Secondary battery, electric device, and method for manufacturing negative electrode sheet

Abstract

Embodiments of the present application disclose a secondary battery, a power consumption device and a manufacturing method of a negative electrode sheet. The secondary battery comprises a negative electrode sheet, a positive electrode sheet and a separator, and the negative electrode sheet, the positive electrode sheet and the separator are sequentially stacked along the thickness direction of the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer, a second negative electrode active material layer and a first gel coating layer. The negative electrode current collector comprises a first surface, a second surface and a third surface, the first negative electrode active material layer is arranged on the first surface, and the second negative electrode active material layer is arranged on the second surface. The first gel coating layer comprises a first part, a second part and a third part, the first part is arranged on the first surface, the second part is arranged on the second surface, the third part is arranged on the third surface, and the third part connects the first part and the second part. In the secondary battery, the first gel coating layer is arranged, which is conducive to reducing the possibility of corner corrosion of the secondary battery and improving the K value problem of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage, and particularly relates to a secondary battery, a power consumption device, and a manufacturing method of a negative electrode sheet. BACKGROUND

[0002] The secondary battery comprises a shell and an electrode sheet and a separator arranged in the shell. The shell usually comprises two protective layers and a metal layer sandwiched between the two protective layers; the electrode sheet comprises a positive electrode sheet and a negative electrode sheet, and the separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrode sheet comprises a current collector, and burrs are often generated at the edge of the current collector during the preparation of the battery cell. The burrs are easy to pierce the protective layer of the shell on the side facing the electrode sheet, leading to the conduction between the electrode sheet and the metal layer in the shell and causing the corner corrosion. In addition, when the secondary battery is shaken, the burrs may also fall off and fall between the electrode sheet and the separator, thereby piercing the separator and causing internal short circuit, leading to abnormal voltage drop of the secondary battery. SUMMARY

[0003] In view of the above situation, it is necessary to provide a secondary battery, a power consumption device, and a manufacturing method of a negative electrode sheet, which are beneficial to wrapping and binding the burrs at the edge of the negative electrode current collector.

[0004] A first aspect of an embodiment of the present application provides a secondary battery comprising a negative electrode sheet, a positive electrode sheet, and a separator, which are sequentially stacked in the thickness direction of the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer, a second negative electrode active material layer, and a first gel coating layer. The negative electrode current collector comprises a first surface and a second surface arranged oppositely in the thickness direction of the negative electrode sheet, and a third surface located at one end of the negative electrode sheet in a first direction perpendicular to the thickness direction of the negative electrode sheet, the third surface connecting the first surface and the second surface; the first negative electrode active material layer is arranged on the first surface, and the second negative electrode active material layer is arranged on the second surface; the first gel coating layer connects the negative electrode current collector, and comprises a first part, a second part, and a third part, the first part connects part of the first surface, the second part connects part of the second surface, and the third part is arranged on the third surface and connects the first part and the second part. In the thickness direction of the negative electrode sheet, the projection of the first part is located in the first surface, and the projection of the second part is located in the second surface.

[0005] In this secondary battery, the burrs at the edge of the negative electrode current collector are wrapped and bound by the first gel coating layer, which can at least bring the following two beneficial effects: (1) wrapping the burrs at the edge of the negative electrode current collector can reduce the possibility of the burrs piercing the protective layer of the shell; (2) binding the burrs at the edge of the negative electrode current collector can reduce the possibility of the burrs falling between the negative electrode sheet and the separator or between the positive electrode sheet and the separator, and reduce the risk of internal short circuit caused by the burrs piercing the separator.

[0006] In one or more embodiments of the present application, at least part of the first portion is stacked on part of the surface of the side of the first negative electrode active material layer away from the first surface in the thickness direction of the negative electrode sheet. The first portion can bind the first negative electrode active material layer, reduce the possibility of active material falling off in the first negative electrode active material layer, reduce the impact of active material falling off on energy density, and can reduce the possibility of internal short circuit of the secondary battery, and improve the K value problem of the secondary battery, where the K value refers to the voltage drop per unit time.

[0007] In one or more embodiments of the present application, at least part of the second portion is stacked on part of the surface of the side of the second negative electrode active material layer away from the second surface in the thickness direction of the negative electrode sheet. The second portion can bind the second negative electrode active material layer, reduce the possibility of active material falling off in the second negative electrode active material layer, reduce the impact of active material falling off on energy density, and can reduce the possibility of internal short circuit of the secondary battery, and improve the K value problem of the secondary battery.

[0008] In one or more embodiments of the present application, the negative electrode sheet, the separator, and the positive electrode sheet are sequentially stacked and then wound to form a wound structure. The negative electrode sheet further includes a negative electrode tab welded to the negative electrode current collector; the positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab, the positive electrode current collector includes a fourth surface and a fifth surface oppositely arranged in the thickness direction thereof, one positive electrode active material layer is arranged on the fourth surface, and one positive electrode active material layer is arranged on the fifth surface, and the positive electrode tab is welded to the positive electrode current collector.

[0009] In one or more embodiments of the present application, the negative electrode sheet, the separator, and the positive electrode sheet are sequentially stacked and then wound to form a wound structure. The negative electrode sheet further includes a negative electrode tab integrally arranged with the negative electrode current collector. The positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab, the positive electrode current collector includes a fourth surface and a fifth surface oppositely arranged in the thickness direction thereof, one positive electrode active material layer is arranged on the fourth surface, and one positive electrode active material layer is arranged on the fifth surface, and the positive electrode tab is integrally arranged with the positive electrode current collector.

[0010] In one or more embodiments of the present application, a plurality of negative electrode sheets, a plurality of separators, and a plurality of positive electrode sheets are stacked in the thickness direction of the negative electrode sheet to form a stacked structure, and adjacent negative electrode sheets and positive electrode sheets are separated by a separator. The negative electrode sheet further includes a negative electrode tab integrally arranged with the negative electrode current collector. The positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab, the positive electrode current collector includes a fourth surface and a fifth surface oppositely arranged in the thickness direction of the positive electrode sheet, the positive electrode active material layer is arranged on at least one of the fourth surface and the fifth surface, and the positive electrode tab is integrally arranged with the positive electrode current collector.

[0011] In one or more embodiments of the present application, in the first direction, the width of the negative tab is D1, and the width of the positive tab is D2, D1>D2. Both ends of the negative tab in the first direction exceed the positive tab, which is conducive to increasing the CB (Cell Balance, the ratio of the capacity of the unit area of the negative electrode to the capacity of the unit area of the positive electrode) of the positive and negative tabs, and reducing the possibility of lithium precipitation of the electrode assembly during the cycle process. The first gel coating is located on the part of the negative tab that exceeds the positive tab in the first direction, which can minimize the impact of the setting of the first gel coating on the thickness of the entire electrode assembly.

[0012] In one or more embodiments of the present application, the separator is bonded to the first gel coating, which is conducive to reducing the possibility of relative movement between the negative tab and the positive tab.

[0013] In one or more embodiments of the present application, the first negative active material layer extends to the edge of the negative current collector provided with the first gel coating, and along the thickness direction of the negative tab, the first part is stacked on part of the surface of the side of the first negative active material layer away from the first surface; along the first direction, the distance from the third surface to the positive tab is L1. Along the first direction, the width of the stacking area of the first part and the first negative active material layer is W1, W1 satisfies: 0.1L1≤W1≤0.5L1. W1≥0.1L1, the width of the first part covering the first negative active material layer is not too small, which is conducive to reducing the possibility of active material detachment of the first negative active material layer; W1≤0.5L1, the distance between the first part and the positive tab is not too close, which is conducive to reducing the possibility of the positive tab and the first part being stacked along the thickness direction of the negative tab, reducing the impact of the setting of the first part on the thickness of the electrode assembly, and reducing the possibility of energy density loss of the secondary battery.

