Electrode assembly and secondary battery

Abstract

The utility model discloses an electrode assembly and a secondary battery, and relates to the technical field of batteries. The electrode assembly comprises a positive pole piece, a negative pole piece, a first diaphragm, a second diaphragm and a supporting structure, the first diaphragm is divided into a roll core part and a roll body part, and the second diaphragm is divided into a roll core part and a roll body part; the supporting structure is fixed on the surface of the first diaphragm roll core part and / or the second diaphragm roll core part; the first diaphragm roll core part, the second diaphragm roll core part and the supporting structure are stacked and wound to form a roll core; the positive pole piece, the second diaphragm winding body part, the negative pole piece and the first diaphragm winding body part are sequentially stacked and wound on the periphery of the winding core to form a winding body. The roll core is arranged in the electrode assembly to serve as the supporting body, so that uniform stress in the electrode assembly is guaranteed, and the purpose of improving wrinkles of the negative electrode piece after full charging is achieved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and more particularly to an electrode assembly and a secondary battery. Background Technology

[0002] Currently, after charging, the negative electrode interface of secondary batteries often exhibits numerous wrinkles, which can easily lead to poor coating and interface defects, resulting in problems such as lithium plating and black spots, posing potential risks to the battery's safety and electrochemical performance. To address the wrinkling problem of the negative electrode, industry technicians have proposed many solutions, such as optimizing winding tension and hot-pressing parameters, adjusting formation schemes, and applying external fixtures for formation. However, the current improvements are not particularly satisfactory. Utility Model Content

[0003] The purpose of this application is to overcome the shortcomings of the prior art and provide an electrode assembly and a secondary battery. This application is based on setting a core inside the electrode assembly as a support, thereby ensuring uniform stress within the electrode assembly and thus improving the wrinkling of the negative electrode sheet after full charging.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] In a first aspect, this application provides an electrode assembly, including a positive electrode, a negative electrode, a first diaphragm, a second diaphragm, and a support structure;

[0006] The first diaphragm is divided into a core portion and a winding portion, and the second diaphragm is divided into a core portion and a winding portion. The support structure is fixed to the surface of the core portion of the first diaphragm and / or the core portion of the second diaphragm. The core portion of the first diaphragm, the core portion of the second diaphragm, and the support structure are formed by stacking and winding.

[0007] The positive electrode, the second diaphragm winding portion, the negative electrode, and the first diaphragm winding portion are sequentially stacked and wound around the outer periphery of the core to form a winding body.

[0008] Preferably, the support structure is fixed on the surface of the first diaphragm core portion, and the first diaphragm core portion, the support structure, and the second diaphragm core portion are sequentially stacked and wound to form a core.

[0009] Preferably, the thickness of the core is 0.8-2.4 mm.

[0010] More preferably, the thickness of the core is any one or a combination of 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2.0mm, 2.2mm, and 2.4mm.

[0011] Preferably, the thickness of the support structure is 0.1-0.4 mm.

[0012] More preferably, the thickness of the support structure is any one or a combination of 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm.

[0013] Preferably, the first diaphragm core portion, the second diaphragm core portion, and the support structure are formed by stacking and winding 1-12 turns to form a core.

[0014] Preferably, the width of the first diaphragm core portion and / or the second diaphragm core portion is L, and the width of the support structure is 4 / 5-5 / 6L.

[0015] Preferably, along the width direction, the support structure is located in the middle of the first diaphragm core portion and / or the second diaphragm core portion.

[0016] Preferably, along the length direction, the distance between the starting end of the support structure and the starting end of the first diaphragm core portion and / or the second diaphragm core portion is 1 / 10-1 / 5L.

[0017] Preferably, the distance between the starting point of the negative electrode winding and the ending point of the core is L1, and the distance between the starting point of the positive electrode winding and the ending point of the core is L2, wherein L2-L1=8-12mm.

[0018] Preferably, an adhesive layer is provided on the surface of the first diaphragm winding portion and / or the second diaphragm winding portion, and the thickness of the adhesive layer is 1-3 μm, specifically 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm.

[0019] Preferably, the adhesive layer is made of polyvinylidene fluoride.

[0020] Preferably, the material of the supporting structure includes polyamide hot melt adhesive or ethylene-vinyl acetate copolymer hot melt adhesive. The hot melt adhesive described in this application has high initial tack and high curing speed.

[0021] More preferably, the melting point of the polyamide hot melt adhesive or the ethylene-vinyl acetate copolymer hot melt adhesive is 110-120°C. This application controls the melting point of the hot melt adhesive within the above range, making the diaphragm less prone to thermal melting.

