Electrochemical device and electronic device

Abstract

The present application provides an electrochemical device, which includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the adjacent positive electrode and negative electrode. The negative electrode includes a negative current collector and a negative active material layer. A negative tab groove exposing the negative current collector is provided in the negative electrode. The negative tab is fixed in the negative tab groove and electrically connected to the negative current collector. A perforated adhesive tape is provided on the surface of the negative tab. The edge of the perforated adhesive tape in the length direction is provided with holes. The holes of the perforated adhesive tape are located in the part of the perforated adhesive tape covering the negative active material layers on both sides of the negative tab groove. By pasting the perforated adhesive tape in the electrochemical device in the manner provided by the present application, the problem of lithium plating in the electrochemical device can be improved.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and mainly relates to an electrochemical device and an electronic device. Background Art

[0002] Lithium-ion batteries have characteristics such as high specific energy, high working voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as electrical energy storage, portable electronic devices, and electric vehicles. With the continuous expansion of the use range of lithium-ion batteries, the market has put forward higher requirements for lithium-ion batteries, such as faster charging speed and longer service life.

[0003] During the cycle of lithium-ion batteries, lithium ions are prone to accumulate at the edge of the adhesive tape at the negative electrode tab, resulting in lithium deposition, which deteriorates the negative electrode interface, causes a rapid decline in cycle performance, and accelerates the volume expansion of lithium-ion batteries. Lithium deposition not only reduces the performance of lithium-ion batteries and significantly shortens the cycle life, but also limits the fast charging capacity of lithium-ion batteries and may cause consequences such as combustion and explosion. In view of this, it is urgent to solve the problem of lithium deposition during the cycle of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device to improve the problem of lithium deposition in the electrochemical device. The specific technical solutions are as follows:

[0005] In the first aspect of this application, an electrochemical device is provided, which includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the adjacent positive electrode and the negative electrode; the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. A negative electrode tab groove exposing the negative electrode current collector is provided in the negative electrode, and a negative electrode tab is fixed in the negative electrode tab groove and electrically connected to the negative electrode current collector; wherein, a perforated adhesive tape is provided on the surface of the negative electrode tab, holes are provided along the edge in the length direction of the perforated adhesive tape, and the holes of the perforated adhesive tape are located in the part of the perforated adhesive tape covering the negative electrode active material layers on both sides of the negative electrode tab groove.

[0006] The inventors of this application have found through in-depth research that by pasting a perforated adhesive tape at the position of the negative electrode tab groove and making the holes of the perforated adhesive tape located in the part of the negative electrode active material layers on both sides of the negative electrode tab groove, while avoiding the burrs around the negative electrode tab from affecting the safety performance of the electrochemical device, by punching holes at the edge in the length direction of the perforated adhesive tape, lithium ions can pass through the holes of the perforated adhesive tape and be transmitted between the positive electrode and the negative electrode, reducing the accumulation of lithium ions at the edge of the perforated adhesive tape, thereby dispersing the lithium ions around the perforated adhesive tape, improving the lithium deposition phenomenon at the negative electrode tab groove position, and further improving the problem of lithium deposition in the electrochemical device.

[0007] In an embodiment of the present application, the positive electrode includes opposite first and second surfaces, and the first surface is close to the negative electrode; the perforated adhesive tape is also pasted at a position corresponding to the negative electrode tab groove on the first surface. The inventors of the present application have found through in-depth research that by pasting the perforated adhesive tape on the first surface of the above positive electrode, lithium ions around the perforated adhesive tape can be dispersed, and the lithium deposition problem of the electrochemical device can be improved.

[0008] In an embodiment of the present application, the perforated adhesive tape is also pasted at a position corresponding to the negative electrode tab groove on the second surface. The inventors of the present application have found through in-depth research that pasting the perforated adhesive tape at the above position can improve the lithium deposition problem of the electrochemical device.

[0009] In an embodiment of the present application, the perforated adhesive tape bypasses the edge of the positive electrode end and is also pasted at a position corresponding to the negative electrode tab groove on the second surface. The inventors of the present application have found through in-depth research that pasting the perforated adhesive tape at the above position can improve the lithium deposition phenomenon at the negative electrode end and further improve the lithium deposition problem of the electrochemical device.

[0010] In an embodiment of the present application, a first perforated area, a second perforated area, and a non-perforated area are provided along the width direction of the perforated adhesive tape. The non-perforated area is located between the first perforated area and the second perforated area. The width w1 of the perforated adhesive tape is 6 mm to 30 mm, the width of the first perforated area is w2, the width of the second perforated area is w3, w2 and w3 are each independently selected from 1 mm to 10 mm, the width w4 of the non-perforated area is 2 mm to 10 mm, and the ratio of the width of the first perforated area or the second perforated area to the width of the non-perforated area is 0.5:1 to 1:1. The inventors of the present application have found through in-depth research that by controlling the width of the perforated adhesive tape to meet the above requirements and synergistically controlling the widths of the first perforated area, the second perforated area, and the non-perforated area within the above ranges, the lithium deposition problem of the electrochemical device can be further improved.

[0011] In an embodiment of the present application, the holes of the perforated adhesive tape satisfy at least one of the following characteristics: (1) the spacing b between the holes is 0 mm to 2 mm, and the minimum diameter c of the circumscribed circle of the hole contour is 0.1 mm to 3 mm; (2) the sum of the areas of the holes in the first perforated area accounts for 20% to 80% of the area of the first perforated area, and the sum of the areas of the holes in the second perforated area accounts for 20% to 80% of the area of the second perforated area; (3) the shape of the holes is at least one of a circle, an ellipse, and a polygon. The inventors of the present application have found through research that by controlling the holes of the perforated adhesive tape to satisfy one, two, or more combinations of the above characteristics, the lithium deposition problem of the electrochemical device can be improved.

[0012] In an embodiment of the present application, the perforated adhesive tape includes an adhesive layer and a substrate layer. The adhesive layer contains polyolefin and / or modified polyolefin, as well as an elastomer, a filler, and an antioxidant. Based on the total mass of the adhesive layer, the mass percentage content of the polyolefin and / or modified polyolefin is 45% to 85%, the mass percentage content of the elastomer is 10% to 35%, the mass percentage content of the filler is 2% to 10%, and the mass percentage content of the antioxidant is 2% to 10%. The inventors of the present application have found through research that by synergistically controlling the mass percentage content of each component in the adhesive layer within the above range, it is beneficial to improve the electrolyte resistance performance and adhesion of the perforated adhesive tape, reduce the swelling degree, thereby improving the safety performance of the electrochemical device, extending the service life of the electrochemical device, and controlling costs.

[0013] In an embodiment of the present application, the adhesive layer satisfies at least one of the following characteristics: (1) the polyolefin includes polyethylene and / or polypropylene, the modified polyolefin includes maleic anhydride-modified polyethylene and / or maleic anhydride-modified polypropylene, and the weight-average molecular weight of the polyolefin and the modified polyolefin are each independently selected from 30,000 to 200,000; (2) the elastomer includes at least one of styrene-ethylene-butene-styrene block copolymer, polyurethane, polyamide, polybutadiene, or polyisobutene; (3) the filler includes at least one of titanium dioxide, talc powder, silica, or calcium carbonate; (4) the antioxidant includes at least one of diphenylamine, trimethyl phosphite, triethyl phosphite, or distearyl thiodipropionate. The inventors of the present application have found through research that by controlling the adhesive layer of the perforated adhesive tape to satisfy one, two, or more combinations of the above conditions, the lithium deposition problem of the electrochemical device can be further improved, and the safety performance of the electrochemical device can be improved.

