Secondary battery and electronic device

Abstract

A secondary battery (100) and an electronic device (1). A secondary battery (100) includes a packaging bag (10) and an electrode assembly (20). The electrode assembly (20) has a wound structure. A negative active material layer (221) of the negative pole piece (22) contains a silicon material, and the mass ratio of the silicon material in the negative active material layer (221) is 4%-50%. The secondary battery (100) also includes one or two positive tabs (30), at least two first negative tabs (40), and a first transfer tab (50). In the thickness direction of the electrode assembly (20), all the first negative electrode tabs (40) are overlapped and connected with the first switching tab (50), and all the positive electrode tabs (30) and the first switching tab (50) extend out of the packaging bag (10) from the same side of the packaging bag (10) and are configured to be electrically connected with an external circuit. One or two first grooves (2110) are formed in a positive electrode active material layer (211) of the positive electrode plate (21); each positive electrode lug (30) is arranged in one first groove (2110) and is electrically connected with the positive electrode current collector (210); and the first negative pole lug (40) and the negative pole current collector (220) of the negative pole piece (22) are integrally arranged and are connected to the end edge of the negative pole current collector (220). The secondary battery (100) can achieve both high energy density and excellent fast charge performance.

Description

Technical Field

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

[0002] Secondary batteries are widely used in electronic products such as electronic mobile devices, power tools, and electric vehicles. Graphite is a widely used negative electrode material in secondary batteries, which has advantages such as high efficiency and stable charge-discharge platforms. However, its low specific capacity per gram hinders the further application of graphite in high-demand fields. Compared with graphite, elemental silicon has a higher theoretical specific capacity, and when used as a negative electrode material, it can improve the energy density of secondary batteries.

[0003] However, silicon has poor electrical conductivity, and the transport of electrons in the silicon bulk phase and the diffusion of active ions are easily blocked, resulting in a decrease in the kinetic performance of secondary batteries, an increase in polarization during high-rate charging, and easy lithium plating on the negative electrode plate. Therefore, for secondary batteries with negative electrode materials including silicon materials, how to make secondary batteries have both a high energy density and excellent fast charging performance has become an urgent problem to be solved. Summary of the Invention

[0004] Therefore, this application proposes a secondary battery and an electronic device having the secondary battery that can have both a high energy density and excellent fast charging performance.

[0005] In the first aspect of this application, a secondary battery is provided, including a packaging bag and an electrode assembly disposed in the packaging bag. The electrode assembly is a wound structure, and the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer contains a silicon material, and the mass ratio of the silicon material in the negative electrode active material layer is 4% to 50%. The secondary battery further includes M positive electrode tabs, N first negative electrode tabs, and a first transfer tab. The thickness direction of the electrode assembly is the first direction. In the first direction, the N first negative electrode tabs overlap and are connected to the first transfer tab. The M positive electrode tabs and the first transfer tab extend out of the packaging bag from the same side of the packaging bag and are configured to be electrically connected to an external circuit respectively. M is 1 or 2, and the positive electrode active material layer is provided with M first grooves, and the M positive electrode tabs are respectively disposed in the M first grooves and electrically connected to the positive electrode current collector. N is greater than or equal to 2, the width direction of the negative electrode plate is the second direction, the second direction is perpendicular to the first direction, and the negative electrode current collector includes a first end edge and a second end edge disposed opposite to each other in the second direction. The N first negative electrode tabs are integrally provided with the negative electrode current collector and connected to the first end edge.

[0006] For a secondary battery in which the negative electrode active material layer includes a silicon material, in this application, the positive electrode tab is disposed in the first groove provided in the positive electrode active material layer and electrically connected to the positive electrode current collector, and the positive electrode tab directly extends out of the packaging bag. Therefore, the adapter tab connected to the positive electrode tab can be omitted, and the insulating layer provided on the positive electrode current collector when die-cutting the positive electrode tab can be omitted, which is beneficial to improving the energy density of the secondary battery. At the same time, this application provides at least two first negative electrode tabs connected in parallel for shunting, which is beneficial to reducing the impedance of the negative electrode tab and improving the kinetic performance of the negative electrode tab. Therefore, the uniformity of the current and the insertion speed of lithium ions during charging can be improved. At the same time, the number of positive electrode tabs is set to 1 or 2 and disposed in the groove, which can better balance the kinetics of the positive and negative electrodes in the silicon system, reduce the risk of lithium deposition on the negative electrode tab with a specific silicon content during high-rate charging, and improve the fast charging performance of the secondary battery. Therefore, this application can enable the secondary battery to have both a relatively high energy density and excellent fast charging performance.

[0007] Based on the first aspect, in some possible implementation manners, the positive electrode current collector includes a first surface facing the winding central axis and a second surface facing away from the first surface. The positive electrode current collector includes a first region and a second region connected in the winding direction. The first surface and the second surface of the first region are both provided with a positive electrode active material layer. The first surface of the second region is provided with a positive electrode active material layer, and the second surface of the second region is not provided with a positive electrode active material layer. Along the winding direction, the length of the first region is greater than the length of the second region. M positive electrode tabs are connected to a position from 1 / 3 to 2 / 3 of the length of the first region in the winding direction. This can make the current flowing through the positive electrode tab more uniform, so it can support a higher-rate charge and discharge current, and also make the active ions uniformly de-embed from the positive electrode active material layer, reduce the risk of lithium deposition on the negative electrode tab during high-rate charging, and improve the fast charging performance of the secondary battery.

[0008] Based on the first aspect, in some possible implementation manners, the M positive electrode tabs are connected to the second surface of the first region. When the negative electrode tab expands in volume due to the insertion of active ions, causing the negative electrode tab to undergo an outward expansion deformation from the inside, the risk of short circuit caused by the edge burrs of the positive electrode tab piercing the separator and contacting the negative electrode tab can be reduced.

[0009] Based on the first aspect, in some possible implementation manners, the packaging bag includes a receiving portion for receiving the electrode assembly and a sealing edge connecting the receiving portion. The positive electrode tab and the first transfer tab extend out of the packaging bag from the sealing edge. Along the extending direction of the positive electrode tab within the sealing edge, the sealing edge sequentially includes a first end and a second end disposed opposite to the first end. Define a winding center plane passing through the winding central axis of the electrode assembly and perpendicular to the first direction. The electrode assembly includes a first portion and a second portion respectively located on both sides of the winding center plane. In the first direction, the first portion is closer to the first end than the second portion, and the M positive electrode tabs are all connected to the first portion. In this way, the bending degree of the positive electrode tab within the packaging bag can be made smaller or even not bent. When the secondary battery undergoes an external short-circuit test, even if the temperature rise of the positive electrode tab causes a certain degree of shrinkage of the separator, the risk of short circuit caused by the contact between the positive electrode tab and the edge of the negative electrode sheet can be reduced.

[0010] Based on the first aspect, in some possible implementation manners, the secondary battery further includes a first bonding member that bonds the surface of the second portion and the inner surface of the receiving portion. The first bonding member can fix the electrode assembly and the packaging bag. Moreover, when the secondary battery undergoes mechanical abuse, the impact force will be first transmitted to the second portion of the electrode assembly through the packaging bag and the first bonding member. On the one hand, the first portion is not directly bonded to the packaging bag. On the other hand, since the transfer tab connected to the positive electrode tab is omitted, the space between the first portion and the sealing edge is relatively large, so it has a certain buffering effect. By setting the positions of the positive electrode tab and the first bonding member, the secondary battery can achieve both high external short-circuit test performance and anti-mechanical abuse performance.

[0011] Based on the first aspect, in some possible implementation manners, the M first negative electrode tabs are respectively connected to the first portion and the second portion, and the number of the first negative electrode tabs connected to the first portion is more than the number of the first negative electrode tabs connected to the second portion. In the first direction, there is a first side from the first portion to the second portion and a second side opposite to the first side in terms of orientation. The first negative electrode tab includes a first segment connecting the first end edge and a second segment connecting the first segment. The first segment extends from the first end edge to the first side, and the second segment is bent relative to the first segment and extends along the second side. The first transfer tab is connected to the second segment. By setting the bending direction of the first negative electrode tab, it is beneficial to make full use of the space between the second portion and the sealing edge, and reduce the thickness after folding of the first negative electrode tab, thereby further improving the energy density of the secondary battery.

