Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, the secondary battery comprises a first pole piece, the first pole piece comprises a first current collector and a first active layer, the first current collector is connected with a first conductive member, the first current collector comprises a first polymer layer and first metal layers, and the first metal layers are arranged on two opposite surfaces of the first polymer layer. A first conductive coating is arranged on the surface, facing the first active layer, of the first current collector. In the thickness direction of the first current collector, a part of the first conductive coating is located between the first current collector and the first active layer, the projection of the first conductive coating covers the first active layer, and a part of the first conductive coating is located between the first current collector and the first conductive piece. The first conductive part is welded to the surface, away from the first current collector, of the first conductive coating, a first welding mark is formed, and the projection of the first welding mark falls into the projection of the first conductive coating in the thickness direction of the first current collector. According to the secondary battery and the electronic equipment provided by the invention, the process yield of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery and an electronic device. Background Art

[0002] As the power source of an electronic device, a secondary battery is the key to ensuring the normal use of the electronic device. A secondary battery usually adopts a composite current collector, and the composite current collector adopts a three-layer sandwich structure of metal-polymer-metal, which can improve the safety performance of the secondary battery. However, the metal layer of the composite current collector is relatively thin, and the metal layer is easily damaged and fractured during the cold pressing process of the electrode sheet, resulting in easy breakage of the electrode sheet, increasing the difficulty of the electrode sheet processing process and reducing the yield rate of the secondary battery manufacturing process.

[0003] In the prior art, it is generally believed in the art that if the coating exceeds the active material layer too much, the thickness of the excess part will increase, affecting the energy density of the battery. Therefore, the coating should not exceed the active material layer too much. And the composite current collector is usually connected with a conductive member to transmit energy. Considering the welding strength, the conductive member is usually welded on the surface of the composite current collector to form a weld mark. If part of the weld mark falls on the composite current collector and part falls on the coating, due to the different welding windows of the two, the welding strength of the weld mark will be poor. Therefore, there should also be a certain distance between the coating and the weld mark. In this case, the applicant of this application has found that due to the thickness difference between the thickness of the welding position of the conductive member and the thickness of the active material layer, different stresses will be generated during the tape running process, and the friction force generated by the tape running will cause wrinkles between the conductive member and the active material layer, resulting in the inward folding of the conductive member and the reduction of the yield rate of the battery manufacturing process. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device, aiming to improve the yield rate of the secondary battery manufacturing process.

[0005] According to a first aspect of the present application, a secondary battery is provided, including a first electrode sheet. The first electrode sheet includes a first current collector and a first active layer. In a first direction, the first current collector includes a connected first coated section and a first bare foil section. In the thickness direction of the first current collector, the first active layer is disposed on the surface of the first coated section, and first conductive members are disposed on the opposite surfaces of the first bare foil section. The first current collector includes a first polymer layer and a first metal layer, and the first metal layer is disposed on the opposite surfaces of the first polymer layer. A first conductive coating is disposed on the surface of the first current collector facing the first active layer. In the thickness direction of the first current collector, a part of the first conductive coating is located between the first current collector and the first active layer, the projection of the first conductive coating covers the first active layer, a part of the first conductive coating is located between the first current collector and the first conductive member, the first conductive member is welded to the surface of the first conductive coating facing away from the first current collector and forms a first welding mark, and along the thickness direction of the first current collector, the projection of the first welding mark falls within the projection of the first conductive coating. The first direction is perpendicular to the thickness direction of the first current collector.

[0006] In the above technical solution, by providing that the first current collector includes a first polymer layer and a first metal layer, and the first metal layer is disposed on the opposite surfaces of the first polymer layer, the safety performance of the secondary battery can be improved. By providing a first conductive coating on the surface of the first current collector facing the first active layer, in the thickness direction of the first current collector, a part of the first conductive coating is located between the first current collector and the first active layer, the projection of the first conductive coating covers the first active layer, the first conductive coating can protect the first current collector, the possibility of damage and fracture of the first metal layer during the cold pressing process of the first electrode sheet can be reduced, the possibility of the first electrode sheet breaking the belt can be reduced, the processing difficulty of the first electrode sheet can be reduced, and thus the process yield of the secondary battery can be improved. In the thickness direction of the first current collector, by providing that a part of the first conductive coating is located between the first current collector and the first conductive member, the first conductive member is welded to the surface of the first conductive coating facing away from the first current collector and forms a first welding mark, and along the thickness direction of the first current collector, the projection of the first welding mark falls within the projection of the first conductive coating, the thickness difference between the first active layer and the first welding mark can be reduced, and thus the possibility of the first electrode sheet wrinkling between the first active layer and the first welding mark can be reduced, and the possibility of the first conductive member folding inwards can be reduced, thereby improving the process yield of the secondary battery.

[0007] In some preferred embodiments, in the first direction, there is a first spacing between the first active layer and the first welding mark. If the first welding mark is welded on the first active layer, it will affect the welding quality of the first welding mark and increase the thickness of the first electrode tab in the thickness direction of the first current collector, thereby affecting the energy density of the secondary battery. By setting a first spacing between the first active layer and the first welding mark, the possibility of the first welding mark being welded on the first active layer can be reduced, thereby improving the welding quality of the first welding mark and the energy density of the secondary battery.

