Secondary battery, electronic device, and method for manufacturing secondary battery

Abstract

The invention relates to a secondary battery, electronic equipment and a manufacturing method of the secondary battery, the secondary battery comprises an electrode assembly, and the electrode assembly comprises a negative plate, a positive plate and a diaphragm. The positive plate comprises a single-sided positive plate arranged on the outermost layer of the electrode assembly in the first direction, and the single-sided positive plate comprises a first positive current collector and a first positive active layer. The first positive current collector comprises a first polymer layer and a first metal layer. First conductive pieces are welded on two opposite surfaces of the second part of the first positive current collector, and a first welding area is formed; the diaphragm comprises a first diaphragm arranged between the single-sided positive plate and the negative plate, a first insulating layer is arranged on the surface, facing the single-sided positive plate, of the first diaphragm, the projection of the first insulating layer on the single-sided positive plate covers the first welding area, the first insulating layer exceeds one side of the first conductive part in the third direction, and the exceeding length is 0.5 mm to 3 mm. According to the secondary battery and the electronic equipment, the problem of short circuit between the positive electrode current collector and the negative electrode active material layer can be solved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, an electronic device, and a method for manufacturing a secondary battery. Background Technology

[0002] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. Current collectors are an important component of secondary batteries, providing support for the active material layer and collecting the current generated by the active material layer for output. Therefore, current collectors have a significant impact on the performance of the electrode plates and electrochemical devices. However, current collectors are prone to short circuits due to contact with active materials of opposite polarity. Summary of the Invention

[0003] The inventors of this application have discovered that existing secondary batteries typically employ composite current collectors (a composite structure of metal-polymer-metal) to improve energy density. These composite current collectors use polymers as the mechanical framework, allowing for thinner metal layers. The current collector needs to be connected to tabs to transfer current to the outside, but conventional ultrasonic welding cannot directly connect the tabs and the composite current collector (prone to poor or excessive soldering). Currently, roll welding is mainly used to place the composite current collector between two layers of metal foil, and then weld the metal foil to the tabs, thus achieving a connection between the composite current collector and the tabs. This improves welding reliability and reduces welding resistance. The composite current collector requires leaving a section of unused foil without an active material layer for metal foil welding. However, since the negative active material layer of the negative electrode usually needs to exceed the positive active material layer of the positive electrode, the empty foil area of ​​the positive composite current collector of the positive electrode corresponds to the negative active material layer. When two metal foils are welded to the empty foil area of ​​the positive composite current collector, the metal burrs in the welding area can easily pierce the separator and form a short circuit with the opposite negative active material layer, thereby reducing the safety performance of the secondary battery.

[0004] The purpose of this application is to provide a secondary battery, an electronic device, and a method for manufacturing a secondary battery, which aims to improve the problem of short circuit between the positive electrode current collector and the negative electrode active material layer.

[0005] According to a first aspect of this application, a secondary battery is provided, including an electrode assembly. The electrode assembly includes a negative electrode, a positive electrode, and a separator. The negative and positive electrode sheets are alternately stacked along a first direction, and a separator is disposed between adjacent negative and positive electrode sheets. The positive electrode includes a single-sided positive electrode. The outermost electrode of the electrode assembly along the first direction is a single-sided positive electrode. The single-sided positive electrode includes a first positive current collector and a first positive active layer. The first positive current collector includes a first portion and a second portion connected sequentially along a second direction. The first portion has the first positive active layer disposed on its surface facing the negative electrode, and the second portion does not have the first positive active layer disposed on its two opposite surfaces along the first direction. The first positive current collector includes a first metal layer and a first polymer layer. The first polymer layer has the first metal layer disposed on its two opposite surfaces along the first direction. A first conductive element is welded to both opposite surfaces of the second portion along the first direction, forming a first welding area. The first conductive element protrudes from the second portion along the second direction. The separator includes a first separator, which is disposed between a single-sided positive electrode and an adjacent negative electrode. A first insulating layer is disposed on the surface of the first separator facing the single-sided positive electrode. The projection of the first insulating layer along a first direction onto the surface of the single-sided positive electrode covers a first welding area. Along a third direction, the length of the first insulating layer is L1, the width of the first conductive element is L2, 1mm≤L1-L2≤6mm, the first insulating layer extends beyond one side of the first conductive element, and the extension length is 0.5mm to 3mm. The first direction, the second direction, and the third direction are perpendicular to each other.

[0006] In the above technical solution, by setting the outermost electrode of the electrode assembly along the first direction as a single-sided positive electrode, the possibility of damage to the outer packaging shell can be reduced. This is because if the outermost electrode of the electrode assembly is a single-sided negative electrode, the copper metal of the current collector of the single-sided negative electrode is prone to electrochemical reaction with the aluminum metal of the shell, thus causing shell damage. The first positive electrode current collector of the single-sided positive electrode has a first positive electrode active layer on its surface facing the negative electrode, which can improve the utilization rate of the positive electrode active material of the single-sided positive electrode, thereby increasing the energy density. By setting the first positive electrode current collector as a structure of two first metal layers sandwiching a first polymer layer, the first metal layer can be made thinner, thereby increasing the energy density of the secondary battery. By welding first conductive elements to both opposite surfaces of the second part of the first positive electrode current collector along the first direction, the positive electrode tab can be easily connected to the first positive electrode current collector through the first conductive elements. By providing a first insulating layer on the surface of the first separator facing the single-sided positive electrode, and having the projection of the first insulating layer along a first direction onto the surface of the single-sided positive electrode covering the first welding area, the first insulating layer can shield the metal burrs in the first welding area, thereby reducing the possibility of the metal burrs in the first welding area piercing the first separator and forming a short circuit with the negative electrode active material layer of the opposite negative electrode. Furthermore, since the first insulating layer is only provided on the outermost first separator of the electrode assembly, the electrode assembly can be fabricated by first stacking the middle layer of electrodes, then providing the first insulating layer to the outermost first separator, and then stacking the single-sided positive electrode, without needing to first bond the insulating layer to the separator and then roll it up before stacking the electrodes. This reduces the possibility that the separator is difficult to roll up after bonding the insulating layer, and also reduces the possibility that the insulating layer will bulge and tear after being rolled up. By limiting 1mm ≤ L1-L2, the first insulating layer can effectively shield the metal burrs in the first welding area. Because an excessively long first insulating layer is prone to folding, thus affecting its effectiveness in shielding the first welding area, the length of the first insulating layer is limited to L1-L2 ≤ 6mm to prevent it from becoming too long. This reduces the likelihood of folding and further improves the effectiveness of the first insulating layer in shielding the metal burrs in the first welding area. The first insulating layer extends beyond the first conductive element in a third direction by 0.5mm to 3mm, meaning that the extension on either side of the first conductive element is 0.5mm to 3mm. By limiting the first insulating layer to extend beyond the first conductive element in a third direction by 0.5mm to 3mm, the first insulating layer can better shield the metal burrs in the first welding area, while preventing it from becoming excessively long and thus reducing the likelihood of folding.

[0007] In some preferred embodiments, along a third direction, the first insulating layer extends beyond both sides of the first conductive element, and the length extending beyond either side of the first conductive element is 0.5 mm to 3 mm, which further enables the first insulating layer to better shield the metal burrs in the first welding area, while the length of the first insulating layer is not too long, so it is not easy to fold.

[0008] In some preferred embodiments, along a third direction, the first conductive element includes a first bent portion and a first main body portion connected in sequence. The first insulating layer extends beyond the first bent portion to the side opposite to the first main body portion, and the extension length is 0.5 mm to 3 mm. During the die-cutting process of the first conductive element, a torque force is generated. The first bent portion can buffer the torque force to reduce the possibility of the first positive current collector tearing due to the torque force. Since the length of the first insulating layer is limited by processing accuracy, by limiting the first insulating layer to extend beyond the first bent portion to the side opposite to the first main body portion, and the extension length is not less than 0.5 mm, it is possible to provide the first insulating layer with sufficient processing accuracy while ensuring that it can effectively cover the metal burrs in the first welding area. By limiting the first insulating layer to extend beyond the first bent portion to the side opposite to the first main body portion, and the extension length is not more than 3 mm, the possibility of the first insulating layer being too long and prone to folding, as well as the possibility of the first insulating layer losing too much energy density of the secondary battery, can be reduced.