[0014] In one or more embodiments of the present application, W1 satisfies: 0.2L1≤W1≤0.4L1. W1≥0.2L1, which is conducive to further reducing the possibility of active material detachment of the first negative active material layer; W1≤0.4L1, which is conducive to further reducing the possibility of the positive tab and the first part being stacked along the thickness direction of the negative tab.

[0015] In one or more embodiments of the present application, the second negative active material layer extends to the edge of the negative current collector provided with the first gel coating, and a second part is stacked on a part of the surface on the side of the second negative active material layer away from the first surface in the thickness direction of the negative sheet. In the first direction, the distance from the third surface to the positive sheet is L1. In the first direction, the width of the stacking area of the second part and the second negative active material layer is W2, and W2 satisfies: 0.1L1≤W2≤0.5L1. W2≥0.1L1, the width of the second part covering the second negative active material layer is not too small, which is conducive to reducing the possibility of active material separation of the second negative active material layer; W2≤0.5L1, the distance between the second part and the positive sheet is not too close, which is conducive to reducing the possibility of the positive sheet and the second part being stacked in the thickness direction of the negative sheet, reducing the impact of the setting of the first part on the thickness of the electrode assembly, and reducing the possibility of energy density loss of the secondary battery.

[0016] In one or more embodiments of the present application, W2 satisfies: 0.2L1≤W2≤0.4L1. W2≥0.2L1, which is conducive to further reducing the possibility of active material separation of the first negative active material layer; W2≤0.4L1, which is conducive to further reducing the possibility of the positive sheet and the second part being stacked in the thickness direction of the negative sheet.

[0017] In one or more embodiments of the present application, the thickness of the positive sheet is T. In the thickness direction of the negative sheet, the maximum distance from the surface of the first part to the first surface is greater than the thickness of the first negative active material layer, and the maximum distance from the surface of the first part to the surface of the first negative active material layer is T1; in the thickness direction of the negative sheet, the maximum distance from the surface of the second part to the second surface is greater than the thickness of the second negative active material layer, and the maximum distance from the surface of the second part to the surface of the second negative active material layer is T2, T1+T2≤T. In the laminated electrode assembly, the first part and the second part of the adjacent two negative sheets are oppositely arranged, and in the wound electrode assembly, the first part and the second part of the wound negative sheet are opposite, setting T1+T2≤T is conducive to reducing the possibility of the first part and the second part contacting, reducing the impact of the setting of the first gel coating on the thickness of the electrode assembly, and reducing the possibility of energy density loss of the secondary battery.

[0018] In one or more embodiments of the present application, T, T1 and T2 satisfy: 0.1T≤T1≤0.5T; 0.1T≤T2≤0.5T. Setting T1≥0.1T, T2≥0.1T, T1 and T2 are not too small, which is conducive to ensuring the wrapping and binding effect of the first gel coating on the burr, and setting T1≤0.5T, T2≤0.5T is conducive to reducing the impact of the setting of the first gel coating on the thickness of the electrode assembly.

[0019] In one or more embodiments of the present application, T, T1 and T2 satisfy: 0.2T≤T1≤0.4T; 0.2T≤T2≤0.4T. Setting 0.2T≤T1, 0.2T≤T2, is conducive to further enhancing the wrapping and binding effect of the first gelatinous coating on the burr, and setting T1≤0.4T, T2≤0.4T, is conducive to further reducing the impact of the setting of the first gelatinous coating on the thickness of the electrode assembly.

[0020] In one or more embodiments of the present application, the negative current collector includes a sixth surface, the third surface and the sixth surface are oppositely arranged along the first direction, and the sixth surface connects the first surface and the second surface. The negative tab includes a second gelatinous coating, the second gelatinous coating includes a fourth portion, a fifth portion and a sixth portion, the fourth portion is arranged on the partial first surface, the fifth portion is arranged on the partial second surface, and the sixth portion is arranged on the sixth surface, and the sixth portion connects the fourth portion and the fifth portion. In this way, the burr can be wrapped and bound from the opposite two surfaces of the negative tab, which is conducive to further reducing the possibility of the edge of the negative current collector piercing the protective layer of the shell, and also conducive to further reducing the possibility of the burr falling between the negative tab and the separator or between the positive tab and the separator, thereby reducing the risk of internal short circuit caused by the burr piercing the separator.

[0021] In one or more embodiments of the present application, the material of the first gelatinous coating includes a hot melt resin.

[0022] In one or more embodiments of the present application, the hot melt resin is selected from at least one of ethylene-vinyl acetate copolymer and polyethylene oxide.

[0023] A second aspect of the embodiments of the present application provides a consumer electronic device including the secondary battery according to any one of the preceding embodiments.

[0024] A third aspect of the embodiments of the present application provides a manufacturing method of a negative tab, the manufacturing method of the negative tab including the following steps:

[0025] arranging a negative active material layer: coating a negative active material on at least a partial surface of the first surface to form the first negative active material layer, and coating the negative active material on at least a partial surface of the second surface to form the second negative active material layer;

[0026] arranging a first gelatinous coating: coating a polymer material on the partial first surface, the third surface and the partial second surface to form the first gelatinous coating.

[0027] In one or more embodiments of the present application, the manufacturing method of the negative tab further includes the following steps:

[0028] The second gel coating is arranged: the negative current collector includes a sixth surface, the third surface and the sixth surface are arranged opposite along the first direction, and the sixth surface is connected to the first surface and the second surface; a polymer material is coated on part of the first surface, the sixth surface and part of the second surface to form a second gel coating. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0030] Figure 2 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application. Figure 1

[0031] Figure 3 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application. Figure 2

[0032] Figure 4 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application. Figure 2

[0033] Figure 5 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0034] Figure 6 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application. Figure 5

[0035] Figure 7 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0036] Figure 8 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0037] Figure 9 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application. Figure 8

[0038] Figure 10 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0039] Figure 11 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0040] Figure 12 is a schematic structural diagram of a secondary battery as a whole in an embodiment of the present application.

[0041] MAIN ELEMENT SYMBOL EXPLANATION

[0042] Secondary battery 100

[0043] Housing 10

[0044] ​​​​​Electrode assembly 20

[0045] Negative electrode sheet 21

[0046] Negative current collector 211

[0047] First face 2111

[0048] Second face 2112

[0049] Third face 2113

[0050] Sixth face 2114

[0051] First negative electrode active material layer 212

[0052] Second negative electrode active material layer 213

[0053] Negative electrode tab 214

[0054] First gel coat layer 215

[0055] First portion 2151

[0056] Second portion 2152

[0057] Third portion 2153

[0058] Second gel coat layer 216

[0059] Fourth portion 2161

[0060] Fifth portion 2162

[0061] Sixth portion 2163

[0062] Positive electrode sheet 22

[0063] Positive current collector 221

[0064] Fourth face 2211

[0065] Fifth face 2212

[0066] Positive electrode active material layer 222

[0067] Positive electrode tab 223

[0068] Insulating layer 224

[0069] Separator 23

[0070] First adapter 30

[0071] Second adapter 40

[0072] First direction X

[0073] The following detailed description will further describe the present application with reference to the above mentioned drawings. DETAILED DESCRIPTION

[0074] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments of the present application.

[0075] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or can exist simultaneously with a middle element. When an element is considered to be "arranged" in another element, it can be directly arranged in the other element or can exist simultaneously with a middle element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0077] In the description of the embodiments of the present application, the technical terms "first", "second", and the like 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 "a plurality of" is two or more, unless otherwise explicitly specified.

[0078] In the description of the embodiments of the present application, 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. The two components described as "vertical" can not be an absolute straight line or plane, but can be approximately straight or planar, and the overall extension direction can be considered as a straight line or plane from a macroscopic point of view.

[0079] The term "parallel" is used to describe the ideal state between two components. In the actual production or use state, there can be an approximate parallel state between the two components. The two components described as "parallel" can not be an absolute straight line or plane, but can be approximately straight or planar, and the overall extension direction can be considered as a straight line or plane from a macroscopic point of view.

[0080] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a particular embodiment logically divided into parts. In some embodiments, various implementations of the application can be combined.