[0014] In an embodiment of the present application, the substrate layer includes at least one of polyethylene terephthalate, polyimide, or polypropylene. The inventors of the present application have found through research that by selecting the above materials as the substrate layer, it is beneficial to improve the electrolyte resistance performance of the perforated adhesive tape, thereby improving the lithium deposition problem of the electrochemical device and improving the safety performance of the electrochemical device.

[0015] In an embodiment of the present application, the thickness of the adhesive layer is 4 μm to 20 μm, and the thickness of the substrate layer is 4 μm to 30 μm. The inventors of the present application have found through research that by controlling the thickness of the adhesive layer and the substrate layer in the perforated adhesive tape within the above range, the safety performance of the electrochemical device can be improved while maintaining the energy density of the electrochemical device.

[0016] In an embodiment of the present application, the adhesion of the perforated adhesive tape after being immersed in an electrolyte at 85°C for 4 hours is 0.2 N / mm to 0.5 N / mm. The inventors of the present application have found through research that when the adhesion of the perforated adhesive tape is within the above range, it is beneficial to improve the lithium deposition problem of the electrochemical device and enhance the safety performance of the electrochemical device.

[0017] In an embodiment of the present application, the thickness A of the perforated adhesive tape after being immersed in an electrolyte at 85°C for 24 hours and the thickness B without being immersed in the electrolyte satisfy: 0 μm < A - B ≤ 2 μm, that is, the swelling degree of the perforated adhesive tape provided by the present application is low, which is beneficial to improving the safety performance and lithium deposition problem of the electrochemical device.

[0018] In an embodiment of the present application, the maximum unilateral glue overflow width of the perforated adhesive tape is 0 mm to 1 mm, that is, the perforated adhesive tape provided by the present application has good thermal stability, which is beneficial to improving the safety performance of the electrochemical device.

[0019] The present application provides an electrochemical device and an electronic device. The electrochemical device includes an electrode assembly, the electrode assembly includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative active material layer provided on at least one surface of the negative current collector. A negative electrode tab groove exposing the negative current collector is provided in the negative electrode, and a negative electrode tab is fixed in the negative electrode tab groove and electrically connected to the negative current collector; wherein, a perforated adhesive tape is provided on the surface of the negative electrode tab, holes are provided at the edges of the perforated adhesive tape along the length direction, and the holes of the perforated adhesive tape are located in the part of the perforated adhesive tape covering the negative active material layers on both sides of the negative electrode tab groove. By pasting the above-mentioned perforated adhesive tape in the electrochemical device, the degree of lithium deposition of the electrochemical device can be effectively reduced. The electronic device of the present application includes the electrochemical device of the present application. Therefore, the electronic device of the present application also has good safety performance.

[0020] Of course, it is not necessarily required to achieve all the above-mentioned advantages simultaneously when implementing any embodiment of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other drawings based on these drawings.

[0022] Figure 1 It is a schematic cross-sectional structure diagram of an electrode assembly along the thickness direction of some embodiments of the present application;

[0023] Figure 2 is Figure 1 a partial enlarged view of part A in

[0024] Figure 3 Schematic structural diagram of the negative electrode pasted with a perforated adhesive tape in some other embodiments of the present application;

[0025] Figure 4 Schematic structural diagram of the perforated adhesive tape in some embodiments of the present application;

[0026] Figure 5 Schematic cross-sectional structural diagram of the electrode assembly along the thickness direction in some embodiments of the present application;

[0027] Figure 6 is Figure 5 Local enlarged view of position B in

[0028] Figure 7 Schematic cross-sectional structural diagram of the electrochemical device along the thickness direction in some embodiments of the present application;

[0029] Figure 8 is Figure 7 Local enlarged view of position C in

[0030] Figure 9 Schematic partial cross-sectional structural diagram of the electrochemical device along the length direction in some embodiments of the present application;

[0031] Figure 10 Schematic partial cross-sectional structural diagram of the electrochemical device along the length direction in some other embodiments of the present application.

[0032] Reference numerals: 10. Negative electrode; 11. Negative electrode tab; 12. Negative electrode current collector; 13. Negative electrode active material layer; 14. Negative electrode tab groove; 20. Separator; 30. Positive electrode; 31. Positive electrode tab; 32. Positive electrode current collector; 33. Positive electrode active material layer; 40. Perforated adhesive tape; 41. Hole; 42. First perforated area; 43. Second perforated area; 44. Non-perforated area; 50. Green glue. Detailed description of the embodiments

[0033] To make the objectives, technical solutions, and advantages of the present application clearer and more understandable, the following examples are provided with reference to the accompanying drawings to further elaborate on the present application in detail. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0034] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries.

[0035] During the cycling of a lithium-ion battery in the prior art, lithium plating occurs due to the accumulation of lithium ions at the edge of the adhesive tape of the negative electrode tab during the transmission process. To solve the above technical problems, the present application provides an electrochemical device and an electronic device.

[0036] In a first aspect of the present application, an electrochemical device is provided, which includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the adjacent positive electrode and negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. A negative electrode tab groove exposing the negative electrode current collector is provided in the negative electrode. The negative electrode tab is fixed in the negative electrode tab groove and electrically connected to the negative electrode current collector. Wherein, a perforated adhesive tape is provided on the surface of the negative electrode tab. The perforated adhesive tape is provided with holes along the edge in the length direction. The holes of the perforated adhesive tape are located in the part of the perforated adhesive tape covering the negative electrode active material layers on both sides of the negative electrode tab groove.

[0037] Exemplarily, as Figures 1 to 3 shown, for the convenience of description, a three-dimensional rectangular coordinate system is established with the width direction of the electrode assembly as the x direction, the length direction of the electrode assembly as the y direction, and the thickness direction of the electrode assembly as the z direction. The electrode assembly includes a negative electrode 10, a positive electrode 30, a separator 20 located between the positive electrode 30 and the negative electrode 10, a perforated adhesive tape 40, and a green adhesive 50. The positive electrode 30 includes a positive electrode tab 31, a positive electrode current collector 32, and a positive electrode active material layer 33. The negative electrode 10 includes a negative electrode tab 11, a negative electrode current collector 12, a negative electrode active material layer 13, and a negative electrode tab groove 14. Along the width direction (x direction) of the electrode assembly, the perforated adhesive tape 40 is pasted in the area where the negative electrode tab 11 is connected to the negative electrode 10 and covers the negative electrode tab groove 14. It can be understood that the area of the perforated adhesive tape 40 is larger than the area of the negative electrode tab groove 14. At the same time, the holes 41 of the perforated adhesive tape 40 are located in the part of the perforated adhesive tape 40 covering the negative electrode active material layers 13 on both sides of the negative electrode tab groove 14. Wherein, the part of the negative electrode active material layers 13 on both sides of the negative electrode tab groove 14 refers to the partial surface of the negative electrode active material layers 13 on both sides of the negative electrode tab groove 14. That is, along the thickness direction (z direction) of the electrode assembly, the orthographic projection of the holes 41 of the perforated adhesive tape 40 on the negative electrode 10 does not overlap with the orthographic projection of the negative electrode tab groove 14 on the negative electrode 10 at all, as Figure 3 shown.