[0012] Based on the first aspect, in some possible implementation manners, the mass percentage of the silicon material in the negative electrode active material layer is 10% to 30%. This can make the negative electrode active material have a higher specific capacity, further improve the energy density of the secondary battery, and at the same time reduce the risk that when there is more silicon material, the number of the first negative electrode tabs needs to be increased accordingly, resulting in a large occupied space for the first negative electrode tabs.

[0013] Based on the first aspect, in some possible implementation manners, M is 1, the secondary battery further includes P second negative electrode tabs and a second transfer tab, where P is greater than or equal to 2. The P second negative electrode tabs are integrally provided with the negative electrode current collector and connected to the first end edge. In the first direction, the P second negative electrode tabs overlap and are connected to the second transfer tab. The first transfer tab and the second transfer tab extend out of the packaging bag from the same side of the packaging bag, and the second transfer tab is configured to be electrically connected to an external circuit. By adding the second transfer tab and connecting at least two second negative electrode tabs to the second transfer tab, it is beneficial to further reduce the impedance of the negative electrode plate, improve the kinetic performance of the negative electrode plate, thereby further reducing the risk of lithium precipitation in the negative electrode plate during high-rate charging, and improving the fast charging performance of the secondary battery.

[0014] Based on the first aspect, in some possible implementation manners, the electrode assembly includes n negative electrode plates in the first direction, N≤n / 2, and P≤n / 2. It is beneficial to further balance the kinetic performance of the positive electrode plate and the negative electrode plate, and reduce the risk of lithium precipitation in the negative electrode plate during high-rate charging. At the same time, it can also reduce the space occupied by the first negative electrode tab and the second negative electrode tab, improve the energy density of the secondary battery, and also reduce the difficulty of folding tabs and welding, and simplify the manufacturing process.

[0015] Based on the first aspect, in some possible implementation manners, in the third direction perpendicular to both the first direction and the second direction, the positive electrode tab is disposed between the first transfer tab and the second transfer tab. It is beneficial for the positive electrode tab to be connected to a predetermined position of the positive electrode current collector, so that the current flowing through the positive electrode plate is more uniform.

[0016] Based on the first aspect, in some possible implementation manners, in the third direction perpendicular to both the first direction and the second direction, the second transfer tab is disposed between the positive electrode tab and the first transfer tab. Since only the second transfer tab is adjacent to the positive electrode tab, it is beneficial to reduce the short-circuit risk caused by the contact between the positive electrode tab and the first transfer tab, and it is also convenient to simplify the operation in the subsequent wiring process.

[0017] Based on the first aspect, in some possible implementation manners, M is 2, and when observed from the first direction, the two positive electrode tabs are separated. It is beneficial to make the current flowing through the positive electrode plate more uniform, so it can support higher-rate charge and discharge currents, and also make the active ions uniformly intercalate and deintercalate from the positive electrode active material layer, reducing the risk of lithium precipitation in the negative electrode plate during high-rate charging.

[0018] Based on the first aspect, in some possible implementation manners, the electrode assembly includes n negative electrode plates in the first direction, N>2 / n. It is beneficial to further balance the kinetic performance of the positive electrode plate and the negative electrode plate, reduce the risk of lithium precipitation in the negative electrode plate during high-rate charging, and improve the fast charging performance of the secondary battery.

[0019] Based on the first aspect, in some possible implementation manners, the difference in the number of layers of the positive electrode tabs connected to the two positive electrode tabs is 1 to 4. This can make the current flowing through the positive electrode tab more uniform, so it can support a higher rate of charge and discharge current. It can also make the active ions uniformly intercalate and deintercalate from the positive electrode active material layer, reduce the risk of lithium deposition on the negative electrode tab during high-rate charging, and improve the fast charging performance of the secondary battery. At the same time, it is also beneficial to improve the problem of deformation of the electrode assembly during multiple charge and discharge processes.

[0020] Based on the first aspect, in some possible implementation manners, in the third direction perpendicular to both the first direction and the second direction, the first transfer tab is disposed between the two positive electrode tabs. This facilitates simplifying the operation during subsequent wiring, and is also beneficial to increasing the distance between the two positive electrode tabs in the third direction, thereby improving the thickness uniformity of the electrode assembly.

[0021] Based on the first aspect, in some possible implementation manners, in the third direction perpendicular to both the first direction and the second direction, one positive electrode tab is disposed between the first transfer tab and the other positive electrode tab. Since only one positive electrode tab is adjacent to the first transfer tab, it is beneficial to reduce the risk of short circuit caused by the contact between the positive electrode tab and the first transfer tab.

[0022] Based on the first aspect, in some possible implementation manners, the silicon material is selected from at least one of elemental silicon, silicon oxide, silicon-carbon material, and silicon alloy.

[0023] The second aspect of this application further provides an electronic device, which includes a battery compartment and the secondary battery as described above disposed in the battery compartment. The electronic device is powered by the above-mentioned secondary battery, and the secondary battery can balance a relatively high energy density and relatively excellent fast charging performance. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of the secondary battery provided by an embodiment of this application when observed from the first direction.

[0025] Figure 2 It is Figure 1 A cross-sectional view of the secondary battery shown along II-II.

[0026] Figure 3 It is Figure 1 A cross-sectional view of the secondary battery shown along III-III.

[0027] Figure 4 It is Figure 1 A cross-sectional view of the secondary battery shown along IV-IV.

[0028] Figure 5A It is Figure 2Schematic diagram of the structure of the positive electrode tab of the secondary battery shown when viewed from the fourth direction after unfolding.

[0029] Figure 5B is Figure 5A Schematic diagram of the structure of the positive electrode tab shown when viewed from the second direction.

[0030] Figure 6A In some embodiments Figure 2 Schematic diagram of the structure of the negative electrode tab of the secondary battery shown when viewed from the fourth direction after unfolding.

[0031] Figure 6B is Figure 6A Schematic diagram of the structure of the negative electrode tab shown when viewed from the second direction.

[0032] Figure 6C In other embodiments Figure 2 Schematic diagram of the structure of the negative electrode tab of the secondary battery shown when viewed from the fourth direction after unfolding.

[0033] Figure 7 Schematic diagram of the structure of the secondary battery shown when viewed from the first direction in other embodiments.

[0034] Figure 8 is Figure 7 Cross-sectional view of the secondary battery shown along VIII-VIII.

[0035] Figure 9 Schematic diagram of the structure of the secondary battery provided in another embodiment of the present application when viewed from the first direction.

[0036] Figure 10 is Figure 9 Cross-sectional view of the secondary battery shown along X-X.

[0037] Figure 11 Schematic diagram of the structure of the secondary battery shown when viewed from the first direction in other embodiments.

[0038] Figure 12 is Figure 11 Cross-sectional view of the secondary battery shown along XII-XII.

[0039] Figure 13 Schematic diagram of the overall structure of the electronic device provided in one embodiment of the present application.

[0040] Description of main component symbols

[0041] Electronic device 1

[0042] Packaging bag 10

[0043] Receiving portion 11

[0044] Edge sealing 12

[0045] Electrode assembly 20

[0046] Positive electrode tab 21

[0047] Negative electrode tab 22

[0048] Separator 23

[0049] Fifth end edge 23A

[0050] Sixth end edge 23B

[0051] Positive electrode ear 30

[0052] First negative electrode ear 40

[0053] First section 41

[0054] Second section 42

[0055] First transfer ear 50

[0056] Second negative electrode ear 60

[0057] Second transfer ear 70

[0058] First bonding member 80

[0059] Secondary batteries 100, 200

[0060] Battery compartment 101

[0061] First end 121

[0062] Second end 122

[0063] First part 201

[0064] Second part 202

[0065] Positive current collector 210

[0066] First surface 210a

[0067] Second surface 210b

[0068] Third end edge 210A

[0069] Fourth end edge 210B

[0070] Positive active material layer 211

[0071] Negative current collector 220

[0072] Third surface 220a

[0073] Fourth surface 220b

[0074] First end edge 220A

[0075] Second end edge 220B

[0076] Negative electrode active material layer 221

[0077] Insulating layer 222

[0078] First region 2101

[0079] Second region 2102

[0080] Third region 2103

[0081] First groove 2110

[0082] Fourth region 2201

[0083] Fifth region 2202

[0084] Sixth region 2203

[0085] Winding central axis O

[0086] Winding direction D

[0087] Winding central plane P

[0088] First direction X

[0089] Second direction Y

[0090] Third direction Z

[0091] Fourth direction X’

[0092] Fifth direction Z’

[0093] First side X1

[0094] Second side X2

[0095] The following specific embodiments will further illustrate the present application in conjunction with the above drawings. Specific embodiments

[0096] The technical solutions in the embodiments of the present application will be clearly and detailedly described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application.

