Electrode assembly, battery monomer and electric equipment

Abstract

The embodiment of the utility model discloses an electrode assembly, a battery monomer and electric equipment, the electrode assembly comprises an anode pole piece, a cathode pole piece and a diaphragm for isolating the anode pole piece from the cathode pole piece, and the anode pole piece, the diaphragm and the cathode pole piece are wound along a winding direction and form a winding structure; the winding structure is provided with a bending area, the cathode pole piece comprises a cathode current collector, the cathode current collector comprises a first bending section located in the bending area, and an oxide layer is arranged on the surface of one side, close to the center of the winding structure, of the first bending section. Through the embodiment of the invention, the problem of how to reduce the lithium precipitation risk at the corner of the battery cell is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrode assembly, a battery cell and an electric device. BACKGROUND

[0002] In recent years, with the popularization of new energy vehicles, the production of lithium ion power batteries has been increasing year by year. The safety problem of the battery cell is also the most concerned thing in the industry. In order to ensure that the lithium ion battery has high safety, all possible safety hazards need to be ruled out.

[0003] The structure of the lithium battery can be divided into winding type and laminated type. At present, the winding type battery cell has become the mainstream due to its mature technology and high efficiency. However, the corner structure of the winding type battery cell is prone to lithium precipitation, especially at the negative corner of the innermost positive electrode attached to the negative electrode side. The main reason is that the greater the corner curvature, the more likely it is to fall off the powder. In addition, the greater the corner curvature, the smaller the CB value of the electric quantity balance value, which leads to insufficient lithium storage of the negative electrode, thereby causing lithium precipitation, which is easy to cause short circuit in the battery and cause serious safety hazards. CONTENT OF THE UTILITY MODEL

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides an electrode assembly, a battery cell and an electric device to solve the problem of how to reduce the risk of lithium precipitation at the corner of the battery cell.

[0005] In a first aspect, the present application provides an electrode assembly, comprising an anode sheet, a cathode sheet and a separator separating the anode sheet and the cathode sheet, the anode sheet, the separator and the cathode sheet being wound along a winding direction and forming a winding structure; the winding structure has a bending area, the cathode sheet comprises a cathode current collector, the cathode current collector comprises a first bending segment located in the bending area, and the first bending segment is provided with an oxidation layer on the surface close to one side of the center of the winding structure.

[0006] In one embodiment of the above-mentioned electrode assembly, the winding structure further comprises a straight area, the anode sheet comprises an anode current collector, the anode current collector comprises a second bending segment located in the bending area and a second straight segment located in the straight area, the second bending segment has a first area arranged away from the center of the winding structure, the specific surface area of the first area of the second bending segment is A, and the specific surface area of the surface of the second straight segment arranged away from the center of the winding structure is B, A > B.

[0007] In one embodiment of the above-mentioned electrode assembly, in the same winding circle of the winding structure, the first area is located on the opposite inner side of the oxidation layer, and the projection of the oxidation layer on the second bending segment covers the first area.

[0008] In one embodiment of the electrode assembly described above, the cathode tab further comprises a first coating layer and a second coating layer; the first coating layer is arranged on the surface of the cathode current collector away from the center of the winding structure; and the second coating layer is arranged on the surface of the cathode current collector close to the center of the winding structure.

[0009] In one embodiment of the electrode assembly described above, the second coating layer and the first coating layer each comprise a carbon layer arranged on the cathode current collector and an active material layer arranged on the carbon layer, and in the second coating layer, the carbon layer is provided with a bare area corresponding to the position of the oxidation layer.

[0010] In one embodiment of the electrode assembly described above, the arc length of the oxidation layer on the first bending section is 0.5-5 mm; the thickness of the oxidation layer is 0.5-2 um; and / or the arc length of the first region on the second bending section is 1-6 mm.

[0011] In one embodiment of the electrode assembly described above, the oxidation layer is a chromate passivation film; and / or the first region of the anode current collector is provided with a microporous structure.

[0012] In one embodiment of the electrode assembly described above, the first region of the anode current collector is provided with a conductive layer, and the thickness of the conductive layer is 0.5-2 um.

