Pole piece, secondary battery and electronic equipment

Abstract

The invention discloses a pole piece, a secondary battery and electronic equipment. The pole piece comprises a first metal layer, a second metal layer and an insulating layer stacked between the first metal layer and the second metal layer, the first metal layer is provided with a plurality of first holes, the second metal layer is provided with a plurality of second holes, the insulating layer is provided with a plurality of third holes, and the first holes, the second holes and the third holes are used for transmitting ions. A first active material layer is arranged on the surface of the first metal layer deviating from the insulating layer, a second active material layer is arranged on the surface of the second metal layer deviating from the insulating layer, and the first active material layer and the second active material layer are opposite in polarity. The pole piece further comprises an isolation layer which is stacked on the surface, deviating from the first metal layer, of the first active material layer, or the isolation layer is stacked on the surface, deviating from the second metal layer, of the second active material layer. Therefore, the manufacturing process of the secondary battery can be simplified, the overhang area can be reduced while the lithium precipitation risk is reduced, and the energy density of the secondary battery is further improved.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, high energy efficiency and long cycle life, and are widely used in the fields of consumer electronics and power storage equipment. Lithium-ion batteries usually include a positive electrode sheet, a separator and a negative electrode sheet that are wound or stacked. Limited by the current process capabilities of the winding and stacking process, lithium-ion batteries need to retain a certain overhang area between the negative electrode sheet and the positive electrode sheet when designing (the active material layer of the negative electrode sheet exceeds the active material layer of the positive electrode sheet) to reduce lithium plating on the electrode sheet and ensure the safety of lithium-ion batteries. However, the overhang area takes up a certain amount of space, which affects the energy density of lithium-ion batteries. Summary of the invention

[0003] The present application aims to provide a pole piece, a secondary battery and an electronic device, aiming to reduce the technical problem of overhang area affecting the energy density of the battery.

[0004] The embodiment of the present application adopts the following technical solutions:

[0005] In the first aspect, the present application proposes a pole piece, comprising a first metal layer, a second metal layer, and an insulating layer stacked between the first metal layer and the second metal layer. The first metal layer is provided with a plurality of first holes, the second metal layer is provided with a plurality of second holes, and the insulating layer is provided with a plurality of third holes, and the first holes, the second holes, and the third holes are used to transmit ions. A first active material layer is provided on the surface of the first metal layer facing away from the insulating layer, and a second active material layer is provided on the surface of the second metal layer facing away from the insulating layer, and the polarity of the first active material layer is opposite to that of the second active material layer. The pole piece also includes an insulating layer, which is stacked on the surface of the first active material layer facing away from the first metal layer, or the insulating layer is stacked on the surface of the second active material layer facing away from the second metal layer; the insulating layer is used to isolate ions.

[0006] In the above technical scheme, the two sides of a single pole piece are respectively provided with a first active material layer and a second active material layer with opposite polarities. During coating, the first active material layer and the second active material layer can be coated symmetrically. Compared with the traditional active material coating on different pole pieces, the misalignment of the first active material layer and the second active material layer can be reduced, and there is no misalignment of the two pole pieces during stacking or winding, which can effectively reduce the risk of lithium plating of the secondary battery and reduce the overhang area, thereby improving the energy density of the secondary battery.

[0007] At the same time, the insulating layer can isolate ions on one side of the first metal layer or the second metal layer, and can limit the transmission of ions inside the electrode through the first hole, the second hole, and the third hole. When the electrode sheets are stacked or stacked and wound, due to the existence of the insulating layer, only a single electrode sheet can be wound or only multiple electrode sheets can be stacked to form an electrode assembly, and there is no need to set an isolation film, which can reduce the stacking process of the isolation film and simplify the manufacturing process of the secondary battery. In addition, limiting the transmission of ions between the first hole, the second hole, and the third hole can make the lithium ions released from the active material layer on one side of the electrode sheet always embedded in the active material layer on the other side of the electrode sheet, so that the lithium ions released from the active material layer can always be embedded in the negative electrode active material layer, which can not only reduce the problem of lithium precipitation, but also reduce the overhang area, or even eliminate the overhang area, which can further improve the energy density of the secondary battery.

[0008] In some embodiments, the first active material layer includes a first region, the first region exceeds the second active material layer on one side of the pole piece length direction, and the length of the first region is L1, L1≤0.5mm; or the second active material layer includes a second region, the second region exceeds the first active material layer on one side of the pole piece length direction, and the length of the second region is L2, L2≤0.5mm. This can reduce the overhang area in the pole piece length direction to less than 0.3mm, thereby improving the energy density of the secondary battery.

[0009] In some other embodiments, the first active material layer includes a third region, the third region exceeds the second active material layer on one side in the width direction of the pole piece, and the width of the third region is W1, W1≤0.5mm; or the second active material layer includes a fourth region, the fourth region exceeds the first active material layer on one side in the width direction of the pole piece, and the width of the fourth region is W2≤0.5mm. This can reduce the overhang area in the width direction of the pole piece to less than 0.5mm, further improving the energy density of the secondary battery.

[0010] In some embodiments, L1≤0.3 mm, or L2≤0.3 mm, which can reduce the overhang area in the length direction of the pole piece to less than 0.3 mm, thereby improving the energy density of the secondary battery.

[0011] In some other embodiments, W1≤0.3 mm, or W2≤0.3 mm, which can reduce the overhang area in the width direction of the pole piece to less than 0.3 mm, further improving the energy density of the secondary battery.

[0012] In some embodiments, L1≤0.1 mm, or L2≤0.1 mm, which can reduce the overhang area in the length direction of the pole piece to less than 0.1 mm, thereby improving the energy density of the secondary battery.

[0013] In some other embodiments, W1≤0.1mm, or W2≤0.1mm. The overhang area in the width direction of the pole piece can be reduced to less than 0.1mm, further improving the energy density of the secondary battery. The solution of the present application can make the overhang area close to 0, or even eliminate the overhang area.

[0014] In some embodiments, the insulating layer includes at least one of aluminum oxide, magnesium oxide, zirconium dioxide, boehmite, titanium dioxide, acrylic acid, polyurethane or epoxy resin. The above materials have excellent insulation and corrosion resistance and can increase the service life of the pole piece.

[0015] In some embodiments, the diameter of the first hole is R1, 300nm≤R1≤600nm; and / or, the diameter of the second hole is R2, 300nm≤R2≤600nm; and / or, the diameter of the third hole is R3, 300nm≤R3≤600nm. The insulating layer can insulate the first metal layer and the second metal layer, and can ensure the smooth passage of lithium ions, thereby improving the transmission efficiency of lithium ions between the first active material layer and the second active material layer.

[0016] In some embodiments, the porosity of the first metal layer is G1, 10% ≤ G1 ≤ 75%; and / or, the porosity of the second metal layer is G2, 10% ≤ G2 ≤ ​​75%; and / or, the porosity of the insulating layer is G3, 30% ≤ G3 ≤ 80%. While improving the ion transmission efficiency, the damage and tearing of the first metal layer, the insulating layer and the second metal layer can be reduced. By limiting the above-mentioned suitable pore size and porosity, it is helpful to evenly distribute the electrolyte inside the pole piece, so that the ion conductivity of each part of the pole piece is consistent, and the overall performance of the secondary battery is improved.

[0017] In some embodiments, 40%≤G1≤60%; and / or, 40%≤G2≤60%; and / or, 50%≤G3≤70%. This can further improve the ion transmission efficiency while reducing the damage and tearing of the first metal layer, the insulating layer, and the second metal layer.

[0018] In some embodiments, along the thickness direction of the pole piece, the thickness of the insulating layer is T, 8μm≤T≤30μm, which can isolate ions while reducing the impact of the insulating layer on the energy density of the secondary battery.

[0019] In some embodiments, along the thickness direction of the pole piece, the thickness of the first metal layer is T1, 0.1μm≤T1≤5μm; and / or, the thickness of the second metal layer is T2, 0.1μm≤T2≤5μm; and / or, the thickness of the insulating layer is T3, 2μm≤T3≤10μm.

[0020] The first metal layer and the second metal layer can have higher electrical conductivity, and can withstand certain bending and tensile stresses, reducing the rupture or damage of the first metal layer and the second metal layer. In some embodiments, along the thickness direction of the pole piece, the thickness of the first metal layer is T1, 0.8μm≤T1≤1.5μm; and / or, the thickness of the second metal layer is T2, 0.8μm≤T2≤1.5μm. Further, the first metal layer and the second metal layer have higher electrical conductivity, and can withstand certain bending and tensile stresses, reducing the rupture or damage of the first metal layer and the second metal layer.

[0021] In some other embodiments, the thickness of the insulating layer is T3, 4 μm ≤ T3 ≤ 6 μm. This further takes into account the insulation between the first metal layer and the second metal layer, facilitates the transmission of ions, and reduces the impact on energy density. In addition, the insulating layer can have a higher mechanical strength.

[0022] In some embodiments, along the thickness direction of the electrode sheet, the thickness of the first active material layer is T4, 25um≤T4≤60um; and / or the thickness of the second active material layer is T5, 25um≤T5≤60um. This can facilitate the electrolyte to fully infiltrate the first active material layer and the second active material layer, and facilitate the electrolyte to quickly and fully enter the first hole, the second hole and the third hole, thereby improving the dynamics of the electrode sheet.

[0023] In some embodiments, a plurality of first grooves are provided on the surface of the first active material layer facing away from the first metal layer. The first grooves penetrate the first active material layer along the length or width direction of the pole piece, which can increase the contact area between the first active material layer and the electrolyte, thereby improving the wetting efficiency of the electrolyte into the first active material layer.

[0024] In some other embodiments, a plurality of second grooves are provided on the surface of the second active material layer facing away from the second metal layer. The second grooves penetrate the second active material layer along the length or width direction of the pole piece, which can increase the contact area between the second active material layer and the electrolyte, thereby improving the wetting efficiency of the electrolyte into the second active material layer.

[0025] In some embodiments, the first metal layer is connected to a first pole lug, and the second metal layer is connected to a second pole lug. Along the thickness direction of the pole piece, the projection of the first pole lug is outside the projection of the second pole lug, and the first pole lug and the second pole lug do not overlap, which can reduce the contact short circuit between the first pole lug and the second pole lug.

[0026] In a second aspect, the present application further proposes a secondary battery, comprising a shell and an electrode assembly disposed in the shell, wherein the electrode assembly comprises a pole piece as in any embodiment of the first aspect described above.