[0009] In some preferred embodiments, the first conductive element includes a second bent portion. Along a third direction, the second bent portion is connected to the side of the first main body portion opposite to the first bent portion. The first insulating layer extends beyond the side of the second bent portion opposite to the first main body portion by 0.5 mm to 3 mm. The second bent portion can buffer the torque force during the die-cutting process, further reducing the possibility of the first positive current collector tearing due to torque force. By limiting the first insulating layer to extend beyond the side of the second bent portion opposite to the first main body portion by at least 0.5 mm, the first insulating layer can effectively shield the metal burrs in the first welding area while providing greater processing precision. By limiting the first insulating layer to extend beyond the side of the second bent portion opposite to the first main body portion by at least 3 mm, the possibility of the first insulating layer being too long and prone to folding, as well as the possibility of the first insulating layer losing too much energy density of the secondary battery, can be reduced.

[0010] In some preferred embodiments, along the second direction, the width of the first insulating layer is W1, 1.4mm≤W1≤4mm, so that the first insulating layer can effectively shield the metal burrs in the first welding area without being too wide, thus avoiding excessive loss of the energy density of the secondary battery.

[0011] In some preferred embodiments, the thickness of the first insulating layer along the first direction is H1, where 10 μm ≤ H1 ≤ 20 μm. This ensures that the first insulating layer provides good puncture resistance without being too thick, thus avoiding excessive loss of the secondary battery's energy density.

[0012] In some preferred embodiments, the first insulating layer includes a first adhesive layer and a first substrate layer. Along a first direction, the first substrate layer is disposed on one surface of the first adhesive layer, and the other surface of the first adhesive layer opposite to the first substrate layer is disposed on the first separator. The thickness of the first adhesive layer is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer is H3, 8μm≤H3≤13μm. The first adhesive layer can improve the adhesion between the first insulating layer and the first separator, and the first substrate layer can improve the puncture resistance of the first insulating layer. By limiting the thickness to 2μm≤H2≤7μm, the first adhesive layer achieves good adhesion without being too thick, thus avoiding an excessive reduction in the energy density of the secondary battery. By limiting the thickness to 8μm≤H3≤13μm, the first substrate layer achieves good insulation without being too thick, thus avoiding an excessive reduction in the energy density of the secondary battery.

[0013] In some preferred embodiments, along the second direction, the width of the first welding area is W2, where 0.8mm ≤ W2 ≤ 3mm. By limiting W2 to 0.8mm ≤ W2, the first welding area has good welding strength, thereby allowing the first conductive element to be firmly attached to the first positive current collector. Since the first insulating layer needs to cover the first welding area, if the width of the first welding area increases, the width of the first insulating layer also needs to increase accordingly. Therefore, by limiting W2 to ≤ 3mm, the width of the first welding area is not too wide, and consequently, the width of the first insulating layer is not too wide, thus avoiding an excessive reduction in the energy density of the secondary battery.

[0014] In some preferred embodiments, 6.5mm≤L2≤15.5mm is used to ensure that the first conductive element and the first positive current collector have good connection strength while the first conductive element is not too long and thus does not excessively reduce the energy density of the secondary battery.

[0015] In some preferred embodiments, the negative electrode sheet includes a first negative current collector and a first negative active layer. The first negative current collector has the first negative active layer disposed on at least one surface along a first direction. The first negative active layer includes a third portion and a fourth portion connected sequentially along a second direction. The projection of the third portion onto the surface of the single-sided positive electrode sheet overlaps with the first portion, and the projection of the fourth portion onto the surface of the single-sided positive electrode sheet overlaps at least partially with the second portion. Along the second direction, the width of the fourth portion is W3, where 0.5 mm ≤ W3 ≤ 2 mm. By limiting W3 to 0.5 mm ≤ W3, the first negative active layer can better absorb lithium ions released from the first positive active layer, reducing the possibility of lithium deposition on the surface of the first negative active layer. By limiting W3 to ≤ 2 mm, the negative active material of the first negative active layer has good energy utilization without excessively reducing the energy density of the secondary battery.

[0016] In some preferred embodiments, the first separator includes a fifth portion and a sixth portion connected sequentially along a second direction. Along the first direction, the projection of the fifth portion onto the surface of the negative electrode overlaps with the first negative electrode active layer. Along the second direction, the sixth portion extends beyond the first negative electrode active layer, and the width of the sixth portion is W4, 0.5mm ≤ W4 ≤ 2mm. By limiting W4 to 0.5mm ≤ W4, the sixth portion of the first separator can shield the first negative electrode active layer, reducing the possibility of a short circuit due to contact between the first negative electrode active layer and the first conductive element. By limiting W4 to ≤ 2mm, the sixth portion of the first separator is not too wide, thus not excessively reducing the energy density of the secondary battery.

[0017] In some preferred embodiments, the first positive electrode active layer includes a seventh portion and an eighth portion, with the eighth portion connected along a second direction to the side of the seventh portion near the first conductive element. Along the first direction, the thickness of the eighth portion is less than the thickness of the seventh portion, and the projection of the first insulating layer onto the surface of the single-sided positive electrode sheet at least partially overlaps with the eighth portion. During cold pressing, the first positive electrode active layer generates torque force. By limiting the thickness of the eighth portion of the first positive electrode active layer to be less than the thickness of the seventh portion, the thinner eighth portion can buffer the torque force, thereby reducing the possibility of the first positive current collector tearing due to torque force. Because the eighth portion is thinner, by limiting the overlap between the projection of the first insulating layer onto the surface of the single-sided positive electrode sheet and at least partially overlap with the eighth portion, the thickness of the electrode assembly along the first direction is not excessively increased, while further increasing the possibility that the first insulating layer will obscure the first welding area.

[0018] In some preferred embodiments, the positive electrode includes a double-sided positive electrode, with a double-sided positive electrode disposed between two adjacent negative electrodes along a first direction. The double-sided positive electrode includes a second positive current collector and a second positive active layer. The second positive current collector includes a ninth portion and a tenth portion connected sequentially along a second direction. The ninth portion has a second positive active layer disposed on both opposite surfaces along the first direction, while the tenth portion does not have a second positive active layer disposed on either opposite surface along the first direction. The second positive current collector includes a second metal layer and a second polymer layer. The second polymer layer has a second metal layer disposed on both opposite surfaces along the first direction. A second conductive element is welded to both opposite surfaces of the tenth portion along the first direction, forming a second welding area. The separator includes a second separator, disposed between the double-sided positive electrode and the negative electrode. A second insulating layer is disposed on the surface of the second separator facing the double-sided positive electrode, and the projection of the second insulating layer along the first direction onto the surface of the double-sided positive electrode covers the second welding area. A double-sided positive electrode is disposed between two adjacent negative electrode sheets along the first direction. A second positive electrode active layer is disposed on both opposite surfaces of the second positive electrode current collector of the double-sided positive electrode, which reduces the number of layers in the second positive electrode current collector, thereby increasing the energy density of the secondary battery. By setting the second positive electrode current collector to a structure of two second metal layers sandwiching a second polymer layer, the second metal layer can be made thinner, further increasing the energy density of the secondary battery. A second conductive element is welded to both opposite surfaces of the tenth portion of the second positive electrode current collector along the first direction, facilitating the connection of the positive electrode tab to the second positive electrode current collector via the second conductive element. A second insulating layer is disposed on the surface of the second separator facing the double-sided positive electrode sheet, and the projection of the second insulating layer along the first direction onto the surface of the double-sided positive electrode sheet covers the second welding area. This allows the second insulating layer to shield the metal burrs in the second welding area, thereby reducing the possibility of the metal burrs in the second welding area piercing the second separator and forming a short circuit with the negative electrode active material layer of the opposite negative electrode sheet.

[0019] In some preferred embodiments, the electrode assembly satisfies at least one of the following conditions: (1) the first metal layer comprises aluminum; (2) the first polymer layer comprises polyolefin; (3) the first conductive element comprises aluminum; and (4) the first insulating layer comprises polyolefin.