[0097] Hereinafter, embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this application will be thorough and detailed and will convey to those skilled in the art.

[0098] In addition, for the sake of brevity and clarity, in the drawings, the dimensions or thicknesses of various components and layers may be exaggerated. Throughout the text, the same numerical values refer to the same elements. As used herein, the terms "and / or", "as well as / or" include any and all combinations of one or more of the associated listed items. In addition, it should be understood that when element A is referred to as being "connected to" element B, element A may be directly connected to element B, or there may be an intermediate element C and elements A and B may be indirectly connected to each other.

[0099] Furthermore, when describing embodiments of the present application, the use of "may" refers to "one or more embodiments of the present application".

[0100] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the present application. As used herein, the singular forms are also intended to include the plural forms unless the context clearly indicates otherwise. It should be further understood that the term "comprises", when used in this specification, refers to the presence of the recited features, values, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0101] Spatially relative terms, such as "above", etc., may be used herein for convenience of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It should be understood that, in addition to the directions described in the figures, spatially relative terms are intended to include different directions of the device or apparatus in use or operation. For example, if the device in the figures is turned over, an element described as "above" or "on" other elements or features will be oriented "below" or "beneath" other elements or features. Thus, the exemplary term "above" can include both upward and downward directions. It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or part from another element, component, region, layer, or part. Thus, a first element, component, region, layer, or part discussed below may be referred to as a second element, component, region, layer, or part without departing from the teachings of the exemplary embodiments.

[0102] In the present application, for the design relationships of greater than, less than, or not equal to between parameter values, the reasonable errors of the measuring device need to be excluded.

[0103] Please refer to Figures 1 to 4 , an embodiment of the present application provides a secondary battery 100, which includes a packaging bag 10, an electrode assembly 20, and an electrolyte (not shown in the figure). The electrode assembly 20 and the electrolyte are both disposed inside the packaging bag 10. In some embodiments, the packaging bag 10 may include a receiving portion 11 and a sealing edge 12 connecting the receiving portion 11. The electrode assembly 20 and the electrolyte are disposed in the receiving portion 11. The sealing edge 12 is used to seal the receiving portion 11.

[0104] As Figure 2 shown, the electrode assembly 20 is a wound structure. The electrode assembly 20 includes a positive electrode tab 21, a negative electrode tab 22, and a separator 23. The separator 23 is disposed between the positive electrode tab 21 and the negative electrode tab 22. The positive electrode tab 21, the separator 23, and the negative electrode tab 22 are sequentially stacked and wound to form the electrode assembly 20. Among them, as Figure 2 shown, the electrode assembly 20 has a winding central axis O perpendicular to the paper surface and a winding direction D that winds around the winding central axis O. The winding direction D is Figure 2 the direction of counterclockwise rotation around the winding central axis O as shown. In some other embodiments, the winding direction D may also be the direction of clockwise rotation. In the present application, a three-dimensional coordinate system is established according to the mutually perpendicular first direction X, second direction Y, and third direction Z. The first direction X is the thickness direction of the electrode assembly 20, the second direction Y is the width direction of the positive electrode tab 21 or the negative electrode tab 22, and in some embodiments, the second direction Y is also the extending direction of the winding central axis O. A winding central plane P is defined as the plane passing through the winding central axis O of the electrode assembly 20 and perpendicular to the first direction X. The electrode assembly 20 includes a first portion 201 and a second portion 202 located on both sides of the winding central plane P, respectively.

[0105] As Figures 2 to 4 shown, the positive electrode tab 21 includes a positive electrode current collector 210 and a positive electrode active material layer 211 disposed on the surface of the positive electrode current collector 210. The positive electrode current collector 210 includes a first surface 210a facing the winding central axis O and a second surface 210b disposed opposite to the first surface 210a. The positive electrode active material layer 211 is disposed on both the first surface 210a and the second surface 210b. In some embodiments, the positive electrode current collector 210 may be made of aluminum foil or nickel foil. The positive electrode active material layer 211 contains a positive electrode active material, and the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO 2 ), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn 2 O4 )), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ), or lithium iron phosphate (LiFePO 4 ), or at least one of them.

[0106] Moreover, please refer to Figure 2 , Figure 5A and Figure 5B , where Figure 5A and Figure 5B are the developed views of the positive electrode tab 21. When the positive electrode tab 21 is unfolded, another three-dimensional coordinate system is established according to the mutually perpendicular fourth direction X', second direction Y, and fifth direction Z'. The fourth direction X' is defined as the stacking direction of the positive electrode current collector 210 and the positive electrode active material layer 211 after the positive electrode tab 21 is unfolded, and the fifth direction Z' is defined as the extending direction from the winding head to the winding tail of the positive electrode tab 21 before winding. The positive electrode current collector 210 may include a first region 2101, a second region 2102, and a third region 2103 that are connected in the winding direction D ( Figure 5A and Figure 5B show the fifth direction Z'). The first surface 210a and the second surface 210b of the first region 2101 are both provided with the positive electrode active material layer 211, that is, the first region 2101 is a double-sided coating area. The first surface 210a of the second region 2102 is provided with the positive electrode active material layer 211, and the second surface 210b of the second region 2102 is not provided with the positive electrode active material layer 211, that is, the second region 2102 is a single-sided empty foil area. The first surface 210a and the second surface 210b of the third region 2103 are not provided with the positive electrode active material layer 211, that is, the third region 2103 is a double-sided empty foil area. As Figure 5A and Figure 5B show, along the winding direction D, the length of the first region 2101 is greater than the length of the second region 2102, thereby improving the energy density of the secondary battery 100. The third region 2103 can be used as the ending section of the electrode assembly 20. On the one hand, the positive electrode current collector 210 can improve the hardness of the electrode assembly 20 and play a role in protecting the electrode assembly 20. On the other hand, it reduces the risk that the electrolyte easily corrodes the negative electrode current collector 220 (such as copper foil) when the negative electrode tab 22 ends.

[0107] As Figures 2 to 4As shown, the negative electrode plate 22 includes a negative electrode current collector 220 and a negative electrode active material layer 221 provided on the surface of the negative electrode current collector 220. The negative electrode current collector 220 includes a third surface 220a facing the winding central axis O and a fourth surface 220b disposed opposite to the third surface 220a, and the negative electrode active material layer 221 is provided on both the third surface 220a and the fourth surface 220b. In some embodiments, the negative electrode current collector 220 may be at least one of a copper foil, a nickel foil, or a carbon-based current collector. The negative electrode active material layer 221 contains a negative electrode active material, and the negative electrode active material includes a silicon material capable of reversibly deintercalating and intercalating active ions. The mass ratio of the silicon material in the negative electrode active material layer 221 is 4% to 50%, so that the negative electrode active material has a high specific capacity, thereby improving the energy density of the secondary battery 100. In some embodiments, the silicon material may be elemental silicon, silicon oxide, silicon-carbon material, or silicon alloy. In the silicon-carbon material, elemental silicon can be dispersed in the pores of the porous carbon material, and the porous carbon material is used to inhibit the volume expansion of elemental silicon during cycling. The active material in the negative electrode active material layer 221 may also include graphite, such as natural graphite or artificial graphite. Since graphite has a certain flexibility, its combination with the silicon material can relieve the overall volume expansion of the negative electrode active material layer 221, improve the cycling performance of the secondary battery 100, and at the same time, graphite and the silicon material as active materials can also make full use of the advantages of both to achieve better electrochemical performance.

