Electrode assembly, electrochemical device and electronic device including the same

Abstract

The present application relates to the field of lithium battery technology, and discloses an electrode assembly and an electrochemical device and an electronic device containing the same. The electrode assembly includes an anode electrode piece, a cathode electrode piece and a separator. The cathode electrode piece includes a cathode current collector and a first cathode covering layer arranged in a straight area of ​​the cathode current collector and a second cathode covering layer in a corner area. The conductivity of the second cathode covering layer is lower than the conductivity of the first cathode covering layer; or, the porosity of the corner area of ​​the separator is smaller than the porosity of its straight area. The electrode assembly of the embodiment of the present application improves the situation of lithium precipitation in the corner by optimizing the corner area of ​​the separator and / or the corner area of ​​the cathode electrode piece. Moreover, the present application only optimizes the corners, which will not have a significant impact on the overall performance of the battery cell.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to an electrode assembly and an electrochemical device and an electronic device comprising the same. Background Art

[0002] In order to solve serious problems such as the global energy crisis, environmental pollution, climate change, and low-carbon economy, the research and development and application of power sources in the fields of electric vehicles, large-scale power sources, and energy storage have become inevitable, and fast charging has become one of the necessary needs of users.

[0003] The battery cells that can be charged quickly must have a high enough charge rate. However, the higher the charge rate, the more likely it is to have purple spots and lithium plating interface problems during use, which can cause the battery cells to fail faster during the cycle.

[0004] Therefore, the prior art needs to be improved urgently. Summary of the invention

[0005] The primary invention objective of the present application is to provide an electrode assembly.

[0006] A second object of the present invention is to provide an electrochemical device comprising the electrode assembly.

[0007] A third invention objective of the present application is to provide an electronic device including the electrochemical device.

[0008] To achieve the purpose of this application, the technical solution adopted is:

[0009] The present application provides an electrode assembly, including an anode electrode sheet, a cathode electrode sheet, and a separator disposed between the anode electrode sheet and the cathode electrode sheet. The anode electrode sheet, the cathode electrode sheet, and the separator are wound into a winding structure, and the winding structure includes a straight area and a corner area connecting the straight area. The cathode electrode sheet includes a cathode current collector and a first cathode covering layer and a second cathode covering layer disposed on the cathode current collector. The first cathode covering layer is located in the straight area of ​​the cathode electrode sheet, and the second cathode covering layer is located in the corner area of ​​the cathode electrode sheet, and the conductivity of the second cathode covering layer is lower than the conductivity of the first cathode covering layer. In the present technical solution, by covering the corner area of ​​the cathode current collector with a cathode covering layer having a lower conductivity than the straight area, the amount of lithium ions released from the cathode in the corner area can be reduced, and the accumulation of lithium ions at the anode in the corner area during charging can be alleviated, thereby improving the risk of lithium plating.

[0010] In some embodiments of the present application, the first cathode covering layer is a first cathode active material layer, and the second cathode covering layer is a second cathode active material layer, and the conductivity of the second cathode active material layer is lower than the conductivity of the first cathode active material layer. In this embodiment, the resistivity can be adjusted by conventional methods such as adjusting the type and content of the conductive agent in the active material, the type of active material, and adding a high resistance material to the active material, so as to achieve the purpose of making the conductivity of the second cathode active material layer lower than the conductivity of the first cathode active material layer.

[0011] In some embodiments of the present application, the first cathode covering layer includes a first cathode active material, the second cathode covering layer includes a second cathode main covering layer and a second cathode sub-covering layer, and the second cathode sub-covering layer is located on the inner surface of the second cathode main covering layer toward the winding center. The second cathode main covering layer is the first cathode active material layer, and the second cathode sub-covering layer is a high-resistance material layer, and the resistance value of the high-resistance material layer is 0.1Ω to 5Ω. In this embodiment, by covering the inner side of the corner area of ​​the cathode pole piece with an extra layer of high-resistance material layer, the conductivity of the inner side of the cathode pole piece is reduced, and the release rate of cathode lithium ions is reduced, thereby reducing the total amount of lithium ions precipitated during a unit charge and discharge cycle, thereby improving the risk of lithium precipitation.

[0012] In some embodiments of the present application, the thickness of the second cathode sub-covering layer is 0.02-0.1 times the thickness of the second cathode main covering layer. In this embodiment, if the second cathode sub-covering layer is too thin, for example, the thickness is less than 0.02 times the thickness of the second cathode main covering layer, it is not possible to effectively reduce the resistance inside the cathode electrode sheet and achieve the effect of reducing the lithium ion escape rate; if the second cathode sub-covering layer is too thick, for example, the thickness is greater than 0.1 times the thickness of the second cathode main covering layer, it is easy to cause a decrease in energy density.

[0013] In some embodiments of the present application, the high resistance material layer includes a ceramic material, preferably, the ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. In addition to providing high resistance to reduce the conductivity of the inner side of the cathode corner area and improve the risk of lithium deposition, the ceramic material can also prevent short circuits during puncture and improve battery safety.

[0014] In some embodiments of the present application, the thickness of the first cathode covering layer is between 50-100 um.