[0020] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0021] Thirdly, this application also proposes a method for manufacturing a secondary battery, used to prepare a secondary battery as described in any embodiment of the first aspect above, comprising: providing a negative electrode sheet, a separator, and a double-sided positive electrode sheet; sequentially stacking the separator, negative electrode sheet, separator, and double-sided positive electrode sheet along a first direction to form a first assembly, wherein the outermost electrode sheet of the first assembly along the first direction is a negative electrode sheet, and a first separator sheet is stacked on the outermost layer of the first assembly along the first direction. Providing a first insulating layer and disposing the first insulating layer on a surface of the first separator of the first assembly facing away from the negative electrode sheet to form a second assembly. Providing a single-sided positive electrode sheet and a first conductive element; welding the first conductive element to two opposing surfaces of a second portion of the first positive current collector of the single-sided positive electrode sheet, forming a first welding area. Stacking and welding the single-sided positive electrode sheet with the first conductive element to two opposing surfaces of the second assembly along the first direction, wherein the projection of the first insulating layer along the first direction on the surface of the single-sided positive electrode sheet covers the first welding area. With the above manufacturing method, when the diaphragm in the middle layer of the electrode assembly does not have an insulating layer, it is not necessary to first bond the insulating layer to the diaphragm and then roll it up before stacking the electrode sheets. This reduces the possibility that the diaphragm is not easy to roll up after bonding the insulating layer, and also reduces the possibility that the diaphragm will bulge and tear after the insulating layer is rolled up.

[0022] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0023] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.

[0024] Figure 1 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application; Figure 2 This is a schematic diagram of the structure of the electrode assembly in some embodiments of this application; Figure 3 This is a schematic diagram of the structure of the first positive current collector in some embodiments of this application; Figure 4 This is a schematic diagram of the structure of a single-sided positive electrode sheet along a first direction in some embodiments of this application; Figure 5 This is a schematic diagram of the structure of the first insulating layer in some embodiments of this application; Figure 6 This is a schematic diagram of the structure of the electrode assembly in some embodiments of this application; Figure 7 This is a schematic diagram of the structure of the second positive current collector in some embodiments of this application; Figure 8This is a schematic diagram of the structure of a double-sided positive electrode sheet along a first direction in some embodiments of this application; Figure 9 This is a schematic diagram of the structure of the second insulating layer in some embodiments of this application.

[0025] Explanation of reference numerals in the attached figures: 100. Secondary batteries; 10. Shell; 20. Electrode assembly; 21. Positive electrode sheet; 211. Single-sided positive electrode sheet; 2111. First positive electrode current collector; 211a. First part; 211b. Second part; 2113. First metal layer; 2114. First polymer layer; 2112. First positive electrode active layer; 211c. Seventh part; 211d. Eighth part; 212. Double-sided positive electrode sheet; 2121. Second positive electrode current collector; 212a. Ninth part; 212b. Tenth part; 2123. Second metal layer; 2124. Second polymer layer; 2122. Second positive electrode active layer; 22. Negative electrode sheet; 221. First negative electrode current collector; 222. First negative electrode active layer; 222a. Third part; 222b. Fourth part; 23. Diaphragm; 231. First diaphragm; 231a. Fifth part; 231b. Sixth part; 232. Second diaphragm; 24. First conductive element; 24a. First welding area; 241. First main body; 242. First bent portion; 243. Second bent portion; 25. First insulating layer; 251. First adhesive layer; 252. First substrate layer; 26. Second conductive element; 26a. Second welding area; 261. Second main body; 262. Third bending portion; 263. Fourth bending portion; 27. Second insulating layer; 271. Second adhesive layer; 272. Second substrate layer; X, first direction; Y, second direction; Z, third direction. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0027] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0028] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0029] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0030] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, combined with numerical descriptions, perpendicularity can refer to the angle between two straight lines within the range of 90 ± 10°, the dihedral angle between two planes within the range of 90° ± 10°, or the angle between a straight line and a plane within the range of 90 ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is a straight line or plane, the component can be considered a "straight line" or "plane".

[0031] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0032] In the first aspect, embodiments of this application provide 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 shown in the figure). The electrolyte wets the electrode assembly 20 inside the housing 10. For the electrode assembly 20 mentioned above, please refer to... Figure 2 , Figure 2 The stacked structure of the electrode assembly 20 is shown. The electrode assembly 20 includes a negative electrode 22, a positive electrode 21, and a separator 23. The positive electrode 21 and the negative electrode 22 are alternately stacked along a first direction X. A separator 23 is disposed between adjacent positive electrode 21 and negative electrode 22, and the separator 23 is used to insulate and separate the positive electrode 21 and the negative electrode 22. In the embodiments of this application, the electrode assembly 20 is described as a stacked structure. In some other embodiments, the electrode assembly 20 may also be a wound structure. For example, the positive electrode 21, the separator 23, and the negative electrode 22 are stacked in sequence and then wound to form a wound electrode assembly 20.

[0033] Regarding the aforementioned positive electrode 21, the positive electrode 21 includes a single-sided positive electrode 211. The outermost electrode of the electrode assembly 20 along the first direction X is a single-sided positive electrode 211, which can reduce the possibility of damage to the outer packaging shell 10. This is because if the outermost electrode of the electrode assembly 20 is a single-sided negative electrode, the copper metal of the current collector of the single-sided negative electrode is prone to electrochemical reaction with the aluminum metal of the shell 10, thereby causing damage to the shell 10. The single-sided positive electrode 211 includes a first positive current collector 2111 and a first positive active layer 2112. The first positive current collector 2111 along the second direction Y includes a first part 211a and a second part 211b connected in sequence. The second direction Y is perpendicular to the first direction X. The first positive active layer 2112 is provided on one surface of the first part 211a facing the negative electrode 22, and the first positive active layer 2112 is not provided on either of the two opposite surfaces of the second part 211b along the first direction X. By setting a first positive electrode active layer 2112 on the surface of the first positive electrode current collector 2111 of the single-sided positive electrode 211 facing the negative electrode 22, the utilization rate of the positive electrode active material of the single-sided positive electrode 211 can be improved, thereby increasing the energy density.

[0034] The first positive electrode active layer 2112 is immersed in the electrolyte within the casing 10 to undergo an electrochemical reaction. The first positive electrode active layer 2112 includes a first positive electrode active material, a conductive agent, a binder, etc. These materials are mixed and stirred evenly and then coated onto the surface of the first portion 211a of the first positive electrode current collector 2111 facing the negative electrode sheet 22, thereby obtaining the first positive electrode active layer 2112. The first positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0035] For the first positive current collector 2111, please refer to... Figure 2 and Figure 3The first positive electrode current collector 2111 includes a first metal layer 2113 and a first polymer layer 2114. The first polymer layer 2114 has a first metal layer 2113 on each of its two opposite surfaces along the first direction X. By configuring the first positive electrode current collector 2111 with a structure of two first metal layers 2113 sandwiching a first polymer layer 2114, the first metal layer 2113 can be made thinner, thereby reducing metal burrs caused by mechanical damage to the secondary battery 100 and reducing the mass of the first positive electrode current collector 2111, thus increasing the mass energy density of the secondary battery 100. The first polymer layer 2114, as the main mechanical support layer of the first positive electrode current collector 2111, can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The first metal layer 2113 can include at least one of aluminum, copper, nickel, titanium, and silver.

[0036] The negative electrode 22 includes a first negative current collector 221 and a first negative active layer 222. The first negative current collector 221 has the first negative active layer 222 disposed on at least one surface along a first direction X. The first negative active layer 222 includes a third portion 222a and a fourth portion 222b connected sequentially along a second direction Y. The projection of the third portion 222a onto the surface of the single-sided positive electrode 211 overlaps with the first portion 211a, and the projection of the fourth portion 222b onto the surface of the single-sided positive electrode 211 overlaps at least partially with the second portion 211b. Along the second direction Y, the width of the fourth portion 222b is W3, where 0.5mm ≤ W3 ≤ 2mm. By limiting W3 to 0.5mm ≤ W3, the first negative active layer 222 can better absorb lithium ions released from the first positive active layer 2112, reducing the possibility of lithium deposition on the surface of the first negative active layer 222. By limiting W3 to ≤ 2mm, the negative electrode active material of the first negative electrode active layer 222 can have a better energy utilization rate without excessively reducing the energy density of the secondary battery 100.

