Bipolar current collector, bipolar electrode sheet, electrochemical device and electronic device

Abstract

A bipolar current collector, a bipolar electrode sheet, an electrochemical device and an electronic device. The bipolar current collector comprises a negative electrode current collector and a positive electrode current collector. The negative electrode current collector comprises a first polymer layer and a first metal layer, wherein the first metal layer is arranged on a surface of the side of the first polymer layer in the direction of thickness, and is a copper layer. The positive electrode current collector comprises a second polymer layer and a second metal layer, wherein the second metal layer is arranged on a surface of the side of the second polymer layer in the direction of thickness, and is an aluminum layer. In the direction of thickness of the bipolar current collector, the first metal layer, the first polymer layer, the second polymer layer, and the second metal layer are arranged in sequence, the first polymer layer being connected to the second polymer layer. The copper layer has a thickness of A μm, and the aluminum layer has a thickness of B μm, where A and B satisfy: 0.8≤A≤3.0 and 1.2≤B / A≤3.5. When applied in an electrochemical device, the bipolar current collector helps improve the energy density and cycling performance of the electrochemical device.

Description

Bipolar current collectors, bipolar electrodes, electrochemical devices, and electronic devices Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a bipolar current collector, a bipolar electrode, an electrochemical device, and an electronic device. Background Technology

[0002] Electrochemical devices, such as lithium-ion batteries, possess advantages such as high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field. Current collectors are an indispensable component of lithium-ion batteries, and bipolar current collectors are increasingly valued for their high toughness and lightweight properties. However, existing bipolar current collectors in lithium-ion batteries suffer from insufficient adhesion strength to the active material layer and significant differences in expansion between the positive and negative electrodes, affecting the electrochemical performance of lithium-ion batteries.

[0003] Summary of the Invention

[0004] The purpose of this application is to provide a bipolar current collector, a bipolar electrode, an electrochemical device, and an electronic device to improve the energy density and cycle performance of the electrochemical device.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of an electrochemical device to explain the invention, the electrochemical device described herein is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides a bipolar current collector, which includes a negative current collector and a positive current collector. The negative current collector includes a first polymer layer and a first metal layer. Along the thickness direction of the bipolar current collector, the first metal layer is disposed on one side surface of the first polymer layer, and the first metal layer is a copper layer. The positive current collector includes a second polymer layer and a second metal layer. Along the thickness direction, the second metal layer is disposed on one side surface of the second polymer layer, and the second metal layer is an aluminum layer. Along the thickness direction of the bipolar current collector, the first metal layer, the first polymer layer, the second polymer layer, and the second metal layer are arranged sequentially, and the first polymer layer is connected to the second polymer layer. The thickness of the copper layer is A μm, and the thickness of the aluminum layer is B μm, where A and B satisfy: 0.8≤A≤3.0 and 1.2≤B / A≤3.5.

[0007] In this application, the negative electrode current collector and the positive electrode current collector are connected by a first polymer layer and a second polymer layer to form a bipolar current collector, and the thickness A of the copper layer and the value of B / A are controlled within the range of this application. This is beneficial for reducing the weight of the current collector in the electrochemical device and increasing the energy density of the electrochemical device. The setting of the thickness A of the copper layer and the relative thickness B / A of the aluminum layer and copper layer is beneficial for reducing the contact resistance of the positive electrode current collector, reducing the ohmic polarization and concentration polarization of the electrochemical device, and improving the cycle performance of the electrochemical device. Therefore, applying the bipolar current collector of this application to an electrochemical device is beneficial for improving the energy density and cycle performance of the electrochemical device.

[0008] In one embodiment of this application, 1.0 ≤ B ≤ 8.0. Controlling the thickness B of the aluminum layer within this range is beneficial for improving the cycle performance and energy density of the electrochemical device.

[0009] In one embodiment of this application, the bipolar current collector further includes an adhesive layer that connects the first polymer layer and the second polymer layer. The adhesive layer helps to improve the strength of the bipolar current collector and enhances the cycle performance of the electrochemical device employing it.

[0010] In one embodiment of this application, the thickness of the first polymer layer is C μm, and the thickness of the second polymer layer is D μm, where C and D satisfy: 1.6 ≤ D ≤ 8.0 and 1.2 ≤ C / D ≤ 3.0. Controlling the thickness D of the second polymer layer and the value of C / D within the above ranges is beneficial for reducing the volume expansion rate during the cycling process of the electrochemical device and improving its cycling performance.

[0011] In one embodiment of this application, 2.0 ≤ C ≤ 10.0. Adjusting the thickness C of the first polymer layer within the above range helps to reduce the volume expansion rate of the electrochemical device during cycling and improve the cycling performance of the electrochemical device.

[0012] In one embodiment of this application, the bipolar current collector satisfies at least one of the following: (1) 1.5 ≤ B / A ≤ 2.5; (2) 1.5 ≤ C / D ≤ 2.5.

[0013] In one embodiment of this application, the materials of the first polymer layer and the second polymer layer each independently include at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyethylene terephthalate. Using materials of the above types as the materials of the first and second polymer layers is beneficial for improving the energy density and cycle performance of the electrochemical device.

