Electrode assembly and electrochemical device

Abstract

The application provides an electrode assembly, an electrochemical device and an electronic device. The electrode assembly comprises a tab and an ear provided on the tab, the ear comprises a metal strip and an ear adhesive provided on the metal strip, and the ear adhesive comprises a first adhesive layer provided on the metal strip and a second adhesive layer provided on the first adhesive layer in the thickness direction of the ear, wherein the projection area of the first adhesive layer in the thickness direction of the ear is greater than the projection area of the second adhesive layer in the thickness direction of the ear.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to an electrode assembly, an electrochemical device and an electronic device. BACKGROUND

[0002] The tab of a secondary battery is generally composed of a metal strip and a tab adhesive. The conventional tab adhesive is hard, which is not conducive to the deformation of the tab at the tab adhesive. During mechanical vibration such as dropping, the electrode assembly moves in the packaging bag, causing the metal strip of the tab to be repeatedly stretched and bent. The hard tab adhesive further limits the position of the tab metal strip being stretched and bent, and the bending position is prone to occur near the lower edge of the tab adhesive, causing stress concentration at this position, metal strip fatigue, and eventually causing the metal strip to break at this position. SUMMARY

[0003] The present application provides an electrode assembly, an electrochemical device and an electronic device to solve the problem of partial breakage of the tab inside the packaging film during mechanical movement such as dropping of the electrode assembly.

[0004] In a first aspect, the present application provides an electrode assembly, comprising a tab and a tab provided on the tab, the tab comprising a metal strip and a tab adhesive provided on the metal strip, along the thickness direction of the tab, the tab adhesive comprising a first adhesive layer provided on the metal strip and a second adhesive layer provided on the first adhesive layer, wherein the projected area A1 of the first adhesive layer along the thickness direction of the tab is greater than the projected area A2 of the second adhesive layer along the thickness direction of the tab.

[0005] In the present application, multiple layers of tab adhesives are provided on the metal strip, and the projected area of the first adhesive layer near the metal strip along the thickness direction of the tab is greater than the projected area of the second adhesive layer along the thickness direction of the tab, so that when the electrode assembly is top-sealed and packaged, the overflow of the second adhesive layer falls on the first adhesive layer rather than directly on the metal strip, thereby facilitating the relief of stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as dropping of the electrode assembly, and further improving the tab breakage.

[0006] According to some embodiments of the present application, A1 is greater than A2, and 8%≤(A1-A2) / A2≤50%.

[0007] According to some embodiments of the present application, the first adhesive layer and the second adhesive layer are arranged such that the projected area A2 of the second adhesive layer along the thickness direction of the tab falls completely within the range of the projected area A1 of the first adhesive layer along the thickness direction of the tab.

[0008] According to some preferred embodiments of the present application, 16%≤(A1-A2) / A2≤38%, in particular, 22%≤(A1-A2) / A2≤30%.

[0009] According to some embodiments of the present application, A1 is 14mm2 from 64 mm to 10 mm 2 A2 is in the range from 10 mm 2 to 56 mm 2 to 56 mm

[0010] According to some embodiments of the present application, the width of the first adhesive layer > the width of the second adhesive layer. When the width of the first adhesive layer close to the metal strip is greater than the width of the second adhesive layer, it is beneficial to alleviate the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling, and to improve the tab breakage condition.

[0011] According to some preferred embodiments of the present application, the width W1 of the first adhesive layer is greater than the width W2 of the second adhesive layer.

[0012] According to some embodiments of the present application, the length of the first adhesive layer > the length of the second adhesive layer. When the length of the first adhesive layer close to the metal strip is greater than the length of the second adhesive layer, it is beneficial to alleviate the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling, and to improve the tab breakage condition.

[0013] According to some preferred embodiments of the present application, the length L1 of the first adhesive layer is greater than the length L2 of the second adhesive layer.

[0014] According to some preferred embodiments of the present application, the length L1 of the first adhesive layer is in the range from 4 mm to 8 mm.

[0015] According to some embodiments of the present application, the width of the first adhesive layer is 3.5 mm to 8 mm. According to some embodiments of the present application, the width of the second adhesive layer is 2.5 mm to 7 mm. When the tab adhesive width is too narrow, the tab encapsulation reliability cannot be guaranteed. When the tab adhesive width is reduced, the tab adhesive area adhered to the outer packaging bag is reduced. When the adhesion area is too small, the adhesion force between the two is less than the external pulling force, and the tab is detached. When the tab adhesive width increases, the tab adhesive edge stress increases, and the stress applied to the metal strip increases, and the tab is prone to breakage. In addition, too wide tab adhesive will also lead to an increase in tab length and an increase in total length of the electrode assembly, reducing the volumetric energy density.

[0016] According to some embodiments of the present application, the thickness of the first adhesive layer < the thickness of the second adhesive layer. When the thickness of the first adhesive layer close to the metal strip is greater than the thickness of the second adhesive layer, it is beneficial to alleviate the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling, and to improve the tab breakage condition.

[0017] According to some embodiments of the present application, the thickness of the first adhesive layer is 10-55 μm. When the thickness of the first adhesive layer is <10 μm, the buffering effect on the stress-strain difference between the second adhesive layer and the metal strip is limited, and thus the tab breakage condition cannot be significantly improved. When the thickness of the first adhesive layer is >55 μm, the thickness of the first adhesive layer is greater than that of the second adhesive layer, the tab adhesive and the metal strip contact edge overflow seriously, the edge stress is poor, and thus the stress increases, cracks are generated, and the tab is prone to breakage.

[0018] According to some embodiments of the present application, the thickness of the second adhesive layer is 20-100 μm. The second adhesive layer is mainly used to form adhesion with the outer packaging bag. When the thickness of the second adhesive layer is <20 μm, the tab packaging reliability cannot be met, and under the action of external force, the second adhesive layer is prone to be pulled and detached from the outer packaging bag, thereby causing the tab to be detached and a liquid leakage risk event of the electrode assembly to occur. When the thickness of the second adhesive layer is >100 μm, the second adhesive layer will overflow seriously, and the overflow can only be controlled on the first adhesive layer. If the second adhesive layer overflows onto the metal strip, the difference in softness and hardness between the second adhesive layer and the metal strip will cause stress concentration at the junction therebetween, and thus the tab is prone to breakage.

