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

Abstract

The application relates to a secondary battery, an electronic device and a manufacturing method of the secondary battery, which comprises an electrode assembly, the electrode assembly comprising a negative electrode sheet, a positive electrode sheet and a separator. The positive electrode sheet comprises a single-sided positive electrode sheet arranged at the outermost layer of the electrode assembly along a first direction, and the single-sided positive electrode sheet comprises a first positive electrode current collector and a first positive electrode active layer. The first positive electrode current collector comprises a first polymer layer and a first metal layer. The opposite surfaces of a second part of the first positive electrode current collector are welded with first conductive pieces, and a first welding area is formed. The separator comprises a first separator arranged between the single-sided positive electrode sheet and the negative electrode sheet, and the surface of the first separator facing the single-sided positive electrode sheet is provided with a first insulating layer. The projection of the first insulating layer on the single-sided positive electrode sheet covers the first welding area. In the third direction, the first insulating layer exceeds one side of the first conductive piece, and the exceeding length is 0.5 mm to 3 mm. The secondary battery and the electronic device can improve the short circuit problem between the positive electrode current collector and the negative electrode active material layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery, an electronic device and a manufacturing method of the secondary battery. BACKGROUND

[0002] As a power supply of an electronic device, a secondary battery is a key to ensure normal use of the electronic device. A current collector is an important component in the secondary battery, which not only provides support for an active material layer, but also collects electric current generated by the active material layer for external output. Therefore, the current collector has an important influence on the performance of the electrode tab and the electrochemical device. However, the current collector is easy to contact the active material of the opposite polarity and cause short circuit. SUMMARY

[0003] The present application inventors have found that, in order to improve the energy density, the existing secondary battery usually adopts a composite current collector (a composite structure of metal-polymer-metal), and the composite current collector uses a polymer as a mechanical performance process framework, so that the metal layer can be made thin. The current collector needs to be connected to a tab to transmit electric current to the outside, but the conventional ultrasonic welding cannot directly connect the tab and the composite current collector together (easy to be false welding or overwelding), and at present, the composite current collector is mainly placed in the middle of two metal foils for welding by roll welding, and then the metal foil is welded with the tab, so as to realize the connection between the composite current collector and the tab, which can improve the reliability of welding and reduce the welding resistance. The composite current collector needs to leave an empty foil section without setting the active material layer for the metal foil welding. However, since the negative active material layer of the negative tab usually needs to be more than the positive active material layer of the positive tab, the empty foil area of the positive composite current collector of the positive tab corresponds to the negative active material layer, and when the empty foil area of the positive composite current collector is welded with two metal foils, the metal burrs of the welding area are easy to pierce the separator and the opposite negative active material layer to form short circuit, thereby reducing the safety performance of the secondary battery.

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

[0005] According to a first aspect of the present application, a secondary battery is provided, comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet, a positive electrode sheet, and a separator, the negative electrode sheet and the positive electrode sheet being alternately stacked along a first direction, and the separator being arranged between adjacent negative electrode sheet and positive electrode sheet. The positive electrode sheet comprises a single-sided positive electrode sheet, the outermost positive electrode sheet of the electrode assembly along the first direction is the single-sided positive electrode sheet, and the single-sided positive electrode sheet comprises a first positive electrode current collector and a first positive electrode active layer. The first positive electrode current collector comprises a first portion and a second portion connected in sequence along a second direction, the first portion is provided with the first positive electrode active layer on a surface facing the negative electrode sheet, and the second portion is not provided with the first positive electrode active layer on opposite surfaces along the first direction. The first positive electrode current collector comprises a first metal layer and a first polymer layer, and the first polymer layer is provided with the first metal layer on opposite surfaces along the first direction. The second portion is welded with a first conductive member on opposite surfaces along the first direction, and a first welding area is formed. The first conductive member protrudes from the second portion along the second direction. The separator comprises a first separator, and the first separator is arranged between the single-sided positive electrode sheet and the adjacent negative electrode sheet, and the first separator is provided with a first insulating layer on a surface facing the single-sided positive electrode sheet. The projection of the first insulating layer on the surface of the single-sided positive electrode sheet along the first direction covers the first welding area. Along a third direction, the length of the first insulating layer is L1, the width of the first conductive member is L2, 1mm≤L1-L2≤6mm, the first insulating layer exceeds one side of the first conductive member, and the exceeding length is 0.5mm to 3mm. The first direction, the second direction and the third direction are perpendicular to each other.

[0006] In the technical solution, the outermost electrode tab of the electrode assembly along the first direction is set as a single-face positive electrode tab, which can reduce the possibility of damage to the shell of the outer package. If the outermost electrode tab of the electrode assembly is a single-face negative electrode tab, the metal copper of the current collector of the single-face negative electrode tab is prone to electrochemical reaction with the metal aluminum of the shell, thereby causing damage to the shell. The first positive electrode active layer is arranged on the surface of the first positive electrode current collector of the single-face positive electrode tab, which can improve the utilization rate of the positive electrode active material of the single-face positive electrode tab, thereby improving the energy density. The first positive electrode current collector is set as a structure of two first metal layers sandwiching a first polymer layer, which can make the first metal layer thinner, thereby improving the energy density of the secondary battery. The first conductive member is welded on the opposite surfaces of the second part of the first positive electrode current collector along the first direction, which facilitates the connection of the positive electrode tab to the first positive electrode current collector through the first conductive member. The first insulating layer is arranged on the surface of the first separator facing the single-face positive electrode tab, and the projection of the first insulating layer on the surface of the single-face positive electrode tab along the first direction covers the first welding area, so that the first insulating layer can shield the metal burrs of the first welding area, thereby reducing the possibility of the metal burrs of the first welding area piercing the first separator and the negative electrode active material layer of the opposite negative electrode tab to form a short circuit. In addition, since the first insulating layer is only arranged on the first separator of the outermost electrode assembly, the electrode assembly can be stacked with the tabs of the intermediate layer first during the preparation process, and then the first insulating layer is arranged on the first separator of the outermost layer, and then the single-face positive electrode tab is stacked, without the need to first bond the insulating layer to the separator and then wind and stack the tabs, thereby reducing the difficulty of winding the separator after bonding the insulating layer, and reducing the possibility of tearing the separator after winding the separator with the bonded insulating layer. By limiting 1mm≤L1-L2, the first insulating layer can better shield the metal burrs of the first welding area. Since the first insulating layer is prone to folding if it is too long, which affects its shielding effect on the first welding area, by limiting L1-L2≤6mm, the length of the first insulating layer is not too long, thereby reducing the possibility of folding of the first insulating layer, and further improving the possibility of the first insulating layer shielding the metal burrs of the first welding area. The first insulating layer exceeds one side of the first conductive member along the third direction, and the exceeding length is 0.5mm to 3mm, which means that when the first insulating layer exceeds one side of the first conductive member, the length of the single-side exceeding is 0.5mm to 3mm. By limiting the first insulating layer to exceed one side of the first conductive member along the third direction, and the exceeding length is 0.5mm to 3mm, the first insulating layer can better shield the metal burrs of the first welding area, and the length of the first insulating layer is not too long, thereby reducing the possibility of folding.

[0007] In some preferred embodiments, the first insulating layer extends beyond both sides of the first conductive member along the third direction, and the length of the first insulating layer extending beyond either side of the first conductive member is 0.5 mm to 3 mm, so that the first insulating layer can better shield the metal burrs of the first welding area, and the length of the first insulating layer is not too long, so that the first insulating layer is not easily folded.

[0008] In some preferred embodiments, the first conductive member includes a first bending portion and a first main body portion connected in sequence along the third direction, and the first insulating layer extends beyond one side of the first bending portion away from the first main body portion, and the length of the first insulating layer extending beyond the one side is 0.5 mm to 3 mm. A torque force is formed in the process of die cutting the first conductive member, and the first bending portion can buffer the torque force to reduce the possibility of tearing the first positive current collector due to the torque force. Since the length of the first insulating layer is limited by the processing precision, by limiting the length of the first insulating layer extending beyond the one side of the first bending portion away from the first main body portion to be not less than 0.5 mm, a larger processing precision space can be given to the first insulating layer while meeting the requirement that the first insulating layer can better shield the metal burrs of the first welding area. By limiting the length of the first insulating layer extending beyond the one side of the first bending portion away from the first main body portion to be not more than 3 mm, the possibility of the first insulating layer being too long and being easily folded can be reduced, and the possibility of the first insulating layer being too long and wasting more energy density of the secondary battery can be reduced.

