Secondary battery and preparation method therefor

Abstract

Provided in the present application are a secondary battery and a preparation method therefor. The outermost electrode plate of an electrode assembly is a first outer electrode plate, wherein the first outer electrode plate comprises a first current collector and a first active material layer, the first current collector having a first surface facing a first direction and a second surface facing a second direction, and the first active material layer being arranged on the second surface. The first direction is a stacking direction of electrode plates and separators of the electrode assembly, and the second direction is opposite to the first direction. The secondary battery further comprises a plurality of first adhesive layers, part of each first adhesive layer being bonded between the first surface and an inner wall of an accommodating portion, and the other part of the first adhesive layer being bonded to the first surface and at least part of a separator. By means of providing the first adhesive layers, the shrinkage of the separators can be reduced, and drop resistance of the secondary battery can be improved.

Description

Secondary battery and preparation method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on December 29, 2023, with application number 202311863247.1 and entitled “Secondary Battery and Method for Making the Same,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery and a preparation method thereof. Background Art

[0004] With the rapid development of the battery industry, the application of laminated batteries with advantages such as high energy density and high safety has become increasingly common. In order to improve the energy density of laminated batteries, the outermost electrode of the electrode assembly of a laminated battery is usually a single-sided coated electrode, that is, the outermost electrode of a laminated battery is usually coated with an active material layer only on the side facing the inner side of the electrode assembly, and the side facing the battery packaging is a blank current collector. However, due to uneven stress on both sides of the outermost single-sided coated electrode of the electrode assembly of a laminated battery, its edges are prone to warping, which reduces the bonding area between the single-sided coated electrode and the isolation membrane, easily causing the isolation membrane to shrink. If the battery is collided, dropped, or internally heated during use, it is easy to cause the positive and negative electrode sheets of the battery to come into contact and cause a short circuit. Summary of the Invention

[0005] The embodiments of the present application aim to provide a secondary battery and a method for preparing the same, so as to reduce the warping of the outermost electrode of the laminated battery, thereby reducing the shrinkage of the isolation membrane and improving the safety performance of the laminated battery.

[0006] In order to solve the technical problems, this application adopts the following technical solutions:

[0007] In a first aspect, the present application proposes a secondary battery comprising a housing and an electrode assembly housed within the housing, the electrode assembly comprising a positive electrode sheet, a separator, and a negative electrode sheet. Along the thickness direction of the positive and negative electrode sheets, a plurality of positive electrode sheets and a plurality of negative electrode sheets are alternately stacked, with a separator disposed between adjacent positive and negative electrode sheets. Along a first direction, the outermost electrode sheet of the electrode assembly is a first outer electrode sheet, the first outer electrode sheet comprising a first current collector and a first active material layer, the first current collector having a first surface facing the first direction and a second surface facing the second direction, the first active material layer disposed on the second surface; wherein the first direction is the stacking direction, and the second direction is opposite to the first direction. The secondary battery further comprises a plurality of first adhesive layers, a portion of the first adhesive layer being bonded between the first surface and the inner wall of the housing, and another portion of the first adhesive layer being bonded to the first surface and at least a portion of the separator.

[0008] In the above technical solution, since the outer side of the first outer electrode sheet of the laminated electrode assembly is generally opposite the receiving portion, and there is no active material layer corresponding to the first outer electrode sheet on the receiving portion, the first outer electrode sheet adopts a structure in which the active material layer is provided on a single side. This can reduce the space occupied by the first outer electrode sheet and improve the volumetric energy density of the secondary battery. A portion of the first adhesive layer is bonded between the first surface and the inner wall of the receiving portion, which can improve the integrity between the electrode assembly and the receiving portion and reduce the movement of the electrode assembly within the receiving portion. The first adhesive layer can also disperse the external force impact on the electrode assembly to the receiving portion, thereby improving the safety of the secondary battery in the event of a fall or impact. In addition, the first adhesive layer can disperse part of the stress on the first outer electrode sheet on the first surface, reducing stress concentration, thereby reducing warping of the first current collector, improving lithium plating in the secondary battery, and alleviating shrinkage of the separator. At the same time, another portion of the first adhesive layer is bonded to the first surface and at least a portion of the isolation film, which can further limit the shrinkage of the isolation film adjacent to the first outer electrode piece, improve the integrity of the electrode assembly, and improve the lithium plating of the secondary battery. It can also reduce the short circuit caused by direct contact between the positive and negative electrodes due to the shrinkage of the isolation film in the secondary battery under conditions such as falling, impact, and high temperature, further improving the safety of the battery. In addition, the thickness of the current collector of the first outer layer of the single-sided coated electrode piece of the existing laminated battery is usually more than 50% greater than the thickness of the current collector of other electrode pieces to alleviate the uneven stress caused by the single-sided coating. Due to the provision of the first adhesive layer, the present application significantly reduces the warpage of the first outer electrode piece, and the first current collector of the first outer electrode piece can be set thinner, reducing the space occupied by the electrode assembly and improving the volume energy density of the secondary battery.

[0009] In some preferred embodiments, the outermost electrode sheet of the electrode assembly is a second outer electrode sheet. The second outer electrode sheet includes a second current collector and a second active material layer. The second current collector has a third surface facing the first direction and a fourth surface facing the second direction. The second active material layer is disposed on the third surface. The secondary battery also includes a plurality of second adhesive layers. A portion of the second adhesive layer is bonded between the fourth surface and the inner wall of the housing, and another portion of the second adhesive layer is bonded to the fourth surface and at least a portion of the separator. The electrode assembly has two outermost electrode sheets, and a second adhesive layer is also disposed on the second outer electrode sheet. This can further improve the energy density, drop resistance, impact resistance, and safety of the secondary battery.