[0019] According to some embodiments of the present application, the elongation at break of the first adhesive layer is greater than that of the second adhesive layer. The elongation at break of the first adhesive layer close to the metal strip is greater than that of the second adhesive layer, which is beneficial to relieve the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling of the electrode assembly, and to improve the tab breakage condition. According to some embodiments of the present application, the elongation at break of the first adhesive layer is ≥300%. According to some embodiments of the present application, the elongation at break of the first adhesive layer is ≥400%. According to some embodiments of the present application, the elongation at break of the first adhesive layer is ≥500%.

[0020] According to some preferred embodiments of the present application, the elongation at break of the first adhesive layer ε1 is greater than the elongation at break of the second adhesive layer ε2.

[0021] According to some preferred embodiments of the present application, 0.19%≤(ε1-ε2) / ε2≤4.30%.

[0022] According to some preferred embodiments of the present application, 0.34%≤(ε1-ε2) / ε2≤1.14%.

[0023] According to some embodiments of the present application, the first adhesive layer comprises polyethylene (PE). According to some embodiments of the present application, the second adhesive layer comprises polypropylene (PP).

[0024] According to some embodiments of the present application, the first adhesive layer further comprises polypropylene, and the mass fraction of the polypropylene in the first adhesive layer is not greater than 80%.

[0025] According to some embodiments of the present application, the second adhesive layer further comprises polyethylene, and the mass percentage of polyethylene in the second adhesive layer is not more than 90%. The higher the PE content of the adhesive layer, the greater the elongation at break, and the softer the adhesive layer.

[0026] According to some embodiments of the present application, a third adhesive layer is arranged on the second adhesive layer. According to some embodiments of the present application, the third adhesive layer satisfies at least one of the following conditions (A) to (C): (A) the projected area A3 of the third adhesive layer along the thickness direction of the tab is smaller than the projected area A2 of the second adhesive layer along the thickness direction of the tab; (B) the thickness T3 of the third adhesive layer < the thickness T2 of the second adhesive layer; (C) the elongation at break ε3 of the third adhesive layer < the elongation at break ε2 of the second adhesive layer.

[0027] In the second aspect of the present application, the present application provides an electrochemical device comprising the electrode assembly according to the first aspect of the present application.

[0028] In the third aspect of the present application, the present application provides an electronic device comprising the electrochemical device according to the second aspect of the present application.

[0029] In the electrode assembly provided by the present application, the multi-layer tab adhesive is arranged on the metal strip, and the projected area of the first adhesive layer close to the metal strip along the thickness direction of the tab is greater than the projected area of the second adhesive layer along the thickness direction of the tab, so that when the electrode assembly is top-sealed and packaged, the overflow of the second adhesive layer falls on the first adhesive layer rather than directly on the metal strip, thereby facilitating the relief of stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling, and thereby improving the tab fracture condition. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The structure of the tab adhesive (with two adhesive layers) in the electrode assembly according to some embodiments of the present application is shown in the following figures. Figure 1A is a side view showing that the thicknesses of the upper and lower tab adhesives are different, the thickness of the first adhesive layer is T1, and the thickness of the second adhesive layer is T2. Figures 1A and 1B are top views showing that the widths of the upper and lower tab adhesives are different, the width of the first adhesive layer at the bottom is W1, which is wider than the width W2 of the second adhesive layer at the top. Figure 1B is a top view Figure 1 Figure 1C is a top view showing that the second adhesive layer is located in the middle of the width direction of the first adhesive layer. Figure 2 Figure 1D is a top view showing that one long side of the second adhesive layer is aligned with one long side of the first adhesive layer.

[0031] Figure 2Structure diagram of the tab adhesive (with two layers of adhesive) in the electrode assembly according to some embodiments of the present application. 2A is a side view showing that the thickness of the upper and lower two layers of tab adhesive is different, the thickness of the first adhesive layer is T1, and the thickness of the second adhesive layer is T2; 2A and 2B are top views showing that the length and width of the upper and lower two layers of tab adhesive are different, the length L1 and width W1 of the bottom layer of the first adhesive layer are greater than the length L2 and width W2 of the upper layer of the second adhesive layer, respectively, 2B is a top view Figure 1 The second adhesive layer is located in the middle of the first adhesive layer in the length and width directions, 2C is a top view Figure 2 The second adhesive layer is located in the middle of the first adhesive layer in the length direction, and one long side of the second adhesive layer is aligned with one long side of the first adhesive layer.

[0032] Figure 3 Structure diagram of the tab adhesive (with three layers of adhesive) in the electrode assembly according to some embodiments of the present application, 3A is a side view showing that the length of the upper, middle and lower three layers of tab adhesive is consistent, 3B-3E are top views showing that the width of the upper, middle and lower three layers of tab adhesive is different, the width of the bottom layer of the first adhesive layer is wider than that of the middle layer of the second adhesive layer, the width of the middle layer of the second adhesive layer is wider than that of the upper layer of the third adhesive layer, 3B is a top view Figure 1 The second adhesive layer is located in the middle of the first adhesive layer in the width direction, and the third adhesive layer is located in the middle of the second adhesive layer in the width direction, 3C is a top view Figure 2 The second adhesive layer is located in the middle of the first adhesive layer in the width direction, and one long side of the third adhesive layer is aligned with one long side of the second adhesive layer, 3D is a top view Figure 3 One long side of the first adhesive layer is aligned with one long side of the second adhesive layer, and the third adhesive layer is located in the middle of the second adhesive layer in the width direction, 3E is a top view Figure 4 One long side of the three layers of adhesive is aligned