[0009] In some preferred embodiments, the first conductive member includes a second bending portion, and the second bending portion is connected to one side of the first main body portion away from the first bending portion along the third direction, and the first insulating layer extends beyond one side of the second bending portion away from the first main body portion, and the length of the first insulating layer extending beyond the one side is 0.5 mm to 3 mm. The second bending portion can buffer the torque force in the die cutting process to further reduce the possibility of tearing the first positive current collector due to the torque force. By limiting the length of the first insulating layer extending beyond the one side of the second bending portion away from the first main body portion to be not less than 0.5 mm, a larger processing precision space can be given to the first insulating layer while meeting the requirement that the first insulating layer can better shield the metal burrs of the first welding area. By limiting the length of the first insulating layer extending beyond the one side of the second bending portion away from the first main body portion to be not more than 3 mm, the possibility of the first insulating layer being too long and being easily folded can be reduced, and the possibility of the first insulating layer being too long and wasting more energy density of the secondary battery can be reduced.

[0010] In some preferred embodiments, the width of the first insulating layer along the second direction is W1, and 1.4 mm≤W1≤4 mm, so that the first insulating layer can better shield the metal burrs of the first welding area, and the first insulating layer is not too wide, and does not waste too much energy density of the secondary battery.

[0011] In some preferred embodiments, the thickness of the first insulating layer is H1, 10 pm≤H1≤20 pm in the first direction. This is to make the first insulating layer meet the better puncture-proof performance, while the first insulating layer is not too thick, and the energy density of the secondary battery is not excessively reduced.

[0012] In some preferred embodiments, the first insulating layer comprises a first adhesive layer and a first substrate layer, a surface of the first adhesive layer is provided with the first substrate layer in the first direction, another surface of the first adhesive layer away from the first substrate layer is provided on the first diaphragm, the thickness of the first adhesive layer is H2, 2 pm≤H2≤7 pm, and the thickness of the first substrate layer is H3, 8 pm≤H3≤13 pm. The first adhesive layer can improve the adhesion of the first insulating layer to the first diaphragm, and the first substrate layer can improve the puncture-proof performance of the first insulating layer. By limiting 2 pm≤H2≤7 pm, the first adhesive layer has better adhesion effect, while the first adhesive layer is not too thick, so as not to excessively reduce the energy density of the secondary battery. By limiting 8 pm≤H3≤13 pm, the first substrate layer has better insulation effect, while the first substrate layer is not too thick, so as not to excessively reduce the energy density of the secondary battery.

[0013] In some preferred embodiments, the width of the first welding area is W2, 0.8 mm≤W2≤3 mm in the second direction. By limiting 0.8 mm≤W2, the first welding area has good welding strength, so that the first conductive member can be firmly fixed 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, so by limiting W2≤3 mm, the width of the first welding area is not too wide, and the width of the first insulating layer is not too wide, so as not to excessively reduce the energy density of the secondary battery.

[0014] In some preferred embodiments, 6.5 mm≤L2≤15.5 mm, so that the first conductive member and the first positive current collector have better connection strength, while the first conductive member is not too long, and the energy density of the secondary battery is not excessively reduced.

[0015] In some preferred embodiments, the negative electrode sheet comprises a first negative current collector and a first negative active layer, the first negative current collector is provided with the first negative active layer on at least one surface thereof along a first direction, the first negative active layer comprises a third portion and a fourth portion connected in sequence along a second direction, a projection of the third portion on a surface of the single-sided positive electrode sheet overlaps the first portion, and a projection of the fourth portion on the surface of the single-sided positive electrode sheet overlaps at least part of the second portion. Along the second direction, the fourth portion has a width W3, and 0.5 mm≤W3≤2 mm. By limiting 0.5 mm≤W3, the first negative active layer can better absorb lithium ions released by the first positive active layer, and the possibility of lithium precipitation on the surface of the first negative active layer is reduced. By limiting W3≤2 mm, the negative active material of the first negative active layer has better energy utilization, and the energy density of the secondary battery is not excessively reduced.

[0016] In some preferred embodiments, the first separator comprises a fifth portion and a sixth portion connected in sequence along the second direction. Along the first direction, a projection of the fifth portion on a surface of the negative electrode sheet overlaps the first negative active layer. Along the second direction, the sixth portion is beyond the first negative active layer, and the sixth portion has a width W4, and 0.5 mm≤W4≤2 mm. By limiting 0.5 mm≤W4, the sixth portion of the first separator can shield the first negative active layer, and the possibility of short circuit caused by the contact between the first negative active layer and the first conductive member is reduced. By limiting W4≤2 mm, the sixth portion of the first separator is not too wide, and the energy density of the secondary battery is not excessively reduced.

[0017] In some preferred embodiments, the first positive active layer comprises a seventh portion and an eighth portion, and the eighth portion is connected to the seventh portion on a side close to the first conductive member along the second direction. Along the first direction, the thickness of the eighth portion is less than the thickness of the seventh portion, and a projection of the first insulating layer on the surface of the single-sided positive electrode sheet overlaps at least part of the eighth portion. During cold pressing, the first positive active layer can form a torque force. By limiting the thickness of the eighth portion of the first positive active layer to be less than the thickness of the seventh portion, the thinner eighth portion can buffer the torque force, so as to reduce the possibility of tearing of the first positive current collector due to the torque force. Since the eighth portion is thinner, by limiting the projection of the first insulating layer on the surface of the single-sided positive electrode sheet to overlap at least part of the eighth portion, the thickness of the electrode assembly along the first direction is not excessively increased, and the possibility of the first insulating layer shielding the first welding area is further improved.

[0018] In some preferred embodiments, the positive electrode sheet comprises a double-sided positive electrode sheet, the double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, the double-sided positive electrode sheet comprises a second positive electrode current collector and a second positive electrode active layer, the second positive electrode current collector comprises a ninth portion and a tenth portion connected in sequence along the second direction, the ninth portion is provided with the second positive electrode active layer on opposite surfaces thereof along the first direction, the tenth portion is not provided with the second positive electrode active layer on opposite surfaces thereof along the first direction, the second positive electrode current collector comprises a second metal layer and a second polymer layer, the second metal layer is arranged on opposite surfaces of the second polymer layer along the first direction, the tenth portion is welded with a second conductive member on opposite surfaces thereof along the first direction, and a second welding area is formed. The separator comprises a second separator, the second separator is arranged between the double-sided positive electrode sheet and the negative electrode sheet, one surface of the second separator facing the double-sided positive electrode sheet is provided with a second insulating layer, and a projection of the second insulating layer on the surface of the double-sided positive electrode sheet along the first direction covers the second welding area. The double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, and the second positive electrode active layer is arranged on opposite surfaces of the second positive electrode current collector of the double-sided positive electrode sheet, so that the number of layers of the second positive electrode current collector can be reduced, and the energy density of the secondary battery can be improved. The second positive electrode current collector is arranged in a structure of two second metal layers sandwiching a second polymer layer, so that the second metal layer can be made thinner, and the energy density of the secondary battery can be improved. The second conductive member is welded on opposite surfaces of the tenth portion of the second positive electrode current collector along the first direction, so that the positive electrode tab can be connected to the second positive electrode current collector through the second conductive member. The second insulating layer is arranged on one surface of the second separator facing the double-sided positive electrode sheet, and a projection of the second insulating layer on the surface of the double-sided positive electrode sheet along the first direction covers the second welding area, so that the second insulating layer can shield the metal burrs of the second welding area, and the possibility of the metal burrs of the second welding area piercing the second separator and the negative electrode active material layer of the negative electrode sheet opposite to the second separator to form a short circuit can be reduced.

[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 member comprises aluminum; and (4) the first insulating layer comprises polyolefin.