[0037] The first negative electrode active layer 222 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The first negative electrode active layer 222 comprises a first negative electrode active material, a conductive agent, a binder, etc. These materials are mixed and stirred evenly and then coated onto at least one surface of the negative electrode current collector along the first direction X, thereby obtaining the first negative electrode active layer 222. The first negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0038] For the first negative electrode current collector 221, the first negative electrode current collector 221 can be a composite current collector (a composite structure of metal-polymer-metal). For example, the first negative electrode current collector 221 includes a polymer layer and a metal layer disposed on opposite surfaces of the polymer layer. The polymer layer, as the main mechanical support layer of the first negative electrode current collector 221, can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The metal layer can include at least one of aluminum, copper, nickel, titanium, and silver. By using the polymer layer as the main mechanical support layer, the metal layer of the first negative electrode current collector 221 can be thinned, thereby reducing metal burrs caused by mechanical damage to the secondary battery 100 and reducing the mass of the first negative electrode current collector 221, thereby increasing the mass energy density of the secondary battery 100. In some other embodiments, the first negative electrode current collector 221 can be a single-layer metal foil, which can include at least one of aluminum, copper, nickel, titanium, and silver.

[0039] In some embodiments, a first conductive element 24 is welded to both opposite surfaces of the second portion 211b of the first positive current collector 2111 along the first direction X, forming a first welding area 24a. The first conductive element 24 protrudes from the second portion 211b along the second direction Y to facilitate the connection of the positive electrode tab to the first positive current collector 2111 via the first conductive element 24. The first conductive element 24 may include at least one of aluminum, copper, nickel, titanium, and silver. Placing the first positive current collector 2111 between the two first conductive elements 24 by roll welding can improve the reliability of the welding and reduce the welding resistance. However, the metal burrs in the first welding area 24a can easily pierce the separator 23 and form a short circuit with the opposite first negative electrode active layer 222, thereby reducing the safety performance of the secondary battery 100.

[0040] There are currently two solutions to the above problems. The first solution is to apply adhesive tape to the first welding area 24a to cover the metal burrs in the first welding area 24a, thereby reducing the possibility of the metal burrs in the first welding area 24a piercing the separator 23 and forming a short circuit with the first negative electrode active layer 222 on the opposite side. However, the adhesive tape application process is cumbersome. Adding an adhesive tape application process to the roll welding process will greatly amplify the process dimensional accuracy error, thereby significantly reducing the electrode manufacturing yield. In addition, the adhesive in the adhesive tape has the ability to dissolve the adhesive of the first positive electrode active layer 2112 of the single-sided positive electrode 211, which will cause the positive electrode active material particles of the first positive electrode active layer 2112 near the first conductive element 24 to fall off. Furthermore, during electrode cutting, the die will stick to the adhesive tape, resulting in poor cutting effect, thereby reducing the electrode manufacturing yield, and requiring more frequent die cleaning, thus reducing production efficiency. The second approach involves providing ceramic layers on both opposite surfaces of the second part 211b along the first direction X, and positioning the ceramic layers along the second direction Y between the first positive electrode active layer 2112 and the first conductive element 24. This allows the first conductive element 24 to extend beyond the first negative electrode active layer 222 along the second direction Y, and the first welding area 24a to extend beyond the first negative electrode active layer 222 along the second direction Y. This reduces the likelihood that metal burrs in the first welding area 24a will easily pierce the separator 23 and form a short circuit with the opposite first negative electrode active layer 222. However, the extended first conductive element 24 increases the head space of the single-sided positive electrode sheet 211, thereby reducing the energy density of the secondary battery 100.

[0041] To address the aforementioned issues, please refer to the embodiments of this application. Figure 2 and Figure 4The separator 23 includes a first separator 231. The first separator 231 is disposed between the single-sided positive electrode 211 and the adjacent negative electrode 22. A first insulating layer 25 is disposed on the surface of the first separator 231 facing the single-sided positive electrode 211. The projection of the first insulating layer 25 on the surface of the single-sided positive electrode 211 along the first direction X covers the first welding area 24a, so that the first insulating layer 25 can block the metal burrs of the first welding area 24a, thereby reducing the possibility that the metal burrs of the first welding area 24a will pierce the first separator 231 and form a short circuit with the negative active material layer of the opposite negative electrode 22. Furthermore, since the first insulating layer 25 is only provided on the outermost first diaphragm 231 of the electrode assembly 20, the electrode assembly 20 can be fabricated by first stacking the middle layer of electrode sheets, then providing the first insulating layer 25 to the outermost first diaphragm 231, and then stacking the single-sided positive electrode sheet 211. This eliminates the need to first bond the insulating layer to the diaphragm 23, then roll it up, and finally stack the electrode sheets. This reduces the likelihood that the diaphragm 23 will be difficult to roll up after bonding the insulating layer, and also reduces the possibility that the diaphragm 23 will bulge and tear after rolling up the insulating layer. Along the third direction Z, the length of the first insulating layer 25 is L1, and the width of the first conductive element 24 is L2, where 1mm ≤ L1 - L2 ≤ 6mm. The first insulating layer 25 extends beyond the first conductive element 24 by 0.5mm to 3mm. The third direction Z is perpendicular to the first direction X and the second direction Y. By limiting 1mm ≤ L1 - L2, the first insulating layer 25 can effectively shield the metal burrs of the first welding area 24a. Because the first insulating layer 25 is prone to folding if it is too long, thus affecting its effectiveness in shielding the first welding area 24a, the length of the first insulating layer 25 is limited to L1-L2≤6mm to prevent it from becoming too long, thereby reducing the possibility of folding and further improving the likelihood of the first insulating layer 25 shielding the metal burrs in the first welding area 24a. Furthermore, by limiting the first insulating layer 25 to extend beyond the first conductive element 24 in a third direction by 0.5mm to 3mm, the first insulating layer 25 can better shield the metal burrs in the first welding area 24a, while ensuring that its length is not too long and thus less prone to folding.

[0042] In some embodiments, along the third direction Z, the first insulating layer 25 extends beyond both sides of the first conductive member 24, and the length extending beyond either side of the first conductive member 24 is 0.5mm to 3mm, which further enables the first insulating layer 25 to better shield the metal burrs of the first welding area 24a, while the length of the first insulating layer 25 is not too long, so it is not easy to fold.

[0043] In some embodiments, along the third direction Z, the first conductive element 24 includes a first bent portion 242 and a first main body portion 241 connected in sequence. The first insulating layer 25 extends beyond the first bent portion 242 to the side opposite to the first main body portion 241, and the length of the extension is 0.5 mm to 3 mm. During the die-cutting process of the first conductive element 24, a torque force is generated. The first bent portion 242 can buffer the torque force to reduce the possibility of the first positive current collector 2111 tearing due to the torque force. Since the length of the first insulating layer 25 is limited by the processing accuracy, by limiting the first insulating layer 25 to the side of the first bent portion 242 opposite to the first main body portion 241, and the length of the extension is not less than 0.5 mm, it is possible to satisfy the requirement that the first insulating layer 25 can better cover the metal burrs of the first welding area 24a, while giving the first insulating layer 25 a larger processing accuracy space. By limiting the first insulating layer 25 to extend beyond the first curved portion 242 to the side opposite to the first main body portion 241, and limiting the extension length to no more than 3mm, the possibility of the first insulating layer 25 being too long and easily folded can be reduced, as can the possibility of the first insulating layer 25 losing too much energy density of the secondary battery 100 due to being too long can be reduced.

[0044] In some embodiments, the first conductive element 24 includes a second bent portion 243 along a third direction Z. The second bent portion 243 is connected to the side of the first main body portion 241 opposite to the first bent portion 242. The first insulating layer 25 extends beyond the side of the second bent portion 243 opposite to the first main body portion 241 by a length of 0.5 mm to 3 mm. The second bent portion 243 can buffer the torque force during the die-cutting process, thereby further reducing the possibility of the first positive current collector 2111 tearing due to torque force. By limiting the first insulating layer 25 to extend beyond the side of the second bent portion 243 opposite to the first main body portion 241 by a length of not less than 0.5 mm, the first insulating layer 25 can effectively shield the metal burrs of the first welding area 24a while providing a larger processing precision space. By limiting the first insulating layer 25 to extend beyond the second curved portion 243 to the side opposite to the first main body portion 241, and limiting the extension length to no more than 3mm, the possibility that the first insulating layer 25 is too long and easily folded can be reduced, as well as the possibility that the first insulating layer 25 is too long and loses too much energy density of the secondary battery 100.

[0045] In some embodiments, along the second direction Y, the width of the first insulating layer 25 is W1, 1.4mm≤W1≤4mm, so that the first insulating layer 25 can effectively shield the metal burrs of the first welding area 24a while not being too wide, thus avoiding excessive loss of energy density of the secondary battery 100.

