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 method of manufacturing the same

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application No. 202311863247.1, filed on December 29, 2023, and entitled "Secondary battery and method of manufacturing the same", the content of which is incorporated herein by reference in its entirety TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to a secondary battery and a method of manufacturing the same. BACKGROUND

[0004] With the rapid development of the battery industry, the application of laminated batteries with advantages of high energy density and high safety is gradually widespread. In order to improve the energy density of the laminated battery, the outermost electrode of the electrode assembly of the laminated battery is usually a single-sided coated electrode, that is, the outermost electrode of the 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 package is empty as a current collector. However, the outermost single-sided coated electrode of the electrode assembly of the laminated battery is prone to warping due to uneven stress on both sides, which reduces the bonding area of the single-sided coated electrode and the separator, and easily causes the separator to shrink. In the case of internal heating of the battery during collision, falling, use, etc., the positive electrode and the negative electrode of the battery are prone to contact and short circuit. SUMMARY

[0005] Embodiments of the present application aim to provide a secondary battery and a method of manufacturing the same to reduce the warping of the outermost electrode of the laminated battery, thereby reducing the shrinkage of the separator and improving the safety performance of the laminated battery.

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

[0007] In a first aspect, the present application provides a secondary battery, comprising a containing portion and an electrode assembly accommodated in the containing portion, the electrode assembly comprising a positive electrode, a separator and a negative electrode, a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked along the thickness direction of the positive electrode and the negative electrode, and the separator is arranged between adjacent positive electrodes and negative electrodes. Along a first direction, the outermost electrode of the electrode assembly is a first outer electrode, the first outer electrode comprises 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 arranged 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 part of the first adhesive layers is bonded between the first surface and the inner wall of the containing portion, and another part of the first adhesive layers is bonded to the first surface and at least part of the separator.

[0008] In the above technical solution, since the first outer layer electrode plate of the laminated electrode assembly is usually opposite to the accommodating portion, and the accommodating portion does not have an active material layer corresponding to the first outer layer electrode plate, the first outer layer electrode plate adopts a structure of single-sided active material layer, which can reduce the space occupied by the first outer layer electrode plate and improve the volume energy density of the secondary battery. A part 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, reduce the movement of the electrode assembly in the accommodating portion, and disperse the external force impact on the electrode assembly to the accommodating portion, thereby improving the safety of the secondary battery under conditions such as falling and impact. In addition, the first adhesive layer can disperse part of the stress on the first outer layer electrode plate at the first surface, reduce stress concentration, and further reduce the warping of the first current collector, thereby improving the lithium precipitation of the secondary battery and relieving the shrinkage of the separator. At the same time, another part of the first adhesive layer bonds the first surface and at least part of the separator, which can further limit the shrinkage of the separator adjacent to the first outer layer electrode plate, improve the integrity of the electrode assembly, and improve the lithium precipitation of the secondary battery, and reduce the short circuit caused by the direct contact of the positive and negative electrodes due to the shrinkage of the separator under conditions such as falling, impact, and high temperature, thereby further improving the safety of the battery. In addition, the thickness of the current collector of the first outer layer of the existing laminated battery is usually more than 50% larger than that of other electrode current collectors, in order to relieve the stress unevenness caused by single-sided coating. The present application can significantly reduce the warping rate of the first outer layer electrode plate due to the setting of the first adhesive layer, and the first current collector of the first outer layer electrode plate can be made thinner, thereby 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 layer electrode plate of the electrode assembly is a second outer layer electrode plate, the second outer layer electrode plate comprises 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 arranged on the third surface. The secondary battery further comprises a plurality of second adhesive layers, a part of the second adhesive layers is bonded between the fourth surface and the inner wall of the accommodating portion, and another part of the second adhesive layers is bonded to the fourth surface and at least part of the separator. The electrode assembly has two outermost layer electrode plates, and the second adhesive layer is also arranged on the second outer layer electrode plate, which can further improve the energy density, anti-falling performance, anti-impact performance, and safety of the secondary battery.

[0010] In some preferred embodiments, the first adhesive layer comprises hot melt adhesive and / or pressure sensitive adhesive. Under a predetermined temperature and / or pressure, the first adhesive layer melts and a part of the first adhesive layer is cast from the first surface to the other layers of the separator of the electrode assembly. After the first adhesive layer solidifies, the layers of the separator are bonded to the first surface, thereby limiting the shrinkage of the separator. The process is simple and can be easily realized during the preparation of the secondary battery.

[0011] In some preferred embodiments, the first adhesive layer has a melting point of T °C, and 50 °C≤T≤70 °C. This temperature range is less likely to damage the secondary battery and is suitable for the press forming of the first adhesive layer. In addition, when the secondary battery is in thermal runaway, the melting of the first adhesive layer can also absorb part of the heat, thereby alleviating the thermal runaway of the secondary battery.