[0013] In a second aspect, the present application provides a battery cell comprising the electrode assembly according to any one of the first aspect.

[0014] In a third aspect, the present application provides a power consumption device comprising the battery cell according to the second aspect.

[0015] The one or more embodiments of the present application described above have at least one or more of the following beneficial effects:

[0016] In the present application, by arranging the oxidation layer on the surface of the cathode current collector close to the center of the winding structure in the bending area of the winding structure, the conductivity between the cathode current collector and the material coated on the cathode current collector is reduced or blocked, thereby reducing or blocking the release of lithium ions and reducing the risk of lithium precipitation caused by too small CB value at the corner of the winding cell.

[0017] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0018] The disclosure of the present application will become more apparent from the following description with reference to the drawings. It is readily understood by those skilled in the art that the drawings are only for the purpose of illustration and are not intended to limit the scope of protection of the present application. In addition, similar numbers in the drawings represent similar components, wherein:

[0019] Figure 1 is a schematic diagram of the electrode assembly structure in an embodiment of the present application;

[0020] Figure 2 is a schematic diagram of a bending area structure in the electrode assembly in an embodiment of the present application;

[0021] Figure 3 is a schematic diagram of a partial cross-sectional structure of the electrode assembly structure in an embodiment of the present application. DETAILED DESCRIPTION

[0022] Some embodiments of the present application will be described below with reference to the drawings. Those skilled in the art will understand that these embodiments are only for the purpose of explaining the technical principles of the present application and are not intended to limit the scope of protection of the present application.

[0023] It should be noted that in the description of the present application, the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the direction or positional relationship of the terms based on the direction or positional relationship shown in the drawings, which is only for the purpose of description and is not intended to indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0024] In addition, it should also be noted that in the description of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "setting", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. Those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0025] As described in the background, the current winding type battery, especially at the negative corner near the innermost positive side attached to the negative corner, has large corner bending, is easy to drop powder and has a small CB value less than 1, which leads to insufficient lithium storage capacity of the negative electrode, thereby easily causing lithium precipitation phenomenon. Based on this, the present application proposes an electrode assembly, which reduces or blocks the electrical conductivity at the negative corner near the innermost positive side attached to the negative corner, thereby avoiding the risk of lithium precipitation caused by powder dropping at the corner of the winding type battery and too small CB value.

[0026] Referring to the drawingsFigure 1 and Figure 2 , Figure 1 is a structural schematic diagram of an electrode assembly according to an embodiment of the present application, Figure 2 is a structural schematic diagram of a bending area of a winding structure according to an embodiment of the present application. As shown in Figure 1 and Figure 2 shown, in one or more embodiments, the electrode assembly of the present application includes an anode pole piece 1, a cathode pole piece 3, and a separator 2 separating the anode pole piece 1 and the cathode pole piece 3, the anode pole piece 1, the separator 2, and the cathode pole piece 3 are wound along a winding direction and form a winding structure; the winding structure has a bending area, the cathode pole piece 3 includes a first coating layer 7, a second coating layer 8, and a cathode current collector 4, the first coating layer 7 is arranged on the surface of the cathode current collector 4 away from the center of the winding structure; the second coating layer 8 is arranged on the surface of the cathode current collector 4 close to the center of the winding structure; the cathode current collector 4 includes a first bending section 41 located in the bending area, and the first bending section 41 is provided with an oxidation layer 6 on the surface close to the center of the winding structure.

[0027] The present application aims to reduce or block the conductivity between the cathode current collector 4 and the material coated on the cathode current collector 4 by arranging the oxidation layer 6 on the surface of the cathode current collector 4 close to the center of the winding structure in the bending area of the winding structure, thereby reducing or blocking the release of lithium ions, so that the number of embedded ions is also reduced, and the lithium precipitation phenomenon is further reduced, that is, the risk of too small CB value at the corner of the winding cell is reduced. In the present application, the cathode current collector 4 is an aluminum foil.