[0038] Exemplarily, as Figure 4As shown, for the convenience of description, a plane rectangular coordinate system is established with the length direction of the perforated adhesive tape as the y' direction and the width direction of the perforated adhesive tape as the x' direction. Holes 41 penetrating the perforated adhesive tape 40 are provided at the edges in the length direction (y' direction) of the perforated adhesive tape 40. Herein, the edges in the length direction (y' direction) of the perforated adhesive tape 40 refer to the two opposite edges along the width direction (x' direction) of the perforated adhesive tape. It can be understood that the holes in the perforated adhesive tape can be uniformly arranged or non-uniformly arranged, as long as the object of the present application can be achieved.

[0039] The inventors of the present application have found through in-depth research that by pasting the perforated adhesive tape at the position of the negative electrode tab groove and making the holes in the perforated adhesive tape located at the parts on both sides of the negative electrode tab groove, while avoiding the burrs around the negative electrode tab from affecting the safety performance of the electrochemical device, by providing holes penetrating the perforated adhesive tape at the edges in the length direction of the adhesive tape, lithium ions can pass through the holes in the perforated adhesive tape and be transmitted between the positive electrode and the negative electrode (as shown by the arrows in Figure 2 ), reducing the accumulation of lithium ions at the edges of the perforated adhesive tape, thereby dispersing the lithium ions around the perforated adhesive tape, improving the lithium deposition phenomenon in the negative electrode tab groove position, and further improving the lithium deposition problem of the electrochemical device.

[0040] In the present application, the positive electrode tab is a metal conductor led out from the positive electrode, and the negative electrode tab is a metal conductor led out from the negative electrode. The positive electrode tab and the negative electrode tab are used to serially connect or parallelly connect other parts of the electrochemical device. The present application has no particular limitation on the materials of the positive electrode tab and the negative electrode tab, as long as the object of the present application can be achieved. For example, the materials of the positive electrode tab and the negative electrode tab known in the art can be adopted. The present application has no particular limitation on the formation method of the negative electrode tab groove, and the known formation methods in the art can be adopted, as long as the object of the present application can be achieved. For example, laser cleaning can be performed in the corresponding negative electrode area, or by first pasting a foamed adhesive tape on the negative electrode current collector, coating the negative electrode active material layer and drying it, and then peeling off the foamed adhesive tape, the negative electrode tab groove can be obtained.

[0041] In an embodiment of the present application, the positive electrode includes opposite first and second surfaces, and the first surface is close to the negative electrode; the perforated adhesive tape is also pasted at the position corresponding to the negative electrode tab groove on the first surface. Exemplarily, as shown in Figure 5 and Figure 6As shown, the perforated adhesive tape 40 is respectively pasted on the surface of the negative electrode tab groove 14 and the surface of the positive electrode active material layer 33 on the first surface of the positive electrode 30, and the pasting position corresponds to the position of the negative electrode tab groove 14. The inventors of the present application have found through in-depth research that by pasting the perforated adhesive tape on the first surface of the above-mentioned positive electrode, compared with the prior art of using non-perforated adhesive tape to paste the corresponding position, the lithium ions around the perforated adhesive tape can be dispersed, and the lithium deposition problem of the electrochemical device can be further improved. In the present application, the first surface and the second surface of the positive electrode are two opposite surfaces along the thickness direction of the positive electrode, wherein the thickness direction of the positive electrode is the same as the thickness direction (z direction) of the electrode assembly.

[0042] In addition, during the use of the electrochemical device, lithium ions will be transmitted from the end of the positive electrode to the adjacent negative electrode, resulting in lithium deposition at the end of the negative electrode. Among them, the end of the positive electrode refers to the side of the positive electrode along its own length direction and close to the negative electrode tab along the extending direction of the negative electrode tab; the end of the negative electrode refers to the side of the negative electrode along its own length direction and close to the negative electrode tab along the extending direction of the negative electrode tab. The length direction of the positive electrode itself and the length direction of the negative electrode itself are the same as the width direction (x direction) of the electrode assembly.

[0043] In an embodiment of the present application, the perforated adhesive tape can also be pasted at a position corresponding to the negative electrode tab groove on the second surface. Exemplarily, as Figures 7 to 9 shown, the perforated adhesive tape 40 is pasted on the surface of the negative electrode tab groove 14, and the perforated adhesive tape 40 is also respectively pasted at positions corresponding to the negative electrode tab groove 14 on the first surface and the second surface of the positive electrode 30. The inventors of the present application have found through research that by pasting the perforated adhesive tape at positions corresponding to the negative electrode tab groove on the above-mentioned first surface and the second surface, the lithium deposition problem caused by the hindered lithium ion transmission and the problem of lithium ions diffusing from the positive electrode end to the adjacent negative electrode end can be improved, and the lithium deposition at the negative electrode end can be improved, and further the lithium deposition problem of the electrochemical device can be improved.

[0044] In an embodiment of the present application, the perforated adhesive tape also bypasses the edge of the positive electrode end and is pasted at a position corresponding to the negative electrode tab groove on the second surface. Exemplarily, as Figure 10 shown, the perforated adhesive tape 40 is pasted on the surface of the negative electrode tab groove 14, the perforated adhesive tape 40 is also pasted at positions corresponding to the negative electrode tab groove 14 on the first surface and the second surface of the positive electrode 30, and the perforated adhesive tape 40 bypasses the end of the positive electrode 30 to wrap the end of the positive electrode 30. The inventors of the present application have found through in-depth research that using the perforated adhesive tape to paste in a wrapping manner at the positive electrode end can better improve the problem of lithium ions diffusing from the positive electrode end to the adjacent negative electrode end, thereby improving the lithium deposition at the negative electrode end and further improving the lithium deposition problem of the electrochemical device.

[0045] In an embodiment of the present application, exemplarily, asFigure 4 As shown, a first punching area 42, a second punching area 43 and a non-punching area 44 are arranged along the width direction (x' direction) of the punched adhesive tape 40, and the non-punching area 44 is located between the first punching area 42 and the second punching area 43. The width w1 of the punched adhesive tape 40 is from 6 mm to 30 mm. For example, w1 can be 6 mm, 12 mm, 18 mm, 24 mm, 30 mm or any range therebetween. The width of the first punching area 42 is w2, and the width of the second punching area 43 is w3. w2 and w3 are each independently selected from 1 mm to 10 mm. For example, w2 can be 1 mm, 2.5 mm, 5 mm, 7.5 mm, 10 mm or any range therebetween, and w3 can be 1 mm, 2.5 mm, 5 mm, 7.5 mm, 10 mm or any range therebetween. The width w4 of the non-punching area 44 is from 2 mm to 10 mm. For example, w4 can be 2 mm, 4 mm, 6 mm, 8 mm, 10 mm or any range therebetween. The ratio of the width of the first punching area 42 or the second punching area 43 to the width of the non-punching area 44 is from 0.5:1 to 1:1. For example, w2:w4 can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1: or any range therebetween, and w3:w4 can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1 or any range therebetween.

[0046] The applicant has found through in-depth research that by controlling the width of the punched adhesive tape and coordinately controlling the widths of the first punching area, the second punching area and the non-punching area within the above ranges, lithium ions can be better dispersed to improve the phenomenon of lithium ion accumulation around the punched adhesive tape, thereby further improving the lithium deposition problem of the electrochemical device. In this application, the widths of the first punching area and the second punching area can be equal or unequal.

