Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, and the secondary battery comprises an electrode assembly which comprises a negative plate and a positive plate. The negative plate comprises a negative current collector, a first negative active layer and a first negative tab, the negative current collector comprises a first surface and a second surface which are opposite to each other along the thickness direction of the negative current collector, and the first negative active layer is arranged on the first surface. The first negative active layer is provided with a first groove, and the first negative tab is arranged in the first groove and electrically connected with the negative current collector. The positive plate comprises a positive current collector and a first positive active layer, and the surface, facing the first negative active layer, of the positive current collector is provided with the first positive active layer. A first insulating layer is arranged between the positive current collector and the first positive active layer, and the projection of the first insulating layer on the surface of the first negative active layer is at least partially overlapped with the first groove along the thickness direction of the positive current collector. According to the secondary battery and the electronic equipment, the problem of lithium precipitation on the surface of the negative electrode active layer can be improved.

Description

Technical Field

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

[0002] As the power source of electronic devices, secondary batteries are the key to ensuring the normal use of electronic devices. In order to increase the charging speed, existing secondary batteries generally have built-in pole ears (that is, the pole ears are set in the grooves in the middle area of ​​the active material layer of the pole piece). For the negative pole ears, grooves are set in the negative active layer to place the negative pole ears, and adhesive tape is pasted on the surface of the positive active layer at the position corresponding to the groove to cover the positive active material in the area corresponding to the groove, so as to reduce the possibility of excessive lithium ions released by the positive active layer during the charging process of the secondary battery, resulting in lithium deposition on the surface of the negative active layer. However, during the charging process of the secondary battery, the positive active material covered by the adhesive tape can still undergo corresponding electrochemical reactions, thereby releasing lithium ions, and the lithium ions will bypass the edge of the adhesive tape and diffuse to the corresponding position of the opposite negative active layer, so that lithium deposition will still occur at the position corresponding to the edge of the adhesive tape on the surface of the negative active layer. Therefore, it is necessary to improve the above problems. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device, aiming to improve the problem of lithium deposition on the surface of the negative electrode active layer.

[0004] According to a first aspect of the present application, a secondary battery is provided, comprising an electrode assembly, wherein the electrode assembly comprises a negative electrode sheet and a positive electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active layer and a first negative electrode tab. Along the thickness direction of the negative electrode current collector, the negative electrode current collector comprises a first surface and a second surface opposite to each other, and the first surface is provided with a first negative electrode active layer. The first negative electrode active layer is provided with a first groove, and the first negative electrode tab is provided in the first groove and is electrically connected to the negative electrode current collector. The positive electrode sheet comprises a positive electrode current collector and a first positive electrode active layer, and the surface of the positive electrode current collector facing the first negative electrode active layer is provided with a first positive electrode active layer. A first insulating layer is provided between the positive electrode current collector and the first positive electrode active layer, and along the thickness direction of the positive electrode current collector, the first insulating layer at least partially overlaps with the first groove.

[0005] In the above technical solution, the first negative electrode tab is arranged in the first groove opened in the first negative electrode active layer to form a tab built-in structure of the negative electrode sheet, thereby achieving a faster charging speed. The first insulating layer is arranged between the positive electrode collector and the first positive electrode active layer, and the projection of the first insulating layer on the surface of the first negative electrode active layer is limited to overlap at least partially with the first groove, so as to reduce the conductivity of the positive electrode collector at the position corresponding to the first groove, thereby reducing the lithium removal ability of the first positive electrode active layer at the position corresponding to the first groove, thereby reducing the possibility of lithium deposition on the surface of the first negative electrode active layer near the first groove.

[0006] In some preferred embodiments, a second insulating layer is provided on the surface of the first positive electrode active layer facing the first negative electrode active layer, and the second insulating layer covers the first groove along the thickness direction of the positive electrode current collector, so that the second insulating layer can cover the positive electrode active material at the position of the first positive electrode active layer corresponding to the first groove, thereby reducing the ability of the first positive electrode active material covered by the second insulating layer to release lithium ions, thereby further reducing the possibility of lithium deposition on the surface of the first negative electrode active layer near the first groove.

[0007] In some preferred embodiments, along the length direction of the positive electrode current collector, opposite sides of the second insulating layer have a first symmetry axis. Along the thickness direction of the positive electrode current collector, the projection of the first insulating layer on the surface of the second insulating layer is symmetrical about the first symmetry axis, so that the projection of the first insulating layer on the surface of the second insulating layer along the thickness direction of the positive electrode current collector covers the second insulating layer as much as possible, so that the first positive electrode active layer can better reduce the lithium removal ability of the first positive electrode active layer at the position corresponding to the first groove under the cooperation of the first insulating layer and the second insulating layer, so as to further reduce the possibility of lithium deposition on the surface of the first negative electrode active layer near the first groove.

[0008] In some preferred embodiments, along the width direction of the positive electrode current collector, the length of the second insulating layer is A1, the length of the first insulating layer is M1, and 0.5≤M1 / A1≤2. By limiting 0.5≤M1 / A1, the first insulating layer can better reduce the conductivity of the positive electrode current collector and the position corresponding to the first groove, so as to better reduce the possibility of lithium deposition on the surface of the first negative electrode active layer near the position of the first groove. By limiting M1 / A1≤2, the length of the first insulating layer will not be too long, and the energy density of the secondary battery will not be excessively reduced.

[0009] In some preferred embodiments, along the length direction of the positive electrode current collector, the width of the second insulating layer is B1, the width of the first insulating layer is N1, and 0.5≤N1 / B1≤2. By limiting 0.5≤N1 / B1, the first insulating layer can better reduce the conductivity of the positive electrode current collector and the corresponding position of the first groove, so as to better reduce the possibility of lithium deposition on the surface of the first negative electrode active layer near the first groove. By limiting N1 / B1≤2, the width of the first insulating layer will not be too long, and the energy density of the secondary battery will not be excessively reduced.

[0010] In some preferred embodiments, the first insulating layer includes a first polymer layer and a first adhesive layer, a surface of the first polymer layer along the thickness direction is provided with the first adhesive layer, the surface of the first adhesive layer away from the first polymer layer is bonded to the positive electrode current collector, along the thickness direction of the positive electrode current collector, the thickness of the first insulating layer is H1, the thickness of the first adhesive layer is H2, the thickness of the first polymer layer is H3, 10μm≤H1≤50μm, 5μm≤H2≤25μm, 5μm≤H3≤25μm. The first adhesive layer can improve the adhesion of the first insulating layer to the positive electrode current collector, and the first polymer layer can improve the insulation effect of the first insulating layer to better reduce the conductivity of the positive electrode current collector covered by the first insulating layer. By limiting 10μm≤H1≤50μm, the first insulating layer will not be too thick while satisfying the requirement of having a good insulation effect, thereby not excessively reducing the energy density of the secondary battery. By limiting 5μm≤H2≤25μm, the first adhesive layer has a good bonding effect, while the first adhesive layer is not too thick, so as not to excessively reduce the energy density of the secondary battery. By limiting 5μm≤H3≤25μm, the first polymer layer has a good insulation effect, while the first polymer layer is not too thick, so as not to excessively reduce the energy density of the secondary battery.