[0081] An embodiment of the application provides a secondary battery, comprising a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheet, the separator and the positive electrode sheet are sequentially stacked along a thickness direction of the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer, a second negative electrode active material layer and a first gel coating layer. The negative electrode current collector comprises a first surface and a second surface oppositely arranged along the thickness direction of the negative electrode sheet, and the negative electrode current collector further comprises a third surface located at one end of the negative electrode sheet along a first direction perpendicular to the thickness direction of the negative electrode sheet, and the third surface connects the first surface and the second surface; the first negative electrode active material layer is arranged on the first surface, and the second negative electrode active material layer is arranged on the second surface; the first gel coating layer connects the negative electrode current collector, and the first gel coating layer comprises a first part, a second part and a third part, the first part connects part of the first surface, the second part connects part of the second surface, and the third part is arranged on the third surface and connects the first part and the second part; along the thickness direction of the negative electrode sheet, a projection of the first part is located in the first surface, and a projection of the second part is located in the second surface.

[0082] In the secondary battery, by arranging the first gel coating layer to wrap and bind the burrs of the edge of the negative electrode current collector, at least the following two beneficial effects can be brought about: (1) wrapping the burrs of the edge of the negative electrode current collector can reduce the possibility of the burrs of the edge of the negative electrode current collector piercing the protective layer of the shell; (2) binding the burrs of the edge of the negative electrode current collector can reduce the possibility of the burrs falling between the negative electrode sheet and the separator or between the positive electrode sheet and the separator, and reduce the risk of internal short circuit caused by the burrs piercing the separator.

[0083] Embodiments of the application will be further described below with reference to the drawings.

[0084] As shown in Figure 1 and Figure 2 An embodiment of the application provides a secondary battery 100, comprising a shell 10 and an electrode assembly 20, the electrode assembly 20 is arranged in the shell 10.

[0085] In some embodiments, as shown in Figure 2 The electrode assembly 20 comprises a negative electrode sheet 21, a positive electrode sheet 22 and a separator 23, the negative electrode sheet 21, the separator 23 and the positive electrode sheet 22 are sequentially stacked along a thickness direction of the negative electrode sheet 21.

[0086] In some embodiments, the diaphragm is an insulating film such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film, to insulate the positive electrode sheet 22 and the negative electrode sheet 21.

[0087] In some embodiments, as shown in Figure 2 , Figure 5 and Figure 6 , the negative electrode sheet 21 includes a negative electrode current collector 211, a first negative electrode active material layer 212, and a second negative electrode active material layer 213. The negative electrode current collector 211 includes a first surface 2111 and a second surface 2112 arranged opposite to each other along the thickness direction of the negative electrode sheet 21. The first negative electrode active material layer 212 is arranged on the first surface 2111, and the second negative electrode active material layer 213 is arranged on the second surface 2112.

[0088] In some embodiments, the negative electrode sheet 21, the diaphragm 23, and the positive electrode sheet 22 are sequentially stacked and wound to form a wound structure.

[0089] In some embodiments, as shown in Figure 6 , for the electrode assembly 20 in a wound structure, the positive electrode sheet 22 includes a positive electrode current collector 221 and a positive electrode active material layer 222, the positive electrode current collector 221 includes a fourth surface 2211 and a fifth surface 2212 arranged opposite to each other along the thickness direction of the positive electrode sheet 22, and one positive electrode active material layer 222 is arranged on the fourth surface 2211 and one positive electrode active material layer 222 is arranged on the fifth surface 2212.

[0090] In some embodiments, as shown in Figure 1 , Figure 2 and Figure 5 , for the electrode assembly 20 in a wound structure, the negative electrode sheet 21 further includes a negative electrode tab 214 welded to the negative electrode current collector 211, and the positive electrode sheet 22 further includes a positive electrode tab 223 welded to the positive electrode current collector 221.

[0091] In other embodiments, as shown in Figure 10 and Figure 11 , for the electrode assembly 20 in a multi-tab wound structure, the negative electrode tab 214 is integrally arranged with the negative electrode current collector 211, and the positive electrode tab 223 is integrally arranged with the positive electrode current collector 221. Figure 8 is a schematic view of the negative electrode sheet in the electrode assembly 20 in a multi-tab wound structure in an unfolded state, Figure 9 is a schematic view of the positive electrode sheet in the electrode assembly 20 in a multi-tab wound structure in an unfolded state.

[0092] In some embodiments, a plurality of negative electrode sheets 21, a plurality of diaphragms 23, and a plurality of positive electrode sheets 22 are stacked along the thickness direction of the negative electrode sheet 21 to form a stacked structure, and any adjacent negative electrode sheet 21 and any adjacent positive electrode sheet 22 are separated by a diaphragm 23.

[0093] In some embodiments, as shown in Figure 8 and Figure 9 For the laminated electrode assembly 20, the positive electrode tab 22 includes a positive electrode current collector 221 and a positive electrode active material layer 222 and a positive electrode lug 223, the positive electrode current collector 221 includes a fourth surface 2211 and a fifth surface 2212 oppositely arranged along the thickness direction of the positive electrode tab 22, and the positive electrode active material layer 222 is arranged on at least one of the fourth surface 2211 and the fifth surface 2212. Specifically, the laminated electrode assembly 20 includes two end portions along the thickness direction of the negative electrode tab 21, the positive electrode tab 22 at the two end portions of the electrode assembly 20 is provided with the positive electrode active material layer 222 only on a single surface of the positive electrode current collector 221, and the positive electrode active material layer 222 is arranged towards the inside of the electrode assembly 20, and the positive electrode tab 22 at the non-end portion of the electrode assembly 20, the fourth surface 2211 and the fifth surface 2212 of the positive electrode current collector 221 of the positive electrode tab 22 are both provided with the positive electrode active material layer 222.

[0094] In some embodiments, for the laminated electrode assembly 20, the negative electrode tab 21 further includes a negative electrode lug 214, and the negative electrode lug 214 is integrally arranged with the negative electrode current collector 211, and the positive electrode tab 22 further includes a positive electrode lug 223, and the positive electrode lug 223 is integrally arranged with the positive electrode current collector 221.

[0095] In some embodiments, as shown in Figure 11 For the electrode assembly 20 with the multi-lug winding structure, when the positive electrode lug 223 is integrally arranged with the positive electrode current collector 221, the positive electrode tab 22 further includes an insulating layer 224, the insulating layer 224 is arranged on the side of the positive electrode active material layer 222 close to the positive electrode lug 223, the first insulating layer 224 connects the positive electrode active material layer 222 and extends to the edge of the side of the positive electrode current collector 221 where the positive electrode lug 223 is arranged. The arrangement of the insulating layer 224 can reduce the possibility of short circuit between the positive electrode tab 22 and the negative electrode tab 21, and is conducive to improving the safety of the secondary battery 100.

[0096] In some embodiments, as shown in Figure 8 and Figure 9 For the electrode assembly 20 with the winding structure or the laminated structure, when the negative electrode lug 214 is integrally arranged with the negative electrode current collector 211 and the positive electrode lug 223 is integrally arranged with the positive electrode current collector 221, the electrode assembly 20 further includes a first adapter 30 and a second adapter 40. The negative electrode lug 214 is provided with a plurality of negative electrode lugs 214, the plurality of negative electrode lugs 214 are stacked to form a negative electrode lug bundle, the first adapter 30 is welded to the negative electrode lug bundle, and a part of the first adapter 30 is exposed to the shell 10; the positive electrode lug 223 is provided with a plurality of positive electrode lugs 223, the plurality of positive electrode lugs 223 are stacked to form a positive electrode lug bundle, the second adapter 40 is welded to the positive electrode lug bundle, and a part of the second adapter 40 is exposed to the shell 10.

[0097] In some embodiments, the positive current collector 221 and the negative current collector 211 are both metal layers. As an exemplary example, the positive current collector 221 can be a metal layer including at least one of aluminum, nickel, tantalum, titanium, such as an aluminum foil. The negative current collector 211 can be a metal layer including at least one of copper, nickel, tantalum, titanium, such as a copper foil.