[0008] In some preferred embodiments, the first spacing is S1, and 0.5 mm ≤ S1 ≤ 1.2 mm. The smaller S1 is, the lower the possibility of the first electrode tab wrinkling at the first spacing, so the process yield rate of the secondary battery is higher, and the additional space occupied by the first conductive member in the first direction is smaller, so the energy density of the secondary battery is higher. When S1 > 1.2 mm, the first electrode tab is likely to wrinkle at the first spacing, resulting in a lower process yield rate of the secondary battery and easily consuming more energy density of the secondary battery. By setting S1 ≤ 1.2 mm, the process yield rate of the secondary battery can be improved and the energy density of the secondary battery can be increased. When S1 < 0.5 mm, due to the deviation of the active material layers on the two surfaces of the electrode tab, when the spacing between the first welding mark and the first active layer is less than 0.5 mm, it cannot be guaranteed that the first welding mark will not overlap with the active material layer on the other surface. When this situation occurs, problems such as positioning errors will occur in the subsequent process, affecting the process yield rate. On the other hand, the overlap of the first welding mark with the active material layer on the other surface will also result in poor welding strength of the first welding mark, affecting the process yield rate. Therefore, it is preferred that S1 ≥ 0.5 mm.

[0009] In some preferred embodiments, in the first direction, the first conductive coating extends beyond one side of the first active layer, and the extended dimension is L1, and 1 mm ≤ L1 ≤ 5 mm. By setting the first conductive coating to extend beyond one side of the first active layer, the first conductive coating can provide a welding space for the first welding mark, thereby improving the welding quality of the first welding mark. When L1 < 1 mm, the welding space provided by the first conductive coating is small, and it is difficult to weld the first conductive member to the first conductive coating, resulting in a lower process yield rate of the secondary battery. By setting L1 ≥ 1 mm, the welding space provided by the first conductive coating can be increased, thereby improving the process yield rate of the secondary battery. When L1 > 5 mm, continuing to increase L1, the improvement of the process yield rate of the secondary battery is not obvious, and it is easy to consume the weight energy density of the secondary battery and increase the cost of the first conductive coating. By setting L1 ≤ 5 mm, the weight energy density of the secondary battery can be increased and the cost can be saved.

[0010] In some preferred embodiments, in the thickness direction of the first current collector, the projection of the first conductive coating covers the first current collector, which is beneficial to further improving the effect of the first conductive coating in protecting the first current collector, and the first conductive coating can block the metal burrs of the first current collector. The first conductive coating can reduce the possibility of short circuit between the first current collector and other electrode sheets, thereby improving the manufacturing yield of the secondary battery.

[0011] In some preferred embodiments, in the thickness direction of the first current collector, the thickness of the first conductive coating is H1, and 0.5 μm ≤ H1 ≤ 3 μm. The larger H1 is, the better the protection effect of the first conductive coating on the first current collector. On the other hand, 0.5 μm ≤ H1 can further reduce the thickness difference between the first welding mark and the first active layer, so the manufacturing yield of the secondary battery is higher. When H1 < 0.5 μm, the protection effect of the first conductive coating on the first current collector is not obvious, resulting in a lower manufacturing yield of the secondary battery. By setting H1 ≥ 0.5 μm, the protection effect of the first conductive coating on the first current collector can be improved, and the thickness difference between the first welding mark and the first active layer can be further reduced, thereby improving the manufacturing yield of the secondary battery. When H1 > 3 μm, continuously increasing H1 does not significantly improve the manufacturing yield of the secondary battery, and it is easy to consume more energy density of the secondary battery. By setting H1 ≤ 3 μm, the energy density of the secondary battery can be improved.

[0012] In some preferred embodiments, the first conductive coating includes at least one of aluminum oxide, silicon oxide, silicon carbide, amorphous carbon, lithium phosphorus oxynitride, and titanium diboride. Aluminum oxide, silicon oxide, silicon carbide, amorphous carbon, lithium phosphorus oxynitride, and titanium diboride have relatively high hardness and good insulation properties, which can improve the anti-extrusion performance of the first conductive coating and can insulate the first current collector well, thereby reducing the possibility of short circuit between the first current collector and other electrode sheets.

[0013] In some preferred embodiments, the resistance of the first conductive coating is from 1 milliohm to 20 milliohms. The greater the resistance of the first conductive coating, the higher the passing rate of the internal short-circuit test before the secondary battery is filled with electrolyte, so the better the safety performance of the secondary battery. When the resistance of the first conductive coating < 1 milliohm, the passing rate of the internal short-circuit test before the secondary battery is filled with electrolyte is relatively low, and the safety performance of the secondary battery is poor. By setting the resistance of the first conductive coating ≥ 1 milliohm, the passing rate of the internal short-circuit test before the secondary battery is filled with electrolyte can be increased, and thus the safety performance of the secondary battery can be improved. When the resistance of the first conductive coating > 20 milliohms, continuing to increase the resistance of the first conductive coating, the increase in the passing rate of the internal short-circuit test before the secondary battery is filled with electrolyte is not obvious, and the first conductive coating easily affects the conductive effect of the first current collector, and the passing rate of the impedance test of the secondary battery will deteriorate. By setting the resistance of the first conductive coating ≤ 20 milliohms, the possibility that the first conductive coating easily affects the conductive effect of the first current collector can be reduced.

[0014] In some preferred embodiments, the first conductive member and the first metal layer are connected and conducted by roll welding, so that the electrons of the first metal layer can be transferred to the first conductive member. Since the first conductive coating is relatively thin, during the process of welding the first conductive member to the first conductive coating by roll welding, the first conductive coating at the welding position can be damaged, so that the first conductive member can be connected and conducted with the first metal layer.

[0015] In some preferred embodiments, a first insulating layer is provided on the surface of the first conductive member facing away from the first current collector, and in the thickness direction of the first current collector, the projection of the first insulating layer covers the first welding mark. The first insulating layer can block the metal burrs of the first welding mark, and can reduce the possibility that the metal burrs of the first welding mark pierce the separator and contact and short-circuit with other electrode plates.