[0108] Moreover, please refer to Figure 2 、 Figure 6A and Figure 6B wherein Figure 6A and Figure 6B are the developed views of the negative electrode plate 22. The negative electrode current collector 220 may include a fourth region 2201, a fifth region 2202, and a sixth region 2203 connected in the winding direction D ( Figure 6A and Figure 6B shown in the fifth direction Z'). The third surface 220a and the fourth surface 220b in the fourth region 2201 are not provided with the negative electrode active material layer 221, that is, the fourth region 2201 is a double-sided empty foil area. The third surface 220a in the fifth region 2202 is not provided with the positive electrode active material layer 211, and the fourth surface 220b in the fifth region 2202 is provided with the negative electrode active material layer 221, that is, the fifth region 2202 is a single-sided empty foil area. The third surface 220a and the fourth surface 220b in the sixth region 2203 are both provided with the negative electrode active material layer 221, that is, the sixth region 2203 is a double-sided coating area.

[0109] As Figure 3 and Figure 4As shown, the negative electrode current collector 220 includes a first end edge 220A and a second end edge 220B that are oppositely disposed in the second direction Y. In the second direction Y, the first end edge 220A is closer to the sealing edge 12 than the second end edge 220B. When viewed from the first direction X, the two edges of the negative electrode active material layer 221 that are oppositely disposed in the second direction Y coincide with the first end edge 220A and the second end edge 220B respectively. The positive electrode current collector 210 includes a third end edge 210A and a fourth end edge 210B that are oppositely disposed in the second direction Y. In the second direction Y, the third end edge 210A is closer to the sealing edge 12 than the fourth end edge 210B. When viewed from the first direction X, the two edges of the positive electrode active material layer 211 that are oppositely disposed in the second direction Y coincide with the third end edge 210A and the fourth end edge 210B respectively. The separator 23 includes a fifth end edge 23A and a sixth end edge 23B that are oppositely disposed in the second direction Y. In the second direction Y, the fifth end edge 23A is closer to the sealing edge 12 than the sixth end edge 23B. To reduce the risk of lithium deposition on the negative electrode tab 22, it can be arranged that in the second direction Y, the first end edge 220A of the negative electrode tab 22 extends beyond the third end edge 210A of the positive electrode tab 21, and the fifth end edge 23A of the separator 23 extends beyond the first end edge 220A of the negative electrode tab 22. Moreover, in the second direction Y, the second end edge 220B of the negative electrode ear extends beyond the fourth end edge 210B of the positive electrode ear 30, and the sixth end edge 23B of the separator 23 extends beyond the second end edge 220B of the negative electrode tab 22.

[0110] As Figure 6C shown, in some other embodiments, the negative electrode tab 22 may further include an insulating layer 222 disposed on the surface of the negative electrode current collector 220. In the second direction Y, the insulating layer 222 is closer to the sealing edge 12 than the negative electrode active material layer 221. The insulating layer 222 can reduce the risk of short circuit caused by burrs generated during the cutting of the first negative electrode ear 40 piercing the separator 23, and can also reduce the risk of short circuit caused by the shrinkage of the separator 23 at high temperatures. Among them, the insulating layer 222 includes inorganic particles and polymers. The inorganic particles include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium dioxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate, and the polymers include at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polyvinylidene difluoride, polytetrafluoroethylene, polyvinyl butyral, waterborne acrylic resin, carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0111] Taking elemental silicon as an example of the silicon material, the test method for the content of the silicon material in the negative electrode active material layer 221 may include the following steps: 1) Under the environmental conditions of 25±5°C, the secondary battery 100 is discharged to 3V at 0.2C and then disassembled, and the negative electrode plate 22 is taken out; 2) Take 1g of the negative electrode plate 22, scrape off the negative electrode active material layer 211 on the negative electrode plate 22 from the negative electrode current collector 210 as a sample, weigh the sample and then place it in a muffle furnace, and bake it in an air atmosphere. The baking temperature is 600°C and the time is 3h. Then, immerse the baked powder in 50 mL of a mixed solution composed of hydrofluoric acid and concentrated nitric acid, heat and digest it for 12h until it is completely dissolved to obtain a digestion solution. Subsequently, dilute the digestion solution with a 20wt.% nitric acid solution, and the dilution ratio is 1:100 to obtain a test solution; 3) Prepare silicon standard solutions with silicon concentrations of 20, 40, 60, 80, and 100 ppm respectively, and use an inductively coupled plasma emission spectrometer (such as the Thermo Fisher 7000 series) to test the silicon standard solutions and draw a standard curve; 4) Clean the inductively coupled plasma emission spectrometer with deionized water and a 20wt.% nitric acid solution, and then test the silicon content of the test solution three times repeatedly. Calculate the average value of the silicon content, with the unit of ppm, and then convert the average value of the above silicon content into a mass percentage according to the dilution ratio to obtain the mass proportion of the silicon material.

[0112] For other types of silicon materials, the above test method can be referred to for testing the mass percentage content of silicon, and then the mass proportion of the silicon material can be obtained according to the chemical formula of the silicon material.

[0113] As Figure 2 and Figure 3 As shown, the secondary battery 100 further includes M positive electrode tabs 30, and M is 1 or 2. The positive electrode active material layer 211 includes M first grooves 2110. The M positive electrode tabs 30 are respectively disposed in the M first grooves 2110 and are electrically connected to the positive electrode current collector 210. In some embodiments, the positive electrode tabs 30 are welded and fixed to the positive electrode current collector 210, thereby improving the connection strength between the positive electrode tabs 30 and the positive electrode current collector 210. When manufacturing the positive electrode plate 21, the first grooves 2110 can be cleaned out in the positive electrode active material layer 211 by means of laser cleaning, so that part of the positive electrode current collector 210 is exposed for subsequent welding of the positive electrode tabs 30; or a foaming glue can be pre-pasted on part of the positive electrode current collector 210, and after coating the positive electrode active material, it is heated to make the foaming glue fall off, so that part of the positive electrode current collector 210 is exposed; or part of the positive electrode active material can be directly scraped off with a scraper, so that part of the positive electrode current collector 210 is exposed.

[0114] As Figure 2 and Figure 4As shown, the secondary battery 100 further includes N first negative electrode tabs 40, where N is greater than or equal to 2. The N first negative electrode tabs 40 are integrally provided with the negative electrode current collector 220 and are connected to the first edge 220A of the negative electrode current collector 220. As Figure 2 shown, in the first direction X, the N first negative electrode tabs 40 overlap. In the embodiments of the present application, the overlapping of the N first negative electrode tabs 40 means that the N first negative electrode tabs 40 are at least partially covered in the first direction X. When manufacturing the negative electrode sheet 22, a part of the area exposed from the negative electrode active material layer 221 may be reserved on the negative electrode current collector 220, so that after the negative electrode sheet 22 is cold-pressed, this part of the area is cut to obtain the first negative electrode tab 40.

[0115] As Figure 1 and Figure 4 shown, the secondary battery 100 further includes a first transfer tab 50, and the first negative electrode tab 40 is connected to the first transfer tab 50. The M positive electrode tabs 30 and the first transfer tab 50 extend out of the packaging bag 10 from the same side of the packaging bag 10 (such as extending out of the packaging bag 10 from the sealing edge 12) and are configured to be electrically connected to an external circuit respectively. In some embodiments, the first negative electrode tab 40 is bent and welded to the first transfer tab 50, thereby improving the connection strength between the first negative electrode tab 40 and the first transfer tab 50. By bending the first negative electrode tab 40, it is beneficial to reduce the space occupied by the first negative electrode tab 40 and further improve the energy density of the secondary battery 100.

[0116] When the secondary battery 100 is charged by electrically connecting to an external circuit through the positive electrode tab 30 and the first transfer tab 50, the positive electrode sheet 21 loses electrons, and active ions (such as lithium ions) are deintercalated from the positive electrode active material layer 211, pass through the separator 23 and are intercalated into the negative electrode active material layer 221. At the same time, electrons sequentially reach the negative electrode sheet 22 via the positive electrode tab 30, the external circuit and the first transfer tab 50, and the electrons obtained by the negative electrode sheet 22 combine with the intercalated active ions.