[0027] In some embodiments, the electrode assembly includes a single pole piece, which is wound several times without the need for an isolation film. There is no isolation film stacking and winding operation, which can further simplify the manufacturing process and further reduce the overhang area or eliminate the need for an overhang area, thereby improving the energy density of the secondary battery.

[0028] In some embodiments, the portion of the pole piece located at the outermost circle of the electrode assembly includes a first surface away from the winding center. The first surface is provided with an insulating layer; and / or, the first surface is provided with a separator; and / or, the secondary battery further includes a first finishing glue, and the first finishing glue is provided on the first surface. It can reduce the shedding of the outermost active material layer, reduce the contact short circuit between the electrode assembly and the shell, and reduce the corrosion of the electrolyte to the pole piece.

[0029] In some embodiments, the electrode assembly includes a plurality of stacked pole pieces, and the insulating layer acts as an isolation membrane. After the pole pieces are stacked, the amount of isolation membrane used and the stacking process of the isolation membrane can be reduced, which not only simplifies the manufacturing process but also improves space utilization, thereby increasing the energy density of the secondary battery.

[0030] In some embodiments, along the stacking direction, the outermost layers on both sides of the electrode assembly are insulating layers, which can reduce the shedding of the outermost active material layer, reduce the short circuit between the electrode assembly and the shell, and reduce the corrosion of the electrolyte to the electrode plate.

[0031] In a third aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the second aspect above.

[0032] 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

[0033] 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 the figures in the drawings do not constitute proportional limitations unless otherwise stated.

[0034] Figure 1 A schematic diagram of the stacked structure of the positive electrode sheet and the negative electrode sheet of the related art (top view);

[0035] Figure 2 A schematic diagram of the stacked structure of a positive electrode sheet and a negative electrode sheet in the related art (side view);

[0036] Figure 3 A partial cross-sectional view of a pole piece of some embodiments of the present application;

[0037] Figure 4A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0038] Figure 5 A schematic diagram of the stacking structure of an electrode assembly in some embodiments of the present application;

[0039] Figure 6a It is a cross-sectional view (length direction) of a pole piece of some embodiments of the present application;

[0040] Figure 6b It is a cross-sectional view (length direction) of a pole piece of some embodiments of the present application;

[0041] Figure 7a A cross-sectional view (width direction) of a pole piece of some embodiments of the present application;

[0042] Figure 7b A cross-sectional view (width direction) of a pole piece of some embodiments of the present application;

[0043] Figure 8 A partial cross-sectional view of a pole piece of some embodiments of the present application;

[0044] Fig. 9 A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0045] Fig.10 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application;

[0046] Fig.11 This is a schematic diagram of the structure of the pole piece of some embodiments of the present application;

[0047] Fig.12 This is a schematic diagram of the structure of the pole piece of some embodiments of the present application;

[0048] Fig.13 A partial structural schematic diagram of a pole piece of some embodiments of the present application;

[0049] Fig.14 This is a schematic structural diagram of a first insulating adhesive according to some embodiments of the present application;

[0050] Fig.15 A cross-sectional view of a pole piece of some embodiments of the present application;

[0051] Fig.16 This is a schematic diagram of the structure of the first adhesive layer of some embodiments of the present application;

[0052] Fig.17 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0053] Fig.18 A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0054] Fig.19 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application;

[0055] Fig. 20 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application;

[0056] Fig.21 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application;

[0057] Fig. 22 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application.

[0058] Description of reference numerals:

[0059] 1000. Secondary battery;

[0060] 100. Electrode assembly;

[0061] 10. Pole piece; 11. First metal layer; 111. First hole; 12. Second metal layer; 121. Second hole; 13. Insulating layer; 131. Third hole; 14. First active material layer; 141. First region; 143. Third region; 15. Second active material layer; 152. Second region; 154. Fourth region; 11a. Composite current collector; 16. Insulating layer; 17. First pole ear; 17a. First insulating glue; 17a1. First substrate; 17a2. First insulating part; 17b. Third insulating glue; 17c. First glue layer; 18. Second pole ear; 18a. Second insulating glue; 18b. Fourth insulating glue; 18c. Second glue layer;

[0062] 20. Isolation film;

[0063] 10a, first paragraph;

[0064] 10b, second paragraph;

[0065] 10c, third section; 10c1, first surface; 10c2, first finishing glue;

[0066] 10d, first outer layer pole piece; 10d1, second surface; 10d2, second finishing glue;

[0067] 10e, inner pole piece;

[0068] 10f, second outer pole piece; 10f1, third surface; 10f2, third finishing glue;

[0069] 101, first inner active material layer; 102, second inner active material layer; 103, second outer active material layer; 104, third outer active material layer; 105, first outer active material layer;

[0070] 200, housing;

[0071] 1a, positive electrode sheet; 11a, positive electrode tab; 1b, negative electrode sheet; 11b, negative electrode tab; 1b1, overhang area;

[0072] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0073] 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.

[0074] Mentioning "embodiment" in the embodiments of the present application means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Lithium-ion batteries (secondary batteries) have the advantages of high energy density, high energy efficiency and long cycle life, and are widely used in the fields of consumer electronics and power storage devices. Figure 1 and Figure 2, a lithium-ion battery generally includes a positive electrode sheet 1a, a separator 20 and a negative electrode sheet 1b. The separator 20, the positive electrode sheet 1a, the separator 20 and the negative electrode sheet 1b are stacked in sequence or stacked and wound in sequence. During the stacking or stacking and winding process of the positive electrode sheet 1a and the negative electrode sheet 1b, the positive electrode sheet 1a and the negative electrode sheet 1b are prone to misalignment, making it difficult to ensure that the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet are completely overlapped.

[0079] If there is an area on the positive electrode sheet 1a that does not correspond to the negative electrode sheet 1b, the lithium ions released from this area may not be embedded in the negative electrode active material layer, which may easily lead to lithium precipitation problems. Therefore, the amount of the negative electrode active material layer is usually increased, for example, an overhang area 1b1 (the area where the negative electrode active material layer exceeds the positive electrode active material layer) is provided on both sides of the width direction of the negative electrode sheet 1b and / or on both sides of the length direction of the negative electrode sheet 1b, to ensure that the negative electrode active material layer has enough margin to embed the lithium ions released from the positive electrode active material layer, thereby reducing lithium precipitation. However, the capacity of the lithium-ion battery is still determined by a smaller positive electrode active material layer, and the overhang area 1b1 takes up space, affecting the energy density of the lithium-ion battery.

[0080] In order to reduce the above problems, in the first aspect, the present application proposes a pole piece 10, please refer to Figure 3 The pole piece 10 includes a first metal layer 11, a second metal layer 12 and an insulating layer 13. Along the thickness direction (third direction Z) of the insulating layer 13, the insulating layer 13 is stacked between the first metal layer 11 and the second metal layer 12. The first metal layer 11 and the second metal layer 12 can be bonded to both sides of the thickness direction (third direction Z) of the insulating layer 13 by gluing, or the first metal layer 11 and the second metal layer 12 can be plated on both sides of the thickness direction (third direction Z) of the insulating layer 13 by evaporation, sputtering or vapor deposition.

[0081] The insulating layer 13 may be made of an organic polymer, which can insulate the first metal layer 11 from the second metal layer 12. For example, the insulating layer 13 may be made of materials such as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PI) or polyimide (PET). For example, taking polyimide (PET) as an example, polyimide (PET) has good insulation and corrosion resistance, good mechanical strength and toughness, can provide good support for the first metal layer 11 and the second metal layer 12, and has stable chemical properties.

[0082] In the embodiment of the present application, by respectively arranging the first metal layer 11 and the second metal layer 12 on both sides of the thickness direction (third direction Z) of the insulating layer 13, the first metal layer 11, the insulating layer 13 and the second metal layer 12 can form a composite current collector 11a, which can take into account the toughness of the polymer layer and the mechanical strength of the metal layer, which not only facilitates the winding of the pole piece 10, but also reduces the damage and tearing of the pole piece 10.

[0083] Among them, along the thickness direction of the pole piece 10 (third direction Z), the thickness of the insulating layer 13 is T3, 2μm≤T3≤10μm. The inventors of the present application have found that if the thickness of the insulating layer 13 is too small, it may be difficult to effectively insulate the first metal layer 11 and the second metal layer 12, affecting the safety of the secondary battery 1000. If the thickness of the insulating layer 13 is too large, it will not only affect the energy density, but also may lengthen the transmission path of lithium ions and affect the transmission efficiency of lithium ions. In the embodiment of the present application, 2μm≤T3≤10μm is defined. , while taking into account the insulation of the first metal layer 11 and the second metal layer 12, it can facilitate the transmission of ions and reduce the impact on energy density. In addition, the insulating layer 13 can have a higher mechanical strength, so that the insulating layer 13 can withstand certain stress and deformation during the production, assembly or use of the secondary battery 1000. For example, during the winding or lamination process of the secondary battery 1000 , the pole piece 10 needs to maintain a good shape and structural stability, and a suitable thickness of the insulating layer 13 helps to improve the mechanical properties of the pole piece 10 , such as tensile strength and bending resistance.

[0084] In some embodiments of the present application, 4 μm ≤ T3 ≤ 6 μm. This can further ensure that the first metal layer 11 and the second metal layer 12 are insulated while facilitating ion transmission and reducing the impact on energy density.

[0085] In an embodiment of the present application, the first metal layer 11 and the second metal layer 12 can be used as the positive and negative conductive substrates of the secondary battery 1000, respectively. For example, the first metal layer 11 is used as the positive conductive substrate, and the second metal layer 12 is used as the negative conductive substrate; or, the first metal layer 11 is used as the negative conductive substrate, and the second metal layer 12 is used as the positive conductive substrate.

[0086] Taking the first metal layer 11 as the positive electrode conductive substrate as an example, the first metal layer 11 can be made of aluminum foil, which has high electrical conductivity and low resistance, and can improve the charging and discharging efficiency of the secondary battery 1000. In addition, the aluminum foil has certain strength and ductility. In the production process such as winding or lamination, the aluminum foil is not easy to break or deform, so as to ensure the structural integrity of the secondary battery 1000. At the same time, the positive electrode of the secondary battery 1000 is at a higher potential during the charging and discharging process. The aluminum foil is relatively stable at this potential and is not easy to chemically react, thereby improving the charging and discharging stability of the secondary battery 1000. In some other embodiments, the first metal layer 11 can also be made of titanium foil, nickel foil or stainless steel foil.