[0046] In some embodiments, the thickness of the first insulating layer 25 along the first direction X is H1, where 10μm≤H1≤20μm. This ensures that the first insulating layer 25 provides good puncture resistance without being too thick, thus avoiding excessive loss of energy density in the secondary battery 100.

[0047] In some embodiments, please refer to Figure 2 and Figure 5 The first insulating layer 25 includes a first adhesive layer 251 and a first substrate layer 252. Along the first direction X, the first substrate layer 252 is disposed on one surface of the first adhesive layer 251, and the other surface of the first adhesive layer 251 facing away from the first substrate layer 252 is disposed on the first separator 231. The thickness of the first adhesive layer 251 is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer 252 is H3, 8μm≤H3≤13μm. The first adhesive layer 251 can improve the adhesion between the first insulating layer 25 and the first separator 231, and the first substrate layer 252 can improve the puncture resistance of the first insulating layer 25. By limiting the thickness to 2μm≤H2≤7μm, the first adhesive layer 251 achieves good adhesion while not being too thick, thus avoiding excessive reduction in the energy density of the secondary battery 100. By limiting the thickness to 8μm≤H3≤13μm, the first substrate layer 252 can have a good insulating effect while not being too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0048] In some embodiments, the first adhesive layer 251 comprises at least one of propylene oxide, polymethyl methacrylate, and styrene-butadiene rubber to provide better adhesion. And / or, the first substrate layer 252 comprises at least one of polyimide, polyethylene terephthalate, polypropylene, and polyethylene to provide better puncture resistance.

[0049] In some embodiments, along the second direction Y, please refer to Figure 2 and Figure 4 The width of the first welding area 24a is W2, 0.8mm ≤ W2 ≤ 3mm. By limiting W2 to 0.8mm ≤ W2, the first welding area 24a has good welding strength, thereby allowing the first conductive element 24 to be firmly attached to the first positive current collector 2111. Since the first insulating layer 25 needs to cover the first welding area 24a, if the width of the first welding area 24a increases, the width of the first insulating layer 25 also needs to increase accordingly. Therefore, by limiting W2 to ≤ 3mm, the width of the first welding area 24a is not too wide, and thus the width of the first insulating layer 25 is not too wide, thus avoiding an excessive reduction in the energy density of the secondary battery 100.

[0050] In some embodiments, 6.5mm≤L2≤15.5mm is used to ensure that the first conductive element 24 and the first positive current collector 2111 have good connection strength while the first conductive element 24 is not too long and thus does not excessively reduce the energy density of the secondary battery 100.

[0051] In some embodiments, the first separator 231 includes a fifth portion 231a and a sixth portion 231b connected sequentially along the second direction Y. Along the first direction X, the projection of the fifth portion 231a onto the surface of the negative electrode 22 overlaps with the first negative electrode active layer 222. Along the second direction Y, the sixth portion 231b extends beyond the first negative electrode active layer 222, and the width of the sixth portion 231b is W4, 0.5mm ≤ W4 ≤ 2mm. By limiting W4 to 0.5mm ≤ W4, the sixth portion 231b of the first separator 231 can shield the first negative electrode active layer 222, reducing the possibility of a short circuit due to contact between the first negative electrode active layer 222 and the first conductive element 24. By limiting W4 to ≤ 2mm, the sixth portion 231b of the first separator 231 is not too wide, thus not excessively reducing the energy density of the secondary battery 100.

[0052] In some embodiments, the first positive electrode active layer 2112 includes a seventh portion 211c and an eighth portion 211d, the eighth portion 211d being connected along the second direction Y to the side of the seventh portion 211c near the first conductive element 24. Along the first direction X, the maximum thickness of the eighth portion 211d is less than the minimum thickness of the seventh portion 211c, and the projection of the first insulating layer 25 onto the surface of the single-sided positive electrode sheet 211 at least partially overlaps with the eighth portion 211d. During cold pressing, the first positive electrode active layer 2112 generates torque force. By limiting the maximum thickness of the eighth portion 211d of the first positive electrode active layer 2112 to be less than the minimum thickness of the seventh portion 211c, the thinner eighth portion 211d can buffer the torque force, thereby reducing the possibility of the first positive electrode current collector 2111 tearing due to the torque force. Because the eighth portion 211d is relatively thin, by limiting the projection of the first insulating layer 25 onto the surface of the single-sided positive electrode 211 to at least partially overlap with the eighth portion 211d, the thickness of the electrode assembly 20 along the first direction X is not excessively increased, while further increasing the likelihood that the first insulating layer 25 will block the first welding area 24a. In some embodiments, the thickness of the eighth portion 211d gradually decreases along the direction from the seventh portion 211c to the eighth portion 211d, so that the eighth portion 211d can better buffer torque forces.

[0053] In some embodiments, please refer to Figure 6 , Figure 7 and Figure 8The positive electrode 21 includes a single-sided positive electrode 212. A single-sided positive electrode 212 is disposed between two adjacent negative electrode 22 along the first direction X. The single-sided positive electrode 212 includes a second positive current collector 2121 and a second positive active layer 2122. The second positive current collector 2121 includes a ninth portion 212a and a tenth portion 212b connected sequentially along the second direction Y. The ninth portion 212a has the second positive active layer 2122 disposed on both opposite surfaces along the first direction X. The tenth portion 212b does not have the second positive active layer 2122 disposed on either opposite surface along the first direction X. The second positive current collector 2121 includes a second metal layer 2123 and a second polymer layer 2124. The second polymer layer 2124 has the second metal layer 2123 disposed on both opposite surfaces along the first direction X. A second conductive element 26 is welded to both opposite surfaces of the tenth portion 212b along the first direction X, forming a second welding area 26a. The separator 23 includes a second separator 232, which is disposed between the single-sided positive electrode 212 and the negative electrode 22. A second insulating layer 27 is disposed on the surface of the second separator 232 facing the single-sided positive electrode 212. The projection of the second insulating layer 27 along the first direction X onto the surface of the single-sided positive electrode 212 covers the second welding area 26a. A single-sided positive electrode 212 is disposed between two adjacent negative electrode 22 along the first direction X. A second positive active layer 2122 is disposed on both opposite surfaces of the second positive current collector 2121 of the single-sided positive electrode 212, which can reduce the number of layers of the second positive current collector 2121, thereby improving the energy density of the secondary battery 100. By setting the second positive current collector 2121 as a structure of two layers of second metal layer 2123 sandwiching a second polymer layer 2124, the second metal layer 2123 can be made thinner, thereby improving the energy density of the secondary battery 100. By welding second conductive elements 26 to both opposite surfaces of the tenth portion 212b of the second positive current collector 2121 along the first direction X, the positive electrode tab can be easily connected to the second positive current collector 2121 via the second conductive elements 26. A second insulating layer 27 is provided on one surface of the second diaphragm 232 facing the single-sided positive electrode 212, and the projection of the second insulating layer 27 along the first direction X onto the surface of the single-sided positive electrode 212 covers the second welding area 26a. This allows the second insulating layer 27 to shield the metal burrs of the second welding area 26a, thereby reducing the possibility of the metal burrs of the second welding area 26a piercing the second diaphragm 232 and forming a short circuit with the negative active material layer of the opposite negative electrode 22. The second conductive element 26 may include at least one of aluminum, copper, nickel, titanium, and silver.

[0054] In some embodiments, the second polymer layer 2124, serving as the main mechanical support layer of the second positive current collector 2121, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The second metal layer 2123 may include at least one of aluminum, copper, nickel, titanium, and silver. The second positive active layer 2122 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The second positive active layer 2122 includes a second positive active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated onto the opposite surfaces of the ninth portion 212a of the second positive current collector 2121 along the first direction X, thereby obtaining the second positive active layer 2122. The second positive active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0055] In some embodiments, along the third direction Z, the length of the second insulating layer 27 is L3, and the width of the second conductive element 26 is L4, where 1mm ≤ L3 - L4 ≤ 6mm. By limiting 1mm ≤ L3 - L4, the second insulating layer 27 can effectively shield the metal burrs of the second welding area 26a. Since an excessively long second insulating layer 27 is prone to folding, thus affecting its effectiveness in shielding the second welding area 26a, limiting L3 - L4 ≤ 6mm ensures that the length of the second insulating layer 27 is not excessive, thereby reducing the possibility of folding and further increasing the likelihood that the second insulating layer 27 can effectively shield the metal burrs of the second welding area 26a.