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

[0013] In some preferred embodiments, the first outer layer electrode tab and / or the second outer layer electrode tab is a positive electrode tab. The current collector of the positive electrode tab is usually aluminum foil, and the current collector of the negative electrode tab is usually copper foil. For soft package secondary batteries, the accommodation portion material is usually an aluminum plastic film. If the outermost single-sided coated electrode tab is a negative electrode tab, the copper foil in the negative electrode tab and the aluminum in the aluminum plastic film may have an electrochemical reaction, causing a safety hazard. In addition, the cost of copper foil is higher than that of aluminum foil. Therefore, it is preferred that the first outer layer electrode tab and / or the second outer layer electrode tab be a positive electrode tab.

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

[0015] In some preferred embodiments, 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 arranged near the first edge and the second edge. During hot pressing, the two first adhesive layers can be cast to both sides of the width direction of the first current collector and bond the separator films on both sides, thereby limiting the shrinkage of the separator film in the width direction; and / or, on the first surface, the first adhesive layer is arranged near the third edge and the fourth edge. During hot pressing, the two first adhesive layers can be cast to both sides of the length direction of the first current collector and bond the separator films on both sides, thereby limiting the shrinkage of the separator film in the length direction.

[0016] In some preferred embodiments, along the first direction, the electrode assembly comprises a plurality of layers of separator film, and the first adhesive layer bonds at least two layers of separator film. The shrinkage of the two separator films is limited, thereby reducing the direct contact between the positive and negative electrode tabs and the short circuit, and effectively improving the safety of the secondary battery. 。

[0017] In a second aspect, the application also provides a preparation method of a secondary battery, comprising:

[0018] The positive electrode sheet, the negative electrode sheet, and the separator are alternately stacked along the thickness direction of the positive electrode sheet and the negative electrode sheet, and the separator is arranged between adjacent positive electrode sheets and negative electrode sheets to form an electrode assembly.

[0019] In 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 a 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] The first adhesive layer is bonded to the first surface;

[0021] The electrode assembly is accommodated in the accommodation portion, and the first adhesive layer is bonded to the inner wall of the accommodation portion;

[0022] At the first preset temperature, the first adhesive layer melts, and the accommodation portion is pressed at the position corresponding to the first adhesive layer on the outer surface of the accommodation portion, so that the molten first adhesive layer is cast to at least part of the separator.

[0023] The above description is only a summary of the technical solutions of the present application. In order to enable the technical means of the present application to be more clearly understood, and to be implemented according to the content of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more obvious and easy to understand, the specific embodiments of the present application are described below. BRIEF DESCRIPTION OF DRAWINGS

[0024] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitation on the embodiments, and elements with the same reference numerals in the drawings represent similar elements, unless otherwise specified, and the drawings do not constitute proportional limitation.

[0025] Fig. 1 is an exploded view of a secondary battery according to some embodiments of the present application;

[0026] Fig. 2 is a structural schematic view of a secondary battery according to some embodiments of the present application;

[0027] Fig. 3 is a schematic view of the internal structure of a secondary battery according to some embodiments of the present application;

[0028] Fig. 4 is a schematic view of the stacking of positive electrode sheets and negative electrode sheets according to some embodiments of the present application;

[0029] Fig. 5 is a schematic view of the structure of a first outer electrode sheet according to some embodiments of the present application;

[0030] Fig. 6 is a schematic view of the structure of various first adhesive layers according to some embodiments of the present application;

[0031] FIG. 7 is a schematic diagram of the distribution of various first adhesive layers on the first surface of some embodiments of the application.

[0032] FIG. 8 is a schematic diagram of the structure of a second outer electrode tab of some embodiments of the application.

[0033] Legend of reference signs:

[0034] 100, secondary battery;

[0035] 10, housing; 11, first housing; 111, first cavity; 12, second housing; 121, second cavity;

[0036] 20, electrode assembly; 21, positive electrode tab; 211, positive current collector; 212, positive active material layer; 22, negative electrode tab; 221, negative current collector; 222, negative active material layer; 23, separator; 24, first outer electrode tab; 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 tab; 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 embodiments of the technical solutions of the application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, and therefore only serve as examples, and cannot limit the protection scope of the application.

[0042] In the description of the embodiments of the application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the application, the meaning of "a plurality of" or "several" is two or more, unless otherwise explicitly specified.