[0010] In some preferred embodiments, the first adhesive layer comprises a hot melt adhesive and / or a pressure-sensitive adhesive. Under a predetermined temperature and / or pressure, the first adhesive layer melts, and a portion of the first adhesive layer is cast from the first surface onto the various separator layers of the other electrode assemblies. Once the first adhesive layer solidifies, the various separator layers are bonded to the first surface, thereby limiting shrinkage of the separators. This process is simple and can be easily implemented during secondary battery manufacturing.

[0011] In some preferred embodiments, the melting point of the first adhesive layer is T°C, 50°C ≤ T ≤ 70°C. This temperature range minimizes damage to the secondary battery and facilitates the compression molding of the first adhesive layer. Furthermore, when the secondary battery experiences thermal runaway, the melting of the first adhesive layer can absorb some of the heat, thereby mitigating thermal runaway.

[0012] In some preferred embodiments, the first adhesive layer includes polyurethane and / or vinyl acetate copolymer. Polyurethane and vinyl acetate copolymer have excellent adhesive properties and chemical corrosion resistance, which can extend the service life of the secondary battery and ensure a stable connection between the electrode assembly and the receiving portion.

[0013] In some preferred embodiments, the first outer electrode sheet and / or the second outer electrode sheet is a positive electrode sheet. The current collector for the positive electrode sheet is typically aluminum foil, and the current collector for the negative electrode sheet is typically copper foil. For soft-pack secondary batteries, the container material is typically an aluminum-plastic film. If the outermost single-sided coated electrode sheet is a negative electrode sheet, the copper foil in the negative electrode sheet and the aluminum in the aluminum-plastic film may undergo an electrochemical reaction, posing a safety hazard. In addition, the cost of copper foil is higher than that of aluminum foil. Therefore, the first outer electrode sheet and / or the second outer electrode sheet is preferably a positive electrode sheet.

[0014] In some preferred embodiments, along the first direction, the thickness of the first adhesive layer is H μm, 3 μm≤H≤20 μm, so that the secondary battery has a higher energy density while improving the bonding stability of each layer of the isolation film.

[0015] In some preferred embodiments, the first current collector has a first edge and a second edge along its width direction, and a third edge and a fourth edge along its length direction. A first adhesive layer is disposed on the first surface near the first edge and the second edge. During hot pressing, the two first adhesive layers can be cast onto both sides of the first current collector in the width direction, and the separators on both sides are bonded together, thereby limiting shrinkage of the separator in the width direction. Alternatively, a first adhesive layer is disposed on the first surface near the third edge and the fourth edge. During hot pressing, the two first adhesive layers can be cast onto both sides of the first current collector in the length direction, and the separators on both sides are bonded together, thereby limiting shrinkage of the separator in the length direction.

[0016] In some preferred embodiments, the electrode assembly includes several layers of separators along the first direction, and the first adhesive layer adheres at least two layers of separators. The contraction of the two separators restricts each other, thereby reducing the direct contact between the positive and negative electrodes and the occurrence of short circuits, which can effectively improve the safety of the secondary battery. 。

[0017] In a second aspect, the present application also proposes a method for preparing a secondary battery, comprising:

[0018] Providing positive electrode sheets, negative electrode sheets, and separators, alternately stacking a plurality of positive electrode sheets and a plurality of negative electrode sheets along the thickness direction of the positive electrode sheets and the negative electrode sheets, and placing separators between adjacent positive electrode sheets and negative electrode sheets to form an electrode assembly;

[0019] Along the first direction, the outermost electrode sheet is a first outer electrode sheet, the first outer electrode sheet has a first surface facing the first direction and a second surface facing the second direction, and the second surface has a first active material layer; wherein the first direction is the stacking direction, and the second direction is opposite to the first direction;

[0020] bonding a first adhesive layer to the first surface;

[0021] Accommodating the electrode assembly in the receiving portion, and bonding the first adhesive layer to the inner wall of the receiving portion;

[0022] At a first preset temperature, the first adhesive layer melts, and the receiving portion is pressed at a position on the outer surface of the receiving portion corresponding to the first adhesive layer, so that the melted first adhesive layer flows onto at least a portion of the isolation film.

[0023] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0025] FIG1 is an exploded view of a secondary battery according to some embodiments of the present application;

[0026] FIG2 is a schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0027] FIG3 is a schematic diagram of the internal structure of a secondary battery according to some embodiments of the present application;

[0028] FIG4 is a schematic diagram of stacking positive and negative electrode sheets according to some embodiments of the present application;

[0029] FIG5 is a schematic structural diagram of a first outer pole piece in some embodiments of the present application;

[0030] FIG6 is a schematic structural diagram of various first adhesive layers according to some embodiments of the present application;

[0031] FIG7 is a schematic diagram showing the distribution of various first adhesive layers on the first surface in some embodiments of the present application;

[0032] FIG8 is a schematic structural diagram of the second outer pole piece in some embodiments of the present application.