[0011] In some preferred embodiments, 10μm≤H1≤20μm, 5μm≤H2≤8μm, and 5μm≤H3≤12μm. By limiting H1≤20μm, the thickness of the first insulating layer can be further reduced, so that the secondary battery has a better energy density. By limiting H2≤8μm, the thickness of the first adhesive layer can be further reduced, so that the secondary battery has a better energy density. By limiting H3≤12μm, the thickness of the first polymer layer can be further reduced, so that the secondary battery has a better energy density.

[0012] In some preferred embodiments, the first adhesive layer includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber, so that the first adhesive layer has a better bonding effect. And / or, the first polymer layer includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene, so that the first polymer layer has a better insulation effect.

[0013] In some preferred embodiments, the first insulating layer includes an inorganic substance, and along the thickness direction of the positive electrode current collector, the thickness of the first insulating layer is H1, 0.1 μm ≤ H1 ≤ 15 μm. By limiting the first insulating layer to include an inorganic substance, the thickness of the first insulating layer can be made thinner while satisfying a good insulation effect. By limiting 0.1 μm ≤ H1 ≤ 15 μm, the first insulating layer will not be too thick while satisfying a good insulation effect, thereby not excessively reducing the energy density of the secondary battery.

[0014] In some preferred embodiments, the first insulating layer includes aluminum oxide and polyvinylidene fluoride, and 0.1 μm ≤ H1 ≤ 5 μm. By limiting the first insulating layer to include aluminum oxide and / or boehmite, the first insulating layer also includes polyvinylidene fluoride, so that the first insulating layer has a better insulating effect. By limiting H1 ≤ 5 μm, the thickness of the first insulating layer can be further reduced, so that the secondary battery has a better energy density.

[0015] In some preferred embodiments, the first insulating layer includes alkaline aluminum chromate and aluminum dichromate, and 0.1 μm ≤ H1 ≤ 5 μm. By limiting the first insulating layer to include alkaline aluminum chromate and aluminum dichromate, the first insulating layer has a better insulating effect. By limiting H1 ≤ 5 μm, the thickness of the first insulating layer can be further reduced, so that the secondary battery has a better energy density.

[0016] In some preferred embodiments, basic aluminum chromate and aluminum dichromate are obtained by reacting the positive electrode current collector with at least one of potassium dichromate and dihydrogen monoxide, so that the first insulating layer is firmly fixed on the surface of the positive electrode current collector.

[0017] In some preferred embodiments, the second insulating layer satisfies at least one of the following features: (1) Along the width direction of the positive electrode current collector, the side of the first groove away from the notch has a first bottom edge, and the side of the second insulating layer close to the first bottom edge exceeds the first bottom edge by a length of 3 mm to 10 mm, so that the second insulating layer can cover the first groove while the second insulating layer is not too long, so as to avoid excessively reducing the energy density of the secondary battery. (2) Along the length direction of the positive electrode current collector, the first groove has a first side edge and a second side edge opposite to each other, the side of the second insulating layer close to the first side edge exceeds the first side edge by a width of 3 mm to 10 mm, and the side of the second insulating layer close to the second side edge exceeds the second side edge by a width of 3 mm to 10 mm, so that the second insulating layer can cover the first groove while the second insulating layer is not too wide, so as to avoid excessively reducing the energy density of the secondary battery. (3) The thickness of the second insulating layer is 10 μm to 50 μm, so that the second insulating layer can have a good insulation effect while the second insulating layer is not too thick, thereby not excessively reducing the energy density of the secondary battery. (4) Along the length direction of the positive electrode current collector, the two opposite sides of the first groove have a second symmetry axis. Along the thickness direction of the positive electrode current collector, the projection of the second insulating layer on the surface of the first negative electrode active layer is symmetrical about the second symmetry axis, so that the projection of the second insulating layer on the surface of the first negative electrode active layer along the thickness direction of the positive electrode current collector can cover the first groove as much as possible, so that the second insulating layer can cover the positive electrode active material at the position corresponding to the first groove of the first positive electrode active layer as much as possible, thereby further reducing the possibility of lithium deposition on the surface of the first negative electrode active layer near the first groove.

[0018] In some preferred embodiments, the negative electrode sheet includes a second negative electrode active layer, the second surface of the negative electrode current collector is provided with the second negative electrode active layer, the second negative electrode active layer is provided with a second groove, and the surface of the positive electrode current collector facing the second negative electrode active layer is provided with the second positive electrode active layer. A third insulating layer is provided between the positive electrode current collector and the second positive electrode active layer, and the third insulating layer and the second groove overlap at least partially along the thickness direction of the positive electrode current collector. The energy density of the secondary battery is improved by providing the second negative electrode active layer on the second surface of the negative electrode current collector and the second positive electrode active layer on the surface of the positive electrode current collector facing the second negative electrode active layer. A second groove is provided on the second negative electrode active layer to provide a receiving space for the equipment for welding the first negative electrode tab. By arranging a third insulating layer between the positive electrode current collector and the second positive electrode active layer, and limiting the projection of the third insulating layer on the surface of the second negative electrode active layer to at least partially overlap with the second groove, the conductivity of the positive electrode current collector at the corresponding position of the second groove is reduced, thereby reducing the lithium desorption ability of the second positive electrode active layer at the corresponding position of the second groove, thereby reducing the possibility of lithium deposition on the surface of the second negative electrode active layer near the second groove.

[0019] In some preferred embodiments, a fourth insulating layer is provided on the surface of the second positive electrode active layer facing the second negative electrode active layer, and the fourth insulating layer covers the second groove along the thickness direction of the positive electrode current collector, so that the fourth insulating layer can cover the positive electrode active material at the position of the second positive electrode active layer corresponding to the second groove, thereby reducing the ability of the second positive electrode active material covered by the fourth insulating layer to release lithium ions, thereby further reducing the possibility of lithium deposition on the surface of the second negative electrode active layer near the second groove.

[0020] In some preferred embodiments, the secondary battery satisfies at least one of the following characteristics: (5) Along the width direction of the positive electrode current collector, the length of the fourth insulating layer is A2, the length of the third insulating layer is M2, 0.5≤M2 / A2≤2, by limiting 0.5≤M2 / A2, so that the third insulating layer can better reduce the conductivity of the positive electrode current collector and the position corresponding to the second groove, so as to better reduce the possibility of lithium deposition on the surface of the second negative electrode active layer near the second groove. By limiting M2 / A2≤2, the length of the third insulating layer will not be too long, and the energy density of the secondary battery will not be excessively reduced. (6) Along the length direction of the positive electrode current collector, the width of the fourth insulating layer is B2, the width of the third insulating layer is N2, 0.5≤N2 / B2≤2, by limiting 0.5≤N2 / B2, so that the third insulating layer can better reduce the conductivity of the positive electrode current collector and the position corresponding to the second groove, so as to better reduce the possibility of lithium deposition on the surface of the second negative electrode active layer near the second groove. By limiting N2 / B2≤2, the width of the third insulating layer will not be too long, and the energy density of the secondary battery will not be excessively reduced. (7) Along the thickness direction of the positive electrode current collector, the thickness of the third insulating layer is H4, 10μm≤H4≤50μm, so that the third insulating layer will not be too thick while having a good insulation effect, thereby not excessively reducing the energy density of the secondary battery.