[0014] In one embodiment of this application, the tensile strength of the negative electrode current collector is 150 MPa to 220 MPa; and / or, the tensile strength of the positive electrode current collector is 150 MPa to 240 MPa. The good tensile strength of both the negative and positive electrode current collectors is beneficial for improving the cycle performance of the electrochemical device.

[0015] In one embodiment of this application, the thickness of the adhesive layer is 1 μm to 4 μm. Controlling the thickness of the adhesive layer within this range is beneficial for improving the strength of the bipolar current collector, increasing the energy density of the electrochemical device, and enhancing its cycle performance.

[0016] In one embodiment of this application, the adhesive layer material includes at least one of epoxy resin, polyacrylic acid, polyurethane, or polyvinyl chloride. The above-mentioned types of adhesive layer materials have good adhesive properties, which is beneficial for improving the strength of the bipolar current collector and enhancing the cycle performance of the electrochemical device.

[0017] A second aspect of this application provides a bipolar electrode, comprising the bipolar current collector described in any of the foregoing embodiments, wherein the bipolar electrode further comprises a negative electrode active material layer disposed on the surface of the copper layer away from the first polymer layer along the thickness direction, and the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 Up to 2.0 g / cm 3 The bipolar electrode also includes a positive active material layer, which is disposed on the surface of the aluminum layer away from the second polymer layer along the thickness direction. The compaction density of the positive active material layer is 2.5 g / cm³. 3 Up to 4.5 g / cm 3 By controlling the compaction density of the negative electrode active material layer and the positive electrode active material layer within the above-mentioned range, the electrochemical device can achieve good cycle performance and high energy density.

[0018] In one embodiment of this application, the peel strength between the negative electrode active material layer and the copper layer is 10 N / m to 20 N / m, and the peel strength between the positive electrode active material layer and the aluminum layer is 12 N / m to 20 N / m.

[0019] A third aspect of this application provides an electrochemical device comprising the bipolar current collector or the bipolar electrode as described in any of the foregoing embodiments. Therefore, the electrochemical device exhibits good cycle performance and high energy density.

[0020] A fourth aspect of this application provides an electrical device comprising the electrochemical apparatus described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0021] The beneficial effects of this application are:

[0022] This application provides a bipolar current collector, a bipolar electrode, an electrochemical device, and an electronic device. The bipolar current collector is formed by connecting the negative and positive current collectors of this application through a first polymer layer and a second polymer layer, with the copper layer thickness A and the B / A value controlled within the range specified in this application. This facilitates reducing the weight of the bipolar current collector and increasing the energy density of the electrochemical device. The copper layer thickness A and the relative thickness B / A of the aluminum and copper layers are set to reduce the contact resistance of the positive current collector, lower the internal resistance of the electrochemical device, and thus improve the cycle performance of the electrochemical device. Therefore, applying the bipolar current collector of this application to an electrochemical device is beneficial for improving the energy density and cycle performance of the electrochemical device. Attached Figure Description

[0023] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0024] Figure 1 is a schematic cross-sectional view of the bipolar current collector along its thickness direction in one embodiment of this application;

[0025] Figure 2 is a schematic cross-sectional view of the bipolar current collector along its thickness direction in another embodiment of this application;

[0026] Figure 3 is a schematic cross-sectional view of the bipolar electrode along its thickness direction in one embodiment of this application;

[0027] Figure 4 is a schematic cross-sectional view of the bipolar electrode along its thickness direction in another embodiment of this application.

[0028] Reference numerals: 1010-Bipolar current collector, 1020-Bipolar electrode, 11-First polymer layer, 12-First metal layer, 101-Negative current collector, 102-Negative active material layer, 21-Second polymer layer, 22-Second metal layer, 201-Positive current collector, 202-Positive active material layer, 122-First side, 222-Second side, 30-Adhesive layer. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0030] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0031] The first aspect of this application provides a bipolar current collector, which includes a negative current collector and a positive current collector. The negative current collector includes a first polymer layer and a first metal layer. Along the thickness direction of the bipolar current collector, the first metal layer is disposed on one side surface of the first polymer layer, and the first metal layer is a copper layer. The positive current collector includes a second polymer layer and a second metal layer. Along the thickness direction, the second metal layer is disposed on one side surface of the second polymer layer, and the second metal layer is an aluminum layer. Along the thickness direction of the bipolar current collector, the first metal layer, the first polymer layer, the second polymer layer, and the second metal layer are arranged sequentially, and the first polymer layer is connected to the second polymer layer. The thickness of the copper layer is A μm, and the thickness of the aluminum layer is B μm, where A and B satisfy: 0.8≤A≤3.0 and 1.2≤B / A≤3.5.

