Electrode assembly and electrochemical apparatus

Abstract

The present application discloses an electrode assembly and an electronic device. The electrode assembly is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet that are stacked. The positive electrode sheet comprises a positive electrode tab, a positive electrode current collector, and a positive electrode active material layer, wherein the positive electrode current collector has a thickness of T1 and a width of W1. In a first direction, the distance between the positive electrode tab and a first finishing end is A; and in a second direction, the distance between the positive electrode tab and a first starting end is B. The negative electrode sheet comprises a negative electrode tab, a negative electrode current collector, and a negative electrode active material layer, wherein the negative electrode current collector has a thickness of T2 and a width of W2. In the first direction, the distance between the negative electrode tab and a second finishing end is C; and in the second direction, the distance between the negative electrode tab and a second starting end is D. 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, so that magnetic fields generated by currents in two directions can cancel out each other, thereby achieving the overall demagnetization effect, effectively reducing the interference of the magnetic fields of the electrode assembly on an electronic device.

Description

Electrode assembly and electrochemical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on September 7, 2023, with application number 202311152361.3, entitled “Electrode Assembly and Electrochemical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments of the present application relate to the field of electrochemical technology, and in particular to an electrode assembly and an electrochemical device. Background Art

[0004] Compared to laminated batteries, wound batteries have the advantages of low cost and easy production and are widely used in consumer and power batteries. Due to the special structure of the spiral involute of the electrode assembly of wound batteries, and the fact that the starting and ending ends of the positive and negative active material layers of the positive and negative electrodes do not usually overlap to prevent lithium deposition, a strong axial magnetic field is usually generated at the two end faces of the battery. For batteries with strong magnetic fields, in some application scenarios, they will cause significant interference to electronic devices, such as large cylindrical batteries interfering with circuit boards, small wound batteries interfering with the current sound of Bluetooth headsets, and affecting wireless charging efficiency. Therefore, reducing the magnetic field of wound batteries is a technical problem that needs to be solved urgently.

[0005] Summary of the Invention

[0006] The embodiments of the present application aim to provide an electrode assembly and an electrochemical device to improve the technical problem of interference of the battery magnetic field on electronic devices.

[0007] In order to solve the technical problems, the embodiments of the present application adopt the following technical solutions:

[0008] In a first aspect, the present application provides an electrode assembly formed by winding a stacked positive electrode sheet, a separator, and a negative electrode sheet. The separator is disposed between the positive and negative electrode sheets, and the positive electrode sheet is located on the side of the negative electrode sheet facing away from the center of the electrode assembly. The positive electrode sheet includes a positive electrode tab, a positive current collector, and a positive active material layer. The positive electrode tab is connected to the positive current collector, and the positive active material layer is disposed on at least one surface of the positive current collector. The positive current collector has a thickness of T1 and a width of W1. Along a first direction, the positive electrode current collector has a positive winding start end and a positive winding end. The end of the positive active material layer closest to the positive winding start end is the first starting end, and the end of the positive active material layer closest to the positive winding end is the first winding end. Along the first direction, the distance from the positive electrode tab to the first winding end is A; along the second direction, the distance from the positive electrode tab to the first starting end is B. The first direction is the winding direction of the electrode assembly, and the second direction is opposite to the first direction. The negative electrode sheet includes a negative electrode tab, a negative electrode current collector, and a negative electrode active material layer. The negative electrode tab is connected to the negative electrode current collector, and the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. The negative electrode current collector has a thickness of T2 and a width of W2. Along the first direction, the negative electrode current collector has a negative electrode winding start end and a negative electrode winding end end. The end of the negative electrode active material layer closest to the negative electrode winding start end is the second starting end, and the end of the negative electrode active material layer closest to the negative electrode winding end end is the second ending end. Along the first direction, the distance from the negative electrode tab to the second ending end is C; along the second direction, the distance from the negative electrode tab to the second starting end is D. 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, where W1<W2.

[0009] In the above technical solution, since the magnetic field generated by the current is proportional to both the current intensity and the current distance, when the total charge flowing through the positive electrode collector and the negative electrode collector in the battery is the same, the current intensity is inversely proportional to the cross-sectional area of ​​the collector. The magnetic field intensity generated by the current distance flowing in the first direction X is reflected by A / (T1*W1)+D / (T2*W2), and the magnetic field intensity generated by the current distance flowing in the second direction Y is reflected by B / (T1*W1)+C / (T2*W2). Controlling 0.8≤[A / (T1*W1)+D / (T2*W2))] / [B / (T1*W1)+C / (T2*W2)]≤1.2 can offset the magnetic fields generated by the currents in the two directions, thereby achieving the effect of overall demagnetization, which can effectively reduce the interference of the magnetic field of the electrode assembly on the electronic equipment.

[0010] Furthermore, 0.94≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.05 can further weaken the magnetic field strength, thereby further reducing the interference of the magnetic field of the electrode assembly on the electronic equipment and ensuring the normal operation of the electronic equipment.

[0011] In some preferred embodiments, the positive electrode current collector includes a first hollow foil segment and a first coated segment, which are arranged sequentially along a first direction. The positive electrode tab is connected to the first hollow foil segment, and the first coated segment is provided with a positive electrode active material layer.