[0087] Taking the second metal layer 12 as the negative electrode conductive substrate as an example, the second metal layer 12 can be made of copper foil, which has high conductivity and low resistance, and can improve the charging and discharging efficiency of the secondary battery 1000. In addition, the copper foil has certain strength and ductility. In the production process such as winding or lamination, the copper foil is not easy to break or deform, so as to ensure the structural integrity of the secondary battery 1000. At the same time, the negative electrode of the lithium-ion battery is at a lower potential during the charging and discharging process. The copper foil is relatively stable at this potential and is not easy to chemically react, thereby improving the charging and discharging stability of the secondary battery 1000. In some other embodiments, the second metal layer 12 can also be made of titanium foil, nickel foil, stainless steel foil or silver foil.

[0088] Please refer to Figure 3 , along the thickness direction of the pole piece, the thickness of the first metal layer is T1, 0.1μm≤T1≤5μm; along the thickness direction of the pole piece 10 (third direction Z), the thickness of the first metal layer 11 is T1, 0.8μm≤T1≤1.5μm, which can make the first metal layer 11 have higher conductivity, and can make the first metal layer 11 able to withstand certain bending and tensile stresses, reducing the rupture or damage of the first metal layer 11. Further, 0.8μm≤T1≤1.5μm, which can further make the first metal layer 11 have higher conductivity, and can make the first metal layer 11 able to withstand certain bending and tensile stresses, reducing the rupture or damage of the first metal layer 11.

[0089] Based on the same inventive concept, the thickness of the second metal layer 12 is T2, 0.1 μm ≤ T1 ≤ 5 μm; this allows the second metal layer 12 to have a higher conductivity, and allows the second metal layer 12 to withstand certain bending and tensile stresses while reducing the breakage or damage of the second metal layer 12. Further, 0.8 μm ≤ T2 ≤ 1.5 μm, which further allows the second metal layer 12 to have a higher conductivity, and allows the second metal layer 12 to withstand certain bending and tensile stresses while reducing the breakage or damage of the second metal layer 12.

[0090] In the embodiments of this application, please refer to Figure 3 , the first metal layer 11 is provided with a first hole 111, the second metal layer 12 is provided with a second hole 121, and the insulating layer 13 is provided with a third hole 131. For example, after the first metal layer 11, the insulating layer 13 and the second metal layer 12 are stacked, a through hole is opened on the composite current collector 11a formed by the first metal layer 11, the insulating layer 13 and the second metal layer 12 by laser drilling, mechanical punching or chemical etching, and the part of the through hole located in the first metal layer 11 is the first hole 111, the part located in the second metal layer 12 is the second hole 121, and the part located in the insulating layer 13 is the third hole 131. Alternatively, the first metal layer 11, the second metal layer 12 and the insulating layer 13 are punched separately, and then the first metal layer 11, the insulating layer 13 and the second metal layer 12 are stacked after punching.

[0091] The first pore 111, the second pore 121 and the third pore 131 are used to transport ions. For example, lithium ions on the side of the first metal layer 11 away from the insulating layer 13 are transported to the second pore 121 of the insulating layer 13 through the first pore 111, and then to the third pore 131 and finally reach the side of the second metal layer 12 away from the insulating layer 13.

[0092] Among them, the diameter of the first hole 111 is R1, 100nm≤R1≤800nm; and / or, the diameter of the second hole 121 is R2, 100nm≤R2≤800nm; and / or, the diameter of the third hole 131 is R3, 200nm≤R3≤1000nm. The insulating layer 13 can insulate the first metal layer 11 and the second metal layer 12, and can ensure the smooth passage of lithium ions, thereby improving the transmission efficiency of lithium ions between the positive and negative active material layers. Preferably, 350nm≤R1≤700nm; and / or, 350nm≤R2≤700nm; and / or, 350nm≤R3≤500nm, which facilitates the transmission of lithium ions while improving the mechanical strength of the pole piece 10.

[0093] For the measurement of each aperture, a scanning electron microscope (SEM) method can be used to perform high-resolution imaging of the surfaces of the first metal layer 11, the second metal layer 12, and the insulating layer 13 using a scanning electron microscope. By observing the micropores (first holes 111, second holes 121, and third holes 131) on the first metal layer 11, the second metal layer 12, and the insulating layer 13, the size and morphology of the micropores can be intuitively understood. Then, the SEM image is processed using image analysis software to measure the diameter or aperture of the micropores.

[0094] The inventor of the present application has found that when the porosity of the first metal layer 11, the second metal layer 12 and the insulating layer 13 is too low, the electrolyte filling amount between the first metal layer 11, the insulating layer 13 and the second metal layer 12 is insufficient, and the ion transmission channel is reduced, which will cause the ion conductivity to decrease, which will cause the secondary battery 1000 to increase in charge and discharge resistance, which is not conducive to the improvement of charge and discharge efficiency and power performance, and may even affect the cycle life of the battery. Higher porosity means that more pore space is filled with electrolyte, which helps to keep the electrolyte inside the electrode 10 sufficient, thereby providing more transmission channels for lithium ions, helping to improve ion conductivity, so that lithium ions can migrate more quickly between the positive electrode active material layer and the negative electrode active material layer, thereby improving the charge and discharge performance of the secondary battery 1000. However, the size of the porosity is generally inversely proportional to the mechanical strength. A higher porosity may lead to a decrease in mechanical strength, which may cause the first metal layer 11, the insulating layer 13 and the second metal layer 12 to be damaged and torn.

[0095] In the embodiment of the present application, the porosity of the first metal layer 11 is limited to G1, 10% ≤ G1 ≤ 75%; and / or, the porosity of the second metal layer is G2, 10% ≤ G2 ≤ ​​75%; and / or, the porosity of the insulating layer is G3, 30% ≤ G3 ≤ 80%. While improving the ion transmission efficiency, the damage and tearing of the first metal layer 11, the insulating layer 13 and the second metal layer 12 can be reduced. By defining the above-mentioned suitable pore size and porosity, it is helpful to evenly distribute the electrolyte inside the pole piece 10, so that the ion conductivity of each part of the pole piece 10 is consistent, and the overall performance of the secondary battery 1000 is improved.

[0096] In the embodiment of the present application, 40%≤G1≤60%; and / or, 40%≤G2≤60%; and / or, 50%≤G3≤70%. This can further improve the ion transmission efficiency while reducing the damage and tearing of the first metal layer, the insulating layer and the second metal layer.

[0097] The porosity can be determined by combining microscopic observation with image analysis, and the surface and cross section of the composite current collector 11a formed by the first metal layer 11, the second metal layer 12 and the insulating layer 13 can be observed with a microscope to obtain a microstructure image. Then, the pores in the image can be identified and measured using image analysis software to calculate the porosity.

[0098] Please refer to Figure 3, along the thickness direction (third direction Z) of the pole piece 10, the surface of the first metal layer 11 away from the insulating layer 13 is provided with a first active material layer 14, and the surface of the second metal layer 12 away from the insulating layer 13 is provided with a second active material layer 15. Since the first hole 111, the second hole 121 and the third hole 131 are used to transmit ions, ions can be transmitted between the first active material layer 14 and the second active material layer 15, and then an electrochemical reaction can be performed. Therefore, the polarities of the first active material layer 14 and the second active material layer 15 can be set to be opposite, that is, in the embodiment of the present application, a single pole piece 10 can include both a positive electrode and a negative electrode.

[0099] For example, the first metal layer 11 is a positive electrode conductive substrate, the first active material layer 14 is a positive electrode active material layer, and the first active material layer 14 includes a positive electrode active material, a conductive agent, and a binder, etc. The above-mentioned material components are mixed and stirred evenly and applied to the first metal layer 11 to obtain the first active material layer 14. Among them, the positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron manganese phosphate.

[0100] The second metal layer 12 is a negative electrode conductive substrate, and the second active material layer 15 is a negative electrode active material layer. The second active material layer 15 includes a negative electrode active material, a conductive agent, and a binder, etc. These materials are mixed, stirred evenly, and applied to the second metal layer 12 to obtain the second active material layer 15. Among them, the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide, silicon alloy, etc.

[0101] In some other embodiments, the first metal layer 11 can also be used as a negative electrode conductive substrate, and the first active material layer 14 is a negative electrode active material layer, the second metal layer 12 is used as a positive electrode conductive substrate, and the second active material layer 15 is a positive electrode active material layer.

[0102] In the embodiment of the present application, the two sides of a single pole piece 10 are respectively the positive electrode active material layer and the negative electrode active material layer. When coating, the positive electrode active material layer and the negative electrode active material layer can be symmetrically coated. Compared with the traditional coating of active materials on different pole pieces, the misalignment of the positive electrode active material layer and the negative electrode active material layer can be reduced, and the overhang area can be reduced while reducing the risk of lithium precipitation, thereby improving the energy density of the secondary battery 1000. In addition, the symmetrical coating of the positive electrode active material layer and the negative electrode active material layer can facilitate the continuous coating of the positive electrode active material layer and the negative electrode active material layer in this case, simplifying the manufacturing process of the pole piece 10 and improving the production efficiency of the secondary battery 1000.

[0103] At the same time, since the two sides of a single electrode sheet 10 are respectively the positive electrode active material layer and the negative electrode active material layer, when preparing the electrode assembly 100, a single electrode sheet 10 can be wound or multiple electrode sheets 10 of a single type can be stacked, which can simplify the manufacturing process. Figure 4 , Figure 4 The winding structure of the electrode assembly 100 is shown. There is no problem of misalignment between the positive electrode sheet and the negative electrode sheet. The overhang area can be reduced or no overhang area is required, which can improve the energy density of the secondary battery 1000. When multiple single-type electrode sheets 10 are stacked, please refer to Figure 5 , Figure 5 The stacking structure of the electrode assembly 100 is shown. Since the first hole 111, the second hole 121 and the third hole 131 can transmit ions, the lithium ions released from the positive electrode active material layer on one side of the electrode 10 can be embedded in the negative electrode active material layer on the other side of the electrode 10, so that the lithium ions released from the positive electrode active material layer can always be embedded in the negative electrode active material layer, which can not only reduce the lithium plating problem, but also reduce the overhang area, thereby improving the energy density of the secondary battery 1000.

[0104] In addition, the insulating layer 13 separates the first metal layer 11 and the second metal layer 12, that is, the insulating layer 13 acts as an isolation film 20. After the pole pieces 10 are stacked or stacked and wound, the amount of isolation film 20 used and the stacking process of the isolation film 20 can be reduced, which can not only simplify the manufacturing process but also improve the space utilization rate, thereby improving the energy density of the secondary battery 1000.