[0032] For ease of understanding, in this application, the width direction of the bipolar current collector is defined as Y, and its thickness direction as Z. It should be understood that the above definitions of direction are for the purpose of describing this application, and the directions defined in this application can be understood based on the relative positions of the elements in the accompanying drawings and the actual product. It is understood that the width, length, and thickness directions of the positive and negative current collectors are the same as those of the bipolar current collector. As shown in Figures 1 and 2, the bipolar current collector 1010 includes a negative current collector 101 and a positive current collector 201. The negative current collector 101 includes a first polymer layer 11 and a first metal layer 12. The first metal layer 12 is disposed on one side of the first polymer layer 11 along the thickness direction Z. The first metal layer 12 is a copper layer, and the thickness of the copper layer is shown as A. The positive current collector 201 includes a second polymer layer 21 and a second metal layer 22. The second metal layer 22 is disposed on one side of the second polymer layer 21 along the thickness direction Z. The second metal layer 22 is an aluminum layer, and the thickness of the aluminum layer is shown as B. Along the thickness direction Z of the bipolar current collector 1010, the first metal layer 12, the first polymer layer 11, the second polymer layer 21, and the second metal layer 22 are arranged sequentially, with the first polymer layer 11 connected to the second polymer layer 21. In one embodiment, as shown in FIG1, the first polymer layer 21 and the second polymer layer 22 are in direct contact and connected. In another embodiment, as shown in FIG2, the first polymer layer 21 and the second polymer layer 22 are connected by an adhesive layer 30.

[0033] For example, A can be 0.8, 1.0, 1.3, 1.6, 1.7, 1.9, 2, 2.2, 2.6, 2.9, 3.0, or any value within any two of the above ranges. Similarly, B / A can be 1.2, 1.4, 1.6, 1.8, 2, 2.1, 2.3, 2.7, 3.0, 3.1, 3.3, 3.5, or any value within any two of the above ranges. If A is less than 0.8, the copper layer thickness is too small, resulting in insufficient copper layer strength and making the negative electrode current collector prone to breakage, affecting its normal use. If A is greater than 3.0, the copper layer thickness is too large, increasing the volume of the negative electrode current collector and reducing the energy density of the electrochemical device. The negative electrode current collector uses a copper layer as the conductive layer, while the positive electrode current collector uses an aluminum layer as the conductive layer. The resistivity of the copper layer is approximately 0.6 times that of the aluminum layer. The relative thickness of the copper and aluminum layers affects the contact impedance of the positive electrode current collector, which in turn affects the cycle performance of the electrochemical device. The density of copper is approximately 3.3 times that of aluminum. The relative thickness of the copper and aluminum layers affects the weight of both the negative and positive electrode current collectors, thus influencing the energy density of the electrochemical device. If the B / A ratio is less than 1.2, the copper layer is relatively too thick, resulting in an excessively heavy negative electrode current collector. Using the negative electrode current collector in an electrochemical device increases its weight, leading to a loss in energy density. If the B / A ratio is greater than 3.5, the aluminum layer is relatively too thick compared to the copper layer, resulting in excessively high contact impedance of the positive electrode current collector. This increases ohmic and concentration polarization in the electrochemical device, thereby reducing its cycle performance.

[0034] Overall, in this application, the negative electrode current collector and the positive electrode current collector are connected by a first polymer layer and a second polymer layer to form a bipolar current collector. The thickness A of the copper layer and the B / A value are controlled within the range specified in this application, which helps to reduce the weight of the current collector in the electrochemical device and increase the energy density of the electrochemical device. The setting of the copper layer thickness A and the relative thickness B / A of the aluminum layer and copper layer helps to reduce the contact resistance of the positive electrode current collector, reduce the ohmic polarization and concentration polarization of the electrochemical device, and improve the cycle performance of the electrochemical device. Therefore, applying the bipolar current collector of this application to an electrochemical device is beneficial to improving the energy density and cycle performance of the electrochemical device.

[0035] In one embodiment of this application, 1.0 ≤ B ≤ 8.0. For example, B is 1.0, 1.6, 2.0, 3.0, 3.3, 4.0, 4.6, 5.0, 5.2, 5.7, 6.0, 6.5, 7.0, 7.3, 8.0, or any value between any two of the above ranges. By controlling the thickness B of the aluminum layer within the above range, the aluminum layer has higher strength, the risk of breakage of the positive electrode current collector is lower, and the positive electrode current collector has a smaller volume. Therefore, when the bipolar current collector formed by connecting the positive electrode current collector and the negative electrode current collector is applied to an electrochemical device, it is beneficial to improve the cycle performance and energy density of the electrochemical device.

[0036] In one embodiment of this application, 1.5 ≤ B / A ≤ 2.5. For example, B / A is 1.5, 1.6, 1.8, 2.0, 2.1, 2.3, 2.5, or any value between any two of the above ranges. Adjusting the value of B / A within the range of 1.5 to 2.5 is beneficial for further improving the energy density and cycle performance of the electrochemical device.

[0037] In one embodiment of this application, the bipolar current collector further includes an adhesive layer connecting the first polymer layer and the second polymer layer. As shown in FIG2, the bipolar current collector 1010 includes a negative electrode current collector 101, a positive electrode current collector 201, and an adhesive layer 30. The adhesive layer 30 connects the first polymer layer 11 and the second polymer layer 21, and the negative electrode current collector 101 and the positive electrode current collector 201 are connected by the adhesive layer 30 to form the bipolar current collector 1010. The adhesive layer improves the adhesion between the positive and negative electrode current collectors, increases the strength of the bipolar current collector, and thus improves the service life of the bipolar current collector, enabling the electrochemical device using the bipolar current collector to have good cycle performance.