[0015] In some embodiments of the present application, the conductivity of the second cathode covering layer is 50%-95% of the conductivity of the first cathode covering layer.

[0016] In some embodiments of the present application, the length of the second cathode covering layer is greater than the corner arc length of the cathode electrode, and the difference between the two is less than or equal to 0.5 mm, so as to ensure that the corner area is completely covered by the active material layer and / or the high resistance material layer, and to ensure that there is no exposed current collector at the junction of the straight area and the corner area, thereby effectively ensuring the improvement of lithium deposition at the corner.

[0017] The present application also provides an electrode assembly, including an anode electrode sheet, a cathode electrode sheet, and an isolation membrane arranged between the anode electrode sheet and the cathode electrode sheet, wherein the anode electrode sheet, the cathode electrode sheet, and the isolation membrane are wound into a winding structure, and the winding structure includes a straight area and a corner area connecting the straight area.

[0018] The porosity of the corner area of ​​the separator is smaller than the porosity of the straight area of ​​the separator. By reducing the porosity of the separator at the corner, the passing rate of lithium ions is reduced, so that the number of lithium ions embedded in the anode after precipitation through the corner of the separator is reduced, thereby reducing the risk of lithium precipitation.

[0019] In some embodiments of the present application, the porosity of the corner area of ​​the isolation membrane is between 10% and 20%, and the porosity of the straight area of ​​the isolation membrane is between 25% and 35%. The porosity of the corner area of ​​the isolation membrane can be controlled by heat pressing the corner area of ​​the isolation membrane to shrink the gap.

[0020] In some embodiments of the present application, the isolation film includes a substrate and an isolation covering layer disposed on the substrate, wherein the thickness of the isolation covering layer at the corner area of ​​the isolation film is greater than the thickness at the straight area of ​​the isolation film. The isolation covering layer is a high resistance material layer, and the resistance value of the high resistance material layer is 0.1Ω to 5Ω.

[0021] In some embodiments of the present application, the high resistance material layer includes a ceramic material, and the preferred ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. In addition to controlling the porosity of the straight area and corner area of ​​the isolation membrane and improving the risk of lithium deposition, the ceramic material can also prevent short circuits during puncture, improve battery safety, and inhibit the shrinkage of the isolation membrane at high temperatures to prevent short circuits between the positive and negative electrodes.

[0022] In some embodiments of the present application, the thickness of the isolation covering layer at the corner area of ​​the isolation membrane is 1.02-1.2 times the thickness at the straight area of ​​the isolation membrane. In this embodiment, if the isolation covering layer of the isolation membrane in the corner area is too thin, for example, the thickness is less than 1.02 times the thickness of the isolation covering layer in the straight area, it is impossible to effectively reduce the porosity of the isolation membrane and inhibit lithium precipitation; if the isolation covering layer of the isolation membrane in the corner area is too thick, for example, the thickness is greater than 1.2 times the thickness of the isolation covering layer in the straight area, it will seriously affect the lithium ion pass rate in the corner area, resulting in a decrease in the charging rate. At the same time, the excessive thickness of the isolation membrane also causes a decrease in energy density.

[0023] In some embodiments of the present application, the thickness of the isolation covering layer at the straight area of ​​the isolation film is between 1.5-2 um.

[0024] In some embodiments of the present application, the length of the isolation covering layer at the corner area of ​​the isolation membrane is greater than the corner arc length of the isolation membrane, and the difference between the two is less than or equal to 0.5 mm, to ensure that the corner area of ​​the isolation membrane is covered by the isolation covering layer.

[0025] The present application also provides an electrochemical device, which includes the electrode assembly as described in any one of the above items.

[0026] The present application also provides an electronic device, which includes the electrochemical device as described above.

[0027] Compared with the prior art, the electrode assembly and the electrochemical device and electronic device comprising the electrode assembly according to the embodiment of the present application have at least the following beneficial technical effects:

[0028] The present application covers the corner area of ​​the cathode current collector with a cathode covering layer having a lower conductivity than that of the straight area, thereby reducing the amount of lithium ions released from the cathode in the corner area, alleviating the accumulation of lithium ions at the anode in the corner area during charging, and thereby improving the risk of lithium plating.

[0029] The present application reduces the conductivity of the inner side of the cathode electrode piece by coating an additional layer of high-resistance material covering layer on the inner side of the corner area of ​​the cathode electrode piece, thereby reducing the rate of lithium ion release from the cathode, thereby reducing the total amount of lithium ions released during a unit charge and discharge cycle, thereby improving the risk of lithium plating.

[0030] The present application reduces the porosity at the corners by thickly coating the slurry at the corners of the isolation membrane, thereby reducing the passage rate of lithium ions, thereby reducing the number of lithium ions embedded in the anode after being precipitated through the corners of the isolation membrane, thereby reducing the risk of lithium precipitation.

[0031] The present application changes the structure of the corner area by performing hot pressing treatment on the corners of the isolation membrane or the isolation membrane substrate, thereby reducing the porosity at the corners and the passage rate of lithium ions, thereby reducing the number of lithium ions embedded in the anode after being precipitated through the corners of the isolation membrane, thereby reducing the risk of lithium precipitation.