[0117] For a secondary battery 100 in which the negative electrode active material layer 221 includes a silicon material, in this application, the positive electrode tab 30 is disposed in the first groove 2110 provided in the positive electrode active material layer 211 and is electrically connected to the positive electrode current collector 210, and the positive electrode plate 21 directly extends out of the packaging bag 10. Compared with the related art in which the positive electrode plate 21 adopts a multi-tab structure and uses an adapter tab to connect the positive electrode tab 30, this application can omit the adapter tab connected to the positive electrode tab 30, and can also omit the influence of the insulating layer (when the multi-tab structure is used, an insulating layer is provided on the surface of the positive electrode current collector 210, which can reduce the risk of burrs generated during the cutting of the positive electrode tab 30 piercing the separator 23) on the energy density when the positive electrode plate 21 adopts a multi-tab structure. Therefore, it is beneficial to improve the energy density of the secondary battery 100. At the same time, this application provides at least two first negative electrode tabs 40 in parallel for shunting, which is beneficial to reducing the impedance of the negative electrode plate 22 and improving the kinetic performance of the negative electrode plate 22. Therefore, the uniformity of the current and the insertion speed of lithium ions during charging can be improved. At the same time, setting the number of positive electrode tabs 30 to 1 or 2 and disposing them in the first groove 2110 can better balance the kinetic performance of the positive and negative electrodes in the silicon system, reduce the risk of lithium deposition on the negative electrode plate 22 with a specific silicon content during high-rate charging, and improve the fast charging performance of the secondary battery 100. In addition, it can also reduce the risk of mismatch in the kinetic performance of the positive and negative electrodes when the number of positive electrode tabs 30 is too large, and it is not conducive to all the positive electrode tabs 30 and the first adapter tab 50 extending out of the packaging bag 10 from the same side of the packaging bag 10 when the number of positive electrode tabs 30 is too large. Therefore, this application can enable the secondary battery 100 to have both a relatively high energy density and excellent fast charging performance.

[0118] As Figure 1 and Figure 2 shown, in some embodiments, the number M of the positive electrode tabs 30 is 2. At this time, both of the two positive electrode tabs 30 and the first adapter tab 50 are configured to be electrically connected to an external circuit. Observed from the first direction X, the two positive electrode tabs 30 are separated from each other. In this way, the problem of uneven thickness of the electrode assembly 20 caused by the thickness superposition of the two positive electrode tabs 30 can be reduced, and it is also beneficial for the two positive electrode tabs 30 to extend out of the packaging bag 10 from the sealing edge 12. Since both of the two positive electrode tabs 30 and the first adapter tab 50 extend out of the packaging bag 10 from the same side of the packaging bag 10, it is convenient to simplify the operation during the subsequent wiring process.

[0119] When the secondary battery 100 is charged by electrically connecting to an external circuit through the two positive electrode tabs 30 and the first adapter tab 50, the current can flow through the two positive electrode tabs 30 respectively. Therefore, providing two positive electrode tabs 30 is beneficial to making the current flowing through the positive electrode plate 21 more uniform, so it can support a higher rate of charge and discharge current, and can also make the active ions uniformly de-embed and embed from the positive electrode active material layer 211, reducing the risk of lithium deposition on the negative electrode plate 22 during high-rate charging.

[0120] Among them, asFigure 2 As shown, a layer of negative electrode current collector 220 and a negative electrode active material layer 221 located on the surface of the negative electrode current collector 220 are defined as a layer of negative electrode plate 22, and the electrode assembly 20 includes n layers of negative electrode plates 22 in the first direction X. When the number M of positive electrode tabs 30 is 2, the number N of first negative electrode tabs 40 can be set to satisfy: N>2 / n, which is beneficial to balance the dynamic properties of the positive electrode plate 21 and the negative electrode plate 22, and reduce the risk of lithium deposition of the negative electrode plate 22 during high-rate charging. In some embodiments, the N first negative electrode tabs 40 are respectively connected to the first part 201 and the second part 202 of the electrode assembly 20. In some embodiments, the N first negative electrode tabs 40 are respectively connected to each sixth region 2203 (i.e., the double-sided coating area) of the negative electrode current collector 220, that is, the number of first negative electrode tabs 40 is the same as the number of layers of the double-sided coating area of ​​the negative electrode plate 22. For simplicity, Figure 2 Only part of the negative electrode sheets 22 in the electrode assembly 20 may be shown for example, i.e., the other part of the negative electrode sheets 22 are omitted, so it can be understood that the actual number of layers of the negative electrode sheets 22 is not limited to that shown in the figure. Similarly, the actual number of layers of the positive electrode sheets 21 is not limited to that shown in the figure.

[0121] In some embodiments, the mass proportion of silicon material in the negative electrode active material layer 221 is 10% to 30%. In this way, the negative electrode active material can have a higher gram capacity, further improving the energy density of the secondary battery 100. At the same time, it also reduces the risk of increasing the number of first negative electrode tabs 40 when there is more silicon material, resulting in the first negative electrode tabs 40 occupying a larger space.

[0122] In some embodiments, Figure 2As shown, a positive electrode current collector layer 210 and a positive electrode active material layer 211 located on the surface of the positive electrode current collector layer 210 are defined as a positive electrode plate 21. The difference in the number of layers of the positive electrode plate 21 connected by two positive electrode tabs 30 is 1 to 4. This can reduce the impedance difference of the positive electrode active material layers 211 on both sides of the positive electrode tab 30, making the current flowing through the positive electrode plate 21 more uniform. Therefore, it can support a higher rate of charge and discharge current, and also enable active ions to be uniformly deintercalated from the positive electrode active material layer 211, reducing the risk of lithium plating on the negative electrode plate 22 during high-rate charging. At the same time, it also reduces the risk of a large distance between the two positive electrode tabs 30 and the winding central axis O (if the distance between the two positive electrode tabs 30 and the winding central axis O is large, the electrode assembly 20 may generate a large torque in the third direction Z, making the electrode assembly 20 prone to torsional deformation after multiple charge and discharge cycles), thereby facilitating the improvement of the problem of deformation of the electrode assembly 20 during multiple charge and discharge processes. In the embodiments of the present application, the calculation steps of the above-mentioned difference in the number of layers include: taking the layer where one of the positive electrode tabs 30 is located as the first layer, and then counting along the first direction X to the position where the other positive electrode tab 30 is located, counting the number of layers of the positive electrode plate 21. After counting to the layer of this positive electrode tab 30, subtracting the number of layers of the two positive electrode tabs 30 is the above-mentioned difference in the number of layers. Among them, Figure 2 It is shown that both positive electrode tabs 30 are connected to the first part 201 of the electrode assembly 20. In other embodiments, two positive electrode tabs 30 can also be respectively connected to the first part 201 and the second part 202 of the electrode assembly 20.

[0123] As Figures 2 to 4 shown, in some embodiments, the positive electrode tabs 30 are both disposed at 1 / 3 to 2 / 3 of the length of the first region 2101 of the positive electrode current collector layer 210 in the winding direction D. Thereby, the impedance difference of the positive electrode active material layers 211 on both sides of the positive electrode tab 30 can be reduced, making the current flowing through the positive electrode plate 21 more uniform. Therefore, it can support a higher rate of charge and discharge current, and also enable active ions to be uniformly deintercalated from the positive electrode active material layer 211, reducing the risk of lithium plating on the negative electrode plate 22 during high-rate charging.

[0124] In some embodiments, the positive electrode tabs 30 are both connected to the second surface 210b of the first region 2101. In this way, if the negative electrode plate 22 expands in volume due to the intercalation of active ions, causing the negative electrode plate 22 to have an outward expansion deformation from the inside, since the positive electrode tabs 30 are connected to the second surface 210b, the risk of short circuit caused by the edge burrs of the positive electrode tabs 30 (the burrs may be generated during the process of cutting the positive electrode tabs 30, but the present application does not limit this) piercing the separator 23 and contacting the negative electrode plate 22 can be reduced.

[0125] In some embodiments, along the extending direction of the positive electrode tab 30 or the first transfer tab 50 within the sealing edge 12, the sealing edge 12 sequentially includes a first end 121 and a second end 122 disposed opposite to the first end 121. In the first direction X, the first portion 201 of the electrode assembly 20 is closer to the first end 121 than the second portion 202. For example, in some embodiments, when viewed from the second direction Y, the first portion 201 may overlap with the sealing edge 12. The M positive electrode tabs 30 are all connected to the first portion 201. Thus, the bending degree of the positive electrode tabs 30 within the packaging bag 10 can be reduced or even not bent. When the secondary battery 100 is subjected to an external short-circuit test (i.e., using a metal conductor to conduct between the positive electrode tab 30 and the first transfer tab 50 of the secondary battery 100, controlling the magnitude of the short-circuit current so that heat accumulates within the secondary battery 100 to test whether the secondary battery 100 can pass the short-circuit test), even if the temperature of the positive electrode tab 30 rises and causes a certain degree of shrinkage of the separator 23, the risk of short circuit caused by the contact between the bent portion of the positive electrode tab 30 and the edge of the negative electrode plate 22 can be reduced.