[0022] More preferably, the viscosity of the polyamide hot melt adhesive or the ethylene-vinyl acetate copolymer hot melt adhesive is 1000-2000 mPa·s.

[0023] This application ensures that the curing strength and time of the hot melt adhesive meet the design requirements by controlling the viscosity of the hot melt adhesive within the above-mentioned range.

[0024] Preferably, both the first diaphragm and the second diaphragm are PP / PE / PP composite membranes.

[0025] Secondly, this application also provides a secondary battery, including the electrode assembly as described above.

[0026] Compared with the prior art, the beneficial effects of this application are as follows:

[0027] This application uses a core inside the electrode assembly as a support, which helps to ensure uniform stress within the electrode assembly, thereby improving the wrinkling of the negative electrode sheet after full charging. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the winding structure of the electrode assembly described in this application.

[0029] Figure 2 This is a schematic diagram of the inner winding structure of the electrode assembly described in this application.

[0030] Figure 3 This is a schematic diagram of the support structure and the first diaphragm core part before winding as described in Embodiment 1, wherein (a) is a three-dimensional view, (b) is a front view, and (c) is a top view.

[0031] Figure 4 This is a schematic diagram of the finished electrode assembly described in this application.

[0032] Figure 1-4 In the middle: 1. Positive electrode sheet; 2. Negative electrode sheet; 3. First diaphragm; 31. First diaphragm core portion; 32. First diaphragm winding body portion; 4. Second diaphragm; 41. Second diaphragm core portion; 42. Second diaphragm winding body portion; 5. Support structure; 6. Core; 7. Winding body; A. Winding start point; B. Core end point. Detailed Implementation

[0033] To better illustrate the purpose, technical solution, and advantages of this application, the following will further describe this application in conjunction with specific embodiments, but the scope of protection and implementation methods of this application are not limited thereto.

[0034] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0035] Example 1

[0036] An electrode assembly, such as Figure 1 and Figure 2As shown, the structure includes a positive electrode 1, a negative electrode 2, a first diaphragm 3, a second diaphragm 4, and a support structure 5. The support structure 5 has a thickness of 0.3 mm and is made of polyamide hot melt adhesive. The melting point of the polyamide hot melt adhesive is 110-120℃, thus ensuring that the melting point of the support structure 5 is lower than that of the first diaphragm 3 and the second diaphragm 4. This prevents the first diaphragm 3 and the second diaphragm 4 from thermally melting during the process of the support structure 5 melting and fixing to the first diaphragm core portion 31 and / or the second diaphragm core portion 41. The viscosity of the polyamide hot melt adhesive is 1000-2000 mPa·s, ensuring that the curing strength and time of the hot melt adhesive meet the design requirements.

[0037] like Figure 1 and Figure 2 As shown, the first diaphragm 3 is divided into a first diaphragm core portion 31 and a first diaphragm winding portion 32, and the second diaphragm 4 is divided into a second diaphragm core portion 41 and a second diaphragm winding portion 42. In this embodiment, the support structure 5 is fixed to the surface of the first diaphragm core portion 31. An adhesive layer is provided on the surfaces of both the first diaphragm winding portion 32 and the second diaphragm winding portion 42. The adhesive layer is made of polyvinylidene fluoride and has a thickness of 2 μm. The first diaphragm winding portion 32 and the second diaphragm winding portion 42 are fixedly connected together by providing the adhesive layer, which helps to improve the stability of the electrode assembly.

[0038] like Figure 2 As shown, the first diaphragm core part 31, the support structure 5, and the second diaphragm core part 41 are stacked in sequence and wound 2.5 turns with A as the starting point to form the core 6. The thickness of the core 6 is 1.5mm.

[0039] It should be noted that the thickness of the first diaphragm 3 and the second diaphragm 4 is only about 10 μm. When calculating the thickness of the core 6, the thickness of the core portion 31 of the first diaphragm and the core portion 41 of the second diaphragm can be ignored.

[0040] like Figure 1 As shown, the positive electrode 1, the second diaphragm winding portion 42, the negative electrode 2, and the first diaphragm winding portion 32 are sequentially stacked and wound around the outer periphery of the core 6 to form a winding body 7.

[0041] like Figure 4 As shown, the core 6 can hold up the R-angles on both sides of the electrode assembly, and at the same time support the sides and R-angles of the electrode assembly, ensuring that the force inside the electrode assembly is uniform, thereby achieving the purpose of improving the wrinkling of the negative electrode sheet after full charging.