[0028] Specifically, in the present application, the cathode pole piece 3, the separator 2, the anode pole piece 1, and the separator 2 are stacked and wound from the inside to the outside with one end as the starting point to form a winding structure. The winding structure has a plurality of winding parts, each winding part has two flat parts arranged oppositely along the thickness direction of the winding structure and two bending parts arranged oppositely along the width direction of the winding structure, the flat parts of the plurality of winding parts constitute a flat area, and the bending parts of the plurality of winding parts constitute a bending area; the flat part includes a first flat section 42 and a second flat section 52 located in the flat area, and the bending part includes a first bending section 41 and a second bending section 51 located in the bending area; wherein, among the plurality of winding parts, the winding part located at the innermost side is the starting turn, and the winding part located at the outermost side is the ending turn.

[0029] It should be noted that in the winding structure, the cathode pole piece 3 is wound into M turns, that is, the cathode current collector 4 is also wound into M turns, so that the first bending section 41 of each turn of the cathode current collector 4 is provided with an oxidation layer 6 on the surface close to the side of the winding structure center; or in the m innermost turns of the cathode current collector 4, the first bending section 41 of each turn of the cathode current collector 4 is provided with an oxidation layer 6 on the surface close to the side of the winding structure center, wherein 2≤m≤50%M, M>50, and m and M are integers; for example, in the winding structure, the cathode pole piece 3 is wound into 100 turns, 2≤m≤50, that is, in the 40 innermost turns of the cathode pole piece 3, from the starting turn, that is, the first turn, to the 40th turn, the first bending section 41 of each turn of the cathode current collector 4 is provided with an oxidation layer 6 on the surface close to the side of the winding structure center.

[0030] It should also be noted that the oxidation layer 6 is obtained by one or more of the following surface treatments of the cathode current collector 4: acid pickling passivation, electrochemical passivation, and chemical deposition passivation.

[0031] For example, the electrochemical passivation is achieved by electrolysis, with the aluminum foil as the anode, and a direct current is applied in the aluminum sulfate solution to cause the surface of the plurality of first bending sections 41 in the aluminum foil to undergo an oxidation reaction to form aluminum oxide. For another example, the chemical deposition passivation is achieved by immersing the plurality of first bending sections 41 in the aluminum foil in an aluminum passivation agent, rinsing with water, and drying, so that an oxide film is formed on the surface.

[0032] In specific embodiments, the chromium salt passivation method is used to treat the surface of the first bending section 41 close to the side of the winding structure center to obtain the oxidation layer 6, and the oxidation layer 6 is a chromium salt passivation film.

[0033] In one embodiment, as described in Figure 1 and Figure 2 the arc length of the oxidation layer 6 on the first bending section 41 is 0.5mm-5mm.

[0034] Specifically, the arc length of the oxidation layer 6 on the first bending section 41 is determined by the arc length of the first bending section 41, and in the winding structure, the arc length of the first bending section 41 increases in the direction away from the center of the winding structure, that is, the arc length of the oxidation layer 6 increases in the direction away from the center of the winding structure, wherein the arc length of the oxidation layer 6 on the first bending section 41 is designed to be 0.5mm-5mm, which can be understood as follows: in the winding structure, the shortest arc length of the plurality of oxidation layers 6 is greater than or equal to 0.5mm, and the oxidation layer 6 with the shortest arc length is close to the starting turn of the winding structure; the longest arc length of the plurality of oxidation layers 6 is less than or equal to 5mm, and the oxidation layer 6 with the longest arc length is close to the end turn of the winding structure; by limiting the arc length of the oxidation layer 6 in the winding structure and combining 2≤m≤50%M, the number of turns of the oxidation layer 6 is determined.

[0035] For example, M is 100, in the winding structure, starting from the starting circle, the arc length of the oxidation layer 6 on the first bending section 41 of the starting circle, i.e., the first circle, can be 0.5 mm, and the arc length of the oxidation layer 6 on the first bending section 41 of the subsequent second, third, and m-th circles gradually increases. Here, when the arc length of the oxidation layer 6 on the first bending section 41 of the m-th circle is less than 5 mm and m is within 2 to 50, the number of circles in which the oxidation layer 6 is arranged can be determined.