[0016] In some preferred embodiments, the secondary battery further comprises a second pole piece with a polarity opposite to that of the first pole piece, the second pole piece and the first pole piece are stacked, the second pole piece comprises a second current collector and a second active layer, and in the second direction, the second current collector comprises a connected second coating section and a second hollow foil section. In the thickness direction of the second current collector, the surface of the second coating section is provided with a second active layer, and the second conductive member is provided on the opposite surfaces of the second hollow foil section. The second direction is perpendicular to the thickness direction of the second current collector. The second current collector comprises a second polymer layer and a second metal layer, and the opposite surfaces of the second polymer layer are provided with a second metal layer, which can improve the safety performance of the secondary battery. The surface of the second current collector facing the second active layer is provided with a second conductive coating, in the thickness direction of the second current collector, part of the second conductive coating is located between the second current collector and the second active layer, and the projection of the second conductive coating covers the second active layer. The second conductive coating can protect the second current collector, reduce the possibility of damage and fracture of the second metal layer of the second pole piece during the cold pressing process, reduce the possibility of the second pole piece breaking, reduce the difficulty of the second pole piece processing process, and thus improve the secondary battery process quality rate. Part of the second conductive coating is located between the second current collector and the second conductive member. The second conductive member is welded to the surface of the second conductive coating facing away from the second current collector to form a second weld mark. Along the thickness direction of the second current collector, the projection of the second weld mark falls within the projection of the second conductive coating, which can reduce the thickness difference between the second active layer and the second weld mark, thereby reducing the possibility of wrinkles on the second electrode between the second active layer and the second weld mark, and reducing the possibility of inward folding of the second conductive member, thereby improving the process efficiency of the secondary battery.

[0017] In some preferred embodiments, in the second direction, there is a second distance between the second active layer and the second weld print, which can reduce the possibility of the second weld print being welded to the second active layer, thereby improving the welding quality of the second weld print and the energy density of the secondary battery.

[0018] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0019] 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

[0020] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the dimensions in the drawings do not constitute proportional limitations.

[0021] Figure 1Schematic diagram of the structure of a secondary battery according to some embodiments of the present application;

[0022] Figure 2 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application;

[0023] Figure 3 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application;

[0024] Figure 4 Schematic diagram of the structure of a first current collector according to some embodiments of the present application;

[0025] Figure 5 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application;

[0026] Figure 6 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application;

[0027] Figure 7 Schematic diagram of the structure of a second current collector according to some embodiments of the present application;

[0028] Figure 8 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application.

[0029] Explanation of reference numerals:

[0030] 100, secondary battery; 10, housing; 20, electrode assembly;

[0031] 21, first electrode tab; 211, first current collector; 2111, first polymer layer; 2112, first metal layer; 211a, first coated section; 211b, first uncoated foil section; 212, first active layer; 213, first conductive coating;

[0032] 22, second electrode tab; 221, second current collector; 2211, second polymer layer; 2212, second metal layer; 221a, second coated section; 221b, second uncoated foil section; 222, second active layer; 223, second conductive coating;

[0033] 23, separator;

[0034] 241, first conductive member; 2411, first welding mark; 242, second conductive member; 2421, second welding mark;

[0035] 251, first insulating layer; 252, second insulating layer;

[0036] X, first direction; Y, third direction. Detailed implementation manners

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly describe the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some, but not all, of the embodiments of this application.

[0038] Reference to "embodiment" in this application means that a specific feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more, unless otherwise specifically defined.

[0040] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this text generally represents an "or" relationship between the associated objects before and after.

[0041] The term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there may be a state approximately vertical between two components. For example, in combination with numerical description, vertical may refer to the included angle range between two straight lines being between 90 ± 10°, vertical may also refer to the dihedral angle range between two planes being between 90 ± 10°, and vertical may further refer to the included angle range between a straight line and a plane being between 90 ± 10°. The two components described as "vertical" may not be absolute straight lines or planes, and may also be approximately straight lines or planes. From a macroscopic perspective, as long as the overall extension direction is a straight line or a plane, the components can be considered "straight lines" or "planes".

[0042] The empty foil section in this application refers to the area where the active material is not coated.

[0043] The technical features involved in different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0044] In a first aspect, an embodiment of this application provides a secondary battery 100. Please refer to Figure 1 , the secondary battery 100 includes a housing 10 and an electrode assembly 20. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not labeled in the figure), and the electrolyte wets the electrode assembly 20 within the housing 10.

[0045] For the above-mentioned electrode assembly 20, please refer to Figure 2 , Figure 2 which shows the laminated structure of the electrode assembly 20. The electrode assembly 20 includes a first electrode tab 21, a separator 23, and a second electrode tab 22. The polarities of the first electrode tab 21 and the second electrode tab 22 are opposite. A separator 23 is disposed between the adjacent second electrode tab 22 and the first electrode tab 21. The first electrode tab 21, the separator 23, and the second electrode tab 22 are sequentially stacked. In the embodiments of the present application, taking the electrode assembly 20 as a laminated structure as an example for illustration, in some other embodiments, the electrode assembly 20 may also be a wound structure. For example, along the thickness direction of the first electrode tab 21 and / or the second electrode tab 22, after the first electrode tab 21, the separator 23, and the second electrode tab 22 are sequentially stacked, they are wound to form a wound electrode assembly 20.

[0046] For the above-mentioned first electrode tab 21, please refer to Figure 3 and Figure 4 , the first electrode tab 21 includes a first current collector 211 and a first active layer 212, and the first active layer 212 is disposed on the surface of the first current collector 211.