[0043] In the description of the embodiments of the present application, the term "and / or" is merely an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0044] In this paper, the term "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is not mutually exclusive with other embodiments. In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0045] In a first aspect, the present application provides a secondary battery 100, please refer to FIG. 1 and FIG. 2, the secondary battery 100 includes a containing part 10, an electrode assembly 20, a tab 30 and a first adhesive layer 40. The containing part 10 is the installation base of the rest of the elements of the secondary battery 100 and the container, the electrode assembly 20 is housed in the containing part 10, and the electrode assembly 20 is the core element of 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 containing part 10, one end of the tab 30 is electrically connected with the electrode assembly 20, and the other end extends out of the containing part 10. Next, taking the secondary battery 100 as a lithium ion battery as an example, the specific structure of the secondary battery 100 is described; 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] Referring to FIGS. 1 and 2, the accommodation portion 10 can be made of a flexible material and can constitute a mounting base, a container, and an outer protective structure of the secondary battery 100. The accommodation portion 10 defines an accommodation cavity (not shown) for accommodating an electrolyte (not shown) and the electrode assembly 20. For example, the accommodation portion 10 includes a first case 11 having a first cavity 111 and a second case 12 having a second cavity 121. The electrode assembly 20 can be disposed in the first cavity 111, and the second case 12 covers the first cavity 111 of the first case 11. The second cavity 121 is in communication with the first cavity 111 to form the accommodation cavity. The two cases can be adhered to each other to seal the accommodation cavity by heat-sealing the connection between the edges of the two cases. In other embodiments, the accommodation portion 10 can be made of a hard material. For example, the accommodation portion 10 can be formed by punching a metal sheet having a thickness of 0.1 to 0.4 mm to ensure the punching strength of the accommodation portion 10. The metal sheet can be made of an electrically conductive metal material such as aluminum, steel, stainless steel, nickel, copper, or magnesium alloy. This allows the accommodation portion 10 to be connected to a certain polarity of the secondary battery 100, for example, as a positive electrode or a negative electrode of the secondary battery 100.

[0047] Referring to FIG. 3, the electrode assembly 20 includes a positive electrode tab 21, a separator 23, and a negative electrode tab 22. A plurality of positive electrode tabs 21 and a plurality of negative electrode tabs 22 are alternately stacked in the thickness direction (first direction Z) of the positive electrode tab 21 and the negative electrode tab 22, and the separator 23 is disposed between adjacent positive electrode tabs 21 and negative electrode tabs 22.

[0048] Referring to FIGS. 3 and 4, the positive electrode tab 21 includes a positive electrode current collector 211 and a positive electrode active material layer 212. The positive electrode current collector 211 can be an aluminum foil having a flat and strip-shaped structure. The positive electrode active material layer 212 can be disposed on at least one surface of the positive electrode current collector 211, for example, on both 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, which are mixed, stirred, and coated on the positive electrode current collector 211 to obtain the positive electrode active material layer 212. 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 manganese iron phosphate, and cobalt-free material.

[0049] For the above negative electrode sheet 22, please refer to FIG. 3 and FIG. 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 is used as a conductive base material, which can adopt a copper foil with a whole flat and strip-shaped structure. In other embodiments, the negative electrode current collector 221 can also adopt a nickel foil or a polymer copper foil (a copper foil surface provided with a high polymer such as polyethylene, polypropylene or polyamide). The negative electrode active material layer 222 can be provided on at least one surface of the negative electrode current collector 221, for example, on the two opposite surfaces of the negative electrode current collector 221 in the thickness direction (the 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, etc. After the above material components are mixed and stirred uniformly, the negative electrode active material layer 222 is obtained by coating on the negative electrode current collector 221. The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide compound or silicon alloy.

[0050] For the above separator film 23, please refer to FIG. 3 and FIG. 4, the positive electrode sheet 21 and the negative electrode sheet 22 are alternately stacked along the first direction Z, and the separator film 23 is provided between the adjacent positive electrode sheet 21 and negative electrode sheet 22. The separator film 23 can adopt a ceramic-containing PE separator film or a PP separator film, etc. to insulate and separate the positive electrode sheet 21 and the negative electrode sheet 22.

[0051] For the above tab 30, please refer to FIG. 1 and FIG. 2, the tab 30 includes a positive electrode tab 31 and a negative electrode tab 32, and the positive electrode tab 31 and the negative electrode tab 32 can both adopt a metal sheet structure, for example, an aluminum sheet, a copper sheet or a nickel sheet. One end of the positive electrode tab 31 is electrically connected with the positive electrode sheet 21 in the above accommodation portion 10, for example, by welding or conductive adhesive bonding, and the other end extends out of the accommodation portion 10. One end of the negative electrode tab 32 is electrically connected with the negative electrode sheet 22 in the above accommodation portion 10, and the other end extends out of the accommodation portion 10 for electrical connection with an external electrical equipment.