[0036] Of course, the arc length of the oxidation layer 6 on the first bending section 41 can also be understood as being 0.5 mm to 5 mm, that is, the arc length of the oxidation layer 6 on the first bending section 41 of any circle in the winding structure is consistent and within 0.5 mm to 5 mm. Specifically, the arc length of the oxidation layer 6 on the first bending section 41 of any circle in the winding structure can be 0.6 mm or 0.8 mm or 1.2 mm or 1.5 mm or 1.9 mm or 2.3 mm or 2.6 mm or 2.9 mm or 3.3 mm or 3.6 mm or 3.9 mm or 4.2 mm or 4.5 mm or 4.8 mm.

[0037] In some embodiments, the thickness of the oxidation layer 6 is 0.5 um to 2 um. The thickness of the oxidation layer 6 is moderate, has a better insulation effect, and uses less material, which is conducive to cost control and occupies less space.

[0038] Specifically, the thickness of the oxidation layer 6 can be 0.6 um or 0.7 um or 0.9 um or 1.1 um or 1.3 um or 1.5 um or 1.7 um or 1.9 um.

[0039] In one embodiment, as shown in Figures 1-3 Specifically, the carbon-coated aluminum foil can provide excellent static conductivity, collect the micro-current of the active material, thereby greatly reducing the contact resistance between the positive electrode material and the current collector and improving the adhesion between the two. At the same time, the carbon-coated aluminum foil plays a role in corrosion and oxidation prevention, and can improve the stability, safety, and reliability of the battery, reduce the dynamic internal resistance of the battery, and improve the consistency and matching of the battery.

[0040] Further, in the second coating layer 8, the carbon layer has a bare area corresponding to the position of the oxidation layer 6.

[0041] Specifically, the carbon layer is first arranged on the surface of the cathode current collector 4 near the center of the winding structure, and then part of the carbon layer is removed to form a bare area to expose the cathode current collector 4. Then, the part of the cathode current collector 4 exposed from the bare area is treated to obtain the oxidation layer 6, which is convenient to process.

[0042] In some embodiments, as shown in Figure 1and Figure 2 As shown in FIG. 1, the winding structure has a flat area, the anode pole piece 1 includes an anode current collector 5 and an anode active material layer coated on both sides of the anode current collector 5, the anode current collector 5 includes a second curved section 51 located at the bending area and a second flat section 52 located at the flat area, the second curved section 51 has a first area located away from the center of the winding structure, the specific surface area of the first area of the second curved section 51 is A, and the specific surface area of the surface of the second flat section 52 located away from the center of the winding structure is B, A > B.

[0043] In this embodiment, by increasing the specific surface area of the surface of the second curved section 51 located away from the center of the winding structure, the amount of negative electrode material coated on the surface of the second curved section 51 located away from the center of the winding structure is increased, thereby being able to receive more lithium ions and reducing the risk of lithium precipitation due to too small CB value. In this application, the anode current collector 5 can be a copper foil.

[0044] Specifically, in the winding structure, the anode pole piece 1 is wound into N turns, that is, the anode current collector 5 is also wound into N turns, so that the surface of the second curved section 51 of the anode current collector 5 located away from the center of the winding structure in each turn can have the first area, or in the innermost n turns of the anode current collector 5, the surface of the second curved section 51 of the anode current collector 5 located away from the center of the winding structure in each turn can have the first area, wherein 2 ≤ n ≤ 50% N, N > 50, and n and N are integers; for example, in the winding structure, the anode pole piece 1 is wound into 100 turns, 2 ≤ n ≤ 50, that is, in the innermost 40 turns of the anode pole piece 1, the surface of the second curved section 51 of the anode current collector 5 located away from the center of the winding structure in each turn from the starting turn, i.e., the first turn, to the 40th turn, has the first area.

[0045] It should be noted that there are many ways to increase the specific surface area of the first area of the second curved section 51, for example, a microporous structure is machined on the first area of the second curved section 51 by micro-etching process or mechanical processing, the microporous structure makes the surface of the first area uneven, thereby increasing the specific surface area of the first area.

[0046] In one possible implementation, as shown in FIG. 1, Figure 1 and Figure 2 The arc length of the first area on the second curved section 51 is 1 mm-6 mm.