[0021] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0022] The inventors of the present application have found that by sticking adhesive tape on the surface of the positive active layer corresponding to the groove in the built-in structure of the negative electrode tab, the possibility of lithium deposition on the surface of the negative active layer due to excessive lithium ion release from the positive active layer during charging of the secondary battery can be reduced. During the charging process, lithium deposition will still occur at the position corresponding to the surface of the negative active layer and the edge of the adhesive tape. By providing an insulating layer between the positive current collector and the positive active layer, and limiting the insulating layer and the groove to at least partially overlap along the thickness direction of the positive current collector, the conductivity of the positive current collector and the corresponding position of the groove can be reduced, thereby reducing the lithium desorption ability of the positive active layer at the corresponding position of the groove, thereby reducing the possibility of lithium deposition on the surface of the negative active layer near the groove.

[0023] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0026] Figure 2 A schematic diagram of the structure of an electrode assembly in some embodiments of the present application;

[0027] Figure 3 for Figure 2 A partial enlarged view of the middle part;

[0028] Figure 4 This is a schematic structural diagram of a positive electrode sheet observed along a first direction in some embodiments of the present application;

[0029] Figure 5 This is a schematic structural diagram of a negative electrode sheet observed along a first direction in some embodiments of the present application;

[0030] Figure 6 A schematic diagram of the structure of the first insulating layer in some embodiments of the present application;

[0031] Figure 7 A schematic diagram of the structure of the second insulating layer in some embodiments of the present application;

[0032] Figure 8 A schematic diagram of the structure of an electrode assembly in some embodiments of the present application;

[0033] Fig. 9 for Figure 8 A partial enlarged view of point B in the middle;

[0034] Fig.10 This is a schematic structural diagram of a positive electrode sheet observed along a first direction in some embodiments of the present application;

[0035] Fig.11 This is a schematic structural diagram of a negative electrode sheet observed along a first direction in some embodiments of the present application;

[0036] Fig.12 A schematic diagram of the structure of the third insulating layer in some embodiments of the present application;

[0037] Fig.13 This is a schematic structural diagram of the fourth insulating layer of some embodiments of the present application.

[0038] Description of reference numerals:

[0039] 100. secondary battery; 10. housing; 20. electrode assembly;

[0040] 21, positive electrode sheet; 211, positive electrode current collector; 212, first positive electrode active layer; 213, second positive electrode active layer;

[0041] 22, negative electrode sheet; 221, negative electrode current collector; 2211, first surface; 2212, second surface; 222, first negative electrode active layer; 2221, first groove; 2222, first bottom edge; 2223, first side edge; 2224, second side edge; 222a, second symmetry axis; 223, second negative electrode active layer; 2231, second groove; 2232, second bottom edge; 2233, third side edge; 2234, fourth side edge; 223a, fourth symmetry axis; 224, first negative electrode tab;

[0042] 23. Diaphragm;

[0043] 24, first insulating layer; 241, first polymer layer; 242, first adhesive layer;

[0044] 25, second insulating layer; 25a, first symmetry axis; 251, second polymer layer; 252, second adhesive layer;

[0045] 26, third insulating layer; 261, third polymer layer; 262, third adhesive layer;

[0046] 27, fourth insulating layer; 27a, third symmetry axis; 271, fourth polymer layer; 272, fourth adhesive layer;

[0047] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0049] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0050] In the description of the embodiments of the present 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 present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0051] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0052] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0053] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1 The secondary battery 100 includes a shell 10 and an electrode assembly 20 . The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the shell 10 .

[0054] For the electrode assembly 20, please refer to Figure 2 , Figure 2 The winding structure of the electrode assembly 20 is shown. The electrode assembly 20 includes a positive electrode sheet 21, a separator 23 and a negative electrode sheet 22. A separator 23 is arranged between the adjacent negative electrode sheets 22 and the positive electrode sheets 21. The positive electrode sheets 21, the separator 23 and the negative electrode sheets 22 are stacked and wound. Exemplarily, along the thickness direction of the positive electrode sheet 21 and / or the negative electrode sheet 22, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are stacked in sequence and then wound to form a wound electrode assembly 20. In the embodiment of the present application, the electrode assembly 20 is taken as an example for explanation as a winding structure. In some other embodiments, the electrode assembly 20 may also be a laminated structure. For example, along the thickness direction of the positive electrode sheet 21 and / or the negative electrode sheet 22, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are stacked in sequence to form a laminated electrode assembly 20.

[0055] For the negative electrode sheet 22, please refer to Figure 3 The negative electrode sheet 22 includes a negative electrode current collector 221, a first negative electrode active layer 222 and a first negative electrode tab 224. Along the thickness direction (first direction X) of the negative electrode current collector 221, the negative electrode current collector 221 includes a first surface 2211 and a second surface 2212 opposite to each other, and the first surface 2211 is provided with the first negative electrode active layer 222. The first negative electrode active layer 222 is provided with a first groove 2221, and the first negative electrode tab 224 is provided in the first groove 2221 and is electrically connected to the negative electrode current collector 221 to form a tab built-in structure, so that the secondary battery 100 can obtain a faster charging speed.

[0056] For the negative electrode current collector 221, the negative electrode current collector 221 may be a composite current collector (a composite structure of metal-polymer-metal), for example, the negative electrode current collector 221 includes a polymer layer and a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the negative electrode current collector 221, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the negative electrode current collector 221 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the negative electrode current collector 221, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the negative electrode current collector 221 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0057] For the first negative electrode active layer 222, the first negative electrode active layer 222 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first negative electrode active layer 222 includes a first negative electrode active material, a conductive agent, a binder, etc. The above materials are mixed and stirred evenly and coated on the first surface 2211 of the negative electrode current collector 221 to obtain the first negative electrode active layer 222. The first negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0058] In the present application, the first negative electrode tab 224 is a metal conductor drawn from the negative electrode sheet 22, and the first negative electrode tab 224 is used to connect in series or in parallel with other parts of the secondary battery 100. The present application has no particular restrictions on the material of the first negative electrode tab 224, as long as the purpose of the present application can be achieved, for example, the negative electrode tab material known in the art can be used. The present application has no particular restrictions on the formation method of the first groove 2221, and the formation method known in the art can be used, as long as the purpose of the present application can be achieved, for example, by laser cleaning in the corresponding first negative electrode active layer 222 area, or by first pasting foam paper on the negative electrode current collector 221, coating the first negative electrode active layer 222 and drying, and peeling off the foam paper to obtain the first groove 2221.

[0059] The positive electrode sheet 21 includes a positive electrode collector 211 and a first positive electrode active layer 212 . The first positive electrode active layer 212 is disposed on a surface of the positive electrode collector 211 facing the first negative electrode active layer 222 .