[0012] Optionally, the positive electrode current collector includes a first hollow foil segment and a first coated segment, which are sequentially arranged along the second direction. The positive electrode tab is connected to the first hollow foil segment, and the first coated segment is provided with a positive electrode active material layer.

[0013] In some preferred embodiments, the positive electrode current collector further includes a second coating segment, wherein the second coating segment, the first bare foil segment, and the first coating segment are sequentially arranged along a first direction. The second coating segment is provided with a positive electrode active material layer. The positive electrode tab is located between the two coating segments, allowing current to flow through the positive electrode active material layers on both coating segments simultaneously, thereby increasing the charge and discharge rate.

[0014] Optionally, the negative electrode current collector includes a second hollow foil segment and a third coated segment, which are sequentially arranged along the second direction. The third coated segment is provided with a negative electrode active material layer, and the negative electrode tab is connected to the second hollow foil segment.

[0015] In some preferred embodiments, the negative electrode current collector includes a second hollow foil segment and a third coated segment, which are sequentially arranged along the first direction. The third coated segment is provided with a negative electrode active material layer, and the negative electrode tab is connected to the second hollow foil segment.

[0016] In some preferred embodiments, the negative electrode current collector further includes a fourth coating segment, wherein the fourth coating segment, the second hollow foil segment, and the third coating segment are sequentially arranged along the first direction. The fourth coating segment is provided with a negative electrode active material layer. The negative electrode tab is located between the two coating segments, allowing current to flow through the negative electrode active material layers on both coating segments simultaneously, thereby increasing the charge and discharge rate.

[0017] In some preferred embodiments, the positive electrode sheet includes multiple positive electrode tabs, each of which is connected to a positive electrode current collector, and the multiple positive electrode tabs are arranged sequentially along a first direction. The distance between the positive electrode tab at the end of the arrangement and the first end in the first direction is A. The distance between the positive electrode tab at the beginning of the arrangement and the first start in the second direction is B. The multiple positive electrode tabs can facilitate increasing the charge and discharge rate.

[0018] In some preferred embodiments, the negative electrode sheet includes multiple negative electrode tabs, each of which is connected to a negative electrode current collector. The multiple negative electrode tabs are arranged sequentially along a first direction. The distance between the negative electrode tab at the end of the arrangement and the second end in the first direction is C. The distance between the negative electrode tab at the beginning of the arrangement and the second beginning in the second direction is D. Multiple negative electrode tabs can facilitate increasing the charge and discharge rate.

[0019] In some preferred embodiments, the electrode assembly further includes a first insulating member and a second insulating member, wherein the first insulating member covers the positive electrode tab and the second insulating member covers the negative electrode tab, thereby isolating the positive electrode tab from the negative electrode tab to reduce the occurrence of short circuits.

[0020] In some preferred embodiments, the first insulating member extends beyond the positive electrode active material layer, thereby reducing the risk of puncture of the separator by structures such as the positive electrode tab and the edges of the positive electrode active material layer, thereby reducing the risk of short circuits. The second insulating member extends beyond the negative electrode active material layer, thereby reducing the risk of puncture of the separator by structures such as the negative electrode tab and the edges of the negative electrode active material layer, thereby further reducing the risk of short circuits.

[0021] In a second aspect, the present application further provides an electronic device comprising a housing and an electrode assembly as described in any embodiment of the first aspect. The electrode assembly is housed in the housing, with the positive electrode tab and the negative electrode tab both extending out of the housing.

[0022] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, which can be implemented in accordance with the contents of the specification, and to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0024] FIG1 is a schematic diagram of the winding structure of an electrode assembly according to some embodiments of the present application;

[0025] FIG2 is a schematic structural diagram of a positive electrode sheet in some embodiments of the present application;

[0026] FIG3 is a schematic diagram of the stacked structure of positive electrode sheets and negative electrode sheets in some embodiments of the present application;

[0027] FIG4 is a schematic structural diagram of a negative electrode sheet in some embodiments of the present application;

[0028] FIG5 is a schematic diagram of the stacked structure of positive electrode sheets and negative electrode sheets in some embodiments of the present application;

[0029] FIG6 is a schematic diagram of the stacked structure of positive electrode sheets and negative electrode sheets in some embodiments of the present application;

[0030] FIG7 is a schematic diagram of the stacked structure of the positive electrode sheet and the negative electrode sheet in some embodiments of the present application;

[0031] FIG8 is a schematic diagram of the stacked structure of positive electrode sheets and negative electrode sheets in some embodiments of the present application;

[0032] FIG9 is a schematic structural diagram of a positive electrode sheet and a negative electrode sheet in some embodiments of the present application;

[0033] FIG10 is a schematic diagram of the structure of the positive electrode sheet and the negative electrode sheet of some embodiments of the present application.