[0052] Please refer to FIG. 3 and FIG. 5, along the first direction Z, the positive electrode sheet 21, the isolation film 23 and the negative electrode sheet 22 are stacked for 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 the first current collector 241 and the first active material layer 242, the first current collector 241 has the first surface 2411 facing the first direction Z and the second surface 2412 facing the second direction G, the first active material layer 242 is arranged on the second surface 2412, and the first surface 2411 is not arranged with the first active material layer 242. The first outer electrode sheet 24 is opposite to the containing portion 10, and the containing portion 10 does not have an active material layer corresponding to the first outer electrode sheet 24, so the first outer electrode sheet 24 adopts a structure of arranging the active material layer on one side, which can reduce the space occupied by the first outer electrode sheet 24 and improve the volume energy density of the secondary battery 100. Wherein, 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, and the first current collector 241 usually adopts an aluminum foil. The aluminum foil has good conductivity and good corrosion resistance. In addition, the aluminum foil also has the characteristics of light weight, easy processing and low cost, which can meet the conductivity and current collection requirements of the current collector inside the secondary battery 100. At the same time, the aluminum foil can also effectively improve the heat dissipation performance of the battery, ensuring that the battery can maintain a lower temperature during operation.

[0054] The current collector of the positive electrode sheet 21 is usually an aluminum foil, and the current collector of the negative electrode sheet 22 is usually a copper foil. For the soft package secondary battery 100, the material of the containing portion 10 is usually an 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 have an electrochemical reaction, causing a safety hazard. In addition, the cost of the copper foil is higher than that of the aluminum foil, therefore, the first outer electrode sheet 24 and / or the second outer electrode sheet 25 is preferably the positive electrode sheet 21.

[0055] For the first adhesive layer 40, referring to FIGS. 3 and 5, a portion of the first adhesive layer 40 is bonded between the first surface 2411 and the inner wall of the accommodation portion 10, which can improve the integrity between the electrode assembly 20 and the accommodation portion 10, reduce the movement of the electrode assembly 20 in the accommodation portion 10, and disperse the external force impact on the electrode assembly 20 to the accommodation portion 10, thereby improving the safety of the secondary battery 100 in the case of falling, impact, etc. In addition, the first adhesive layer 40 can disperse part of the stress on the first outer layer tab 24 at the first surface 2411, reduce stress concentration, and further reduce the warpage of the first current collector 241, thereby improving the lithium precipitation of the secondary battery 100 and relieving the shrinkage of the separator 23. At the same time, another portion of the first adhesive layer 40 is bonded to the first surface 2411 and at least part of the separator 23, which can further limit the shrinkage of the separator 23 adjacent to the first outer layer tab, improve the integrity of the electrode assembly 20, improve the lithium precipitation of the secondary battery 100, and reduce the short circuit caused by the direct contact of the positive and negative electrodes due to the shrinkage of the separator 23 in the case of falling, impact, high temperature, etc., thereby further improving the safety of the battery. In addition, the first outer layer single-coated tab of the existing stacked battery usually sets the current collector to be more than 50% (20 μm or more) thicker than the current collectors of other tabs to relieve the stress unevenness caused by single-coated, and the present application can set the first current collector 241 of the first outer layer tab 24 to be thinner due to the setting of the first adhesive layer 40, thereby reducing the space occupied by the electrode assembly 20 and improving the volume energy density of the secondary battery 100.

[0056] Since the setting of the first adhesive layer 40 can reduce the warpage of the first current collector 241, the setting of the first adhesive layer 40 is particularly suitable for the positive tab 21. The first outer layer single-coated tab of the existing stacked battery usually sets the current collector to be more than 50% (20 μm or more) thicker than the current collectors of other tabs to relieve the stress unevenness caused by single-coated, and in the embodiment of the present application, the thickness of the first current collector 241 can be appropriately reduced since the first adhesive layer 40 itself can reduce the warpage of the first current collector 241, for example, the first current collector 241 with a thickness of 7 μm to 12 μm is used to improve the energy density of the secondary battery 100.

[0057] The first adhesive layer 40 includes hot melt adhesive. When the first surface 2411 of the first outer layer electrode tab 24 is provided with the first adhesive layer 40, at a predetermined temperature, the first adhesive layer 40 melts and a part of the first adhesive layer 40 flows from the first surface 2411 to the layer separation films 23 of the other electrode assemblies 20. After the first adhesive layer 40 solidifies, the layer separation films 23 are bonded to the first surface 2411, thereby limiting the shrinkage of the layer separation films 23. Alternatively, the first adhesive layer 40 includes pressure sensitive adhesive. When the first surface 2411 of the first outer layer electrode tab 24 is provided with the first adhesive layer 40, when the electrode assembly 20 is accommodated in the case, the first adhesive layer 40 is bonded between the electrode assembly 20 and the inner wall of the case by installing the electrode assembly 20 or the case, and a part of the first adhesive layer 40 flows to the layer separation films 23 when pressed, so that the layer separation films 23 are bonded to the first surface 2411 of the first outer layer electrode tab 24, thereby limiting the shrinkage of the layer separation films 23.