[0032] The present application only optimizes the corners and will not have a significant impact on the overall performance of the battery cell. Various battery cell structures are applicable to the solution of the present application.

[0033] The technical solution of the present application is applicable to single-layer coating and multi-layer coating, and the double-layer coating in the technical solution of the present application does not cause the problem of thinning. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a schematic diagram of the structure of the electrode assembly of the embodiment of the present application. Figure 1 ;

[0036] Figure 2 This is a schematic diagram of the structure of the electrode assembly of the embodiment of the present application. Figure 2 ;

[0037] Figure 3 Schematic diagram of the coating position of the isolation film;

[0038] Figure 4 It is a schematic diagram of the structure of the corner area of ​​the isolation membrane after heat pressing treatment;

[0039] Figure 5 It is a schematic diagram of the local structure of the covering layer of the isolation membrane;

[0040] Figure 6 It is a schematic diagram of the coating position of the cathode electrode;

[0041] Figure 7 It is a schematic diagram of the local structure of the covering layer of the cathode electrode;

[0042] Figure 8 is a schematic diagram of a partial structure of a covering layer of a cathode electrode piece in another embodiment;

[0043] In the figure, 1, anode pole piece; 11, anode current collector; 12, anode covering layer; 2, cathode pole piece; 21, cathode current collector; 22, cathode covering layer; 3, isolation membrane. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0045] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0046] like Figure 1 and 2 As shown, an embodiment of the present application relates to an electrode assembly, including an anode electrode sheet 1, a cathode electrode sheet 2 and an isolation membrane 3 arranged between the anode electrode sheet 1 and the cathode electrode sheet 2, the anode electrode sheet 1, the cathode electrode sheet 2 and the isolation membrane 3 are wound into a winding structure (flat battery cell), and the winding structure includes a straight area and a corner area connecting the straight area.

[0047] Among them, the anode electrode plate 1 includes an anode current collector 11 (which can be a copper foil) and an anode covering layer 12 arranged on the anode current collector 11, the cathode electrode plate 2 includes a cathode current collector 21 and a cathode covering layer 22 arranged on the cathode current collector 21 (which can be an aluminum foil), and the isolation film 3 includes a substrate and an isolation covering layer arranged on the substrate. Figure 1 and Figure 2 In the figure, X1 represents the straight area of ​​the battery cell, and X2 represents the corner area of ​​the battery cell. In the following description, the positions and lengths of the straight areas and corner areas of each component are marked with specific marks in the relevant drawings.

[0048] As an improvement of the electrode assembly of the present application, the cathode covering layer 22 includes a first cathode covering layer and a second cathode covering layer. The first cathode covering layer is located in the straight area of ​​the cathode electrode piece 2, and the second cathode covering layer is located in the corner area of ​​the cathode electrode piece 2, and the conductivity of the second cathode covering layer is lower than the conductivity of the first cathode covering layer. In this improved solution, an active material covering layer with lower conductivity is applied to the corner area of ​​the cathode current collector 21, and the amount of lithium ions released from the cathode in the corner area is reduced, thereby alleviating the accumulation of lithium ions at the anode in the corner area during charging, thereby improving the risk of lithium plating.

[0049] As an improvement of the electrode assembly of the present application, the first cathode covering layer is a first cathode active material layer A1, the second cathode covering layer is a second cathode active material layer A2, the conductivity of the second cathode active material layer A2 is lower than the conductivity of the first cathode active material layer A1, and the formed covering layer structure is as follows Figure 7 shown.

[0050] As an improvement of the electrode assembly of the present application, the first cathode covering layer includes a first cathode active material layer A1, the second cathode covering layer includes a second cathode main covering layer and a second cathode sub-covering layer, and the second cathode sub-covering layer is located on the inner surface of the second cathode main covering layer toward the winding center. The second cathode main covering layer is the first cathode active material layer A1, the second cathode sub-covering layer is a high resistance material layer A3, the resistance value of the high resistance material layer A3 is 0.1Ω to 5Ω, and the covering layer structure formed is as follows Figure 8 As shown, the final battery cell is as follows Figure 2 In this improved solution, by covering the inner side of the corner area of ​​the first cathode active material layer A1 with an additional high resistance material layer A3, the conductivity of the inner side of the cathode electrode 2 is reduced, the release rate of cathode lithium ions is reduced, and the total amount of lithium ions released during the unit charge and discharge cycle is reduced, thereby improving the risk of lithium deposition.

[0051] As an improvement of the electrode assembly of the present application, the high resistance material layer A3 may include a ceramic material, and preferably the ceramic slurry is at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. The high resistance material layer A3 may also include a binder, a dispersant, and a conductive agent, and its resistance value may be adjusted by adjusting the ratio of the conductive agent.

[0052] As an improvement of the electrode assembly of the present application, the thickness of the first cathode covering layer is between 50-100 um.

[0053] As an improvement of the electrode assembly of the present application, the thickness of the second cathode sub-covering layer is 0.02-0.1 times the thickness of the second cathode main covering layer. In this improvement, if the second cathode sub-covering layer is too thin, for example, the thickness is less than 0.02 times the thickness of the second cathode main covering layer, it is not possible to effectively reduce the resistance on the inner side of the cathode electrode sheet and achieve the effect of reducing the lithium ion escape rate; if the second cathode sub-covering layer is too thick, for example, the thickness is greater than 0.1 times the thickness of the second cathode main covering layer, it is easy to cause a decrease in energy density.