[0033] Figure 4 Structure diagram of the tab adhesive (with three layers of adhesive) in the electrode assembly according to some embodiments of the present application, 4A is a side view showing that the thickness of the upper, middle and lower three layers of tab adhesive is different, the thickness of the first adhesive layer is T1, the thickness of the second adhesive layer is T2, and the thickness of the third adhesive layer is T3; 4B-4E are top views showing that the length / width of the upper, middle and lower three layers of tab adhesive is different, the length L1 / width W1 of the bottom layer of the first adhesive layer is greater than the length L2 / width W2 of the middle layer of the second adhesive layer, respectively, the length L2 / width W2 of the middle layer of the second adhesive layer is greater than the length L3 / width W3 of the upper layer of the third adhesive layer, respectively, 4B is a top view Figure 1 The second adhesive layer is located in the middle of the first adhesive layer in the length / width direction, and the third adhesive layer is located in the middle of the second adhesive layer in the length / width direction, 4C is a top view Figure 2 The second adhesive layer is located in the middle of the first adhesive layer in the length / width direction, and the third adhesive layer is located in the middle of the second adhesive layer in the length direction and one long side is aligned with one long side of the second adhesive layer, 4D is a top view Figure 3The first adhesive layer is located in the middle of the length direction of the second adhesive layer, and one long side is aligned with one long side of the second adhesive layer. The third adhesive layer is located in the middle of the length / width direction of the second adhesive layer. 4E-Top view Figure 4 The second adhesive layer is located in the middle of the length direction of the first adhesive layer. The third adhesive layer is located in the middle of the length direction of the second adhesive layer, and one long side of the three adhesive layers is aligned.

[0034] Figure 5 The structure of the tab adhesive (with three adhesive layers) in the electrode assembly according to some embodiments of the present application is shown in the schematic diagram. 5A is a side view showing that the lengths of the first and second adhesive layers are different, the lengths of the second and third adhesive layers are the same, and the length of the first adhesive layer is greater than that of the second and third adhesive layers. 5B-5E are top views showing that the widths of the upper, middle and lower three adhesive layers are different. The width of the first adhesive layer is greater than that of the second adhesive layer, and the width of the second adhesive layer is greater than that of the third adhesive layer. 5B-Top view Figure 1 The second adhesive layer is located in the middle of the length / width direction of the first adhesive layer. The third adhesive layer is located in the middle of the width direction of the second adhesive layer. 5C-Top view Figure 2 The second adhesive layer is located in the middle of the length / width direction of the first adhesive layer. One long side of the third adhesive layer is aligned with one long side of the second adhesive layer. 5D-Top view Figure 3 The second adhesive layer is located in the middle of the length direction of the first adhesive layer. The third adhesive layer is located in the middle of the length / width direction of the second adhesive layer. 5E-Top view Figure 4 The second and third adhesive layers are located in the middle of the length direction of the first adhesive layer, and one long side of the three adhesive layers is aligned.

[0035] Figure 6 The overflow of the tab adhesive (with two adhesive layers) in the electrode assembly according to some embodiments of the present application is shown in the schematic diagram.

[0036] Figure 7 The structure of the metal strip containing the tab adhesive in the electrode assembly of Comparative Example 1 is shown in the schematic diagram. The metal strip is bonded with a single layer of tab adhesive on both sides.

[0037] Figure 8 The structure of the metal strip containing the tab adhesive in the electrode assembly of Example 1 is shown in the schematic diagram. The metal strip is still bonded with a single layer of tab adhesive on one side, but is bonded with a double layer of tab adhesive on the other side.

[0038] Figure 9 The structure of the metal strip containing the tab adhesive in the electrode assembly of Example 2 is shown in the schematic diagram. The metal strip is bonded with a double layer of tab adhesive on both sides.

[0039] Figure 10 The structure of the metal strip containing the tab adhesive in the electrode assembly of Example 3 is shown in the schematic diagram. The metal strip is bonded with a triple layer of tab adhesive on both sides. DETAILED DESCRIPTION

[0040] For the purposes of the present application, the technical solutions and advantages thereof, the technical solutions of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and serve to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0041] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or singular value can be combined with any other point or singular value to form a range not explicitly recited, either as a lower or upper limit, or in combination with other lower or upper limits.

[0042] In the description herein, unless otherwise specified, "above", "below" include the number itself.

[0043] Unless otherwise defined, the terms used in the present application have the meanings commonly understood by a person of ordinary skill in the art. Unless otherwise specified, the values of each parameter mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the embodiments of the present application).

[0044] The list of items connected by the terms "at least one of", "at least one", "at least one of", or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0045] Electrode assembly

[0046] In a first aspect, the present application provides an electrode assembly, which comprises a tab and a tab ear arranged on the tab, the tab ear comprising a metal strip and a tab ear adhesive arranged on the metal strip, along the thickness direction of the tab ear, the tab ear adhesive comprises a first adhesive layer arranged on the metal strip and a second adhesive layer arranged on the first adhesive layer, wherein the projected area of the first adhesive layer along the thickness direction of the tab ear is greater than the projected area of the second adhesive layer along the thickness direction of the tab ear.

[0047] In the present application, multiple layers of tab gum are arranged on the metal strip, and the projection area of the first gum layer close to the metal strip along the thickness direction of the tab is greater than the projection area of the second gum layer along the thickness direction of the tab, so that when the electrode assembly is top-sealed and packaged, the overflow of the second gum layer falls on the first gum layer instead of directly falling on the metal strip, thereby facilitating the relief of stress concentration of the tab metal strip at the junction with the tab gum during mechanical vibration such as falling, and thereby improving the tab fracture condition.

[0048] According to some embodiments of the present application, the width of the first gum layer > the width of the second gum layer. When the width of the first gum layer close to the metal strip is greater than the width of the second gum layer, it is beneficial to relieve the stress concentration of the tab metal strip at the junction with the tab gum during mechanical vibration such as falling, and to improve the tab fracture condition.

[0049] According to some embodiments of the present application, the length of the first gum layer > the length of the second gum layer. When the length of the first gum layer close to the metal strip is greater than the length of the second gum layer, it is beneficial to relieve the stress concentration of the tab metal strip at the junction with the tab gum during mechanical vibration such as falling, and to improve the tab fracture condition.