[0060] For the positive electrode current collector 211, the positive electrode current collector 211 may be a composite current collector (a composite structure of metal-polymer-metal), for example, the positive electrode current collector 211 includes a polymer layer and a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the positive electrode current collector 211, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the positive electrode current collector 211 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the positive electrode current collector 211, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the positive electrode current collector 211 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0061] For the first positive electrode active layer 212, the first positive electrode active layer 212 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first positive electrode active layer 212 includes a first positive electrode active material, a conductive agent, a binder, etc. The above materials are mixed and stirred evenly and coated on the surface of the positive electrode current collector 211 facing the first negative electrode active layer 222, thereby obtaining the first positive electrode active layer 212. The first positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0062] In some embodiments, please refer to Figure 2 and Figure 3 , a second insulating layer 25 is provided on the surface of the first positive electrode active layer 212 facing the first negative electrode active layer 222, and along the thickness direction (first direction X) of the positive electrode current collector 211, the projection of the second insulating layer 25 on the surface of the first negative electrode active layer 222 covers the first groove 2221, so that the second insulating layer 25 can cover the positive electrode active material at the corresponding position of the first positive electrode active layer 212 and the first groove 2221, thereby reducing the ability of the first positive electrode active material covered by the second insulating layer 25 to release lithium ions, thereby further reducing the possibility of lithium deposition at the position near the first groove 2221 on the surface of the first negative electrode active layer 222. However, during the charging process of the secondary battery 100, the positive electrode active material covered by the second insulating layer 25 can still undergo corresponding electrochemical reactions, thereby releasing lithium ions, and the lithium ions will bypass the edge of the second insulating layer 25 and diffuse to the corresponding position of the opposite negative electrode active layer, so that lithium deposition will still occur at the corresponding position of the surface of the first negative electrode active layer 222 and the edge of the second insulating layer 25.

[0063] To improve the above problems, in the embodiments of this application, please refer to Figure 2 and Figure 3 A first insulating layer 24 is provided between the positive current collector 211 and the first positive active layer 212. Along the thickness direction of the positive current collector 211, the projection of the first insulating layer 24 on the surface of the first negative active layer 222 at least partially overlaps with the first groove 2221, so as to reduce the conductivity of the positive current collector 211 at a position corresponding to the first groove 2221, thereby reducing the lithium desorption ability of the first positive active layer 212 at a position corresponding to the first groove 2221, thereby reducing the possibility of lithium deposition on the surface of the first negative active layer 222 near the first groove 2221.

[0064] In some embodiments, please refer to Figure 3 and Figure 4 , along the length direction (second direction Y) of the positive current collector 211, the second insulating layer 25 has a first symmetry axis 25a on opposite sides. Along the thickness direction of the positive current collector 211, the projection of the first insulating layer 24 on the surface of the second insulating layer 25 is symmetrical about the first symmetry axis 25a, so that the projection of the first insulating layer 24 on the surface of the second insulating layer 25 along the thickness direction of the positive current collector 211 can cover the second insulating layer 25 as much as possible, so that the first positive active layer 212 can better reduce the lithium desorption ability of the first positive active layer 212 corresponding to the first groove 2221 under the cooperation of the first insulating layer 24 and the second insulating layer 25, so as to further reduce the possibility of lithium deposition at the position of the surface of the first negative active layer 222 near the first groove 2221.

[0065] In some embodiments, along the width direction (third direction Z) of the positive electrode current collector 211, the length of the second insulating layer 25 is A1, the length of the first insulating layer 24 is M1, and 0.5≤M1 / A1≤2. By limiting 0.5≤M1 / A1, the first insulating layer 24 can better reduce the conductivity of the positive electrode current collector 211 and the first groove 2221 corresponding position, so as to better reduce the possibility of lithium deposition on the surface of the first negative electrode active layer 222 near the first groove 2221. By limiting M1 / A1≤2, the length of the first insulating layer 24 will not be too long, and the energy density of the secondary battery 100 will not be excessively reduced.

[0066] In some embodiments, along the length direction of the positive current collector 211, the width of the second insulating layer 25 is B1, the width of the first insulating layer 24 is N1, and 0.5≤N1 / B1≤2. By limiting 0.5≤N1 / B1, the first insulating layer 24 can better reduce the conductivity of the positive current collector 211 and the first groove 2221 corresponding position, so as to better reduce the possibility of lithium deposition on the surface of the first negative active layer 222 near the first groove 2221. By limiting N1 / B1≤2, the width of the first insulating layer 24 will not be too long, and the energy density of the secondary battery 100 will not be excessively reduced.

[0067] In some embodiments, please refer to Figure 3 and Figure 6 The first insulating layer 24 includes a first polymer layer 241 and a first adhesive layer 242. The first adhesive layer 242 is provided on one surface of the first polymer layer 241 in the thickness direction. The surface of the first adhesive layer 242 away from the first polymer layer 241 is bonded to the positive electrode current collector 211. In the thickness direction of the positive electrode current collector 211, the thickness of the first insulating layer 24 is H1, the thickness of the first adhesive layer 242 is H2, and the thickness of the first polymer layer 241 is H3. 10μm≤H1≤50μm, 5μm≤H2≤25μm, and 5μm≤H3≤25μm. The first adhesive layer 242 can improve the adhesion between the first insulating layer 24 and the positive electrode current collector 211, and the first polymer layer 241 can improve the insulation effect of the first insulating layer 24 to better reduce the conductivity of the positive electrode current collector 211 covered by the first insulating layer 24. By limiting 10μm≤H1≤50μm, the first insulating layer 24 can have a good insulation effect while not being too thick, thereby not excessively reducing the energy density of the secondary battery 100. By limiting 5μm≤H2≤25μm, the first adhesive layer 242 can have a good adhesion effect while not being too thick, thereby not excessively reducing the energy density of the secondary battery 100. By limiting 5μm≤H3≤25μm, the first polymer layer 241 can have a good insulation effect while not being too thick, thereby not excessively reducing the energy density of the secondary battery 100.

[0068] In some embodiments, 10μm≤H1≤20μm, 5μm≤H2≤8μm, and 5μm≤H3≤12μm. By limiting H1≤20μm, the thickness of the first insulating layer 24 is further reduced, so that the secondary battery 100 has a better energy density. By limiting H2≤8μm, the thickness of the first adhesive layer 242 is further reduced, so that the secondary battery 100 has a better energy density. By limiting H3≤12μm, the thickness of the first polymer layer 241 is further reduced, so that the secondary battery 100 has a better energy density.

[0069] In some embodiments, the first adhesive layer 242 includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber, so that the first adhesive layer 242 has a better bonding effect. And / or, the first polymer layer 241 includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene, so that the first polymer layer 241 has a better insulation effect.

[0070] In some embodiments, the first insulating layer 24 includes an inorganic substance, and along the thickness direction of the positive electrode current collector 211, the thickness of the first insulating layer 24 is H1, 0.1 μm ≤ H1 ≤ 15 μm. By limiting the first insulating layer 24 to include an inorganic substance, the thickness of the first insulating layer 24 can be made thinner while satisfying a good insulation effect. By limiting 0.1 μm ≤ H1 ≤ 15 μm, the first insulating layer 24 will not be too thick while satisfying a good insulation effect, thereby not excessively reducing the energy density of the secondary battery 100.

[0071] In some embodiments, the first insulating layer 24 includes aluminum oxide and / or boehmite, and the first insulating layer 24 also includes polyvinylidene fluoride, 0.1 μm ≤ H1 ≤ 5 μm. By limiting the first insulating layer 24 to include aluminum oxide and / or boehmite, and the first insulating layer 24 also includes polyvinylidene fluoride, the first insulating layer 24 has a better insulation effect. By limiting H1 ≤ 5 μm, the thickness of the first insulating layer 24 is further reduced, so that the secondary battery 100 has a better energy density.