[0098] In some embodiments, the positive active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganate.

[0099] In some embodiments, the negative active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, silicon-carbon material.

[0100] In some embodiments, the negative tab 214 and the positive tab 223 are disposed on the same side or on different sides of the electrode assembly 20.

[0101] In some embodiments, as shown in FIG. 1A, the negative tab 214 and the positive tab 223 are disposed on the same side of the electrode assembly 20. Figure 5 and Figure 6 In some embodiments, as shown in FIG. 1A, the negative tab 214 and the positive tab 223 are disposed on the same side of the electrode assembly 20.

[0102] It should be noted that, as shown in FIG. 1A, Figure 3 Figure 3 ​The definitions of the first portion 2151, the second portion 2152 and the third portion 2153 are as follows: along the thickness direction of the negative plate 21, when the projection of a certain portion of the first gel coating 215 is located inside the negative current collector 211, if the portion is on the same side of the negative current collector 211 as the first surface 2111, the portion belongs to the first portion 2151, if the portion is on the same side of the negative current collector 211 as the second surface 2112, the portion belongs to the second portion 2152, and the rest is the third portion 2153. In addition, the division of the first portion 2151, the second portion 2152 and the third portion 2153 is the division of the overall structure of the first gel coating 215, and does not mean that the first gel coating 215 is formed by splicing three independent structures, in other words, the first gel coating 215 can be assembled by multiple components, or can be a one-piece structure.

[0103] It should be noted that the first portion 2151 provided on the first surface 2111 is any one of the following cases: first, the first portion 2151 is provided on one side of the first negative active material layer 212 along the length or width direction of the negative current collector 211, the first portion 2151 is in contact with or separated from the first negative active material layer 212, the surface of the first portion 2151 facing the negative current collector 211 only contacts the first surface 2111, and more commonly, the first portion 2151 is in contact with the first negative active material layer 212; second, the first negative active material layer 212 is provided between the first portion 2151 and the first surface 2111, and the surface of the first portion 2151 facing the negative current collector 211 only contacts the first negative active material layer 212; third, the first negative active material layer 212 is provided between the first portion 2151 and the first surface 2111, and the surface of the first portion 2151 facing the negative current collector 211 is partially in contact with the first negative active material layer 212 and partially in contact with the first surface 2111.

[0104] The second portion 2152 provided on the second surface 2112 includes the following cases: first, as shown in FIG. 21B, the second portion 2152 is provided on one side of the second negative active material layer 213 along the length or width direction of the negative current collector 211, the second portion 2152 is in contact with or separated from the second negative active material layer 213, the surface of the second portion 2152 facing the negative current collector 211 only contacts the second surface 2112, and more commonly, the second portion 2152 is in contact with the second negative active material layer 213; second, as shown in FIG. 21C, the second negative active material layer 213 is provided between the second portion 2152 and the second surface 2112, and the surface of the second portion 2152 facing the negative current collector 211 only contacts the second negative active material layer 213; third, as shown in FIG. 21D, the second negative active material layer 213 is provided between the second portion 2152 and the second surface 2112, and the surface of the second portion 2152 facing the negative current collector 211 is partially in contact with the second negative active material layer 213 and partially in contact with the second surface 2112. Figure 7 Figure 4 ​As shown, the second negative electrode active material layer 213 is disposed between the second part 2152 and the second surface 2112, and the surface of the second part 2152 facing the negative electrode current collector 211 is in contact with the second negative electrode active material layer 213 only; thirdly, the second negative electrode active material layer 213 is disposed between the second part 2152 and the second surface 2112, and a portion of the surface of the second part 2152 facing the negative electrode current collector 211 is in contact with the second negative electrode active material layer 213 and a portion is in contact with the second surface 2112.

[0105] In this secondary battery 100, by providing a first colloidal coating 215 to wrap and bind the edge of the negative electrode current collector 211, at least the following two beneficial effects can be achieved: (1) Wrapping the burrs on the edge of the negative electrode current collector 211 can reduce the possibility that the burrs on the edge of the negative electrode current collector 211 will puncture the protective layer of the casing 10, thereby helping to reduce the possibility of corner corrosion of the secondary battery 100; (2) Binding the burrs on the edge of the negative electrode current collector 211 reduces the possibility that the burrs will fall between the negative electrode plate 21 and the separator 23 or between the positive electrode plate 22 and the separator 23, reduces the risk of internal short circuit caused by the burrs puncturing the separator 23, and improves the problem of poor K value of the secondary battery 100, where K value refers to the voltage drop per unit time.

[0106] In some embodiments, such as Figure 6 As shown, along the thickness direction of the negative electrode sheet 21, at least a portion of the first part 2151 is stacked on a portion of the surface of the first negative electrode active material layer 212 facing away from the first surface 2111. The first part 2151 can bind the first negative electrode active material layer 212, reducing the possibility of active material falling off from the first negative electrode active material layer 212, thereby reducing the possibility of internal short circuit in the secondary battery 100 and improving the problem of poor K value in the secondary battery 100.

[0107] In some embodiments, such as Figure 6 As shown, along the thickness direction of the negative electrode sheet 21, at least a portion of the second portion 2152 is stacked on a portion of the surface of the second negative electrode active material layer 213 on the side opposite to the second surface 2112. The second portion 2152 can bind the second negative electrode active material layer 213, reducing the possibility of active material falling off from the second negative electrode active material layer 213, thereby reducing the possibility of internal short circuit in the secondary battery 100 and improving the K-value defect problem of the secondary battery 100.

[0108] In some embodiments, such as Figure 10As shown, the negative tab 214 is integrally arranged with the negative current collector 211, and the negative tab 214 and the first gel coating layer 215 are arranged on the same side of the negative current collector 211. The first gel coating layer 215 can wrap and bind burrs generated in the process of die-cutting the negative tab 214, reduce the possibility of the burrs piercing the protective layer of the shell 10, and also reduce the possibility of the burrs piercing the separator 23.

[0109] In some embodiments, the negative tab 214 is integrally arranged with the negative current collector 211, and the negative tab 214 and the first gel coating layer 215 are arranged on different sides of the negative current collector 211. The first gel coating layer 215 is not blocked by the negative tab 214 when arranged, which is conducive to reducing the difficulty of arranging the first gel coating layer 215.

[0110] In some embodiments, as shown in FIG. 2A, the first gel coating layer 215 is arranged on the negative tab 214. Figure 2 As shown, along the first direction X, the width of the negative tab 21 is D1, the width of the positive tab 22 is D2, D1>D2, the third face 2113 is located at one end of the negative tab 21 along the first direction X, and both ends of the negative tab 21 along the first direction X exceed the positive tab 22. This is conducive to increasing the CB (Cell Balance, ratio of unit area negative electrode capacity to unit area positive electrode capacity) of the positive and negative tabs and reducing the possibility of lithium precipitation of the electrode assembly during the cycle process.

[0111] In some embodiments, as shown in FIG. 2A, the first gel coating layer 215 is arranged on the negative tab 214. Figure 2 As shown, the first gel coating layer 215 is located on the part of the negative tab 21 that exceeds the positive tab 22 in the first direction X. In this way, the influence of the arrangement of the first gel coating layer 215 on the thickness of the entire electrode assembly 20 can be reduced as much as possible.

[0112] In some embodiments, as shown in FIG. 2A, the first gel coating layer 215 is arranged on the negative tab 214. Figure 2 As shown, along the first direction X, the distance from the third face 2113 to the positive tab 22 is L1. The value of L1 is measured by the following method: a CCD length measuring instrument measures the width of the negative current collector 211 along the first direction X, which is recorded as the first width, a CCD length measuring instrument measures the width of the positive current collector 221 along the first direction X, which is recorded as the second width, and L1=(first width-second width) / 2.