[0020] In a second aspect, the present application further provides an electronic device comprising the secondary battery according to any one of the embodiments of the first aspect.

[0021] In a third aspect, the application also provides a manufacturing method of a secondary battery, for manufacturing the secondary battery of any one of the above embodiments of the first aspect, comprising: providing a negative electrode sheet, a separator, and a double-faced positive electrode sheet; stacking the separator, the negative electrode sheet, the separator, and the double-faced positive electrode sheet in sequence along a first direction to form a first assembly, wherein the negative electrode sheet is the outermost electrode sheet of the first assembly along the first direction, and the first separator 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 away from the negative electrode sheet to form a second assembly. Providing a single-faced positive electrode sheet and a first conductive member, and welding the first conductive member to the opposite surfaces of the second portion of the first positive current collector of the single-faced positive electrode sheet to form a first welding area. Stacking the single-faced positive electrode sheet with the first conductive member welded to the opposite surfaces of the second portion of the first positive current collector of the single-faced positive electrode sheet on the opposite surfaces of the second assembly along the first direction, wherein the projection of the first insulating layer on the surface of the single-faced positive electrode sheet along the first direction covers the first welding area. By the above manufacturing method, when the separator of the electrode assembly is not provided with an insulating layer, the separator does not need to be wound after being bonded with the insulating layer and then stacked with the electrode sheets, thereby reducing the possibility that the separator is not easy to wind after being bonded with the insulating layer, and reducing the possibility that the separator is torn due to the bulging after being wound with the insulating layer.

[0022] Additional layers and advantages of embodiments of the application will be described in part in the description that follows, and demonstrated, by way of non-limiting examples, through implementations of the embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0023] One or more embodiments are illustrated by way of example in the accompanying drawings that are not necessarily drawn to scale, in which like references indicate similar elements, and in which:

[0024] Figure 1 Structure diagram of a secondary battery of some embodiments of the application;

[0025] Figure 2 Structure diagram of an electrode assembly of some embodiments of the application;

[0026] Figure 3 Structure diagram of a first positive current collector of some embodiments of the application;

[0027] Figure 4 Structure diagram of a single-faced positive electrode sheet along a first direction of some embodiments of the application;

[0028] Figure 5 Structure diagram of a first insulating layer of some embodiments of the application;

[0029] Figure 6 Structure diagram of an electrode assembly of some embodiments of the application;

[0030] Figure 7 Structure diagram of a second positive current collector for some embodiments of the present application;

[0031] Figure 8 Structure diagram of a double-sided positive electrode sheet along a first direction for some embodiments of the present application;

[0032] Figure 9 Structure diagram of a second insulating layer for some embodiments of the present application.

[0033] Explanation of reference signs:

[0034] 100, secondary battery;

[0035] 10, case;

[0036] 20, electrode assembly;

[0037] 21, positive electrode sheet; 211, single-sided positive electrode sheet; 2111, first positive current collector; 211a, first portion; 211b, second portion; 2113, first metal layer; 2114, first polymer layer; 2112, first positive active layer; 211c, seventh portion; 211d, eighth portion; 212, double-sided positive electrode sheet; 2121, second positive current collector; 212a, ninth portion; 212b, tenth portion; 2123, second metal layer; 2124, second polymer layer; 2122, second positive active layer;

[0038] 22, negative electrode sheet; 221, first negative current collector; 222, first negative active layer; 222a, third portion; 222b, fourth portion;

[0039] 23, separator; 231, first separator; 231a, fifth portion; 231b, sixth portion; 232, second separator;

[0040] 24, first conductive member; 24a, first welding area; 241, first main body portion; 242, first curved portion; 243, second curved portion;

[0041] 25, first insulating layer; 251, first adhesive layer; 252, first base material layer;

[0042] 26, second conductive member; 26a, second welding area; 261, second main body portion; 262, third curved portion; 263, fourth curved portion;

[0043] 27, second insulating layer; 271, second adhesive layer; 272, second base material layer;

[0044] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0045] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application.

[0046] In the present application, the phrase "embodiments" means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily all refer to the same embodiments, nor are they necessarily mutually exclusive or alternative embodiments to other embodiments.

[0047] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified.

[0048] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0049] The term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be an approximate vertical state between the two components. For example, in combination with numerical description, vertical can refer to the included angle between two straight lines within the range of 90±10°, vertical can also refer to the dihedral angle between two planes within the range of 90°±10°, and vertical can also refer to the included angle between a straight line and a plane within the range of 90±10°. The two components described as "vertical" can not be absolute straight lines or planes, but can be approximately straight lines or planes, and as a whole, the overall extension direction is a straight line or a plane, which can be considered as a "straight line" or a "plane".

[0050] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0051] In a first aspect, embodiments of the present 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), and the electrolyte infiltrates the electrode assembly 20 in the housing 10.

[0052] For the above electrode assembly 20, please refer to Figure 2 , Figure 2 The electrode assembly 20 is shown in a stack structure. The electrode assembly 20 includes negative electrode sheets 22, positive electrode sheets 21, and separators 23, the positive electrode sheets 21 and the negative electrode sheets 22 are alternately stacked along the first direction X, and the separators 23 are arranged between adjacent positive electrode sheets 21 and negative electrode sheets 22, and the separators 23 are used to insulate and separate the positive electrode sheets 21 and the negative electrode sheets 22. In the embodiments of the present application, the electrode assembly 20 is taken as an example to illustrate the stack structure, and in some other embodiments, the electrode assembly 20 can also be in a wound structure, for example, the positive electrode sheets 21, the separators 23 and the negative electrode sheets 22 are sequentially stacked and then wound to form a wound electrode assembly 20.

[0053] For the above positive electrode sheet 21, the positive electrode sheet 21 includes a single-sided positive electrode sheet 211, and the outermost electrode sheet of the electrode assembly 20 along the first direction X is the single-sided positive electrode sheet 211, which can reduce the possibility of damage to the shell 10 of the outer package, because if the outermost electrode sheet of the electrode assembly 20 is a single-sided negative electrode sheet, the metal copper of the current collector of the single-sided negative electrode sheet is easy to have an electrochemical reaction with the metal aluminum of the shell 10, thereby causing the shell 10 to be damaged. The single-sided positive electrode sheet 211 includes a first positive electrode current collector 2111 and a first positive electrode active layer 2112, and the first positive electrode current collector 2111 includes a first portion 211a and a second portion 211b connected in sequence along a second direction Y perpendicular to the first direction X, and the first portion 211a is provided with the first positive electrode active layer 2112 on one surface facing the negative electrode sheet 22, and the second portion 211b is not provided with the first positive electrode active layer 2112 on opposite surfaces along the first direction X. By providing the first positive electrode active layer 2112 on one surface of the first positive electrode current collector 2111 of the single-sided positive electrode sheet 211 facing the negative electrode sheet 22, the utilization rate of the positive electrode active material of the single-sided positive electrode sheet 211 can be improved, thereby improving the energy density.

[0054] For the above first positive electrode active layer 2112, the first positive electrode active layer 2112 is soaked in the above electrolyte within the shell 10 to have an electrochemical reaction. The first positive electrode active layer 2112 includes a first positive electrode active material, a conductive agent, a binder, etc., the above materials are uniformly mixed and stirred and coated on one 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 can 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] For the first positive electrode 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, and the first polymer layer 2114 is provided with the first metal layer 2113 on both surfaces in the first direction X. By setting the first positive electrode current collector 2111 as a structure of two first metal layers 2113 sandwiching the first polymer layer 2114, the first metal layer 2113 can be made thinner, thereby reducing the metal burrs caused by mechanical damage of the secondary battery 100, and reducing the mass of the first positive electrode current collector 2111, thereby improving 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), and the first metal layer 2113 can include at least one of aluminum, copper, nickel, titanium, and silver.