[0033] Description of reference numerals:

[0034] 100. Secondary battery;

[0035] 10. Accommodation portion; 11. First housing; 111. First cavity; 12. Second housing; 121. Second cavity;

[0036] 20. Electrode assembly; 21. Positive electrode sheet; 211. Positive current collector; 212. Positive active material layer; 22. Negative electrode sheet; 221. Negative current collector; 222. Negative active material layer; 23. Separator; 24. First outer electrode sheet; 241. First current collector; 241a. First edge; 241b. Second edge; 241c. Third edge; 241d. Fourth edge; 2411. First surface; 2412. Second surface; 242. First active material layer; 25. Second outer electrode sheet; 251. Second current collector; 2511. Third surface; 2512. Fourth surface; 252. Second active material layer;

[0037] 30. Tab; 31. Positive tab; 32. Negative tab;

[0038] 40. First adhesive layer;

[0039] 50. Second adhesive layer;

[0040] Z, first direction; G, second direction; Y, third direction; X, fourth direction. DETAILED DESCRIPTION

[0041] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0042] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" and "several" mean more than two, unless otherwise specifically defined.

[0043] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0044] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive with other embodiments. Furthermore, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not conflict with each other.

[0045] In the first aspect, the present application proposes a secondary battery 100. Please refer to Figures 1 and 2. The secondary battery 100 includes a housing 10, an electrode assembly 20, a tab 30, and a first adhesive layer 40. The housing 10 is a mounting base and container for the remaining components of the secondary battery 100. The electrode assembly 20 is housed in the housing 10. The electrode assembly 20 is the core component for the secondary battery 100 to realize charging and discharging. The first adhesive layer 40 is bonded between the electrode assembly 20 and the inner wall of the housing 10. One end of the tab 30 is electrically connected to the electrode assembly 20, and the other end extends out of the housing 10. Next, taking the secondary battery 100 as a lithium-ion battery as an example, the specific structure of the secondary battery 100 is explained; it can be understood that in other embodiments of the present application, the secondary battery 100 can also be a sodium-ion battery or other forms of secondary battery.

[0046] Regarding the above-mentioned accommodating portion 10, please refer to Figures 1 and 2. The accommodating portion 10 can be made of a flexible material, which constitutes the mounting base, container and outer protective structure of the secondary battery 100. The accommodating portion 10 is defined by a accommodating cavity (not shown in the figure), which can be used to accommodate the electrolyte (not shown in the figure) and the above-mentioned electrode assembly 20. For example, the accommodating portion 10 includes a first shell 11 and a second shell 12, the first shell 11 is provided with a first pit cavity 111, and the second shell 12 is provided with a second pit cavity 121. The above-mentioned electrode assembly 20 can be placed in the first pit cavity 111, the second shell 12 covers the first pit cavity 111 of the first shell 11, and the second pit cavity 121 is connected to the first pit cavity 111 to form a accommodating cavity. The connection between the edges of the two shells can be sealed by hot pressing to make the two shells bonded to each other to seal the accommodating cavity. In other embodiments, the housing portion 10 may also be made of a hard material. For example, the housing portion 10 may be formed by punching a metal sheet. The thickness of the metal sheet may be set to 0.1 to 0.4 mm to ensure the punching strength of the housing portion 10. The metal sheet may be made of a conductive metal material such as aluminum, steel, stainless steel, nickel, copper, or magnesium alloy. This allows the housing portion 10 to draw a certain polarity of the secondary battery 100, for example, the housing portion 10 itself may serve as the positive or negative electrode of the secondary battery 100.

[0047] The electrode assembly 20 is accommodated in the accommodating portion 10. Referring to FIG3 , the electrode assembly 20 includes a positive electrode sheet 21, a separator 23, and a negative electrode sheet 22. Along the thickness direction (first direction Z) of the positive electrode sheet 21 and the negative electrode sheet 22, a plurality of positive electrode sheets 21 and a plurality of negative electrode sheets 22 are alternately stacked, and a separator 23 is provided between adjacent positive electrode sheets 21 and negative electrode sheets 22.

[0048] Regarding the above-mentioned positive electrode sheet 21, please refer to Figures 3 and 4. The positive electrode sheet 21 includes a positive electrode current collector 211 and a positive electrode active material layer 212. The positive electrode current collector 211 can be made of aluminum foil that is flat and has a strip-shaped structure. The positive electrode active material layer 212 can be arranged on at least one surface of the positive electrode current collector 211. For example, the positive electrode active material layer 212 is arranged on two opposite surfaces in the thickness direction (first direction Z) of the positive electrode current collector 211. The positive electrode active material layer 212 includes a positive electrode active material, a conductive agent, and a binder. These materials are mixed, stirred evenly, and coated on the positive electrode current collector 211 to obtain the positive electrode active material layer 212. Among them, the positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron manganese phosphate, and cobalt-free materials.

[0049] Regarding the negative electrode sheet 22, referring to Figures 3 and 4, the negative electrode sheet 22 includes a negative electrode current collector 221 and a negative electrode active material layer 222. The negative electrode current collector 221 serves as a conductive substrate and can be a flat, strip-shaped copper foil. In other embodiments, the negative electrode current collector 221 can also be made of nickel foil or polymer copper foil (copper foil with a polymer such as polyethylene, polypropylene, or polyamide disposed on its surface). The negative electrode active material layer 222 can be disposed on at least one surface of the negative electrode current collector 221, for example, on two opposing surfaces in the thickness direction (first direction Z) of the negative electrode current collector 221. The negative electrode active material layer 222 includes a negative electrode active material, a conductive agent, and a binder. These components are mixed, stirred, and then coated on the negative electrode current collector 221 to form the negative electrode active material layer 222. The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxides, or silicon alloys.

[0050] Regarding the separator 23, referring to Figures 3 and 4, the positive electrode sheets 21 and the negative electrode sheets 22 are alternately stacked along a first direction Z, with a separator 23 disposed between adjacent positive electrode sheets 21 and negative electrode sheets 22. The separator 23 can be a ceramic PE separator or PP separator, etc., to insulate and separate the positive electrode sheets 21 and the negative electrode sheets 22.