[0058] In the present embodiment, the melting point of the first adhesive layer 40 is T ℃, and 50 ℃≤T≤70 ℃. When the temperature reaches the melting point, the first adhesive layer 40 melts and flows to the layer separation films 23. For example, when the first adhesive layer 40 includes hot melt adhesive and pressure sensitive adhesive, the first adhesive layer 40 melts and flows to the layer separation films 23 by applying a pressure of 1.0 MPa to 2.5 MPa to the first adhesive layer 40 in an environment of 60 ℃ to 90 ℃. This temperature range causes less damage to the secondary battery 100, and facilitates the pressure bonding of the first adhesive layer 40. In addition, when the secondary battery 100 is in thermal runaway, the melting of the first adhesive layer 40 can absorb part of the heat, thereby alleviating the thermal runaway of the secondary battery 100.

[0059] The electrolyte needs to be filled in the accommodation portion 10, and the electrolyte is usually corrosive, which can corrode the first adhesive layer 40 and affect 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 carbonate, ethylene carbonate dimethyl, additives such as flame retardants and inhibitors, etc. In the present embodiment, the first adhesive layer 40 can include polyurethane and / or vinyl acetate copolymer. The polyurethane and the vinyl acetate copolymer have good bonding properties and chemical corrosion resistance, which can prolong the service life of the secondary battery 100 and ensure the stable connection between the electrode assembly 20 and the accommodation portion 10.

[0060] For the thickness of the first adhesive layer 40, if the thickness is too large, the energy density of the battery is affected, and if the thickness is too small, the electrode assembly 20 and the accommodation portion 10 can be unstable. In the embodiment of the present application, the thickness of the first adhesive layer 40 is H μm in the first direction Z, and 3≤H≤20, so that the secondary battery 100 has a high energy density while ensuring the stable adhesion of the electrode assembly 20 and the accommodation portion 10. For example, the hot melt adhesive and / or the pressure sensitive adhesive with a thickness of 8 μm to 80 μm is coated on the first surface 2411 of the first outer electrode sheet 24, and after a part of the hot melt adhesive and / or the pressure sensitive adhesive is cast to adhere the respective layers of the isolation film 23, the first adhesive layer 40 with a thickness of 3 μm to 20 μm is formed on the first surface 2411, so that the secondary battery 100 has a high energy density and improves the adhesion stability of the respective layers of the isolation film 23.

[0061] In the embodiment of the present application, the first adhesive layer 40 is cast to adhere at least two layers of the isolation film 23, for example, to adhere two layers of the isolation film 23, which are the first isolation film and the second isolation film, respectively. The shrinkage of the first isolation film can drive the second isolation film to stretch, and similarly, the shrinkage of the second isolation film can drive the first isolation film to stretch. In this way, the shrinkage of the first isolation film and the second isolation film can be limited by each other, thereby reducing the direct contact between the positive and negative electrode sheets to cause short circuit, and effectively improving the safety of the secondary battery 100.

[0062] For the shape of the first adhesive layer 40, please refer to FIGS. 5 and 6. When viewed in the direction perpendicular to the first surface 2411 (the second direction G), the first adhesive layer 40 can be linear, curved, intermittent point, or intermittent point line, etc. When the first adhesive layer 40 is coated on the first surface 2411 of the first outer electrode sheet 24, the first adhesive layer 40 can be 10 mm away from the edge of the first surface 2411, and after the first adhesive layer 40 is hot-pressed, a part of the first adhesive layer 40 can be cast to the respective layers of the isolation film 23.

[0063] For example, referring to FIG. 3 and FIG. 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, and the first surface 2411 is provided with the first adhesive layer 40 near the first edge 241a and the second edge 241b. During hot pressing, the two first adhesive layers 40 can be cast to both sides of the width direction of the first current collector 241, and the two sides of the isolation film 23 are bonded, so as to limit the shrinkage of the isolation film 23 in the width direction. And / or, 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, and the first surface 2411 is provided with the first adhesive layer 40 near the third edge 241c and the fourth edge 241d. During hot pressing, the two first adhesive layers 40 can be cast to both sides of the length direction of the first current collector 241, and the two sides of the isolation film 23 are bonded, so as to limit the shrinkage of the isolation film 23 in the length direction. Alternatively, the first surface 2411 is provided with at least two first adhesive layers 40, which can be cast to the isolation film 23.

[0064] Referring to FIG. 3 and FIG. 8, along the second direction G, the outermost electrode sheet of the electrode assembly 20 is the second outer electrode sheet 25, which 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 can also be single-sided coated, for example, only the third surface 2511 is provided with the second active material layer 252, and the fourth surface 2512 is opposite to the accommodation portion 10. The accommodation portion 10 does not have an active material layer corresponding to the second outer electrode sheet 25, so the fourth surface 2512 can be provided with an empty foil (without an active material layer) to reduce the space occupied by the second outer electrode sheet 25 and improve the volume energy density of the secondary battery 100.