[0034] Description of reference numerals:

[0035] 100. Electrode assembly;

[0036] 10. Positive electrode sheet; 11. Positive electrode current collector; 11a. First main surface; 111. First coating section; 112. First bare foil section; 113. Second coating section; 114. Positive electrode winding starting end; 115. Positive electrode winding ending end; 12. Positive electrode active material layer; 121. First starting end; 122. First ending end; 13. Positive electrode tab; 13a. First starting tab; 13b. First ending tab;

[0037] 20. Negative electrode sheet; 21. Negative electrode current collector; 21a. Second main surface; 211. Third coating section; 212. Second bare foil section; 213. Fourth coating section; 214. Negative electrode winding starting end; 215. Negative electrode winding ending end; 22. Negative electrode active material layer; 221. Second starting end; 222. Second ending end; 23. Negative electrode tab; 22a. Second starting tab; 23b. Second ending tab;

[0038] 30. Isolation film;

[0039] 40. a first insulating member;

[0040] 50. Second insulating member;

[0041] X, first direction; Y, second direction; Z, third direction; H, fourth direction. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0043] It should be noted that when an element is described as being “disposed on” another element, it may be directly on the other element, or one or more intervening elements may be present therebetween. When an element is described as being “connected” or “welded” to another element, it may be directly connected / welded to the other element, or one or more intervening elements may be present therebetween.

[0044] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0045] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive with other embodiments. Furthermore, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not conflict with each other.

[0046] In the first aspect, the present application proposes an electrode assembly 100. Please refer to Figure 1. The electrode assembly 100 includes a positive electrode sheet 10, an isolation film 30 and a negative electrode sheet 20. The positive electrode sheet 10, the isolation film 30 and the negative electrode sheet 20 are stacked and wound to form a wound electrode assembly 100. The positive electrode sheet 10 is located on the side of the negative electrode sheet 20 away from the winding center of the electrode assembly 100. The isolation film 30 is arranged between the positive electrode sheet 10 and the negative electrode sheet 20 to separate the two.

[0047] With reference to FIG2 , the positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 may be disposed on at least one surface of the positive electrode current collector 11. For example, the positive electrode current collector 11 may be a flat, strip-shaped structure. Along the thickness direction (fourth direction H) of the positive electrode current collector 11, the positive electrode current collector 11 includes two first major surfaces 11 a disposed opposite each other. The positive electrode active material layer 12 may be disposed on both first major surfaces 11 a.

[0048] The positive electrode current collector 11 can be made of aluminum foil or a composite aluminum foil with a polymer layer. The positive electrode current collector 11 has a thickness T1 (thickness along the fourth direction H) and a width W1 (width along the third direction Z). The positive electrode active material layer 12 includes a positive electrode active material, a conductive agent, a binder, and deionized water. These materials are mixed, stirred, and applied to the at least one first major surface 11a to form the positive electrode active material layer 12. The positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron manganese phosphate, and cobalt-free materials.

[0049] Referring further to FIG. 3 , the positive electrode sheet 10 further includes a positive electrode tab 13 , which is electrically connected to the positive electrode current collector 11 , for example, by welding, connecting with conductive adhesive, or integrally forming the positive electrode tab 13 with the positive electrode current collector 11 . After the positive electrode sheet 10 , separator 30 , and negative electrode sheet 20 are stacked and wound to form the electrode assembly 100 , the positive electrode tab 13 extends in a third direction Z. The positive electrode tab 13 can be a metal sheet that connects the positive electrode sheet 10 to an external circuit, such as a conductive metal sheet such as an aluminum sheet or a nickel sheet, for electrical connection to the external circuit.

[0050] Along the first direction X, the positive electrode current collector 11 has a positive electrode winding starting end 114 and a positive electrode winding ending end 115. The positive electrode active material layer 12 has a first starting end 121 and a first ending end 122. The end of the positive electrode active material layer 12 closest to the positive electrode winding starting end 114 is the first starting end 121, and the end of the positive electrode active material layer 12 closest to the positive electrode winding ending end 115 is the first ending end 122. The positive electrode tab 13 can be positioned near the first starting end 121, near the first ending end 122, or between the first starting end 121 and the first ending end 122. Along the first direction X, the distance from the positive electrode tab 13 to the first ending end 122 is A. Along the second direction Y, the distance from the positive electrode tab 13 to the first starting end 121 is B. The first direction X is the winding direction of the electrode assembly 100 (i.e., the winding direction after the positive electrode sheet 10, separator 30, and negative electrode sheet 20 are stacked and wound. When not wound, the first direction X can also be considered the length direction of the positive electrode sheet 10, separator 30, or negative electrode sheet 20). The second direction Y is opposite to the first direction X. It should be noted that the first starting end 121 and the first ending end 122 are not necessarily on the same side of the positive electrode active material layer 12. The end of the positive electrode active material layer 12 closest to the positive electrode winding starting end 114 of the positive electrode current collector 11 is the first starting end 121, and the end closest to the positive electrode winding ending end 115 of the positive electrode current collector 11 is the first ending end 122.

[0051] With reference to Figures 3 and 4 , the negative electrode sheet 20 has opposite polarity to the positive electrode sheet 10. The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 may be disposed on at least one surface of the negative electrode current collector 21. For example, the negative electrode current collector 21 may be a flat, strip-shaped structure. Along the thickness direction (fourth direction H) of the negative electrode current collector 21, the negative electrode current collector 21 includes two opposing second major surfaces 21 a. The negative electrode active material layer 22 may be disposed on both second major surfaces 21 a.