[0047] In an embodiment of this application, the holes of the punched adhesive tape satisfy at least one of the following characteristics:

[0048] (1) The pitch b of the holes is from 0 mm to 2 mm, and the minimum diameter c of the circumscribed circle of the contour of the holes is from 0.1 mm to 3 mm. As Figure 4 shown, the pitch of the holes 41 is the minimum linear distance between the contours of two adjacent holes 41. For example, b can be 0 mm, 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm or any range therebetween, and c can be 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm or any range therebetween. The inventors of this application have found that by making the pitch and diameter of the holes satisfy the above ranges, the holes in the punched adhesive tape can be more evenly dispersed, enabling lithium ions to better transport between the positive electrode and the negative electrode, thereby improving the lithium deposition problem of the electrochemical device.

[0049] (2) The proportion of the total area of the holes in the first punching area to the area of the first punching area is 20% to 80%, preferably 30% to 70%; the proportion of the total area of the holes in the second punching area to the area of the second punching area is 20% to 80%, preferably 30% to 70%. For example, the proportion of the total area of the holes in the first punching area to the area of the first punching area can be 20%, 30%, 40%, 50%, 60%, 70%, 80% or any range therebetween, and the proportion of the total area of the holes in the second punching area to the area of the second punching area can be 20%, 30%, 40%, 50%, 60%, 70%, 80% or any range therebetween.

[0050] The inventors of the present application have found through research that when the proportion of the total area of the holes in the first punching area to the area of the first punching area, or the proportion of the total area of the holes in the second punching area to the area of the second punching area is too small (for example, less than 20%), lithium ions cannot be effectively dispersed through the holes of the punching adhesive tape and are likely to accumulate around the punching adhesive tape, and the improvement of the lithium deposition problem of the electrochemical device is not obvious; when the proportion of the total area of the holes in the first punching area to the area of the first punching area, or the proportion of the total area of the holes in the second punching area to the area of the second punching area is too large (for example, greater than 80%), the adhesion of the punching adhesive tape decreases and the negative electrode tab cannot be effectively constrained, which will affect the safety performance of the electrochemical device. Therefore, by controlling the area of the holes in the first punching area and the second punching area within the above ranges, the lithium deposition problem of the electrochemical device can be improved, and the electrochemical device can have good safety performance.

[0051] (3) The shape of the holes is at least one of a circle, an ellipse, and a polygon. Among them, the polygon may include, but is not limited to, a triangle, a quadrilateral, a pentagon, etc. The above hole shapes are more conducive to the preparation of the punching adhesive tape. The inventors of the present application have found through research that by controlling the holes of the punching adhesive tape to meet one, two or more combinations of the above characteristics, the lithium deposition problem of the electrochemical device can be improved.

[0052] In an embodiment of the present application, the perforated adhesive tape comprises an adhesive layer and a substrate layer. The adhesive layer contains polyolefin and / or modified polyolefin, as well as an elastomer, a filler, and an antioxidant. Based on the total mass of the adhesive layer, the mass percentage content of polyolefin and / or modified polyolefin is 45% to 85%. For example, the mass percentage content of polyolefin and / or modified polyolefin can be 45%, 50%, 60%, 70%, 80%, 85%, or any range therebetween. Among them, when only polyolefin is contained and no modified polyolefin is contained, the mass percentage content of polyolefin and / or modified polyolefin refers to the mass percentage content of polyolefin; when only modified polyolefin is contained and no polyolefin is contained, the mass percentage content of polyolefin and / or modified polyolefin refers to the mass percentage content of modified polyolefin; when both polyolefin and modified polyolefin are contained, the mass percentage content of polyolefin and / or modified polyolefin refers to the sum of the mass percentage contents of polyolefin and modified polyolefin. The mass percentage content of the elastomer is 10% to 35%. For example, the mass percentage content of the elastomer can be 10%, 15%, 20%, 25%, 30%, 35%, or any range therebetween. The mass percentage content of the filler is 2% to 10%. For example, the mass percentage content of the filler can be 2%, 4%, 6%, 8%, 10%, or any range therebetween. The mass percentage content of the antioxidant is 2% to 10%. For example, the mass percentage content of the antioxidant can be 2%, 4%, 6%, 8%, 10%, or any range therebetween.

[0053] The inventors of the present application have found through research that when the mass percentage content of polyolefin and / or modified polyolefin is too low (for example, less than 45%), it will affect the electrolyte resistance performance, adhesion, and swelling degree performance of the perforated adhesive tape. When the mass percentage content of polyolefin and / or modified polyolefin is too high (for example, higher than 85%), it will cause the flexibility of the adhesive layer to deteriorate and waste of polyolefin and / or modified polyolefin, resulting in an increase in the cost of the electrochemical device. By regulating the mass percentage content of polyolefin and / or modified polyolefin within the above range, it is beneficial to improve the electrolyte resistance performance and adhesion of the perforated adhesive tape, reduce the swelling degree, enable the perforated adhesive tape to effectively bind the negative electrode tab, thereby improving the safety performance of the electrochemical device, extending the service life of the electrochemical device, and controlling the cost. In addition, further synergistically controlling the mass percentage content of each component in the adhesive layer within the above range is beneficial to improving the electrolyte resistance performance and adhesion of the perforated adhesive tape, reducing the swelling degree, thereby improving the safety performance of the electrochemical device and extending the life of the electrochemical device.

[0054] In an embodiment of the present application, the adhesive layer satisfies at least one of the following characteristics:

[0055] (1) The polyolefin includes polyethylene and / or polypropylene, and the modified polyolefin includes maleic anhydride modified polyethylene and / or maleic anhydride modified polypropylene. The weight average molecular weight of the polyolefin and the modified polyolefin are each independently selected from 30,000 to 200,000. For example, the weight average molecular weight of the polyolefin can be 30,000, 55,000, 100,000, 155,000, 200,000 or any range therebetween, and the weight average molecular weight of the modified polyolefin can be 30,000, 55,000, 100,000, 155,000, 200,000 or any range therebetween. The inventors of the present application have found through research that by regulating the weight average molecular weight of the polyolefin and the modified polyolefin within the above range, it is beneficial to improve the adhesion of the perforated adhesive tape, enable the perforated adhesive tape to effectively bind the tab, and at the same time reduce the number of lithium ions precipitated from below the perforated adhesive tape after long-term immersion in the electrolyte, further improving the lithium precipitation problem of the electrochemical device and enhancing the safety performance of the electrochemical device.

[0056] (2) The elastomer includes at least one of styrene-ethylene-butene-styrene block copolymer, polyurethane, polyamide, polybutadiene or polyisobutene. Among them, the elastomer refers to a polymer material that deforms significantly under weak stress and can quickly return to a state and size close to the original after stress relaxation. The inventors of the present application have found through research that by adding the above elastomer to the adhesive layer, the adhesion of the perforated adhesive tape can be further improved. When the adhesion of the perforated adhesive tape is too low, it cannot effectively bind the negative tab, and at the same time, after long-term immersion in the electrolyte, lithium ions are likely to precipitate from below the perforated adhesive tape, resulting in lithium precipitation in the electrochemical device. By selecting the above elastomer, the lithium precipitation problem of the electrochemical device can be improved, and the safety performance of the electrochemical device can be enhanced.

[0057] (3) The filler includes at least one of titanium dioxide, talc, silica or calcium carbonate. The inventors of the present application have found through research that by selecting the above filler, it is beneficial to improve the electrolyte resistance performance of the perforated adhesive tape. When the perforated adhesive tape is immersed in the electrolyte for a long time, it can slow down the precipitation of lithium ions below the perforated adhesive tape, further improving the lithium precipitation problem of the electrochemical device and enhancing the safety performance of the electrochemical device.