[0054] As an improvement of the electrode assembly of the present application, the thickness of the second cathode main covering layer is consistent with the thickness of the first cathode covering layer, which is between 50-100um, and the thickness of the second cathode sub-covering layer is 0.02-0.1 times the thickness of the second cathode main covering layer.

[0055] As an improvement of the electrode assembly of the present application, the conductivity of the second cathode covering layer is 50%-95% (including the end value) of the conductivity of the first cathode covering layer, preferably 70%-90% (including the end value).

[0056] As an improvement of the electrode assembly of the present application, the length of the second cathode covering layer is greater than the corner arc length of the cathode pole piece 2, and the difference between the two is less than or equal to 0.5mm, so as to ensure that the corner area is completely covered by the second cathode active material layer A2 or the high resistance material layer A3, and to ensure that there is no current collector exposed at the junction of the straight area and the corner area, thereby effectively ensuring the improvement of lithium precipitation at the corner. The corner arc length of the cathode pole piece 2 can be calculated according to the following formula: cathode corner arc length C = π * [D0 + (n-1) ΔT] / 2, where D0 = the innermost corner diameter of the anode pole piece 1 + the thickness of the isolation film 3 + the thickness of the double-sided anode pole piece 1, n is the number of battery cell layers, ΔT = the thickness of the isolation film 3 * 2 + the thickness of the double-sided anode pole piece 1 + the thickness of the double-sided cathode pole piece 2.

[0057] In the above improvement, the mass ratio of each component of the first cathode active material layer A1 can be: cathode main material 92%-97%; conductive agent 1.5%-4%; binder 1.5%-4%. The cathode main material can be independently selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, NCM ternary material, lithium nickel manganese oxide, and lithium-rich manganese.

[0058] In the above improvement, the mass ratio of each component of the second cathode active material layer A2 can be: cathode main material 92%-97%; conductive agent 1.0%-3%; binder 2.5%-4%. The cathode main material can be independently selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, NCM ternary material, lithium nickel manganese oxide, and lithium-rich manganese.

[0059] In the above improvement, the high resistance material layer A3 may contain ceramic material. Taking the ceramic material as aluminum oxide as an example, during preparation, the aluminum oxide fine powder is first mixed with water, and then additives such as dispersant, binder, and conductive agent are added in sequence, and then stirred and coated on the corresponding parts of the pole piece to form the high resistance material layer A3. Preferably, the mass ratio of each component of the high resistance material layer A3 can be: aluminum oxide 85-95%; dispersant 2-5%; binder 2-6%; conductive agent 2-10%. In addition to providing high resistance to reduce the conductivity of the inner side of the cathode corner area and improve the risk of lithium plating, the ceramic material can also prevent short circuit during puncture and improve battery safety.

[0060] In the above improvement, in order to achieve that the conductivity of the second cathode active material layer A2 is lower than that of the first cathode active material layer A1, so that the conductivity of the second cathode active material layer A2 is 50%-95% of the conductivity of the first cathode active material layer A1, the second cathode active material layer A2 may be stirred in at least the following two other ways:

[0061] The first one is to reduce the content of the conductive agent in the second cathode active material layer A2 to 10%-90%, preferably 50%, of the first cathode active material layer A1, and the other components are the same.

[0062] The second type is doping with additives that can increase the cathode resistance, such as rare earth elements.

[0063] As an improvement of the electrode assembly of the present application, the porosity of the corner area of ​​the separator 3 is less than the porosity of the straight area of ​​the separator 3. In this improved solution, since the porosity at the corner of the separator 3 is small, the passage rate of lithium ions is reduced, so that the number of lithium ions embedded in the anode after precipitation through the corner of the separator 3 is reduced, thereby reducing the risk of lithium precipitation.

[0064] In the present application, two preferred methods are proposed to achieve "the porosity of the corner area of ​​the isolation membrane 3 is smaller than the porosity of its straight area", the first one is by improving the coating method, and the second one is by using a hot pressing process.

[0065] In the above improvement, the porosity of the corner area of ​​the isolation membrane 3 is between 10% and 20%, and the porosity of the straight area of ​​the isolation membrane is between 25% and 35%.

[0066] As an improvement of the electrode assembly of the present application, it is known that the isolation film 3 includes a substrate and an isolation covering layer arranged on the substrate. In this improved solution, the thickness of the isolation covering layer at the corner area of ​​the isolation film 3 is greater than its thickness at the straight area of ​​the isolation film 3. The covering layer formed is as follows Figure 3 and Figure 5 As shown, the final battery cell is as follows Figure 1 As shown, Figure 1 The isolating membrane 3 in the middle corner area is represented by a thicker dotted line, and the isolating membrane 3 in the straight area is represented by a normal dotted line. The isolating covering layer is a high-resistance material layer B, and the resistance value of the high-resistance material layer B is 0.1Ω to 5Ω. In this improved solution, by thickly coating the high-resistance slurry at the corners of the isolating membrane 3, the porosity at the corners is reduced, the pass rate of lithium ions is reduced, and the number of lithium ions embedded in the anode after precipitation through the corners of the isolating membrane 3 is reduced, thereby reducing the risk of lithium precipitation.