[0052] The negative electrode current collector 21 can be made of copper foil or a composite copper foil with a polymer layer. The thickness of the negative electrode current collector 21 is T2 (thickness along the fourth direction H) and the width is W2 (width along the third direction Z). The material of the polymer layer can be selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyamide, polyimide, polyvinyl chloride, and polystyrene. The positive electrode active material layer 12 includes a negative electrode active material, a conductive agent, a binder, and deionized water. The above materials are mixed, stirred evenly, and applied to the at least one first major surface 11a to obtain the positive electrode active material layer 12. The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, silicon, silicon oxide, silicon-carbon composite, and silicon alloy. In some other embodiments, the positive electrode plate 10 can also be a negative electrode plate, and the negative electrode plate 20 can be a positive electrode plate, which is not limited in this application.

[0053] The negative electrode sheet 20 also includes a negative electrode tab 23, which is electrically connected to the negative electrode current collector 21. For example, the negative electrode tab 23 and the negative electrode current collector 21 can be welded, connected with conductive adhesive, or integrally formed. After the positive electrode sheet 10, separator 30, and negative electrode sheet 20 are stacked and wound to form the electrode assembly 100, the negative electrode tab 23 and the positive electrode tab 13 both extend in the third direction Z. The negative electrode tab 23 can be a metal sheet that connects the negative electrode sheet 20 to an external circuit, such as a conductive metal sheet such as a copper sheet or a nickel sheet, for electrical connection to the external circuit.

[0054] Along the first direction X, the negative electrode current collector 21 has a negative electrode winding starting end 24 and a negative electrode winding ending end 25. The negative electrode active material layer 22 has a second starting end 221 and a second ending end 222. The end of the negative electrode active material layer 22 closest to the negative electrode winding starting end 24 is the second starting end 221, and the end of the negative electrode active material layer 22 closest to the negative electrode winding ending end 25 is the second ending end 222. The negative electrode tab 23 can be positioned near the second starting end 221, near the second ending end 222, or between the second starting end 221 and the first ending end 122. Along the first direction X, the distance from the negative electrode tab 23 to the second ending end 222 is C. Along the second direction Y, the distance from the negative electrode tab 23 to the second starting end 221 is D.

[0055] It should be noted that the second starting end 221 and the second ending end 222 are not necessarily on the same side of the negative electrode active material layer 22. The end of the negative electrode active material layer 22 closest to the negative electrode winding starting end 24 of the negative electrode current collector 21 is the second starting end 221, and the end closest to the negative electrode winding ending end 25 of the negative electrode current collector 21 is the second ending end 222.

[0056] In addition, the distance from the negative electrode tab 23 to the second end 222 refers to the distance between the side of the negative electrode tab 23 closest to the second end 222 and the second end 222; the distance from the negative electrode tab 23 to the second starting end 221 refers to the distance between the side of the negative electrode tab 23 closest to the second starting end 221 and the second starting end 221. The same applies to the positive electrode tab 13.

[0057] Where, 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, and W1<W2. When current flows through the positive electrode tab 13 and the positive electrode active material layer 12, a first current path is formed along the first direction X from the positive electrode tab 13 to the first end 122. A second current path is formed along the second direction Y from the positive electrode tab 13 to the first start end 121. The currents in the first and second current paths flow in opposite directions.

[0058] When the current flows through the negative electrode active material layer 22 via the negative electrode tab 23, a third current path is formed along the first direction X between the negative electrode tab 23 and the second end 222; and a fourth current path is formed along the second direction Y between the negative electrode tab 23 and the second starting end 221. The current flows in opposite directions in the third current path and the fourth current path. The direction of current refers to the direction in which electric charge flows in a conductor. By definition, the direction of current is defined as the direction in which positive charge flows. The above-mentioned positive electrode sheet 10 and negative electrode sheet 20 have opposite polarities, the first current path and the fourth current path have the same direction, and the second current path and the third current path have opposite directions.

[0059] The magnetic field of the wound electrode assembly 100 is the magnetic field generated by the current passing through the electrode assembly 100. When current passes through the electrode assembly 100, a circular magnetic field is formed around it. According to Ampere's circuit theorem, the magnetic field generated by current is proportional to both the current intensity and the distance traveled. When the total charge flowing through the positive and negative current collectors 11 and 21 in a battery is the same, the current intensity is inversely proportional to the cross-sectional area of ​​the current collectors. In the embodiment of the present application, the magnetic field strength generated by the distance of the current flowing in the first direction X is reflected by A / (T1*W1)+D / (T2*W2), and the magnetic field strength generated by the distance of the current flowing in the second direction Y is reflected by B / (T1*W1)+C / (T2*W2). Controlling 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2 can offset the magnetic fields generated by the currents in the two directions, thereby achieving the effect of overall demagnetization, which can effectively reduce the interference of the magnetic field of the electrode assembly 100 on the electronic equipment.

[0060] Preferably, 0.94≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.05, which can further weaken the magnetic field strength, thereby further reducing the interference of the magnetic field of the electrode assembly 100 on the electronic equipment and ensuring the normal operation of the electronic equipment.

[0061] Regarding the separator 30, referring to FIG1 , the separator 30 is disposed between the positive electrode sheet 10 and the negative electrode sheet 20 to separate them. The separator 30 can be bonded between the positive electrode sheet 10 and the negative electrode sheet 20 to improve the overall bonding strength of the electrode assembly 100. The separator 30 can be one or more of a polyethylene separator, a ceramic-containing polyethylene-coated separator, an adhesive-coated polyethylene-coated separator, a polypropylene separator, and a polypropylene-coated separator.