[0058] (4) The antioxidant includes at least one of diphenylamine, trimethyl phosphite, triethyl phosphite or distearyl thiodipropionate. The inventors of the present application have found through research that by selecting the above antioxidant, the electrolyte resistance performance of the perforated adhesive tape can be improved. When the perforated adhesive tape is immersed in the electrolyte for a long time, it can slow down the precipitation of lithium ions below the perforated adhesive tape, further improving the lithium precipitation problem of the electrochemical device and enhancing the safety performance of the electrochemical device.

[0059] The inventors of the present application have found through research that by controlling the adhesive layer of the perforated adhesive tape to meet one, two or more combinations of the above conditions, the safety performance and lithium deposition problem of the electrochemical device can be further improved.

[0060] In one embodiment of the present application, the substrate layer includes at least one of polyethylene terephthalate, polyimide or polypropylene. The inventors of the present application have found through research that by selecting the above materials as the substrate layer, it is beneficial to improve the electrolyte resistance performance of the perforated adhesive tape. When the perforated adhesive tape is soaked in the electrolyte for a long time, the precipitation of lithium ions below the perforated adhesive tape can be slowed down, the lithium deposition problem of the electrochemical device can be further improved, and the safety performance of the electrochemical device can be improved.

[0061] In one embodiment of the present application, the thickness of the adhesive layer is 4 μm to 20 μm. For example, the thickness of the adhesive layer can be 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any range therebetween; the thickness of the substrate layer is 4 μm to 30 μm. For example, the thickness of the substrate layer can be 4 μm, 5 μm, 10 μm, 12 μm, 20 μm, 25 μm, 30 μm or any range therebetween. The inventors of the present application have found through research that when the thickness of the adhesive layer is too small (for example, less than 4 μm), performance changes are more likely to occur during soaking in the electrolyte, affecting the adhesion of the perforated adhesive tape, and thus affecting the safety performance of the electrochemical device. Within a certain range, the adhesion of the adhesive tape shows an increasing trend with the increase of the thickness of the adhesive layer. However, when the thickness of the adhesive layer is too large (for example, greater than 20 μm), the adhesion of the adhesive layer tends to remain unchanged, but it will affect the energy density of the electrochemical device. When the thickness of the substrate layer is too small (for example, less than 4 μm), the supporting effect on the adhesive layer is weak, resulting in a poor fixing effect on the negative electrode tab. When the thickness of the substrate layer is too large (for example, greater than 30 μm), the effect is equivalent to that of the examples within the scope of the present application, but it will affect the energy density of the electrochemical device. By controlling the thickness of the adhesive layer and the substrate layer in the perforated adhesive tape within the above ranges, the energy density of the electrochemical device can be maintained, and the safety performance of the electrochemical device can be improved.

[0062] In an embodiment of the present application, the adhesion of the perforated adhesive tape after being immersed in the electrolyte at 85°C for 4 hours is 0.2 N / mm to 0.5 N / mm. That is, the perforated adhesive tape of the present application has good adhesion, can effectively bind the tab, and is beneficial to improving the safety performance of the electrochemical device. When the adhesion of the perforated adhesive tape is too low (less than 0.2 N / mm), after being immersed in the electrolyte for a long time, lithium ions are likely to precipitate from below the perforated adhesive tape, resulting in lithium precipitation in the electrochemical device. By controlling the adhesion of the perforated adhesive tape within the above range, the lithium precipitation problem of the electrochemical device can be improved. For example, the adhesion of the perforated adhesive tape after being immersed in the electrolyte at 85°C for 4 hours can be 0.2 N / mm, 0.3 N / mm, 0.4 N / mm, 0.5 N / mm, or any range therebetween. Among them, the adhesion test of the perforated adhesive tape after being immersed in the electrolyte at 85°C for 4 hours is to first hot-press the perforated adhesive tape and then immerse it in the electrolyte, and finally test its adhesion.

[0063] In an embodiment of the present application, the thickness A of the perforated adhesive tape after being immersed in the electrolyte at 85°C for 24 hours and the thickness B without being immersed in the electrolyte satisfy: 0 μm < A - B ≤ 2 μm. That is, the perforated adhesive tape provided by the present application has a low swelling degree, which is beneficial to improving the safety performance of the electrochemical device. When the swelling degree of the perforated adhesive tape is too high (A - B > 2 μm), the lithium ion transmission is blocked, affecting the rate performance of the electrochemical device. By controlling the swelling degree of the perforated adhesive tape within the above range, the lithium precipitation problem of the electrochemical device can be improved while maintaining its rate performance. For example, the value of A - B can be 0.01 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any range therebetween.

[0064] In an embodiment of the present application, the maximum unilateral glue overflow width of the perforated adhesive tape is 0 mm to 1 mm. That is, the perforated adhesive tape provided by the present application has good thermal stability, so it can better bind the negative tab and improve the safety performance of the electrochemical device. For example, the maximum unilateral glue overflow width of the perforated adhesive tape can be 0 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or any range therebetween. In the present application, the maximum unilateral glue overflow width of the perforated adhesive tape refers to half of the difference between the maximum width of the perforated adhesive tape after hot-pressing at a temperature of 85°C and a pressure of 1 MPa for 1 hour and the width of the perforated adhesive tape without hot-pressing.

[0065] In the present application, the perforated adhesive tape may further include a release paper, which is disposed on the surface of the adhesive layer facing away from the substrate layer. The release paper in the perforated adhesive tape is provided to prevent the surface of the adhesive layer from contacting a non-adhesive target surface or itself, so as to avoid adhesion between the adhesive layer and the non-adhesive target surface or itself during the use of the perforated adhesive tape. Those skilled in the art can select any suitable release paper material or size in the art according to actual needs. In some embodiments, the release paper may be disposed on any exposed surface of the adhesive layer on one side, for example, but not limited to, the surface of the adhesive layer facing away from the substrate layer or the surface of the side of the adhesive layer. In some embodiments, the release paper is torn off before the adhesive layer in the perforated adhesive tape is adhered to the target surface. In some embodiments, the release paper includes a single-sided silicone release film or a double-sided silicone release film.

[0066] The present application does not particularly limit the preparation method of the perforated adhesive tape, as long as the purpose of the present application can be achieved. For example, the present application may adopt the following method for preparing the perforated adhesive tape, which includes the following steps: mixing the raw materials of the adhesive layer in a certain proportion to obtain an adhesive layer slurry, then coating the adhesive layer slurry on the substrate layer, drying to obtain an adhesive tape, and further punching holes at the edges in the length direction of the adhesive tape. The present application does not particularly limit the punching method, as long as the purpose of the present application can be achieved. For example, it can be by one of laser punching or mechanical punching. Among them, the substrate layer can be first treated with a non-silicone release agent and then the surface is corona-treated, and the drying temperature can be 60°C to 120°C.

[0067] The positive electrode in the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the positive electrode generally includes a positive electrode current collector and a positive electrode active material layer. Among them, the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved. For example, it can include but is not limited to aluminum foil, aluminum alloy foil, or composite current collector, etc. In the present application, the thickness of the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness is 8μm to 12μm. In the present application, the positive electrode active material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector. The present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0068] In the present application, the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not particularly limited as long as the object of the present application can be achieved. For example, it may include at least one of composite oxides of lithium and transition metal elements. The transition metal element in the present application is not particularly limited as long as the object of the present application can be achieved. For example, it may include at least one of nickel, manganese, cobalt or iron. Specifically, the positive electrode active material may include at least one of lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium iron phosphate or lithium titanate.