[0051] Regarding the tabs 30, please refer to Figures 1 and 2. The tabs 30 include a positive tab 31 and a negative tab 32. Both the positive tab 31 and the negative electrode tab 32 can be made of metal sheets, such as aluminum, copper, or nickel. One end of the positive tab 31 is electrically connected to the positive electrode tab 21 within the housing 10, for example, by welding or conductive adhesive, while the other end extends outside the housing 10. One end of the negative tab 32 is electrically connected to the negative electrode tab 22 within the housing 10, while the other end extends outside the housing 10 for electrical connection to external electrical equipment.

[0052] Referring to Figures 3 and 5 , along a first direction Z, the positive electrode sheet 21, the separator 23, and the negative electrode sheet 22 are stacked in several layers. The outermost electrode sheet of the electrode assembly 20 in the first direction Z is the first outer electrode sheet 24. The first outer electrode sheet 24 includes a first current collector 241 and a first active material layer 242. The first current collector 241 has a first surface 2411 facing the first direction Z and a second surface 2412 facing the second direction G. The first active material layer 242 is disposed on the second surface 2412, while the first surface 2411 is not provided with the first active material layer 242. The outer side of the first outer electrode sheet 24 faces the receiving portion 10. The receiving portion 10 does not have an active material layer corresponding to the first outer electrode sheet 24. Therefore, the first outer electrode sheet 24 adopts a structure in which the active material layer is disposed on a single side. This reduces the space occupied by the first outer electrode sheet 24 and improves the volumetric energy density of the secondary battery 100. The first direction Z is opposite to the second direction G.

[0053] The first outer electrode sheet 24 can be the positive electrode sheet 21. The first current collector 241 is typically made of aluminum foil, which has excellent electrical conductivity and corrosion resistance. Furthermore, aluminum foil is lightweight, easy to process, and inexpensive, meeting the electrical conductivity and current collection requirements of the internal current collector of the secondary battery 100. Furthermore, aluminum foil effectively improves the heat dissipation performance of the battery, ensuring that the battery maintains a low temperature during operation.

[0054] The current collector of the positive electrode sheet 21 is usually aluminum foil, and the current collector of the negative electrode sheet 22 is usually copper foil. For the soft-pack secondary battery 100, the material of its accommodating portion 10 is usually aluminum-plastic film. If the outermost single-sided coated electrode sheet is the negative electrode sheet 22, the copper foil in the negative electrode sheet 22 and the aluminum in the aluminum-plastic film may undergo an electrochemical reaction, causing a safety hazard, and the cost of copper foil is higher than that of aluminum foil. Therefore, it is preferred that the first outer electrode sheet 24 and / or the second outer electrode sheet 25 is the positive electrode sheet 21.

[0055] Regarding the above-mentioned first adhesive layer 40, please refer to Figures 3 and 5. A portion of the first adhesive layer 40 is bonded between the first surface 2411 and the inner wall of the accommodating portion 10, which can improve the integrity between the electrode assembly 20 and the accommodating portion 10 and reduce the movement of the electrode assembly 20 in the accommodating portion 10. The first adhesive layer 40 can also disperse the external force impact on the electrode assembly 20 to the accommodating portion 10, thereby improving the safety of the secondary battery 100 in the event of falling, impact, etc.; and, the first adhesive layer 40 can disperse part of the stress on the first outer electrode 24 on the first surface 2411, reduce stress concentration, and thereby reduce warping of the first current collector 241, thereby improving lithium plating of the secondary battery 100 and alleviating the shrinkage of the isolation membrane 23. At the same time, another portion of the first adhesive layer 40 is bonded to the first surface 2411 and at least a portion of the separator 23, further limiting the shrinkage of the separator 23 adjacent to the first outer electrode sheet, improving the integrity of the electrode assembly 20, and improving lithium deposition in the secondary battery 100. Furthermore, the secondary battery 100 can be reduced from being dropped, impacted, or subjected to high temperatures, thereby reducing the risk of short circuits caused by direct contact between the positive and negative electrodes due to shrinkage of the separator 23, further enhancing battery safety. Furthermore, in existing laminated batteries, the first outer layer of the single-sided coated electrode sheet typically has a current collector that is at least 50% thicker (at least 20 μm) than that of other electrode sheets to alleviate the uneven stress caused by the single-sided coating. However, in the present application, the provision of the first adhesive layer 40 significantly reduces the warpage of the first outer electrode sheet 24, allowing the first current collector 241 of the first outer electrode sheet 24 to be made thinner, reducing the space occupied by the electrode assembly 20 and increasing the volumetric energy density of the secondary battery 100.

[0056] Because the provision of the first adhesive layer 40 can reduce warping of the first current collector 241, the provision of the first adhesive layer 40 is particularly suitable for the positive electrode sheet 21. In existing laminated batteries, the first outer layer of the single-sided coated electrode sheet typically has the current collector set to be more than 50% thicker (more than 20 μm) than the current collectors of other electrode sheets to alleviate the uneven stress caused by the single-sided coating. In the embodiments of the present application, because the first adhesive layer 40 itself can reduce the warping of the first current collector 241, the thickness of the first current collector 241 can also be appropriately reduced, for example, using a first current collector 241 with a thickness of 7 μm to 12 μm, to improve the energy density of the secondary battery 100.