[0047] For the first current collector 211, the first current collector 211 includes a first metal layer 2112 and a first polymer layer 2111. Along the thickness direction (the third direction Y) of the first current collector 211, the first metal layer 2112 is disposed on the opposite two surfaces of the first polymer layer 2111. The first active layer 212 is disposed on the surface of the first metal layer 2112 facing away from the first polymer layer 2111. The first polymer layer 2111 serves as the main mechanical support layer of the first current collector 211 and may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), polyimide, polytetrafluoroethylene, and polyester. The first metal layer 2112 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. The first current collector 211 can reduce the thickness of the metal layer by using the first polymer layer 2111 as the main mechanical support layer, thereby reducing the metal burrs generated when the secondary battery 100 is mechanically damaged, and reducing the mass of the first current collector 211, thereby improving the quality of the secondary battery 100. In some other embodiments, the first current collector 211 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0048] In some embodiments, the first metal layer 2112 is disposed on the opposite two surfaces of the first polymer layer 2111 by electroplating. Alternatively, the first metal layer 2112 is disposed on the opposite two surfaces of the first polymer layer 2111 by evaporation plating.

[0049] For the above-mentioned first active layer 212, the first active layer 212 is infiltrated by the above-mentioned electrolyte solution within the housing 10 to undergo an electrochemical reaction. The first active layer 212 includes a positive electrode active material, a conductive agent, a binder, etc. The above-mentioned various materials are mixed and stirred evenly and coated on the surface of the first metal layer 2112 facing away from the first polymer layer 2111, thereby obtaining the first active layer 212. The positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminate, lithium manganese oxide, and lithium manganese iron phosphate.

[0050] In some embodiments, in the first direction X, the first current collector 211 includes a connected first coated section 211a and a first bare foil section 211b. In the thickness direction of the first current collector 211, the first active layer 212 is disposed on the surface of the first coated section 211a, and first conductive members 241 are disposed on the opposite two surfaces of the first bare foil section 211b. The first conductive members 241 can assist the first current collector 211 in transmitting electrons. A first conductive coating 213 is disposed on the surface of the first current collector 211 facing the first active layer 212. In the thickness direction of the first current collector 211, a part of the first conductive coating 213 is located between the first current collector 211 and the first active layer 212, and the projection of the first conductive coating 213 covers the first active layer 212. The first conductive coating 213 can protect the first current collector 211, can reduce the possibility of damage and fracture of the first metal layer 2112 during the cold pressing process of the first electrode tab 21, can reduce the possibility of the first electrode tab 21 breaking, can reduce the processing difficulty of the first electrode tab 21, and further can improve the process yield of the secondary battery 100. Considering the welding strength, the first conductive members 241 are usually welded to the surface of the first current collector 211 to form welding marks. In order to prevent the welding marks from falling on the first conductive coating 213, a certain distance is required between the first conductive coating 213 and the welding marks, which increases the length of the first electrode tab 21. Due to the thickness difference between the thickness of the welding position of the first conductive members 241 and the thickness of the first active layer 212, different stresses will be generated during the tape running process, and the friction force generated by the tape running will cause wrinkles between the first conductive members 241 and the first active layer 212, resulting in the inward folding of the first conductive members 241, thereby affecting the process yield of the secondary battery 100. In some embodiments, the first conductive members 241 can be aluminum foils. Among them, the first direction X is perpendicular to the thickness direction of the first current collector 211, and the first direction X can be the width direction or the length direction of the first current collector 211.

[0051] To improve the above problems, in the embodiments of the present application, in the thickness direction of the first current collector 211, a part of the first conductive coating 213 is located between the first current collector 211 and the first conductive member 241. The first conductive member 241 is welded to the surface of the first conductive coating 213 facing away from the first current collector 211, and a first welding mark 2411 is formed. Along the thickness direction of the first current collector 211, the projection of the first welding mark 2411 falls within the projection of the first conductive coating 213, which can reduce the thickness difference between the first active layer 212 and the first welding mark 2411. Furthermore, the possibility of the first electrode sheet 21 wrinkling between the first active layer 212 and the first welding mark 2411 can be reduced, and the possibility of the first conductive member 241 folding inwards can be reduced, thereby improving the process yield of the secondary battery 100.

[0052] In some embodiments, in the first direction X, there is a first spacing between the first active layer 212 and the first welding mark 2411. If the first welding mark 2411 is welded to the first active layer 212, it will affect the welding quality of the first welding mark 2411 and increase the thickness of the first electrode sheet 21 in the thickness direction of the first current collector 211, thereby affecting the energy density of the secondary battery 100. By setting a first spacing between the first active layer 212 and the first welding mark 2411, the possibility of the first welding mark 2411 being welded to the first active layer 212 can be reduced, and further, the welding quality of the first welding mark 2411 can be improved, and the energy density of the secondary battery 100 can be improved.

[0053] In some embodiments, the first spacing is S1, and 0.5 mm ≤ S1 ≤ 1.2 mm. The smaller S1 is, the lower the possibility of the first electrode sheet 21 wrinkling at the first spacing, so the process yield of the secondary battery 100 is higher, and the space occupied by the first conductive member 241 in the first direction X is smaller, so the energy density of the secondary battery 100 is higher. When S1 > 1.2 mm, the first electrode sheet 21 is likely to wrinkle at the first spacing, resulting in a lower process yield of the secondary battery 100 and easily consuming more energy density of the secondary battery 100. By setting S1 ≤ 1.2 mm, the process yield of the secondary battery 100 can be improved, and the energy density of the secondary battery 100 can be improved. When S1 < 0.5 mm, due to the deviation of the active material layers on the two surfaces of the electrode sheet, when the spacing between the first welding mark 2411 and the first active layer 212 is less than 0.5 mm, the first welding mark 2411 may overlap with the active material layer on the other surface. When this situation occurs, problems such as positioning errors will occur in the subsequent process, affecting the process yield. On the other hand, the overlap of the first welding mark 2411 with the active material layer on the other surface will also result in poor welding strength of the first welding mark 2411, affecting the process yield. Therefore, it is preferably S1 ≥ 0.5 mm.

