Secondary battery, electric equipment and preparation method of secondary battery

Abstract

The invention relates to the technical field of energy storage, in particular to a secondary battery, electric equipment and a preparation method of the secondary battery. The secondary battery comprises an electrode assembly, the electrode assembly comprises a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure, the first pole piece comprises a first pole lug, a first current collector and a first active substance layer, and the first active substance layer is arranged in the width direction of the first pole piece. The first current collector comprises a first coating section and a first empty foil section located at at least one end of the first coating section, and the first active material layer is arranged on the first surface of the first coating section and / or the second surface of the first coating section in the thickness direction of the first pole piece. The first empty foil section comprises a first part and a second part connected with the first coating section, and the first part is connected with the second part and is laminated with the second part along the thickness direction of the first pole piece.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery, an electrical device, and a method for preparing the secondary battery. Background Art

[0002] With the continuous pursuit of high energy density, electrodes tend to be designed with higher active material coating, higher compaction density and thinner current collector thickness, which causes the active material of the electrode assembly to expand and shrink more when it is compressed or the battery cell is charged and discharged, increases the electrode deformation, and increases the local stress on the electrode current collector, which makes the current collector break more likely to occur. Summary of the invention

[0003] After a large number of experiments, the inventors found that the rupture of the current collector often starts from the edge of the current collector. As the battery is used for a longer time, the damaged area gradually increases until it spreads to the entire current collector, eventually leading to the rupture of the current collector. In view of this, the present application provides a secondary battery, an electrical device, and a method for preparing a secondary battery, which can improve the problem of current collector rupture.

[0004] In the first aspect, an embodiment of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure, the first pole piece includes a first pole ear, a first current collector and a first active material layer, along the width direction of the first pole piece, the first current collector includes a first coating section and a first empty foil section located at at least one end of the first coating section, along the thickness direction of the first pole piece, the first active material layer is arranged on the first surface of the first coating section and / or the second surface of the first coating section. The first empty foil section refers to a portion of the current collector located at at least one end of the first coating section in the width direction where the first active material layer is not arranged. The first empty foil section includes a first portion and a second portion connected to the first coating section, the first portion is connected to the second portion and is stacked with the second portion along the thickness direction of the first pole piece. By arranging a first empty foil segment at the edge of the first pole piece and stacking the first part and the second part of the first empty foil segment, the thickness of the edge of the first current collector is increased, thereby increasing the strength of the edge of the first current collector, which can effectively reduce the occurrence of overall fracture of the current collector caused by tearing of the edge of the current collector.

[0005] In the above embodiments, in the same winding layer, the first part is closer to the winding center of the electrode assembly than the second part. The first part is arranged to be closer to the winding center of the electrode assembly than the second part. After the electrode assembly is wound, the first part is wound into the interior of the electrode assembly, which is conducive to reducing the occurrence of rebound and warping of the first part after bending.

[0006] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the first part is L1, the width of the second part is L2, and 0≤L2-L 1≤0.4mm. L2-L 1≤0.4mm means that the difference between the widths of the first part and the second part is less than or equal to 0.4mm, that is, the overlapping area of ​​the first part and the second part is large, and the fracture strength of the edge of the first current collector is greater at this time. At the same time, the first empty foil segment occupies less space in the width direction of the first pole piece, which is conducive to improving the energy density of the secondary battery, and the first part has a certain bending length, which improves the bending convenience of the first part; when L2-L 1<0, that is, the width of the first part is greater than the width of the second part, at this time, the first part will cover part of the first active material layer on the first coating section, and L2-L1≥0 can reduce the occupation of the first empty foil segment for the first active material layer in the first coating section, thereby reducing the influence of the first empty foil segment on the energy density of the secondary battery.

[0007] In one or more of the above embodiments, the first pole piece further includes an adhesive member, which is disposed on the first surface of the first empty foil segment and connected between the first portion and the second portion. The adhesive member is disposed to fix the relative position of the first portion and the second portion, thereby reducing the occurrence of rebound and warping of the first portion after bending.

[0008] In one or more of the above embodiments, the adhesive member is a single-sided adhesive, a double-sided adhesive or a hot-melt adhesive.

[0009] In one or more of the above embodiments, the adhesive is a hot melt adhesive, so that the first part and the second part are laminated and then hot pressed to bond the adhesive between the first part and the second part.

[0010] In one or more of the above embodiments, the material of the adhesive member includes at least one of polyamide, reactive polyurethane or polyethersulfone. The above materials are all thermoplastic polymer materials with heat resistance, acid resistance and insulation properties, and can form strong adhesion with metals, and can provide adhesion for effective fixation between the first part and the second part.

[0011] In one or more of the above embodiments, the melting temperature of the hot melt adhesive is T, 45°C ≤ T ≤ 65°C. In this temperature range, the hot melt adhesive has good thermoplasticity. If the temperature is too low, the hot melt adhesive is not very sticky; if the temperature is too high, the hot melt adhesive has too low viscosity and strong fluidity, and is easily squeezed out of the first empty foil segment and overflows onto the surface of the first active material layer, affecting the transmission path of the positive electrode, resulting in limited capacity and low capacity of the battery cell.

[0012] In one or more of the above embodiments, the thickness of the thickest part of the adhesive is H2, 5um≤H2≤20um. The thickest part of the adhesive is controlled to be above 5um so that the adhesive has sufficient bonding strength. The thickest part of the adhesive is controlled to be below 20um to reduce the occupation of the adhesive in the thickness direction.