[0126] In some embodiments, the secondary battery 100 further includes a first adhesive member 80 that adhesively bonds the outer surface of the second portion 202 and the inner surface of the accommodating portion 11. The first adhesive member 80 can fix the electrode assembly 20 and the packaging bag 10, reducing the risk of the electrode assembly 20 moving within the packaging bag 10 when the secondary battery 100 undergoes mechanical abuse (such as vibration, collision, dropping, etc.). Moreover, when the secondary battery 100 undergoes mechanical abuse, the impact force will first be transmitted to the second portion 202 of the electrode assembly 20 through the packaging bag 10 and the first adhesive member 80. On the one hand, the first portion 201 is not directly adhesively bonded to the packaging bag 10. On the other hand, since the transfer tab connected to the positive electrode tab 30 is omitted, the space between the first portion 201 and the sealing edge 12 in the second direction Y is relatively large, thus having a certain buffering effect. That is, through the position setting of the positive electrode tab 30 and the first adhesive member 80, the secondary battery 100 can take into account both high external short-circuit test performance and anti-mechanical abuse performance. Further, the tail of the third region 2103 of the positive current collector 210 in the winding direction D is located in the second portion 202. The first adhesive member 80 can also adhesively bond and fix the tail of the third region 2103. Among them, the first adhesive member 80 can be a double-sided tape or a hot melt adhesive, and its specific material can be selected from at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol.

[0127] In some embodiments, the M first negative electrode tabs 40 are respectively connected to the first part 201 and the second part 202, and the number of the first negative electrode tabs 40 connected to the first part 201 is more than that of the first negative electrode tabs 40 connected to the second part 202. Since the first negative electrode tabs 40 are more connected to the first part 201 and the positive electrode tabs 30 are also connected to the first part 201, the space between the second part 202 and the sealing edge 12 is larger than the space between the first part 201 and the sealing edge 12. Although Figure 1 indicates that the first part 201 has a specific vector direction to illustrate the thickness direction of the electrode assembly 20, it can be understood that the opposite direction of the above-indicated direction can also be the thickness direction of the electrode assembly 20. Therefore, on the first direction X, there is a first side X1 from the first part 201 to the second part 202 and a second side X2 opposite to the orientation of the first side X1. Since the first negative electrode tabs 40 are bent, the first negative electrode tabs 40 include a first section 41 connected to the first end edge 220A and a second section 42 connected to the first section 41, and the second section 42 is bent relative to the first section 41. The first section 41 extends from the first end edge 220A towards the first side X1, that is, towards the space between the second part 202 and the sealing edge 12, and the second section 42 extends along the second side X2, and the first transfer tab 50 is connected to the second section 42. By setting the bending direction of the first negative electrode tabs 40, it is beneficial to make full use of the space between the second part 202 and the sealing edge 12 and reduce the thickness after folding of the first negative electrode tabs 40, thereby further improving the energy density of the secondary battery 100.

[0128] Moreover, it can be understood that since some of the first negative electrode tabs 40 are connected to the second part 202 of the electrode assembly 20, when the secondary battery 100 undergoes mechanical abuse, the impact force will be first transmitted to the first part 201 of the electrode assembly 20 through the packaging bag 10 and the first bonding member 80, and the first negative electrode tabs 40 are bent, so the first negative electrode tabs 40 can provide a relatively large buffer space, making the secondary battery 100 have a high anti-mechanical abuse performance.

[0129] Such as Figure 1As shown, in the third direction Z, the first transfer tab 50 is disposed between two positive tabs 30. Correspondingly, the two positive tabs 30 are approximately disposed at the 1 / 3 and 2 / 3 positions of the length of the first region 2101 of the positive current collector 210 in the winding direction D, which is conducive to realizing the positional relationship between the first transfer tab 50 and the two positive tabs 30, and also facilitates simplifying the operation in the subsequent wiring process. In addition, considering that the positive tab 30 is welded and fixed to the positive current collector 210, glue may be applied to the surface of the positive tab 30 and the position of the negative electrode plate 22 corresponding to the positive tab 30 to reduce the influence of welding burrs, resulting in an increase in the thickness of the electrode assembly 20 at the position corresponding to the positive tab 30. However, the first transfer tab 50 has a relatively small influence on the thickness of the electrode assembly 20 (the first transfer tab 50 is integrally provided with the negative current collector 220). Therefore, by disposing the first transfer tab 50 between the two positive tabs 30, the first transfer tab 50 can increase the distance between the two positive tabs 30 in the third direction Z, thereby reducing the risk of increased thickness non-uniformity of the electrode assembly 20 when the two positive tabs 30 are relatively close (for example, when the number of layers of the positive electrode plates 21 connected by the two positive tabs 30 differs relatively little). As Figure 7 and Figure 8 shown, in some other embodiments, it is also possible to set that in the third direction Z, one positive tab 30 is disposed between the first transfer tab 50 and the other positive tab 30. Since only one positive tab 30 is adjacent to the first transfer tab 50, it is conducive to reducing the short-circuit risk caused by the contact between the positive tab 30 and the first transfer tab 50. Correspondingly, the two positive tabs 30 are approximately disposed at the 1 / 3 and 1 / 2 positions of the length of the first region 2101 in the winding direction D, or the two positive tabs 30 are approximately disposed at the 1 / 2 and 2 / 3 positions of the length of the first region 2101 of the positive current collector 210 in the winding direction D.

[0130] Please refer to Figure 9 and Figure 10 , another embodiment of the present application further provides a secondary battery 200. The difference from the above-mentioned secondary battery 100 is that the number M of the positive tabs 30 is 1.

[0131] At this time, the secondary battery 200 further includes P second negative electrode tabs 60 and one second connection tab 70, where P is greater than or equal to 2. The P second negative electrode tabs 60 are integrally provided with the negative electrode current collector 220 and connected to the first end edge 220A. In the first direction X, the P second negative electrode tabs 60 overlap. In the first direction X, the first negative electrode tab 40 and the second negative electrode tabs 60 are separated from each other. The second negative electrode tabs 60 are connected to the second connection tab 70. In some embodiments, the second negative electrode tabs 60 are welded and fixed to the second connection tab 70, thereby improving the connection strength between the second negative electrode tabs 60 and the second connection tab 70. The positive electrode tab 30, the first connection tab 50, and the second connection tab 70 extend out of the packaging bag 10 from the same side of the packaging bag 10, and are all configured to be electrically connected to an external circuit. Setting the positive electrode tab 30, the first connection tab 50, and the second connection tab 70 to extend out of the packaging bag 10 from the same side of the packaging bag 10 facilitates simplifying the operation during subsequent wiring.

[0132] When the secondary battery 200 is charged by being electrically connected to an external circuit through the positive electrode tab 30, the first connection tab 50, and the second connection tab 70, the current will pass through the second connection tab 70 in addition to passing through the first connection tab 50. Therefore, by adding the second connection tab 70 and connecting at least two second negative electrode tabs 60 to the second connection tab 70, it is beneficial to further reduce the impedance of the negative electrode plate 22, improve the kinetic performance of the negative electrode plate 22, thereby further reducing the risk of lithium plating on the negative electrode plate 22 during high-rate charging, and improving the fast charging performance of the secondary battery 200. In addition, since the first negative electrode tab 40 and the second negative electrode tabs 60 are separated from each other in the first direction X, the risk of uneven thickness of the electrode assembly 20 caused by the thickness stacking of the first negative electrode tab 40 and the second negative electrode tabs 60 can be reduced, which is beneficial to improving the deformation of the electrode assembly 20 during multiple charge and discharge processes. Among them, when manufacturing the negative electrode plate 22, a part of the area exposed from the negative electrode active material layer 221 can be reserved on the negative electrode current collector 220, and this part of the area is cut after cold pressing to obtain the first negative electrode tab 40 and the second negative electrode tabs 60 at the same time.