[0054] In some embodiments, in the first direction X, the first conductive coating 213 extends beyond one side of the first active layer 212, and the extended dimension is L1, where 1 mm ≤ L1 ≤ 5 mm. By setting the first conductive coating 213 to extend beyond one side of the first active layer 212, the first conductive coating 213 can provide a welding space for the first solder pad 2411, thereby improving the welding quality of the first solder pad 2411. When L1 < 1 mm, the welding space provided by the first conductive coating 213 is small, and it is difficult to weld the first conductive member 241 to the first conductive coating 213, resulting in a low process yield of the secondary battery 100. By setting L1 ≥ 1 mm, the welding space provided by the first conductive coating 213 can be increased, thereby improving the process yield of the secondary battery 100. When L1 > 5 mm, further increasing L1 does not significantly improve the process yield of the secondary battery 100, and it is easy to consume the energy density of the secondary battery 100 and increase the cost of the first conductive coating 213. By setting L1 ≤ 5 mm, the energy density of the secondary battery 100 can be increased and the cost can be saved.

[0055] In some embodiments, in the thickness direction of the first current collector 211, the projection of the first conductive coating 213 covers the first current collector 211, which is beneficial to further improving the effect of the first conductive coating 213 in protecting the first current collector 211. In addition, the first conductive coating 213 can block the metal burrs of the first current collector 211, and the first conductive coating 213 can reduce the possibility of short circuit between the first current collector 211 and other electrode plates, thereby improving the process yield of the secondary battery 100.

[0056] In some embodiments, in the thickness direction of the first current collector 211, the thickness of the first conductive coating 213 is H1, where 0.5 μm ≤ H1 ≤ 3 μm. The larger H1 is, the better the protection effect of the first conductive coating 213 on the first current collector 211. On the other hand, 0.5 μm ≤ H1 can further reduce the thickness difference between the first solder pad 2411 and the first active layer 212, so the process yield of the secondary battery 100 is higher. When H1 < 0.5 μm, the protection effect of the first conductive coating 213 on the first current collector 211 is not obvious, resulting in a low process yield of the secondary battery 100. By setting H1 ≥ 0.5 μm, the protection effect of the first conductive coating 213 on the first current collector 211 can be improved, and the thickness difference between the first solder pad 2411 and the first active layer 212 can be further reduced, thereby improving the process yield of the secondary battery 100. When H1 > 3 μm, further increasing H1 does not significantly improve the process yield of the secondary battery 100, and it is easy to consume more energy density of the secondary battery 100. By setting H1 ≤ 3 μm, the energy density of the secondary battery 100 can be increased.

[0057] In some embodiments, the first conductive coating 213 includes at least one of aluminum oxide, silicon oxide, silicon carbide, amorphous carbon, lithium phosphorus oxynitride, and titanium diboride. Aluminum oxide, silicon oxide, silicon carbide, amorphous carbon, lithium phosphorus oxynitride have relatively high hardness and good insulation properties, which can improve the extrusion resistance of the first conductive coating 213 and can insulate the first current collector 211 well, thereby reducing the possibility of short circuit between the first current collector 211 and other electrode sheets.

[0058] In some embodiments, the resistance of the first conductive coating 213 is from 1 milliohm to 20 milliohms. The greater the resistance of the first conductive coating 213, the higher the passing rate of the internal short circuit test before the secondary battery 100 is filled with electrolyte, so the better the safety performance of the secondary battery 100. When the resistance of the first conductive coating 213 is less than 1 milliohm, the passing rate of the internal short circuit test before the secondary battery 100 is filled with electrolyte is relatively low, and the safety performance of the secondary battery 100 is poor. By setting the resistance of the first conductive coating 213 ≥ 1 milliohm, the passing rate of the internal short circuit test before the secondary battery 100 is filled with electrolyte can be improved, and thus the safety performance of the secondary battery 100 can be improved. When the resistance of the first conductive coating 213 is greater than 20 milliohms, if the resistance of the first conductive coating 213 is further increased, the improvement of the passing rate of the internal short circuit test before the secondary battery 100 is filled with electrolyte is not obvious, and the first conductive coating 213 easily affects the conductive effect of the first current collector 211, and the passing rate of the impedance test of the secondary battery 100 will deteriorate. By setting the resistance of the first conductive coating 213 ≤ 20 milliohms, the possibility that the first conductive coating 213 easily affects the conductive effect of the first current collector 211 can be reduced.

[0059] In some embodiments, the first conductive member 241 and the first metal layer 2112 are connected and electrically conducted by roll welding, so that the electrons of the first metal layer 2112 can be transferred to the first conductive member 241. Since the first conductive coating 213 is relatively thin, during the process of welding the first conductive member 241 to the first conductive coating 213 by roll welding, the first conductive coating 213 at the welding position can be damaged, so that the first conductive member 241 can be connected and electrically conducted with the first metal layer 2112.

[0060] In some embodiments, please refer to Figure 5 , a first insulating layer 251 is provided on the surface of the first conductive member 241 facing away from the first current collector 211. In the thickness direction of the first current collector 211, the projection of the first insulating layer 251 covers the first welding mark 2411. The first insulating layer 251 can block the metal burrs of the first welding mark 2411, and can reduce the possibility that the metal burrs of the first welding mark 2411 pierce the separator 23 and come into contact with other electrode sheets to cause a short circuit. In some embodiments, the first insulating layer 251 includes polyolefin.