[0057] The first adhesive layer 40 comprises a hot melt adhesive. When the first adhesive layer 40 is provided on the first surface 2411 of the first outer electrode sheet 24, at a predetermined temperature, the first adhesive layer 40 melts and a portion of the first adhesive layer 40 flows from the first surface 2411 to the various layers of the separators 23 of the other electrode assemblies 20. After the first adhesive layer 40 solidifies, the various layers of the separators 23 are bonded to the first surface 2411, thereby limiting the shrinkage of the separators 23. Alternatively, the first adhesive layer 40 comprises a pressure-sensitive adhesive. When the first adhesive layer 40 is provided on the first surface 2411 of the first outer electrode sheet 24, when the electrode assembly 20 is housed in a housing, the first adhesive layer 40 is bonded between the electrode assembly 20 and the inner wall of the housing by installing the electrode assembly 20 or the housing. Furthermore, when pressed, a portion of the first adhesive layer 40 can flow to the various layers of the separators 23, thereby bonding the various layers of the separators 23 to the first surface 2411 of the first outer electrode sheet 24, thereby limiting the shrinkage of the separators 23.

[0058] The melting point of the first adhesive layer 40 is T°C, 50°C ≤ T ≤ 70°C. When the temperature reaches this melting point, the first adhesive layer 40 can be melted, cast, and bonded to the various layers of the separator 23. For example, when the first adhesive layer 40 comprises a hot melt adhesive and a pressure-sensitive adhesive, applying a pressure of 1.0 MPa to 2.5 MPa to the first adhesive layer 40 at a temperature of 60°C to 90°C can cause a portion of the first adhesive layer 40 to melt and cast onto the various layers of the separator 23. This temperature range minimizes damage to the secondary battery 100 and facilitates the compression molding of the first adhesive layer 40. Furthermore, when the secondary battery 100 experiences thermal runaway, the melting of the first adhesive layer 40 can absorb some of the heat, thereby mitigating thermal runaway.

[0059] Regarding the material of the first adhesive layer 40, the housing portion 10 needs to be filled with an electrolyte. Typically, the electrolyte is corrosive and can easily corrode the first adhesive layer 40, affecting the bonding stability of the first adhesive layer 40. For example, the electrolyte includes lithium salt compounds such as lithium hexafluorophosphate, lithium tetrafluoroborate, or lithium perchlorate, carbonate solvents such as glycol dimethyl ether, dimethyl dicarbonate, and ethylene dimethyl carbonate, and additives such as flame retardants and inhibitors. In an embodiment of the present application, the first adhesive layer 40 may include polyurethane and / or vinyl acetate copolymer. Polyurethane and vinyl acetate copolymer have excellent bonding properties and chemical corrosion resistance, which can extend the service life of the secondary battery 100 and ensure a stable connection between the electrode assembly 20 and the housing portion 10.

[0060] As for the thickness of the first adhesive layer 40, if its thickness is too large, it will affect the energy density of the battery, and if the thickness is too small, it may cause instability between the electrode assembly 20 and the accommodating portion 10. In the embodiment of the present application, along the first direction Z, the thickness of the first adhesive layer 40 is Hμm, 3≤H≤20, so that the secondary battery 100 has a higher energy density while ensuring stable bonding between the electrode assembly 20 and the accommodating portion 10. For example, a hot melt adhesive and / or pressure sensitive adhesive with a thickness of 8μm to 80μm is coated on the first surface 2411 of the first outer electrode sheet 24, and after a portion of the hot melt adhesive and / or pressure sensitive adhesive is cast and bonded to each layer of the isolation film 23, a first adhesive layer 40 with a thickness of 3μm to 20μm is formed on the first surface 2411, so that the secondary battery 100 has a higher energy density and improves the bonding stability of each layer of the isolation film 23.

[0061] Among them, after the first adhesive layer 40 is cast, it is bonded to at least two layers of isolation films 23, for example, two layers of isolation films 23 are bonded, namely a first isolation film and a second isolation film. The contraction of the first isolation film can drive the expansion of the second isolation film, and similarly, the contraction of the second isolation film can drive the expansion of the first isolation film. In this way, the contraction of the first isolation film and the second isolation film can be mutually restricted, thereby reducing the direct contact between the positive and negative pole pieces and the occurrence of short circuits, which can effectively improve the safety of the secondary battery 100.

[0062] Regarding the shape of the first adhesive layer 40, please refer to Figures 5 and 6. When observed in a direction perpendicular to the first surface 2411 (the second direction G), the first adhesive layer 40 can be in the shape of a straight line, a curve, intermittent dots, or an intermittent dot-line, etc. When the first adhesive layer 40 is coated on the first surface 2411 of the first outer electrode 24, the first adhesive layer 40 can be 10 mm away from the edge of the first surface 2411. After hot pressing the first adhesive layer 40, part of the first adhesive layer 40 can be easily cast onto each layer of the isolation film 23.

[0063] For example, referring to Figures 3 and 7, along the width direction (third direction Y) of the first current collector 241, the first current collector 241 has a first edge 241a and a second edge 241b. A first adhesive layer 40 is disposed on the first surface 2411 near the first edge 241a and the second edge 241b. During hot pressing, the two first adhesive layers 40 can be cast onto both sides of the first current collector 241 in the width direction, bonding the separator 23 on both sides, thereby limiting shrinkage of the separator 23 in the width direction. Alternatively, along the length direction (fourth direction X) of the first current collector 241, the first current collector 241 has a third edge 241c and a fourth edge 241d. A first adhesive layer 40 is disposed on the first surface 2411 near the third edge 241c and the fourth edge 241d. During hot pressing, the two first adhesive layers 40 can be cast onto both sides of the first current collector 241 along the length direction, bonding the separator 23 on both sides, thereby limiting shrinkage of the separator 23 in the length direction. Alternatively, at least two first adhesive layers 40 can be interlaced on the first surface 2411 to ensure that they can be cast onto each layer of the separator 23.