[0038] In one embodiment of this application, as shown in Figures 1 and 2, the thickness of the first polymer layer 11 is C μm, and the thickness of the second polymer layer 21 is D μm, where C and D satisfy: 1.6 ≤ D ≤ 8.0 and 1.2 ≤ C / D ≤ 3.0. For example, D can be 1.6, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, or any value within any two of the above ranges. For example, C / D can be 1.2, 1.5, 1.7, 1.9, 2.0, 2.1, 2.3, 2.6, 2.8, 3.0, or any value within any two of the above ranges. The expansion rate of the negative electrode active material is often greater than that of the positive electrode active material. Controlling the values ​​of D and C / D within the above ranges facilitates the absorption of the expansion of the negative electrode active material by the first polymer layer, thereby reducing the volume expansion rate of the electrochemical device during cycling. Therefore, the electrochemical device, while already possessing a high energy density, can further improve its cycling performance.

[0039] In one embodiment of this application, 2.0 ≤ C ≤ 10.0. For example, C is 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, or any value between any two of the above ranges. Controlling the thickness C of the first polymer layer within the above range is beneficial for the first polymer layer to absorb the expansion of the negative electrode active material, reducing the volume expansion rate of the electrochemical device during cycling, and improving the energy density and cycle performance of the electrochemical device.

[0040] In one embodiment of this application, 1.5 ≤ C / D ≤ 2.5. For example, C / D is 1.5, 1.7, 1.9, 2.0, 2.1, 2.3, 2.5, or any value between any two of the above ranges. By adjusting the value of C / D within the above range, the electrochemical device achieves better cycle performance while maintaining a high energy density.

[0041] In one embodiment of this application, 1.5 ≤ B / A ≤ 2.5; 1.5 ≤ C / D ≤ 2.5. For example, B / A is 1.5, 1.6, 1.8, 2.0, 2.1, 2.3, 2.5, or any value between any two of the above ranges. For example, C / D is 1.5, 1.7, 1.9, 2.0, 2.1, 2.3, 2.5, or any value between any two of the above ranges. Simultaneously controlling B / A and C / D within the above ranges is beneficial for further improving the energy density and cycle performance of the electrochemical device.

[0042] In one embodiment of this application, the materials of the first polymer layer and the second polymer layer each independently include at least one of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), or polyethylene terephthalate (PET). These materials are characterized by low density, light weight, high temperature resistance, and resistance to electrolyte corrosion. Using these materials as the materials for the first and second polymer layers is beneficial for achieving a lighter weight for the bipolar current collector, exhibiting good stability during use in the electrochemical device, and effectively absorbing the expansion and deformation of the positive and negative electrode active materials. Therefore, applying the bipolar current collector to the electrochemical device is beneficial for improving the energy density and cycle performance of the electrochemical device.

[0043] In one embodiment of this application, the material of the first polymer layer may be the same as or different from the material of the second polymer layer. Exemplarily, in some embodiments, the material of the first polymer layer is the same as the material of the second polymer layer. In other embodiments, the material of the first polymer layer is different from the material of the second polymer layer. Using the same material for the first and second polymer layers facilitates the adhesion between the first and second polymer layers, and in the preparation process of the bipolar current collector, it helps to reduce production costs and accelerate production efficiency.

[0044] In one embodiment of this application, the tensile strength of the negative electrode current collector is between 150 MPa and 220 MPa. For example, the tensile strength of the negative electrode current collector is 150 MPa, 160 MPa, 168 MPa, 182 MPa, 193 MPa, 203 MPa, 212 MPa, 220 MPa, or any value between any two of the above ranges. The negative electrode current collector has good tensile strength. Using the negative electrode current collector to prepare bipolar current collectors is beneficial for achieving higher tensile strength in the bipolar current collector. This, in turn, allows for better impact resistance in electrochemical devices under conditions such as impacts, thereby improving the safety performance of the electrochemical device while maintaining high energy density and good cycle performance.

[0045] In one embodiment of this application, the tensile strength of the positive electrode current collector is between 150 MPa and 240 MPa. For example, the tensile strength of the positive electrode current collector is 150 MPa, 161 MPa, 168 MPa, 179 MPa, 190 MPa, 200 MPa, 209 MPa, 214 MPa, 224 MPa, 230 MPa, 236 MPa, 240 MPa, or any value between any two of the above ranges. This indicates that the positive electrode current collector has good tensile strength. Using the positive electrode current collector to prepare bipolar current collectors is beneficial for achieving higher tensile strength in bipolar devices. Furthermore, its application in electrochemical devices provides better impact resistance under conditions such as impacts, thereby improving the safety performance of the electrochemical device while maintaining high energy density and good cycle performance.