[0013] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the adhesive is equal to the overlapping width of the first part and the second part. After the first part and the second part overlap, when observed along the thickness direction of the first pole piece, the adhesive is located between the first part and the second part, which can better bond the first part and the second part, and can also reduce the space occupied by the adhesive in the width direction of the first pole piece, which is beneficial to improving the energy density of the secondary battery.

[0014] In one or more of the above embodiments, the first pole piece further includes an insulating member, which is disposed on the second surface of the first empty foil segment, thereby isolating the second pole piece from contacting the first empty foil segment and playing a role of insulating protection.

[0015] In one or more of the above embodiments, the material of the insulating member includes a ceramic material. In one or more of the above embodiments, the ceramic material includes at least one of aluminum oxide, magnesium oxide, silicon nitride, silicon carbide, and boehmite.

[0016] In one or more of the above embodiments, along the width direction of the first pole piece, the projection of the insulating member is located within the projection of the first active material layer. Along the thickness direction of the first pole piece, the thickness of the first empty foil segment provided with the insulating member does not exceed the first active material layer, and the first empty foil segment and the insulating member do not occupy additional space in the thickness direction of the electrode assembly, which is conducive to improving the energy density of the secondary battery.

[0017] In one or more of the above embodiments, along the thickness direction of the first pole piece, the projection of the insulating member is located within the projection of the second pole piece. The first empty foil segment and the insulating member do not occupy additional space in the length direction of the electrode assembly, which is beneficial to improving the energy density of the secondary battery.

[0018] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the second pole piece beyond the first active material layer is Δd, 0.2mm≤Δd≤1.4mm. The width Δd of the second pole piece beyond the first active material layer is controlled between 0.2mm and 1.4mm, which is conducive to leaving enough space for the setting of the first empty foil area.

[0019] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the orthographic projection of the first empty foil segment in the thickness direction of the first pole piece is W1, 0.2mm≤W1≤1.4mm. The width W1 of the first empty foil segment is controlled between 0.2mm and 1.4mm, which is the same as the range of the single-side width Δd of the second pole piece beyond the first active material layer. Along the width direction of the first pole piece, the width of the first empty foil segment does not exceed that of the second pole piece, and the first empty foil segment does not occupy additional space in the length direction of the electrode assembly, which is conducive to improving the energy density of the secondary battery.

[0020] In one or more of the above embodiments, along the thickness direction of the first pole piece, the maximum distance between the insulating member on the first portion and the insulating member on the second portion is H1, 31 um≤H1≤100 um.

[0021] In one or more of the above embodiments, a thickness of a layer of insulating member is H3, 5um≤H3≤20um.

[0022] In one or more of the above embodiments, the first current collector further includes a connecting portion, and the first pole tab is welded to the connecting portion. The first pole tab is directly welded to the connecting portion of the first current collector to improve the connection stability of the first pole tab.

[0023] In one or more of the above embodiments, a plurality of first pole tabs are provided, each of which is connected to the first portion and is integrally provided with the first portion, and the first pole tab includes a bent portion connected to the first portion and a lead-out portion extending along the width direction of the first pole piece. The bent portion of the first pole tab is folded in half together with the first portion, which is beneficial to improving the root strength of the first pole tab, thereby improving the problem of the pole tab root fracture caused by expansion and stress concentration at the pole tab root of the multi-pole tab battery cell.

[0024] In one or more of the above embodiments, the outermost pole piece of the electrode assembly is the first pole piece. In the electrode assembly of the wound structure, in order to reduce the waste of the active material layer, the outermost pole piece is generally a single-sided active material layer, which results in the outermost pole piece being lower in strength than the pole piece with a double-sided active material layer, and is more prone to current collector fracture. Applying this technical solution to the outermost pole piece of the wound electrode assembly can reduce the occurrence of outermost pole piece fracture.

[0025] In one or more of the above embodiments, the first pole piece is a positive pole.

[0026] In a second aspect, an embodiment of the present application provides an electrical device, comprising a secondary battery in one or more of the above embodiments.

[0027] In a third aspect, an embodiment of the present application provides a method for preparing a secondary battery, which is used to prepare the secondary battery in one or more of the above embodiments, comprising the following steps:

[0028] Providing a first current collector, dividing the first current collector into a first coating section and a first unfolded empty foil section located at at least one end of the first coating section along a width direction of the first current collector, and disposing a first active material layer on a first surface of the first coating section and / or a second surface of the first coating section;

[0029] Bending, the first unfolded empty foil segment includes a first portion and a second portion connected to the first coated segment, and the first portion is bent toward the second portion so that the first portion and the second portion are stacked along the thickness direction of the first electrode sheet to obtain the first empty foil segment.

[0030] In one or more of the above embodiments, the bending direction of the first portion is toward the winding center of the electrode assembly.

[0031] In one or more of the above embodiments, along the width direction of the first current collector, the widths of the first portion and the second portion are equal; the width of the first unfolded empty foil segment is W2, 0.4 mm≤W2≤2.8 mm.

[0032] In one or more of the above embodiments, before the bending step, the step further includes:

[0033] An adhesive is provided on the first surface of the first part and / or the first surface of the second part; after bending, the first surface of the first part faces the first surface of the second part.

[0034] In one or more of the above embodiments, the following steps are also included:

[0035] An insulating member is provided. The insulating member is provided on the second surface of the first portion and the second surface of the second portion.

[0036] In the secondary battery of the present application, since at least one end of the first coating section along the width direction of the first pole piece is a first empty foil section, after the first part and the second part at least partially overlap, the first pole piece is thickened on both sides in the width direction. During the pressure or charge and discharge process of the secondary battery, the thickness of the side of the first current collector in the width direction is increased to increase the fracture resistance of the first pole piece and improve the problem of the first current collector being fractured by the expansion force during the cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the overall structure of a secondary battery in one embodiment of the present application.