[0069] In the present application, the positive electrode active material layer may further include a conductive agent. The conductive agent in the present application is not particularly limited as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0070] In the present application, the positive electrode active material layer may further include a binder. The binder in the present application is not particularly limited as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber or polyvinylidene fluoride.

[0071] Optionally, the positive electrode may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer in the present application is not particularly limited and may be a commonly used conductive layer in the art. For example, it may include but is not limited to the above conductive agent and the above binder.

[0072] In the present application, the negative electrode active material layer may be disposed on one surface in the thickness direction of the negative electrode current collector, or may be disposed on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here may be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. The present application is not particularly limited as long as the object of the present application can be achieved.

[0073] The negative electrode current collector in the present application is not particularly limited as long as the object of the present application can be achieved. For example, it may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector, etc. In the present application, the thickness of the current collector of the negative electrode is not particularly limited as long as the object of the present application can be achieved. For example, the thickness is 4 μm to 12 μm.

[0074] In the present application, the negative electrode active material layer includes a negative electrode active material. Among them, the negative electrode active material is not particularly limited as long as the object of the present application can be achieved. For example, it may include, but is not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 or at least one of Li-Al alloys.

[0075] In the present application, a conductive agent may also be included in the negative electrode active material layer. The present application does not particularly limit the conductive agent as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned conductive agents.

[0076] In the present application, a binder may also be included in the negative electrode active material layer. The present application does not particularly limit the binder as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned binders.

[0077] Optionally, the negative electrode may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode active material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. The conductive layer may include, but is not limited to, the above-mentioned conductive agent and the above-mentioned binder.

[0078] The electrochemical device of the present application further includes a separator. The present application does not particularly limit the separator as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) membranes based on polytetrafluoroethylene, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, aramid membranes, woven membranes, non-woven fabrics, microporous membranes, composite membranes, separator papers, rolled membranes or spun membranes, etc. The separator of the present application may have a porous structure, and the size of the pore diameter is not particularly limited as long as the object of the present application can be achieved. For example, the size of the pore diameter may be 0.01 μm to 1 μm. In the present application, the thickness of the separator is not particularly limited as long as the object of the present application can be achieved. For example, the thickness may be 5 μm to 500 μm.

[0079] For example, the separator may include a separator substrate layer and a surface treatment layer. The separator substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure. The material of the separator substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, etc. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the separator substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0080] The polymer layer contains a polymer, and the material of the polymer may include, but is not limited to, at least one of polypropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyethylene ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene, etc. The inorganic layer may include, but is not limited to, inorganic particles and a binder. There is no particular limitation on the inorganic particles in this application. For example, it may include, but is not limited to, at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, etc. There is no particular limitation on the binder in the inorganic layer in this application. For example, it may include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0081] There is no particular limitation on the electrochemical device of this application, and it may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0082] The preparation process of the electrochemical device is well-known to those skilled in the art, and there is no particular limitation in this application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound structure electrode assembly, placing the electrode assembly into a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or, stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly, placing the electrode assembly into a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0083] The second aspect of the present application provides an electronic device, which includes the electrochemical device provided by the first aspect of the present application.

[0084] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include but is not limited to laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0085] Examples

[0086] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0087] Testing method and device :

[0088] Lithium plating test:

[0089] (1) Lithium plating test of lithium-ion battery at 10°C: At 10°C, the lithium-ion battery is left standing for 5 min, then charged at a constant current of 1.5C to 4.25V, then charged at a constant current of 1.2C to 4.48V, and then charged at a constant voltage of 4.48V to 0.02C; left standing for 5 min, discharged at a constant current of 1C to 3.4V, and then discharged at a constant current of 0.2C to 3.0V. After repeating the above steps 9 times, left standing for 5 min, then charged at a constant current of 1C to 4.48V, and then charged at a constant voltage of 4.48V to 0.02C, and finally left standing for 5 min to disassemble and observe the degree of lithium plating at the negative electrode tab groove and the negative electrode end.

[0090] (2) Lithium plating test of lithium-ion battery at 25 °C: At 25 °C, the lithium-ion battery is left standing for 5 min, then charged at a constant current of 1.5C to 4.25V, then charged at a constant current of 1.2C to 4.48V, then charged at a constant voltage of 4.48V to 0.02C, and left standing for 5 min; then discharged at a constant current of 1C to 3.4V, and then discharged at a constant current of 0.2C to 3.0V. After repeating the above steps 9 times, leave it standing for 5 min, then charge at a constant current of 1C to 4.48V, then charge at a constant voltage of 4.48V to 0.02C, and finally leave it standing for 5 min, disassemble and observe the degree of lithium plating in the negative electrode tab groove and the negative electrode end.

[0091] (3) Lithium plating test of lithium-ion battery at 45 °C: At 45 °C, the lithium-ion battery is left standing for 5 min, then charged at a constant current of 1.5C to 4.25V, then charged at a constant current of 1.2C to 4.48V, then charged at a constant voltage of 4.48V to 0.02C, and left standing for 5 min; then discharged at a constant current of 1C to 3.4V, and then discharged at a constant current of 0.2C to 3.0V. After repeating the above steps 9 times, leave it standing for 5 min, then charge at a constant current of 1C to 4.48V, then charge at a constant voltage of 4.48V to 0.02C, and finally leave it standing for 5 min, disassemble and observe the degree of lithium plating in the negative electrode tab groove and the negative electrode end.

[0092] Among them, no lithium plating is found or the lithium plating area < 10% is herein called no lithium plating; the lithium plating area ≥ 10% is called lithium plating.

[0093] Adhesion test:

[0094] Stick the punched adhesive tape of each example and the adhesive tape in the comparative example on the aluminum foil respectively, cut them into strip samples of 20 mm × 60 mm, perform hot pressing treatment for 40 min under the conditions of a temperature of 85 °C and a pressure of 1 MPa, then soak them in the electrolyte at 85 °C for 4 h, then paste the samples on the steel plate through double-sided tape (Nitto 5000NS) (the adhesion length is not less than 40 mm), fix the steel plate at the corresponding position of the high-speed tensile machine, pull the other end of the sample that is not adhered to the steel plate, put the sample into the chuck and clamp it. Among them, the angle between the pulled part of the sample and the steel plate in space is 180°, and the chuck pulls at a speed of 50 mm / min. Finally, the average value of the pulling force in the stable area is recorded as the adhesion force after soaking in the electrolyte.

[0095] Among them, the organic solvent of the electrolyte is ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and the mass ratio of EC:PC:DEC:EP = 3:1:3:3. The solute is lithium hexafluorophosphate (LiPF6), and the concentration of LiPF6 is 1 mol / L.

[0096] Glue overflow test:

[0097] Measure the initial width of the adhesive tape, and then heat-press the adhesive tape at a temperature of 85 °C and a pressure of 1 MPa for 1 h, and then measure the maximum width of the adhesive tape as the glue overflow width. For the perforated adhesive tape in each example and the adhesive tape in the comparative example, 10 samples are tested. The maximum unilateral glue overflow width of the adhesive tape is half of the average value of the difference between the glue overflow width and the initial width of the 10 samples.

[0098] Swelling thickness test:

[0099] Cut the adhesive tape into strips with a size of 20 mm × 60 mm, measure the initial thickness of the adhesive tape and record it as B, then stick the adhesive tape on the aluminum foil, soak it in the electrolyte for 24 h at a soaking temperature of 85 °C, take it out and dry it after soaking, and measure the thickness of the edge of the adhesive tape with a micrometer within 5 min and record it as A. Randomly select 10 places for measurement, and the average value obtained is the swelling thickness A - B of the adhesive tape. For the perforated adhesive tape in each example and the adhesive tape in the comparative example, 10 samples are tested. The swelling thickness of the adhesive tape is the average value of A - B of the 10 samples. Among them, the electrolyte is the same as the electrolyte in the above-mentioned adhesion test.