[0133] Among them, a negative electrode current collector layer 220 and a negative electrode active material layer 221 located on the surface of the negative electrode current collector layer 220 are defined as a negative electrode tab 22, and the electrode assembly 20 includes n layers of negative electrode tabs 22 in the first direction X. When the number M of the positive electrode tabs 30 is 1, the number N of the first negative electrode tabs 40 and the number P of the second negative electrode tabs 60 satisfy: N≤n / 2, P≤n / 2. In this way, it is beneficial to balance the kinetic performance of the positive electrode tab 21 and the negative electrode tab 22, and reduce the risk of lithium precipitation in the negative electrode tab 22 during high-rate charging. At the same time, the space occupied by the first negative electrode tab 40 and the second negative electrode tab 60 can also be reduced, the energy density of the secondary battery 200 can be improved, and the difficulty of folding the tab and welding can also be reduced, simplifying the manufacturing process. In some embodiments, the N first negative electrode tabs 40 are respectively connected to the first part 201 and the second part 202 of the electrode assembly 20, and the P second negative electrode tabs 60 are respectively connected to the first part 201 and the second part 202 of the electrode assembly 20. In some embodiments, the N first negative electrode tabs 40 and the P second negative electrode tabs 60 are both connected to the sixth region 2203 (i.e., the double-sided coating region) of the negative electrode current collector 220. Among them, the number of the first negative electrode tabs 40 can be the same as or different from that of the second negative electrode tabs 60. The specific numbers of the first negative electrode tabs 40 and the second negative electrode tabs 60 can be changed within the above range, so as to adjust the impedance of the negative electrode tab 22, so that the secondary battery 200 can meet different charge and discharge rate requirements.

[0134] As Figure 9 shown, in some embodiments, in the third direction Z, the positive electrode tab 30 is disposed between the first transfer tab 50 and the second transfer tab 70. Correspondingly, the positive electrode tab 30 can be respectively disposed at the 1 / 2 position of the length of the first region 2101 of the positive electrode current collector 210 in the winding direction D, so as to facilitate the realization of the positional relationship among the positive electrode tab 30, the first transfer tab 50, and the second transfer tab 70, and also facilitate the current flowing through the positive electrode tab 21 to be more uniform. As Figure 11 and Figure 12 shown, in other embodiments, it can also be set that in the third direction Z, the second transfer tab 70 is disposed between the positive electrode tab 30 and the first transfer tab 50. Since only the second transfer tab 70 is adjacent to the positive electrode tab 30, it is beneficial to reduce the short-circuit risk caused by the contact between the positive electrode tab 30 and the first transfer tab 50, and it is also convenient to simplify the operation in the subsequent wiring process. Correspondingly, the positive electrode tab 30 can be respectively disposed at the 2 / 3 position of the length of the first region 2101 of the positive electrode current collector 210 in the winding direction D.

[0135] Among them, the secondary battery 100 or 200 of the present application includes all devices capable of undergoing an electrochemical reaction. Specifically, the secondary battery 100 or 200 includes all kinds of primary batteries, secondary batteries, fuel cells, solar cells, and capacitors (such as supercapacitors). Optionally, the secondary battery may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0136] Please refer to Figure 13 , an embodiment of the present application further provides an electronic device 1. The electronic device 1 includes a battery compartment 101 and a secondary battery 100 (or secondary battery 200) accommodated in the battery compartment 101. The electronic device 1 is powered by the above-mentioned secondary battery 100, and the secondary battery 100 can balance a relatively high energy density and excellent fast charging performance. Among them, the secondary battery 100 of the present application is applicable to the electronic device 1 in various fields. In one embodiment, the electronic device 1 of the present application may be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium ion capacitor, etc.

[0137] The preparation method and performance of the secondary battery provided by the present application will be described below through specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0138] Example 1

[0139] (1) Preparation of the positive electrode sheet 21: The positive electrode active material lithium cobaltate (LiCoO 2) Super P (conductive carbon black), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are mixed in a weight ratio of 96.5:1.5:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%. The slurry is stirred evenly. Two pieces of foam rubber are pre-stuck on a partial surface of the positive current collector 210 with a thickness of 8 μm, i.e., aluminum foil. The slurry is evenly coated on one surface of the aluminum foil, and heated to make the foam rubber fall off to expose a partial surface of the aluminum foil, and then dried at 90 °C. The above coating steps are repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode plate. The initial positive electrode plate is cold-pressed to obtain a positive active material layer 211 with a single coating thickness of 77 μm, and then through processes such as cutting, the positive electrode plate 21 is obtained. However, two positive electrode tabs 30 are welded on the exposed aluminum foil.

[0140] (2) Preparation of the negative electrode plate 22: Artificial graphite, silicon-carbon material, Super P (conductive carbon black), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) as negative active materials are mixed in a weight ratio of 69:5:6:19:1, and deionized water is added as a solvent to prepare a slurry with a weight percentage of 55 wt%. The slurry is evenly coated on one surface of the negative current collector 220 with a thickness of 5 μm, i.e., copper foil, leaving an empty foil area at the edge of the copper foil, and dried at 110 °C. The above steps are repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode plate. The initial negative electrode plate is roll-pressed to obtain a negative active material layer 221 with a coating thickness of 70 μm. Then, the negative electrode plate is pre-cut, and then the reserved empty foil area is die-cut to obtain a plurality of first negative electrode tabs 40, and finally slit to obtain the negative electrode plate 22.

[0141] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as organic solvents are mixed in a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium hexafluorophosphate (LiPF 6 ) is added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0142] (4) Preparation of the separator 23: A polyethylene (PE) film with a thickness of 9 μm is selected.

[0143] (5) Assembly of the secondary battery 100: The positive electrode tab 21, the separator 23, and the negative electrode tab 22 are stacked and wound in sequence to obtain the electrode assembly 20. The number N of the first negative electrode tabs 21 is equal to the number of layers of the double-sided coated area of the negative electrode tab 22 after winding. The first negative electrode ear 40 is stacked and welded to the first transfer ear 50, and the material of the first transfer ear 50 is copper. Then, the aluminum plastic film (with a thickness of 150 μm) formed with a pit is placed in the assembly fixture with the pit surface facing up, and the electrode assembly 20 is placed in the pit. The electrolyte is injected into the pit of the aluminum plastic film, and the first transfer ear 50 and the two positive electrode ears 30 are led out of the aluminum plastic film. The first transfer ear 50 is located between the two positive electrode ears 30. Then, formation and encapsulation are performed to obtain Figures 1 to 4 the secondary battery 100 shown.

[0144] Example 2

[0145] The difference from Example 1 is that by adjusting the position of the positive electrode ear 30 relative to the positive current collector 210, after encapsulation, one positive electrode ear 30 is located between the first transfer ear 50 and the other positive electrode ear 30. Obtain Figure 7 and Figure 8 the secondary battery 100 shown.

[0146] Example 3

[0147] The difference from Example 1 is that the number of positive electrode ears 30 is one. Two second negative electrode ears 60 are also obtained by cutting the negative electrode tab 22. The second negative electrode ears 60 are stacked and welded to the second transfer ear 70, and the material of the second transfer ear 70 is copper. After encapsulation, the positive electrode ear 30 is located between the first transfer ear 50 and the second transfer ear 70, and obtain Figure 9 and Figure 10 the secondary battery 200 shown.

[0148] Example 4

[0149] The difference from Example 3 is that by adjusting the position of the positive electrode ear 30 relative to the positive current collector 210, after encapsulation, the second transfer ear 70 is located between the positive electrode ear 30 and the first transfer ear, and obtain Figure 11 and Figure 12 the secondary battery 200 shown.

[0150] Comparative Example 1

[0151] The difference from Example 1 is that when manufacturing the positive electrode tab, multiple positive electrode ears are obtained through a cutting process, and the number of positive electrode ears is equal to the number of layers of the double-sided coated area of the positive electrode tab after winding. Then, the positive electrode ears are stacked and welded to the positive transfer ear, and the material of the positive transfer ear is aluminum. After encapsulation, the positive transfer ear and the first transfer ear are led out of the aluminum plastic film.