[0067] As an improvement of the electrode assembly of the present application, the high resistance material layer B can be a ceramic material, and the ceramic slurry is preferably at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. The high resistance material layer B can also include a binder, a dispersant, and a conductive agent, and its resistance value can be adjusted by adjusting the ratio of the conductive agent. Taking the ceramic material as aluminum oxide as an example, during preparation, the aluminum oxide fine powder is first mixed with water, and then additives such as a dispersant, a binder, and a conductive agent are added in sequence, and then stirred and coated on the corresponding position of the isolation membrane 3 to obtain a high resistance material layer B. Preferably, the mass ratio of each component of the high resistance material layer B is: aluminum oxide 85-95%; dispersant 2-5%; binder 2-6%; conductive agent 2-10%. In addition to controlling the porosity of the straight area and corner area of ​​the isolation membrane and improving the risk of lithium precipitation, the ceramic material can also prevent short circuits during puncture, improve battery safety, and inhibit the shrinkage of the isolation membrane at high temperature to prevent short circuits between the positive and negative electrodes.

[0068] As an improvement of the electrode assembly of the present application, the thickness of the isolation covering layer at the corner area of ​​the isolation membrane 3 is 1.02-1.2 times of its thickness at the straight area of ​​the isolation membrane 3, that is, the total thickness of the covering layer at the corner area of ​​the isolation membrane 3 is 102%-120% of the thickness of the covering layer at the straight area. In this improvement, if the isolation covering layer of the isolation membrane 3 in the corner area is too thin, for example, the thickness is less than 1.02 times the thickness of the isolation covering layer in the straight area, it is impossible to effectively reduce the porosity of the isolation membrane and inhibit lithium precipitation; if the isolation covering layer of the isolation membrane 3 in the corner area is too thick, for example, the thickness is greater than 1.2 times the thickness of the isolation covering layer in the straight area, it will seriously affect the lithium ion pass rate in the corner area, resulting in a decrease in the charging rate, and the excessive thickness of the isolation membrane will also cause a decrease in energy density.

[0069] As an improvement of the electrode assembly of the present application, the thickness of the isolation covering layer in the straight area of ​​the isolation membrane 3 is between 1.5-2um. Based on the total thickness of the covering layer in the corner area of ​​the isolation membrane 3 being at least 102% of the thickness of the covering layer in the straight area, the thickness of the covering layer in the corner area can be calculated.

[0070] As an improvement of the electrode assembly of the present application, the length of the isolation covering layer at the corner area of ​​the isolation membrane 3 is greater than the corner arc length of the isolation membrane 3, and the difference between the two is less than or equal to 0.5 mm, so as to ensure that the corner area of ​​the isolation membrane 3 is covered by the isolation covering layer. The corner arc length of the isolation membrane 3 can be calculated according to the following formula: isolation membrane 3 corner arc length C = [D0 + (n-1) ΔT] / 2, where D0 = the innermost corner diameter of the anode pole piece 1 + the thickness of the double-sided anode pole piece 1, n is the number of battery cell layers, ΔT = the thickness of the isolation membrane 3 + the thickness of the double-sided anode pole piece 1 + the thickness of the double-sided cathode pole piece 2.

[0071] As an improvement of the electrode assembly of the present application, when the hot pressing process is used for processing, the specific process steps may include at least the following two:

[0072] The first method is that after the substrate is manufactured, the corner area of ​​the substrate is hot pressed before the high resistance material layer B is coated, and the subsequent coating and drying process of the high resistance material layer B is carried out normally after the hot pressing is completed. The hot pressing temperature is 60°C ± 20°C, the time is 4s ± 2s, and the pressure is 0.2MPa ± 0.05MPa. The above are preferred hot pressing conditions, but are not limited to the above conditions.

[0073] The second method is to continue coating the high resistance material layer B after the substrate is made, and then heat press the corner area of ​​the isolation film 3 after coating and drying. The heat press temperature is 60°C ± 20°C, the time is 4s ± 2s, and the pressure is 0.2MPa ± 0.05MPa. The above are preferred heat press conditions, but are not limited to the above conditions.

[0074] In the above-mentioned improvement scheme, the corners of the isolation film 3 or the isolation film substrate are subjected to heat pressing to shrink the gap, so that the structure of the corner area is changed, such as Figure 3 and Figure 4 As shown, the porosity at the corner is reduced, the passing rate of lithium ions is reduced, so that the number of lithium ions embedded in the anode after being precipitated through the corner of the isolation membrane 3 is reduced, thereby reducing the risk of lithium precipitation.