[0046] In this application, tensile strength can be understood as tensile strength known in the art. This application does not impose any particular limitation on the method of controlling the tensile strength of the positive and negative current collectors, as long as the purpose of this application can be achieved. For example, the tensile strength of the positive current collector can be achieved by controlling at least one of the thickness of the aluminum layer, the thickness of the second polymer layer, or the material of the second polymer layer; the tensile strength of the negative current collector can be achieved by controlling at least one of the thickness of the copper layer, the thickness of the first polymer layer, or the material of the first polymer layer.

[0047] In one embodiment of this application, as shown in FIG2, the thickness T of the adhesive layer 30 is... 30 The thickness ranges from 1 μm to 4 μm. For example, the thickness of the adhesive layer can be 1 μm, 2 μm, 2.3 μm, 2.7 μm, 3 μm, 3.6 μm, 4 μm, or any value between any two of the above ranges. Controlling the thickness of the adhesive layer within this range allows the bipolar current collector to have both suitable thickness and good adhesion properties. Therefore, when the bipolar current collector is applied to an electrochemical device, the electrochemical device exhibits high energy density and good cycle performance.

[0048] In one embodiment of this application, the adhesive layer material includes at least one of epoxy resin, polyacrylic acid, polyurethane, or polyvinyl chloride. The above-mentioned adhesive layer materials have good adhesive properties, which is beneficial for obtaining a bipolar current collector with good performance after the positive and negative current collectors are bonded together.

[0049] A second aspect of this application provides a bipolar electrode, comprising the bipolar current collector described in any of the foregoing embodiments, wherein the bipolar electrode further comprises a negative electrode active material layer disposed on the surface of the first metal layer away from the first polymer layer along the thickness direction Z, and the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 Up to 2.0 g / cm 3 The bipolar electrode also includes a positive electrode active material layer, which is disposed on the surface of the second metal layer away from the second polymer layer along the thickness direction Z. The compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 Up to 4.5 g / cm 3 .

[0050] It should be noted that the width, length, and thickness directions of the positive and negative electrode active material layers are the same as those of the bipolar current collector. As shown in Figures 3 and 4, the bipolar electrode 1020 includes a bipolar current collector 1010, a negative electrode active material layer 102, and a positive electrode active material layer 202. The negative electrode active material layer 102 is disposed on the first side 122 of the first metal layer 12, which is the side of the first metal layer 12 away from the first polymer layer 11 along the thickness direction Z. The positive electrode active material layer 202 is disposed on the second side 222 of the second metal layer 22, which is the side of the second metal layer 22 away from the second polymer layer 21 along the thickness direction Z.

[0051] For example, the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 Up to 2.0 g / cm 3 For example, the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 1.2g / cm 31.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 Or any value between any two of the above ranges. For example, the compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 Up to 4.5 g / cm 3 For example, the compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 2.7g / cm 3 2.9g / cm 3 3.0g / cm 3 3.2g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 4.0g / cm 3 4.3g / cm 3 4.5g / cm 3 Or any value between any two of the above ranges.

[0052] By controlling the compaction density of the negative electrode active material layer within the aforementioned range, the risk of breakage of the negative electrode active material is low, good contact exists between the particles of the negative electrode active material, and the surface of the negative electrode active material particles exhibits good interfacial stability. This also allows the negative electrode active material layer to have a relatively low thickness while containing a large amount of negative electrode active material. Similarly, by controlling the compaction density of the positive electrode active material layer within the aforementioned range, the risk of breakage of the positive electrode active material is low, good contact exists between the particles of the positive electrode active material, and the surface of the positive electrode active material particles exhibits good interfacial stability. This also allows the positive electrode active material layer to have a relatively low thickness while containing a large amount of positive electrode active material. Thus, the application of bipolar electrodes in electrochemical devices enables the electrochemical devices to have good cycle performance and high energy density.

[0053] This application does not impose any particular restrictions on the method of controlling the compaction density of the positive and negative electrode active material layers, as long as the purpose of this application can be achieved. For example, it can be achieved by adjusting the pressure of the cold-pressed positive and negative electrode sheets.

[0054] In one embodiment of this application, the peel strength between the negative electrode active material layer and the copper layer is 10 N / m to 20 N / m. For example, the peel strength between the negative electrode active material layer and the copper layer is 10 N / m, 12 N / m, 13 N / m, 15 N / m, 17 N / m, 20 N / m, or any value between any two of the above ranges. Thus, the bipolar electrode, when applied in an electrochemical device, enables the electrochemical device to have good cycle performance.

[0055] In one embodiment of this application, the peel strength between the positive electrode active material layer and the aluminum layer is between 12 N / m and 20 N / m. For example, the peel strength between the positive electrode active material layer and the aluminum layer is 12 N / m, 14 N / m, 15 N / m, 16 N / m, 18 N / m, 19 N / m, 20 N / m, or any value between any two of the above ranges. Thus, the bipolar electrode, when applied in an electrochemical device, enables the electrochemical device to have good cycle performance.