[0065] Referring to FIG. 3 and FIG. 8, the secondary battery 100 also includes a plurality of second adhesive layers 50. A part of the second adhesive layer 50 is bonded between the fourth surface 2512 and the inner wall of the accommodation portion 10, so as to improve the integrity between the electrode assembly 20 and the accommodation portion 10 and reduce the movement of the electrode assembly 20 in the accommodation portion 10. In addition, the second adhesive layer 50 can disperse part of the stress borne by the second outer electrode sheet 25 on the fourth surface 2512, reduce stress concentration, and further reduce the 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, which can further improve the energy density, drop resistance, impact resistance and safety of the secondary battery 100.

[0066] The other part of the second adhesive layer 50 bonds the fourth surface 2512 and at least part of the separation film 23, which can further limit the shrinkage of the separation film 23, improve the integrity of the electrode assembly 20, reduce the direct contact between the positive and negative electrode plates to cause short circuit, and further improve the impact resistance of the secondary battery 100. Moreover, due to the arrangement of the second adhesive layer 50, the warpage rate of the second outer electrode plate 25 is significantly reduced, and the second current collector 251 of the second outer electrode plate 25 can be arranged to be thinner, thereby reducing the space occupied by the electrode assembly 20 and improving the volume energy density of the secondary battery 100. Similar to the first adhesive layer 40, the second adhesive layer 50 can also use hot melt adhesive and / or pressure sensitive adhesive, and the melting point thereof is 50-70°C.

[0067] The second outer electrode plate 25 can be the positive electrode plate 21, and the second current collector 251 uses aluminum foil. Due to the arrangement of the first adhesive layer 40, the warpage of the first current collector 241 is reduced, and therefore the arrangement of the first adhesive layer 40 is particularly suitable for the positive electrode plate 21. Alternatively, the second outer electrode plate 25 can be the negative electrode plate 22, and the second current collector 251 uses copper foil. The copper foil itself has high strength and is not easy to deform, and the arrangement of the second adhesive layer 50 can also reduce the warpage 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 volume energy density of the secondary battery 100.

[0068] In the embodiments of the present application, the structure that the first outer electrode plate 24 is single-sidedly provided with an active material layer can reduce the space occupied by the first outer electrode plate 24 and improve the volume energy density of the secondary battery 100. Part of the first adhesive layer 40 is bonded between the first surface 2411 and the inner wall of the accommodation portion 10, which can improve the integrity between the electrode assembly 20 and the accommodation portion 10 and reduce the movement of the electrode assembly 20 in the accommodation portion 10. Moreover, the first adhesive layer 40 can disperse part of the stress borne by the first outer electrode plate 24 at the first surface 2411, reduce stress concentration, and further reduce the warpage of the first current collector 241, thereby relieving the shrinkage of the separation film 23 and improving the impact resistance of the secondary battery 100. At the same time, the other part of the first adhesive layer 40 bonds the first surface 2411 and at least part of the separation film 23, which can further limit the shrinkage of the separation film 23, improve the integrity of the electrode assembly 20, reduce the direct contact between the positive and negative electrode plates to cause short circuit, and further improve the impact resistance of the secondary battery 100. In addition, due to the arrangement of the first adhesive layer 40, the warpage rate of the first outer electrode plate 24 is significantly reduced, and the first current collector 241 of the first outer electrode plate 24 can be arranged to be 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, the embodiments of the present application also provide a method for preparing the secondary battery according to any one of the embodiments of the first aspect, which comprises:

[0070] S100, providing a positive electrode sheet, a negative electrode sheet, and a separator, and alternately stacking a plurality of positive electrode sheets and a plurality of negative electrode sheets along the thickness direction of the positive electrode sheet and the negative electrode sheet, and arranging the separator 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 has a first active material layer; wherein the first direction is the stacking direction, and the second direction is opposite to the first direction;

[0072] S300, bonding a first adhesive layer on the first surface; the first adhesive layer can be arranged at a position not more than 10 mm away from the first surface;

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

[0074] S500, at a first preset temperature, the first adhesive layer is melted, and the accommodating portion is pressed at a position corresponding to the first adhesive layer on the outer surface of the accommodating portion, so that the melted first adhesive layer is cast on at least part of the separator, so that the first surface is bonded with the separator, to limit the shrinkage of the separator and improve the impact resistance of the secondary battery.

[0075] In the embodiments of the present application, lithium ion batteries are taken as examples for drop test.

[0076] Embodiment 1

[0077] Preparation of lithium ion battery

[0078] (1) Preparation of positive electrode sheet: mix positive active material lithium cobaltate (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) according to the weight ratio of 97.5:1.0:1.5, add N-methyl pyrrolidone (NMP) as a solvent, adjust the slurry to a solid content of 75wt%, and stir uniformly. Select an aluminum foil with a length of 87mm, a width of 60mm, and a thickness of 8μm as a positive current collector, cut the positive current collector aluminum foil at one end of the length direction, reserve a positive tab with a length of 7mm and a width of 5mm, and the uncut part is a coating part with a length of 80mm and a width of 60mm, uniformly coat the slurry on one surface of the coating part, and dry to obtain a positive electrode sheet coated with a positive active material layer on one surface. Repeat the above steps on the other surface of the coating part to obtain a positive electrode sheet coated with a positive active material layer on both surfaces. Among them, reserve a positive electrode sheet coated with a positive active material layer on one surface as a first outer electrode sheet.