[0105] For the overhang area in the length direction (first direction X) of the electrode sheet 10, in the embodiment of the present application, a single electrode sheet 10 includes a positive electrode active material layer and a negative electrode active material layer, which can reduce the overhang area. Figure 6a , taking the first active material layer 14 as the negative electrode active material layer and the second active material layer 15 as the positive electrode active material layer as an example, along the length direction (first direction X) of the pole piece 10, the first active material layer 14 includes a first region 141, and the first region 141 exceeds the second active material layer 15 on one side of the length direction (first direction X) of the pole piece 10, and the length of the first region 141 is L1, and L1≤0.5mm. The overhang area on one side of the length direction (first direction X) of the pole piece 10 can be reduced to less than 0.5mm, thereby improving the energy density of the secondary battery 1000. The other side of the first active material layer 14 can also be configured similarly.

[0106] Furthermore, L1≤0.3mm, the overhang area in the length direction (first direction X) of the pole piece 10 is reduced to less than 0.3mm, further improving the energy density of the secondary battery 1000. In some other implementations, L1≤0.1mm can also be used, which can reduce the overhang area on one side of the length direction (first direction X) of the pole piece 10 to less than 0.1mm, further improving the energy density of the secondary battery 100. By adopting the solution of the present application, the overhang area in the length direction (first direction X) of the pole piece 10 can be made close to 0, or even no overhang area exists.

[0107] Alternatively, in some other embodiments, the second active material layer 15 is a negative electrode active material layer, and the first active material layer 14 is a positive electrode active material layer. Figure 6b The second active material layer 15 includes a second region 152, which exceeds the first active material layer 15 on one side of the pole piece 10 in the length direction (first direction X), and the length of the second region 152 is L2, L2≤0.5mm. The overhang area on one side of the pole piece 10 in the length direction (first direction X) can be reduced to less than 0.5mm, thereby improving the energy density of the secondary battery 1000. The other side of the first active material layer 14 can also be configured similarly.

[0108] Optionally, L2≤0.3mm; further, L2≤0.1mm, and by adopting the solution of the present application, the overhang area on one side of the length direction (first direction X) of the pole piece 10 can be made close to 0, or even the overhang area does not exist.

[0109] For the overhang area in the width direction (second direction Y) of the electrode sheet 10, in the embodiment of the present application, the first active material layer 14 is a negative electrode active material layer and the second active material layer 15 is a positive electrode active material layer. Figure 7a , the first active material layer 14 includes a third region 143, the third region 143 exceeds the second active material layer 15 on one side of the width direction (second direction Y) of the pole piece 10, and the width of the third region 143 is W1, W1≤0.5mm. The side of the width direction (second direction Y) of the pole piece 10 can be reduced to less than 0.5mm, thereby improving the energy density of the secondary battery 1000. Further, W1≤0.3mm; further, W1≤0.1mm, by adopting the solution of the present application, the overhang area on one side of the width direction (second direction Y) of the pole piece 10 can be made close to 0, or even no overhang area exists.

[0110] Alternatively, in some other embodiments, the second active material layer 15 is a negative electrode active material layer, and the first active material layer 14 is a positive electrode active material layer. Figure 7b , the second active material layer 15 includes a fourth region 154, the fourth region 154 exceeds the first active material layer 14 on one side of the width direction (second direction Y) of the pole piece 10, and the width of the fourth region 154 is W2≤0.5mm. The overhang area on one side of the width direction (second direction Y) of the pole piece 10 can be reduced to less than 0.5mm, thereby improving the energy density of the secondary battery 1000. Further, W2≤0.3mm; further, W2≤0.1mm, by adopting the solution of the present application, the overhang area on one side of the width direction (second direction Y) of the pole piece 10 can be made close to 0, or even no overhang area exists.

[0111] It should be noted that the overhang area is preferably arranged in the negative electrode active material layer, so that the negative electrode active material layer can have enough margin to embed the lithium ions released from the positive electrode active material layer, thereby reducing the risk of lithium plating.

[0112] In the embodiment of the present application, active material layers with opposite polarities are respectively arranged on both sides of the composite current collector 11a in the thickness direction (third direction Z), and the first hole 111, the second hole 121 and the third hole 131 are arranged to transmit ions, so that ions can be transmitted not only outside the pole piece 10, but also inside the pole piece 10, which effectively improves the dynamics of the pole piece 10. Therefore, the pole piece 10 in the embodiment of the present application can adapt to an active material layer with a larger thickness. For example, please refer to Figure 7a , along the thickness direction (third direction Z) of the electrode sheet 10, the thickness of the first active material layer 14 is T4, 25μm≤T4≤100μm; and / or the thickness of the second active material layer 15 is T5, 25μm≤T5≤100μm. The energy density of the secondary battery 1000 can be increased by providing an active material layer with a thicker thickness.

[0113] In some other embodiments, 60μm≤T4≤100μm; and / or, 60μm≤T5≤100μm, which can further improve the energy density of the secondary battery 1000. T4 can be selected from any value between 60μm and 100μm, for example, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 95μm, 100μm, etc. Similarly, T5 can be selected from any value between 60μm and 100μm, for example, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.

[0114] Please refer to Figure 8In the embodiment of the present application, the pole piece 10 further includes an insulating layer 16, which is stacked on the surface of the first active material layer 14 away from the first metal layer 11, or the insulating layer 16 is stacked on the surface of the second active material layer 15 away from the second metal layer 12. Optionally, the insulating layer 16 can be bonded to the first metal layer 11 or the second metal layer 12 by gluing.

[0115] The insulating layer 16 can isolate ions. For example, the insulating layer 16 includes at least one of aluminum oxide, magnesium oxide, zirconium dioxide, boehmite, titanium dioxide, acrylic acid, polyurethane or epoxy resin. The above materials have good insulation and corrosion resistance, which can increase the service life of the pole piece 10.

[0116] Optionally, along the thickness direction of the pole piece 10 (the third direction Z), the thickness of the insulating layer 16 is T, 8 μm≤T≤30 μm, which can reduce the impact of the insulating layer 16 on the energy density of the secondary battery 1000 while isolating ions.

[0117] The insulating layer 16 can isolate ions on one side of the first metal layer 11 or the second metal layer 12, making it difficult or impossible for ions on both sides of the pole piece 10 to be transmitted, and limiting the transmission of ions inside the pole piece 10 through the first hole 111, the second hole 121 and the third hole 131. When the pole pieces 10 are stacked or stacked and wound, due to the presence of the insulating layer 16, only a single pole piece 10 is wound or only a plurality of pole pieces 10 are stacked to form the electrode assembly 100. For example, please refer to Fig. 9 and Fig.10 , Fig. 9 shows the winding structure of the electrode assembly 100, Fig.10 The lamination structure of the electrode assembly 100 is shown. There is no need to provide a separation film 20 , which can reduce the lamination process of the separation film 20 and further simplify the manufacturing process of the secondary battery 1000 .

[0118] Moreover, the insulating layer 16 can limit the transmission of ions between the first hole 111, the second hole 121 and the third hole 131, so that the lithium ions released from the positive electrode active material layer on one side of the pole piece 10 can always be embedded in the negative electrode active material layer on the other side of the pole piece 10, so that the lithium ions released from the positive electrode active material layer can always be embedded in the negative electrode active material layer, which can not only reduce the lithium plating problem, but also reduce the overhang area, or even eliminate the overhang area, and further improve the energy density of the secondary battery 1000. When the insulating layer 16 is set, because the insulating layer 16 limits the transmission of ions between the first hole 111, the second hole 121 and the third hole 131, the risk of lithium plating is sealed, and the overhang area can also be easily reduced to less than 0.5mm, or even 0.3mm, 0.1mm, and there is no overhang area, which fully improves the energy density of the secondary battery 1000.

[0119] In the embodiment of the present application, active material layers with opposite polarities are respectively arranged on both sides of the composite current collector 11a in the thickness direction (third direction Z), and ions are transmitted by arranging the first hole 111, the second hole 121 and the third hole 131, and an insulating layer 16 is arranged on the side of the first metal layer 11 or the second metal layer 12 away from the insulating layer 13, and the ion transmission inside the pole piece 10 is limited by the insulating layer 16. In order to allow the electrolyte to quickly and fully enter the first hole 111, the second hole 121 and the third hole 131, along the thickness direction (third direction Z) of the pole piece 10, the thickness of the first active material layer 14 is T4, 25μm≤T4≤60μm; and / or, the thickness of the second active material layer 15 is T5, 25μm≤T5≤60μm. T4 can select any value from 25μm to 60μm, for example, T4 can select 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, etc. Similarly, T5 can select any value from 25μm to 60μm, for example, T5 can select 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, etc. This allows the electrolyte to fully infiltrate the first active material layer 14 and the second active material layer 15, and allows the electrolyte to quickly and fully enter the first hole 111, the second hole 121, and the third hole 131, thereby improving the dynamics of the pole piece 10.

[0120] In some embodiments, please refer to Figure 8 , a plurality of first grooves 141 are provided on the surface of the first active material layer 14 away from the first metal layer 11. The provision of the first grooves 141 can increase the contact area between the first active material layer 14 and the electrolyte, thereby increasing the infiltration efficiency of the electrolyte on the first active material layer 14, and can facilitate the electrolyte to quickly reach the first hole 111, the second hole 121 and the third hole 131, so that ions can be transported inside the pole piece 10, further improving the dynamics of the pole piece 10. Based on the same inventive concept, a plurality of second grooves 151 are provided on the surface of the second active material layer 15 away from the second metal layer 12. When the pole piece 10 includes an insulating layer 16, the insulating layer 16 can also cover the first groove 141 or the second groove 151, which can reduce the powdering and shedding of the active material layer.

[0121] In some other embodiments, the first groove 141 penetrates the first active material layer 14 along the length direction (first direction X) or the width direction (second direction Y) of the pole piece 10, which can facilitate the electrolyte to enter the first groove 141 along the length direction or the width direction of the pole piece 10 and infiltrate the first active material layer 14, thereby improving the dynamics of the pole piece 10.

[0122] In some other embodiments, the second groove 151 penetrates the second active material layer 15 along the length direction (first direction X) or width direction (second direction Y) of the pole piece 10, which can facilitate the electrolyte to enter the second groove 151 through the length or width direction of the pole piece 10 and infiltrate the second active material layer 15, further improving the dynamics of the pole piece 10. When the pole piece 10 includes an insulating layer 16, it can facilitate the electrolyte to enter the first groove 141 or the second groove 151 from the length direction (first direction X) or width direction (second direction Y) of the pole piece 10, which can also improve the dynamics of the pole piece 10. Therefore, the first active material layer 14 and the second active material layer 15 can be appropriately thickened, for example, 25μm≤T4≤80μm, 25μm≤T5≤80μm, to improve the energy density of the secondary battery 1000. T4 can select any value from 25μm to 80μm, for example, T4 can select 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, etc. Similarly, T5 can select any value from 25μm to 80μm, for example, T5 can select 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, etc.

