20 into the steel shell 10, and after the electrolyte injection, encapsulation, standing, hot pressing formation, shaping and other processes, the secondary battery 100 is obtained.

[0112] The preparation process of the secondary battery 100 in Comparative Example 1 is basically the same as that in Example 1. The difference is that the secondary battery 100 in Comparative Example 1 does not have a first filler 30.

[0113] The preparation method of the secondary battery 100 in Examples 2-15 is basically the same as that in Example 1. The difference lies in the parameters related to the first filler 30 in Examples 2-15, which are different from those in Example 1. The specific differences are recorded in Table 1. In the secondary battery 100 of Examples 1-15, H1 = 2.98 mm, H2 = 2.52 mm, W1 = 2.20 mm, and L1 = 73.65 mm.

[0114] After the secondary batteries 100 in Comparative Example 1 and Examples 1-15 were prepared, long-cycle lithium plating tests were performed on all batteries in each group. The specific test process is as follows:

[0115] 1) Maintain the test temperature at 25℃;

[0116] 2) Let the secondary battery 100 stand for 30 minutes;

[0117] 3) Charge at a constant current of 5C to 4.25V, then charge at a constant voltage of 3C;

[0118] 4) Charge at 3C constant current to 4.35V, then charge at constant voltage to 1.5C;

[0119] 5) Charge at a constant current of 1.5C to 4.45V, then charge at a constant voltage to 0.05C;

[0120] 6) Let stand for 5 minutes;

[0121] 7) Discharge at a constant current of 0.7C to 3V;

[0122] 8) Let stand for 5 minutes;

[0123] 9) Repeat steps 3 through 8 800 times;

[0124] 10) Disassemble the secondary battery 100, observe the lithium plating situation, and count the number of secondary batteries 100 with lithium plating in each group.

[0125] After the test, the experimental results were recorded in Table 1.

[0126] Table 1

[0127] Note: In Table 1, " / " indicates that there is no such data, and N represents the number of secondary batteries that exhibit lithium plating.

[0128] As shown in Table 1, the number of secondary batteries 100 exhibiting lithium plating in Examples 1-15 is less than that in Comparative Example 1. It is evident that the first filler 30 provides support for the electrode assembly 20 at the step of the housing 10, thereby increasing the pressure resistance of the electrode assembly 20 during the formation process. This improves the adhesion between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23, and also improves the interface yield after formation, thus reducing the likelihood of lithium plating in the secondary battery 100 during long-term cycling.

[0129] In Examples 2-7, the secondary battery 100 satisfies H2≤H3≤H1. Compared to Examples 1 and 8, the number of secondary batteries 100 exhibiting lithium plating is reduced in Examples 2-7. It is evident that setting H3≥H2 ensures that the thickness of the first filler 30 along the first direction X is not too small, which is beneficial for improving the support effect of the first filler 30 on the electrode assembly 20; setting H3≤H1 ensures that the thickness of the first filler 30 along the first direction X is not too large, which is beneficial for improving the pressure consistency of the electrode assembly 20 during the formation process.

[0130] In Examples 4-6, the secondary battery 100 satisfies H2+0.7(H1-H2)≤H3≤H2+0.9(H1-H2). The number of secondary batteries 100 exhibiting lithium plating in Examples 4-6 is lower than that in Example 3; and the number of secondary batteries 100 exhibiting lithium plating in Examples 4-6 is no higher than that in Example 7. It can be seen that setting H3≥H2+0.7(H1-H2) ensures that the thickness of the first filler 30 along the first direction X is not too small, which is beneficial for further improving the support effect of the first filler 30 on the electrode assembly 20; setting H3≤H2+0.9(H1-H2) ensures that the thickness of the first filler 30 along the first direction X is not too large, which is beneficial for balancing the pressure resistance of the electrode assembly 20 during the formation process and material costs.

[0131] In Examples 5 and 10-11, the secondary battery 100 satisfies 0.6W1≤W≤0.9W1. Compared with Examples 9 and 12, the number of secondary batteries 100 exhibiting lithium plating in Examples 5 and 10-11 is reduced. It can be seen that setting W≥0.6W1 prevents the dimension of the first filler 30 along the second direction Y from being too small, which is beneficial for increasing the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the second direction Y, thereby improving the supporting effect of the first filler 30 on the electrode assembly 20. Setting W≤0.9W1 prevents the dimension of the first filler 30 along the second direction Y from being too large, which is beneficial for reducing the possibility that the first filler 30 supporting the first part 201 and affecting the pressure resistance of the first part 201 during the formation process.

[0132] In Examples 5 and 11, the secondary battery 100 satisfies 0.8W1 ≤ W ≤ 0.9W1. Compared to Example 10, the number of secondary batteries 100 exhibiting lithium plating is reduced in Examples 5 and 11. It is evident that setting W ≥ 0.8W1 prevents the dimension of the first filler 30 along the second direction Y from becoming too small, which is beneficial for further increasing the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the second direction Y, thereby improving the supporting effect of the first filler 30 on the electrode assembly 20.