[0062] In some other embodiments, referring to FIG. 3 , the electrode assembly 100 further includes a first insulating member 40 and a second insulating member 50 . The first insulating member 40 is disposed on the positive electrode active material layer 12 and covers the positive electrode tab 13 . The second insulating member 50 is disposed on the negative electrode active material layer 22 and covers the negative electrode tab 23 , thereby reducing the possibility of a short circuit caused by direct contact between the positive electrode tab 13 and the negative electrode tab 23 . Furthermore, the first insulating member 40 covers the interface between the positive electrode active material layer 12 and the positive electrode tab 13 , thereby reducing the possibility of structures such as protruding burrs on the edges of the positive electrode tab 13 and the positive electrode active material layer 12 piercing the separator, thereby reducing the possibility of a short circuit. The second insulating member 50 covers the interface between the negative electrode active material layer 22 and the negative electrode tab 23 , thereby reducing the possibility of structures such as protruding burrs on the edges of the negative electrode tab 23 and the negative electrode active material layer 22 piercing the separator, thereby further reducing the possibility of a short circuit.

[0063] Referring to Figure 5 , the positive electrode tab 13 is positioned near the first starting end 121. The positive electrode current collector 11 includes a first hollow foil segment 112 and a first coated segment 111. The first hollow foil segment 112 and the first coated segment 111 are sequentially positioned along the first direction X. The first coated segment 111 is the portion of the positive electrode current collector 11 where the first active material layer is positioned, while the first hollow foil segment 112 is the portion of the positive electrode current collector 11 where the positive active material layer 12 is not positioned. The positive electrode tab 13 is directly electrically connected to the positive electrode current collector 11 at the first hollow foil segment 112. The first starting end 121 is positioned near the first hollow foil segment 112. Along the first direction X, the distance A from the positive electrode tab 13 to the first tail end 122 is 0. However, the positive electrode tab 13 does not have the positive active material layer 12 in the second direction Y. That is, along the second direction Y, the distance B from the positive electrode tab 13 to the first starting end 121 is 0.

[0064] The negative electrode tab 23 is positioned near the second starting end 221. The negative electrode current collector 21 includes a second hollow foil segment 212 and a third coated segment 211, which are arranged sequentially along the first direction X. The third coated segment 211 is the portion where the negative electrode active material layer 22 is disposed, while the second hollow foil segment 212 is the portion where the negative electrode active material layer 22 is not disposed. The negative electrode tab 23 is directly electrically connected to the negative electrode current collector 21 at the second hollow foil segment 212. The second starting end 221 is positioned near the second hollow foil segment 212. Along the first direction X, the distance C from the negative electrode tab 23 to the second tail end 222 is 0. In the second direction Y, the negative electrode tab 23 is free of the negative electrode active material layer 22. That is, along the second direction Y, the distance D from the negative electrode tab 23 to the second starting end 221 is 0. At this time, 0.8≤[A / (T1*W1)] / [C / (T2*W2)]≤1.2, which can improve the demagnetization effect of the electrode assembly 100.

[0065] Referring to Figure 6 , the positive electrode current collector 11 further includes a second coating segment 113. The second coating segment 113, the first bare foil segment 112, and the first coating segment 111 are sequentially arranged along a first direction X. The second coating segment 113 is also provided with a positive electrode active material layer 12. Along the first direction X, the distance from the positive electrode tab 13 to the first tail end 122 is A; along the second direction Y, the distance from the positive electrode tab 13 to the first starting end 121 is B. The negative electrode tab 23 is positioned near the second starting end 221. Along the first direction X, the distance from the negative electrode tab 23 to the second tail end 222 is C; along the second direction Y, the distance from the negative electrode tab 23 to the second starting end 221 is 0. The direction of current A is opposite to that of current C. In this case, 0.8 ≤ [A / (T1*W1)] / [B / (T1*W1)+C / (T2*W2)] ≤ 1.2, achieving an optimal demagnetization effect.

[0066] Referring to Figure 7 , the positive electrode tab 13 is positioned near the first starting end 121. Along the first direction X, the distance A between the positive electrode tab 13 and the first tail end 122 is measured. Along the second direction Y, the distance B between the positive electrode tab 13 and the first starting end 121 is 0. The negative electrode current collector 21 also includes a fourth coating segment 213. The fourth coating segment 213, the second hollow foil segment 212, and the third coating segment 211 are sequentially arranged along the first direction X. The fourth coating segment 213 is provided with a negative electrode active material layer 22. Along the first direction X, the distance C between the negative electrode tab 23 and the second tail end 222 is measured. Along the second direction Y, the distance D between the negative electrode tab 23 and the second starting end 221 is measured. In this case, 0.8 ≤ [A / (T1*W1) + D / (T2*W2)] / [C / (T2*W2)] ≤ 1.2, achieving optimal demagnetization performance.

[0067] 8 , when the positive electrode active material layer 12 exists in both the first direction X and the second direction Y of the positive electrode tab 13, and the negative electrode active material layer 22 exists in both the first direction X and the second direction Y of the negative electrode tab 23, then 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, and a better demagnetization effect can be achieved.