[0072] In some embodiments, the first insulating layer 24 includes alkaline aluminum chromate and aluminum dichromate, and 0.1 μm ≤ H1 ≤ 5 μm. By limiting the first insulating layer 24 to include alkaline aluminum chromate and aluminum dichromate, the first insulating layer 24 has a better insulating effect. By limiting H1 ≤ 5 μm, the thickness of the first insulating layer 24 is further reduced, so that the secondary battery 100 has a better energy density.

[0073] In some embodiments, basic aluminum chromate and aluminum dichromate are obtained by reacting the positive electrode current collector 211 with at least one of potassium dichromate and dihydrogen monoxide, so that the first insulating layer 24 is firmly fixed on the surface of the positive electrode current collector 211 .

[0074] In some embodiments, please refer to Figure 3 and Figure 5, along the width direction of the positive electrode current collector 211, the side of the first groove 2221 away from the notch has a first bottom side 2222, and the side of the second insulating layer 25 close to the first bottom side 2222 exceeds the first bottom side 2222 by 3mm to 10mm, so that the second insulating layer 25 can cover the first groove 2221 while the second insulating layer 25 is not too long, so as to avoid excessively reducing the energy density of the secondary battery 100. In some embodiments, along the length direction of the positive electrode current collector 211, the first groove 2221 has a first side 2223 and a second side 2224 opposite to each other, and the side of the second insulating layer 25 close to the first side 2223 exceeds the first side 2223 by 3mm to 10mm, and the side of the second insulating layer 25 close to the second side 2224 exceeds the second side 2224 by 3mm to 10mm, so that the second insulating layer 25 can cover the first groove 2221 while the second insulating layer 25 is not too wide, so as to avoid excessively reducing the energy density of the secondary battery 100. In some embodiments, the thickness of the second insulating layer 25 is 10 μm to 50 μm, so that the second insulating layer 25 is not too thick while having a good insulating effect, thereby not excessively reducing the energy density of the secondary battery 100. In some embodiments, along the length direction of the positive current collector 211, the first groove 2221 has a second symmetry axis 222a on opposite sides. Along the thickness direction of the positive current collector 211, the projection of the second insulating layer 25 on the surface of the first negative active layer 222 is symmetrical about the second symmetry axis 222a, so that the projection of the second insulating layer 25 on the surface of the first negative active layer 222 along the thickness direction of the positive current collector 211 blocks the first groove 2221 as much as possible, so that the second insulating layer 25 can cover the positive active material at the corresponding position of the first positive active layer 212 and the first groove 2221 as much as possible, thereby further reducing the possibility of lithium deposition on the surface of the first negative active layer 222 near the first groove 2221.

[0075] In some embodiments, please refer to Figure 3 and Figure 7 The second insulating layer 25 includes a second polymer layer 251 and a second bonding layer 252. The second bonding layer 252 is provided on one surface of the second polymer layer 251 along the thickness direction. The surface of the second bonding layer 252 facing away from the second polymer layer 251 is bonded to the first positive electrode active layer 212. The second bonding layer 252 can improve the adhesion of the second insulating layer 25 to the first positive electrode active layer 212. The second polymer layer 251 can improve the insulating effect of the second insulating layer 25 to better reduce the lithium desorption ability of the positive electrode active material covered by the second insulating layer 25.

[0076] In some embodiments, please refer to Figure 8 and Fig. 9The negative electrode sheet 22 includes a second negative electrode active layer 223. The second negative electrode active layer 223 is provided on the second surface 2212 of the negative electrode collector 221. The second negative electrode active layer 223 is provided with a second groove 2231. The second positive electrode active layer 213 is provided on the surface of the positive electrode collector 211 facing the second negative electrode active layer 223. A third insulating layer 26 is provided between the positive electrode collector 211 and the second positive electrode active layer 213. Along the thickness direction of the positive electrode collector 211, the projection of the third insulating layer 26 on the surface of the second negative electrode active layer 223 at least partially overlaps with the second groove 2231. By providing the second negative electrode active layer 223 on the second surface 2212 of the negative electrode collector 221 and providing the second positive electrode active layer 213 on the surface of the positive electrode collector 211 facing the second negative electrode active layer 223, the energy density of the secondary battery 100 is improved. A second groove 2231 is provided in the second negative electrode active layer 223 to provide a receiving space for the equipment for welding the first negative electrode tab 224. A third insulating layer 26 is provided between the positive electrode current collector 211 and the second positive electrode active layer 213, and the projection of the third insulating layer 26 on the surface of the second negative electrode active layer 223 is limited to overlap at least partially with the second groove 2231, so as to reduce the conductivity of the positive electrode current collector 211 and the corresponding position of the second groove 2231, thereby reducing the lithium removal ability of the second positive electrode active layer 213 at the corresponding position of the second groove 2231, thereby reducing the possibility of lithium deposition on the surface of the second negative electrode active layer 223 near the second groove 2231.

[0077] In some embodiments, a fourth insulating layer 27 is provided on the surface of the second positive electrode active layer 213 facing the second negative electrode active layer 223, and along the thickness direction of the positive electrode current collector 211, the projection of the fourth insulating layer 27 on the surface of the second negative electrode active layer 223 covers the second groove 2231, so that the fourth insulating layer 27 can cover the positive electrode active material at the corresponding position of the second positive electrode active layer 213 and the second groove 2231, thereby reducing the ability of the second positive electrode active material covered by the fourth insulating layer 27 to release lithium ions, thereby further reducing the possibility of lithium deposition on the surface of the second negative electrode active layer 223 near the second groove 2231.

[0078] In some embodiments, please refer to Fig. 9 and Fig.10, along the length direction of the positive current collector 211, the fourth insulating layer 27 has a third symmetry axis 27a on two opposite sides. Along the thickness direction of the positive current collector 211, the projection of the third insulating layer 26 on the surface of the fourth insulating layer 27 is symmetrical about the third symmetry axis 27a, so that the projection of the third insulating layer 26 on the surface of the fourth insulating layer 27 along the thickness direction of the positive current collector 211 can cover the fourth insulating layer 27 as much as possible, so that the second positive active layer 213 can better reduce the lithium desorption ability of the second positive active layer 213 corresponding to the second groove 2231 under the cooperation of the third insulating layer 26 and the fourth insulating layer 27, so as to further reduce the possibility of lithium deposition at the position of the second negative active layer 223 near the second groove 2231.