[0113] In some embodiments, as shown in FIG. 2A, the first gel coating layer 215 is arranged on the negative tab 214. Figure 5 and Figure 6 As shown, the first negative active material layer 212 extends to the edge of the negative current collector 211 where the first gel coating layer 215 is arranged, and along the thickness direction of the negative tab 21, the first part 2151 is arranged on the surface of the part of the first negative active material layer 212 away from the first face 2111.

[0114] In some embodiments, as shown in FIG. 2A, the first gel coating layer 215 is arranged on the negative tab 214. Figure 5 and Figure 6As shown, the width of the first portion 2151 and the laminated region of the first negative active material layer 212 along the first direction X is W1, and W1 satisfies: 0.1L1≤W1≤0.5L1. W1≥0.1L1, the width of the first portion 2151 covering the first negative active material layer 212 is not too small, which is conducive to reducing the possibility of active material detachment of the first negative active material layer 212; W1≤0.5L1, the distance between the first portion 2151 and the positive electrode sheet 22 is not too close, which is conducive to reducing the possibility of the positive electrode sheet 22 and the first portion 2151 being laminated along the thickness direction of the negative electrode sheet 21, reducing the influence of the setting of the first portion 2151 on the thickness of the electrode assembly 20, reducing the possibility of the secondary battery 100 losing energy density, and facilitating the electrolyte to infiltrate the electrode assembly 20.

[0115] Here, the laminated region of the first portion 2151 and the first negative active material layer 212 refers to the region of the first negative active material layer 212 along the thickness direction of the negative electrode sheet 21, the surface of which away from the negative electrode current collector 211 is in contact with the first portion 2151.

[0116] In some embodiments, W1 satisfies: 0.2L1≤W1≤0.4L1. W1≥0.2L1, which is conducive to further reducing the possibility of active material detachment of the first negative active material layer 212; W1≤0.4L1, which is conducive to further reducing the possibility of the positive electrode sheet 22 and the first portion 2151 being laminated along the thickness direction of the negative electrode sheet 21.

[0117] In some embodiments, as shown in Figure 5 and Figure 6 The second negative active material layer 213 extends to the edge of the negative electrode current collector 211 provided with the first gel coating layer 215, and the second portion 2152 is laminated on part of the surface of the side of the second negative active material layer 213 away from the first surface 2111 along the thickness direction of the negative electrode sheet 21.

[0118] In some embodiments, as shown in Figure 5 and Figure 6As shown, along the first direction X, the width of the second portion 2152 and the stacking region of the second negative active material layer 213 is W2, W2 satisfies: 0.1L1≤W2≤0.5L1. W2≥0.1L1, the width of the second portion 2152 covering the second negative active material layer 213 is not too small, which is conducive to reducing the possibility of active material separation of the second negative active material layer 213; W2≤0.5L1, the distance between the second portion 2152 and the positive sheet 22 is not too close, which is conducive to reducing the possibility of the positive sheet 22 and the second portion 2152 being stacked along the thickness direction of the negative sheet 21, reducing the influence of the setting of the first portion 2151 on the thickness of the electrode assembly 20, and reducing the possibility of the energy density of the secondary battery 100 being lost.

[0119] Here, the stacking region of the second portion 2152 and the second negative active material layer 213 refers to the region of the surface of the second negative active material layer 213 away from the negative current collector 211 along the thickness direction of the negative sheet 21 and in contact with the second portion 2152.

[0120] In some embodiments, W2 satisfies: 0.2L1≤W2≤0.4L1. W2≥0.2L1 is conducive to further reducing the possibility of active material separation of the first negative active material layer 212; W2≤0.4L1 is conducive to further reducing the possibility of the positive sheet 22 and the second portion 2152 being stacked along the thickness direction of the negative sheet 21.

[0121] In some embodiments, as shown in Figure 2 and Figure 6 The thickness of the positive sheet 22 is T. Along the thickness direction of the negative sheet 21, the maximum distance from the surface of the first portion 2151 to the first surface 2111 is greater than the thickness of the first negative active material layer 212, and the maximum distance from the surface of the first portion 2151 to the surface of the first negative active material layer 212 is T1; along the thickness direction of the negative sheet 21, the maximum distance from the surface of the second portion 2152 to the second surface 2112 is greater than the thickness of the second negative active material layer 213, and the maximum distance from the surface of the second portion 2152 to the surface of the second negative active material layer 213 is T2, T1+T2≤T. In the electrode assembly 20 of the stacking type, the first portion 2151 and the second portion 2152 of the adjacent two negative sheets 21 are oppositely arranged, and in the electrode assembly 20 of the winding type, the first portion 2151 and the second portion 2152 of the negative sheet 21 after winding are opposite, setting T1+T2≤T is conducive to reducing the possibility of the first portion 2151 and the second portion 2152 being in contact, reducing the influence of the setting of the first gel coating 215 on the thickness of the electrode assembly 20, and reducing the possibility of the energy density of the secondary battery 100 being lost.

[0122] Note that the thickness of the positive electrode sheet 22 refers to the thickness of one positive current collector 221 and two positive active material layers 222.

[0123] In some embodiments, T, T1 and T2 satisfy: 0.1T≤T1≤0.5T; 0.1T≤T2≤0.5T. Setting T1≥0.1T, T2≥0.1T, T1 and T2 are not too small, which is conducive to ensuring the wrapping and binding effect of the first gelatinous coating 215 on the burr, setting T1≤0.5T, T2≤0.5T, which is conducive to reducing the impact of the setting of the first gelatinous coating 215 on the thickness of the electrode assembly 20, and facilitating the electrolyte to infiltrate the electrode assembly 20.

[0124] In some embodiments, T, T1 and T2 satisfy: 0.2T≤T1≤0.4T; 0.2T≤T2≤0.4T. Setting 0.2T≤T1, 0.2T≤T2, which is conducive to further enhancing the wrapping and binding effect of the first gelatinous coating 215 on the burr, setting T1≤0.4T, T2≤0.4T, which is conducive to further reducing the impact of the setting of the first gelatinous coating 215 on the thickness of the electrode assembly 20.

[0125] In the embodiment where the negative current collector 211 is integrally provided with the negative tab 214, the first negative active material layer 212 and the second negative active material layer 213 each include a main body region and a thinned region. The thinned region is formed because, when the first negative active material layer 212 and the second negative active material layer 213 are coated, an empty foil region of the negative current collector 211 that is not covered by the first negative active material layer 212 and the second negative active material layer 213 needs to be left out. The negative tab 214 is formed by die cutting the negative current collector 211 from the empty foil region. At the edge of the first negative active material layer 212 and the second negative active material layer 213 close to the empty foil region, the negative active material flows in the direction of the empty foil region and a thinned region appears. The thickness of the first negative active material layer 212 and the second negative active material layer 213 in the thickness direction of the negative electrode sheet 21 in the thinned region is smaller than the thickness of the main body region. When T1 is measured, if the first negative active material layer 212 has a thinned region, T1 refers to the maximum distance from the surface of the first portion 2151 to the surface of the main body region of the first negative active material layer 212. When T2 is measured, if the second negative active material layer 213 has a thinned region, T2 refers to the maximum distance from the surface of the second portion 2152 to the surface of the main body region of the second negative active material layer 213.

[0126] It should be added that, as Figure 7As shown, for the scheme in which the first portion 2151 is not completely overlaid on the partial surface of the side of the first negative active material layer 212 facing away from the first surface 2111, T1 is still the maximum distance from the surface of the first portion 2151 to the surface of the first negative active material layer 212; for the scheme in which the second portion 2152 is not completely overlaid on the partial surface of the side of the second negative active material layer 213 facing away from the first surface 2111, T2 is still the maximum distance from the surface of the second portion 2152 to the surface of the second negative active material layer 213.