[0056] For the above-mentioned negative electrode sheet 22, the negative electrode sheet 22 includes a first negative electrode current collector 221 and a first negative electrode active layer 222, the first negative electrode current collector 221 is provided with the first negative electrode active layer 222 on at least one surface in the first direction X, and the first negative electrode active layer 222 includes a third portion 222a and a fourth portion 222b connected in sequence in the second direction Y, the projection of the third portion 222a on the surface of the single-sided positive electrode sheet 211 overlaps the first portion 211a, and the projection of the fourth portion 222b on the surface of the single-sided positive electrode sheet 211 overlaps at least part of the second portion 211b. In the second direction Y, the width of the fourth portion 222b is W3, and 0.5mm≤W3≤2mm. By limiting 0.5mm≤W3, the first negative electrode active layer 222 can better absorb the lithium ions released by the first positive electrode active layer 2112, and reduce the possibility of lithium precipitation on the surface of the first negative electrode active layer 222. By limiting W3≤2mm, the negative electrode active material of the first negative electrode active layer 222 has better energy utilization rate, without excessively reducing the energy density of the secondary battery 100.

[0057] For the above-mentioned first negative electrode active layer 222, the first negative electrode active layer 222 is infiltrated by the above-mentioned electrolyte in the shell 10 to generate an electrochemical reaction. The first negative electrode active layer 222 includes a first negative electrode active material, a conductive agent, a binder, etc., the above-mentioned materials are uniformly mixed and stirred and coated on at least one surface of the above-mentioned negative electrode current collector in the first direction X, thereby obtaining the first negative electrode active layer 222. The first negative electrode active material can include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0058] For the first negative current collector 221, the first negative current collector 221 can be a composite current collector (a composite structure of metal-polymer-metal), for example, the first negative current collector 221 includes a polymer layer and a metal layer arranged on opposite surfaces of the polymer layer, the polymer layer serves as the main mechanical support layer of the first negative current collector 221, and can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the metal layer can include at least one of aluminum, copper, nickel, titanium, and silver. By taking the polymer layer as the main mechanical support layer, the first negative current collector 221 can thin the metal layer, thereby reducing the metal burrs caused by mechanical damage of the secondary battery 100, and reducing the mass of the first negative current collector 221, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the first negative current collector 221 can be a single-layer metal foil, which can include at least one of aluminum, copper, nickel, titanium, and silver.

[0059] In some embodiments, the second part 211b of the first positive current collector 2111 has a first conductive piece 24 welded on both surfaces along the first direction X, and forms a first welding area 24a, and the first conductive piece 24 protrudes from the second part 211b along the second direction Y to facilitate the connection of the positive tab to the first positive current collector 2111 through the first conductive piece 24, and the first conductive piece 24 can include at least one of aluminum, copper, nickel, titanium, and silver. By roll welding the first positive current collector 2111 between two first conductive pieces 24, the reliability of the welding can be improved and the welding resistance can be reduced. However, the metal burrs of the first welding area 24a are easy to pierce the separator 23 and the opposite first negative active layer 222 to form a short circuit, thereby reducing the safety performance of the secondary battery 100.

[0060] For the above problems, there are two solutions at present. The first solution is to paste adhesive paper on the first welding area 24a, so that the adhesive paper blocks the metal burrs of the first welding area 24a, thereby reducing the possibility that the metal burrs of the first welding area 24a pierce the diaphragm 23 and the opposite first negative active layer 222 to form a short circuit. However, the adhesive paper pasting process is complicated, and adding the adhesive paper pasting process in the roll welding process greatly enlarges the process size precision error, thereby greatly reducing the jelly piece manufacturing yield. In addition, the glue in the adhesive paper has a dissolving ability to the adhesive of the first positive active layer 2112 of the single-sided positive jelly piece 211, which can cause the positive active material particles of the first positive active layer 2112 near the first conductive part 24 to fall off. In addition, the knife die will be adhered to the glue of the adhesive paper when the jelly piece is cut, which causes the cutting effect to be poor, thereby reducing the jelly piece manufacturing yield, and the knife die cleaning frequency needs to be increased, thereby reducing the production efficiency. The second solution is to set ceramic layers on the opposite surfaces of the second part 211b along the first direction X, and make the ceramic layers located between the first positive active layer 2112 and the first conductive part 24 along the second direction Y, which can make the first conductive part 24 exceed the first negative active layer 222 along the second direction Y, so that the first welding area 24a exceeds the first negative active layer 222 along the second direction Y, thereby reducing the possibility that the metal burrs of the first welding area 24a pierce the diaphragm 23 and the opposite first negative active layer 222 to form a short circuit. However, the excess first conductive part 24 increases the head space of the single-sided positive jelly piece 211, thereby reducing the energy density of the secondary battery 100.

[0061] To improve the above problems, in the embodiments of the present application, please refer to Figure 2 and Figure 4The diaphragm 23 comprises a first diaphragm 231, and the first diaphragm 231 is arranged between the single-face positive electrode sheet 211 and the adjacent negative electrode sheet 22. A surface of the first diaphragm 231 facing the single-face positive electrode sheet 211 is provided with a first insulating layer 25. A projection of the first insulating layer 25 on the surface of the single-face positive electrode sheet 211 along the first direction X covers the first welding area 24a, so that the first insulating layer 25 can shield the metal burrs of the first welding area 24a, thereby reducing the possibility of the metal burrs of the first welding area 24a piercing the first diaphragm 231 and the negative active material layer of the opposite negative electrode sheet 22 to form a short circuit. In addition, since the first insulating layer 25 is only arranged on the first diaphragm 231 at the outermost layer of the electrode assembly 20, the electrode assembly 20 can be stacked with the electrode sheets in the middle layer first, and then the first insulating layer 25 is arranged on the first diaphragm 231 at the outermost layer, and then the single-face positive electrode sheet 211 is stacked, without the need to first bond the insulating layer to the diaphragm 23 and then roll up and stack the electrode sheets, thereby reducing the possibility that the diaphragm 23 is not easy to roll up after the insulating layer is bonded, and reducing the possibility that the diaphragm 23 is torn after being rolled up after the insulating layer is bonded. Along the third direction Z, the length of the first insulating layer 25 is L1, the width of the first conductive part 24 is L2, 1mm≤L1-L2≤6mm, the first insulating layer 25 exceeds one side of the first conductive part 24, and the exceeding length is 0.5mm to 3mm, and the third direction Z is perpendicular to the first direction X and the second direction Y respectively. By limiting 1mm≤L1-L2, the first insulating layer 25 can better shield the metal burrs of the first welding area 24a. Since the first insulating layer 25 is too long and is easy to fold, thereby affecting the shielding effect of the first welding area 24a, by limiting L1-L2≤6mm, the length of the first insulating layer 25 is not too long, thereby reducing the possibility of folding of the first insulating layer 25, and further improving the possibility of the first insulating layer 25 shielding the metal burrs of the first welding area 24a. By limiting the first insulating layer 25 to exceed one side of the first conductive part 24 along the third direction, and the exceeding length is 0.5mm to 3mm, the first insulating layer 25 can better shield the metal burrs of the first welding area 24a, and the length of the first insulating layer 25 is not too long, thereby not being easy to fold.

[0062] In some embodiments, along the third direction Z, the first insulating layer 25 exceeds both sides of the first conductive part 24, and the length of the first insulating layer 25 exceeding any side of the first conductive part 24 is 0.5mm to 3mm, further making the first insulating layer 25 better shield the metal burrs of the first welding area 24a, and the length of the first insulating layer 25 is not too long, thereby not being easy to fold.

[0063] In some embodiments, along the third direction Z, the first conductive member 24 comprises a first bending portion 242 and a first body portion 241 connected in sequence, the first insulating layer 25 exceeds a side of the first bending portion 242 away from the first body portion 241, and the exceeding length is 0.5mm to 3mm. A torque force is formed in the process of die cutting the first conductive member 24, and the first bending portion 242 can buffer the torque force to reduce the possibility of tearing the first positive current collector 2111 due to the torque force. Since the length of the first insulating layer 25 is limited by the processing precision, by limiting the first insulating layer 25 to exceed the side of the first bending portion 242 away from the first body portion 241, and the exceeding length is not less than 0.5mm, the first insulating layer 25 can better shield the metal burrs of the first welding area 24a while giving the first insulating layer 25 a larger processing precision space. By limiting the first insulating layer 25 to exceed the side of the first bending portion 242 away from the first body portion 241, and the exceeding length is not more than 3mm, the possibility of the first insulating layer 25 being too long and being easily folded can be reduced, and the possibility of the first insulating layer 25 being too long and wasting more energy density of the secondary battery 100 can be reduced.