[0100] Example 1-1

[0101] <Preparation of the positive electrode>

[0102] Mix the positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent Super P, and the binder polyvinylidene fluoride in a mass ratio of 97:1.4:1.6, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry, where the solid content of the positive electrode slurry is 75 wt%. Uniformly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 9 μm, dry the aluminum foil at 85 °C to obtain a positive electrode with a single-sided coating of a positive electrode active material layer with a coating thickness of 110 μm. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode with a double-sided coating of the positive electrode active material. Then, after cold pressing, slicing, and slitting, dry it under vacuum conditions at 85 °C for 8 h to obtain a positive electrode with a specification of 74 mm × 851 mm. Among them, the positive electrode includes a positive electrode tab. In this application, as Figure 2 shown, the green glue is pasted at the following positions: (1) the connection area where the positive electrode tab is connected to the positive electrode; (2) the surfaces of the two negative electrodes adjacent to the positive electrode where the positive electrode tab is located, and the pasting position corresponds to the position of the above connection area. Among them, the green glue is purchased from Dongguan Aozhong New Materials Technology Co., Ltd.

[0103] <Preparation of the negative electrode>

[0104] The artificial graphite as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) as the thickening agent, and styrene-butadiene rubber (SBR) as the binder are mixed according to a mass ratio of 96.4∶1.5∶0.5∶1.6. Deionized water is added and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, where the solid content of the negative electrode slurry is 70 wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and the copper foil is dried at 110 °C to obtain a negative electrode with a negative electrode active material layer coated on one side and a coating thickness of 130 μm. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode with the negative electrode active material coated on both sides. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 12 h to obtain a negative electrode with a specification of 76 mm × 867 mm. Among them, the negative electrode includes a negative electrode tab. And a negative electrode tab groove is set by laser cleaning.

[0105] <Preparation of electrolyte>

[0106] In an argon atmosphere glove box with a water content < 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and ethyl propionate (EP) are evenly mixed according to a mass ratio of 1∶1∶1 to form a basic solvent. Finally, LiPF6 is added and dissolved and stirred evenly to form an electrolyte. Based on the total mass of the electrolyte, the mass percentage content of LiPF6 is 12.5%, and the balance is the basic solvent.

[0107] <Preparation of separator>

[0108] A polyethylene porous polymer film is used as the separator.

[0109] <Preparation of adhesive tape>

[0110] The adhesive tape includes an adhesive layer provided on one surface of a base material layer. Among them, the thickness of the adhesive tape is 24 μm, the thickness of the adhesive layer is 12 μm, and the thickness of the base material layer is 12 μm.

[0111] Polypropylene, elastomeric polyurethane, filler titanium dioxide, and antioxidant diphenylamine are mixed evenly according to a mass ratio of 60∶25∶7.5∶7.5, and then coated on the base material layer and dried at 120 °C to obtain the adhesive tape. Further, using the method of laser drilling, holes are drilled on both sides of the edge in the length direction of the drilled adhesive tape according to a hole pitch b = 0.6 mm and a hole diameter c = 0.8 mm. Among them, the molecular weight of polypropylene is 115,000, the width of the first drilling area is 8 mm, the width of the second drilling area is 8 mm, the width of the non-drilling area is 9 mm, and the shape of the hole is circular.

[0112] The base material layer is a polyethylene terephthalate film.

[0113] <Preparation of lithium-ion battery>

[0114] Paste a 25 mm × 45 mm adhesive tape on the surface of the negative electrode tab groove, as well as on the first surface and the second surface of the positive electrode and around the end of the positive electrode. The pasting position is opposite to the position of the negative electrode tab groove. Then stack the positive electrode, separator, and negative electrode in sequence, with the separator in the middle of the positive electrode and the negative electrode to play an insulating role, and wind to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film packaging bag, inject electrolyte after drying, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, capacity measurement, degassing, and trimming. Among them, the formation conditions are constant current charging at 0.02C to 3.3V, then constant current charging at 0.1C to 3.6V, and finally constant current charging at 0.2C to 4.45V.

[0115] Examples 1-2 to 1-4

[0116] Except for adjusting the pasting position of the perforated adhesive tape according to Table 1, the rest is the same as Example 1-1.

[0117] Examples 2-1 to 2-8

[0118] Except for adjusting the width w1 of the perforated adhesive tape, as well as the width w2 of the first perforated area, the width w3 of the second perforated area, the width w4 of the non-perforated area, the hole spacing b, the hole diameter c, and the hole shape in the perforated adhesive tape according to Table 2, the rest is the same as Example 1-3.

[0119] Examples 3-1 to 3-7

[0120] Except for adjusting the components of Adhesive Layer Component 1 and its weight average molecular weight according to Table 4, the rest is the same as Example 1-3.

[0121] Examples 4-1 to 4-7

[0122] Except for adjusting the mass percentage content of Adhesive Layer Component 1, the composition of Adhesive Layer Component 2, and the mass percentage content of each component according to Table 5, the rest is the same as Example 1-3.

[0123] Examples 5-1 to 5-6

[0124] Except for adjusting the thickness of the adhesive layer and the substrate layer, as well as the material of the substrate layer according to Table 6, the rest is the same as Example 1-3.

[0125] Comparative Example 1

[0126] Except for using green glue instead of the perforated adhesive tape, the rest is the same as Example 1-1.

[0127] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 6.

[0128] Table 1

[0129]

[0130]

[0131] Note: In Table 1, " / " indicates that the corresponding preparation parameter does not exist.

[0132] It can be seen from Examples 1-1 to 1-4 and Comparative Example 1 that the lithium-ion batteries in the embodiments of the present application include perforated adhesive tapes, which can effectively improve the problem of lithium deposition in the lithium-ion batteries. The pasting position of the perforated adhesive tape usually affects the performance of the electrochemical device. It can be seen from Examples 1-1 to 1-4 that by pasting the perforated adhesive tape at a position within the scope of the present application, the problem of lithium deposition in the lithium-ion battery can be effectively improved.

[0133] Table 2

[0134]

[0135] Note: In Table 2, " / " indicates that the corresponding preparation parameter does not exist.

[0136] Table 3

[0137]

[0138] The width w1 of the perforated adhesive tape, the width w2 of the first perforated area, the width w3 of the second perforated area, the width w4 of the non-perforated area, the ratio w3∶w4 of the width of the second perforated area to the width of the non-perforated area, as well as the hole pitch b, the hole diameter c, and the shape of the holes usually also affect the performance of the electrochemical device. It can be seen from Examples 1-3, 2-1 to 2-8 that by adjusting the above parameters within the scope of the present application, the obtained perforated adhesive tape has a high bonding strength, a low swelling thickness, and a low maximum unilateral glue overflow width. At the same time, by pasting the perforated adhesive tape at a position within the scope of the present application, the problem of lithium deposition in the electrochemical device can be improved. In addition, it can be seen from Examples 1-3, 2-7, and 2-8 that when the sum of the areas of the holes in the first perforated area accounts for too large a proportion of the area of the first perforated area or the sum of the areas of the holes in the second perforated area accounts for too large a proportion of the area of the second perforated area, the bonding strength of the perforated adhesive tape decreases significantly. However, since lithium ions can be better transported, the problem of lithium deposition in the electrochemical device can be improved. But when the sum of the areas of the holes in the first perforated area accounts for too small a proportion of the area of the holes in the first perforated area or the sum of the areas of the holes in the second perforated area accounts for too small a proportion of the area of the second perforated area, the transport of lithium ions is affected, and thus the problem of lithium deposition in the electrochemical device cannot be improved. By adjusting the proportion of the sum of the areas of the holes in the first perforated area to the area of the first perforated area and the proportion of the sum of the areas of the holes in the second perforated area to the area of the second perforated area within the scope of the present application, the problem of lithium deposition in the electrochemical device can be improved.