[0079] In some embodiments, along the width direction of the positive current collector 211, the length of the fourth insulating layer 27 is A2, the length of the third insulating layer 26 is M2, 0.5≤M2 / A2≤2, by limiting 0.5≤M2 / A2, so that the third insulating layer 26 can better reduce the conductivity of the positive current collector 211 and the corresponding position of the second groove 2231, so as to better reduce the possibility of lithium deposition on the surface of the second negative active layer 223 near the second groove 2231. By limiting M2 / A2≤2, the length of the third insulating layer 26 will not be too long, and the energy density of the secondary battery 100 will not be excessively reduced. In some embodiments, along the length direction of the positive current collector 211, the width of the fourth insulating layer 27 is B2, and the width of the third insulating layer 26 is N2, 0.5≤N2 / B2≤2. By limiting 0.5≤N2 / B2, the third insulating layer 26 can better reduce the conductivity of the positive current collector 211 and the corresponding position of the second groove 2231, so as to better reduce the possibility of lithium deposition on the surface of the second negative active layer 223 near the second groove 2231. By limiting N2 / B2≤2, the width of the third insulating layer 26 will not be too long, and the energy density of the secondary battery 100 will not be excessively reduced. In some embodiments, along the thickness direction of the positive current collector 211, the thickness of the third insulating layer 26 is H4, 10μm≤H4≤50μm, so that the third insulating layer 26 will not be too thick while satisfying the good insulation effect, thereby not excessively reducing the energy density of the secondary battery 100.

[0080] For the third insulating layer 26, please refer to Fig. 9 and Fig.12The third insulating layer 26 includes a third polymer layer 261 and a third adhesive layer 262. The third adhesive layer 262 is provided on one surface of the third polymer layer 261 in the thickness direction. The surface of the third adhesive layer 262 away from the third polymer layer 261 is bonded to the positive electrode current collector 211. The thickness of the third adhesive layer 262 is H5, and the thickness of the third polymer layer 261 is H6, 5μm≤H5≤25μm, 5μm≤H6≤25μm. The third adhesive layer 262 can improve the adhesion of the third insulating layer 26 to the positive electrode current collector 211, and the third polymer layer 261 can improve the insulation effect of the third insulating layer 26 to better reduce the conductivity of the positive electrode current collector 211 covered by the third insulating layer 26. By limiting 5μm≤H5≤25μm, the third adhesive layer 262 has a good adhesive effect, and the third adhesive layer 262 is not too thick, so as not to excessively reduce the energy density of the secondary battery 100. By limiting 5μm≤H6≤25μm, the third polymer layer 261 has a good insulation effect, and the third polymer layer 261 is not too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0081] In some embodiments, 10μm≤H4≤20μm, 5μm≤H5≤8μm, and 5μm≤H6≤12μm. By limiting H4≤20μm, the thickness of the third insulating layer 26 is further reduced, so that the secondary battery 100 has a better energy density. By limiting H5≤8μm, the thickness of the third adhesive layer 262 is further reduced, so that the secondary battery 100 has a better energy density. By limiting H6≤12μm, the thickness of the third polymer layer 261 is further reduced, so that the secondary battery 100 has a better energy density.

[0082] In some embodiments, the third adhesive layer 262 includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber, so that the third adhesive layer 262 has a better bonding effect. And / or, the third polymer layer 261 includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene, so that the third polymer layer 261 has a better insulation effect.

[0083] In some embodiments, the third insulating layer 26 includes an inorganic substance, and along the thickness direction of the positive electrode current collector 211, the thickness of the third insulating layer 26 is H1, 0.1 μm≤H4≤15 μm. By limiting the third insulating layer 26 to include an inorganic substance, the thickness of the third insulating layer 26 can be made thinner while satisfying a good insulation effect. By limiting 0.1 μm≤H4≤15 μm, the third insulating layer 26 will not be too thick while satisfying a good insulation effect, thereby not excessively reducing the energy density of the secondary battery 100.

[0084] In some embodiments, the third insulating layer 26 includes aluminum oxide and / or boehmite, and the third insulating layer 26 also includes polyvinylidene fluoride, 0.1 μm≤H4≤5 μm. By limiting the third insulating layer 26 to include aluminum oxide and / or boehmite, and the third insulating layer 26 also includes polyvinylidene fluoride, the third insulating layer 26 has a better insulation effect. By limiting H4≤5 μm, the thickness of the third insulating layer 26 is further reduced, so that the secondary battery 100 has a better energy density.

[0085] In some embodiments, the third insulating layer 26 includes alkaline aluminum chromate and aluminum dichromate, and 0.1 μm ≤ H4 ≤ 5 μm. By limiting the third insulating layer 26 to include alkaline aluminum chromate and aluminum dichromate, the third insulating layer 26 has a better insulation effect. By limiting H4 ≤ 5 μm, the thickness of the third insulating layer 26 is further reduced, so that the secondary battery 100 has a better energy density.

[0086] In some embodiments, basic aluminum chromate and aluminum dichromate are obtained by reacting the positive electrode current collector 211 with at least one of potassium dichromate and dihydrogen monoxide, so that the third insulating layer 26 is firmly fixed on the surface of the positive electrode current collector 211 .

[0087] In some embodiments, please refer to Fig. 9 and Fig.11, along the width direction of the positive electrode current collector 211, the side of the second groove 2231 away from the notch has a second bottom edge 2232, and the side of the fourth insulating layer 27 close to the second bottom edge 2232 exceeds the second bottom edge 2232 by 3mm to 10mm, so that the fourth insulating layer 27 can cover the second groove 2231 while the fourth insulating layer 27 is not too long, so as to avoid excessively reducing the energy density of the secondary battery 100. In some embodiments, along the length direction of the positive electrode current collector 211, the second groove 2231 has a third side edge 2233 and a fourth side edge 2234 opposite to each other, and the side of the fourth insulating layer 27 close to the third side edge 2233 exceeds the third side edge 2233 by 3mm to 10mm, and the side of the fourth insulating layer 27 close to the fourth side edge 2234 exceeds the fourth side edge 2234 by 3mm to 10mm, so that the fourth insulating layer 27 can cover the second groove 2231 while the fourth insulating layer 27 is not too wide, so as to avoid excessively reducing the energy density of the secondary battery 100. In some embodiments, the thickness of the fourth insulating layer 27 is 10 μm to 50 μm, so that the fourth insulating layer 27 has a good insulation effect while not being too thick, thereby not excessively reducing the energy density of the secondary battery 100. In some embodiments, along the length direction of the positive current collector 211, the second groove 2231 has a fourth symmetry axis 223a on opposite sides. Along the thickness direction of the positive current collector 211, the projection of the fourth insulating layer 27 on the surface of the second negative active layer 223 is symmetrical about the fourth symmetry axis 223a, so that the projection of the fourth insulating layer 27 on the surface of the second negative active layer 223 along the thickness direction of the positive current collector 211 blocks the second groove 2231 as much as possible, so that the fourth insulating layer 27 can cover the positive active material at the corresponding position of the second positive active layer 213 and the second groove 2231 as much as possible, thereby further reducing the possibility of lithium deposition on the surface of the second negative active layer 223 near the second groove 2231.

[0088] In some embodiments, please refer to Fig. 9 and Fig.13 The fourth insulating layer 27 includes a fourth polymer layer 271 and a fourth bonding layer 272. The fourth bonding layer 272 is provided on one surface of the fourth polymer layer 271 along the thickness direction. The surface of the fourth bonding layer 272 facing away from the fourth polymer layer 271 is bonded to the second positive electrode active layer 213. The fourth bonding layer 272 can improve the adhesion of the fourth insulating layer 27 to the second positive electrode active layer 213. The fourth polymer layer 271 can improve the insulation effect of the fourth insulating layer 27 to better reduce the lithium desorption ability of the positive electrode active material covered by the fourth insulating layer 27.