[0047] Specifically, the arc length of the first region on the second curved segment 51 is determined by the arc length of the second curved segment 51, and in the winding structure, the arc length of the second curved segment 51 is increasing in the direction away from the center of the winding structure, that is, the arc length of the first region is increasing in the direction away from the center of the winding structure, wherein the arc length of the first region on the second curved segment 51 is designed to be 1mm-6mm, which can be understood as that in the winding structure, the shortest arc length of the plurality of first regions is greater than or equal to 1mm, and the longest arc length of the plurality of first regions is less than or equal to 6mm, and by limiting the first region in the winding structure and combining 2≤n≤50%N, the number of turns of the first region is determined.

[0048] For example, N is 100, and in the winding structure, the arc length of the first region on the second curved segment 51 of the starting turn, that is, the first turn, is 1mm, and the arc length of the first region on the second curved segment 51 of the subsequent second, third, … turns is gradually increased, so that when the arc length of the first region on the second curved segment 51 of the nth turn is 6mm and n is within 2-50, the number of turns of the first region is determined.

[0049] Of course, the arc length of the first region on the second curved segment 51 is designed to be 1mm-6mm, which can also be understood as that in the winding structure, the arc length of the first region on the second curved segment 51 of any turn is consistent and within 1mm-6mm, and specifically, in the winding structure, the arc length of the first region on the second curved segment 51 of any turn can be 1.5mm or 1.8mm or 2.3mm or 2.6mm or 2.9mm or 3.4mm or 3.6mm or 3.8mm or 4.3mm or 4.7mm or 4.9mm or 5.2mm or 5.5mm or 5.8mm.

[0050] In one possible implementation, the first region of the anode current collector 5 is provided with a conductive layer 10, and by providing the conductive layer 10 in the first region, the ion transmission is accelerated, the ion intercalation resistance is reduced, the lithium intercalation capacity of the anode corner portion is improved, and the problem of lithium precipitation caused by the fact that ions cannot be timely intercalated into the anode corner portion 3 due to the problems of fewer transmission channels and higher intercalation resistance is reduced.

[0051] It should be noted that the material for making the conductive layer 10 is one or a combination of more of carbon nanotubes, conductive carbon black, conductive graphite, graphene, or nanocarbon fibers.

[0052] Further, the thickness of the conductive layer 10 is 0.5um-2um, so that the ion transmission capacity is improved while the material is controlled, and specifically, the thickness of the conductive layer 10 can be 0.6um or 0.8um or 1.2um or 1.4um or 1.6um or 1.8um.

[0053] In a possible implementation, in the same winding turn of the winding structure, the first region is located at the opposite inner side of the oxidation layer 6, and the projection of the oxidation layer 6 covers the first region.

[0054] In the same yin-bao-yang structure, not only is the oxidation layer 6 arranged at the first bending section 41, but also the specific surface area of the first region on the second bending section 51 is increased, so that the ion intercalation capacity of the anode tab 1 located at the bending area is greater than the ion extraction capacity of the cathode tab 3 located at the bending area, and the existence of excess ions that cannot be intercalated into the anode tab 1 located at the bending area is avoided, and then the anode tab 1 located at the bending area is precipitated.

[0055] Further, the application also provides a battery monomer, which comprises the electrode assembly as described above. Based on the above-mentioned implementation, by arranging the structure at the corner of the electrode assembly, the problem of lithium precipitation at the corner of the winding type battery cell can be optimized without affecting the overall design of the battery cell, and the safety performance of the winding type battery cell is improved, thereby improving the safety performance of the battery monomer. The specific structure and principle effect of the electrode assembly are described in the above-mentioned implementation, and the repeated parts will not be described again.

[0056] Further, the application also provides a power consumption device, which comprises the battery monomer as described above. Based on the above-mentioned implementation, by arranging the structure at the corner of the electrode assembly, the problem of lithium precipitation at the corner of the winding type battery cell can be optimized without affecting the overall design of the battery cell, and the safety performance of the winding type battery cell is improved, thereby improving the safety performance of the battery monomer and the power consumption device using the battery monomer. The specific structure and principle effect of the electrode assembly are described in the above-mentioned implementation, and the repeated parts will not be described again.