[0050] According to some embodiments of the present application, the length of the first gum layer is in the range of 4mm to 8mm, for example 4.0mm, 4.2mm, 4.5mm, 4.8mm, 5.0mm, 5.3mm, 5.5mm, 5.8mm, 6.0mm, 6.5mm, 7.0mm, 7.5mm, 8mm.

[0051] According to some embodiments of the present application, the length of the second gum layer is in the range of 4mm to 8mm, for example 4.0mm, 4.2mm, 4.5mm, 4.8mm, 5.0mm, 5.3mm, 5.5mm, 5.8mm, 6.0mm, 6.5mm, 7.0mm, 7.5mm, 8mm.

[0052] According to some embodiments of the present application, the width of the first adhesive layer is 3.5mm to 8mm. In some embodiments, the width of the first adhesive layer is 3.5mm, 3.8mm, 4.0mm, 4.2mm, 4.5mm, 4.8mm, 5.0mm, 5.3mm, 5.5mm, 5.8mm, 6.0mm, 6.5mm, 7.0mm, 7.5mm, 8mm, or a range formed by any two of them. According to some embodiments of the present application, the width of the second adhesive layer is 2.5mm to 7mm. In some embodiments, the width of the second adhesive layer is 2.5mm, 2.8mm, 3.0mm, 3.5mm, 3.8mm, 4.0mm, 4.2mm, 4.5mm, 4.8mm, 5.0mm, 5.3mm, 5.5mm, 5.8mm, 6.0mm, 6.5mm, 7.0mm, or a range formed by any two of them. When the tab adhesive width is too narrow, the tab encapsulation reliability cannot be guaranteed. When the tab adhesive width is reduced, the adhesive area between the tab adhesive and the outer packaging bag is reduced. When the adhesive area is too small, the adhesion force between the two is less than the external pulling force, and the tab is detached. When the tab adhesive width is increased, the stress on the edge of the tab adhesive is increased, and the stress applied to the metal strip is increased, and the tab is prone to breakage. In addition, if the tab adhesive is too wide, the length of the tab will increase, the total length of the electrode assembly will increase, and the volume energy density will decrease.

[0053] According to some embodiments of the present application, the thickness of the first adhesive layer is less than the thickness of the second adhesive layer. When the thickness of the first adhesive layer near the metal strip is greater than the thickness of the second adhesive layer, it is beneficial to alleviate the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as falling of the electrode assembly, and to improve the tab breakage. According to some embodiments of the present application, the difference between the thickness of the second adhesive layer and the thickness of the first adhesive layer is 5μm to 50μm. In some embodiments, the difference between the thickness of the second adhesive layer and the thickness of the first adhesive layer is 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or a range formed by any two of them. In some embodiments, the difference between the thickness of the second adhesive layer and the thickness of the first adhesive layer is 10μm to 35μm.

[0054] In the present application, the thickness of the adhesive layer refers to the total thickness of the adhesive layers on both sides of the metal strip.

[0055] According to some embodiments of the present application, the thickness of the first adhesive layer is 10-55 μm. In some embodiments, the thickness of the first adhesive layer is 10 μm, 14 μm, 18 μm, 20 μm, 25 μm, 28 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, or a range defined by any two of them. When the thickness of the first adhesive layer is <10 μm, the buffering effect on the stress-strain difference between the second adhesive layer and the metal strip is limited, and thus the tab breakage condition cannot be significantly improved. When the thickness of the first adhesive layer is >55 μm, the thickness of the first adhesive layer is greater than that of the second adhesive layer, and the tab adhesive and the metal strip contact edge overflow seriously, the edge stress is poor, and thus the stress increases, cracks are generated, and the tab is prone to breakage.

[0056] According to some embodiments of the present application, the thickness of the second adhesive layer is 20-100 μm. In some embodiments, the thickness of the second adhesive layer is 20 μm, 25 μm, 28 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or a range defined by any two of them. The second adhesive layer is mainly used to form adhesion with the outer packaging bag, and when the thickness of the second adhesive layer is <20 μm, the tab packaging reliability cannot be met, and under the action of external force, the second adhesive layer is prone to be pulled and debonded from the outer packaging bag, thereby causing the tab to be debonded and a dangerous event of electrode assembly liquid leakage. When the thickness of the second adhesive layer is >100 μm, the second adhesive layer will overflow seriously, and the overflow cannot be controlled only on the first adhesive layer. If the second adhesive layer overflows onto the metal strip, the difference in hardness between the second adhesive layer and the metal strip will cause stress concentration at the junction therebetween, and thus the tab is prone to breakage.

[0057] According to some embodiments of the present application, the elongation at break of the first adhesive layer is > the elongation at break of the second adhesive layer. The elongation at break of the first adhesive layer near the metal strip is greater than that of the second adhesive layer, which is conducive to relieving the stress concentration of the tab metal strip at the junction with the tab adhesive during mechanical vibration such as dropping of the electrode assembly, and improving the tab breakage condition. According to some embodiments of the present application, the difference between the elongation at break of the first adhesive layer and the elongation at break of the second adhesive layer is 50-650%. In some embodiments, the difference between the elongation at break of the first adhesive layer and the elongation at break of the second adhesive layer is 100%, 120%, 200%, 300%, 400%, 500%, or a range defined by any two of them. In some embodiments, the difference between the elongation at break of the first adhesive layer and the elongation at break of the second adhesive layer is 100-500%.

[0058] According to some embodiments of the present application, the first adhesive layer has an elongation at break ≥ 300%. In some embodiments, the first adhesive layer has an elongation at break of 350%, 400%, 450%, 500%, 550%, 600%, 650%, 700%, 750%, 800%, or a range defined by any two of them. According to some embodiments of the present application, the first adhesive layer has an elongation at break of 300% to 800%.