[0056] In some embodiments, along the third direction Z, the second conductive element 26 includes a third curved portion 262 and a second main body portion 261 connected in sequence. The second insulating layer 27 extends beyond the third curved portion 262 to the side opposite to the second main body portion 261, and the extended length is 0.5 mm to 3 mm. During the die-cutting process of the second conductive element 26, a torque force is generated. The third curved portion 262 can buffer the torque force to reduce the possibility of the second positive current collector 2121 tearing due to the torque force. Since the length of the second insulating layer 27 is limited by the processing accuracy, by limiting the second insulating layer 27 to the side opposite to the second main body portion 261 beyond the third curved portion 262, and the extended length is not less than 0.5 mm, it is possible to satisfy the requirement that the second insulating layer 27 can better cover the metal burrs of the second welding area 26a, while giving the second insulating layer 27 a larger processing accuracy space. By limiting the second insulating layer 27 to extend beyond the third curved portion 262 to the side opposite to the second main body portion 261, and limiting the extension length to no more than 3mm, the possibility of the second insulating layer 27 being too long and easily folded can be reduced, as can the possibility of the second insulating layer 27 losing too much energy density of the secondary battery 100 due to being too long can be reduced.

[0057] In some embodiments, the second conductive element 26 includes a fourth bend 263 along a third direction Z. The fourth bend 263 is connected to the side of the second main body 261 opposite to the third bend 262. The second insulating layer 27 extends beyond the side of the fourth bend 263 opposite to the second main body 261 by a length of 0.5 mm to 3 mm. The fourth bend 263 can buffer the torque force during the die-cutting process, thereby further reducing the possibility of the second positive current collector 2121 tearing due to torque force. By limiting the second insulating layer 27 to extend beyond the side of the fourth bend 263 opposite to the second main body 261 by a length of not less than 0.5 mm, the second insulating layer 27 can effectively shield the metal burrs of the second welding area 26a while providing greater processing precision space. By limiting the second insulating layer 27 to extend beyond the fourth curved portion 263 to the side opposite to the second main body portion 261, and limiting the extension length to no more than 3mm, the possibility of the second insulating layer 27 being too long and easily folded can be reduced, as can the possibility of the second insulating layer 27 losing too much energy density of the secondary battery 100 due to being too long.

[0058] In some embodiments, along the second direction Y, the width of the second insulating layer 27 is W5, 1.4mm ≤ W5 ≤ 4mm, so that the second insulating layer 27 can effectively shield the metal burrs of the second welding area 26a without being too wide, thus avoiding excessive loss of the energy density of the secondary battery 100. Along the first direction X, the thickness of the second insulating layer 27 is H4, 10μm ≤ H4 ≤ 20μm, so that the second insulating layer 27 can provide good puncture resistance without being too thick, thus avoiding excessive loss of the energy density of the secondary battery 100.

[0059] In some embodiments, please refer to Figure 6 and Figure 9The second insulating layer 27 includes a second adhesive layer 271 and a second substrate layer 272. Along the first direction X, the second substrate layer 272 is disposed on one surface of the second adhesive layer 271, and the other surface of the second adhesive layer 271 facing away from the second substrate layer 272 is disposed on the second separator 232. The thickness of the second adhesive layer 271 is H5, 2μm≤H5≤7μm, and the thickness of the second substrate layer 272 is H6, 8μm≤H6≤13μm. The second adhesive layer 271 can improve the adhesion between the second insulating layer 27 and the second separator 232, and the second substrate layer 272 can improve the puncture resistance of the second insulating layer 27. By limiting the thickness to 2μm≤H5≤7μm, the second adhesive layer 271 achieves good adhesion while not being too thick, thus avoiding excessive reduction in the energy density of the secondary battery 100. By limiting the thickness to 8μm≤H6≤13μm, the second substrate layer 272 can have a good insulating effect while not being too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0060] In some embodiments, the second adhesive layer 271 comprises at least one of propylene oxide, polymethyl methacrylate, and styrene-butadiene rubber to provide better adhesion. And / or, the second substrate layer 272 comprises at least one of polyimide, polyethylene terephthalate, polypropylene, and polyethylene to provide better puncture resistance.

[0061] In some embodiments, please refer to Figure 6 and Figure 8 Along the second direction Y, the width of the second welding area 26a is W6, where 0.8mm ≤ W6 ≤ 3mm. By limiting W6 to 0.8mm ≤ W6, the second welding area 26a has good welding strength, thereby allowing the second conductive element 26 to be firmly attached to the second positive current collector 2121. Since the second insulating layer 27 needs to cover the second welding area 26a, if the width of the second welding area 26a increases, the width of the second insulating layer 27 also needs to increase accordingly. Therefore, by limiting W6 to ≤ 3mm, the width of the second welding area 26a is not too wide, thus preventing the width of the second insulating layer 27 from becoming too wide and excessively reducing the energy density of the secondary battery 100.

[0062] In some embodiments, 6.5mm≤L4≤15.5mm is used to ensure that the second conductive element 26 and the second positive current collector 2121 have good connection strength while the second conductive element 26 is not too long and thus does not excessively reduce the energy density of the secondary battery 100.

[0063] In some embodiments, the electrode assembly 20 satisfies at least one of the following conditions: (1) the first metal layer 2113 comprises aluminum; (2) the first polymer layer 2114 comprises polyolefin; (3) the first conductive element 24 comprises aluminum; and (4) the first insulating layer 25 comprises polyolefin.

[0064] A second aspect of this application also provides an electronic device including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and 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, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0065] A third aspect of this application also provides a method for manufacturing a secondary battery 100, used to prepare a secondary battery 100 as described in any embodiment of the first aspect above, comprising: providing a negative electrode 22, a separator 23, and a single-sided positive electrode 212; sequentially stacking the separator 23, the negative electrode 22, the separator 23, and the single-sided positive electrode 212 along a first direction X to form a first assembly, wherein the outermost electrode of the first assembly along the first direction X is the negative electrode 22, and a first separator 231 is stacked on the outermost layer of the first assembly along the first direction X; providing a first insulating layer 25; disposing the first insulating layer 25 on a surface of the first separator 231 of the first assembly facing away from the negative electrode 22 to form a second assembly; providing a single-sided positive electrode 211 and a first conductive element 24; welding the first conductive element 24 to the two opposing surfaces of the second portion 211b of the first positive current collector 2111 of the single-sided positive electrode 211, and forming a first welding area 24a. A single-sided positive electrode 211, to which a first conductive element 24 is stacked and welded along the first direction X, is placed on opposite surfaces of the second component. The projection of the first insulating layer 25 along the first direction X onto the surface of the single-sided positive electrode 211 covers the first welding area 24a. Through this manufacturing method, when the separator 23 in the intermediate layer of the electrode assembly 20 does not have an insulating layer, it is unnecessary to first bond the insulating layer to the separator 23, then roll it up, and finally stack the electrode. This reduces the possibility that the separator 23 will be difficult to roll up after bonding the insulating layer, and also reduces the possibility that the separator 23 will bulge and tear after being rolled up with the insulating layer bonded to it.

[0066] Test section: 1. Energy density improvement test of lithium-ion batteries: Energy density calculation method: Using the adhesive application method, the roll welding and adhesive paper are overlapped on the cell thickness to protect the junction of the positive and negative electrodes. The coating of the insulating ceramic layer on the edge of the positive electrode can be eliminated. Compared with the ceramic layer coating + roll welding process, the energy density is improved by reducing the head space. Calculation logic: Energy density improvement = (ceramic layer width + roll welding width - overlap width of adhesive and roll welding) / cell length * 100%.

[0067] 2. Drop test: In a test environment of 20±5℃, a metal drop floor was used to drop the metal floor from a height of 1.8m, dropping it once from the head and tail sides and once from the four corners, for a total of 7 rounds of testing. The drop order was (head -> tail -> head right corner -> tail right corner -> head left corner -> tail left corner (angle: 45±15 degrees, 6 times per round)). The judgment criteria were: no fire, no explosion, no smoke, and no leakage.

[0068] 3. Adhesive tape folding test: The folding of the adhesive tape can be directly visually identified by the stacking equipment, and the corresponding data can be directly obtained on the production site. The calculation logic is: adhesive tape folding ratio = adhesive tape folded electrode / total number of electrodes * 100%.