[0064] Referring to Figures 3 and 8 , along the second direction G, the outermost electrode sheet of the electrode assembly 20 is the second outer electrode sheet 25. The second outer electrode sheet 25 includes a second current collector 251 and a second active material layer 252. The second current collector 251 has a third surface 2511 facing the first direction Z and a fourth surface 2512 facing the second direction G. The second outer electrode sheet 25 may also be coated on one side, for example, the second active material layer 252 is provided only on the third surface 2511, and the fourth surface 2512 is opposite to the accommodating portion 10. Since there is no active material layer corresponding to the second outer electrode sheet 25 on the accommodating portion 10, the fourth surface 2512 may be provided with a blank foil (no active material layer is provided) to reduce the space occupied by the second outer electrode sheet 25 and improve the volumetric energy density of the secondary battery 100.

[0065] Referring to Figures 3 and 8 , the secondary battery 100 further includes several second adhesive layers 50. A portion of the second adhesive layer 50 is bonded between the fourth surface 2512 and the inner wall of the housing 10 to enhance the integrity between the electrode assembly 20 and the housing 10 and reduce movement of the electrode assembly 20 within the housing 10. Furthermore, the second adhesive layer 50 disperses some of the stress on the second outer electrode sheet 25 on the fourth surface 2512, reducing stress concentration and, consequently, warping of the second outer electrode sheet 25. The electrode assembly has two outermost electrode sheets, and the second adhesive layer 50 is also provided on the second outer electrode sheet 25, further improving the energy density, drop resistance, impact resistance, and safety of the secondary battery 100.

[0066] Another portion of the second adhesive layer 50 is bonded to the fourth surface 2512 and at least a portion of the separator 23, further limiting the shrinkage of the separator 23, improving the integrity of the electrode assembly 20, reducing short circuits caused by direct contact between the positive and negative electrodes, and further enhancing the impact resistance of the secondary battery 100. Furthermore, the provision of the second adhesive layer 50 significantly reduces the warpage of the second outer electrode sheet 25, allowing the second current collector 251 of the second outer electrode sheet 25 to be made thinner, reducing the space occupied by the electrode assembly 20 and increasing the volumetric energy density of the secondary battery 100. Similar to the first adhesive layer 40, the second adhesive layer 50 can also be made of hot melt adhesive and / or pressure-sensitive adhesive with a melting point of 50°C to 70°C.

[0067] The second outer electrode sheet 25 can be the positive electrode sheet 21, and the second current collector 251 is made of aluminum foil. The provision of the first adhesive layer 40 can reduce warping of the first current collector 241, and therefore the provision of the first adhesive layer 40 is particularly suitable for the positive electrode sheet 21. Alternatively, the second outer electrode sheet 25 can be the negative electrode sheet 22, and the second current collector 251 is made of copper foil. Copper foil itself has high strength and is not easily deformed. The provision of the second adhesive layer 50 can also reduce warping of the second current collector 251. Therefore, the thickness of the copper foil can be appropriately reduced to reduce the space occupied by the electrode assembly 20 and improve the volumetric energy density of the secondary battery 100.

[0068] In the embodiment of the present application, the structure of the first outer electrode sheet 24 with an active material layer on a single surface can reduce the space occupied by the first outer electrode sheet 24 and improve the volumetric energy density of the secondary battery 100. A portion of the first adhesive layer 40 is bonded between the first surface 2411 and the inner wall of the housing 10, improving the integrity between the electrode assembly 20 and the housing 10 and reducing movement of the electrode assembly 20 within the housing 10. Furthermore, the first adhesive layer 40 can partially distribute the stress on the first outer electrode sheet 24 on the first surface 2411, reducing stress concentration and thereby reducing warping of the first current collector 241, alleviating shrinkage of the separator 23 and improving the impact resistance of the secondary battery 100. Meanwhile, another portion of the first adhesive layer 40 is bonded to the first surface 2411 and at least a portion of the separator 23, further limiting shrinkage of the separator 23, improving lithium plating in the secondary battery, and improving the integrity of the electrode assembly 20, reducing short circuits caused by direct contact between the positive and negative electrode sheets 22, and further improving the impact resistance of the secondary battery 100. In addition, due to the provision of the first adhesive layer 40 , the warpage of the first outer electrode sheet 24 is significantly reduced, and the first current collector 241 of the first outer electrode sheet 24 can be set thinner, thereby reducing the space occupied by the electrode assembly 20 and improving the volume energy density of the secondary battery 100 .

[0069] In a second aspect, an embodiment of the present application further provides a method for preparing a secondary battery as described in any embodiment of the first aspect above, comprising:

[0070] S100, providing positive electrode sheets, negative electrode sheets, and separators, and alternately stacking a plurality of positive electrode sheets and a plurality of negative electrode sheets along the thickness direction of the positive electrode sheets and the negative electrode sheets, and placing separators between adjacent positive electrode sheets and negative electrode sheets to form an electrode assembly;

[0071] S200, along a first direction, the outermost electrode sheet is a first outer electrode sheet, the first outer electrode sheet has a first surface facing the first direction and a second surface facing a second direction, the second surface having a first active material layer; wherein the first direction is a stacking direction, and the second direction is opposite to the first direction;

[0072] S300, bonding a first adhesive layer to the first surface; the first adhesive layer may be disposed at a position no more than 10 mm away from the first surface;

[0073] S400, accommodating the electrode assembly in the receiving portion, and bonding the first adhesive layer to the inner wall of the receiving portion;

[0074] S500, at a first preset temperature, the first adhesive layer is melted, and the accommodating portion is pressed at a position on the outer surface of the accommodating portion corresponding to the first adhesive layer, so that the melted first adhesive layer flows to at least a portion of the isolation film, thereby bonding the first surface to the isolation film to limit the shrinkage of the isolation film and improve the impact resistance of the secondary battery.