[0059] According to some embodiments of the present application, the second adhesive layer has an elongation at break ≥ 140%. In some embodiments, the second adhesive layer has an elongation at break of 140%, 160%, 200%, 250%, 300%, 330%, 350%, 400%, 430%, 450%, 500%, 600%, 630%, 650%, 750%, or a range defined by any two of them. According to some embodiments of the present application, the second adhesive layer has an elongation at break of 300% to 650%.

[0060] According to some embodiments of the present application, the first adhesive layer has an elongation at break ε1 greater than the second adhesive layer has an elongation at break ε2, especially 0.19% ≤ (ε1-ε2) / ε2 ≤ 4.30%, preferably 0.34% ≤ (ε1-ε2) / ε2 ≤ 1.14%.

[0061] According to some embodiments of the present application, the first adhesive layer comprises polyethylene. According to some embodiments of the present application, the second adhesive layer comprises polypropylene. According to some embodiments of the present application, the first adhesive layer further comprises polypropylene, and the mass percentage of polypropylene in the first adhesive layer is no more than 80%. According to some embodiments of the present application, the second adhesive layer further comprises polyethylene, and the mass percentage of polyethylene in the second adhesive layer is no more than 90%.

[0062] According to some embodiments of the present application, a third adhesive layer is disposed on the second adhesive layer. According to some embodiments of the present application, the third adhesive layer has a projected area along the tab thickness direction smaller than the projected area of the second adhesive layer along the tab thickness direction. In some embodiments, the thickness of the third adhesive layer < the thickness of the second adhesive layer. In some embodiments, the elongation at break of the third adhesive layer < the elongation at break of the second adhesive layer.

[0063] In the present application, one object is greater than another object means that the one object is greater than the another object, and the difference between them is greater than 5%. Similarly, in the present application, one object is smaller than another object means that the one object is smaller than the another object, and the difference between them is greater than 5%. The difference between two objects means the difference between the larger object and the smaller object, divided by the smaller object.

[0064] According to some embodiments of the present application, the tab includes a positive tab and a negative tab.

[0065] The positive electrode tab can include a positive current collector and a positive active material layer. In some embodiments, the positive current collector can include, but is not limited to, aluminum. In some embodiments, the positive active material layer includes a positive active material, which includes, but is not limited to, lithium cobalt oxide (LiCo02), lithium nickel cobalt manganese (NCM) ternary material, lithium iron phosphate (LiFeP04), or lithium manganese oxide (LiMn204). In some embodiments, the positive active material layer further includes a binder and, optionally, a conductive material. The binder improves the binding between the positive active material particles and each other, and also improves the binding between the positive active material and the current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc. In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative. The positive electrode can be prepared by a method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent can include, but is not limited to, N-methyl pyrrolidone.

[0066] The negative electrode sheet can include a negative current collector and a negative active material layer. According to some embodiments of the present application, the negative active material layer includes a negative active material, which can include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, lithium metal alloys, a material capable of doping / de-doping lithium, or a transition metal oxide, such as Si, SiOx (0 < x < 2), etc. The material capable of reversibly intercalating / deintercalating lithium ions can be a carbon material. The carbon material can be any carbon-based negative active material commonly used in lithium-ion rechargeable electrochemical devices. Examples of the carbon material include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon can be amorphous or plate-shaped, small piece-shaped, spherical, or fiber-shaped natural graphite or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, meso-phase pitch carbonization products, baked coke, etc. Both low crystalline carbon and high crystalline carbon can be used as the carbon material. As a low crystalline carbon material, soft carbon and hard carbon can be generally included. As a high crystalline carbon material, natural graphite, crystalline graphite, pyrolytic carbon, meso-phase pitch-based carbon fiber, meso-phase carbon microbeads, meso-phase pitch, and high-temperature calcined carbon (such as petroleum or coke derived from coal tar pitch) can be generally included.

[0067] According to some embodiments of the present application, the negative active material layer includes a binder, and the binder can include various binder polymers, such as polyvinylidene-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, nylon, etc., but is not limited thereto.

[0068] According to some embodiments of the present application, the negative active material layer further includes a conductive material to improve the conductivity of the electrode. Any conductive material can be used as the conductive material, as long as it does not cause chemical changes. Examples of the conductive material include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.; metal-based materials, such as metal powder or metal fiber including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof. The current collector can be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof. The negative current collector used in the present application can be selected from a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0069] According to some embodiments of the present application, the electrode assembly further includes a separator. The material and shape of the separator are not particularly limited according to the present application, and can be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, and the like.

[0070] For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0071] The surface treatment layer is provided on at least one surface of the substrate layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0072] The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0073] The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0074] Electrochemical device

[0075] In a second aspect, the present application provides an electrochemical device including the electrode assembly according to the first aspect of the present application.

[0076] The electrochemical device of the present application further includes an electrolyte including a lithium salt and a nonaqueous solvent.

[0077] In some embodiments of the present application, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, the lithium salt can be selected as LiPF6because it can give high ionic conductivity and improve the cycle characteristics.

[0078] The non-aqueous solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0079] The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0080] Examples of the chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and a combination thereof. Examples of the fluorinated carbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, and a combination thereof.

[0081] Examples of the carboxylic acid ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, caprolactone, and a combination thereof.

[0082] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and a combination thereof.

[0083] Examples of the other organic solvent are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid ester, and a combination thereof.

[0084] According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to, all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0085] Electronic device

[0086] The electronic device of the present application can be any device using the electrochemical device of the second aspect of the present application.

[0087] In some embodiments, the electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery or a lithium ion capacitor, etc.

[0088] In order to achieve the above-mentioned object and enable the person skilled in the art to understand the present application scheme, the following describes the specific embodiments of the present application as follows, and it is declared that the described embodiments are only partial embodiments of the present application, but not all embodiments.

[0089] I. Test method

[0090] 1. Elongation at break ε test:

[0091] Prepare an adhesive film with a fixed thickness of 80 μm, and cut it into a test sample with a width of 25 mm and a length of 130 mm using a punching machine. Fix the test sample to the test fixture of a high-iron tensile testing machine to test the tensile strength of the substrate, with a tensile speed of 10 mm / min and a standard distance of 100 mm between the two fixtures of the tensile testing machine. Record the tensile strength and displacement curve, and when the displacement point Lbreak of the sample is broken, the displacement point at break is Lbreak, then the elongation at break ε = L 断 / 100 x 100%.