[0057] The effects of the embodiments of the application will be illustrated more specifically through the following examples. It should be understood that the embodiments of the application are not limited to these examples only.

[0058] Example 1

[0059] Preparation of the cathode tab: first, the aluminum foil is coated with an active layer on both sides, wherein the active layer comprises a carbon layer; then, starting from the winding start end, the active layer on the inner surface of the twenty first bending sections 41 (corresponding to the corners after winding) is removed (the removal method is one or more of laser cleaning, mechanical scraping or foaming glue), and the pure aluminum foil is exposed, and then the exposed aluminum foil is subjected to a chromate passivation method for passivation treatment, to form a dense aluminum chromate oxide film, i.e., the oxidation layer 6, the thickness of the oxidation layer 6 is 1 um, and the oxidation layer 6 is dried and rolled to obtain the cathode tab; wherein the passivation treatment can also use an electrochemical passivation method, a chemical deposition passivation method, etc.

[0060] Preparation of the anode tab: the copper foil is coated with an active layer on both sides, dried, and rolled to obtain the anode tab;

[0061] The above anode electrode sheet, cathode electrode sheet and separator are wound into a core, and a battery monomer is obtained after packaging, liquid injection and aging treatment.

[0062] Example 2

[0063] The cathode electrode sheet is prepared as follows: first, the aluminum foil is coated with an active layer on both sides, wherein the active layer includes a carbon layer; then, starting from the winding starting end, the active layer on the inner side surface of the twenty first bending sections 41 (corresponding to the corners after winding) is removed (the removal method is one or more of laser cleaning, mechanical scraping or foaming glue), and the pure aluminum foil is exposed, and then the exposed aluminum foil is subjected to chromate passivation to perform passivation treatment on the surface to form a dense aluminum chromate oxide film, i.e., an oxidation layer 6, the thickness of the oxidation layer 6 is 1 um, and the cathode electrode sheet is obtained after drying and rolling; wherein the passivation treatment can also use electrochemical passivation method, chemical deposition passivation method, etc.

[0064] The anode electrode sheet is prepared as follows: starting from the winding starting end, the twenty first regions of the copper foil (corresponding to the corners after winding) are subjected to micro-etching on the smooth surface of the copper foil through a micro-etching process (a porous copper foil can also be manufactured by punching on the surface of the copper foil through mechanical processing), so as to produce a concave-convex shape and increase the specific surface area of the copper foil; then, the copper foil is coated with an active layer on both sides, dried, and rolled to obtain the anode electrode sheet.

[0065] The above anode electrode sheet, cathode electrode sheet and separator are wound into a core, and a battery monomer is obtained after packaging, liquid injection and aging treatment.

[0066] Example 3

[0067] The cathode electrode sheet is prepared as follows: first, the aluminum foil is coated with an active layer on both sides, wherein the active layer includes a carbon layer; then, starting from the winding starting end, the active layer on the inner side surface of the twenty first bending sections 41 (corresponding to the corners after winding) is removed (the removal method is one or more of laser cleaning, mechanical scraping or foaming glue), and the pure aluminum foil is exposed, and then the exposed aluminum foil is subjected to chromate passivation to perform passivation treatment on the surface to form a dense aluminum chromate oxide film, i.e., an oxidation layer 6, the thickness of the oxidation layer 6 is 1 um, and the cathode electrode sheet is obtained after drying and rolling; wherein the passivation treatment can also use electrochemical passivation method, chemical deposition passivation method, etc.

[0068] The anode electrode sheet is prepared as follows: starting from the winding starting end, the twenty first regions of the copper foil (corresponding to the corners after winding) are subjected to micro-etching on the smooth surface of the copper foil through a micro-etching process (a porous copper foil can also be manufactured by punching on the surface of the copper foil through mechanical processing), so as to produce a concave-convex shape and increase the specific surface area of the copper foil; then, a layer of carbon nanotube conductive glue with a thickness of 1 um is coated on the region, and finally, an active layer is coated on both sides, dried, and rolled to obtain the anode electrode sheet.