[0075] Preparation Example

[0076] Preparation of the anode plate 1:

[0077] The anode active material includes an anode material capable of absorbing and releasing lithium (Li), and may include but is not limited to: carbon materials, metal compounds, oxides, sulfides, lithium nitrides (such as LiN3), lithium metal, metals that form alloys with lithium, and polymer materials. In this preparation example, graphite is used as the anode active material, and graphite, a binder styrene butadiene rubber SBR, and a dispersant carboxymethyl cellulose CMC are mixed in a weight ratio of 97%: 1%: 2%, and diluted with an appropriate amount of distilled water, and then stirred in a vacuum mixer to form a uniform anode slurry, and the anode slurry is coated on a single side of a copper foil (anode current collector 11) to form an anode covering layer 12, and the coated single-sided pole piece is placed in a high-temperature oven at 85°C for drying to obtain an anode pole piece 1.

[0078] Preparation of the isolation film 3:

[0079] See also Figure 3 , Figure 3It is a schematic diagram of the coating position of the isolation membrane 3, a represents the coating width, C1, C2 and C3 all represent corner areas, both sides of the corner areas are straight areas, and b represents the coating length of the straight area. Among them, the length of the corner areas C1, C2 and C3 of the isolation membrane 3, with each additional layer of battery cells, the corner circumference will become longer. The calculation formula of the corner area length of the isolation membrane 3 is as follows: C = [D0 + (n-1) ΔT] / 2, D0 = the innermost circle corner diameter of the anode pole piece 1 + the thickness of the double-sided anode pole piece 1, n is the number of battery cell layers, ΔT = the thickness of the isolation membrane 3 + the thickness of the double-sided anode pole piece 1 + the thickness of the double-sided cathode pole piece 2. It should be specially noted that: C2 = π * [D0 + (n-1) ΔT'] / 2, ΔT' = the thickness of the isolation membrane 3 + the thickness of the double-sided anode pole piece 1.

[0080] Preparation of high resistance material layer B: After mixing aluminum oxide fine powder with water, dispersant, binder and conductive agent additives are added in sequence, and the first slurry can be obtained after stirring. The first slurry is applied to the corresponding position of the isolation membrane 3 to form a high resistance material layer B. The mass ratio of each component of the first slurry is: aluminum oxide 91%; dispersant 3%; binder 3%; conductive initiator 3%. In the following preparation scheme of the isolation membrane 3, the first slurry components used are consistent. The first slurry can be applied in three ways, the first is to apply it on the inner side of the isolation membrane 3, the second is to apply it on the outer side of the isolation membrane 3, and the third is to apply it on both the inner and outer sides. In the following preparation scheme of the isolation membrane 3, both the inner and outer sides are selected for coating, and the coating method remains consistent in all preparation schemes.

[0081] Isolation film 3-1: After the substrate is manufactured, before the first slurry is applied, the corner area of ​​the substrate (i.e., the corner area of ​​the isolation film 3) is hot pressed, and after the hot pressing is completed, the subsequent first slurry coating step is carried out normally to obtain the isolation film 3. The hot pressing temperature is 60°C ± 20°C, the time is 4s ± 2s, and the pressure is 0.2MPa ± 0.05MPa.

[0082] Isolation film 3-2: After the substrate is manufactured and the first slurry is coated normally, the isolation film 3 is obtained. The corner area of ​​the isolation film 3 is hot pressed. The hot pressing temperature is 60°C ± 20°C, the time is 4s ± 2s, and the pressure is 0.2MPa ± 0.05MPa.

[0083] Isolation film 3-3: After the substrate of the isolation film 3 is made, 2-4 mg of the first slurry is sprayed on the entire substrate according to a conventional coating process. After the first slurry is completely dried, the isolation film 3 is unfolded, and the first slurry is sprayed on the corner area of ​​the isolation film 3 with a spraying weight of 0.01-0.02 mg. The coating width is consistent with the width of the straight area. The coating thickness is 5% of the first coating thickness, and the isolation film 3 is obtained.

[0084] Isolation membrane 3-4: After the substrate of the isolation membrane 3 is manufactured, 2-4 mg of the first slurry is sprayed on the entire substrate according to a conventional coating process, and the coating thickness of the corner area and the straight area is consistent, so as to obtain the isolation membrane 3.

[0085] Preparation of the cathode electrode 2:

[0086] See also Figure 6 , Figure 6 Schematic diagram of the coating position of the cathode electrode piece 2, d represents the coating width, F1, F2 and F3 all represent corner areas, both sides of the corner areas are straight areas, and e represents the coating length of the straight area. Among them, the lengths of the corner areas F1, F2 and F3 of the cathode electrode piece 2 can be calculated according to the following formula: C = π*[D0+(n-1)ΔT] / 2, where D0 = the innermost corner diameter of the anode electrode piece 1 + the thickness of the isolation film 3 + the thickness of the double-sided anode electrode piece 1, n is the number of battery cell layers, ΔT = the thickness of the isolation film 3*2 ​​+ the thickness of the double-sided anode electrode piece 1 + the thickness of the double-sided cathode electrode piece 2.

[0087] Preparation of the first cathode active material layer A1: Lithium cobalt oxide is selected as the cathode active material, and the first cathode active material is prepared according to the composition of 95% cathode main material, 3% conductive carbon black as a conductive agent, and 2% polyvinylidene fluoride PVDF as a binder. The first cathode active material is coated on the corresponding position to form the first cathode active material layer A1. In the following preparation scheme of the cathode electrode sheet 2, the components of the first cathode active material layer A1 used are consistent.