[0092] 2. Cell drop test:

[0093] 1) Put the cells containing different tab adhesives into suitable drop fixtures, and drop them from a height of 1.8 meters to the surface of a steel plate;

[0094] 2) The falling sequence: up-down-right up-right down-left up-left down, one round, a total of 15 rounds;

[0095] 3) Disassemble the battery cell, count whether the tab breaks after falling 15 rounds, and whether the tab and the packaging bag are debonded: if there is no tab breakage, the tab breakage test is passed; if there is no tab debonding, the tab debonding test is passed.

[0096] II. Examples and Comparative Examples

[0097] Example 1

[0098] Tab adhesive preparation: The tab adhesive can be divided into single-layer tab adhesive and multi-layer tab adhesive. The multi-layer tab adhesive is composed of multiple adhesive films. The adhesive film close to the surface of the metal strip is the first adhesive layer, and the adhesive film on the surface of the first adhesive layer is the second adhesive layer. By analogy, the adhesive film on the surface of the second adhesive layer is the third adhesive layer. The main material of each adhesive layer is polyethylene resin PE, polypropylene resin PP or a blend of the two, and the elongation at break of the adhesive film is changed by adjusting the PE content in the main material.

[0099] After the raw materials are uniformly mixed, they are poured into an extruder to form an adhesive film by extrusion. The thickness of the adhesive film is controlled by a metering pump, and the multi-layer adhesive film is co-extruded and compounded by a distributor to form a multi-layer adhesive film structure.

[0100] The tab structure of the present example is shown in Figure 8 The metal strip on one side is a single-layer tab adhesive, and the other side is a double-layer tab adhesive. The single-layer tab adhesive is composed of a first adhesive layer, and the double-layer tab adhesive is composed of a first adhesive layer and a second adhesive layer. The main material of the single-layer tab adhesive is composed of 100% mass fraction of PE, with an elongation at break of 750%, a thickness of 70 μm, and a width of 5 mm. The first adhesive layer of the double-layer tab adhesive is composed of 100% mass fraction of PE, with an elongation at break of 750%, a thickness T1 of 20 μm, and a width W1 of 5 mm. The second adhesive layer is composed of 100% mass fraction of PP (0% mass fraction of PE), with an elongation at break of 140%, a thickness T2 of 50 μm, and a width W2 of 4 mm.

[0101] Tab preparation: The above tab adhesive is attached to the preheated aluminum metal strip and copper metal strip, and the tab adhesive is welded to the metal strip by a high-frequency welding machine. After cooling and cutting, the positive tab and the negative tab are formed, respectively.

[0102] The positive and negative tabs are respectively welded to the positive and negative tabs, and then the positive tab, the separator, and the negative tab are stacked in order with the separator between the positive and negative tabs to achieve the isolation effect, and the electrode assembly is obtained by winding. Then the electrode assembly is placed in an aluminum plastic film packaging shell, wherein the tab rubber is exposed at a position 0.5mm away from the edge of the top seal of the aluminum plastic film, and the aluminum plastic film and the tab are tightly bonded by hot pressing to achieve the top aluminum plastic film packaging of the battery and the insulation between the metal belt and the aluminum plastic film. Finally, the above device is dried and then injected with electrolyte, and then the finished battery is obtained after vacuum packaging, standing, formation, degassing, and edge cutting processes.

[0103] Examples 2 to 13

[0104] Referring to Example 1, the structure and parameter changes are shown in Table 1.

[0105] Comparative Examples 1 to 11

[0106] Referring to Example 1, the structure and parameter changes are shown in Table 1.

[0107] III. Test Results

[0108] The test results of the examples and comparative examples are shown in Table 2, wherein:

[0109] A1 represents the projected area of the first adhesive layer along the thickness direction of the tab; A2 represents the projected area of the second adhesive layer along the thickness direction of the tab; A3 represents the projected area of the third adhesive layer along the thickness direction of the tab;

[0110] L1 represents the length of the first adhesive layer; L2 represents the length of the second adhesive layer; L3 represents the length of the third adhesive layer;

[0111] T1 represents the thickness of the first adhesive layer; T2 represents the thickness of the second adhesive layer; T3 represents the thickness of the third adhesive layer;

[0112] W1 represents the width of the first adhesive layer; W2 represents the width of the second adhesive layer; W3 represents the width of the third adhesive layer;

[0113] ε1 represents the elongation at break of the first adhesive layer; ε2 represents the elongation at break of the second adhesive layer; ε3 represents the elongation at break of the third adhesive layer;

[0114] P indicates passing;

[0115] PE mass ratio = (PE mass + PP mass) / (PE mass + PP mass) x 100%.

[0116]

[0117]

[0118]

[0119] Table 2

[0120] Group Drop effect - tab breakage Drop effect - tab delamination Example 1 4 / 10P 10 / 10P Example 2 5 / 10P 10 / 10P Example 3 7 / 10P 10 / 10P Example 4 8 / 10P 10 / 10P Example 5 6 / 10P 10 / 10P Example 6 5 / 10P 10 / 10P Example 7 8 / 10P 7 / 10P Example 8 6 / 10P 10 / 10P Example 9 6 / 10P 10 / 10P Example 10 7 / 10P 7 / 10P Example 11 10 / 10P 10 / 10P Example 12 9 / 10P 10 / 10P Example 13 5 / 10P 10 / 10P Example 14 9 / 10P 9 / 10P Example 15 10 / 10P 10 / 10P Comparative Example 1 1 / 10P 10 / 10P Comparative Example 2 0 / 10P 10 / 10P Comparative Example 3 3 / 10P 10 / 10P Comparative Example 4 2 / 10P 10 / 10P Comparative Example 5 4 / 10P 4 / 10P Comparative Example 6 1 / 10P 10 / 10P Comparative Example 7 4 / 10P 10 / 10P Comparative Example 8 7 / 10P 3 / 10P Comparative Example 9 4 / 10P 10 / 10P Comparative Example 10 2 / 10P 10 / 10P Comparative Example 11 4 / 10P 10 / 10P Comparative Example 12 4 / 10P 10 / 10P Comparative Example 13 7 / 10P 4 / 10P

[0121] The metal strip in Comparative Example 1 contains the tab adhesive, and the upper and lower sides are both single-layer structures (as shown in Figure 7 The adhesive layer has a thickness of 80 μm and a width of 5 mm, and is composed of 100% PP. The adhesive layer is hard, and the elongation at break is only 140%.