[0061] In some embodiments, please refer to Figure 6 andFigure 7 In addition, the secondary battery 100 further includes a second electrode sheet 22 having a polarity opposite to that of the first electrode sheet 21. The second electrode sheet 22 and the first electrode sheet 21 are stacked. The second electrode sheet 22 includes a second current collector 221 and a second active layer 222. In the second direction, the second current collector 221 includes a connected second coating section 221a and a second bare foil section 221b. In the thickness direction of the second current collector 221, the second active layer 222 is disposed on the surface of the second coating section 221a, and second conductive members 242 are disposed on opposite surfaces of the second bare foil section 221b. The second current collector 221 includes a second polymer layer 2211 and a second metal layer 2212. The second metal layer 2212 is disposed on opposite surfaces of the second polymer layer 2211, which can improve the safety performance of the secondary battery 100. A second conductive coating 223 is disposed on the surface of the second current collector 221 facing the second active layer 222. In the thickness direction of the second current collector 221, a part of the second conductive coating 223 is located between the second current collector 221 and the second active layer 222, and the projection of the second conductive coating 223 covers the second active layer 222. The second conductive coating 223 can protect the second current collector 221, reduce the possibility of damage and fracture of the second metal layer 2212 during the cold pressing process of the second electrode sheet 22, reduce the possibility of the second electrode sheet 22 breaking, reduce the processing difficulty of the second electrode sheet 22, and thus improve the process yield of the secondary battery 100. A part of the second conductive coating 223 is located between the second current collector 221 and the second conductive members 242. The second conductive members 242 are welded to the surface of the second conductive coating 223 facing away from the second current collector 221 and form a second welding mark 2421. The projection of the second conductive coating 223 covers the second welding mark 2421, which can reduce the distance between the second active layer 222 and the second welding mark 2421, reduce the length of the second electrode sheet 22, and thus reduce the possibility of inward folding of the second electrode sheet 22 at the position of the distance between the second active layer 222 and the second welding mark 2421, thereby improving the process yield of the secondary battery 100. Herein, the second direction is perpendicular to the thickness direction of the second current collector 221, and the second direction can be the width direction or the length direction of the second current collector 221.

[0062] In some embodiments, in the second direction, there is a second distance between the second active layer 222 and the second welding mark 2421, which can reduce the possibility of the second welding mark 2421 being welded to the second active layer 222, thereby improving the welding quality of the second welding mark 2421 and the energy density of the secondary battery 100.

[0063] In some embodiments, please refer to Figure 8, a second insulating layer 252 is disposed on the surface of the second conductive member 242 facing away from the second current collector 221. In the thickness direction of the second current collector 221, the projection of the second insulating layer 252 covers the second welding mark 2421. The second insulating layer 252 can block the metal burrs of the second welding mark 2421, and can reduce the possibility that the metal burrs of the second welding mark 2421 pierce the separator 23 and contact and short-circuit other electrode plates.

[0064] In some embodiments, the second polymer layer 2211 may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the second metal layer 2212 may include at least one of aluminum, copper, nickel, titanium, and silver. In some other embodiments, the second current collector 221 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0065] In some embodiments, the second active layer 222 includes a negative electrode active material, a conductive agent, a binder, etc. The above-mentioned materials are mixed and stirred evenly and coated on the surface of the second current collector 221 facing the first active layer 212, so as to obtain the second active layer 222. The second active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0066] In some embodiments, the second conductive member 242 may be a copper foil.

[0067] In the second aspect of the present application, an electronic device is further proposed, including the secondary battery 100 according to any one of the embodiments in the first aspect above. The electronic device in the embodiments of the present application is not particularly limited, and it may be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth headsets, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, and so on. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, and an electric aircraft toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spaceship, etc.

[0068] Test part:

[0069] 1. Secondary battery process yield test:

[0070] Process yield (for a single process) = the output quantity of this process / the output quantity of the previous process × 100%

[0071] Total process yield = yield of process 1 × yield of process 2 ×... × yield of process X.

[0072] 2. Secondary battery volume energy density test:

[0073] The volumetric energy density of a secondary battery = battery capacity × discharge plateau / volume, with the basic unit being Wh / L.

[0074] 3. Internal short - circuit test before injecting electrolyte into the secondary battery:

[0075] Before injecting electrolyte into the secondary battery, apply a voltage of 100V between the anode and cathode tabs of the secondary battery, measure the current value between the two tabs. If it is greater than the specified value (such as 20 mA), it is defined as an internal short - circuit.

[0076] Pass rate = (number of cells with test < 20 mA) / (total number of cells) × 100%.

[0077] 4. Impedance test of the secondary battery:

[0078] Use an AC impedance test instrument to measure the internal resistance of the secondary battery by clamping the anode and cathode tabs of the secondary battery with alligator clips; set the internal resistance specification. Different secondary batteries have different internal resistance values. The internal resistance specification of the secondary battery in this application is 17 ± 2 mΩ.

[0079] Pass rate = (number of cells within the internal resistance specification) / (total number of cells) × 100%.

[0080] Example 1

[0081] <Preparation of the first electrode sheet>:

[0082] The first electrode sheet is a positive electrode sheet. Mix lithium cobaltate (LiCoO₂), carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:1.5, add N - methylpyrrolidone (NMP) as a solvent, and prepare a slurry with a solid content of 75 wt%, and stir evenly.

[0083] Select polyethylene terephthalate as the first polymer layer with a thickness of 5 μm. On the two surfaces of the first polymer layer, set a first metal layer made of aluminum with a thickness of 1.5 μm to obtain a first current collector. In the first direction, the first current collector includes a connected first coating section and a first bare - foil section. Coat the above - mentioned slurry on the surface of the first coating section and dry it to obtain a first active layer. On the opposite two surfaces of the first bare - foil section, set a first conductive member, and the first conductive member is an aluminum foil.