[0079] (2) Preparation of the negative electrode tab: Graphite is used as the negative active material. The negative active material graphite, binder styrene-butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2. Deionized water is added as a solvent to prepare a slurry with a solid content of 70 wt%, and the slurry is stirred uniformly. A copper foil with a length of 88.2 mm, a width of 60 mm, and a thickness of 5 μm is selected as the negative current collector. The negative current collector copper foil is cut at one end in the length direction, leaving a negative tab with a length of 7 mm and a width of 5 mm. The uncut part is a coated part with a length of 81.2 mm and a width of 60 mm. The slurry is uniformly coated on one surface of the coated part, and the coated part is dried to obtain a negative electrode tab coated with a negative active material layer on one side. The above steps are repeated on the other surface of the coated part to obtain a negative electrode tab coated with a negative active material layer on both sides. One of the negative electrode tabs coated with a negative active material layer on one side is reserved as a second outer tab

[0080] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC: EMC: DEC = 30:50:20 to form a base organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the base organic solvent to dissolve and mix uniformly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0081] (4) Preparation of the separator: A polyethylene porous membrane is used as the base layer. An aluminum oxide ceramic and PVDF binder-containing ceramic layer is coated on one side surface of the base layer as a separator (CCS). The mass percentage of aluminum oxide ceramic in the ceramic layer is 95%.

[0082] (5) Preparation of the electrode assembly: The above positive electrode tabs, separators, and negative electrode tabs are alternately stacked in 10 layers. The bottommost tab is the second outer tab, and the topmost tab is the first outer tab. The separators are arranged between adjacent positive and negative electrode tabs to form an electrode assembly for use 。

[0083] (6) Assembly of the electrode assembly: The punched aluminum plastic film (housing part) is placed in the assembly jig with the pit surface facing up. An 8 μm-thick polyurethane adhesive layer (initial thickness of the first adhesive layer, melting point 60°C) is arranged on the outer surface edge of the first outer tab of the electrode assembly. The electrode assembly is placed in the pit, and a low-density polyethylene seal is arranged at both tabs. An external force is applied to compress the electrode assembly. Then, another punched aluminum plastic film with the pit surface facing down is placed on the electrode assembly, and the four sides of the two aluminum plastic films are heat-sealed by hot pressing. The aluminum plastic film corresponding to the polyurethane adhesive layer is hot-pressed at 80°C to form the first adhesive layer. The hot-pressing pressure is controlled at 2.0 Mpa, so that the polyurethane adhesive layer is cast onto each layer of the separator.

[0084] (7) Liquid injection packaging: electrolyte is injected into the assembled electrode assembly, and through the processes of vacuum packaging, standing, hot pressing formation, shaping, etc., a lithium ion battery is obtained.

[0085] The related parameters of Examples 2 to 17 and Comparative Example 1 are shown in Table 1 below, wherein no first adhesive layer and second adhesive layer are provided in Comparative Example 1.

[0086] Drop test:

[0087] The lithium ion battery is loaded into a clamp, and the drop equipment is used to drop freely from a position 1.5 m away from the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), and the process is repeated for 100 rounds. After the drop test is completed, the appearance of the lithium ion battery is checked, and the pass judgment criteria are: no smoke, no fire, and no liquid leakage. The lithium ion battery is disassembled, the flow adhesion of the first adhesive layer is observed, and the thickness of the first adhesive layer between the first outer electrode sheet and the accommodating portion (the thickness of the first adhesive layer after crimping) is recorded.

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

[0089] Table 1

[0090] According to Table 1 above, in combination with Examples 1 to 17 and Comparative Example 1, it can be seen that when the 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 part 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, reduce the movement of the electrode assembly in the accommodating portion, and 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 under drop, impact, etc. In addition, the first adhesive layer can disperse part of the stress on the first outer electrode sheet on the first surface, reduce stress concentration, thereby reducing the warping of the first current collector, improving lithium precipitation of the secondary battery, and relieving the shrinkage of the separator. When the lithium ion battery is subjected to drop impact, the separator can always separate the positive and negative electrode sheets, which can reduce the occurrence of short circuit and improve the drop resistance of the lithium ion battery. At the same time, another part of the first adhesive layer bonds the first surface and at least part of the separator, which can further limit the shrinkage of the separator adjacent to the first outer electrode sheet, improve the integrity of the electrode assembly, reduce the direct contact between the positive and negative electrode sheets to cause short circuit, and further improve the drop resistance of the secondary battery.