[0123] Preferably, 40 μm≤T4≤80 μm, 40 μm≤T5≤80 μm, so as to further improve the energy density of the secondary battery 1000 .

[0124] In some embodiments, please refer to Figures 11 to 13 The electrode piece 10 further includes a first electrode tab 17, which includes a first portion 171 and a third portion 172. The first portion 171 is connected to the first metal layer 11, and along the thickness direction (third direction Z) of the electrode piece 10, the projection of the third portion 172 does not overlap with the projection of the first metal layer 11. For example, the third portion 172 extends out of the first metal layer 11 from one side of the electrode piece 10 in the width direction (second direction Y). The first electrode tab 17 can transmit the current during the charge and discharge process of the secondary battery 1000 to the first active material layer 14, or transmit the current of the first active material layer 14 to the outside.

[0125] The inventor of the present application has found that cutting burrs will be generated during the cutting process of the tab, and burrs may also appear on the edge of the metal layer. After the tab is connected to the metal layer, the edge burrs may be squeezed by the tab and bend toward the metal layer on the other side. In the embodiment of the present application, since the first metal layer 11 and the second metal layer 12 are insulated only by the insulating layer 13, the distance between the first metal layer 11 and the second metal layer 12 is relatively close, which may cause the burrs to contact and short-circuit with the metal layer on the other side.

[0126] To reduce the above problems, in the embodiments of this application, please refer to Figures 11 to 13 , the pole piece 10 further includes a first insulating glue 17a, which is disposed on the surface of the third portion 172 facing the second metal layer 12, and the first insulating glue 17a is connected to the first metal layer 11, and the first insulating glue 17a can effectively reduce the contact between the first pole ear 17 and the second metal layer 12, thereby reducing the occurrence of short circuits. In some other embodiments, the lengths of the first metal layer 11 and the second metal layer 12 can also be set to be less than the length of the insulating layer 13, or the widths of the first metal layer 11 and the second metal layer 12 can be set to be less than the width of the insulating layer 13, so that the insulating layer 13 fully isolates the first metal layer 11 and the second metal layer 12, thereby reducing the occurrence of short circuits.

[0127] In some embodiments, please refer to Fig.14 The first insulating glue 17a includes a first substrate 17a1, and the first substrate 17a1 can be made of at least one of polyethylene (PE), polypropylene (PP), polyphenylene sulfide (PPS) or polycarbonate (PC), etc., which can cover the burrs of the first electrode ear 17 and insulate the first electrode ear 17 from the second metal layer 12.

[0128] Optionally, the first insulating glue 17a also includes a first insulating portion 17a2, and the first insulating portion 17a2 can be filled in the first matrix 17a1, wherein the first insulating portion 17a2 includes at least one of aluminum oxide, magnesium oxide or zirconium oxide. Aluminum oxide, magnesium oxide and zirconium oxide are all materials with high resistivity, which can improve the resistivity, help reduce the leakage of current in the first insulating glue 17a, and reduce the risk of internal short circuit of the secondary battery 1000. In addition, the first insulating portion 17a2 can increase the toughness and impact resistance of the first insulating glue 17a, thereby reducing the deformation of the secondary battery 1000 during production, assembly or use. At the same time, each of the above-mentioned first insulating portions 17a2 has a high melting point and thermal stability, which can reduce the exposure of the first pole ear 17 caused by the softening and deformation of the first insulating glue 17a due to high temperature, thereby reducing the short circuit caused by the contact between the first pole ear 17 and the second metal layer 12.

[0129] In some embodiments, please refer to Figures 11 to 13 The pole piece 10 further includes a third insulating glue 17b, which is disposed on the surface of the first pole ear 17 away from the second metal layer 12, and the third insulating glue 17b is connected to the first metal layer 11. When the pole piece 10 is stacked or stacked and wound, the first pole ear 17 may directly face the second active material layer 15. The third insulating glue 17b can be effectively isolated from the second active material layer 15 adjacent to the first pole ear 17, thereby reducing the contact short circuit between the burr and the second active material layer 15.

[0130] In some other embodiments, along the thickness direction of the pole piece 10 (the third direction Z), the projection of the third insulating glue 17b partially overlaps with the projection of the first metal layer 11, which can increase the bonding area and thus the bonding strength on one hand, and can make the third insulating glue 17b effectively isolate the portion of the first pole ear 17 located on the pole piece 10 on the other hand, thereby reducing the burrs of this portion from contacting and short-circuiting with the adjacent second active material layer 15.

[0131] In some embodiments, along the thickness direction (third direction Z) of the pole piece 10, the projection of the first insulating glue 17a is located within the projection of the third insulating glue 17b. After the pole piece 10 is stacked or wound, the third insulating glue 17b may face the second active material layer 15, while the first insulating glue 17a is aimed at the edge of the second metal layer 12. The third insulating glue 17b needs to cover a larger area, and the first insulating glue 17a can effectively isolate the first pole ear 17 from the edge of the second metal layer 12. Therefore, the size of the first insulating glue 17a can be set to be smaller than the size of the third insulating glue 17b.

[0132] For example, see Fig.11 and Fig.12 , along the width direction of the pole piece 10 (the second direction Y), the length of the first insulating glue 17a is L3, 0.5mm≤L3≤5mm, preferably, 1mm≤L3≤1.5mm. The length of the third insulating glue 17b layer can be set to be slightly larger than the length of the first insulating glue 17a, to ensure that the third insulating glue 17b can be partially set on the first metal layer 11, for example, along the width direction of the pole piece 10 (the second direction), the length of the third insulating glue 17b layer is 0.8mm to 10mm, preferably 1.5mm to 2.5mm. In the embodiment of the present application, by reasonably allocating the amount of the first insulating glue 17a and the second insulating glue 18a, the extension of each insulating glue to the active material layer can be reduced.

[0133] In some other embodiments, along the length direction (first direction X) of the electrode piece 10, the width of the first insulating glue 17a is greater than the width of the first electrode tab 17, and both sides of the first insulating glue 17a in the width direction (second direction Y) respectively exceed the first electrode tab 17. For example, please refer to Fig.11 and Fig.12, along the length direction of the electrode 10 (first direction X), the width of the first insulating glue 17a is W4, and the width of the first pole ear 17 is W5, 0≤W4-W5≤1mm, which can make the first pole ear 17 and the second metal layer 12 fully isolated, reducing the occurrence of short circuit. Similarly, the width of the third insulating glue 17b can also be set to be greater than or equal to the width of the first pole ear 17, and can be set similarly to the width of the first insulating glue 17a, for example, the width of the third insulating glue 17b is 0mm to 1mm. Optionally, both sides of the third insulating glue 17b in the width direction (second direction Y) respectively exceed the first pole ear 17, so that the first pole ear 17 can be insulated from the adjacent second active material layer 15.

[0134] In some embodiments, please refer to Fig.13 The first insulating glue 17a can also be connected to the third insulating glue 17b to form a structure covering the root of the first electrode tab 17 (the connection with the edge of the first metal layer 11), thereby fully isolating the cutting burrs of the first electrode tab 17.

[0135] Regarding the thickness of the first insulating glue 17a, the inventor of the present application has found that if the thickness of the first insulating glue 17a is too small, it may be difficult to effectively cover the burrs, and if the thickness is too large, the first insulating glue 17a may flow or extend to the first active material layer 14, affecting the energy density of the secondary battery 1000. Fig.13 , along the thickness direction of the pole piece 10 (third direction Z), the thickness of the first insulating glue 17a is T6, 0.03mm≤T6≤0.3mm, which can isolate the burrs while reducing the impact on the first active material layer 14. Preferably, 0.03mm≤T6≤0.08mm, further reducing the amount of the first insulating glue 17a, and isolating the burrs. Based on the same inventive concept, in the embodiment of the present application, the thickness of the third insulating glue 17b can also be selected from 0.03mm to 0.3mm, preferably 0.03mm to 0.08mm.

[0136] For the connection between the first pole tab 17 and the first metal layer 11, the first pole tab 17 can be connected to the first metal layer 11 by welding or bonding. Taking welding as an example, welding facilitates the formation of a strong metal bond between the first pole tab 17 and the first metal layer 11, thereby improving the connection strength between the first pole tab 17 and the first metal layer 11. However, welding will produce welding burrs, which may contact and short-circuit the second metal layer 12. Therefore, in the embodiment of the present application, it is preferred to bond the first pole tab 17 to the first metal layer 11 by bonding.

[0137] Please refer to Fig.11 , Fig.12 as well as Fig.15The pole piece 10 also includes a first adhesive layer 17c, and the first pole ear 17 is bonded to the first metal layer 11 through the first adhesive layer 17c. The bonding method does not produce burrs, which can reduce the risk of short circuit. And bonding can make the stress more evenly distributed on the contact surface between the first pole ear 17 and the first metal layer 11, reducing the risk of damage and tearing of the pole piece 10 due to stress concentration. At the same time, compared with welding, the bonding process is relatively simple and easy to operate, which can simplify the manufacturing process and improve production efficiency.

[0138] In some embodiments, the first adhesive layer 17c may be made of conductive adhesive, for example, please refer to Fig.16 The first adhesive layer 17c includes a first adhesive portion 17c1 and a first conductive portion 17c2. The first conductive portion 17c2 is filled in the first adhesive portion 17c1. The first electrode tab 17 and the first metal layer 11 can be connected through the first adhesive layer 17c. For example, the first adhesive portion 17c1 includes at least one of epoxy resin (EP), acrylic resin (ACR) or polyimide (PI). The above materials not only have good adhesive properties, but also have good chemical corrosion resistance and high temperature resistance, which can improve the connection strength between the first electrode tab 17 and the first metal layer 11 and extend the service life. The first conductive portion 17c2 includes at least one of silver, copper, nickel or carbon nanotubes, which can improve the conductivity of the first adhesive layer 17c, reduce the resistance between the first electrode tab 17 and the first metal layer 11, and improve the current carrying capacity.