[0064] In some embodiments, the first conductive member 24 comprises a second bending portion 243, along the third direction Z, the second bending portion 243 is connected to a side of the first body portion 241 away from the first bending portion 242, the first insulating layer 25 exceeds a side of the second bending portion 243 away from the first body portion 241, and the exceeding length is 0.5mm to 3mm. The second bending portion 243 can buffer the torque force in the die cutting process to further reduce the possibility of tearing the first positive current collector 2111 due to the torque force. By limiting the first insulating layer 25 to exceed the side of the second bending portion 243 away from the first body portion 241, and the exceeding length is not less than 0.5mm, the first insulating layer 25 can better shield the metal burrs of the first welding area 24a while giving the first insulating layer 25 a larger processing precision space. By limiting the first insulating layer 25 to exceed the side of the second bending portion 243 away from the first body portion 241, and the exceeding length is not more than 3mm, the possibility of the first insulating layer 25 being too long and being easily folded can be reduced, and the possibility of the first insulating layer 25 being too long and wasting more energy density of the secondary battery 100 can be reduced.

[0065] 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 better shield the metal burrs of the first welding area 24a while not being too wide and not wasting too much energy density of the secondary battery 100.

[0066] In some embodiments, along the first direction X, the thickness of the first insulating layer 25 is H1, 10 pm ≤ H1 ≤ 20 pm. This is to make the first insulating layer 25 meet the better puncture-proof performance, while the first insulating layer 25 is not too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0067] In some embodiments, referring 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, one surface of the first adhesive layer 251 is provided with the first substrate layer 252, the other surface of the first adhesive layer 251 away from the first substrate layer 252 is provided on the first diaphragm 231, the thickness of the first adhesive layer 251 is H2, 2 pm ≤ H2 ≤ 7 pm, and the thickness of the first substrate layer 252 is H3, 8 pm ≤ H3 ≤ 13 pm. The first adhesive layer 251 can improve the adhesion of the first insulating layer 25 to the first diaphragm 231, and the first substrate layer 252 can improve the puncture-proof performance of the first insulating layer 25. By limiting 2 pm ≤ H2 ≤ 7 pm, the first adhesive layer 251 has better adhesion effect, while the first adhesive layer 251 is not too thick, so as not to excessively reduce the energy density of the secondary battery 100. By limiting 8 pm ≤ H3 ≤ 13 pm, the first substrate layer 252 has better insulation effect, while the first substrate layer 252 is not too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0068] In some embodiments, the first adhesive layer 251 includes at least one of propylene oxide, polymethyl methacrylate, and styrene-butadiene rubber, so that the first adhesive layer 251 has better adhesion effect. And / or, the first substrate layer 252 includes at least one of polyimide, polyethylene terephthalate, polypropylene, and polyethylene, so that the first substrate layer 252 has better puncture-proof performance.

[0069] In some embodiments, along the second direction Y, referring to Figure 2 and Figure 4 , the width of the first welding area 24a is W2, 0.8 mm ≤ W2 ≤ 3 mm. By limiting 0.8 mm ≤ W2, the first welding area 24a has good welding strength, so that the first conductive part 24 can be firmly fixed 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, so by limiting W2 ≤ 3 mm, the width of the first welding area 24a is not too wide, so that the width of the first insulating layer 25 is not too wide, so as not to excessively reduce the energy density of the secondary battery 100.

[0070] In some embodiments, 6.5mm≤L2≤15.5mm, so that the first conductive member 24 has a good connection strength with the first positive current collector 2111, while the first conductive member 24 is not too long, and the energy density of the secondary battery 100 is not excessively reduced.

[0071] In some embodiments, the first separator 231 includes a fifth portion 231a and a sixth portion 231b connected in sequence along the second direction Y. Along the first direction X, a projection of the fifth portion 231a on the surface of the negative electrode sheet 22 overlaps the first negative active layer 222. Along the second direction Y, the sixth portion 231b is beyond the first negative active layer 222, and the width of the sixth portion 231b is W4, 0.5mm≤W4≤2mm. By limiting 0.5mm≤W4, the sixth portion 231b of the first separator 231 can cover the first negative active layer 222, reducing the possibility of the first negative active layer 222 contacting the first conductive member 24 and short-circuiting. By limiting W4≤2mm, the sixth portion 231b of the first separator 231 is not too wide, and the energy density of the secondary battery 100 is not excessively reduced.

[0072] In some embodiments, the first positive active layer 2112 includes a seventh portion 211c and an eighth portion 211d connected to the seventh portion 211c near the first conductive member 24 along the second direction Y. 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 a projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 overlaps at least part of the eighth portion 211d. The first positive active layer 2112 will form a torque force during cold pressing. By limiting the maximum thickness of the eighth portion 211d of the first positive 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, reducing the possibility of the first positive current collector 2111 tearing due to the torque force. Since the eighth portion 211d is thin, by limiting the projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 to overlap at least part of the eighth portion 211d, the thickness of the electrode assembly 20 along the first direction X is not excessively increased, while the possibility of the first insulating layer 25 covering the first welding area 24a is further improved. In some embodiments, the thickness of the eighth portion 211d gradually decreases in the direction from the seventh portion 211c to the eighth portion 211d, so that the eighth portion 211d can better buffer the torque force.

[0073] In some embodiments, please refer to Figure 6 , Figure 7 and Figure 8The positive sheet 21 includes a single-sided positive sheet 212, the single-sided positive sheet 212 is arranged between two adjacent negative sheets 22 along the first direction X, the single-sided positive sheet 212 includes a second positive current collector 2121 and a second positive active layer 2122, the second positive current collector 2121 includes a ninth part 212a and a tenth part 212b connected in sequence along the second direction Y, the ninth part 212a is provided with the second positive active layer 2122 on the opposite surfaces along the first direction X, the tenth part 212b is not provided with the second positive active layer 2122 on the opposite surfaces 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 is provided with the second metal layer 2123 on the opposite surfaces along the first direction X. The tenth part 212b is welded with a second conductive part 26 on the opposite surfaces along the first direction X, and a second welding area 26a is formed. The separator 23 includes a second separator 232, the second separator 232 is arranged between the single-sided positive sheet 212 and the negative sheet 22, one surface of the second separator 232 facing the single-sided positive sheet 212 is provided with a second insulating layer 27, and a projection of the second insulating layer 27 on the surface of the single-sided positive sheet 212 along the first direction X covers the second welding area 26a. The single-sided positive sheet 212 is arranged between two adjacent negative sheets 22 along the first direction X, and the opposite surfaces of the second positive current collector 2121 of the single-sided positive sheet 212 are provided with the second positive active layer 2122, so that the number of layers of the second positive current collector 2121 can be reduced, thereby improving the energy density of the secondary battery 100. By arranging the second positive current collector 2121 in a structure of two second metal layers 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 the second conductive part 26 on the opposite surfaces of the tenth part 212b of the second positive current collector 2121 along the first direction X, the positive tab can be connected to the second positive current collector 2121 through the second conductive part 26. By arranging the second insulating layer 27 on one surface of the second separator 232 facing the single-sided positive sheet 212, and the projection of the second insulating layer 27 on the surface of the single-sided positive sheet 212 along the first direction X covers the second welding area 26a, so that the second insulating layer 27 can block 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 separator 232 and the negative active material layer of the opposite negative sheet 22 to form a short circuit. The second conductive part 26 can include at least one of aluminum, copper, nickel, titanium, and silver.

[0074] In some embodiments, the second polymer layer 2124, as the main mechanical support layer of the second positive current collector 2121, can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the second metal layer 2123 can include at least one of aluminum, copper, nickel, titanium, and silver. The second positive active layer 2122 is soaked in the electrolyte in the shell 10 to generate an electrochemical reaction. The second positive active layer 2122 includes a second positive active material, a conductive agent, a binder, and the like, which are uniformly mixed and stirred and coated on the opposite surfaces of the ninth part 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 can 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.