[0069] Example 1 <Preparation of the positive electrode>: Lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly.

[0070] Polyethylene terephthalate (PET) was selected as the polymer layer. Two aluminum metal layers were deposited on the two surfaces of the polymer layer to obtain the positive electrode current collector. The above slurry was coated on the surface of one metal layer of the positive electrode current collector, leaving a blank section for the positive electrode foil. The slurry was dried to obtain a single-sided positive electrode sheet with a positive active material layer coated on one side. The above steps were repeated on the other metal layer to obtain a double-sided positive electrode sheet with a positive active material layer coated on both sides.

[0071] <Preparation of negative electrode sheet>: Using graphite as the negative electrode active material, graphite, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are mixed in a weight ratio of 96:2:2. Deionized water is added as a solvent to prepare a slurry with a solid content of 70wt%, and the mixture is stirred evenly.

[0072] Polyethylene terephthalate (PET) was selected as the polymer layer. Two copper metal layers were deposited on the two surfaces of the polymer layer. The aforementioned slurry was then coated on one of the metal layers, leaving a blank section for the negative electrode foil. The slurry was dried to obtain a single-sided composite negative electrode sheet with a negative electrode active material layer coated on one side. The above steps were repeated on the other metal layer to obtain a double-sided composite negative electrode sheet with a negative electrode active material layer coated on both sides.

[0073] <Preparation of the diaphragm>: A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one side of the substrate layer as a separator (CCS). The mass percentage of alumina ceramic in the ceramic layer is 95%.

[0074] <Electrolyte Preparation>: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent, dissolved, and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0075] <Preparation of Ceramic Layer>: In battery cell production, the ceramic layer is prepared during the coating process. The insulating ceramic layer slurry and the positive electrode active material slurry are fed into the extrusion mechanism together. In the extrusion coating machine, different slurry strips are placed at different positions. The position, size and weight of the slurry to be coated are set by the opening of the extrusion coating (the ceramic layer is usually coated on the edge of the positive electrode active material, and there is a certain interaction area between the two, which needs to be specially defined. In the interaction area, the ceramic layer is on top and away from the current collector, and the active material layer is on the bottom and close to the current collector). A positive electrode sheet with a ceramic layer is obtained, and the thickness of the ceramic layer is 25μm.

[0076] <Preparation of Adhesive Tape>: Preparation process of adhesive tape: First, prepare polypropylene adhesive. Take polypropylene adhesive and heat it to 160~190℃ to completely liquefy it. Then, coat the adhesive onto two layers of release film (one complete release film and one grooved release film; place the complete release film on the bottom layer, apply the adhesive to the grooves of the second release film, and then scrape off the excess adhesive with a scraper to make the surface of the adhesive tape smooth). After cooling and curing, the adhesive tape with release film is obtained. The thickness of the adhesive tape is 15μm.

[0077] <Preparation of Lithium-ion Batteries>: An aluminum conductive element is welded adjacent to the ceramic layer on the empty foil section of the double-sided positive electrode sheet with a ceramic layer. The double-sided positive electrode sheet, separator, and negative electrode sheet are stacked sequentially to form a preliminary electrode assembly. Adhesive tape is applied to the outermost surface of the separator of the preliminary electrode assembly facing away from the negative electrode sheet, corresponding to the positive-negative electrode junction area below the negative electrode tab. An aluminum conductive element is welded to the empty foil section of the single-sided positive electrode sheet. The single-sided positive electrode sheet is then stacked on the outermost layer of the preliminary electrode assembly, and the adhesive tape of the separator covers the solder marks on the conductive element of the single-sided positive electrode sheet, forming the final electrode assembly. The final electrode assembly is then hot-pressed. The final electrode assembly is placed in an aluminum-plastic film packaging bag, electrolyte is injected, and it is sealed to obtain a lithium-ion battery.

[0078] The relevant parameters in Comparative Examples 1 to 8 and Examples 2 to 17 are shown in Table 1 below.

[0079] Among them, Comparative Examples 1 to 3 only have ceramic layers in the empty foil sections of all positive current collectors, and no adhesive paper is placed on the diaphragm.

[0080] Comparative Examples 4 to 6 only provided adhesive tape on all positive conductive parts, without providing a ceramic layer on the empty foil section of the positive current collector, and without providing adhesive tape on the diaphragm.

[0081] Comparative Examples 7 to 8 and Examples 7 to 17 only have adhesive tape on the separator corresponding to all positive electrode conductive elements, and no ceramic layer is provided on the empty foil section of the positive electrode current collector. Among them, Comparative Examples 7 to 8 and Examples 7 to 9 differ only in the length of the portion of the separator with adhesive tape extending beyond the width of the conductive element. Examples 10 to 13 differ only in the width of the separator with adhesive tape. Examples 14 to 17 differ only in the thickness of the separator with adhesive tape.

[0082] In Examples 1 to 3, adhesive paper is provided on the diaphragm corresponding to the single-sided positive electrode conductive element, and a ceramic layer is provided on the empty foil section of the double-sided positive electrode current collector, with only the width of the ceramic layer being different.

[0083] Examples 4 to 6 all have adhesive paper on the diaphragm corresponding to the single-sided positive electrode conductive element, and all have adhesive paper on the double-sided positive electrode conductive element, with the only difference being the length of the portion of the diaphragm with adhesive paper extending beyond the width of the positive electrode conductive element.

[0084] The steps of setting adhesive tape on the positive electrode conductive component in Comparative Examples 4 to 6 and Examples 4 to 6 above are as follows: the adhesive tape is pasted on the surface of the conductive component of the positive electrode sheet and covers the welding area of ​​the conductive component.

[0085] It should be explained that the phrase "the length of the adhesive tape extending beyond the width of the positive conductive element on one side" refers to the adhesive tape extending beyond the width of the positive conductive element on either side of its width direction. Similarly, the phrase "the length of the adhesive tape extending beyond the width of the positive conductive element on one side" also refers to the adhesive tape extending beyond the width of the positive conductive element on either side of its width direction.

[0086] Table 1

[0087]

[0088] Note: In Table 1, " / " indicates that the parameter is not included.

[0089] According to Table 1 above, and in conjunction with Comparative Examples 1 to 6 and Examples 7 to 9, by setting a ceramic layer in the current collector so that the welding area between the conductive element and the current collector protrudes beyond the opposite polarity of the active material layer in the length and / or width direction of the current collector, the battery cell can achieve a good drop test pass rate, which means it can effectively reduce the risk of short circuits. However, this method excessively reduces the energy density of the battery cell. Using adhesive tape covering the welding area on the conductive element can effectively reduce the risk of short circuits without excessively reducing the energy density of the battery cell. However, this method has problems such as reduced electrode manufacturing yield, detachment of active material particles near the conductive element, and reduced production efficiency. Using adhesive tape on the separator corresponding to the conductive element can effectively reduce the risk of short circuits without excessively reducing the energy density of the battery cell. In practical applications, using adhesive tape on the separator, compared to using adhesive tape on the conductive element, can better improve the problems of low electrode manufacturing yield, active material particle detachment, and low production efficiency.

[0090] Based on Comparative Examples 7 and 8 and Examples 7 and 9, it can be seen that when the length of the adhesive tape on one side of the conductive component corresponding to the diaphragm extends beyond the width of the conductive component by more than 3 mm, that is, the sum of the lengths of the adhesive tape extending beyond the width of the conductive component on both sides is greater than 6 mm, the folding ratio of the adhesive tape is relatively large, thus affecting the adhesive tape's ability to cover the soldering area of ​​the conductive component. In practical applications, when the length of the adhesive tape on one side of the conductive component corresponding to the diaphragm extends beyond the width of the conductive component by less than 0.5 mm, that is, the sum of the lengths of the adhesive tape extending beyond the width of the conductive component on both sides is less than 1 mm, the adhesive tape cannot effectively cover the soldering area of ​​the conductive component. Therefore, it is necessary to limit the sum of the lengths of the adhesive tape extending beyond the width of the conductive component on both sides to between 1 mm and 6 mm.