[0088] Preparation of the second cathode active material layer A2: The cathode main material of the second cathode active material layer A2 is the same as that of the first cathode active material layer A1, which is lithium cobalt oxide, and the second cathode active material is prepared according to the composition of 95% lithium cobalt oxide, 2% conductive carbon black, and 3% polyvinylidene fluoride PVDF, and the second cathode active material is coated on the corresponding position to form the second cathode active material layer A2. In the following preparation scheme of the cathode electrode sheet 2, the components of the second cathode active material layer A2 used are consistent.

[0089] Preparation of the high resistance material layer A3: After mixing aluminum oxide fine powder with water, dispersant, binder, conductive agent and other additives are added in sequence, and a third slurry is obtained after stirring. The third slurry is applied to the corresponding position to form the high resistance material layer A3. The mass ratio of each component of the third slurry is: aluminum oxide 91%; dispersant 3%; binder 3%; conductive agent 3%. In the following preparation scheme of the cathode electrode sheet 2, the components of the third slurry used are consistent.

[0090] Cathode plate 2-1: During coating, the first cathode active material is first coated on the straight area of ​​the cathode current collector 21, leaving the corner area empty during coating. After the coating is dried, the second cathode active material is sprayed on the corner area. The thickness and width of the two coatings are the same, so that the conductivity of the corner area of ​​the cathode plate 2 finally formed is 70% of that of the straight area.

[0091] Cathode pole piece 2-2: During coating, the first cathode active material is firstly uniformly coated on the cathode current collector 21. After the coating is dried, the third slurry is sprayed on the inner side of the corner area of ​​the cathode current collector 21, so that the total thickness of the covering layer at the corner area is 101%-105% of the total thickness of the covering layer at the straight area, and the conductivity of the corner area of ​​the cathode pole piece 2 finally formed is 78% of that of the straight area.

[0092] Cathode electrode sheet 2 - 3 : The first cathode active material is used to spray the entire cathode current collector 21 according to a conventional coating process, and the coating thickness of the corner area is consistent with that of the straight area.

[0093] Example 1

[0094] Cell preparation:

[0095] The anode electrode sheet 1, the isolation membrane 3-1 and the cathode electrode sheet 2-3 are selected, and the pole ears are welded on the anode electrode sheet 1 and the cathode electrode sheet 2-3. Then, the anode electrode sheet 1, the isolation membrane 3-1 and the cathode electrode sheet 2-3 are stacked in sequence and wound in the same direction to form a battery cell 1.

[0096] Preparation of electrolyte:

[0097] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7 to obtain an organic solvent, and then fully dried LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0098] Preparation of lithium-ion secondary batteries:

[0099] The battery cell 1 is placed in an aluminum-plastic film packaging bag, and after the tabs are drawn out, the process of packaging, injecting the above electrolyte, vacuum packaging, standing, forming, shaping, etc. is performed to obtain a lithium-ion secondary battery.

[0100] Example 2

[0101] The anode electrode sheet 1, the isolation membrane 3-2 and the cathode electrode sheet 2-3 are selected to make a battery cell 2, and the remaining steps are the same as those in Example 1.

[0102] Example 3

[0103] The anode electrode sheet 1 , the isolation membrane 3 - 3 and the cathode electrode sheet 2 - 3 are selected to make a battery cell 3 , and the remaining steps are the same as those in Example 1.

[0104] Example 4

[0105] The anode electrode sheet 1 , the isolation membrane 3 - 4 and the cathode electrode sheet 2 - 1 are selected to make a battery cell 4 , and the remaining steps are the same as those in Example 1.

[0106] Example 5

[0107] The anode electrode sheet 1, the isolation membrane 3-4 and the cathode electrode sheet 2-2 are selected to make a battery cell 5, and the remaining steps are the same as those in Example 1.

[0108] Comparative Example 1

[0109] The anode electrode sheet 1, the separators 3-4 and the cathode electrode sheets 2-3 are selected to make a battery cell 6, and the remaining steps are the same as those in Example 1. The battery cell 6 of this embodiment is consistent with the prior art battery cell prepared by a conventional coating process and can be used as a comparative example.

[0110] Experimental example

[0111] 10 cells were selected from each of cells 1-5 for lithium deposition test. The lithium deposition test cycle process was as follows: at room temperature, the cells were charged at a constant current of 1C to a voltage of 4.48V, and then charged at a constant voltage to a current of 200mA, and then discharged at a constant current of 0.5C to 3.0V. This was a cycle process, and the process was cycled 100 times. The above batteries were disassembled in a dry room with a humidity of less than 5%, and the state of the anode electrode 1 was recorded by taking photos. The lithium deposition degree of the lithium-ion battery was judged according to the following standards:

[0112] No lithium deposition at the corners: no lithium deposition on the surface of the negative electrode;

[0113] Slight lithium deposition at the corner: The lithium deposition area on the surface of the negative electrode is less than 10%;

[0114] Severe lithium deposition: The lithium deposition area on the surface of the negative electrode is greater than 30%;

[0115] The number of cells where lithium deposition occurred on the anode electrode 1 was counted, and the results are shown in Table 1 below:

[0116] plan Lithium deposition at the corner Number of cells with lithium deposition at the corners Battery 1 Slight lithium deposition at the corner 1 Battery 2 Slight lithium deposition at the corner 2 Battery 3 No lithium deposition at corners 0 Battery 4 No lithium deposition at corners 0 Battery 5 No lithium deposition at corners 0 Battery 6 Severe lithium deposition at corners 10

[0117] Table 1

[0118] In summary, it can be seen from Table 1 above that, compared with the battery cell 6 using a conventional coating process, the lithium battery of the present application improves the corner lithium deposition by optimizing the corner area of ​​the separator 3 and / or the corner area of ​​the cathode electrode 2. Moreover, the present application only optimizes the corners, which will not have a significant impact on the overall performance of the battery cell.