[0122] The metal strip in Comparative Example 2 contains the tab adhesive, and the structure is the same as that in Comparative Example 1. The only difference is that the thickness of the adhesive layer is increased to 100 μm.

[0123] The metal strip in Example 1 contains the tab adhesive on one side, which is the same as that in the comparative examples (as shown in Figure 8 The other side contains a double-layer tab adhesive. The first adhesive layer is close to the metal strip, and the second adhesive layer is further away from the metal strip. The first adhesive layer has a thickness T1 of 20 μm, a width W1 of 5 mm, and is composed of 100% PE. The adhesive layer is soft, and the elongation at break can reach 750%. The second adhesive layer has a thickness T2 of 50 μm, a width W2 of 4 mm, and is composed of 100% PP. The adhesive layer is hard, and the elongation at break is 140%.

[0124] The metal strip in Example 2 contains a double-layer tab adhesive on both sides (as shown in Figure 9 The properties of the double-layer tab adhesive are the same as those in Example 1.

[0125] The metal strip in Example 3 contains a three-layer tab adhesive on both sides (as shown in Figure 10 The first adhesive layer is close to the metal strip, the second adhesive layer is further away from the metal strip, and the third adhesive layer is the outermost layer. The first adhesive layer has a thickness T1 of 20 μm, a width W1 of 5.5 mm, and is composed of 100% PE. The adhesive layer is soft, and the elongation at break can reach 750%. The second adhesive layer has a thickness T2 of 35 μm, a width W2 of 4.5 mm, and is composed of 50% PE + 50% PP. The adhesive layer is relatively soft, and the elongation at break is 430%. The third adhesive layer has a thickness T3 of 45 μm, a width W3 of 4 mm, and is composed of 100% PP. The adhesive layer is relatively hard, and the elongation at break is 140%.

[0126] By comparing the drop results of Comparative Example 1 and Example 1, Example 2, or Comparative Example 2 and Example 3, it can be seen that the lug structure and performance of the present application are optimized, which can significantly improve the lug fracture pass rate of the drop test, and the lug glue on both sides of the metal strip is more capable of improving the drop pass rate than only one side. Because the conventional lug glue is harder than the metal strip, when subjected to external force, the deformations of the two are different, thereby pulling each other, causing stress concentration, especially at the edge of the lug glue and the metal strip, cracks are generated, and then the metal strip is broken. Therefore, the first glue layer uses a soft glue layer with high elongation, which can increase the deformation amount of the lug glue under stress, reduce stress concentration, and slow down the deformation of the metal strip under stress, thereby improving the drop-lug fracture pass rate.

[0127] Examples 4 to 6 and Comparative Examples 3, 4 have basically the same preparation method as Example 2, except that the first glue layer thickness T1 of Example 4 is 10 μm, the first glue layer thickness T1 of Example 5 is 20 μm, the first glue layer thickness T1 of Example 6 is 55 μm, the second glue layer thickness T2 is 60 μm, the first glue layer thickness T1 of Comparative Example 3 is 8 μm, and the first glue layer thickness T1 of Comparative Example 4 is 57 μm.

[0128] By comparing the drop results of Examples 4 to 6 and Comparative Examples 3, 4, it can be seen that the first glue layer thickness T1 should be limited to 10 μm-55 μm, and T1 < T2. When T1 < 10 μm, the first (soft) glue layer is too thin, and the buffering effect on the stress strain difference between the second (hard) glue layer and the metal strip is very limited, so it cannot significantly improve the lug fracture. When T1 > 55 μm, T1 > T2, the lug glue and the metal strip contact edge overflow glue seriously, which increases the edge stress difference, so the stress increases, cracks are generated, and the lug is broken.

[0129] Examples 7, 8 and Comparative Examples 5, 6 have basically the same preparation method as Example 2, except that the second glue layer thickness T2 of Example 7 is 20 μm, the second glue layer thickness T2 of Example 8 is 100 μm, the second glue layer thickness T2 of Comparative Example 5 is 18 μm, and the second glue layer thickness T2 of Comparative Example 6 is 103 μm.

[0130] From the drop results of Example 7, Example 8 and Comparative Example 5, Comparative Example 6, it can be seen that the second adhesive layer thickness T2 should be limited to 20 μm to 100 μm. The second adhesive layer mainly forms an adhesive bond with the outer packaging bag. When the second adhesive layer T2 < 20 μm, the tab encapsulation reliability cannot be met, and under the action of external force, the second adhesive layer is easily pulled and debonded from the outer packaging bag, thereby causing the tab to debond and a risk of cell leakage. When the second adhesive layer T2 > 100 μm, the second adhesive layer will have serious overflow, and even if W1 > W2, the overflow cannot be controlled to be only on the first adhesive layer. When the second hard adhesive layer overflows onto the metal strip, the difference in hardness between the second hard adhesive layer and the metal strip will cause stress concentration at the interface between the second hard adhesive layer and the metal strip, thereby causing the tab to break.

[0131] Example 9, Example 10 and Comparative Examples 7 to 9 have the same preparation method as Example 2, except that the first adhesive layer width W1 of Example 9 is 8 mm and the second adhesive layer width W2 is 7 mm, the first adhesive layer width W1 of Example 10 is 3.5 mm and the second adhesive layer width W2 is 2.5 mm, the first adhesive layer width W1 of Comparative Example 7 is 8.5 mm and the second adhesive layer width W2 is 7.5 mm, the first adhesive layer width W1 of Comparative Example 8 is 4 mm and the second adhesive layer width W2 is 2 mm, and the first adhesive layer width W1 of Comparative Example 9 is 4 mm and the second adhesive layer width W2 is 5 mm.