[0139] Table 4

[0140]

[0141] The types and weight-average molecular weights of polyolefins and / or modified polyolefins in the adhesive layer of the perforated adhesive tape also affect the performance of the perforated adhesive tape and the performance of the electrochemical device. It can be seen from Examples 1-3, Examples 3-1 to 3-7 that the perforated adhesive tape made of the adhesive layer components within the scope of this application has higher adhesion, lower swelling thickness and maximum unilateral glue overflow width. At the same time, pasting the perforated adhesive tape at the position within the scope of this application can improve the lithium deposition problem of the electrochemical device and is also beneficial to improving the safety performance of the electrochemical device. In addition, it can be seen from Examples 1-3, Examples 3-1 to 3-4 that when the molecular weight of the polyolefin is within the scope of this application, the perforated adhesive tape has good adhesion and lower swelling thickness, thereby being able to improve the lithium deposition problem of the electrochemical device.

[0142] Table 5

[0143]

[0144] The content of polyolefins and / or modified polyolefins in the adhesive layer of the perforated adhesive tape, and the types and contents of elastomers, fillers, and antioxidants also affect the performance of the perforated adhesive tape and the performance of the electrochemical device. It can be seen from Examples 1-3, Examples 4-1 to 4-7 that the perforated adhesive tape made of the adhesive layer components within the scope of this application has higher adhesion, lower swelling thickness and maximum unilateral glue overflow width. At the same time, pasting the perforated adhesive tape at the position within the scope of this application can improve the safety performance of the electrochemical device and improve the lithium deposition problem of the electrochemical device.

[0145] Table 6

[0146]

[0147]

[0148] The thickness of the adhesive layer of the perforated adhesive tape, the types and thicknesses of the base material layers also affect the performance of the perforated adhesive tape and the performance of the electrochemical device. It can be seen from Examples 1-3, Examples 5-1 to 5-6 that the perforated adhesive tape made of the adhesive layer and the base material layer within the scope of this application has higher adhesion, lower swelling thickness and maximum unilateral glue overflow width. At the same time, pasting the perforated adhesive tape at the position within the scope of this application can improve the lithium deposition problem of the electrochemical device.

[0149] It should be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0150] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0151] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrochemical device, which includes an electrode assembly, the electrode assembly includes a positive electrode, a negative electrode and a separator, and the separator is disposed between the adjacent positive electrode and the negative electrode; The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. A negative electrode tab groove exposing the negative electrode current collector is provided in the negative electrode, and a negative electrode tab is fixed in the negative electrode tab groove and electrically connected to the negative electrode current collector; Among them, A perforated adhesive tape is provided on the surface of the negative electrode tab. The edge of the perforated adhesive tape in the length direction is provided with holes, and the holes penetrate through the perforated adhesive tape. The holes of the perforated adhesive tape are located in the part of the perforated adhesive tape covering the negative electrode active material layers on both sides of the negative electrode tab groove.

2. The electrochemical device according to claim 1, wherein, The positive electrode includes an opposite first surface and a second surface, and the first surface is close to the negative electrode; The perforated adhesive tape is also pasted at a position corresponding to the negative electrode tab groove on the first surface.

3. The electrochemical device according to claim 2, wherein, The perforated adhesive tape is also pasted at a position corresponding to the negative electrode tab groove on the second surface.

4. The electrochemical device according to claim 2, wherein, The perforated adhesive tape also bypasses the edge of the positive electrode end and is pasted at a position corresponding to the negative electrode tab groove on the second surface.

5. The electrochemical device according to claim 1, wherein, A first perforated area, a second perforated area and a non-perforated area are provided along the width direction of the perforated adhesive tape. The non-perforated area is located between the first perforated area and the second perforated area. The width w1 of the perforated adhesive tape is 6 mm to 30 mm; the width of the first perforated area is w2, the width of the second perforated area is w3, and w2 and w3 are each independently selected from 1 mm to 10 mm; the width w4 of the non-perforated area is 2 mm to 10 mm, and the ratio of the width of the first perforated area or the second perforated area to the width of the non-perforated area is 0.5:1 to 1:

1.

6. The electrochemical device according to claim 5, wherein, The holes of the perforated adhesive tape satisfy at least one of the following characteristics: (1) The pitch b of the holes is 0.1 mm to 2 mm, and the minimum diameter c of the circumscribed circle of the contour of the holes is 0.1 mm to 2 mm; (2) The proportion of the total area of the holes in the first perforated area to the area of the first perforated area is 20% to 80%, and the proportion of the total area of the holes in the second perforated area to the area of the second perforated area is 20% to 80%; (3) The shape of the holes is at least one of a circle, an ellipse or a polygon.

7. The electrochemical device according to claim 1, wherein, The perforated adhesive tape includes an adhesive layer and a base material layer. The adhesive layer contains polyolefin and / or modified polyolefin, as well as an elastomer, a filler and an antioxidant. Based on the total mass of the adhesive layer, the mass percentage content of the polyolefin and / or modified polyolefin is 45% to 85%, the mass percentage content of the elastomer is 10% to 35%, the mass percentage content of the filler is 2% to 10%, and the mass percentage content of the antioxidant is 2% to 10%.

8. The electrochemical device according to claim 7, wherein, The adhesive layer satisfies at least one of the following characteristics: (1) The polyolefin includes polyethylene and / or polypropylene, the modified polyolefin includes maleic anhydride modified polyethylene and / or maleic anhydride modified polypropylene, and the weight average molecular weight of the polyolefin and the modified polyolefin are each independently selected from 30,000 to 200,000; (2) The elastomer includes at least one of styrene-ethylene-butene-styrene block copolymer, polyurethane, polyamide, polybutadiene or polyisobutene; (3) The filler includes at least one of titanium dioxide, talc powder, silica or calcium carbonate; (4) The antioxidant includes at least one of diphenylamine, trimethyl phosphite, triethyl phosphite or distearyl thiodipropionate.

9. The electrochemical device according to claim 7, wherein, The substrate layer includes at least one of polyethylene terephthalate, polyimide or polypropylene.

10. The electrochemical device according to claim 7, wherein, The thickness of the adhesive layer is 4 µm to 20 µm, and the thickness of the substrate layer is 4 µm to 30 µm.

11. The electrochemical device according to claim 1, wherein, The adhesion of the perforated adhesive paper after being immersed in the electrolyte at 85°C for 4 h is 0.2 N / mm to 0.5 N / mm.

12. The electrochemical device according to claim 1, wherein, The thickness A of the perforated adhesive paper after being immersed in the electrolyte at 85°C for 24 h and the thickness B without being immersed in the electrolyte satisfy: 0 µm < A - B ≤ 2 µm.

13. The electrochemical device according to claim 1, wherein, The maximum unilateral overflow width of the perforated adhesive paper is 0 mm to 1 mm.

14. An electronic device, which comprises the electrochemical device according to any one of claims 1 to 13.

Images