[0042] like Figure 3 As shown, along the length direction, the distance between the starting end of the support structure 5 and the starting end of the first diaphragm core portion 31 is 1 / 10L. Figure 2As shown, the distance between the starting point of the winding of the negative electrode 2 and the ending point B of the core is L1, and the distance between the starting point of the winding of the positive electrode 1 and the ending point B of the core is L2, where L2-L1=10mm.

[0043] like Figure 3 As shown, the width of the first diaphragm core portion 31 is L, the width of the support structure 5 is 4 / 5L, and the distance between the two sides of the support structure 5 in the width direction and the two sides of the first diaphragm core portion 31 in the width direction is 1 / 10L, which makes the negative electrode sheet less prone to wrinkles.

[0044] Example 2

[0045] An electrode assembly differs from Embodiment 1 only in that the thickness of the support structure 5 is 0.1 mm, the first diaphragm core portion 31, the support structure 5, and the second diaphragm core portion 41 are stacked in sequence and wound 12 turns with A as the starting point to form a core 6, and the thickness of the core 6 is 2.4 mm.

[0046] Example 3

[0047] An electrode assembly differs from Embodiment 1 only in that the thickness of the support structure 5 is 0.4 mm, the first diaphragm core portion 31, the support structure 5, and the second diaphragm core portion 41 are stacked in sequence and wound around A as the starting point to form a core 6, and the thickness of the core 6 is 0.8 mm.

[0048] Example 4

[0049] An electrode assembly differs from Embodiment 1 only in that the support structure 5 is made of ethylene-vinyl acetate copolymer hot melt adhesive.

[0050] Example 5

[0051] An electrode assembly differs from Embodiment 1 only in that the support structure 5 is simultaneously fixed to the surfaces of the first diaphragm core portion 31 and the second diaphragm core portion 41, and the thickness of the support structure 5 is 0.15 mm.

[0052] Example 6

[0053] An electrode assembly differs from Embodiment 1 only in that neither the surface of the first diaphragm winding portion 32 nor the surface of the second diaphragm winding portion 42 is provided with an adhesive layer.

[0054] In summary, this application provides overall support to the electrode assembly by setting a core inside the electrode assembly, which effectively improves the problem of wrinkles appearing at the interface of the negative electrode sheet after full charging. This greatly enhances the overall safety and electrochemical performance of the electrode assembly and helps to improve product competitiveness.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. An electrode assembly, characterized in that, It includes a positive electrode, a negative electrode, a first diaphragm, a second diaphragm, and a supporting structure; The first diaphragm is divided into a core portion and a winding portion, and the second diaphragm is divided into a core portion and a winding portion; The support structure is fixed to the surface of the first diaphragm core portion and / or the second diaphragm core portion; The first diaphragm core portion, the second diaphragm core portion, and the support structure are stacked and wound together to form a core. The positive electrode, the second diaphragm winding portion, the negative electrode, and the first diaphragm winding portion are sequentially stacked and wound around the outer periphery of the core to form a winding body.

2. The electrode assembly according to claim 1, characterized in that, The support structure is fixed on the surface of the first diaphragm core portion, and the first diaphragm core portion, the support structure, and the second diaphragm core portion are stacked and wound in sequence to form a core.

3. The electrode assembly according to claim 1, characterized in that, The thickness of the core is 0.8-2.4 mm.

4. The electrode assembly according to claim 1, characterized in that, The thickness of the support structure is 0.1-0.4 mm; And / or, the first diaphragm core portion, the second diaphragm core portion, and the support structure are formed by stacking and winding 1-12 turns to form a core.

5. The electrode assembly according to claim 1, characterized in that, The width of the first diaphragm core portion and / or the second diaphragm core portion is L, and the width of the support structure is 4 / 5-5 / 6L.

6. The electrode assembly according to claim 5, characterized in that, Along the width direction, the support structure is located in the middle of the first diaphragm core portion and / or the second diaphragm core portion.

7. The electrode assembly according to claim 5, characterized in that, Along the length direction, the distance between the starting end of the support structure and the starting end of the first diaphragm core portion and / or the second diaphragm core portion is 1 / 10-1 / 5L.

8. The electrode assembly according to claim 1, characterized in that, The distance between the starting point of the negative electrode winding and the ending point of the core is L1, and the distance between the starting point of the positive electrode winding and the ending point of the core is L2, where L2-L1 = 8-12mm.

9. The electrode assembly according to claim 1, characterized in that, An adhesive layer is provided on the surface of the first diaphragm winding portion and / or the second diaphragm winding portion, and the thickness of the adhesive layer is 1-3 μm.

10. A secondary battery comprising the electrode assembly as described in any one of claims 1-9.

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