[0038] Figure 2 for Figure 1 Schematic diagram of the exploded view of the secondary battery.

[0039] Figure 3 It is a schematic diagram of the cross-sectional structure of an electrode assembly in one embodiment of the present application.

[0040] Figure 4 It is a schematic diagram of a partial cross-sectional structure of an electrode assembly in one embodiment of the present application.

[0041] Figure 5 It is a schematic diagram of the cross-sectional structure of an electrode assembly in another embodiment of the present application.

[0042] Figure 6 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0043] Figure 7It is a schematic diagram of the structure in which the first pole piece is unfolded in one embodiment of the present application.

[0044] Figure 8 It is a schematic diagram of the structure after the first part and the second part are stacked in one embodiment of the present application.

[0045] Main component symbols

[0046] 001 Secondary battery

[0047] 100 Shell

[0048] 110 cavity

[0049] 200 Electrode Assembly

[0050] 210 First Pole

[0051] 211 First Collection of Fluid

[0052] 2111 First Surface

[0053] 2112 Second Surface

[0054] 2113 First coating section

[0055] 2114 First empty foil segment

[0056] 2114a Part 1

[0057] 2114b Part 2

[0058] 2115 Connection

[0059] 212 first active material layer

[0060] 213 Adhesive parts

[0061] 214 Insulation

[0062] 220 Second pole piece

[0063] 221 Second Episode Fluid

[0064] 222 second active material layer

[0065] 230 Diaphragm

[0066] 300 First Tab

[0067] 310 Bending part

[0068] 320 Leading part

[0069] 400 Second Tab

[0070] 002 Electrical equipment DETAILED DESCRIPTION

[0071] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0072] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centrally arranged element at the same time. When an element is considered to be "set on" another element, it can be directly set on the other element or there may be a centrally arranged element at the same time. In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of the two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned description of the drawings are intended to cover non-exclusive inclusions.

[0074] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0075] Mentioning "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. In the absence of conflict, the various implementation methods in this application can be combined with each other. In the method steps, S1, S2, etc. only represent the names of the steps, and do not limit the order of the steps.

[0076] It should be noted that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary and should not constitute any limitation to the present application.

[0077] An embodiment of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure, the first pole piece includes a first pole ear, a first current collector and a first active material layer, along the width direction of the first pole piece, the first current collector includes a first coating section and a first empty foil section located at at least one end of the first coating section, and the first active material layer is arranged on the first surface of the first coating section and / or the second surface of the first coating section. The first empty foil section refers to a portion of the current collector located at at least one end of the first coating section in the width direction where the first active material layer is not arranged. The first empty foil section includes a first portion and a second portion connected to the first coating section, the first portion is bent toward the second portion and is stacked with the second portion along the thickness direction of the first pole piece.

[0078] In the above-mentioned secondary battery, since at least one end of the first coating section along the width direction of the first pole piece is a first empty foil section, after the first part overlaps with the second part, the first pole piece is thickened on both sides in the width direction. When the secondary battery is under pressure or during charging and discharging, the thickness of the side of the first current collector in the width direction is increased to increase the fracture strength of the first pole piece and improve the problem of the first current collector being broken by the expansion force during the cycle.

[0079] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the features in the following embodiments and examples can be combined with each other.

[0080] See also Figure 1 and Figure 2 The embodiment of the present application provides a secondary battery 001, which includes an electrode assembly 200 and a first pole tab 300, wherein the first pole tab 300 is connected to the electrode assembly 200. The secondary battery 001 also includes a second pole tab 400, wherein the second pole tab 400 is connected to the electrode assembly 200, and the first pole tab 300 and the second pole tab 400 have different polarities.

[0081] In one embodiment, the secondary battery 001 further includes a housing 100, the housing 100 having a cavity 110, and the electrode assembly 200 is disposed in the cavity 110 in the housing 100. A portion of the first electrode tab 300 extends out of the housing 100 and is used to be electrically connected to an external structure. A portion of the second electrode tab 400 extends out of the housing 100 and is used to be electrically connected to an external structure.

[0082] In another embodiment, the first tab 300 is connected to a conductive first adapter (not shown), the first adapter partially extends out of the housing 100 and is used to electrically connect to an external structure. The second tab 400 is connected to a conductive second adapter (not shown), the second adapter partially extends out of the housing 100 and is used to electrically connect to an external structure.

[0083] In one embodiment, the shell 100 includes at least one of a steel shell, a resin shell or an aluminum-plastic film. For example, when the secondary battery 001 is a square hard-shell battery, the shell 100 includes a steel shell or a resin shell. When the secondary battery 001 is a soft-pack battery, the shell 100 includes an aluminum-plastic film.

[0084] See also Figure 3 and Figure 4 In one embodiment, the electrode assembly 200 includes a first electrode plate 210, a second electrode plate 220 and a diaphragm 230, the diaphragm 230 is disposed between the first electrode plate 210 and the second electrode plate 220, and the first electrode plate 210, the second electrode plate 220 and the diaphragm 230 are stacked and wound to form a winding structure.

[0085] In one embodiment, the outermost electrode piece of the electrode assembly 200 is the first electrode piece 210 .

[0086] In another embodiment, the outermost electrode piece of the electrode assembly 200 is the second electrode piece 220 .

[0087] In one embodiment, the first electrode 210 is a positive electrode.

[0088] In another embodiment, the first electrode 210 is a negative electrode.