[0127] In the foregoing embodiments, when measuring T, a section can be taken from the positive electrode sheet 22, and the section along the thickness direction of the positive electrode sheet 22 is observed under 5-25 times magnification using an optical microscope (OM) and the thickness thereof is measured. When measuring W1, W2, T1 and T2, a section can be taken from the negative electrode sheet 21, and the section along the thickness direction of the negative electrode sheet 21 is observed under 5-25 times magnification using an optical microscope (OM). Specifically, when measuring T1, a tangent line is made at the first portion 2151, the tangent line is perpendicular to the thickness direction of the negative electrode sheet 21, a connecting line is made between the tangent line and the surface of the first negative active material layer 212, the connecting line is perpendicular to the tangent line, and the length of the connecting line is T1; when measuring T2, a tangent line is made at the second portion 2152, the tangent line is perpendicular to the thickness direction of the negative electrode sheet 21, a connecting line is made between the tangent line and the surface of the second negative active material layer 213, the connecting line is perpendicular to the tangent line, and the length of the connecting line is T2; when measuring W1, the distance from the end surface of the negative current collector 211 to the edge of the first portion 2151 on the surface of the first negative active material layer 212 is W1, the end surface of the negative current collector 211 refers to the end surface thereof on the same side as the first gel coating layer 215 in the first direction X; and when measuring W2, the distance from the end surface of the negative current collector 211 to the edge of the second portion 2152 on the surface of the second negative active material layer 213 is W2, the end surface of the negative current collector 211 refers to the end surface thereof on the same side as the first gel coating layer 215 in the first direction X.

[0128] In some embodiments, as shown in FIGS. 1A and 1B, the negative current collector 211 includes a third surface 2113, the third surface 2113 is opposite to the first surface 2111 along the first direction X, and the third surface 2113 is connected to the first surface 2111 and the second surface 2112. Figure 6 and Figure 7 As shown, the negative current collector 211 includes a sixth surface 2114, the third surface 2113 and the sixth surface 2114 are opposite to each other along the first direction X, and the sixth surface 2114 is connected to the first surface 2111 and the second surface 2112. The negative electrode sheet 21 includes a second gel coating layer 216, the second gel coating layer 216 includes a fourth portion 2161, a fifth portion 2162 and a sixth portion 2163, Figure 4The boundaries of the fourth part 2161, the fifth part 2162, and the sixth part 2163 are indicated by a dashed line. The fourth part 2161 is located on the first surface 2111, the fifth part 2162 is located on the second surface 2112, and the sixth part 2163 is located on the sixth surface 2114, connecting the fourth part 2161 and the fifth part 2162. This allows burrs to be wrapped and restrained from both opposite sides of the negative electrode 21, further reducing the possibility of burrs on the edge of the negative current collector 211 piercing the protective layer of the casing 10. It also further reduces the possibility of burrs falling between the negative electrode 21 and the separator 23 or between the positive electrode 22 and the separator 23, thus lowering the risk of internal short circuits caused by burrs piercing the separator 23.

[0129] In some embodiments, the diaphragm 23 adheres to the first colloidal coating 215, which helps to reduce the possibility of relative movement between the negative electrode 21 and the positive electrode 22.

[0130] In some embodiments, the diaphragm 23 is also bonded with a second colloidal coating 216, which helps to further reduce the possibility of relative movement between the negative electrode 21 and the positive electrode 22.

[0131] In some embodiments, at least one of the first colloidal coating 215 and the second colloidal coating 216 is made of a hot melt resin.

[0132] In some embodiments, the hot melt resin is selected from at least one of ethylene-vinyl acetate copolymer and polyethylene oxide.

[0133] In some embodiments, the material of at least one of the first colloidal coating 215 and the second colloidal coating 216 further includes a tackifier.

[0134] In some embodiments, the tackifier is at least one of acrylic resin, EVA resin, and polyurethane.

[0135] In some embodiments, the hot melt resin has a mass percentage content of 50wt% to 90wt% in the first colloidal coating 215 or the second colloidal coating 216, and the tackifier has a mass percentage content of 10wt% to 50wt% in the first colloidal coating 215 or the second colloidal coating 216.

[0136] In some embodiments, at least one of the first colloidal coating 215 and the second colloidal coating 216 may further include a cellulose reinforcement.

[0137] like Figure 12 As shown, embodiments of this application also provide an electrical device, which includes a secondary battery 100 as described in any of the foregoing embodiments.

[0138] In some embodiments, the electrically powered devices include, but are not limited to, mobile phones, watches, notebook computers, power tools, and electric toys.

[0139] Embodiments of the present application also provide a negative electrode sheet 21 manufacturing method, which comprises the following steps:

[0140] Setting a negative electrode active material layer: coating a negative electrode active material on at least part of the surface of the first face 2111 to form a first negative electrode active material layer 212, and coating a negative electrode active material on at least part of the surface of the second face 2112 to form a second negative electrode active material layer 213.

[0141] Setting a first gel coating layer 215: coating a polymer material on part of the first face 2111, the third face 2113, and part of the second face 2112 to form the first gel coating layer 215.

[0142] In some embodiments, the negative electrode sheet 21 manufacturing method comprises the following steps:

[0143] Welding: welding the negative electrode tab 214 to the part of the divided negative electrode current collector 211 that is not covered by the negative electrode active material layer. The part not covered by the negative electrode active material layer can be the end portion in the length direction of the negative electrode sheet 21, or the middle portion in the length direction of the negative electrode sheet 21. If the tab is welded to the middle portion in the length direction of the negative electrode sheet 21, part of the negative electrode active material layer needs to be removed after coating the negative electrode active material layer to form an empty foil area for welding the tab. The method for removing the negative electrode active material layer includes: using laser etching to remove, or pasting foam tape or tearable tape on the area where the negative electrode active material needs to be removed before coating the negative electrode active material layer.

[0144] It should be noted that the steps of setting the first gel coating layer 215 and welding do not have strict time sequence requirements. The first gel coating layer 215 can be set first and then welded, or the welding can be performed first and then the first gel coating layer 215 is set.

[0145] In some embodiments, the negative electrode sheet 21 manufacturing method comprises the following steps:

[0146] Die cutting: the negative electrode current collector 211 has an empty foil area that is not covered by the first negative electrode active material layer 212 and the second negative electrode active material layer 213, and the empty foil area is die cut to form a plurality of negative electrode tabs 214; the face of the negative electrode current collector 211 located on the side where the negative electrode tab 214 is provided is the third face 2113; or, the face of the negative electrode current collector 211 formed on the side opposite to the negative electrode tab 214 in the dividing step is the third face 2113; both the first negative electrode active material layer 212 and the second negative electrode active material layer 213 extend to the edge of the negative electrode current collector 211 on the same side as the third face 2113.

[0147] It is to be noted that when the third face 2113 is the face of the negative current collector 211 on the side where the negative tab 214 is provided, the first gel coating layer 215 is provided after the die cutting, and when the third face 2113 is the face of the negative current collector 211 on the side opposite to the negative tab 214, the step of die cutting and the step of providing the first gel coating layer 215 do not have strict time sequence requirements, and the first gel coating layer 215 can be provided after the die cutting or the die cutting can be performed after the first gel coating layer 215 is provided.

[0148] In some embodiments, the negative tab 21 manufacturing method further comprises the following steps:

[0149] The second gel coating layer 216 is provided: the negative current collector 211 comprises a sixth face 2114, the third face 2113 and the sixth face 2114 are oppositely arranged along the first direction, and the sixth face 2114 connects the first face 2111 and the second face 2112; a polymer material is coated on part of the first face 2111, the sixth face 2114 and part of the second face 2112 to form the second gel coating layer 216.

[0150] To verify the influence of the dimensions of the first gel coating layer 215 on the performance of the secondary battery 100, the inventors conducted the following experiments:

[0151] The experiments include one group of comparative examples and 14 groups of embodiments, and each group of comparative examples and embodiments includes 35 secondary batteries 100. The secondary batteries 100 used in the comparative examples do not have the first gel coating layer 215 on the negative tab 21, the secondary batteries 100 in the embodiments have the first gel coating layer 215 on the negative tab 21, and the rest are the same. The secondary batteries 100 in different groups of embodiments only differ in the parameters listed in Table 1 below, and the rest are the same.