[0068] Optionally, the first empty foil segment 112 and the first coated segment 111 may also be arranged sequentially along the second direction Y, the positive electrode tab 13 is connected to the first empty foil segment 112, and the first coated segment 111 is provided with the positive electrode active material layer 12. In this case, A is 0. Similarly, the second empty foil segment 212 and the third coated segment 211 are arranged sequentially along the second direction Y, the third coated segment 211 is provided with the negative electrode active material layer 22, and the negative electrode tab 23 is connected to the second empty foil segment 212. In this case, C is 0.

[0069] In some embodiments, referring to Figures 9 and 10, the positive electrode sheet 10 includes a plurality of positive electrode tabs 13. The plurality of positive electrode tabs 13 are sequentially arranged along a first direction X and electrically connected to a positive electrode current collector 11. The plurality of positive electrode tabs 13 extend from a third direction Z. Along the first direction X, the positive electrode tab 13 at the starting end of the arrangement (denoted as the first starting tab 13a) is disposed near the first starting end 121, and the positive electrode tab 13 at the end of the arrangement (denoted as the first ending tab 13b) is disposed near the first ending end 122.

[0070] The first starting end 121 may be located in the first direction X of the first starting tab 13 a , or may be located in the second direction Y of the first starting tab 13 a .

[0071] Referring to Figure 9 , the first starting end 121 is located in the second direction Y of the first starting tab 13a, and the first ending end 122 is located in the first direction X of the first ending tab 13b. Along the second direction Y, the distance B from the first starting tab 13a to the first starting end 121 is measured; along the first direction X, the distance A from the first ending tab 13b to the first ending end 122 is measured. A common region E exists between the first starting tab 13a and the first ending tab 13b. Current flows through this common region in both the first direction X and the second direction Y. Therefore, this common region E is negligible. Furthermore, regardless of the number of positive tabs 13 disposed within this common region E, it can be ignored.

[0072] Referring to FIG. 10 , when the first starting end 121 is in the first direction X of the first starting tab 13 a and the first ending end 122 is in the second direction Y of the first ending tab 13 b , a common area E exists between the first starting tab 13 a and the first ending tab 13 b , which directly satisfies the requirement that the current passing distances in both directions are equal.

[0073] When the negative electrode sheet 20 includes multiple negative electrode tabs 23, they can be arranged similarly to the above-mentioned positive electrode sheet 10. Referring to Figure 9, along the first direction X, the negative electrode tab 23 at the starting end of the arrangement (denoted as the second starting tab 23a) is arranged near the second starting end 221, and the negative electrode tab 23 at the end of the arrangement (denoted as the second ending tab 23b) is arranged near the second ending end 222. The second starting end 221 is in the second direction Y of the second starting tab 23a, and the second ending end 222 is in the first direction X of the second ending tab 23b. Along the second direction Y, the distance from the second starting tab 23a to the second starting end 221 is D; along the first direction X, the distance from the second ending tab 23b to the second ending end 222 is C. There is a common area F between the second starting tab 23a and the second ending tab 23b. Current in the first direction X and the second direction Y will flow through the common area at the same time. Therefore, the common area F can be ignored. At the same time, no matter how many negative tabs 23 are set in the common area F, they can be ignored.

[0074] Referring to FIG. 10 , when the second starting end 221 is in the first direction X of the second starting pole tab 23 a and the second ending end 222 is in the second direction Y of the second ending pole tab 23 b , a common area F is formed between the second starting pole tab 23 a and the second ending pole tab 23 b . This directly ensures that the current passing distances in both directions are equal, thereby further improving the demagnetization effect.

[0075] In the embodiment of the present application, 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, that is, the distance of the current flowing through the electrode assembly 100 in the first direction X is approximately the same as the distance of the current flowing through the second direction Y, so that the magnetic fields generated by the currents in the two directions can be offset, thereby achieving the effect of overall demagnetization, which can effectively reduce the interference of the magnetic field of the electrode assembly 100 on electronic equipment.

[0076] In the embodiment of the present application, a wound lithium-ion battery is taken as an example to perform a magnetic field strength test on it.

[0077] Example 1

[0078] Preparation of positive electrode sheet:

[0079] The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. Aluminum foil with a thickness T1 of 9μm is used as the positive electrode current collector. The aluminum foil is divided into the second coating section, the first empty foil section and the first coating section along the length direction of the aluminum foil. The slurry is evenly coated on the first coating section and the second coating section on one surface of the aluminum foil. The end of the second coating section is marked as the first starting end, and the end of the first coating section away from the second coating section is marked as the first ending end. Drying at 90℃, the positive electrode active material weight is 17.2mg / cm 2 After completing the above steps, the positive electrode sheet is coated on one side. The above steps are then repeated on the other side of the positive electrode sheet to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer. After coating, the sheet is cold pressed, cut, and slit to obtain a positive electrode sheet with a specification of 1210 mm x 72.7 mm (width W1).

[0080] Preparation of negative electrode sheet:

[0081] The negative electrode active material graphite powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 97.5:1:1.5, and then deionized water is added as a solvent to prepare a slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness T2 of 5μm is used as the negative electrode current collector, and the negative electrode current collector is divided into a fourth coating section, a second empty foil section, and a third coating section along its length. The slurry is evenly coated on the third coating section and the fourth coating section of one surface of the copper foil. The end of the fourth coating section away from the third coating section is recorded as the second starting end, and the end of the third coating section away from the fourth coating section is recorded as the second ending end. Drying at 110°C obtains a negative electrode active material weight of 9.1mg / cm 2 Single-sided negative electrode sheet. After completing the above steps, the negative electrode sheet is coated on one side. Repeat the above steps on the other side of the negative electrode sheet to obtain a negative electrode sheet coated on both sides with the negative electrode active material layer. After coating, the negative electrode sheet is cold pressed, cut, and slit to obtain a negative electrode sheet with a specification of 1220 mm x 74.2 mm (width W2).