[0089] In one embodiment, the first electrode 210 includes a first current collector 211 and a first active material layer 212. Along the thickness direction of the first current collector 211, the first current collector 211 has two opposite surfaces, namely a first surface 2111 and a second surface 2112. The first active material layer 212 is disposed on the first surface 2111 and / or the second surface 2112.

[0090] Specifically, along the width direction of the first electrode sheet 210 , the first current collector 211 includes a first coating segment 2113 and first empty foil segments 2114 located at both ends of the first coating segment 2113 , and the first active material layer 212 is disposed on the first surface 2111 of the first coating segment 2113 .

[0091] In another embodiment, the first active material layer 212 is disposed on the second surface 2112 of the first coating section 2113 .

[0092] In yet another embodiment, the first active material layer 212 is disposed on both the first surface 2111 and the second surface 2112 of the first coating section 2113 .

[0093] In one embodiment, the first empty foil segment 2114 includes a first portion 2114a and a second portion 2114b connected to the first coating segment 2113, the first portion 2114a is bent toward the second portion 2114b and is stacked with the second portion 2114b along the thickness direction of the first electrode 210. Figure 3 or Figure 5 , the first part 2114a and the second part 2114b are divided by the bend, i.e., the dotted line in the figure. Since at least one end of the first coating section 2113 along the width direction of the first pole piece 210 is the first empty foil section 2114, after the first part 2114a overlaps with the second part 2114b, the first pole piece 210 is thickened on at least one side in its width direction. When the secondary battery 001 is under pressure or during charging and discharging, the thickness of the side of the first current collector 211 in the width direction is increased to increase the fracture resistance of the first pole piece 210, and improve the problem of the first current collector 211 being broken by the expansion force during the cycle.

[0094] In one embodiment, see Figure 3 Both ends of the first pole piece 210 in the width direction are first empty foil segments 2114, so that both sides of the first pole piece 210 in the width direction are thickened, further enhancing the fracture resistance of the first pole piece 210.

[0095] Since both ends of the first coating section 2113 along the width direction of the first pole piece 210 are first empty foil sections 2114, for ease of description, the following description is directed to the first empty foil section 2114 at one end of the first coating section 2113. It is worth noting that the sizes, bending directions and bending distances of the first empty foil sections 2114 at both ends of the first coating section 2113 along the width direction of the first pole piece 210 can be the same or different, and other corresponding changes and deformations can be made according to the technical concept of the present application, and all these changes and deformations should belong to the protection scope of the claims of the present application.

[0096] In one embodiment, the first pole piece 210, the second pole piece 220 and the diaphragm 230 are stacked to form a winding layer, and the winding layer is wound to form a winding structure. In the same winding layer, the first portion 2114a is closer to the winding center of the electrode assembly 200 than the second portion 2114b. That is, the first active material layer 212 on the first surface 2111 of the first coating section 2113 is oriented toward the winding center of the electrode assembly 200, and the first portion 2114a is bent toward the first active material layer 212 on the first surface 2111 of the first coating section 2113, so that after the winding layer is wound, the first portion 2114a is located on the inner side of the winding structure compared to the second portion 2114b, which improves the problem of the first portion 2114a rebounding after bending, and is conducive to improving the stability of the stacking of the first portion 2114a and the second portion 2114b.

[0097] In another embodiment, in the same winding layer, the first portion 2114a is farther from the winding center of the electrode assembly 200 than the second portion 2114b. That is, the first active material layer 212 on the second surface 2112 of the first coating section 2113 is away from the winding center of the electrode assembly 200, and the first portion 2114a is bent toward the first active material layer 212 on the second surface 2112 of the first coating section 2113.

[0098] In one embodiment, along the width direction of the first pole piece 210, the width of the first portion 2114a is L1, and the width of the second portion 2114b is L2, 0≤L2-L1≤0.4mm, so that after the first portion 2114a and the second portion 2114b are stacked, the space occupied in the width direction of the first pole piece 210 is minimized, which is beneficial to improving the energy density of the secondary battery 001, and the overlapping area of ​​the first portion 2114a and the second portion 2114b is relatively large, which can further enhance the fracture resistance of the edge of the first pole piece 210. At the same time, the widths of the first portion 2114a and the second portion 2114b are equal, and the first portion 2114a has a sufficient bending length, which improves the bending convenience of the first portion 2114a. Compared with the case where the width of the first portion 2114a is greater than the width of the second portion 2114b, the occupation of the first empty foil segment 2114 on the first active material layer 212 in the first coating segment 2113 can be reduced, thereby reducing the impact of the first empty foil segment 2114 on the energy density of the secondary battery 001.

[0099] In one embodiment, the first pole piece 210 also includes an adhesive 213, which is disposed on the first surface 2111 of the first empty foil segment 2114, and the adhesive 213 is disposed between the first portion 2114a and the second portion 2114b, and bonds the first portion 2114a and the second portion 2114b to fix the relative position of the first portion 2114a and the second portion 2114b, which is beneficial to improving the stability of the stacking of the first portion 2114a and the second portion 2114b and improving the problem of the first portion 2114a rebounding after bending.

[0100] In one embodiment, the adhesive 213 is disposed on the first surface 2111 of the first part 2114a, and both surfaces of the adhesive 213 are adhesive. After the first part 2114a and the second part 2114b overlap, the adhesive 213 bonds the first part 2114a and the second part 2114b to fix the relative positions of the first part 2114a and the second part 2114b.

[0101] In another embodiment, the adhesive 213 is disposed on the first surface 2111 of the second part 2114b, and both surfaces of the adhesive 213 are adhesive. After the first part 2114a and the second part 2114b overlap, the adhesive 213 bonds the first part 2114a and the second part 2114b to fix the relative positions of the first part 2114a and the second part 2114b.