[0089] In the second aspect of the present application, an electronic device is also proposed, including a secondary battery 100 as in any embodiment of the first aspect described above. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices include but are not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, spacecraft, and the like.

[0090] Test part:

[0091] 1. Capacity retention and expansion rate test of lithium-ion batteries:

[0092] The thickness of the tested fresh battery is D0. The battery cell is fully charged and then discharged to 3.0V. The discharge capacity is recorded as C0. It is fully charged at a rate of 3C and then discharged at 1C to 3.0V. The discharge capacity is recorded as C1. The full charge and discharge are repeated, and the discharge capacity is recorded each time. The capacity retention rate is C1 / C0 for each discharge capacity. The thickness of the tested battery cell is D every 100 full charges, and the expansion rate is D / D0-1.

[0093] 2. Lithium plating test of lithium-ion batteries:

[0094] The lithium-ion battery is dissected to observe the degree of lithium deposition near the negative electrode ear protective glue, and the average width of the lithium deposition interface is measured as the width of the lithium deposition interface.

[0095] Example 1

[0096] <Preparation of negative electrode sheet>:

[0097] The negative electrode active material graphite / silicon / silicon carbon material, conductive agent (conductive carbon black, conductive carbon tube), adhesive, and dispersant are mixed according to the weight ratio, deionized water (H2O) is added as a solvent, and a slurry with a certain solid content is prepared and stirred evenly. The slurry is evenly coated on the front and back sides of the negative electrode collector copper foil, dried at a certain temperature, and then cold pressed, stripped, and cleaned according to the required specifications to obtain the required negative electrode sheet. The negative electrode sheet has a slot in the middle of the electrode sheet for welding the pole ear.

[0098] <Pretreatment of positive electrode current collector>:

[0099] Pre-treating the positive electrode current collector aluminum foil at the position corresponding to the negative electrode tab, and performing insulation treatment at this position, where the treatment area is m long and n wide;

[0100] The treated area of ​​the positive electrode current collector aluminum foil is passivated with a dichromate solution (potassium dichromate, dihydrogen monoxide, etc.) to form a passivation insulating layer of alkaline aluminum chromate and aluminum dichromate in the treated area. The thickness of the passivation insulating layer is 2μm. The main passivation treatment processes are: degreasing, passivation, cleaning, and drying.

[0101] Passivation insulation layer material testing method and instrument: EDS element analysis; first, the sample is prepared on a thin discharge support, and then the instrument is debugged to determine the test position and working parameters, etc.; finally, the sample surface is scanned to obtain a series of spectra, and the type and content of elements on the material surface are confirmed by spectrum analysis.

[0102] <Preparation of positive electrode sheet>:

[0103] The positive electrode active material (lithium cobalt oxide, ternary material, etc.), conductive agent (conductive carbon black, conductive carbon tube), polyvinylidene fluoride (PVDF) are mixed according to the weight ratio, N-methylpyrrolidone (NMP) is added as a solvent, and a slurry with a certain solid content is prepared and stirred evenly. The slurry is evenly coated on the front and back sides of the positive electrode current collector aluminum foil, dried at a certain temperature, and then cold pressed and striped according to the required specifications to obtain the required positive electrode sheet. The positive electrode sheet has a slot in the middle of the electrode sheet for welding the pole ear.

[0104] <Electrolyte Preparation>:

[0105] In a dry argon atmosphere, organic solvents such as ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a certain proportion, and then lithium salts and additives are added to the organic solvents to dissolve and mix evenly to obtain an electrolyte of a certain concentration.

[0106] <Preparation of lithium-ion batteries>:

[0107] A polyethylene (PE) separator is selected, and the negative electrode sheet, separator, and positive electrode sheet are welded and glued on a winding machine, and then wound to obtain a bare cell, which is placed in an aluminum-plastic film, and finally a lithium-ion battery is obtained after top and side sealing, liquid injection, formation, and aging. A protective glue is attached to the surface of the positive electrode sheet corresponding to the position of the negative electrode sheet, and the length of the protective glue is a and the width is b; wherein the processing size satisfies m / a=0.5, n / b=0.5.

[0108] The relevant parameters in Comparative Example 1 and Examples 2 to 15 are shown in Table 1 below, wherein Comparative Example 1 does not pretreat the positive electrode current collector, and Examples 2 to 15 differ from Example 1 in only the ratios of the sizes m / a and n / b.

[0109] Table 1

[0110]

[0111]

[0112] Note: “ / ” in Table 1 means that the parameter is not included.

[0113] According to Table 1 above, combined with Comparative Example 1 and Examples 1 to 19, it can be seen that for the negative electrode tab built-in structure, by pasting adhesive tape on the surface of the positive electrode active layer at the position corresponding to the groove, lithium deposition will still occur at the position corresponding to the edge of the adhesive tape on the surface of the negative electrode active layer. By providing an insulating layer between the positive electrode current collector and the positive electrode active layer, and limiting the projection of the insulating layer on the surface of the negative electrode active layer to at least partially overlap with the groove, the possibility of lithium deposition on the surface of the negative electrode active layer near the groove can be reduced.

[0114] In combination with Examples 1 to 19, it can be seen that when the values ​​of m / a and n / b are both lower than 0.5, lithium precipitation on the surface of the negative electrode active layer is more obvious, it is difficult for the lithium battery to obtain a good capacity retention rate, and the expansion rate is high. When the values ​​of m / a and n / b are both higher than 2, lithium precipitation on the surface of the negative electrode active layer is not obvious, the lithium battery has a good capacity retention rate, and the expansion rate is low. When the values ​​of a and b are fixed, the higher the values ​​of m / a and n / b, the larger the area of ​​the insulating layer will be, thereby excessively reducing the energy density of the secondary battery. Therefore, the value range of m / a and n / b is limited to 0.5 to 2, which can better reduce the occurrence of lithium precipitation on the surface of the negative electrode active layer near the groove position.

[0115] The relevant parameters in Examples 16 to 36 are shown in Table 2 below, wherein the ratios of the processing sizes m / a and n / b in Examples 16 to 36 are all 1. The positive electrode current collector pretreatment methods in Examples 16 to 22 are all passivation treatments, and only the thickness of the insulating layer formed after the passivation treatment is different. The positive electrode current collector pretreatment methods in Examples 23 to 29 are all coated with mixed inorganic substances to form an insulating layer, and only the thickness of the insulating layer formed is different. The positive electrode current collector pretreatment methods in Examples 30 to 36 are all bonding insulating adhesive layers, and only the thickness of the insulating adhesive layer is different.

[0116] The above-mentioned pretreatment method of coating the mixed inorganic substance on the positive electrode current collector to form an insulating layer is: coating a mixture of aluminum oxide and polyvinylidene fluoride on the positive electrode current collector aluminum foil, and drying to form an insulating layer.

[0117] The above-mentioned pretreatment method for bonding the insulating adhesive layer on the positive electrode current collector is: bonding the insulating adhesive layer on the positive electrode current collector aluminum foil, the insulating adhesive layer includes a polymer layer and an adhesive layer arranged on one surface of the polymer layer, the adhesive layer includes polypropylene, and the polymer layer is a polyethylene terephthalate film.