[0082] Preparation of isolation membrane:

[0083] A 5μm thick polyethylene porous membrane is used as the substrate layer, and a 3μm ceramic layer is coated on the middle part of one surface of the substrate layer (the middle part in the width direction, i.e., the second part, and the parts at both ends in the width direction, i.e., the first part and the third part), and a 2μm thick PVDF adhesive layer is coated on both surfaces of the substrate layer. The adhesive layer covers the ceramic layer in the second part, and the first part and the third part do not contain a ceramic layer.

[0084] Electrode assembly preparation

[0085] A nickel sheet is used as the positive electrode tab, and the positive electrode tab is welded to the first empty foil area of ​​the positive electrode current collector aluminum foil, wherein the distance A from the positive electrode tab to the first tail end is 500 mm, and the distance B from the positive electrode tab to the first starting end is 500 mm.

[0086] A copper sheet is used as the negative electrode tab, and the negative electrode tab is welded to the second empty foil area of ​​the negative electrode current collector copper foil, wherein the distance C from the negative electrode tab to the second tail end is 505 mm, and the distance D from the negative electrode tab to the second starting end is 505 mm.

[0087] The negative electrode sheet and the separator positive electrode sheet are stacked in sequence, and are wound starting from the first starting end to form a wound electrode assembly.

[0088] Lithium-ion battery preparation

[0089] The electrode assembly is subjected to processes such as aluminum-plastic film packaging, liquid injection, and chemical formation to prepare a lithium-ion battery.

[0090] Example 2

[0091] The differences from Example 1 are: A=450 mm; B=550 mm; C=580 mm; D=440 mm; T1=8.5 μm; and T2=6.5 μm.

[0092] Example 3

[0093] The differences from Example 1 are: A=450 mm; B=550 mm; C=560 mm; and D=450 mm.

[0094] Example 4

[0095] The differences from Example 1 are: A=500 mm; B=500 mm; C=560 mm; and D=450 mm.

[0096] Example 5

[0097] The differences from Example 1 are: A=550 mm; B=450 mm; C=560 mm; and D=450 mm.

[0098] Example 6

[0099] The differences from Example 1 are: A=550 mm; B=450 mm; C=510 mm; and D=500 mm.

[0100] Example 7

[0101] The differences from Example 1 are: A=600 mm; B=400 mm; C=510 mm; D=500 mm; T1=7 μm; and T2=6 μm.

[0102] Example 8

[0103] The difference from Example 1 is that the first empty foil segment is located at the starting end of the winding of the positive electrode sheet, the positive electrode current collector has only the first coating segment, and the first coating segment is located in the first direction (winding direction) of the first empty foil segment, and the distance A from the positive electrode tab to the first tail end is 1000 mm; there is no active material layer in the second direction (opposite direction of the winding direction) of the positive electrode tab, and B is 0.

[0104] The second empty foil segment is located at the starting end of the winding of the negative electrode sheet. The negative electrode current collector has only the third coating segment, and the third coating segment is located in the first direction (winding direction) of the second empty foil segment. The distance from the negative electrode tab to the second tail end is C = 1020 mm; there is no active material layer in the second direction of the negative electrode tab, D = 0; T1 = 8 μm; T2 = 6.5 μm.

[0105] Example 9

[0106] The difference from Example 1 is that A=950 mm; B=100 mm.

[0107] The second empty foil segment is located at the starting end of the winding of the negative electrode sheet. The negative electrode current collector has only the third coating segment, and the third coating segment is located in the first direction (winding direction) of the second empty foil segment. The distance from the negative electrode tab to the second tail end is B = 1020 mm; there is no active material layer in the second direction of the negative electrode tab, D = 0; T1 = 7.5 μm; T2 = 7 μm.

[0108] Example 10

[0109] Unlike Example 1, the first empty foil segment is located at the starting end of the positive electrode sheet. The positive electrode current collector has only the first coated segment, and the first coated segment is located in the first direction (winding direction) of the first empty foil segment. The distance A from the positive electrode tab to the first end is 1000 mm. There is no active material layer in the second direction (opposite to the winding direction) of the positive electrode tab, and B = 0. C = 920 mm; D = 90 mm; T1 = 8.5 μm; T2 = 5.5 μm.

[0110] Comparative Example 1

[0111] The differences from Example 1 are: A=400 mm; B=500 mm; C=610 mm; and D=400 mm.

[0112] Comparative Example 2

[0113] The differences from Example 1 are: A=600 mm; B=400 mm; C=460 mm; and D=550 mm.

[0114] Magnetic field strength test:

[0115] Test instruments: AP audio analyzer and 711 simulated headphones;

[0116] Test environment: anechoic room, background sound is -15DB (decibel);

[0117] Pass standard; sound ≤-5DB;

[0118] The test method is to place the headphones in a test environment. The audio analyzer sends a standard silent test audio, which passes through the headphones and is then transmitted to the audio analyzer. The emitted and received audio can be analyzed to measure the noise floor of the headphones. The magnetic field strength can be determined based on the noise floor of the headphones.