[0102] In another embodiment, the adhesive 213 is simultaneously disposed on the first surface 2111 of the first portion 2114a and the first surface 2111 of the second portion 2114b. After the first portion 2114a overlaps with the second portion 2114b, the adhesive 213 on the first surface 2111 of the first portion 2114a and the adhesive 213 on the first surface 2111 of the second portion 2114b are bonded to improve the bonding strength.

[0103] In one embodiment, the adhesive member 213 is a single-sided adhesive.

[0104] In one embodiment, the adhesive member 213 is a double-sided tape.

[0105] In one embodiment, the adhesive 213 is hot melt adhesive.

[0106] In one embodiment, the melting temperature of the hot melt adhesive is T, 45°C≤T≤65°C.

[0107] In one embodiment, the material of the adhesive member 213 includes at least one of polyamide, reactive polyurethane or polyethersulfone.

[0108] In one embodiment, the first pole piece 210 further includes an insulating member 214 , which is disposed on the second surface 2112 of the first empty foil segment 2114 . The insulating member 214 attached to the second surface 2112 of the first empty foil segment 2114 plays an isolation and protection role.

[0109] In one embodiment, along the width direction of the first pole piece 210, the projection of the insulating member 214 is located within the projection range of the first active material layer 212, that is, along the thickness direction of the first pole piece 210, the insulating member 214 does not exceed the first active material layer 212, thereby not affecting the thickness of the entire electrode assembly 200, which is beneficial to maintaining the energy density of the electrode assembly 200.

[0110] See also Figure 3 and Figure 4 In one embodiment, the second pole piece 220 includes a second current collector 221 and a second active material layer 222, and the second active material layer 222 is disposed on at least one surface of the second current collector 221. Along the width direction of the first pole piece 210, the width of the second pole piece 222 beyond the first active material layer 212 is Δd, and 0.2 mm ≤ Δd ≤ 1.4 mm.

[0111] In one embodiment, along the width direction of the first pole piece 210, the width of the first empty foil segment 2114 is W1, 0.2mm≤W1≤1.4mm, and W1<Δd. That is, the width of the first portion 2114a and the second portion 2114b after being stacked is between 0.2mm and 1.4mm, and in the width direction of the first pole piece 210, the width of the first empty foil segment 2114 does not exceed the width of the second pole piece 220, so as not to affect the size of the entire electrode assembly 200 along the width direction of the first pole piece 210, which is conducive to maintaining the energy density of the electrode assembly 200.

[0112] In one embodiment, along the thickness direction of the first pole piece 210, the maximum distance between the insulating member 214 on the first portion 2114a and the insulating member 214 on the second portion 2114b is H1, 31um≤H1≤100um. Among them, at least one layer of adhesive 213, the first portion 2114a and the second portion 2114b are included between the insulating member 214 on the first portion 2114a and the insulating member 214 on the second portion 2114b.

[0113] In one embodiment, along the thickness direction of the first pole piece 210 , the thickness of the thickest part of the adhesive 213 is H2, and 5um≤H2≤20um.

[0114] In one embodiment, along the width direction of the first pole piece 210, the width of the adhesive member 213 is equal to the overlapping width of the first portion 2114a and the second portion 2114b. It should be noted that, due to the influence of manufacturing errors, the difference between the width of the adhesive member 213 and the overlapping width of the first portion 2114a and the second portion 2114b and the ratio of the overlapping width of the first portion 2114a and the second portion 2114b are greater than or equal to -5%, and less than or equal to 5%, which is regarded as the case where the width of the adhesive member 213 is equal to the overlapping width of the first portion 2114a and the second portion 2114b.

[0115] In one embodiment, along the bending direction of the first hollow foil segment 2114 , a thickness of a layer of the insulating member 214 is H3, and 5 um≤H3≤20 um.

[0116] In one embodiment, the material of the insulating member includes a ceramic material.

[0117] In one embodiment, the ceramic material includes at least one of aluminum oxide, magnesium oxide, silicon nitride, silicon carbide, and boehmite.

[0118] In one embodiment, the secondary battery 001 further includes a first pole tab 300, and the first current collector 211 further includes a connecting portion 2115, and the first pole tab 300 is welded to the connecting portion 2115. The connecting portion 2115 serves to facilitate welding of the first pole tab 300, and the connecting portion 2115 is not provided with an active material layer. The connecting portion 2115 can be located at the head of the first pole sheet 210, or at the middle of the first pole sheet 210.

[0119] See also Figure 5 In other embodiments, the secondary battery 001 further includes a first pole tab 300, and a plurality of first pole tabs 300 are provided. Each first pole tab 300 is connected to the first portion 2114a and is integrally provided with the first portion 2114a. The first pole tab 300 includes a bending portion 310 connected to the first portion 2114a and a lead-out portion 320 extending along the width direction of the first pole piece 210. After the bending portion 310 is bent together with the first portion 2114a, it is beneficial to strengthen the root strength of the plurality of first pole tabs 300. At the same time, the stress concentration at the root of the first pole tab 300 is eliminated by folding the insulating member 214, thereby improving the problem of the pole tab root fracture caused by the expansion of the multi-pole tab battery cell and the stress concentration at the pole tab root.

[0120] See also Figure 6 One embodiment of the present application further provides an electric device 002, comprising the secondary battery 001 in one or more of the above embodiments.