[0091] At the same time, compared with Comparative Example 1, the interface black spots are significantly reduced in Examples 1 to 17, because the warping of the first outer electrode sheet is reduced, the combination of the active material layer and the first current collector is more stable, the lithium ion precipitation is reduced, and the lithium precipitation can be effectively improved.

[0092] In Example 1, the first adhesive layer is thin, and the bonding force between the first adhesive layer and the accommodating portion is small, which may result in bonding failure, so that the drop resistance of the lithium ion battery is not as good as that of other examples. In Example 9, the first adhesive layer is thick, and the gap between the electrode assembly and the accommodating portion is also large, which may need to rely on the first adhesive layer to support the electrode assembly in the accommodating portion, and the first adhesive layer is polyurethane, which has low strength, and may result in bonding failure when the lithium ion battery falls, and has a large loss on the energy density of the battery. Therefore, in the examples of the present application, the thickness of the first adhesive layer is preferably 3-20 μm.

[0093] As can be seen from Examples 12 and 13 and Examples 16 and 17, when the second adhesive layer is used, the risk of drop failure of the lithium ion battery can be further reduced. The electrode assembly has two outermost electrode sheets, and the second adhesive layer is arranged 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 pointed out that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; under the idea of the present application, the technical features in the above examples or different examples can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the present application.

Claims

1.A secondary battery, comprising a containing portion and an electrode assembly accommodated in the containing portion, the electrode assembly comprising positive electrode sheets, separator films, and negative electrode sheets, a plurality of the positive electrode sheets and a plurality of the negative electrode sheets being alternately stacked along a thickness direction of the positive electrode sheets and the negative electrode sheets, and the separator films being provided between adjacent ones of the positive electrode sheets and the negative electrode sheets, characterized in that: along a first direction, an outermost sheet of the electrode assembly is a first outermost sheet, the first outermost 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 a second direction, and the first active material layer being provided on the second surface; wherein the first direction is a 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 layers being bonded between the first surface and an inner wall of the containing portion, and another portion of the first adhesive layers being bonded to the first surface and at least part of the separator films; along a second direction, an outermost sheet of the electrode assembly is a second outermost sheet, the second outermost sheet comprising a second current collector and a second active material layer, the second current collector having a third surface facing the first direction and a fourth surface facing the second direction, and the second active material layer being provided on the third surface; the secondary battery further comprises a plurality of second adhesive layers, a portion of the second adhesive layers being bonded between the fourth surface and the inner wall of the containing portion, and another portion of the second adhesive layers being bonded to the fourth surface and at least part of the separator films; the first adhesive layers comprise hot melt adhesive and / or pressure sensitive adhesive; the first adhesive layers have a melting point of T ℃, and 50 ℃≤T≤70 ℃; the first adhesive layers comprise polyurethane and / or vinyl acetate copolymer; the first outermost sheet and / or the second outermost sheet is a positive electrode sheet; along the first direction, the first adhesive layers have a thickness of H μm, and 3 μm≤H≤20 μm; along a width direction of the first current collector, the first current collector has a first edge and a second edge; along a 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 layers are provided at positions close to the first edge and the second edge; and / or, on the first surface, the first adhesive layers are provided at positions close to the third edge and the fourth edge; along the first direction, the electrode assembly comprises a plurality of the separator films, and the first adhesive layers bond at least two of the separator films. The method comprises: providing positive electrode sheets, negative electrode sheets, and separator films; and alternately stacking a plurality of the positive electrode sheets and a plurality of the negative electrode sheets along a thickness direction of the positive electrode sheets and the negative electrode sheets, and providing the separator films between adjacent ones of the positive electrode sheets and the negative electrode sheets to form an electrode assembly. ​ 2. The secondary battery according to claim 1, characterized by ​ ​ 3. The secondary battery according to claim 1 or 2, characterized by ​ 4. The secondary battery according to any one of claims 1 to 3, characterized by, ​ 5. The secondary battery according to any one of claims 1 to 4, characterized by, ​ 6. The secondary battery according to claim 2, characterized by ​ 7. The secondary battery according to any one of claims 1 to 6, characterized by ​ 8. The secondary battery according to any one of claims 1 to 7, characterized by, ​ ​ ​ 9. The secondary battery according to any one of claims 1 to 8, characterized by, ​ 10. A method of producing the secondary battery according to any one of claims 1 to 9, characterized by, ​ ​ In the first direction, the outermost pole piece adopts a first outer pole piece, the first outer pole piece has a first surface facing the first direction and a second surface facing a second direction, 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; The first adhesive layer is bonded to the first surface; The electrode assembly is accommodated in the accommodation portion, and the first adhesive layer is bonded to the inner wall of the accommodation portion; At a first preset temperature, the first adhesive layer melts, and the accommodation portion is pressed at a position corresponding to the first adhesive layer on the outer surface of the accommodation portion, so that the melted first adhesive layer is cast to at least part of the separation film.

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