[0152] The assembly process of the secondary batteries in the comparative examples is as follows:

[0153] (1) Preparation of the positive electrode sheet 22: An active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material having a solid content of 75 wt%, which was then stirred uniformly. An aluminum foil having a thickness of 10 pm was used as the positive electrode current collector 221. The positive electrode active material was uniformly coated on the fourth face 2211 of the positive electrode current collector 221 using a slot coater, and then dried at 90°C to obtain a positive electrode sheet 22 having the positive electrode active material coated on one side. At this time, the thickness of the positive electrode active material layer 222 in the thickness direction of the positive electrode current collector 221 was 90 pm. The above coating step was repeated on the fifth face 2212 of the positive electrode current collector 221. The coated positive electrode sheet 22 was then cold-pressed, and the thickness of the positive electrode active material layer 222 after cold-pressing was 80 pm. Thereafter, the positive electrode tab 223 was welded to the portion of the positive electrode current collector 221 that was not covered by the positive electrode active material layer 222, which was the end portion in the length direction of the positive electrode sheet 22.

[0154] (2) Preparation of the negative electrode sheet 21: An active material, artificial graphite, conductive carbon black (Super P), styrene butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2, and deionized water was added as a solvent to prepare a negative electrode active material having a weight percentage of 50 wt%, which was then stirred uniformly. A copper foil having a thickness of 10 pm was used as the negative electrode current collector 211. The negative electrode active material was uniformly coated on the first face 2111 of the negative electrode current collector 211 using a slot coater, and then dried at 110°C to obtain a negative electrode sheet 21 having a first negative electrode active material layer 212 coated thereon. The above step was repeated on the second face 2112 of the negative electrode current collector 211 to obtain a negative electrode sheet 21 having a second negative electrode active material layer 213 coated thereon. At this time, the thickness of the first negative electrode active material layer 212 and the second negative electrode active material layer 213 in the thickness direction of the negative electrode current collector 211 was 90 pm. The coated negative electrode sheet 21 was then cold-pressed, and the thickness of the first negative electrode active material layer 212 and the second negative electrode active material layer 213 after cold-pressing was 80 pm. Thereafter, the negative electrode tab 214 was welded to the portion of the negative electrode current collector 211 that was not covered by the first negative electrode active material layer 212 and the second negative electrode active material layer 213, which was the end portion in the length direction of the negative electrode sheet 21.

[0155] (3) Preparation of electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of EC: EMC: DEC = 30: 50: 20 to form a base organic solvent, then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base organic solvent to dissolve and mix uniformly, to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0156] (4) Preparation of separator film: A 7 μm thick polyethylene porous polymer film was used as the separator film.

[0157] (5) Preparation of electrode assembly 20: The positive electrode sheet 22, the separator film and the negative electrode sheet 21 were stacked along the thickness direction of the negative electrode sheet 21 and then wound to obtain the electrode assembly 20.

[0158] (6) Assembly of secondary battery 100: The punched aluminum plastic film was placed in the assembly fixture with the pit surface facing up, and the electrode assembly 20 was placed in the pit and pressed tightly. Then another punched aluminum plastic film was placed on the electrode assembly 20 with the pit surface facing down, and the three edges of the two aluminum plastic films were heat sealed by hot pressing, and the unsealed edge was the side of the shell 10 where the negative tab 214 and the positive tab 223 protruded. Then the electrolyte was injected through the unsealed edge, and the secondary battery 100 was obtained after vacuum packaging, standing, hot pressing, shaping and other processes.

[0159] The manufacturing method of the negative electrode sheet 21 in the secondary battery 100 in Examples 1-14 further includes the setting step of the first gel coating 215 in the foregoing content, and the other preparation processes and parameters are the same as those of the comparative example. Within the allowable range of manufacturing errors, the secondary batteries 100 in Examples 1-14 satisfy T1 = T2 and W1 = W2.

[0160] After the preparation of the secondary batteries 100 in the comparative example and Examples 1-14, the thickness of the secondary batteries 100 in the group was measured and the pressure drop per unit time was tested.

[0161] The method for measuring the thickness was to measure the thickness of the secondary battery under the condition of 700 g of force by using a flat plate thickness gauge (PPG).

[0162] The method for testing the pressure drop per unit time was to measure the voltage of the secondary battery 100 when it stored 60% of the capacity under the condition of 25±5℃, and record it as the first voltage. After standing for 48 hours, the voltage was measured again, and recorded as the second voltage. The pressure drop per unit time was recorded as K, K = (first voltage-second voltage) / standing time. The average value of the pressure drop per unit time in the comparative example and the examples was the average value of the pressure drop per unit time of 35 secondary batteries in the group.

[0163] After the pressure drop per unit time is measured, 10 secondary batteries 100 are randomly selected from each group for drop experiments, and another 10 secondary batteries 100 are randomly selected for cycle tests.

[0164] The drop experiment includes the following steps:

[0165] (1) The voltage of the secondary battery 100 at 25±5°C is tested, and is recorded as the third voltage.

[0166] (2) The secondary battery 100 is placed in a drop fixture (fixture weight 150g, PP material), and is dropped from a height of 1.5m to a cement floor in the up, down, left, right, front, back, upper left corner, upper right corner, lower right corner, and lower left corner directions of the secondary battery 100, respectively, for one round, and is tested for three rounds.

[0167] (3) After 48h of standing at 25±5°C, the voltage of the secondary battery 100 is tested again, and the test result is recorded as the fourth voltage. The pressure drop of each secondary battery 100 after 48h of three rounds of drop is the third voltage minus the fourth voltage. The average pressure drop of each group after 48h of three rounds of drop is the average value of the pressure drop of the 10 secondary batteries in the group after 48h of three rounds of drop.

[0168] The cycle test includes the following steps:

[0169] (1) The secondary battery 100 prepared above is charged at a constant current of 0.5C, charged at a constant voltage of 0.05C to the upper limit cutoff voltage, and is left to stand for 10min, and is discharged at 1C to the lower limit cutoff voltage, and is left to stand for 10min. The above process is recorded as one cycle (1cl), and the above charge and discharge process is repeated 800 times (800cls).

[0170] (2) The secondary battery 100 is disassembled, and the lithium precipitation is observed, and is recorded as no lithium precipitation, slight lithium precipitation, and moderate lithium precipitation according to the degree of lithium precipitation, wherein no lithium precipitation: lithium precipitation area is equal to 0; slight lithium precipitation: 0 < lithium precipitation area / negative electrode area ≤ 5%; moderate lithium precipitation: 5% < lithium precipitation area / negative electrode area ≤ 15%; severe lithium precipitation: 15% < lithium precipitation area / negative electrode area. Here, the negative electrode area refers to the area of the negative electrode active material layer (the area of the first negative electrode active material layer 212 or the second negative electrode active material layer 213) where lithium crystals are precipitated.

[0171] After the experiment, the experimental data is arranged to obtain Table 1 as follows:

[0172] Table 1

[0173]

[0174] Note: " / " represents no experimental data.

[0175] As can be seen from the comparison between the comparative example and any one of examples 1-14, when the first gel coating 215 is not provided, the pressure drop of the secondary battery 100 after falling is larger, and the average value of the pressure drop per unit time is also larger. It can be seen that, by providing the first gel coating 215, the possibility of the burr falling between the positive plate and the separator or between the negative plate and the separator can be reduced, which is conducive to improving the problem of poor K value (i.e., voltage drop per unit time) of the secondary battery 100.

[0176] In examples 3-7, W1 satisfies 0.1L1≤W1≤0.5L1. Compared with examples 1-2, the average thickness of the secondary battery only slightly increases, and the average value of the pressure drop per unit time and the average pressure drop after 3 rounds of falling for 48H are both significantly reduced. It can be seen that, under this condition, the width of the first portion 2151 covering the first negative active material layer 212 is not too small, which is conducive to reducing the possibility of active material separation of the first negative active material layer 212. Compared with example 8, the secondary battery in examples 3-7 does not appear lithium precipitation in the 800c l s cycle test. It can be seen that, under this condition, the width of the first portion 2151 covering the first negative active material layer 212 is not too large, which is conducive to the electrolyte wetting the electrode assembly 20.