[0084] The first current collector is provided with a first conductive coating on the surface facing the first active layer. The material of the first conductive coating is alumina, and the thickness H1 of the first conductive coating is 2 μm. In the thickness direction of the first current collector, a part of the first conductive coating is located between the first current collector and the first active layer, the projection of the first conductive coating covers the first active layer, a part of the first conductive coating is located between the first current collector and the first conductive member, the first conductive member is welded to the surface of the first conductive coating facing away from the first current collector, and a first welding mark is formed. Along the thickness direction of the first current collector, the projection of the first welding mark falls within the projection of the first conductive coating. In the first direction, there is a first spacing S1 of 1.2 mm between the first active layer and the first welding mark, and the dimension L1 of the first conductive coating exceeding one side of the first active layer is 4 mm. The resistance of the first conductive coating is 17 milliohms.

[0085] <Preparation of the second electrode sheet>:

[0086] The second electrode sheet is a negative electrode sheet. Using graphite as the negative active material, the negative active material graphite, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70 wt% is prepared and stirred evenly.

[0087] Copper foil is selected as the second current collector, and the above slurry is coated on the surface of the second current collector and an empty foil area is reserved. The slurry is dried to obtain a second electrode sheet with a second active layer coated on the surface.

[0088] <Preparation of the separator>:

[0089] Using a polyethylene porous membrane as the base layer, a ceramic layer containing alumina ceramic and PVDF binder is coated on one side surface of the base layer as the separator (CCS), wherein the mass percentage content of alumina ceramic in the ceramic layer is 95%.

[0090] <Preparation of the electrolyte>:

[0091] In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent and dissolved and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0092] <Preparation of the secondary battery>:

[0093] The first electrode sheet, the separator, and the second electrode sheet are stacked in sequence to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then electrolyte is injected. After vacuum packaging, standing, forming, capacity measurement, degassing, edge trimming and other processes, a secondary battery is obtained.

[0094] The relevant parameters in Comparative Example 1 and Examples 1 to 14 are shown in Table 1 below.

[0095] Among them, the projection of the first welding mark in Comparative Example 1 does not fall within the projection of the first conductive coating. The first spacing S1 in Examples 1 to 6 is different. The dimension L1 of the first conductive coating extending beyond one side of the first active layer in Example 1 and Examples 7 to 10 is different. The thickness H1 of the first conductive coating in Example 1 and Examples 11 to 14 is different.

[0096] Table 1

[0097]

[0098]

[0099] According to Table 1 above, in combination with Comparative Example 1 and Examples 1 to 14, in the thickness direction of the first current collector, by setting a part of the first conductive coating between the first current collector and the first conductive member, the first conductive member is welded to the surface of the first conductive coating facing away from the first current collector, and a first welding mark is formed. Along the thickness direction of the first current collector, the projection of the first welding mark falls within the projection of the first conductive coating, which can reduce the thickness difference between the first active layer and the first welding mark, and further reduce the possibility of wrinkling of the first electrode sheet between the first active layer and the first welding mark, and reduce the possibility of inward folding of the first conductive member, thereby improving the process yield of the secondary battery.

[0100] Combined with Embodiments 1 to 6, it can be seen that the first spacing between the first active layer and the first welding mark is S1. The smaller S1 is, the lower the possibility that the first pole piece wrinkles at the first spacing. Therefore, the process yield rate of the secondary battery is higher, and the space additionally occupied by the first conductive member in the first direction is smaller. Therefore, the volume energy density of the secondary battery is higher. When S1 > 1.2 mm, the first pole piece is likely to wrinkle at the first spacing, resulting in a lower process yield rate of the secondary battery and easily consuming more volume energy density of the secondary battery. By setting S1 ≤ 1.2 mm, the process yield rate of the secondary battery can be improved, and the volume energy density of the secondary battery can be increased. When S1 < 0.5 mm, due to the deviation of the active material layers on the two surfaces of the pole piece, when the spacing between the first welding mark and the first active layer is less than 0.5 mm, it cannot be guaranteed that the first welding mark does not overlap with the active material layer on the other surface. When this situation occurs, problems such as positioning errors will occur in the subsequent process, affecting the process yield rate. On the other hand, the overlap of the first welding mark with the active material layer on the other surface will also result in poor welding strength of the first welding mark, affecting the process yield rate. Therefore, it is preferably S1 ≥ 0.5 mm.

[0101] Combined with Embodiment 1 and Embodiments 7 to 10, it can be seen that the size by which the first conductive coating extends beyond the first active layer in the first direction is L1. When L1 < 1 mm, the welding space that the first conductive coating can provide is small, and it is difficult to weld the first conductive member to the first conductive coating, resulting in a lower process yield rate of the secondary battery. By setting L1 ≥ 1 mm, the welding space that the first conductive coating can provide can be increased, and thus the process yield rate of the secondary battery can be improved. However, the larger L1 is, the greater the weight of the secondary battery is. Therefore, the weight energy density of the secondary battery is lower. Continuing to increase L1, when L1 > 5 mm, the improvement of the process yield rate of the secondary battery is not obvious, and it is easy to consume more weight energy density of the secondary battery. Therefore, by setting L1 ≤ 5 mm, the weight energy density of the secondary battery can be increased, and the cost of the first conductive coating can be reduced. It should be noted that when S1 remains unchanged, the influence of the first conductive coating on the space occupied by the first pole piece in the first direction is small. Therefore, the change of L1 has little influence on the volume energy density of the secondary battery, and it is difficult to reflect the change of L1 through the volume energy density of the secondary battery.

[0102] Combined with Embodiment 1 and Embodiments 11 to 14, it can be seen that the thickness of the first conductive coating is H1. The larger H1 is, the better the protection effect of the first conductive coating on the first current collector. On the other hand, when 0.5μm ≤ H1, the thickness difference between the first welding mark and the first active layer can be further reduced, so the process yield of the secondary battery is higher. When H1 < 0.5μm, the protection effect of the first conductive coating on the first current collector is not obvious, resulting in a lower process yield of the secondary battery. By setting H1 ≥ 0.5μm, the protection effect of the first conductive coating on the first current collector can be improved, and the thickness difference between the first welding mark and the first active layer can be further reduced, thereby improving the process yield of the secondary battery. When H1 > 3μm, continuing to increase H1, the improvement of the process yield of the secondary battery is not obvious, and it is easy to consume more energy density of the secondary battery. By setting H1 ≤ 3μm, the energy density of the secondary battery can be improved.