[0139] Regarding the width of the first adhesive layer 17c, the inventors of the present application have found that if the width of the first adhesive layer 17c is too small, the bonding performance between the first electrode 17 and the first metal layer 11 may be affected. If the width of the first adhesive layer 17c is too large, it may cover part of the first active material layer 14, affecting the energy density of the secondary battery 1000, and may also cause adhesive overflow, resulting in a short circuit with the second active material layer 15 or the second metal layer 12. In the embodiments of the present application, please refer to Fig.12 , along the length direction (first direction X) of the electrode 10, the width of the first adhesive layer 17c is W3, 3mm≤W3≤10mm, which can improve the bonding performance between the first electrode tab 17 and the first metal layer 11 while reducing the coverage of the first active material layer 14 and reducing the generation of adhesive overflow. Further, 3mm≤W3≤6mm.

[0140] In some embodiments, the pole piece 10 further includes a second pole ear 18 and a second insulating glue 18a, see Figures 11 to 13, similar to the above-mentioned first pole tab 17 and the first insulating glue 17a, the second pole tab 18 includes a second portion 181 and a fourth portion 182, the second portion 181 is connected to the second metal layer 12, and along the thickness direction (third direction Z) of the pole piece 10, the projection of the fourth portion 182 does not overlap with the projection of the second metal layer 12. For example, the fourth portion 182 extends from one side of the width direction (second direction Y) of the pole piece 10, the second insulating glue 18a is arranged on the surface of the fourth portion 182 facing the first metal layer 11, and the second insulating glue 18a is connected to the second metal layer 12. The cutting burrs of the second pole tab 18 and the contact between the burrs of the second metal layer 12 and the first metal layer 11 can be effectively reduced, thereby reducing the occurrence of short circuits.

[0141] In some embodiments, the pole piece 10 further includes a fourth insulating adhesive 18b, see Figures 11 to 13 The fourth insulating glue 18b is disposed on the surface of the second pole tab 18 away from the first metal layer 11, and the fourth insulating glue 18b is connected to the second metal layer 12. When the pole pieces 10 are stacked or stacked and wound, the second pole tab 18 may face the first active material layer 14. By disposing the fourth insulating glue 18b, the risk of short circuit caused by contact with the first active material layer 14 adjacent to the second pole tab 18 can be reduced.

[0142] In some other embodiments, along the thickness direction (third direction Z) of the pole piece 10, the projection of the fourth insulating glue 18b partially overlaps with the projection of the second metal layer 12, which can increase the bonding area and bonding strength on the one hand, and can effectively isolate the portion of the second pole tab 18 located on the pole piece 10 on the other hand, thereby reducing the burrs of this portion from contacting and short-circuiting with the adjacent first active material layer 14. Optionally, the second insulating glue 18a can also be connected to the fourth insulating glue 18b to form a structure covering the root of the second pole tab 18 (the connection with the edge of the second metal layer 12), thereby fully isolating the cutting burrs of the second pole tab 18.

[0143] The second pole ear 18 can be connected to the second metal layer 12 by welding or bonding. In the embodiment of the present application, the pole piece 10 also includes a second adhesive layer 18c. The second pole ear 18 is bonded to the second metal layer 12 through the second adhesive layer 18c. The bonding method will not produce burrs and can reduce the risk of short circuit.

[0144] In some embodiments, please refer to Figures 11 to 13 , along the thickness direction (third direction Z) of the pole piece 10, the projection of the first pole ear 17 is located outside the projection of the second pole ear 18, that is, the first pole ear 17 and the second pole ear 18 do not overlap, which can reduce the risk of contact short circuit between the first pole ear 17 and the second pole ear 18. Wherein, multiple first pole ears 17 and second pole ears 18 can be provided, and it is ensured that the first pole ears 17 and the second pole ears 18 do not overlap in the thickness direction (third direction Z) of the pole piece 10.

[0145] In the second aspect, the present application also proposes a secondary battery 1000, please refer to Fig.17 The secondary battery 1000 includes a housing 200 and an electrode assembly 100 disposed in the housing 200. The electrode assembly 100 includes a separator 20 and a pole piece 10 as described in any embodiment of the first aspect. The first pole tab 17 and the second pole tab 18 extend from the housing 200 to the outside of the housing 200. The first pole tab 17 and the second pole tab 18 are used to conduct with an external circuit. In some embodiments, the first pole tab 17 and the second pole tab 18 may both include an adapter (not shown in the figure) and extend out of the housing 200 through the adapter.

[0146] In some embodiments, the electrode assembly 100 may adopt a winding structure, please refer to Figure 4 The electrode assembly 100 includes a separator 20 and a single pole piece 10. The separator 20 and the single pole piece 10 are stacked and wound several times to form a wound electrode assembly 100, which can simplify the manufacturing process. When the single pole piece 10 is wound, there is no stacking or winding misalignment problem, which can reduce the overhang area or eliminate the need to set the overhang area, and can improve the energy density of the secondary battery 1000.

[0147] In some other embodiments, please refer to Fig. 9 The secondary battery 1000 also includes an insulating layer 16. The setting of the insulating layer 16 allows a single electrode sheet 10 to be wound to form an electrode assembly 100 without the need to set a separation film 20. Without the stacking and winding operations of the separation film 20, the manufacturing process can be further simplified, and the overhang area can be further reduced or the overhang area does not need to be set, which can improve the energy density of the secondary battery 1000.

[0148] In some embodiments, please refer to Fig.18 Along the winding direction of the pole piece 10, the pole piece 10 includes a first section 10a, a second section 10b and a third section 10c. The first section 10a forms the innermost pole piece 10 of the electrode assembly 100, the third section 10c forms the outermost pole piece 10 of the electrode assembly 100, and the second section 10b is connected between the first section 10a and the third section 10c.

[0149] The first section 10a includes a first inner active material layer 101 facing the winding center, the second section 10b includes a second inner active material layer 102 facing the winding center and a second outer active material layer 103 away from the winding center, and the third section 10c includes a third outer active material layer 104 away from the winding center. Along the thickness direction of the pole piece 10, the thickness of the first inner active material layer 101 is H1, the thickness of the second inner active material layer 102 is H2, the thickness of the second outer active material layer 103 is H3, and the thickness of the third outer active material layer 104 is H4. H1<H2; and / or, H4<H3.

[0150] Along the thickness direction of the pole piece 10, both sides of the second inner active material layer 102 have corresponding opposite polarity active material layers. Since the first hole 111, the second hole 121 and the third hole 131 are used to transmit ions, the second inner active material layer 102 can react with the opposite polarity active material layers on both sides respectively. Therefore, the thickness of the second inner active material layer 102 can be set to be larger. The first inner active material layer 101 has an opposite polarity active material layer only on one side away from the winding center. Therefore, the thickness of the first inner active material layer 101 can be set to be less than the thickness of the second inner active material layer 102, which can facilitate the full reaction of each active material layer and improve the energy density of the secondary battery 1000. For example, (1 / 3)H2≤H1≤(2 / 3)H2. Further, the thickness of the first inner active material layer 101 can be set to be about half of the thickness of the second inner active material layer 102.

[0151] Based on the same inventive concept, the thickness of the third outer active material layer 104 can be set to be less than the thickness of the second outer active material layer 103, further improving the energy density of the secondary battery 1000. For example, (1 / 3)H3≤H4≤(2 / 3)H3, and further, the thickness of the third outer active material layer 104 can be set to be about half of the thickness of the second outer active material layer 103.

[0152] In some embodiments, the portion of the pole piece 10 located at the outermost circle of the electrode assembly 100 includes a first surface 10c1 away from the winding center, and the isolation film 20 can extend to the first surface 10c1, which can reduce the shedding of the outermost active material layer, reduce the contact short circuit between the electrode assembly 100 and the shell 200, and reduce the corrosion of the electrolyte to the pole piece 10.

[0153] In some other embodiments, please refer to Fig.18The secondary battery 1000 further includes a first finishing glue 10c2, which is disposed on the first surface 10c1. The first finishing glue 10c2 can reduce the shedding of the outermost active material layer, reduce the contact short circuit between the electrode assembly 100 and the shell 200, and reduce the corrosion of the electrolyte to the electrode sheet 10. The first finishing glue 10c2 can be made of hot melt adhesive and / or pressure sensitive adhesive, and the first finishing glue 10c2 can be bonded between the shell 200 and the electrode assembly 100 to improve the integrity of the secondary battery 1000 and reduce the movement of the electrode assembly 100 in the shell 200. Optionally, the first finishing glue 10c2 and the isolation film 20 can also be disposed on the first surface 10c1 at the same time. For example, the isolation film 20 is disposed on a portion of the first surface 10c1, and the first finishing glue 10c2 is disposed on the other portion, and the first finishing glue 10c2 can be directly bonded to a portion of the isolation film 20.

[0154] In some other embodiments, when the pole piece 10 includes an insulating layer 16, the insulating layer 16 can form the outermost layer of the electrode assembly 100, or the insulating layer 16 is provided on the first surface 10c1, and the first finishing glue 10c2 and the insulating film 20 do not need to be provided, which can further simplify the manufacturing steps. When the pole piece 10 includes an insulating layer 16, the insulating film 20 or the first finishing glue 10c2 can also be provided on the insulating layer 16, which can further reduce the contact between the electrode assembly 100 and the housing 200, and reduce the corrosion of the pole piece 10.

[0155] In some embodiments, please refer to Figure 5 The electrode assembly 100 can adopt a stacked structure, in which a plurality of pole pieces 10 and a plurality of isolation films 20 are alternately stacked in sequence, and the insulating layer 13 of the pole piece 10 acts as the isolation film 20. After the pole pieces 10 are stacked, the amount of isolation film 20 used and the stacking process of the isolation film 20 can be reduced, which can not only simplify the manufacturing process, but also improve the space utilization rate, thereby improving the energy density of the secondary battery 1000.

[0156] In some other embodiments, a Z-shaped isolation film 20 may also be used. For example, please refer to Fig.19 A plurality of pole pieces 10 are stacked in sequence, and a single isolation film 20 is sequentially inserted between two adjacent pole pieces 10 . This can also reduce the amount of isolation film 20 used, which not only simplifies the manufacturing process, but also improves space utilization, thereby improving the energy density of the secondary battery 1000 .

[0157] In some embodiments, please refer to Fig.19, the plurality of pole pieces 10 are divided into a first outer pole piece 10d, an inner pole piece 10e and a second outer pole piece 10f. Along the stacking direction (third direction Z), the first outer pole piece 10d and the second outer pole piece 10f are respectively the outermost pole pieces on both sides of the electrode assembly 100, and the inner pole piece 10e is located between the first outer pole piece 10d and the second outer pole piece 10f. The first outer pole piece 10d includes a first outer active material layer 105 facing away from the inner pole piece 10e. The inner pole piece 10e includes a first inner active material layer 101 facing the first outer pole piece 10d, and a second inner active material layer 102 facing the second outer pole piece 10f. The second outer pole piece 10f includes a second outer active material layer 103 facing away from the inner pole piece 10e. In this embodiment, along the stacking direction (third direction Z), the thickness of the first outer active material layer 105 is H5, the thickness of the first inner active material layer 101 is H6, the thickness of the second inner active material layer 102 is H7, and the thickness of the second outer active material layer 103 is H8. H5<H6; and / or, H8<H7.