[0075] In the embodiment of the present application, a lithium-ion battery is taken as an example and a drop test is performed on it.

[0076] Example 1

[0077] Preparation of lithium-ion batteries

[0078] (1) Preparation of positive electrode sheet: The positive electrode 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. Aluminum foil with a length of 87mm, a width of 60mm, and a thickness of 8μm is selected as the positive electrode current collector. One end of the positive electrode current collector aluminum foil is cut in the longitudinal direction to reserve a positive electrode tab with a length of 7mm and a width of 5mm. The uncut portion is a coating portion with a length of 80mm and a width of 60mm. The slurry is evenly coated on one surface of the coating portion and dried to obtain a positive electrode sheet with a positive electrode active material layer coated on one side. The above steps are repeated on the other surface of the coating portion to obtain a positive electrode sheet with a positive electrode active material layer coated on both sides. Among them, a positive electrode plate coated with a positive electrode active material layer on one side is reserved as the first outer layer plate.

[0079] (2) Preparation of negative electrode sheet: Using graphite as the negative electrode active material, the negative electrode active material graphite, the binder styrene butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70wt% is prepared and stirred evenly. A copper foil with a length of 88.2mm, a width of 60mm and a thickness of 5μm is selected as the negative electrode current collector. One end of the negative electrode current collector copper foil is cut in the longitudinal direction to reserve a negative electrode tab with a length of 7mm and a width of 5mm. The uncut part is a coating part with a length of 81.2mm and a width of 60mm. The slurry is evenly coated on one surface of the coating part and dried to obtain a negative electrode sheet with a negative electrode active material layer coated on one side. Repeat the above steps on the other surface of the coating part to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. Among them, a negative electrode sheet with a negative electrode active material layer coated on one side is reserved as the second outer layer sheet.

[0080] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were 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) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0081] (4) Preparation of isolation membrane: A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one surface of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramic in the ceramic layer is 95%.

[0082] (5) Preparation of electrode assembly: The above-mentioned positive electrode sheets, separators and negative electrode sheets are alternately stacked in 10 layers in sequence. The bottom electrode sheet uses the second outer electrode sheet, and the top electrode sheet uses the first outer electrode sheet. Separators are set between adjacent positive and negative electrode sheets to form an electrode assembly for standby use. 。

[0083] (6) Assembly of the electrode assembly: Place the aluminum-plastic film (accommodation part) with the pits formed in it into the assembly fixture, with the pits facing upwards. Set a polyurethane adhesive layer with a thickness of 8 μm on the outer edge of the first outer layer of the electrode assembly (the initial thickness of the first adhesive layer, melting point 60°C), place the electrode assembly in the pit, and set a low-density polyethylene sealing part at the two tabs, and apply external force to press it tightly. Then cover the electrode assembly with the pit side facing downwards on another aluminum-plastic film with the pits formed in it, and heat-seal the four sides of the two aluminum-plastic films by hot pressing. In an environment of 80°C, the aluminum-plastic film is hot-pressed to form the first adhesive layer corresponding to the polyurethane adhesive layer, wherein the hot pressing pressure is controlled at 2.0 MPa, so that the polyurethane adhesive layer is cast onto each layer of the isolation film.

[0084] (7) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and after vacuum packaging, static standing, hot pressing, shaping and other processes, the lithium-ion battery is produced.

[0085] Relevant parameters of Examples 2 to 17 and Comparative Example 1 are shown in Table 1 below, wherein the first adhesive layer and the second adhesive layer are not provided in Comparative Example 1.

[0086] Drop test:

[0087] Place the lithium-ion battery in a fixture and drop it from a height of 1.5m using a drop device in the following sequence: head-to-tail-head right corner-to-tail right corner-to-head left corner-to-tail left corner (angle: 45±15°). Repeat 100 times. After the drop test, inspect the lithium-ion battery's appearance. The drop test passing criteria are: no smoke, no fire, and no leakage. Disassemble the lithium-ion battery, observe the cast adhesive bond of the first adhesive layer, and record the thickness of the first adhesive layer between the first outer electrode and the housing (the thickness after the first adhesive layer is crimped).

[0088] The test results are shown in Table 1 below.

[0089] Table 1

[0090] According to Table 1 above, combined with Examples 1 to 17 and Comparative Example 1, it can be seen that when a first adhesive layer is used between the electrode assembly and the accommodating portion, the drop resistance of the lithium-ion battery can be effectively improved. This is because a portion of the first adhesive layer is bonded between the first surface and the inner wall of the accommodating portion, which can improve the integrity between the electrode assembly and the accommodating portion and reduce the movement of the electrode assembly in the accommodating portion. The first adhesive layer can also disperse the external force impact on the electrode assembly to the accommodating portion, thereby improving the safety of the secondary battery in situations such as falling and impact. In addition, the first adhesive layer can disperse part of the stress on the first outer layer electrode sheet on the first surface, reduce stress concentration, and thereby reduce the warping of the first current collector, improve the lithium plating of the secondary battery, and alleviate the shrinkage of the isolation membrane. When the lithium-ion battery is subjected to a drop impact, the isolation membrane can always separate the positive and negative electrode sheets, reduce the occurrence of short circuits, and improve the drop resistance of the lithium-ion battery. At the same time, another part of the first adhesive layer is bonded to the first surface and at least part of the isolation film, which can further limit the shrinkage of the isolation film adjacent to the first outer electrode, improve the integrity of the electrode assembly, reduce the short circuit caused by direct contact between the positive and negative electrodes, and further improve the drop resistance of the secondary battery.