[0133] In Examples 5 and 14-15, the secondary battery 100 satisfies 0.9L1≤L≤L1. Compared to Example 13, the number of secondary batteries 100 exhibiting lithium plating in Examples 5 and 14-15 is reduced. It can be seen that setting L≥0.9L1 prevents the dimension of the first filler 30 along the third direction Z from becoming too small, which is beneficial for increasing the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the third direction Z, thereby improving the supporting effect of the first filler 30 on the electrode assembly 20. Setting L≤L1 prevents the dimension of the first filler 30 along the second direction Y from becoming too large, which is beneficial for reducing the possibility of the first filler 30 encroaching on the internal space of the housing 10.

[0134] In Examples 5 and 15, the secondary battery 100 satisfies 0.95L1≤L≤L1, and compared to Example 14, the number of secondary batteries 100 exhibiting lithium plating is further reduced. It is evident that setting L≥0.95L1 prevents the dimension of the first filler 30 along the third direction Z from becoming too small, which is beneficial for further increasing the dimension of the portion of the electrode assembly 20 supported by the first filler 30 along the third direction Z, thereby improving the supporting effect of the first filler 30 on the electrode assembly 20.

[0135] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application.

Claims

1. A secondary battery (100), characterized in that, include: The housing (10) includes a first wall (11), a second wall (12), a third wall (13), a fourth wall (14), and a surrounding wall (15). The first wall (11) and the second wall (12) are arranged opposite each other along a first direction (X), and the first wall (11) and the third wall (13) are arranged opposite each other along the first direction (X). The third wall (13) is located on the side of the second wall (12) along a second direction (Y). The fourth wall (14) connects the second wall (12) and the surrounding wall (15). The third wall (13) and the enclosure wall (15) connect the first wall (11), the second wall (12), the third wall (13) and the fourth wall (14), and together with the first wall (11), the second wall (12), the third wall (13) and the fourth wall (14) enclose the first space (16); along the first direction (X), the distance between the first wall (11) and the second wall (12) is less than the distance between the first wall (11) and the third wall (13); An electrode assembly (20) is housed in the first space (16). The electrode assembly (20) includes a positive electrode (21), a negative electrode (22), and a separator (23). The positive electrode (21) includes a first positive electrode (211) and a second positive electrode (212). Along the second direction (Y), the size of the first positive electrode (211) is larger than the size of the second positive electrode (212). The negative electrode (22) includes a first negative electrode (221) and a second negative electrode (222). Along the second direction (Y), the size of the first negative electrode (221) is larger than the size of the second negative electrode (222). A plurality of first positive electrodes (211), a plurality of separators (23), and a plurality of first negative electrodes (221) are alternately stacked along the first direction (X) to form a first part (201) of the electrode assembly (20). The second positive electrode (212), a plurality of the separators (23) and a plurality of the second negative electrode (222) are alternately stacked along the first direction (X) to form the second part (202) of the electrode assembly (20). The first part (201) and the second part (202) are stacked along the first direction (X). The second part (202) is located on the side of the first part (201) facing the third wall (13). The projection of the second part (202) along the first direction (X) is within the range of the third wall (13). The second part (202) is separate from the fourth wall (14). A first gap is formed between the first part (201) and the fourth wall (14). The first direction (X) is the thickness direction of the positive electrode (21), and the second direction (Y) is perpendicular to the first direction (X). A first filler (30) is disposed in the first gap along the first direction (X), the first filler (30) being located between the first portion (201) and the third wall (13), and along the second direction (Y), the first filler (30) being located between the fourth wall (14) and the second portion (202).

2. The secondary battery (100) as described in claim 1, characterized in that, The thickness of the second part (202) along the first direction (X) is H1, the distance between the second wall (12) and the third wall (13) along the first direction (X) is H2, H1 > H2, and the thickness of the first filler (30) along the first direction (X) is H3, H2 ≤ H3 ≤ H1.

3. The secondary battery (100) as described in claim 1, characterized in that, H2+0.7(H1-H2)≤H3≤H2+0.9(H1-H2).

4. The secondary battery (100) as described in claim 1, characterized in that, The first filler (30) is separate from the second part (202).

5. The secondary battery (100) as described in claim 1 or 4, characterized in that, Along the second direction (Y), the distance between the fourth wall (14) and the second part (202) is W1, and the dimension of the first filler (30) along the second direction (Y) is W, 0.6W1≤W≤0.9W1.

6. The secondary battery (100) as described in claim 5, characterized in that, 0.8W1≤W≤0.9W1.

7. The secondary battery (100) as described in claim 1, characterized in that, The electrode assembly (20) has a dimension of L1 along the third direction (Z), and the first filler (30) has a dimension of L along the third direction (Z). The third direction (Z) is perpendicular to the first direction (X) and the second direction (Y), and 0.9L1≤L≤L1.

8. The secondary battery (100) as described in claim 7, characterized in that, 0.95L1≤L≤L1.

9. The secondary battery (100) as described in claim 1, characterized in that, The first filler (30) is a hot melt pressure-sensitive adhesive or an expanding adhesive.

10. The secondary battery (100) according to any one of claims 1-9, characterized in that, The first positive electrode (211) has a dimension D1 along the second direction (Y), and the second positive electrode (212) has a dimension D2, where 0.1D1≤D2≤0.9D1; and / or The first negative electrode (221) has a dimension of D3 along the second direction (Y), and the second negative electrode (222) has a dimension of D4, where 0.1D3≤D4≤0.9D3.

11. An electrical appliance, characterized in that, Includes the secondary battery (100) as described in any one of claims 1-10.

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