[0158] Along the thickness direction of the pole piece 10 (third direction Z), both sides of the first inner active material layer 101 have corresponding heteropolar active material layers. Since the first hole 111, the second hole 121 and the third hole 131 are used to transmit ions, the first inner active material layer 101 can react with the heteropolar active material layers on both sides. Therefore, the thickness of the first inner active material layer 101 can be set to be larger. The first outer active material layer 105 has a heteropolar active material layer on only one side. Therefore, the thickness of the first outer active material layer 105 can be set to be less than the thickness of the first inner active material layer 101, which can facilitate the full reaction of each active material layer, improve the utilization rate of the active material, and improve the energy density of the secondary battery 1000. For example, (1 / 3)H6≤H5≤(2 / 3)H6. Further, the thickness of the first inner active material layer 101 can be set to be about half of the thickness of the second inner active material layer 102.

[0159] Based on the same inventive concept, the thickness of the second outer active material layer 103 can be set to be smaller than the thickness of the second inner active material layer 102, further improving the energy density of the secondary battery 1000. For example, (1 / 3)H7≤H8≤(2 / 3)H7, and further, the thickness of the third outer active material layer 104 can be set to be about half of the thickness of the second outer active material layer 103.

[0160] In some embodiments, the plurality of pole pieces 10 are divided into a first outer pole piece 10d and a second outer pole piece 10f. Along the stacking direction (third direction Z), the first outer pole piece 10d and the second outer pole piece 10f are respectively the outermost pole pieces 10 on both sides of the electrode assembly 100. The first outer pole piece 10d includes a second surface 10d1 facing away from the second outer pole piece 10f, and the second outer pole piece 10f includes a third surface 10f1 facing away from the first outer pole piece 10d. The second surface 10d1 is provided with an isolation film 20, and the third surface 10f1 is provided with an isolation film 20, which can reduce the shedding of the outermost active material layer, reduce the contact short circuit between the electrode assembly 100 and the shell 200, and reduce the corrosion of the electrolyte to the pole piece 10.

[0161] In some other embodiments, please refer to Fig. 20 The secondary battery 1000 also includes a second finishing glue 10d2 and a third finishing glue 10f2. The second surface 10d1 is provided with the second finishing glue 10d2, and the third surface 10f1 is provided with the third finishing glue 10f2. The second finishing glue 10d2 and the third finishing glue 10f2 can reduce the shedding of the outermost active material layer, reduce the contact short circuit between the electrode assembly 100 and the shell 200, and reduce the corrosion of the electrolyte to the electrode sheet 10. The second finishing glue 10d2 and the third finishing glue 10f2 can both be made of hot melt adhesive and / or pressure sensitive adhesive. The second finishing glue 10d2 and / or the third finishing glue 10f2 can also be bonded to the shell 200 to improve the integrity of the secondary battery 1000 and reduce the movement of the electrode assembly 100 in the shell 200.

[0162] When the pole piece 10 includes an insulating layer 16, please refer to Fig.21 , the outermost layers on both sides of the electrode assembly 100 in the stacking direction (third direction Z) may also be an insulating layer 16, or the second surface 10d1 and the third surface 10f1 may be provided with an insulating layer 16, and there is no need to provide the second finishing glue 10d2, the third finishing glue 10f2 or the isolation film 20, which can further simplify the steps. Alternatively, the insulating layer 16 and the isolation film 20 are provided to reduce the contact between the electrode assembly 100 and the housing 200, or the insulating layer 16, the isolation film 20 and the second finishing glue 10d2 or the third finishing glue 10f2 are provided at the same time, on the one hand, the electrode assembly 100 and the housing 200 are bonded, and on the other hand, the pole piece 10 is protected, the tearing of the pole piece 10 is reduced, and the corrosion of the pole piece 10 is reduced.

[0163] In some embodiments, please refer to Fig. 22, the electrode assembly 100 further includes a first outer electrode sheet 10d and a second outer electrode sheet 10f. Along the stacking direction (third direction Z), the first outer electrode sheet 10d and the second outer electrode sheet 10f are respectively the outermost electrode sheets 10 on both sides of the electrode assembly 100. The first outer electrode sheet 10d includes an insulating layer 13, and the insulating layer 13 is provided with a first metal layer 11 or a second metal layer 12 only on the surface facing the second outer electrode sheet 10f. The metal layer on one side of the above-mentioned electrode sheet 10 can be directly removed to expose the insulating layer 13, and then the housing 200 can be directly isolated by the insulating layer 13, which can reduce the contact short circuit between the electrode assembly 100 and the housing 200, and reduce the corrosion of the electrolyte to the electrode sheet 10.

[0164] Based on the same inventive concept, the second outer electrode piece 10f includes an insulating layer 13, and the insulating layer 13 is only provided with a first metal layer 11 or a second metal layer 12 on the surface facing the first outer electrode piece 10d, which can further prevent the electrode assembly 100 from short-circuiting with the shell 200 and reduce the corrosion of the electrolyte to the electrode piece 10.

[0165] In some other embodiments, when the outermost layer is an insulating layer 13, please refer to Fig. 22 , the electrode sheet 10 includes an inner electrode sheet 10e, and along the stacking direction (third direction Z), the inner electrode sheet 10e is located between the first outer electrode sheet 10d and the second outer electrode sheet 10f. The inner electrode sheet 10e includes a first inner active material layer 101 facing the first outer electrode sheet 10d, and a second inner active material layer 102 facing the second outer electrode sheet 10f. The first outer electrode sheet 10d includes a first outer active material layer 105 facing the inner electrode sheet 10e, and the second outer electrode sheet 10f includes a second outer active material layer 103 facing the inner electrode sheet 10e. Along the stacking direction (third direction Z), the thickness of the first outer active material layer 105 is H5, the thickness of the first inner active material layer 101 is H6, the thickness of the second inner active material layer 102 is H7, and the thickness of the second outer active material layer 103 is H8. H5<H7; and / or, H8<H6. This can facilitate the full reaction of each active material layer, improve the utilization rate of the active material, and increase the energy density of the secondary battery 1000 .

[0166] In the third aspect, the present application also proposes an electronic device, including a secondary battery 1000 as in any embodiment of the second 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, etc. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, spacecraft, etc.

[0167] Experiment 1: Lithium deposition test of lithium-ion batteries

[0168] Embodiment A1:

[0169] <Preparation of pole piece>:

[0170] A polyimide (PET) insulating layer with a thickness of 5 μm is selected, and a first metal layer of aluminum foil and a second metal layer of copper foil are sputtered on two surfaces in the thickness direction of the insulating layer to form a composite current collector. A through hole is opened in the thickness direction of the composite current collector by a laser punching process (the part located on the first metal layer is the first hole, the part located on the second metal layer is the second hole, and the part located on the insulating layer is the third hole), wherein the thickness of the aluminum foil is 1.5 μm, and the thickness of the copper foil is 1.5 μm.

[0171] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10 5 ) are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under a vacuum stirrer until a positive electrode slurry with a solid content of 75wt% and a uniform system is obtained. The positive electrode slurry is evenly and continuously coated on the surface of the aluminum foil and dried at 110°C to obtain a pole piece coated with a positive electrode active material layer on one side.

[0172] The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene butadiene rubber (SBR) are mixed in a weight ratio of 87:10.5:1:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and stirred evenly. The negative electrode slurry is evenly and continuously coated on the surface of the copper foil, and after drying, a pole piece with a positive electrode active material layer on one side and a negative electrode active material layer on the other side is obtained. Among them, the negative electrode active material layer exceeds the positive electrode active material layer L1 on one side of the length direction, L1=0.5mm, and the other side of the length direction is flush with the positive electrode active material layer. The negative electrode active material layer exceeds the positive electrode active material layer W1 on one side of the width direction, W1=0.5mm, and the other side of the width direction is flush with the positive electrode active material layer.

[0173] <Electrolyte Preparation>

[0174] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0175] <Ear connection>

[0176] The positive electrode tab slots are cleaned out on the positive electrode active material layer by laser cleaning process, and the negative electrode tab slots are cleaned out on the negative electrode active material layer. Copper and carbon nanotube conductive particles are added to the epoxy resin to form a first adhesive layer and a second adhesive layer. The aluminum tab is bonded to the first metal layer by the first adhesive layer, and the nickel tab is bonded to the second metal layer by the second adhesive layer.

[0177] Polyethylene is selected as the first matrix, and an alumina insulating material is filled in the first matrix to form a first insulating glue, and the second insulating glue, the third insulating glue and the fourth insulating glue are similarly prepared. The first insulating glue is set on the side of the positive electrode tab facing the second metal layer, and the third insulating glue is set on the side away from the second metal layer. The second insulating glue is set on the side of the negative electrode tab facing the first metal layer, and the fourth insulating glue is set on the side away from the first metal layer. An insulating layer of aluminum oxide is set on the side of the negative active material layer away from the insulating layer, and the thickness of the insulating layer is 10μm.

[0178] <Preparation of lithium-ion batteries>

[0179] The electrode assembly was obtained by winding the pole pieces prepared above, and the electrode assembly was hot pressed at a pressure of 5 MPa, a temperature of 65°C, and a holding time of 10 seconds. The electrode assembly was placed in an aluminum-plastic film shell, and after the whole was dehydrated at 80°C, the electrolyte was injected and packaged to form a lithium-ion battery.

[0180] The relevant parameters in Examples A1 to A5 and Comparative Examples A1 to A7 are shown in Table 1. In Comparative Examples A1 to A2, conventional separators, positive electrode sheets, separators and negative electrode sheets are stacked and wound.

[0181] Lithium deposition test method:

[0182] Place the secondary battery at a test temperature of 25°C for 30 minutes, and then charge it to 4.5V according to the following charging steps:

[0183] (1) 4C constant current charging to 4.2V;

[0184] (2) 3.5C constant current charging to 4.33V;

[0185] (3) 2.5C constant current charging to 4.38V;

[0186] (4) 2C constant current charging to 4.5V;

[0187] (5) 1.5C constant current charging to 4.5V, constant voltage charging to 0.02C;

[0188] After standing for 10 minutes, discharge according to the following steps:

[0189] 0.2C DC discharge to 3V.