[0132] From the drop results of Example 9, Example 10 and Comparative Examples 7 to 9, it can be seen that the first adhesive layer width W1 should be limited to 3.5 mm to 8 mm, the second adhesive layer width W2 should be limited to 2.5 mm to 7 mm, and W1 > W2. When the tab adhesive width is too narrow, the tab encapsulation reliability cannot be guaranteed. As the tab adhesive width decreases, the tab adhesive bonding area with the outer packaging bag decreases. When the bonding area is too small, the adhesive force between the tab adhesive and the outer packaging bag is less than the pulling force of the external force, and the tab debonds. When the tab adhesive width increases, the stress at the edge of the tab adhesive increases, and the stress applied to the metal strip also increases, and the tab is prone to breakage. Moreover, a too wide tab adhesive will increase the length of the tab and the total length of the cell, thereby reducing the volume energy density. When W1 > W2, the second adhesive layer overflow will not exceed the first adhesive layer, as shown in FIG. 8. If W1 < W2, the second adhesive layer will overflow onto the metal strip, and the difference in hardness between the hard adhesive and the metal strip will increase the stress concentration at the interface between the hard adhesive and the metal strip, thereby causing the tab to break. Figure 6

[0133] ​Examples 11-13 and Comparative Examples 10, 11 were prepared in the same manner as Example 2, except that in Example 11, the second adhesive layer had a composition of 90% PE and 10% PP and an elongation at break of 630%, in Example 12, the first adhesive layer had a composition of 80% PE and 20% PP and an elongation at break of 580%, the second adhesive layer had a composition of 50% PE and 50% PP and an elongation at break of 430%, and in Example 13, the first adhesive layer had a composition of 20% PE and 80% PP and an elongation at break of 300%, in Comparative Example 10, the first adhesive layer had a composition of 18% PE and 82% PP and an elongation at break of 250%, and in Comparative Example 11, the first adhesive layer had a composition of 20% PE and 80% PP and an elongation at break of 300%, and the second adhesive layer had a composition of 100% PE and an elongation at break of 750%.

[0134] Comparing the drop results of Examples 11-13 and Comparative Examples 10, 11, it can be seen that the first adhesive layer has a PE mass fraction of 20-100% and a PP mass fraction of 0-80%, the second adhesive layer has a PE mass fraction of 0-90% and a PP mass fraction of 10-100%, and the first adhesive layer has an elongation at break of 300% or more, and the elongation at break of the first adhesive layer is greater than that of the second adhesive layer. The higher the PE content in the adhesive layer, the softer the adhesive layer and the higher the elongation at break. When the PE content in the first adhesive layer is less than 20%, i.e., the elongation at break is less than 300%, the first adhesive layer is not soft enough to form a poor strain with the metal strip, the stress is concentrated at the junction of the adhesive layer and the metal strip, and the tab breaks, thus having no obvious improvement on the drop. In addition, when the elongation at break of the first adhesive layer is less than that of the second adhesive layer, even if the softness of the second adhesive layer is increased, it is not the layer in direct contact with the metal strip, and the stress at the junction of the tab adhesive and the metal strip is still caused by the first adhesive layer and the metal strip, thus having no improvement effect on the drop-tab breakage.

[0135] Comparing Example 11 with Comparative Examples 12 and 13, it can be found that when (A1-A2) / A2 is less than 8%, it cannot be guaranteed that the second adhesive layer does not overflow the first adhesive layer, which may increase the difference in hardness between the hard adhesive and the metal strip, concentrate the stress at the junction of the adhesive and the metal strip, and thus increase the risk of tab breakage. At the same time, when (A1-A2) / A2 is greater than 50%, the area of the second adhesive layer is too small, which may cause degradation of tab packaging reliability, such as increasing tab debonding and increasing the risk of electrode assembly liquid leakage. In addition, further comparing Example 12 with Example 15 and Example 2 with Example 5, it can be found that when 22%≤(A1-A2) / A2≤30%, the tab breakage can be further improved.

Claims

1. An electrode assembly comprising a tab sheet and a tab provided on the tab sheet, the tab comprising a metal tape and a tab gum provided on the metal tape, the tab gum comprising a first gum layer provided on the metal tape and a second gum layer provided on the first gum layer in a direction of a thickness of the tab, wherein, A1 is greater than A2, and 8%≤(A1-A2) / A2≤50%; a projection of the second adhesive layer along the tab thickness direction falls completely within a range of a projection of the first adhesive layer along the tab thickness direction; an elongation at break of the first adhesive layer ε1 is greater than an elongation at break of the second adhesive layer ε2, and 0.19%≤(ε1-ε2) / ε2≤4.30%.

2. The electrode assembly of claim 1, wherein, 16%≤(A1-A2) / A2≤38%.

3. The electrode assembly of claim 1, wherein, 22%≤(A1-A2) / A2≤30%.

4. The electrode assembly of claim 1, wherein, A1 is in the range of 14 mm 2 to 64 mm 2 ; A2 is in the range of 10 mm 2 to 56 mm 2 .

5. The electrode assembly of claim 4, wherein, The thickness of the second adhesive layer is in a range of 20 μm to 100 μm.

6. The electrode assembly of claim 4, wherein, The thickness of the second adhesive layer is in a range of 40 μm to 80 μm.

7. The electrode assembly of claim 1, wherein, An elongation at break of the first adhesive layer ε1 is greater than an elongation at break of the second adhesive layer ε2, and 0.34%≤(ε1-ε2) / ε2≤1.14%.

8. The electrode assembly of claim 1, wherein, The first adhesive layer comprises polyethylene; and / or the second adhesive layer comprises polypropylene.

9. An electrochemical device comprising the electrode assembly according to any one of claims 1-8.

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