[0056] This application does not impose any particular restrictions on the method of controlling the peel strength between the negative electrode active material layer and the copper layer, or the peel strength between the positive electrode active material layer and the aluminum layer, as long as the purpose of this application can be achieved. For example, the peel strength between the negative electrode active material layer and the copper layer can be achieved by controlling the content of the binder in the negative electrode active material layer and the surface roughness of the copper layer, and the peel strength between the positive electrode active material layer and the aluminum layer can be achieved by controlling the content of the binder in the positive electrode active material layer and the surface roughness of the aluminum layer.

[0057] This application does not impose any particular limitation on the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the positive electrode active material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements, which may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, and these elements can further improve the stability of the positive electrode active material. This application does not impose any particular limitation on the thickness of the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm. Optionally, the positive electrode active material layer may also include at least one of a positive electrode conductive agent or a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode conductive agent and positive electrode binder in the positive electrode active material layer, as long as it achieves the purpose of this application. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0058] The present application places no particular restrictions on the negative electrode active material layer, as long as the object of the present application can be achieved. For example, the negative electrode active material layer of the present application contains a negative electrode active material. The present application places no particular restrictions on the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or at least one of metallic lithium. The present application places no particular restrictions on the thickness of the negative electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer may further include at least one of a negative electrode conductive agent, a dispersant or a negative electrode binder. The present application places no particular restrictions on the types of the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer, as long as the object of the present application can be achieved. The present application places no particular restrictions on the mass ratio of the negative electrode active material, the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer, as long as the object of the present application can be achieved.

[0059] The present application places no particular restrictions on the method for preparing the bipolar electrode sheet, as long as the object of the present application can be achieved. In one embodiment of the present application, the method for preparing the bipolar electrode sheet includes, but is not limited to, the following steps: (1) plating a first metal layer on one surface of the first polymer layer to obtain a negative electrode current collector; uniformly coating a negative electrode paste on the surface of the first metal layer on the side away from the first polymer layer in the thickness direction, drying, cold pressing and slitting to obtain a negative electrode sheet; (2) plating a second metal layer on one surface of the second polymer layer to obtain a positive electrode current collector; uniformly coating a positive electrode paste on the surface of the second metal layer on the side away from the second polymer layer in the thickness direction, drying, cold pressing and slitting to obtain a positive electrode sheet; (3) overlapping the other surface of the first polymer layer that does not contact the first metal layer with the other surface of the second polymer layer that does not contact the second metal layer, and after hot pressing treatment, connecting the first polymer layer to the second polymer layer to form a bipolar electrode sheet.

[0060] In another embodiment of this application, the method for preparing a bipolar electrode includes, but is not limited to, the following steps: (i) depositing a first metal layer on one surface of a first polymer layer to obtain a negative current collector; uniformly coating a negative electrode slurry on the surface of the first metal layer away from the first polymer layer along the thickness direction, drying it, and then cold pressing and slitting it to obtain a negative electrode sheet; (ii) depositing a second metal layer on one surface of a second polymer layer to obtain a positive current collector; uniformly coating a positive electrode slurry on the surface of the second metal layer away from the second polymer layer along the thickness direction, drying it, and then cold pressing and slitting it to obtain a positive electrode sheet; (iii) coating an adhesive layer material on one of the other surfaces of the first polymer layer that are not in contact with the first metal layer and the other surface of the second polymer layer that are not in contact with the second metal layer, stacking the other surface, rolling it first and then drying it, so that an adhesive layer is formed between the negative current collector and the positive current collector, and the first polymer layer and the second polymer layer are connected by the adhesive layer to form a bipolar electrode sheet.

[0061] The above-described preparation method involves separately preparing positive and negative electrode sheets, which are then combined to form a bipolar electrode sheet. This process is simple and ensures good adhesion between the layers of the bipolar electrode sheet, significantly reducing the probability of layer delamination. In this application, both the positive and negative active material layers are single-sided, and are cold-pressed separately before being combined to form the bipolar electrode sheet. This facilitates control over the compaction density of both layers, ensuring suitable compaction densities. Consequently, the resulting bipolar electrode sheet, when applied to an electrochemical device, provides excellent cycle performance and high energy density.

[0062] This application does not impose any particular restrictions on the method of depositing the first metal layer in steps (1) and (i) above, as long as the purpose of this application can be achieved. For example, the first metal layer can be deposited on the surface of the first polymer layer by electroplating. This application does not impose any particular restrictions on the process parameters of electroplating, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of drying and cold pressing in steps (1) and (i) above, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the method of depositing the second metal layer in steps (2) and (ii) above, as long as the purpose of this application can be achieved. For example, the second metal layer can be deposited on the surface of the second polymer layer by vacuum evaporation. This application does not impose any particular restrictions on the process parameters of vacuum evaporation, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of drying and cold pressing in steps (2) and (ii) above, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of the hot pressing treatment in step (3) above. Those skilled in the art can select the appropriate parameters according to actual needs, as long as the purpose of this application can be achieved. For example, the hot pressing temperature can be 70°C to 90°C, the pressure 4t to 6t, and the time 5min to 20min. This application also does not impose any particular restrictions on the process parameters of the rolling and drying in step (iii) above. Those skilled in the art can select the appropriate parameters according to actual needs, as long as the purpose of this application can be achieved. For example, the rolling pressure can be 4t to 6t, and the drying temperature can be 70°C to 90°C.