[0118] Table 2

[0119]

[0120]

[0121] According to the above Table 2, combined with Examples 16 to 22, it can be seen that if the insulating layer is formed by passivation treatment, when the thickness of the insulating layer is less than 0.1 μm, lithium deposition on the surface of the negative electrode active layer is more obvious, and when the thickness of the insulating layer is higher than 5 μm, lithium deposition on the surface of the negative electrode active layer is not obvious. If the insulating layer is too thick, the energy density of the secondary battery will be reduced too much. Therefore, the thickness of the insulating layer formed by passivation treatment is limited to 0.1 μm to 5 μm.

[0122] In combination with Examples 23 to 29, it can be seen that if the insulating layer is formed by coating a mixed inorganic substance, when the thickness of the insulating layer is less than 0.1 μm, lithium deposition on the surface of the negative electrode active layer is more obvious, and when the thickness of the insulating layer is higher than 5 μm, lithium deposition on the surface of the negative electrode active layer is not obvious. If the insulating layer is too thick, the energy density of the secondary battery will be reduced too much. Therefore, the thickness of the insulating layer formed by coating a mixed inorganic substance is limited to 0.1 μm to 5 μm.

[0123] In combination with Examples 30 to 36, it can be seen that if the insulating layer is formed by bonding an insulating glue layer, when the thickness of the insulating layer is not less than 10 μm, lithium deposition on the surface of the negative electrode active layer is not obvious, and if the insulating layer is too thick, the energy density of the secondary battery will be reduced too much, so the upper limit of the thickness of the insulating layer needs to be limited.

[0124] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises a negative electrode sheet and a positive electrode sheet; the negative electrode sheet comprises a negative electrode current collector, a first negative electrode active layer and a first negative electrode tab, wherein along the thickness direction of the negative electrode current collector, the negative electrode current collector comprises a first surface and a second surface opposite to each other, wherein the first surface is provided with the first negative electrode active layer; the first negative electrode active layer is provided with a first groove, wherein the first negative electrode tab is provided in the first groove and is electrically connected to the negative electrode current collector; the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active layer, wherein the first positive electrode active layer is provided on the surface of the positive electrode current collector facing the first negative electrode active layer; It is characterized in that A first insulating layer is disposed between the positive electrode current collector and the first positive electrode active layer. Along the thickness direction of the positive electrode current collector, the first insulating layer at least partially overlaps with the first groove.

2. The secondary battery according to claim 1, characterized in that: A second insulating layer is disposed on a surface of the first positive electrode active layer facing the first negative electrode active layer, and along a thickness direction of the positive electrode current collector, the second insulating layer covers the first groove.

3. The secondary battery according to claim 2, characterized in that: Along the length direction of the positive current collector, two opposite sides of the second insulating layer have a first symmetry axis; along the thickness direction of the positive current collector, the projection of the first insulating layer on the surface of the second insulating layer is symmetrical about the first symmetry axis.

4. The secondary battery according to claim 3, characterized in that: Along the width direction of the positive electrode current collector, the length of the second insulating layer is A1, the length of the first insulating layer is M1, and 0.5≤M1 / A1≤2.

5. The secondary battery according to claim 3, characterized in that: Along the length direction of the positive electrode current collector, the width of the second insulating layer is B1, the width of the first insulating layer is N1, and 0.5≤N1 / B1≤2.

6. The secondary battery according to claim 1, characterized in that: The first insulating layer includes a first polymer layer and a first bonding layer. The first bonding layer is provided on a surface of the first polymer layer along the thickness direction. The surface of the first bonding layer facing away from the first polymer layer is bonded to the positive electrode current collector. Along the thickness direction of the positive electrode current collector, the thickness of the first insulating layer is H1, the thickness of the first bonding layer is H2, and the thickness of the first polymer layer is H3, 10μm≤H1≤50μm, 5μm≤H2≤25μm, and 5μm≤H3≤25μm.

7. The secondary battery according to claim 6, characterized in that: 10μm≤H1≤20μm, 5μm≤H2≤8μm, 5μm≤H3≤12μm.

8. The secondary battery according to claim 6, characterized in that: The first adhesive layer includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber; and / or the first polymer layer includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene.

9. The secondary battery according to claim 1, characterized in that: The first insulating layer includes an inorganic substance. Along the thickness direction of the positive electrode current collector, the thickness of the first insulating layer is H1, and 0.1 μm≤H1≤15 μm.

10. The secondary battery according to claim 9, characterized in that: The first insulating layer includes aluminum oxide and / or boehmite, and the first insulating layer also includes polyvinylidene fluoride, 0.1 μm≤H1≤5 μm.

11. The secondary battery according to claim 9, characterized in that: The first insulating layer includes basic aluminum chromate and aluminum dichromate, and 0.1 μm≤H1≤5 μm.

12. The secondary battery according to claim 11, characterized in that: The basic aluminum chromate and the aluminum dichromate are obtained by reacting the positive electrode current collector with at least one of potassium dichromate and dihydrogen monoxide.

13. The secondary battery according to claim 2, characterized in that: The second insulating layer satisfies at least one of the following characteristics: (1) Along the width direction of the positive electrode current collector, the first groove has a first bottom edge on a side away from the notch, and the second insulating layer has a side close to the first bottom edge that exceeds the first bottom edge by a length of 3 mm to 10 mm; (2) Along the length direction of the positive electrode current collector, the first groove has a first side and a second side opposite to each other, a side of the second insulating layer close to the first side exceeds the first side by a width of 3 mm to 10 mm, and a side of the second insulating layer close to the second side exceeds the second side by a width of 3 mm to 10 mm; (3) The thickness of the second insulating layer is 10 μm to 50 μm; (4) Along the length direction of the positive electrode current collector, opposite sides of the first groove have a second symmetry axis; along the thickness direction of the positive electrode current collector, the projection of the second insulating layer on the surface of the first negative electrode active layer is symmetrical about the second symmetry axis.

14. The secondary battery according to any one of claims 1 to 13, characterized in that: The negative electrode sheet comprises a second negative electrode active layer, the second negative electrode active layer is arranged on the second surface of the negative electrode current collector, the second negative electrode active layer is provided with a second groove, and the second positive electrode active layer is arranged on the surface of the positive electrode current collector facing the second negative electrode active layer; A third insulating layer is disposed between the positive electrode current collector and the second positive electrode active layer. Along the thickness direction of the positive electrode current collector, the third insulating layer at least partially overlaps with the second groove.

15. The secondary battery according to claim 14, characterized in that: A fourth insulating layer is disposed on a surface of the second positive electrode active layer facing the second negative electrode active layer, and along a thickness direction of the positive electrode current collector, the fourth insulating layer covers the second groove.

16. The secondary battery according to claim 15, characterized in that: The secondary battery satisfies at least one of the following characteristics: (5) Along the width direction of the positive electrode current collector, the length of the fourth insulating layer is A2, the length of the third insulating layer is M2, and 0.5≤M2 / A2≤2; (6) Along the length direction of the positive electrode current collector, the width of the fourth insulating layer is B2, the width of the third insulating layer is N2, and 0.5≤N2 / B2≤2; (7) Along the thickness direction of the positive electrode current collector, the thickness of the third insulating layer is H4, 10 μm≤H4≤50 μm.

17. An electronic device, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 16.

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