[0121] An embodiment of the present application further provides a method for preparing a secondary battery 001, which is used to prepare the secondary battery 001 in one or more of the above embodiments, and includes the following steps:

[0122] S1. Providing a first current collector 211: see Figure 7 , along the width direction of the first current collector 211, the first current collector 211 is divided into a first coating section 2113 and a first unfolded empty foil section located at at least one end of the first coating section 2113, and a first active material layer 212 is provided on the first surface 2111 of the first coating section 2113 and / or the second surface 2112 of the first coating section 2113. The first active material layer 212 can be coated on the first coating section 2113 by slit coating, spray coating, spin coating, gravure printing, etc., or a film of the first active material layer 212 can be prepared by a dry method, and then the first active material layer 212 is assembled with the first current collector 211.

[0123] In one embodiment, the width of the first unrolled empty foil segment is W2, and 0.4 mm≤W2≤2.8 mm.

[0124] S2. Setting an adhesive 213: Setting an adhesive 213 on the first surface 2111 of the first part 2114a and / or the first surface 2111 of the second part 2114b. After bending, the first surface 2111 of the first part 2114a faces the first surface 2111 of the second part 2114b. Along the width direction of the first current collector 211, the width of the adhesive 213 is equal to the overlapping width of the first part 2114a and the second part 2114b.

[0125] S3.Bending: Please refer to Figure 7 and Figure 8 The first unfolded empty foil segment includes a first portion 2114a and a second portion 2114b connected to the first coated segment 2113. The first portion 2114a is bent toward the second portion 2114b so that the first portion 2114a and the second portion 2114b are stacked along the thickness direction of the first electrode 210 to obtain the first empty foil segment 2114.

[0126] In one embodiment, the adhesive 213 may be firstly arranged on the first surface 2111 of the first portion 2114a and / or the first surface 2111 of the second portion 2114b and the first unfolded empty foil segment is subjected to a bending step, and then the first active material layer 212 may be arranged on the first surface 2111 of the first coating segment 2113 and / or the second surface 2112 of the first coating segment 2113. In one embodiment, along the width direction of the first current collector 211, the width of the first portion 2114a is L1, the width of the second portion 2114b is L2, and L1=L2. In another embodiment, L1>L2. In yet another embodiment, L1<L2.

[0127] In one embodiment, after the first portion 2114a and the second portion 2114b are stacked along the thickness direction of the first pole piece 210 and the adhesive 213 is provided, the folded area is hot pressed at a temperature of 45° C. to 65° C. for a time of 3s to 6s.

[0128] S4. Disposing the insulating member 214: Disposing the insulating member 214 on the second surface 2112 of the first portion 2114a and the second surface 2112 of the second portion 2114b.

[0129] The step S4 may be arranged before the step S3 or after the step S3. When the step S4 is arranged before the step S3, it is beneficial to protect the second surface 2112 of the first current collector 211 through the insulating member 214.

[0130] In one embodiment, the bending direction of the first portion 2114 a is toward the winding center of the electrode assembly 200 .

[0131] In order to verify the improvement effect of the stacking arrangement of the first portion 2114a and the second portion 2114b on the damage to the first pole piece 210, the following test was performed:

[0132] (1) Battery cycle test: Take 10 secondary batteries 001 for the comparative example and each group of examples for testing, place each secondary battery 001 in a 55°C environment and let it stand for 30 minutes, and then charge and discharge it according to the following steps. Charge to 4.2V at a constant current of 2.5C, and then charge to 0.5C at a constant voltage; then charge to 4.45V at a constant current of 0.5C, and then charge to 0.02C at a constant voltage; let it stand for 5 minutes, discharge to 3V at a constant current of 1C, and let it stand for 5 minutes. This is one cycle. Cycle 1000 times according to the above cycle steps and record the number of cycles when the cycle capacity retention rate of the comparative example and the example drops sharply during the cycle test. After the cycle test, disassemble the secondary battery 001, observe with the naked eye whether the first pole piece 210 is damaged, and record the number of tears or breaks in the first pole piece 210. The cycle test pole piece damage rate = (number of damaged pole pieces / 10) × 100%.

[0133] The specific implementation of the secondary battery 001 in the embodiment and the comparative example is described below.

[0134] Embodiment 1:

[0135] A secondary battery 001, the assembly process is as follows:

[0136] (1) Preparation of anode electrode: Mix the anode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, prepare a slurry with a weight percentage of 70wt%, and stir evenly. The slurry is evenly coated on both surfaces of the anode current collector copper foil with a thickness of 8μm along the thickness direction. Dry at 110°C to obtain an anode electrode with a coating thickness of 150μm. Prepare the anode electrode according to the preparation method of the secondary battery 001 above, and weld the pole ear in the middle of the anode electrode.

[0137] (2) Preparation of cathode electrode: The cathode active material lithium cobalt oxide (Li CoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on both surfaces of the cathode current collector aluminum foil with a thickness of 12μm in the thickness direction to form a first coating section 2113, and empty foil areas are reserved at both ends of the aluminum foil in the width direction. Along the width direction of the aluminum foil, both ends of the first coating section 2113 are the first unfolded empty foil sections. The first unfolded empty foil section includes a first portion 2114a and a second portion 2114b connected to the first coating section 2113. Along the width direction of the first current collector 211, the width of the first portion 2114a is L1, and the width of the second portion 2114b is L2, L1=1.4mm, L2=0.6mm.

[0138] Then, the cathode plate is dried at 90° C. to obtain a cathode active material layer having a thickness of 100 μm. The first current collector 211 of the cathode plate further includes a connecting portion 2115 , which is located in the middle of the first current collector 211 , and a cathode tab is welded on the connecting portion 2115 .

[0139] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0140] (4) Preparation of isolation film: A three-layer isolation film is used, which includes a first adhesive layer, a first substrate layer and a second adhesive layer stacked in layers. The first substrate layer is made of polyethylene (PE), and both the first adhesive layer and the second adhesive layer contain a first adhesive and boehmite.