[0119] The test results are shown in Table 1 below:

[0120] Table 1:

[0121] The magnetic field strength affects the size of the headphone background noise. The greater the magnetic field strength, the greater the headphone background noise, and the smaller the magnetic field strength, the smaller the headphone background noise. Combined with the above Table 1, combined with Examples 1 to 10 and Comparative Examples 1 to 2, it can be seen that when 0.78≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, the headphone background noise is less than or equal to -5DB, which can significantly reduce the magnetic field strength, thereby reducing the impact on the headphone current sound. In the embodiment of the present application, 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2 is selected. In combination with Examples 1, 5, and 6, it can be seen that when 0.94≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.05, the headphone noise floor is less than or equal to -5.8 dB, which can further reduce the headphone noise floor. In the embodiments of the present application, 0.94≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.05 is selected. In addition, in combination with Examples 1 to 10, it can be seen that when [A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)] is closer to 1, the headphone noise floor is smaller, which can minimize the impact of the magnetic field on the headphone current sound.

[0122] In a second aspect, an embodiment of the present application further proposes an electrochemical device, comprising a shell and an electrode assembly as described in any embodiment of the first aspect above, wherein the electrode assembly is accommodated in the shell, and the positive electrode tab and the negative electrode tab both extend out of the shell.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrode assembly, formed by winding a stacked positive electrode sheet, a separator and a negative electrode sheet, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet is located on a side of the negative electrode sheet away from the winding center of the electrode assembly, characterized in that: The positive electrode sheet comprises a positive electrode tab, a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode tab is connected to the positive electrode current collector, and the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector; the positive electrode current collector has a thickness of T1 and a width of W1; Along the first direction, the positive electrode current collector has a positive electrode winding starting end and a positive electrode winding ending end, the end of the positive electrode active material layer closest to the positive electrode winding starting end is the first starting end, and the end of the positive electrode active material layer closest to the positive electrode winding ending end is the first ending end. Along the first direction, the distance from the positive electrode ear to the first ending end is A; along the second direction, the distance from the positive electrode ear to the first starting end is B; the first direction is the winding direction of the electrode assembly, and the second direction is opposite to the first direction; The negative electrode sheet comprises a negative electrode tab, a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode tab is connected to the negative electrode current collector, and the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector; the negative electrode current collector has a thickness of T2 and a width of W2; Along the first direction, the negative electrode current collector has a negative electrode winding starting end and a negative electrode winding ending end, the end of the negative electrode active material layer closest to the negative electrode winding starting end is the second starting end, and the end of the negative electrode active material layer closest to the negative electrode winding ending end is the second ending end; along the first direction, the distance from the negative electrode tab to the second ending end is C; along the second direction, the distance from the negative electrode tab to the second starting end is D; 0.8≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.2, where W1<W2.

2. The electrode assembly according to claim 1, characterized in that: 0.94≤[A / (T1*W1)+D / (T2*W2)] / [B / (T1*W1)+C / (T2*W2)]≤1.

05.

3. The electrode assembly according to claim 1 or 2, characterized in that: The positive electrode current collector comprises a first empty foil segment and a first coating segment, and the first empty foil segment and the first coating segment are sequentially arranged along the first direction; The positive electrode tab is connected to the first empty foil segment, and the first coating segment is provided with the positive electrode active material layer.

4. The electrode assembly according to claim 3, characterized in that: The positive electrode current collector further includes a second coating section, wherein the second coating section, the first empty foil section and the first coating section are sequentially arranged along the first direction; The second coating section is provided with the positive electrode active material layer.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that: The positive electrode current collector comprises a first empty foil segment and a first coated segment, and the first empty foil segment and the first coated segment are sequentially arranged along the second direction; The positive electrode tab is connected to the first empty foil segment, and the first coating segment is provided with the positive electrode active material layer.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: The negative electrode current collector comprises a second empty foil segment and a third coated segment, and the second empty foil segment and the third coated segment are sequentially arranged along the first direction; The third coating section is provided with the negative electrode active material layer, and the negative electrode tab is connected to the second empty foil section.

7. The electrode assembly according to claim 6, characterized in that: The negative electrode current collector further includes a fourth coating segment, wherein the fourth coating segment, the second empty foil segment and the third coating segment are sequentially arranged along the first direction; The fourth coating section is provided with the negative electrode active material layer.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that: The negative electrode current collector comprises a second empty foil segment and a third coated segment, and the second empty foil segment and the third coated segment are sequentially arranged along the second direction; The third coating section is provided with the negative electrode active material layer, and the negative electrode tab is connected to the second empty foil section.

9. The electrode assembly according to any one of claims 1 to 8, characterized in that: The electrode assembly also includes a first insulating member and a second insulating member; The first insulating member is disposed on the positive electrode active material layer, and the first insulating member covers the positive electrode tab. The second insulating member is disposed on the negative electrode active material layer, and the second insulating member covers the negative electrode tab.

10. An electrochemical device, characterized in that: comprising a housing and an electrode assembly as claimed in any one of claims 1 to 9; The electrode assembly is accommodated in the shell, and the positive electrode tab and the negative electrode tab both extend out of the shell.

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