[0063] A third aspect of this application provides an electrochemical device comprising the bipolar current collector or the bipolar electrode as described in any of the foregoing embodiments. Therefore, the electrochemical device exhibits good cycle performance and high energy density.

[0064] In one embodiment of this application, the electrochemical device further includes a diaphragm. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. The diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application.

[0065] The electrochemical device of this application also includes a packaging bag and an electrolyte. This application does not impose any particular limitation on the packaging bag and electrolyte; they can be any packaging bag and electrolyte known in the art, as long as they achieve the purpose of this application.

[0066] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0067] This application does not impose any particular limitation on the preparation method of the electrochemical device, as long as it can achieve the purpose of this application. For example, the preparation method of the electrochemical device includes, but is not limited to, the following steps: stacking a diaphragm and bipolar electrodes, winding them to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or, stacking a diaphragm and bipolar electrodes, then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device.

[0068] A fourth aspect of this application provides an electrical device comprising the electrochemical apparatus described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0069] The electrical equipment used in this application is not particularly limited and can be any electrical equipment known in the prior art. For example, the electrical equipment may include, but is not limited to: laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0070] Example

[0071] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0072] Test methods and equipment:

[0073] Tensile strength test:

[0074] At an ambient temperature of 25℃, the lithium-ion battery was discharged to 2V at 0.2C and then disassembled. The bipolar electrode was removed and soaked in dimethyl carbonate (DMC) for 20 minutes. The bipolar electrode was then placed in an oven and dried at 80℃ for 12 hours. After removing the negative and positive active material layers on the surface of the bipolar electrode, it was soaked in N,N-dimethylformamide (DMF) for 1 hour. The edges of the first and second polymer layers were separated with a cutter and then separated from the first and second polymer layers using a clamp. If an adhesive layer was present, the edges of the adhesive layer and the first polymer layer, as well as the adhesive layer and the second polymer layer, were separated with a cutter and then separated from the adhesive layer using a clamp, resulting in a negative current collector and a positive current collector. The negative and positive current collectors were then placed in an oven and dried at 80℃ for 12 hours for later use.

[0075] (1) Test of tensile strength Rm1 of negative electrode current collector:

[0076] Take a negative electrode current collector and cut it into a sample with a width × length of 15mm × 200mm. Measure the thickness h1 (μm) of the sample with a micrometer. Perform a tensile test using a high-speed rail tensile testing machine at room temperature and pressure. Set the initial position and make the sample 50mm long between the clamps. Perform the tensile test at a speed of 50mm / min. Record the load L1 (N) at which the sample breaks. The tensile strength Rm1 = L1 / (15×h1)×1000.

[0077] (2) Test of tensile strength Rm2 of positive electrode current collector:

[0078] Take a positive current collector and cut it into a sample with a width × length of 15mm × 200mm. Measure the thickness h2 (μm) of the sample with a micrometer. Perform a tensile test using a high-speed rail tensile testing machine at room temperature and pressure. Set the initial position and make the sample 50mm long between the clamps. Perform the tensile test at a speed of 50mm / min. Record the load L2 (N) at which the sample breaks. The tensile strength Rm2 = L2 / (15×h2)×1000.

[0079] Test of compaction density:

[0080] At an ambient temperature of 25℃, the lithium-ion battery was discharged to 2V at 0.2C and then disassembled. The bipolar electrode was removed, soaked in dimethyl carbonate (DMC) for 20 minutes, and then placed in an oven to dry at 80℃ for 12 hours before the following tests were performed.

[0081] (1) Testing of the compaction density of the negative electrode active material:

[0082] The thickness T1 (μm) of the negative electrode active material layer was measured using a micrometer, and the material was cut into 1mm × 1mm sheets. The weight m1 (g) of the sheets was measured using a balance. The negative electrode active material layer on the surface of the sheets was removed, and the remaining weight m2 (g) of the sheets was measured using a balance. The compaction density PD1 (g / cm³) of the negative electrode active material layer was also measured. 3 )=(m1-m2) / ((T1×1×1)×10 -6 ).

[0083] (2) Testing of the compaction density of the positive electrode active material:

[0084] The thickness T2 (μm) of the positive electrode active material layer was measured using a micrometer, and the material was cut into 1mm × 1mm sheets. The weight m3 (g) of the sheets was measured using a balance. The positive electrode active material layer on the surface of the sheets was removed, and the remaining weight m4 (g) of the sheets was measured using a balance. The compaction density PD2 (g / cm³) of the positive electrode active material layer was also measured. 3 )=(m3-m4) / ((T2×1×1)×10 -6 ).

[0085] Peel strength test:

[0086] At an ambient temperature of 25℃, the lithium-ion battery was discharged to 2V at 0.2C and then disassembled. The bipolar electrode was removed, soaked in dimethyl carbonate (DMC) for 20 minutes, and then placed in an oven to dry at 80℃ for 12 hours before the following tests were performed.