[0075] 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 part 26 is L4, 1mm≤L3-L4≤6mm. By limiting 1mm≤L3-L4, the second insulating layer 27 can better shield the metal burrs of the second welding area 26a. Since the second insulating layer 27 is too long and is easy to fold, which affects its shielding effect of the metal burrs of the second welding area 26a, by limiting L3-L4≤6mm, the length of the second insulating layer 27 is not too long, thereby reducing the possibility of folding of the second insulating layer 27, and further improving the possibility of the second insulating layer 27 shielding the metal burrs of the second welding area 26a.

[0076] In some embodiments, along the third direction Z, the second conductive part 26 includes a third bending part 262 and a second main body part 261 connected in sequence, and the second insulating layer 27 exceeds one side of the third bending part 262 away from the second main body part 261, and the exceeding length is 0.5mm to 3mm. A torque force is formed in the process of die cutting the second conductive part 26, and the third bending part 262 can buffer the torque force to reduce the possibility of tearing of the second positive current collector 2121 due to the torque force. Since the length of the second insulating layer 27 is limited by the processing precision, by limiting the second insulating layer 27 to exceed one side of the third bending part 262 away from the second main body part 261, and the exceeding length is not less than 0.5mm, the second insulating layer 27 can better shield the metal burrs of the second welding area 26a while giving the second insulating layer 27 a larger processing precision space. By limiting the second insulating layer 27 to exceed one side of the third bending part 262 away from the second main body part 261, and the exceeding length is not more than 3mm, the possibility of the second insulating layer 27 being too long and being easy to fold can be reduced, and the possibility of the second insulating layer 27 being too long and wasting more energy density of the secondary battery 100 can be reduced.

[0077] In some embodiments, the second conductive member 26 includes a fourth curved portion 263 connected to a side of the second main portion 261 away from the third curved portion 262 along the third direction Z, the second insulating layer 27 extends beyond the fourth curved portion 263 away from the second main portion 261, and the extending length is 0.5 mm to 3 mm. The fourth curved portion 263 can buffer the torque force in the die-cutting process to further reduce the possibility of tearing the second positive current collector 2121 due to the torque force. By limiting the second insulating layer 27 to extend beyond the fourth curved portion 263 away from the second main portion 261, and the extending length is not less than 0.5 mm, the second insulating layer 27 can better shield the metal burrs of the second welding area 26a while giving the second insulating layer 27 a larger processing precision space. By limiting the second insulating layer 27 to extend beyond the fourth curved portion 263 away from the second main portion 261, and the extending length is not more than 3 mm, the possibility of the second insulating layer 27 being too long and easily folded can be reduced, and the possibility of the second insulating layer 27 being too long and wasting more energy density of the secondary battery 100 can be reduced.

[0078] In some embodiments, along the second direction Y, the width of the second insulating layer 27 is W5, 1.4 mm≤W5≤4 mm, so that the second insulating layer 27 can better shield the metal burrs of the second welding area 26a while the second insulating layer 27 is not too wide and does not waste too much energy density of the secondary battery 100. Along the first direction X, the thickness of the second insulating layer 27 is H4, 10 μm≤H4≤20 μm. So that the second insulating layer 27 has better puncture resistance while the second insulating layer 27 is not too thick and does not waste too much energy density of the secondary battery 100.

[0079] 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. A surface of the second adhesive layer 271 is provided with the second substrate layer 272 along the first direction X. Another surface of the second adhesive layer 271, which is away from the second substrate layer 272, is provided on the second diaphragm 232. The thickness of the second adhesive layer 271 is H5, and 2 pm≤H5≤7 pm. The thickness of the second substrate layer 272 is H6, and 8 pm≤H6≤13 pm. The second adhesive layer 271 can improve the adhesion of the second insulating layer 27 to the second diaphragm 232. The second substrate layer 272 can improve the puncture resistance of the second insulating layer 27. By limiting 2 pm≤H5≤7 pm, the second adhesive layer 271 has good adhesion while not being too thick, so as not to excessively reduce the energy density of the secondary battery 100. By limiting 8 pm≤H6≤13 pm, the second substrate layer 272 has good insulation while not being too thick, so as not to excessively reduce the energy density of the secondary battery 100.

[0080] In some embodiments, the second adhesive layer 271 includes at least one of propylene oxide, polymethyl methacrylate, and styrene-butadiene rubber, so that the second adhesive layer 271 has good adhesion. And / or, the second substrate layer 272 includes at least one of polyimide, polyethylene terephthalate, polypropylene, and polyethylene, so that the second substrate layer 272 has good puncture resistance.

[0081] In some embodiments, please refer to Figure 6 and Figure 8 The width of the second welding area 26a along the second direction Y is W6, and 0.8 mm≤W6≤3 mm. By limiting 0.8 mm≤W6, the second welding area 26a has good welding strength, so that the second conductive member 26 can be firmly fixed 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≤3 mm, the width of the second welding area 26a is not too wide, so that the width of the second insulating layer 27 is not too wide, and the energy density of the secondary battery 100 is not excessively reduced.

[0082] In some embodiments, 6.5 mm≤L4≤15.5 mm, so that the second conductive member 26 and the second positive current collector 2121 have good connection strength, and the second conductive member 26 is not too long, so as not to excessively reduce the energy density of the secondary battery 100.

[0083] 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 member 24 comprises aluminum. (4) the first insulating layer 25 comprises polyolefin.

[0084] The second aspect of the present application further provides an electronic device comprising the secondary battery 100 according to any one of the above embodiments of the first aspect. The electronic device according to the embodiments of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device includes, but is not limited to, a Bluetooth headset, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, and the like. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, an electric plane toy, and the like, and the spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

[0085] The third aspect of the present application further provides a manufacturing method of the secondary battery 100, for preparing the secondary battery 100 according to any one of the above embodiments of the first aspect, comprising: providing the negative electrode sheet 22, the separator 23, and the single-face positive electrode sheet 212, stacking the separator 23, the negative electrode sheet 22, the separator 23, and the single-face positive electrode sheet 212 in sequence along the first direction X to form a first assembly, wherein the negative electrode sheet 22 is the outermost electrode sheet of the first assembly along the first direction X, and the first separator 231 is the outermost layer of the first assembly along the first direction X. Providing the first insulating layer 25, and disposing the first insulating layer 25 on the surface of the first separator 231 of the first assembly away from the negative electrode sheet 22 to form a second assembly. Providing the single-face positive electrode sheet 211 and the first conductive member 24, and welding the first conductive member 24 to the opposite surfaces of the second part 211b of the first positive current collector 2111 of the single-face positive electrode sheet 211 to form a first welding area 24a. Stacking the single-face positive electrode sheet 211 with the first conductive member 24 welded to the opposite surfaces of the second assembly along the first direction X, wherein the projection of the first insulating layer 25 on the surface of the single-face positive electrode sheet 211 along the first direction X covers the first welding area 24a. Through the above manufacturing method, when the separator 23 in the electrode assembly 20 does not have an insulating layer, it is not necessary to first bond the insulating layer to the separator 23, then roll up the separator 23, and then stack the electrode sheets, thereby reducing the possibility that the separator 23 is not easy to roll up after the insulating layer is bonded thereto, and reducing the possibility that the separator 23 is torn after being rolled up with the insulating layer.

[0086] Test section:

[0087] 1. Test of energy density improvement of lithium ion battery:

[0088] Energy density calculation method: use the method of pasting adhesive, overlap the roll welding and adhesive tape on the thickness of the battery cell, protect the positive electrode tab and the negative electrode junction position, can cancel the positive electrode edge insulation ceramic layer coating, compared with the ceramic layer + roll welding process, the energy density is improved in the head space is reduced, calculation logic: energy density improvement = (ceramic layer width + roll welding width - pasting and roll welding overlap width) / cell length * 100%.

[0089] 2. Drop test:

[0090] Drop from 1.8m drop height along the head-tail 2 sides 1 time, 4 corners 1 time, a total of 7 rounds of tests, drop order (head -> tail -> head right corner -> tail right corner -> head left corner -> tail left corner (angle: 45±15 degrees, 6 times per round)); judgment criteria: no fire, no explosion, no smoke, no leakage.