[0177] The secondary batteries in examples 10-13 satisfy 0.1T≤T1≤0.5T. Compared with example 9, the average thickness of the secondary battery only slightly increases, and the average value of the pressure drop per unit time and the average pressure drop after 3 rounds of falling for 48H are both significantly reduced. It can be seen that, under this condition, the maximum distance from the surface of the first portion 2151 to the surface of the first negative active material layer 212 is not too small, which is conducive to ensuring the wrapping and binding effect of the first gel coating 215 on the burr. Compared with example 14, the secondary battery in examples 10-13 does not appear lithium precipitation in the 800c l s cycle test. It can be seen that, under this condition, the maximum distance from the surface of the first portion 2151 to the surface of the first negative active material layer 212 is not too large, which is conducive to the electrolyte wetting the electrode assembly 20.

[0178] Those skilled in the art should understand that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application. Any appropriate changes and variations made to the above examples within the spirit and principles of the present application fall within the disclosure range of the present application.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode, a positive electrode, and a separator, wherein the negative electrode, the separator, and the positive electrode are stacked sequentially along the thickness direction of the negative electrode. The negative electrode includes: The negative electrode current collector includes a first surface and a second surface disposed opposite to each other along the thickness direction of the negative electrode sheet. The negative electrode current collector also includes a third surface located at one end of the negative electrode sheet along a first direction, the first direction being perpendicular to the thickness direction of the negative electrode sheet. The third surface connects the first surface and the second surface. A first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer is disposed on the first surface and the second negative electrode active material layer is disposed on the second surface; A first colloidal coating is connected to the negative electrode current collector. The first colloidal coating includes a first part, a second part, and a third part. The first part is connected to the first surface, the second part is connected to the second surface, and the third part is disposed on the third surface and connects the first part and the second part. Along the thickness direction of the negative electrode sheet, the projection of the first part lies within the first surface, and the projection of the second part lies within the second surface; Along the first direction, the distance from the third surface to the positive electrode is L1; Along the first direction, the width of the overlapping area between the first portion and the first negative electrode active material layer is W1, where W1 satisfies: 0.1L1≤W1≤0.5L1; The thickness of the positive electrode sheet is T, the maximum distance from the surface of the first part to the surface of the first negative electrode active material layer is T1, and the maximum distance from the surface of the second part to the surface of the second negative electrode active material layer is T2. T, T1 and T2 satisfy: 0.1T≤T1≤0.5T; 0.1T≤T2≤0.5T.

2. The secondary battery as described in claim 1, characterized in that, Along the thickness direction of the negative electrode sheet, at least a portion of the first portion is stacked on a portion of the surface of the first negative electrode active material layer facing away from the first surface; and / or Along the thickness direction of the negative electrode sheet, at least a portion of the second part is stacked on a portion of the surface of the second negative electrode active material layer on the side opposite to the second surface.

3. The secondary battery as described in claim 1, characterized in that, The negative electrode, the separator, and the positive electrode are stacked in sequence and then wound to form a wound structure; The negative electrode sheet also includes a negative electrode tab, which is welded to the negative electrode current collector; The positive electrode sheet includes a positive current collector, a positive active material layer, and a positive tab. The positive current collector includes a fourth surface and a fifth surface disposed opposite to each other along its thickness direction. One positive active material layer is disposed on the fourth surface, and one positive active material layer is disposed on the fifth surface. The positive tab is welded to the positive current collector.

4. The secondary battery as described in claim 1, characterized in that, The negative electrode, the separator, and the positive electrode are stacked in sequence and then wound to form a wound structure; The negative electrode sheet also includes a negative electrode tab, which is integrally disposed with the negative electrode current collector; The positive electrode sheet includes a positive current collector, a positive active material layer, and a positive tab. The positive current collector includes a fourth surface and a fifth surface disposed opposite to each other along the thickness direction of the positive electrode sheet. One positive active material layer is disposed on the fourth surface, and one positive active material layer is disposed on the fifth surface. The positive tab is integrally disposed with the positive current collector.

5. The secondary battery as described in claim 1, characterized in that, Multiple negative electrode sheets, multiple separators, and multiple positive electrode sheets are stacked along the thickness direction of the negative electrode sheets to form a stacked structure, and adjacent negative electrode sheets and positive electrode sheets are separated by the separators; The negative electrode sheet also includes a negative electrode tab, which is integrally disposed with the negative electrode current collector; The positive electrode sheet includes a positive current collector, a positive active material layer, and a positive tab. The positive current collector includes a fourth surface and a fifth surface disposed opposite to each other along the thickness direction of the positive electrode sheet. The positive active material layer is disposed on at least one of the fourth surface and the fifth surface. The positive tab is integrally disposed with the positive current collector.

6. The secondary battery as described in claim 2, characterized in that, Along the first direction, the width of the negative electrode is D1, and the width of the positive electrode is D2, where D1 > D2; Both ends of the negative electrode sheet extend beyond the positive electrode sheet along the first direction; The first colloidal coating is located on the portion of the negative electrode sheet that extends beyond the positive electrode sheet in the first direction.

7. The secondary battery as described in claim 6, characterized in that, The diaphragm adheres to the first colloidal coating.

8. The secondary battery as described in claim 7, characterized in that, The first negative electrode active material layer extends to the edge of the negative electrode current collector where the first colloidal coating is provided, and along the thickness direction of the negative electrode sheet, the first portion is superimposed on a portion of the surface of the first negative electrode active material layer on the side opposite to the first surface.

9. The secondary battery as described in claim 8, characterized in that, W1 satisfies: 0.2L1≤W1≤0.4L1.

10. The secondary battery as described in claim 7, characterized in that, Along the thickness direction of the negative electrode sheet, the maximum distance from the surface of the first portion to the first surface is greater than the thickness of the first negative electrode active material layer; Along the thickness direction of the negative electrode sheet, the maximum distance from the surface of the second portion to the second surface is greater than the thickness of the second negative electrode active material layer; T1+T2≤T.

11. The secondary battery as described in claim 10, characterized in that, T, T1, and T2 satisfy: 0.2T≤T1≤0.4T; 0.2T≤T2≤0.4T.

12. The secondary battery as described in claim 1, characterized in that, The negative electrode current collector includes a sixth surface, the third surface and the sixth surface are arranged opposite to each other along the first direction, and the sixth surface connects the first surface and the second surface; The negative electrode sheet includes a second colloidal coating, which includes a fourth part, a fifth part, and a sixth part. The fourth part is disposed on a portion of the first surface, the fifth part is disposed on a portion of the second surface, and the sixth part is disposed on the sixth surface. The sixth part connects the fourth part and the fifth part.

13. The secondary battery as described in claim 1, characterized in that, The material of the first colloidal coating includes a hot melt resin.

14. The secondary battery as described in claim 13, characterized in that, The hot melt resin is selected from at least one of ethylene-vinyl acetate copolymer and polyethylene oxide.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-14.

16. A method for manufacturing a negative electrode sheet, used to manufacture the negative electrode sheet in the secondary battery as described in claim 1, characterized in that, Includes the following steps: A negative electrode active material layer is formed by coating at least a portion of the surface of the first side with a negative electrode active material to form the first negative electrode active material layer; and by coating at least a portion of the surface of the second side with a negative electrode active material to form the second negative electrode active material layer. A first colloidal coating is formed by coating a portion of the first surface, the third surface, and a portion of the second surface with a polymer material.

17. The method for manufacturing the negative electrode sheet as described in claim 16, characterized in that, Includes the following steps: A second colloidal coating is provided: the negative electrode current collector includes a sixth surface, the third surface and the sixth surface are arranged opposite to each other along the first direction, and the sixth surface connects the first surface and the second surface; a polymer material is coated on a portion of the first surface, the sixth surface and a portion of the second surface to form the second colloidal coating.

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