[0119] The present application also relates to an electrochemical device, which comprises the electrode assembly as described in any one of the above improvements.

[0120] The present application also relates to an electronic device, which includes the electrochemical device as described above. The above is only a preferred embodiment of the present application. It should be noted that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present application, and these improvements and substitutions should also be regarded as the protection scope of the present application.

Claims

1. An electrode assembly, comprising an anode electrode sheet, a cathode electrode sheet and a separator disposed between the anode electrode sheet and the cathode electrode sheet, wherein the anode electrode sheet, the cathode electrode sheet and the separator are wound into a winding structure, wherein the winding structure comprises a straight region and a corner region connecting the straight regions, characterized in that: The cathode electrode sheet includes a cathode current collector and a first cathode covering layer and a second cathode covering layer disposed on the cathode current collector; The first cathode covering layer is located in a straight region of the cathode pole piece, and the second cathode covering layer is located in a corner region of the cathode pole piece. The conductivity of the second cathode covering layer is lower than the conductivity of the first cathode covering layer.

2. The electrode assembly according to claim 1, characterized in that: The first cathode covering layer is a first cathode active material layer, and the second cathode covering layer is a second cathode active material layer, wherein the conductivity of the second cathode active material layer is lower than the conductivity of the first cathode active material layer.

3. The electrode assembly according to claim 1, characterized in that: The first cathode covering layer is a first cathode active material layer, the second cathode covering layer includes a second cathode main covering layer and a second cathode sub-covering layer, and the second cathode sub-covering layer is located on the inner side surface of the second cathode main covering layer toward the winding center; The second cathode main covering layer is the first cathode active material layer, and the second cathode sub-covering layer is a high resistance material layer. The resistance value of the high resistance material layer is 0.1Ω to 5Ω.

4. The electrode assembly according to claim 3, characterized in that: The thickness of the second cathode sub-covering layer is 0.02-0.1 times the thickness of the second cathode main covering layer.

5. The electrode assembly according to claim 3, characterized in that: The high resistance material layer includes a ceramic material.

6. The electrode assembly according to claim 5, characterized in that: The ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide and boron nitride.

7. The electrode assembly according to any one of claims 2 to 6, characterized in that: The thickness of the first cathode covering layer is between 50-100 um.

8. The electrode assembly according to any one of claims 1 to 3, characterized in that: The electrical conductivity of the second cathode covering layer is 50% to 95% of the electrical conductivity of the first cathode covering layer.

9. The electrode assembly according to any one of claims 1 to 3, characterized in that: The length of the second cathode covering layer is greater than the corner arc length of the cathode electrode piece, and the difference between the length of the second cathode covering layer is less than or equal to 0.5 mm.

10. The electrode assembly according to claim 1, characterized in that: The porosity of the corner region of the isolation film is smaller than the porosity of the straight region of the isolation film.

11. The electrode assembly according to claim 10, characterized in that: The porosity of the corner area of ​​the isolation membrane is between 10% and 20%; the porosity of the straight area of ​​the isolation membrane is between 25% and 35%.

12. The electrode assembly according to claim 10, characterized in that: The isolation film comprises a substrate and an isolation covering layer disposed on the substrate, wherein the thickness of the isolation covering layer at the corner area of ​​the isolation film is greater than the thickness of the isolation covering layer at the straight area of ​​the isolation film; The isolation cover layer is a high resistance material layer, and the resistance value of the high resistance material layer is 0.1Ω to 5Ω.

13. The electrode assembly according to claim 12, characterized in that: The high resistance material layer includes a ceramic material.

14. The electrode assembly according to claim 13, characterized in that: The ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide and boron nitride.

15. The electrode assembly according to claim 12, characterized in that: The thickness of the isolation cover layer at the corner region of the isolation film is 1.02-1.2 times the thickness of the isolation cover layer at the straight region of the isolation film.

16. The electrode assembly according to claim 12 or 15, characterized in that: The thickness of the isolation covering layer at the straight area of ​​the isolation film is between 1.5 and 2 um.

17. The electrode assembly according to claim 12, wherein: The length of the isolation covering layer at the corner area of ​​the isolation membrane is greater than the corner arc length of the isolation membrane, and the difference between the length of the isolation covering layer and the corner arc length is less than or equal to 0.5 mm.

18. An electrochemical device, characterized in that: It comprises the electrode assembly according to any one of claims 1 to 17.

19. An electronic device, characterized in that: It comprises the electrochemical device according to claim 18.

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