[0152] Comparative Example 2

[0153] The difference from Example 1 is that when manufacturing the negative electrode sheet, a piece of foaming glue is first pasted on a part of the surface of the copper foil, and then the slurry is coated. After heating to make the foaming glue fall off to expose a part of the surface of the copper foil, after subsequent processes such as cutting to obtain the negative electrode sheet, a negative electrode tab is welded on the exposed copper foil. After encapsulation, the negative electrode tab and the two positive electrode tabs are led out of the aluminum-plastic film, and the negative electrode tab is located between the two positive electrode tabs.

[0154] The secondary batteries of each comparative example and example were tested for energy density and fast charging performance, and the test results are recorded in Table 1.

[0155] The steps for testing the energy density are as follows: 1) At a test temperature of 25 °C, the secondary battery is left standing for 5 min, discharged at a constant current of 0.2C (CC) to the cut-off voltage, left standing for 5 min again, charged at a constant current of 0.2C to the limiting voltage, and then charged at a constant voltage (CV) under the limiting voltage until the current decreases to 0.025C. After standing for 5 min, it is discharged at a constant current of 0.2C to the cut-off voltage, and the capacity of the secondary battery is recorded. The capacity is multiplied by the plateau voltage to obtain the energy D; 2) The length, width, and height of the secondary battery are measured with an optical detector to calculate the volume T. The energy density (ED) = D / T, with the unit of Wh / L. Then, taking the energy density of the secondary battery of the comparative example as the reference (100%), the ratio of the energy density of the secondary battery of each example to the reference energy density is calculated.

[0156] The steps for testing the fast charging performance of the secondary battery are as follows: 1) At a test temperature of 25 °C, the secondary battery is left standing for 5 min, charged at a constant current of 4C to 4.25V, and the time required for constant current charging is recorded. Then, it is charged at a constant voltage of 4.25V until the current is 0.05C, and the time required for full charge is recorded; 2) The electrode assembly is disassembled to check whether lithium deposition occurs on the surface of the negative electrode sheet.

[0157] Table 1

[0158] Energy density Constant current charging time Full charge time Interface condition Comparative example 1 100％ 7 min 21 min Lithium deposition Comparative example 2 107％ 0.5 min 38 min Slot lithium deposition Example 1 103.7％ 6 min 24 min No lithium deposition Example 2 103.7％ 6 min 24 min No lithium deposition Example 3 104.2％ 4 min 26 min No lithium deposition Example 4 104.2％ 4 min 26 min No lithium deposition

[0159] As can be seen from the data in Table 1, compared with Comparative Examples 1-2, the energy density of the secondary batteries of Examples 1-4 is improved, and at the same time, the charging time is shortened during high-rate charging, and no lithium deposition occurs at the interface. Therefore, the secondary battery also has excellent fast charging performance.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising a packaging bag and an electrode assembly disposed in the packaging bag, wherein the electrode assembly is a winding structure, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein: The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon material, and the mass proportion of the silicon material in the negative electrode active material layer is 4% to 50%; The secondary battery further includes M positive electrode tabs, N first negative electrode tabs and a first adapter tab, the thickness direction of the electrode assembly is a first direction, in the first direction, the N first negative electrode tabs overlap and are connected to the first adapter tab, and the M positive electrode tabs and the first adapter tabs extend out of the packaging bag from the same side of the packaging bag and are configured to be electrically connected to an external circuit respectively; M is 1 or 2, the positive electrode active material layer is provided with M first grooves, and the M positive electrode tabs are respectively provided in the M first grooves and electrically connected to the positive electrode current collector; N is greater than or equal to 2, the width direction of the negative electrode plate is the second direction, the second direction is perpendicular to the first direction, the negative electrode collector includes a first end edge and a second end edge that are oppositely arranged in the second direction, and the N first negative electrode tabs are integrally arranged with the negative electrode collector and connected to the first end edge.

2. The secondary battery according to claim 1, wherein The positive electrode current collector comprises a first surface facing the winding center axis and a second surface away from the first surface, the positive electrode current collector comprises a first region and a second region connected in the winding direction, the first surface and the second surface located in the first region are both provided with the positive electrode active material layer, the first surface located in the second region is provided with the positive electrode active material layer, and the second surface located in the second region is not provided with the positive electrode active material layer; Along the winding direction, the length of the first region is greater than the length of the second region, and the M positive electrode tabs are connected to 1 / 3 to 2 / 3 of the length of the first region in the winding direction.

3. The secondary battery according to claim 1, wherein The positive electrode current collector comprises a first surface facing the winding center axis and a second surface away from the first surface, the positive electrode current collector comprises a first region and a second region connected in the winding direction, the first surface and the second surface located in the first region are both provided with the positive electrode active material layer, the first surface located in the second region is provided with the positive electrode active material layer, and the second surface located in the second region is not provided with the positive electrode active material layer; Along the winding direction, the length of the first region is greater than the length of the second region, and the M positive electrode tabs are connected to the second surface of the first region.

4. The secondary battery according to any one of claims 1 to 3, wherein The packaging bag includes a housing portion for accommodating the electrode assembly and an edge seal connecting the housing portion, the positive electrode tab and the first transfer tab extend out of the packaging bag from the edge seal, and along the extending direction of the positive electrode tab in the edge seal, the edge seal includes a first end and a second end arranged opposite to the first end in sequence; a plane passing through the winding center axis of the electrode assembly and perpendicular to the first direction is defined as a winding center plane, the electrode assembly includes a first part and a second part respectively located on both sides of the winding center plane, in the first direction, the first part is closer to the first end than the second part, and the M positive electrode tabs are all connected to the first part.

5. The secondary battery according to claim 4, wherein: The secondary battery further includes a first adhesive member that bonds a surface of the second portion and an inner surface of the receiving portion.

6. The secondary battery according to claim 4, wherein: M first negative electrode tabs are respectively connected to the first part and the second part, the number of the first negative electrode tabs connected to the first part is greater than the number of the first negative electrode tabs connected to the second part; in the first direction, there is a first side from the first part to the second part and a second side opposite to the first side, the first negative electrode tab includes a first section connected to the first end edge and a second section connected to the first section, the first section extends from the first end edge to the first side, the second section is bent relative to the first section and extends along the second side, and the first transfer tab is connected to the second section.

7. The secondary battery according to any one of claims 1 to 6, wherein The silicon material accounts for 10% to 30% by mass in the negative electrode active material layer.

8. The secondary battery according to any one of claims 1 to 7, wherein M is 1, and the secondary battery further includes P second negative electrode tabs and a second adapter tab, P is greater than or equal to 2, the P second negative electrode tabs are integrally arranged with the negative electrode collector and connected to the first end edge, and in the first direction, the P second negative electrode tabs overlap and are connected to the second adapter tab, the first adapter tab and the second adapter tab extend out of the packaging bag from the same side of the packaging bag, and the second adapter tab is configured to be electrically connected to an external circuit.

9. The secondary battery according to claim 8, wherein: The electrode assembly includes n layers of negative electrode sheets in the first direction, N≤n / 2, P≤n / 2.

10. The secondary battery according to claim 8 or 9, wherein: In a third direction perpendicular to both the first direction and the second direction, the positive electrode tab is arranged between the first switching tab and the second switching tab.

11. The secondary battery according to claim 8 or 9, wherein: In a third direction perpendicular to both the first direction and the second direction, the second transfer tab is disposed between the positive electrode tab and the first transfer tab.

12. The secondary battery according to any one of claims 1 to 7, wherein: M is 2, and when viewed from the first direction, the two positive electrode tabs are separated.

13. The secondary battery according to claim 12, wherein The electrode assembly includes n layers of negative electrode sheets in the first direction, where N>2 / n.

14. The secondary battery according to claim 12 or 13, wherein: The difference in the number of layers of the positive electrode sheets connected to the two positive electrode tabs is 1 to 4.

15. The secondary battery according to any one of claims 12 to 14, wherein In a third direction perpendicular to both the first direction and the second direction, the first transfer tab is disposed between the two positive electrode tabs.

16. The secondary battery according to any one of claims 12 to 14, wherein In a third direction perpendicular to both the first direction and the second direction, one of the positive electrode tabs is disposed between the first transfer tab and the other positive electrode tab.

17. The secondary battery according to any one of claims 1 to 16, wherein: The silicon material is selected from at least one of elemental silicon, silicon oxide, silicon-carbon material and silicon alloy.

18. An electronic device, wherein: The invention comprises a battery compartment and a secondary battery as claimed in any one of claims 1 to 17 arranged in the battery compartment.

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