[0141] (5) Preparation of electrode assembly 200: The cathode electrode sheet, the isolation membrane and the anode electrode sheet are stacked and arranged, and the stacked structure is wound. The electrode sheet on the outermost circle of the wound structure is the cathode electrode sheet, and the cathode electrode ear is connected to the first empty foil section 2114 of the cathode electrode sheet.

[0142] (6) Assembly of the electrode assembly 200: Place the aluminum-plastic film with the holes punched and formed in an assembly fixture, with the holes facing upward, and place the electrode assembly 200 in the holes, and apply external force to press it. Then, cover the electrode assembly 200 with another aluminum-plastic film with the holes punched and formed, with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly 200.

[0143] (7) Liquid injection and packaging: The electrolyte is injected into the assembled electrode assembly 200, and the secondary battery 001 is obtained through processes such as vacuum packaging, static standing, hot pressing, and shaping.

[0144] Embodiment 2: The difference from Embodiment 1 is that, along the width direction of the first current collector 211 , the width of the first portion 2114 a is L1 , the width of the second portion 2114 b is L2 , L1=1.2 mm, L2=0.8 mm.

[0145] Embodiment 3: The difference from Embodiment 1 is that, along the width direction of the first current collector 211 , the width of the first portion 2114 a is L1 , the width of the second portion 2114 b is L2 , L1=1.0 mm, L2=1.0 mm.

[0146] Embodiment 4: A blank foil area is reserved at one end of the aluminum foil in the width direction. Along the width direction of the aluminum foil, one end of the first coating section 2113 is the first unfolded blank foil section. The first unfolded blank foil section includes a first portion 2114a and a second portion 2114b connected to the first coating section 2113. Along the width direction of the first current collector 211, the width of the first portion 2114a is L1, and the width of the second portion 2114b is L2. L1 = 1.4 mm, L2 = 0.6 mm

[0147] Comparative Example 1: The difference from Example 1 is that in Comparative Example 1, along the width direction of the first pole piece 210, the first current collector 211 only includes the first coating section 2113, a connecting groove is opened in the first coating section 2113 to expose a portion of the first current collector 211 below the connecting groove, and the first pole ear 300 is welded to the portion of the first current collector 211 where the connecting groove is exposed, wherein the position of the connecting groove is the same as the position of the connecting portion 2115 in Example 1, and the remaining steps are the same as Example 1.

[0148] The main parameter control and test results of each embodiment and comparative example are shown in Table 1:

[0149] Table 1

[0150]

[0151] Note: “ / ” represents that the secondary battery 001 has no sudden drop in cycle capacity within 1000 cycles.

[0152] According to the above Table 1 and combined Figure 3It can be seen that in comparative example 1, after a certain number of charging cycles (398 cycles), the cycle capacity retention rate of the first pole piece 210 drops sharply. Compared with comparative example 1, in embodiments 1 to 3, after the first part 2114a and the second part 2114b overlap, the first pole piece 210 is thickened on both sides in the width direction. During the battery cycle test of the secondary battery 001, by increasing the thickness of the side of the first current collector 211 in the width direction, the average number of cycles before the cycle drops sharply is significantly increased, and the edge fracture of the first pole piece 210 is significantly reduced, thereby achieving the effect of increasing the fracture resistance of the first pole piece 210, which is beneficial to the problem of the fracture of the first current collector 211 during the cycle.

[0153] According to the above Table 1, compared with Example 3, in Example 1, along the width direction of the first electrode sheet 210, the width of the first portion 2114a is 0.8 mm larger than the width of the second portion 2114b. Although the secondary battery 001 can pass the battery cycle test, the first portion 2114a partially overlaps with the first active material layer 212 after being folded, which slightly affects the fracture strength of the first electrode sheet 210.

[0154] According to the above Table 1, compared with Example 3, in Example 2, along the width direction of the first electrode sheet 210, the width of the first portion 2114a is 0.4 mm larger than the width of the second portion 2114b. Although the secondary battery 001 can pass the battery cycle test, the first portion 2114a partially overlaps with the first active material layer 212 after being folded, which slightly affects the fracture strength of the first electrode sheet 210.

[0155] Compared with Example 1, in Example 2, along the width direction of the first pole piece 210, the width difference between the first portion 2114a and the second portion 2114b is reduced, the average number of cycles before the cycle of the secondary battery 001 drops sharply is slightly increased, and the damage rate of the pole piece in the cycle test of the secondary battery 001 is slightly reduced. Therefore, when the average overlapping width of the first portion 2114a and the second portion 2114b is the same, the smaller the range of the overlapping width of the first portion 2114a and the second portion 2114b, the larger the overlapping area, and the higher the fracture resistance of the first pole piece 210.

[0156] Compared with comparative example 1, in Example 4, the first empty foil segment 2114 is arranged on one side of the first pole piece 210, and the cycle life of the secondary battery 001 is improved, and the pole piece damage rate is reduced; however, compared with Example 1 in which the first empty foil segment 2114 is arranged on both sides of the first pole piece 210, the cycle life of the secondary battery 001 in Example 4 is lower, and the pole piece damage rate is higher. This shows that only arranging the first empty foil segment 2114 on one side of the first pole piece 210 can play a certain effect of reducing the pole piece breakage, but when the first empty foil segment 2114 is arranged on both sides of the first pole piece 210, a better effect will be obtained.