[0091] 3. Adhesive tape folding test:

[0092] Adhesive tape folding can be directly visually identified in the lamination equipment, and the corresponding data can be directly put forward in the production site, calculation logic: adhesive tape folding ratio = adhesive tape folding tab / total tab quantity * 100%.

[0093] Example 1

[0094] <Preparation of positive electrode tab>:

[0095] The positive electrode active material lithium cobaltate (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75wt% was prepared and stirred uniformly.

[0096] Polyethylene terephthalate was selected as the polymer layer, and two metal layers of aluminum were evaporated on the two surfaces of the polymer layer to obtain a positive current collector. The above slurry was coated on the surface of the positive current collector-metal layer and a positive empty foil section was reserved. The slurry was dried to obtain a single-sided positive electrode tab coated with a positive active material layer on one side. On the other metal layer, the above steps were repeated to obtain a double-sided positive electrode tab coated with a positive active material layer on both sides.

[0097] <Preparation of negative electrode tab>:

[0098] Graphite was used as the negative electrode active material, and the negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96:2:2, deionized water was added as a solvent, and a slurry with a solid content of 70wt% was prepared and stirred uniformly.

[0099] Polyethylene terephthalate is selected as the polymer layer, two metal layers of copper material are evaporated on the two surfaces of the polymer layer, the slurry is coated on the surface of one metal layer and the negative electrode empty foil section is reserved. The slurry is dried to obtain a single-sided composite negative electrode sheet coated with a negative electrode active material layer on one side. On the other metal layer, the above steps are repeated to obtain a double-sided composite negative electrode sheet coated with a negative electrode active material layer on both sides.

[0100] <Preparation of the separator>:

[0101] A polyethylene porous membrane is used as the base layer, and a ceramic layer containing aluminum oxide ceramic and a PVDF binder is coated on one side surface of the base layer as a separator (CCS), wherein the mass percentage of aluminum oxide ceramic in the ceramic layer is 95%.

[0102] <Preparation of the electrolyte>:

[0103] In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of EC: EMC: DEC = 30:50:20 to form a basic organic solvent, then lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix uniformly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0104] <Preparation of the ceramic layer>:

[0105] In the production of the battery cell, the ceramic layer is prepared in 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, the position, size and weight of the slurry are set by the opening of the extrusion coating at different positions in different slurry strips (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 limited. The interaction area of the ceramic layer is far away from the current collector, and the active material layer is close to the current collector). The positive electrode sheet with the ceramic layer is obtained, and the thickness of the ceramic layer is 25 μm.

[0106] <Preparation of the adhesive paper>:

[0107] The preparation process of the adhesive paper is as follows: first, prepare polypropylene adhesive, heat the polypropylene adhesive to 160-190℃ to completely liquefy; then coat the adhesive on two layers of release film (one layer of complete release film and one layer of release film with grooves, place the complete release film on the lower layer, coat the adhesive in the grooves of the second layer of release film, and then use a scraper to remove the excess adhesive to make the surface of the adhesive paper flat), and cool and solidify to obtain adhesive paper with release film. The thickness of the adhesive paper is 15 μm.

[0108] <Preparation of the lithium ion battery>:

[0109] The conductive member of aluminum material is welded on the empty foil section of the double-sided positive electrode sheet with ceramic layer. The double-sided positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked to form a preliminary electrode assembly. The adhesive paper is pasted on the surface of the outermost separator of the preliminary electrode assembly away from the negative electrode sheet corresponding to the positive and negative electrode junction area below the negative electrode tab. The conductive member of aluminum material is welded on the empty foil section of the single-sided positive electrode sheet. The single-sided positive electrode sheet is stacked on the outermost layer of the preliminary electrode assembly, and the adhesive paper of the separator covers the welding mark of the conductive member of the single-sided positive electrode sheet to form a final electrode assembly. The final electrode assembly is subjected to hot pressing. The final electrode assembly is placed in an aluminum plastic film packaging bag, electrolyte is injected, and the lithium ion battery is packaged.

[0110] The related parameters in Comparative Examples 1 to 8 and Examples 2 to 17 are shown in Table 1.

[0111] Among them, Comparative Examples 1 to 3 only set ceramic layers on the empty foil sections of all positive electrode current collectors, and do not set adhesive papers on the separators.

[0112] Comparative Examples 4 to 6 only set adhesive papers on all positive electrode conductive members, and do not set ceramic layers on the empty foil sections of the positive electrode current collectors, nor do they set adhesive papers on the separators.

[0113] Comparative Examples 7 to 8 and Examples 7 to 17 only set adhesive papers on the separators corresponding to all positive electrode conductive members, and do not set ceramic layers on the empty foil sections of the positive electrode current collectors. Among them, Comparative Examples 7 to 8 and Examples 7 to 9 only differ in the length of the part of the adhesive paper on one side of the separator beyond the width of the conductive member. Examples 10 to 13 only differ in the width of the adhesive paper on the separator. Examples 14 to 17 only differ in the thickness of the adhesive paper on the separator.

[0114] Examples 1 to 3 all set adhesive papers on the separators corresponding to the single-sided positive electrode conductive members, and all set ceramic layers on the empty foil sections of the double-sided positive electrode current collectors, and only differ in the width of the ceramic layer.

[0115] Examples 4 to 6 all set adhesive papers on the separators corresponding to the single-sided positive electrode conductive members, and all set adhesive papers on the double-sided positive electrode current collectors, and only differ in the length of the part of the adhesive paper on one side of the separator beyond the width of the positive electrode conductive member.

[0116] The step of setting adhesive papers on the positive electrode conductive members in the above-mentioned Comparative Examples 4 to 6 and Examples 4 to 6 is: pasting the adhesive paper on the surface of the conductive member of the positive electrode sheet, and covering the welding area of the conductive member.

[0117] It needs to be explained that the length of the part of the adhesive paper on one side of the separator beyond the width of the positive electrode conductive member refers to the length of the part of the adhesive paper on any one side of the two sides in the width direction of the positive electrode conductive member beyond the width of the positive electrode conductive member. Similarly, the length of the part of the adhesive paper on one side of the positive electrode conductive member beyond the width of the conductive member refers to the length of the part of the adhesive paper on any one side of the two sides in the width direction of the positive electrode conductive member beyond the width of the positive electrode conductive member.

[0118] Table 1

[0119]

[0120]

[0121] Note: " / " in Table 1 means not containing the parameter.

[0122] According to Table 1 above, in combination with Comparative Examples 1 to 6 and Examples 7 to 9, it can be seen that by providing a ceramic layer on the current collector, so that the welding area of the conductive member and the current collector protrudes in the length and / or width direction of the current collector beyond the active material layer of the opposite polarity on the opposite side, the battery cell can obtain good drop test pass rate, that is, the risk of short circuit of the battery cell can be better improved, but this way excessively consumes the energy density of the battery cell. By providing adhesive paper covering the welding area on the conductive member, the risk of short circuit of the battery cell can be better improved, and the energy density of the battery cell will not be excessively consumed, but this way has the problems of reducing the manufacturing yield of the pole piece, causing the active material particles near the conductive member to fall off, and reducing the production efficiency. By providing adhesive paper on the separator corresponding to the conductive member, the risk of short circuit of the battery cell can be better improved, and the energy density of the battery cell will not be excessively consumed, and in actual application, compared with providing adhesive paper on the conductive member, providing adhesive paper on the separator can better improve the problems of low manufacturing yield of the pole piece, falling off of the active material particles, and low production efficiency.

[0123] In combination with Comparative Examples 7 to 8 and Examples 7 to 9, it can be seen that when the side of the conductive member corresponding to the separator provided with adhesive paper exceeds the length of the width part of the conductive member by more than 3 mm, that is, the sum of the lengths of the width part of the conductive member exceeded by the two sides of the adhesive paper is more than 6 mm, the folding ratio of the adhesive paper is large, thereby affecting the adhesive paper from shielding the welding area of the conductive member. In actual application, when the side of the conductive member corresponding to the separator provided with adhesive paper exceeds the length of the width part of the conductive member by less than 0.5 mm, that is, the sum of the lengths of the width part of the conductive member exceeded by the two sides of the adhesive paper is less than 1 mm, the adhesive paper cannot better shield the welding area of the conductive member. Therefore, it is necessary to limit the sum of the lengths of the width part of the conductive member exceeded by the two sides of the adhesive paper provided on the separator corresponding to the conductive member to 1 mm to 6 mm.