[0190] The above charge and discharge process is one cycle. After repeating 100 cycles, when the battery is in a fully charged state (the battery is designed to have a maximum voltage of 4.5V), the secondary battery is disassembled to obtain the pole piece. If the lithium deposition area on the pole piece surface is greater than or equal to 10mm 2 , then it is judged as lithium deposition. Each group tests 10 pieces, the number of lithium deposition pieces is X, and the lithium deposition rate is X / 10.

[0191] Table 1

[0192]

[0193] According to the above Table 1, in combination with Examples A1 to A5 and Comparative Examples A1 to A7, it can be known that for a wound electrode assembly, when a first hole, a second hole and a third hole for transmitting ions are provided on the composite current collector, and a first active material layer and a second active material layer with opposite polarities are provided on the metal layers on both sides of the composite current collector, the risk of lithium plating of the lithium-ion battery can be significantly reduced. This is because when coating, the two sides of a single pole piece are respectively the positive electrode active material layer and the negative electrode active material layer. When coating, the symmetrical coating of the positive electrode active material layer and the negative electrode active material layer can be adopted. Compared with the traditional active material coating on different pole pieces, the misalignment of the positive electrode active material layer and the negative electrode active material layer can be reduced, and the overhang area can be reduced while reducing the risk of lithium plating. At the same time, because the two sides of a single pole piece are respectively the positive electrode active material layer and the negative electrode active material layer, when preparing the electrode assembly, the single pole piece can be wound, which can simplify the manufacturing process. When a single electrode sheet is wound, there is no problem of misalignment between the positive electrode sheet and the negative electrode sheet in stacking and winding, the overhang area can be reduced or there is no need to set the overhang area, which can improve the energy density of the secondary battery.

[0194] In combination with Example A1 to Example A5, when the first hole, the second hole and the third hole for transmitting ions are provided on the composite current collector, and an isolation layer is provided, the risk of lithium plating can be further reduced. This is because the isolation layer can limit the transmission of ions between the first hole, the second hole and the third hole, so that the lithium ions released from the active material layer on one side of the pole piece can always be embedded in the active material layer on the other side of the pole piece, so that the lithium ions released from the active material layer can always be embedded in the negative electrode active material layer, which can not only reduce the problem of lithium plating, but also reduce the overhang area, or even eliminate the overhang area.

[0195] The relevant parameters in Examples B1 to B10 and Comparative Examples B1 to B2 are shown in Table 2. Among them, the electrode assemblies of the laminated structure are adopted in Examples B1 to B10 and Comparative Examples B1 to B2.

[0196] Table 2

[0197]

[0198]

[0199] According to Table 2 above, combined with Examples B1 to B5 and Comparative Examples B1 to B7, it can be seen that for a laminated electrode assembly, when a first hole, a second hole, and a third hole for transmitting ions are provided on the composite current collector, and a first active material layer and a second active material layer with opposite polarities are provided on the metal layers on both sides of the composite current collector, the risk of lithium plating can also be reduced. This is because when multiple pole pieces of a single type are stacked, the lithium ions released from the positive active material layer on one side of the pole piece can be embedded in the negative active material layer on the other side of the pole piece, so that the lithium ions released from the positive active material layer can always be embedded in the negative active material layer, which can not only reduce the problem of lithium plating, but also reduce the overhang area and improve the energy density of the secondary battery.

[0200] When the first hole, the second hole and the third hole for ion transmission are arranged on the composite current collector, and an isolation layer is arranged, the risk of lithium plating can be further reduced. This is because the isolation layer can limit the transmission of ions between the first hole, the second hole and the third hole, so that the lithium ions released from the active material layer on one side of the pole piece can always be embedded in the active material layer on the other side of the pole piece, so that the lithium ions released from the active material layer can always be embedded in the negative electrode active material layer, which can not only reduce the problem of lithium plating, but also reduce the overhang area, or even eliminate the overhang area.

[0201] In combination with Table 1 and Table 2, in the embodiment of the present application, L1≤0.5mm and W1≤0.5mm can be selected. Further, L1≤0.3mm and W1≤0.3mm can be selected. L1≤0.1mm and W1≤0.1mm can also be selected. Even L1=0mm and W1=0=mm.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pole piece, comprising a first metal layer, a second metal layer and an insulating layer stacked between the first metal layer and the second metal layer, characterized in that: The first metal layer is provided with a plurality of first holes, the second metal layer is provided with a plurality of second holes, the insulating layer is provided with a plurality of third holes, and the first holes, the second holes and the third holes are used for transmitting ions; A first active material layer is disposed on a surface of the first metal layer away from the insulating layer, and a second active material layer is disposed on a surface of the second metal layer away from the insulating layer, wherein the first active material layer and the second active material layer have opposite polarities; The pole piece further includes an insulating layer, which is stacked on a surface of the first active material layer away from the first metal layer, or the insulating layer is stacked on a surface of the second active material layer away from the second metal layer; the insulating layer is used to isolate ions.

2. The pole piece according to claim 1, characterized in that: The first active material layer includes a first region, the first region exceeds the second active material layer on one side of the pole piece in the length direction, and the length of the first region is L1, L1≤0.5mm; or, the second active material layer includes a second region, the second region exceeds the first active material layer on one side of the pole piece in the length direction, and the length of the second region is L2, L2≤0.5mm; and / or, The first active material layer includes a third region, the third region exceeds the second active material layer on one side of the electrode width direction, and the width of the third region is W1, W1≤0.5mm; or, the second active material layer includes a fourth region, the fourth region exceeds the first active material layer on one side of the electrode width direction, and the width of the fourth region is W2≤0.5mm.

3. The pole piece according to claim 1, characterized in that: The first active material layer includes a first region, the first region exceeds the second active material layer on one side of the pole piece in the length direction, and the length of the first region is L1, L1≤0.3mm; or, the second active material layer includes a second region, the second region exceeds the first active material layer on one side of the pole piece in the length direction, and the length of the second region is L2, L2≤0.3mm; and / or, The first active material layer includes a third region, the third region exceeds the second active material layer on one side of the pole piece width direction, and the width of the third region is W1, W1≤0.3mm; or, the second active material layer includes a fourth region, the fourth region exceeds the first active material layer on one side of the pole piece width direction, and the width of the fourth region is W2≤0.3mm.

4. The pole piece according to claim 1, characterized in that: The first active material layer includes a first region, the first region exceeds the second active material layer on one side of the pole piece in the length direction, and the length of the first region is L1, L1≤0.1mm; or, the second active material layer includes a second region, the second region exceeds the first active material layer on one side of the pole piece in the length direction, and the length of the second region is L2, L2≤0.1mm; and / or, The first active material layer includes a third region, the third region exceeds the second active material layer on one side of the electrode width direction, and the width of the third region is W1, W1≤0.1mm; or, the second active material layer includes a fourth region, the fourth region exceeds the first active material layer on one side of the electrode width direction, and the width of the fourth region is W2≤0.1mm.

5. The pole piece according to claim 1, characterized in that: The insulating layer includes at least one of aluminum oxide, magnesium oxide, zirconium dioxide, boehmite, titanium dioxide, acrylic acid, polyurethane or epoxy resin.

6. The pole piece according to claim 1, characterized in that: The diameter of the first hole is R1, 100nm≤R1≤800nm; and / or the diameter of the second hole is R2, 100nm≤R2≤800nm; and / or the diameter of the third hole is R3, 200nm≤R3≤1000nm.

7. The pole piece according to claim 1, characterized in that: The porosity of the first metal layer is G1, 10%≤G1≤75%; and / or the porosity of the second metal layer is G2, 10%≤G2≤75%; and / or the porosity of the insulating layer is G3, 30%≤G3≤80%.

8. The pole piece according to claim 7, characterized in that: 40%≤G1≤60%; and / or, 40%≤G2≤60%; and / or, 50%≤G3≤70%.

9. The pole piece according to claim 1, characterized in that: Along the thickness direction of the pole piece, the thickness of the insulating layer is T, 8 μm≤T≤30 μm.

10. The pole piece according to claim 1, characterized in that: Along the thickness direction of the pole piece, the thickness of the first metal layer is T1, 0.1μm≤T1≤5μm; and / or the thickness of the second metal layer is T2, 0.1μm≤T2≤5μm; and / or the thickness of the insulating layer is T3, 2μm≤T3≤10μm.

11. The pole piece according to claim 10, characterized in that: Along the thickness direction of the pole piece, the thickness of the first metal layer is T1, 0.8μm≤T1≤1.5μm; and / or the thickness of the second metal layer is T2, 0.8μm≤T2≤1.5μm; and / or the thickness of the insulating layer is T3, 4μm≤T3≤6μm.

12. The pole piece according to claim 1, characterized in that: Along the thickness direction of the pole piece, the thickness of the first active material layer is T4, 25um≤T4≤60um; and / or the thickness of the second active material layer is T5, 25um≤T5≤60um.

13. The pole piece according to any one of claims 1 to 11, characterized in that: A plurality of first grooves are provided on a surface of the first active material layer away from the first metal layer, and the first grooves penetrate the first active material layer along the length or width direction of the pole piece; and / or, A plurality of second grooves are arranged on a surface of the second active material layer facing away from the second metal layer, and the second grooves penetrate the second active material layer along the length or width direction of the pole piece.

14. The pole piece according to any one of claims 1 to 11, characterized in that: The first metal layer is connected to a first pole tab, and the second metal layer is connected to a second pole tab; Along the thickness direction of the pole piece, the projection of the first pole tab is located outside the projection of the second pole tab.

15. A secondary battery, comprising a housing and an electrode assembly disposed in the housing, characterized in that: The electrode assembly comprises a pole piece as claimed in any one of claims 1 to 14.

16. The secondary battery according to claim 15, characterized in that: The electrode assembly includes a single pole piece, and the single pole piece is wound several times.

17. The secondary battery according to claim 16, characterized in that: The portion of the pole piece located at the outermost circle of the electrode assembly includes a first surface facing away from the winding center; The first surface is provided with the insulating layer; and / or, the first surface is provided with a separation film; and / or, the secondary battery further includes a first finishing glue, and the first finishing glue is provided on the first surface.

18. The secondary battery according to claim 17, characterized in that: The electrode assembly includes a plurality of stacked pole pieces.

19. The secondary battery according to claim 18, characterized in that: Along the stacking direction, the outermost layers on both sides of the electrode assembly are respectively the insulating layers.

20. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 15 to 19.

Images