[0069] The above anode pole piece, cathode pole piece and separator are wound into a core, and a battery monomer is obtained after packaging, liquid injection and aging treatment.

[0070] Comparative Example 1

[0071] The cathode pole piece is prepared by double-sided coating of an aluminum foil with an active layer, drying, and rolling to obtain the cathode pole piece;

[0072] The anode pole piece is prepared by double-sided coating of a copper foil with an active layer, drying, and rolling to obtain the anode pole piece;

[0073] The above anode pole piece, cathode pole piece and separator are wound into a core, and a battery monomer is obtained after packaging, liquid injection and aging treatment.

[0074] The battery monomers prepared in Examples 1 to 3 and Comparative Example 1 are subjected to charge-discharge cycle test, after 100 charge-discharge cycles, the battery monomer after the last charge-discharge cycle is fully charged again, and then the battery monomer is disassembled to observe whether there is lithium precipitation in the bending area of the battery monomer.

[0075] The test results of the battery monomers prepared in Examples 1 to 3 and Comparative Example 1 are shown in Table 1:

[0076] Table 1

[0077]

[0078] From the test results of Examples 1 to 3 and Comparative Example 1, it can be seen that by modifying the surface of the aluminum foil and copper foil on one side of the corner of the winding type battery cell, the risk of lithium precipitation caused by too small CB value at the corner of the winding type battery cell is reduced.

[0079] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0080] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. An electrode assembly, characterized by, The electrode assembly comprises an anode pole piece (1), a cathode pole piece (3), and a separator (2) separating the anode pole piece (1) and the cathode pole piece (3), the anode pole piece (1), the separator (2), and the cathode pole piece (3) are wound along a winding direction and form a winding structure; the winding structure has a bending area, the cathode pole piece (3) comprises a cathode current collector (4), the cathode current collector (4) comprises a first bending segment (41) located at the bending area, and the first bending segment (41) is provided with an oxidation layer (6) on a surface close to a side of the center of the winding structure.

2. The electrode assembly of claim 1, wherein, The winding structure has a flat area, the anode pole piece (1) comprises an anode current collector (5), the anode current collector (5) comprises a second bending segment (51) located at the bending area and a second flat segment (52) located at the flat area, the second bending segment (51) has a first area arranged away from the center of the winding structure, the specific surface area of the first area of the second bending segment (51) is A, and the specific surface area of a surface of the second flat segment (52) arranged away from the center of the winding structure is B, A > B.

3. The electrode assembly of claim 2, wherein, In the same winding layer of the winding structure, the first area is located on the opposite inner side of the oxidation layer (6), and the projection of the oxidation layer (6) on the second bending segment (51) covers the first area.

4. The electrode assembly of any one of claims 1 to 3, wherein, The cathode pole piece (3) comprises a first coating layer and a second coating layer; the first coating layer is arranged on a surface of the cathode current collector (4) away from the center of the winding structure; and the second coating layer is arranged on a surface of the cathode current collector (4) close to the center of the winding structure.

5. The electrode assembly of claim 4, wherein, The second coating layer and the first coating layer each comprise a carbon layer arranged on the cathode current collector (4) and an active material layer arranged on the carbon layer, and in the second coating layer, the carbon layer is provided with a bare area corresponding to the position of the oxidation layer (6).

6. The electrode assembly of claim 2 or 3, wherein, The arc length of the oxidation layer (6) on the first bending segment (41) is 0.5 mm-5 mm; the thickness of the oxidation layer (6) is 0.5 um-2 um; and / or, the arc length of the first area on the second bending segment (51) is 1 mm-6 mm.

7. The electrode assembly of claim 2 or 3, wherein The oxidation layer (6) is a chromate passivation film; and / or, the first area of the anode current collector (5) is provided with a microporous structure.

8. The electrode assembly of claim 2 or 3, wherein, The first area of the anode current collector (5) is provided with a conductive layer (10), and the thickness of the conductive layer (10) is 0.5 um-2 um.

9. A battery cell characterized by, The battery cell comprises the electrode assembly as claimed in any one of claims 1-8.

10. An electric device, characterized by The battery cell comprises the electrode assembly as claimed in any one of claims 1-8.

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