[0091] As can be seen from Examples 10 to 13, when the width of the adhesive tape corresponding to the conductive component and the diaphragm is greater than 4 mm, the energy density of the battery cell will be excessively lost. In practical applications, when the width of the adhesive tape corresponding to the conductive component and the diaphragm is less than 1.4 mm, the adhesive tape cannot effectively cover the welding area of ​​the conductive component. Therefore, the width of the adhesive tape corresponding to the conductive component and the diaphragm needs to be limited to 1.4 mm to 4 mm.

[0092] As can be seen from Examples 14 to 17, when the thickness of the adhesive paper for the diaphragm corresponding to the conductive component is less than 10 μm, the pass rate of the cell drop test is low. In practical applications, when the thickness of the adhesive paper for the diaphragm corresponding to the conductive component is greater than 20 μm, the energy density of the cell will be excessively lost. Therefore, the thickness of the adhesive paper for the diaphragm corresponding to the conductive component needs to be limited to 10 μm to 20 μm.

[0093] Based on Comparative Examples 1 to 3 and Examples 1 to 3, it can be seen that compared with setting ceramic layers on all positive current collectors, only removing the ceramic layer from the positive current collector of the outermost single-sided positive electrode sheet and replacing it with adhesive paper corresponding to the separator of the positive conductive component can enable the battery cell to achieve a good drop test pass rate. At the same time, in practical applications, removing the ceramic layer from the positive current collector of the outermost single-sided positive electrode sheet can slightly increase the energy density of the battery cell.

[0094] As can be seen from Comparative Examples 4 to 6 and Examples 4 to 6, compared with the use of adhesive tape on all positive electrode conductive components, simply removing the adhesive tape from the conductive components of the outermost single-sided positive electrode sheet and replacing it with adhesive tape on the separator corresponding to the positive electrode conductive component can still result in a good drop test pass rate and good energy density for the battery cell.

[0095] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a negative electrode, a positive electrode and a separator, wherein the negative electrode and the positive electrode are alternately stacked along a first direction, and the separator is disposed between adjacent negative electrode and positive electrode; The positive electrode includes a single-sided positive electrode. The outermost electrode of the electrode assembly along the first direction is the single-sided positive electrode. The single-sided positive electrode includes a first positive current collector and a first positive active layer. The first positive current collector along the second direction includes a first part and a second part connected in sequence. The first part has the first positive active layer disposed on one surface facing the negative electrode. The second part does not have the first positive active layer disposed on either of its opposite surfaces along the first direction. The first positive current collector includes a first metal layer and a first polymer layer. The first polymer layer has the first metal layer disposed on both opposite surfaces along the first direction. Its features are, The second part has a first conductive element welded to both opposite surfaces along the first direction, forming a first welding area; the first conductive element protrudes from the second part along the second direction; the diaphragm includes a first diaphragm, the first diaphragm is disposed between the single-sided positive electrode and the adjacent negative electrode, the surface of the first diaphragm facing the single-sided positive electrode is provided with a first insulating layer, the first insulating layer covers the first welding area on the projection of the single-sided positive electrode along the first direction, the first direction being perpendicular to the second direction; The electrode assembly satisfies at least one of the following conditions: (1) The first metal layer comprises aluminum; (2) The first polymer layer comprises a polyolefin; (3) The first conductive component comprises aluminum; (4) The first insulating layer comprises polyolefin.

2. The secondary battery according to claim 1, characterized in that, Along a third direction, the first insulating layer extends beyond one side of the first conductive element by a length of 0.5 mm to 3 mm, and the first direction, the second direction, and the third direction are perpendicular to each other.

3. The secondary battery according to claim 2, characterized in that, Along the third direction, the first conductive element includes a first bent portion and a first main body portion connected in sequence, and the first insulating layer extends beyond the first bent portion to the side opposite to the first main body portion, with an extension length of 0.5 mm to 3 mm.

4. The secondary battery according to claim 3, characterized in that, The first conductive element includes a second curved portion along the third direction. The second curved portion is connected to the side of the first main body portion away from the first curved portion. The first insulating layer extends beyond the side of the second curved portion away from the first main body portion by a length of 0.5 mm to 3 mm.

5. The secondary battery according to claim 1, characterized in that, Along the second direction, the width of the first insulating layer is W1, 1.4mm≤W1≤4mm.

6. The secondary battery according to claim 1, characterized in that, Along the first direction, the thickness of the first insulating layer is H1, where 10μm≤H1≤20μm.

7. The secondary battery according to claim 1, characterized in that, The first insulating layer includes a first adhesive layer and a first substrate layer. Along the first direction, the first substrate layer is disposed on one surface of the first adhesive layer, and the other surface of the first adhesive layer opposite to the first substrate layer is disposed on the first diaphragm. The thickness of the first adhesive layer is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer is H3, 8μm≤H3≤13μm.

8. The secondary battery according to claim 1, characterized in that, Along the second direction, the width of the first welding area is W2, 0.8mm≤W2≤3mm.

9. The secondary battery according to claim 1, characterized in that, The length of the first conductive element along the third direction is L2, 6.5mm≤L2≤15.5mm, and the first direction, the second direction and the third direction are perpendicular to each other.

10. The secondary battery according to claim 1, characterized in that, The negative electrode sheet includes a first negative electrode current collector and a first negative electrode active layer. The first negative electrode active layer is disposed on at least one surface of the first negative electrode current collector along the first direction. The first negative electrode active layer includes a third part and a fourth part connected in sequence along the second direction. The projection of the third part on the surface of the single-sided positive electrode sheet overlaps with the first part, and the projection of the fourth part on the surface of the single-sided positive electrode sheet overlaps with at least part of the second part. Along the second direction, the width of the fourth portion is W3, where 0.5mm ≤ W3 ≤ 2mm.

11. The secondary battery according to claim 10, characterized in that, The first separator includes a fifth part and a sixth part connected in sequence along the second direction; along the first direction, the projection of the fifth part on the surface of the negative electrode overlaps with the first negative electrode active layer; along the second direction, the sixth part extends beyond the first negative electrode active layer, and the width of the sixth part is W4, 0.5mm≤W4≤2mm.

12. The secondary battery according to claim 1, characterized in that, The first positive electrode active layer includes a seventh part and an eighth part, the eighth part being connected along the second direction to the side of the seventh part close to the first conductive element; along the first direction, the thickness of the eighth part is less than the thickness of the seventh part, and the projection of the first insulating layer on the surface of the single-sided positive electrode sheet overlaps at least partially with the eighth part.

13. The secondary battery according to any one of claims 1-12, characterized in that, The positive electrode includes a double-sided positive electrode, and the double-sided positive electrode is disposed between two adjacent negative electrodes along the first direction. The double-sided positive electrode includes a second positive current collector and a second positive active layer. The second positive current collector includes a ninth part and a tenth part connected in sequence along the second direction. The second positive active layer is disposed on both opposite surfaces of the ninth part along the first direction, and the second positive active layer is not disposed on either opposite surface of the tenth part along the first direction. The second positive current collector includes a second metal layer and a second polymer layer. The second metal layer is disposed on both opposite surfaces of the second polymer layer along the first direction. The tenth part has a second conductive element welded to both opposite surfaces along the first direction, forming a second welding area; the diaphragm includes a second diaphragm, the second diaphragm is disposed between the double-sided positive electrode and the negative electrode, a second insulating layer is disposed on one surface of the second diaphragm facing the double-sided positive electrode, and the projection of the second insulating layer along the first direction on the surface of the double-sided positive electrode covers the second welding area.

14. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1-13.

15. A method for manufacturing a secondary battery, used to prepare a battery as described in claim 1. The secondary battery according to any one of the 13 is characterized in that, include: The negative electrode, the separator, and the double-sided positive electrode are provided. The separator, the negative electrode, the separator, and the double-sided positive electrode are stacked sequentially along the first direction to form a first assembly. The outermost electrode of the first assembly along the first direction is the negative electrode, and the outermost layer of the first assembly along the first direction is stacked with a first separator. The first insulating layer is provided and disposed on a surface of the first diaphragm of the first component opposite to the negative electrode to form a second component; The single-sided positive electrode sheet and the first conductive element are provided, and the first conductive element is welded to the two opposing surfaces of the second portion of the first positive current collector of the single-sided positive electrode sheet to form the first welding area. The single-sided positive electrode sheet on which the first conductive element is stacked and welded to the two opposite surfaces of the second component along the first direction, wherein the projection of the first insulating layer along the first direction on the surface of the single-sided positive electrode sheet covers the first welding area.

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