[0091] At the same time, compared with Comparative Example 1, the interface black spots in Examples 1 to 17 are significantly reduced. This is because the warping of the first outer electrode is reduced, and the combination of the active material layer and the first current collector is more stable, which reduces the precipitation of lithium ions and effectively improves lithium plating.

[0092] In Example 1, the first adhesive layer is relatively thin, and the bonding force between the first adhesive layer and the receiving portion is relatively weak, which may lead to adhesive failure, resulting in the lithium-ion battery's drop resistance being inferior to that of other embodiments. In Example 9, the first adhesive layer is relatively thick, and the gap between the electrode assembly and the receiving portion is also increased. It may be necessary to rely on the first adhesive layer to support the electrode assembly in the receiving portion. However, the first adhesive layer is made of polyurethane, which is not very strong. When the lithium-ion battery is dropped, it may cause adhesive failure and a significant loss of battery energy density. Therefore, in the embodiments of the present application, the preferred thickness of the first adhesive layer is 3μm to 20μm.

[0093] Combining Examples 12 and 13 with Examples 16 and 17, it can be seen that the use of a second adhesive layer can further reduce the risk of drop failure of lithium-ion batteries. The electrode assembly has two outermost electrode sheets, and a second adhesive layer is also provided on the second outermost electrode sheet, which can further improve the energy density, drop resistance, impact resistance, and safety of the secondary battery.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising a housing portion and an electrode assembly received within the housing portion, the electrode assembly including a positive electrode plate, a separator, and a negative electrode plate. Along the thickness direction of the positive electrode plate and the negative electrode plate, a plurality of the positive electrode plates and a plurality of the negative electrode plates are alternately stacked, and the separator is disposed between adjacent positive electrode plates and negative electrode plates. It is characterized in that: Along a first direction, the outermost electrode plate of the electrode assembly is a first outermost electrode plate, the first outermost electrode plate including a first current collector and a first active material layer. The first current collector has a first surface facing the first direction and a second surface facing a second direction, and the first active material layer is disposed on the second surface; wherein, the first direction is the stacking direction, and the second direction is opposite to the first direction; The secondary battery further includes a plurality of first adhesive layers, a part of the first adhesive layer being bonded between the first surface and the inner wall of the housing portion, and another part of the first adhesive layer bonding the first surface and at least part of the separator.

2. The secondary battery according to claim 1, characterized in that, Along the second direction, the outermost electrode plate of the electrode assembly is a second outermost electrode plate, the second outermost electrode plate including a second current collector and a second active material layer. The second current collector has a third surface facing the first direction and a fourth surface facing the second direction, and the second active material layer is disposed on the third surface; The secondary battery further includes a plurality of second adhesive layers, a part of the second adhesive layer being bonded between the fourth surface and the inner wall of the housing portion, and another part of the second adhesive layer bonding the fourth surface and at least part of the separator.

3. The secondary battery according to claim 1 or 2, characterized in that, The first adhesive layer includes a hot melt adhesive and / or a pressure sensitive adhesive.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The melting point of the first adhesive layer is T °C, 50 °C ≤ T ≤ 70 °C.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The first adhesive layer includes polyurethane and / or vinyl acetate copolymer.

6. The secondary battery according to claim 2, characterized in that, The first outermost electrode plate and / or the second outermost electrode plate is a positive electrode plate.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, Along the first direction, the thickness of the first adhesive layer is H μm, 3 μm ≤ H ≤ 20 μm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, Along the width direction of the first current collector, the first current collector has a first edge and a second edge; along the length direction of the first current collector, the first current collector has a third edge and a fourth edge; On the first surface, the first adhesive layer is disposed at positions close to the first edge and the second edge; and / or, On the first surface, the first adhesive layer is disposed at positions close to the third edge and the fourth edge.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, Along the first direction, the electrode assembly includes a plurality of layers of the separator, and the first adhesive layer bonds at least two layers of the separator.

10. A method for manufacturing a secondary battery according to any one of claims 1 to 9, characterized in that, Including: Providing a positive electrode plate, a negative electrode plate, and a separator, and alternately stacking a plurality of the positive electrode plates and a plurality of the negative electrode plates along the thickness direction of the positive electrode plate and the negative electrode plate, and disposing the separator between adjacent positive electrode plates and negative electrode plates to form an electrode assembly; Along the first direction, the outermost electrode tab uses a first outermost electrode tab, the first outermost electrode tab having a first surface facing the first direction and a second surface facing the second direction, the second surface having a first active material layer; wherein, the first direction is the direction of lamination, and the second direction is opposite to the first direction; Bond a first adhesive layer to the first surface; Place the electrode assembly in the accommodating portion and bond the first adhesive layer to the inner wall of the accommodating portion; At a first preset temperature, the first adhesive layer melts, and press the accommodating portion at a position corresponding to the first adhesive layer on the outer surface of the accommodating portion, such that the molten first adhesive layer flows onto at least a portion of the separator film.

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