[0124] In combination with Examples 10 to 13, it can be seen that when the width of the adhesive paper provided on the separator corresponding to the conductive member is greater than 4 mm, the energy density of the battery cell will be excessively consumed, and in actual application, when the width of the adhesive paper provided on the separator corresponding to the conductive member is less than 1.4 mm, the adhesive paper cannot better shield the welding area of the conductive member. Therefore, it is necessary to limit the width of the adhesive paper provided on the separator corresponding to the conductive member to 1.4 mm to 4 mm.

[0125] It can be known from Examples 14 to 17 that when the thickness of the adhesive paper arranged on the conductive member corresponding to the separator is less than 10 μm, the drop test pass rate of the battery cell is low, and in actual application, when the thickness of the adhesive paper arranged on the conductive member corresponding to the separator is greater than 20 μm, the energy density of the battery cell will be excessively consumed, and therefore the thickness of the adhesive paper arranged on the conductive member corresponding to the separator is required to be limited to 10 μm to 20 μm.

[0126] It can be known from Comparative Examples 1 to 3 and Examples 1 to 3 that compared with arranging ceramic layers on all positive current collectors, arranging adhesive paper on the positive conductive member corresponding to the separator instead of arranging ceramic layers on the positive current collector of the outermost single-sided positive plate can make the battery cell obtain a good drop test pass rate, and in actual application, arranging adhesive paper on the positive conductive member corresponding to the separator instead of arranging ceramic layers on the positive current collector of the outermost single-sided positive plate can slightly improve the energy density of the battery cell.

[0127] It can be known from Comparative Examples 4 to 6 and Examples 4 to 6 that compared with arranging adhesive paper on all positive conductive members, arranging adhesive paper on the positive conductive member corresponding to the separator instead of arranging adhesive paper on the conductive member of the outermost single-sided positive plate can also make the battery cell obtain a good drop test pass rate and a good energy density.

[0128] The above description is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet, a positive electrode sheet, and a separator, the negative electrode sheet and the positive electrode sheet being alternately stacked along a first direction, the separator being disposed between adjacent negative electrode sheets and positive electrode sheets; the positive electrode sheet comprises a single-sided positive electrode sheet, the single-sided positive electrode sheet being the outermost electrode sheet of the electrode assembly along the first direction, the single-sided positive electrode sheet comprising a first positive electrode current collector and a first positive electrode active layer, the first positive electrode current collector comprising a first portion and a second portion connected in sequence along a second direction, the first portion being provided with the first positive electrode active layer on one surface thereof facing the negative electrode sheet, the second portion being free of the first positive electrode active layer on opposite surfaces thereof along the first direction; the first positive electrode current collector comprising a first metal layer and a first polymer layer, the first polymer layer being provided with the first metal layer on opposite surfaces thereof along the first direction; characterized in that the second portion is welded with a first conductive member on opposite surfaces thereof along the first direction, and forms a first welding area; the first conductive member protrudes from the second portion along the second direction; the separator comprises a first separator, the first separator being disposed between the single-sided positive electrode sheet and the adjacent negative electrode sheet, the first separator being provided with a first insulating layer on a surface thereof facing the single-sided positive electrode sheet, the first insulating layer covering the first welding area in a projection of the single-sided positive electrode sheet along the first direction; along a third direction, the first insulating layer extends beyond one side of the first conductive member 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.

2. The secondary battery according to claim 1, characterized by along the third direction, the first conductive member comprises a first curved portion and a first main body portion connected in sequence, the first insulating layer extends beyond one side of the first curved portion away from the first main body portion by a length of 0.5 mm to 3 mm.

3. The secondary battery according to claim 2, characterized by the first conductive member comprises a second curved portion, along the third direction, the second curved portion is connected to one side of the first main body portion away from the first curved portion, the first insulating layer extends beyond one side of the second curved portion away from the first main body portion by a length of 0.5 mm to 3 mm.

4. The secondary battery according to claim 1, characterized by along the second direction, the first insulating layer has a width W1, 1.4 mm≤W1≤4 mm.

5. The secondary battery according to claim 1, characterized by along the first direction, the first insulating layer has a thickness H1, 10 μm≤H1≤20 μm.

6. The secondary battery according to claim 1, characterized by the first insulating layer comprises a first adhesive layer and a first substrate layer, along the first direction, one surface of the first adhesive layer is provided with the first substrate layer, the other surface of the first adhesive layer away from the first substrate layer is provided on the first separator, the first adhesive layer has a thickness H2, 2 μm≤H2≤7 μm, and the first substrate layer has a thickness H3, 8 μm≤H3≤13 μm.

7. The secondary battery according to claim 1, characterized by along the second direction, the first welding area has a width W2, 0.8 mm≤W2≤3 mm.

8. The secondary battery according to claim 1, characterized by the first conductive member has a length L2 along the third direction, 6.5 mm≤L2≤15.5 mm.

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

10. The secondary battery according to claim 9, characterized by The first separator along the second direction includes a fifth part and a sixth part connected in sequence; along the first direction, a projection of the fifth part on the surface of the negative electrode sheet overlaps the first negative electrode active layer; along the second direction, the sixth part exceeds the first negative electrode active layer, and the width of the sixth part is W4, and 0.5 mm≤W4≤2 mm.

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

12. The secondary battery according to any one of claims 1 to 11, characterized by The positive electrode sheet includes a double-sided positive electrode sheet, the double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, the double-sided positive electrode sheet includes a second positive electrode current collector and a second positive electrode active layer, the second positive electrode current collector along the second direction includes a ninth part and a tenth part connected in sequence, the second positive electrode active layer is arranged on opposite surfaces of the ninth part along the first direction, the tenth part is not provided with the second positive electrode active layer on opposite surfaces thereof along the first direction, and the second positive electrode current collector includes a second metal layer and a second polymer layer, the second polymer layer along the first direction is provided with the second metal layer on opposite surfaces thereof; The tenth part along the first direction is welded with a second conductive member on opposite surfaces thereof, and a second welding area is formed; the separator includes a second separator, the second separator is arranged between the double-sided positive electrode sheet and the negative electrode sheet, one surface of the second separator facing the double-sided positive electrode sheet is provided with a second insulating layer, and a projection of the second insulating layer on the surface of the double-sided positive electrode sheet covers the second welding area along the first direction.

13. The secondary battery according to any one of claims 1 to 11, characterized by The electrode assembly satisfies at least one of the following conditions: (1) the first metal layer includes aluminum; (2) the first polymer layer includes polyolefin; (3) the first conductive member includes aluminum; (4) the first insulating layer includes polyolefin.

14. An electronic device, comprising: The secondary battery includes the electrode assembly.

15. A manufacturing method of a secondary battery for producing the secondary battery according to any one of claims 1 to 13, characterized by, The secondary battery includes: The negative electrode sheet, the separator, and the double-faced positive electrode sheet are provided, and the separator, the negative electrode sheet, the separator, and the double-faced positive electrode sheet are sequentially stacked in the first direction to form a first assembly, wherein the outermost electrode sheet of the first assembly in the first direction is the negative electrode sheet, and the outermost layer of the first assembly in the first direction is stacked with a first separator; The first insulating layer is provided, and the first insulating layer is arranged on a surface of the first separator of the first assembly away from the negative electrode sheet to form a second assembly; The single-faced positive electrode sheet and the first conductive member are provided, and the first conductive member is welded to opposite surfaces of the second part of the first positive electrode current collector of the single-faced positive electrode sheet, and the first welding area is formed; The single-faced positive electrode sheet with the first conductive member welded to opposite surfaces of the second part of the first positive electrode current collector is stacked on opposite surfaces of the second assembly in the first direction, wherein the projection of the first insulating layer on the surface of the single-faced positive electrode sheet in the first direction covers the first welding area.

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