[0157] In addition, for ordinary technicians in this field, various other corresponding changes and modifications can be made according to the technical concept of this application, and all these changes and modifications should fall within the protection scope of the claims of this application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet and a diaphragm, the diaphragm is arranged between the first electrode sheet and the second electrode sheet, the first electrode sheet, the second electrode sheet and the diaphragm are stacked and wound to form a winding structure, It is characterized in that The first pole piece comprises: First pole lug; A first current collector, along the width direction of the first pole piece, the first current collector comprising a first coating section and a first empty foil section located at at least one end of the first coating section; and A first active material layer, along the thickness direction of the first electrode sheet, the first active material layer is arranged on the first surface of the first coating section and / or the second surface of the first coating section; The first empty foil segment includes a first portion and a second portion connected to the first coated segment, wherein the first portion is connected to the second portion and is stacked with the second portion along a thickness direction of the first pole piece.

2. The secondary battery according to claim 1, It is characterized in that In the same winding layer, the first portion is closer to the winding center of the electrode assembly than the second portion.

3. The secondary battery according to claim 1, It is characterized in that Along the width direction of the first pole piece, the width of the first portion is L1, the width of the second portion is L2, and 0≤L2-L1≤0.4 mm.

4. The secondary battery according to claim 1, It is characterized in that The first pole piece further includes an adhesive member, which is disposed on a first surface of the first empty foil segment and is bonded between the first portion and the second portion in a thickness direction of the first pole piece.

5. The secondary battery according to claim 4, It is characterized in that The adhesive member is single-sided adhesive, double-sided adhesive or hot-melt adhesive.

6. The secondary battery according to claim 5, It is characterized in that The adhesive is a hot melt adhesive, and the material of the adhesive includes at least one of polyamide, reactive polyurethane or polyethersulfone.

7. The secondary battery according to claim 5, It is characterized in that The melting temperature of the hot melt adhesive is T, 45°C≤T≤65°C.

8. The secondary battery according to claim 4, It is characterized in that The thickness of the thickest part of the adhesive is H2, 5um≤H2≤20um; and / or Along the width direction of the first pole piece, the width of the adhesive member is equal to the overlapping width of the first portion and the second portion.

9. The secondary battery according to claim 1, It is characterized in that The first pole piece further includes an insulating member, and the insulating member is arranged on the second surface of the first empty foil segment.

10. The secondary battery according to claim 9, It is characterized in that The material of the insulating member includes ceramic material.

11. The secondary battery according to claim 10, It is characterized in that The ceramic material includes at least one of aluminum oxide, magnesium oxide, silicon nitride, silicon carbide, and boehmite.

12. The secondary battery according to claim 9, It is characterized in that Along the width direction of the first pole piece, the projection of the insulating member is located within the projection of the first active material layer.

13. The secondary battery according to claim 9, It is characterized in that Along the thickness direction of the first pole piece, the projection of the insulating member is located within the projection of the second pole piece.

14. The secondary battery according to claim 13, It is characterized in that Along the width direction of the first pole piece, the width of a single side of the second pole piece beyond the first active material layer is Δd, and 0.2 mm≤Δd≤1.4 mm.

15. The secondary battery according to claim 14, It is characterized in that Along the width direction of the first pole piece, the width of the orthographic projection of the first empty foil segment in the thickness direction of the first pole piece is W1, and 0.2 mm≤W1≤1.4 mm.

16. The secondary battery according to claim 12, It is characterized in that Along the thickness direction of the first pole piece, the maximum distance between the insulating member on the first portion and the insulating member on the second portion is H1, 31 um≤H1≤100 um.

17. The secondary battery according to claim 12, It is characterized in that The thickness of one layer of the insulating member is H3, 5um≤H3≤20um.

18. The secondary battery according to claim 1, It is characterized in that The first current collector further includes a connecting portion, and the first electrode tab is welded to the connecting portion.

19. The secondary battery according to claim 1, It is characterized in that There are a plurality of first pole tabs, each of which is connected to the first portion and integrally provided with the first portion, and the first pole tab includes a bending portion connected to the first portion and a lead-out portion extending along a width direction of the first pole piece.

20. The secondary battery according to any one of claims 1 to 19, It is characterized in that The outermost pole piece of the electrode assembly is the first pole piece.

21. The secondary battery according to any one of claims 1 to 19, It is characterized in that The first pole piece is a positive pole.

22. An electrical device, It is characterized in that Comprising the secondary battery as claimed in any one of claims 1 to 21.

23. A method for preparing a secondary battery, for preparing the secondary battery as claimed in claim 1, It is characterized in that The following steps are involved: Providing a first current collector, dividing the first current collector into a first coating section and a first unfolded empty foil section located at at least one end of the first coating section along a width direction of the first current collector, and disposing a first active material layer on a first surface of the first coating section and / or a second surface of the first coating section; Bending, the first unfolded empty foil segment includes a first portion and a second portion connected to the first coated segment, and the first portion is bent toward the second portion so that the first portion and the second portion are stacked along the thickness direction of the first pole piece to obtain a first empty foil segment.

24. The method for preparing a secondary battery according to claim 23, It is characterized in that The bending direction of the first portion is toward the winding center of the electrode assembly.

25. The method for preparing a secondary battery according to claim 23, It is characterized in that Along the width direction of the first current collector, the widths of the first portion and the second portion are equal; the width of the first unfolded empty foil segment is W2, 0.4 mm≤W2≤2.8 mm.

26. The method for preparing a secondary battery according to claim 23, It is characterized in that Before the bending step, it also includes: An adhesive is provided on the first surface of the first part and / or the first surface of the second part; after bending, the first surface of the first part faces the first surface of the second part.

27. The method for preparing a secondary battery according to claim 23, It is characterized in that The following steps are also included: An insulating member is provided on the second surface of the first portion and the second surface of the second portion.

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