[0103] The relevant parameters in Embodiment 1 and Embodiments 11 to 14 are shown in Table 2 below.

[0104] Among them, the resistances of the first conductive coatings in Embodiment 1 and Embodiments 11 to 14 are different. The resistance of the first conductive coating is related to its thickness, so the change in the thickness of the first conductive coating will cause the change in the resistance of the first conductive coating.

[0105] Table 2

[0106]

[0107]

[0108] According to Table 2 above, combined with Embodiment 1 and Embodiments 11 to 14, it can be seen that the larger the resistance of the first conductive coating is, the higher the passing rate of the internal short-circuit test before liquid injection of the secondary battery is, so the safety performance of the secondary battery is better. When the resistance of the first conductive coating < 1 mΩ, the passing rate of the internal short-circuit test before liquid injection of the secondary battery is relatively low, and the safety performance of the secondary battery is poor. By setting the resistance of the first conductive coating ≥ 1 mΩ, the passing rate of the internal short-circuit test before liquid injection of the secondary battery can be improved, and thus the safety performance of the secondary battery can be improved. When the resistance of the first conductive coating > 20 mΩ, continuing to increase the resistance of the first conductive coating, the improvement of the passing rate of the internal short-circuit test before liquid injection of the secondary battery is not obvious, and the first conductive coating is likely to affect the conductive effect of the first current collector, resulting in a worse passing rate of the impedance test of the secondary battery. By setting the resistance of the first conductive coating ≤ 20 mΩ, the possibility that the first conductive coating affects the conductive effect of the first current collector can be reduced.

[0109] The above are only embodiments of the present application, and do not thus limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present application.

Claims

1. A secondary battery includes a first electrode sheet, the first electrode sheet includes a first current collector and a first active layer. In a first direction, the first current collector includes a connected first coated section and a first bare foil section; in the thickness direction of the first current collector, the first active layer is disposed on the surface of the first coated section, and first conductive members are disposed on opposite surfaces of the first bare foil section; The first current collector includes a first polymer layer and a first metal layer, and the first metal layer is disposed on opposite surfaces of the first polymer layer; It is characterized in that A first conductive coating is disposed on the surface of the first current collector facing the first active layer; in the thickness direction of the first current collector, a part of the first conductive coating is located between the first current collector and the first active layer, the projection of the first conductive coating covers the first active layer, a part of the first conductive coating is located between the first current collector and the first conductive member, the first conductive member is welded to the surface of the first conductive coating facing away from the first current collector, and a first welding mark is formed. Along the thickness direction of the first current collector, the projection of the first welding mark falls within the projection of the first conductive coating, and the first direction is perpendicular to the thickness direction of the first current collector.

2. The secondary battery according to claim 1, wherein In the first direction, there is a first spacing between the first active layer and the first welding mark.

3. The secondary battery according to claim 2, characterized in that, The first spacing is S1, and 0.5 mm ≤ S1 ≤ 1.2 mm.

4. The secondary battery according to claim 1, characterized in that, In the first direction, the first conductive coating extends beyond one side of the first active layer, and the extended dimension is L1, and 1 mm ≤ L1 ≤ 5 mm.

5. The secondary battery according to claim 1, wherein In the thickness direction of the first current collector, the projection of the first conductive coating covers the first current collector.

6. The secondary battery according to claim 1, characterized in that, In the thickness direction of the first current collector, the thickness of the first conductive coating is H1, and 0.5 μm ≤ H1 ≤ 3 μm.

7. The secondary battery according to claim 1, wherein The first conductive coating includes at least one of aluminum oxide, silicon oxide, silicon carbide, amorphous carbon, lithium phosphorus oxynitride, and titanium diboride.

8. The secondary battery according to claim 1, characterized in that, The resistance of the first conductive coating is from 1 milliohm to 20 milliohms.

9. The secondary battery according to claim 1, wherein The first conductive member and the first metal layer are connected and electrically conducted by a roll welding method.

10. The secondary battery according to claim 1, characterized in that, A first insulating layer is disposed on the surface of the first conductive member facing away from the first current collector. In the thickness direction of the first current collector, the projection of the first insulating layer covers the first welding mark.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The secondary battery further includes a second electrode sheet having a polarity opposite to that of the first electrode sheet. The second electrode sheet and the first electrode sheet are laminated. The second electrode sheet includes a second current collector and a second active layer. In a second direction, the second current collector includes a connected second coated section and a second bare foil section; in the thickness direction of the second current collector, the second active layer is disposed on the surface of the second coated section, and second conductive members are disposed on opposite surfaces of the second bare foil section; The second current collector includes a second polymer layer and a second metal layer, and the second metal layer is disposed on opposite surfaces of the second polymer layer; The second current collector is provided with a second conductive coating on the surface facing the second active layer; in the thickness direction of the second current collector, a part of the second conductive coating is located between the second current collector and the second active layer, the projection of the second conductive coating covers the second active layer, a part of the second conductive coating is located between the second current collector and the second conductive member, the second conductive member is welded to the surface of the second conductive coating facing away from the second current collector, and a second welding mark is formed. Along the thickness direction of the second current collector, the projection of the second welding mark falls within the projection of the second conductive coating, and the second direction is perpendicular to the thickness direction of the second current collector.

12. The secondary battery according to claim 11, wherein In the second direction, there is a second distance between the second active layer and the second welding mark.

13. An electronic device, characterized in that, It includes a secondary battery according to any one of claims 1 to 12.

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