[0087] (1) Test of peel strength F1 between the negative electrode active material layer and the copper layer:

[0088] 1) Sample preparation: Prepare a sample with a width of 30 mm and a length of 150 mm from the bipolar electrode obtained above. Ensure that the surface of the sample is clean and flat.

[0089] 2) Clamping method: Use clamps to clamp and fix the sample to ensure that the bonding interface between the negative electrode active material layers is within the clamping area.

[0090] 3) Peel Test: Using a peel strength tester (BLD-200H electronic peel tester), place a fixture with a suitable sample size into the instrument. Then, peel the negative electrode active material layer and the copper layer at a constant speed (100 mm / min) until they are completely separated. Simultaneously, record the applied force L1 during the peel process.

[0091] 4) Data recording and analysis: Record the force L1 applied during the peeling process, and the formula for calculating the peel strength is F1=L1 / A, where A is the peel length of the sample.

[0092] (2) Test of peel strength F2 between the positive electrode active material layer and the aluminum layer:

[0093] 1) Sample preparation: Prepare a sample with a width of 30 mm and a length of 150 mm from the bipolar electrode obtained above. Ensure that the surface of the sample is clean and flat.

[0094] 2) Clamping method: Use clamps to clamp and fix the sample to ensure that the bonding interface between the positive electrode active material layers is within the clamping area.

[0095] 3) Peel Test: Using a peel strength tester (BLD-200H electronic peel tester), place a fixture with a suitable sample size into the instrument. Then, peel the positive electrode active material layer and the aluminum layer at a constant speed (usually 100 mm / min) until they are completely separated. Simultaneously, record the applied force L2 during the peel process.

[0096] 4) Data recording and analysis: Record the force L2 applied during the peeling process, and the formula for calculating the peel strength is F2=L2 / A, where A is the peel length of the sample.

[0097] Energy density testing:

[0098] At an ambient temperature of 25℃, a lithium-ion battery is charged to 4.30V with a constant current of 0.2C, then charged to 0.05C with a constant voltage of 4.30V, and left to stand for 5 minutes; then discharged to 2.0V with a constant current of 0.2C, and left to stand for 5 minutes. The discharge energy at this point is taken as the energy E of the lithium-ion battery; and the weight of the lithium-ion battery is measured as m. Calculate the energy density of the lithium-ion battery.

[0099] The formula for calculating energy density is: Energy density (Wh / kg) = E / m.

[0100] Cyclic performance testing:

[0101] (1) Capacity retention test:

[0102] At an ambient temperature of 25℃, the lithium-ion battery is charged to 4.3V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.3V, and left to stand for 10 minutes; then discharged to 2.0V with a constant current of 4C, and left to stand for 15 minutes. This constitutes one cycle. This cycle is repeated 1000 times. The discharge capacity of the first cycle is recorded as the initial capacity Q0, and the discharge capacity of the 1000th cycle is recorded as Q2. The capacity retention rate of the lithium-ion battery is then calculated.

[0103] The formula for calculating capacity retention rate is: Capacity retention rate (%) = Q2 / Q0 × 100%.

[0104] (2) Test of cyclic expansion rate:

[0105] At an ambient temperature of 25℃, the lithium-ion battery was charged to 4.3V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.3V, left to stand for 10 minutes, and then discharged to 3.6V with a constant current of 4C. The initial thickness of the lithium-ion battery was measured and recorded as T0.

[0106] At an ambient temperature of 25℃, the lithium-ion battery was charged to 4.3V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.3V, and allowed to rest for 10 minutes. Then it was discharged to 2.0V with a constant current of 4C, and allowed to rest for 15 minutes. This constitutes one cycle, and the cycle was repeated 1000 times. Then, the lithium-ion battery was charged to 4.3V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.3V, and allowed to rest for 10 minutes. The thickness of the lithium-ion battery was measured and recorded as T2.

[0107] The formula for calculating the cyclic expansion rate is: Cyclic expansion rate (%) = (T2-T0) / T0 × 100%.

[0108] Internal resistance testing:

[0109] The lithium-ion battery was placed in an environment of 25°C and charged to 4.3V with a constant current of 1C. Then it was charged to 0.05C with a constant voltage of 4.3V and left to stand for 10 minutes. Then it was discharged to 3.6V with a constant current of 4C. The internal resistance of the lithium-ion battery was obtained by applying a 1kHz AC signal to the lithium-ion battery and measuring its AC voltage drop using an internal resistance tester (HIOKI Corporation, BT3554).

[0110] Example 1-1

[0111] <Preparation of negative electrode>

[0112] A negative electrode current collector is obtained by electroplating a copper layer on one surface of the first polymer layer. The thickness of the first polymer layer is C = 3.0 μm, and the material of the first polymer layer is PET (weight-average molecular weight = 3 × 10⁻⁶). 4 The thickness of the copper layer is A = 2.0 μm. The surface of the copper layer that is in contact with the second polymer layer is denoted as the first surface, and the surface that is not in contact with the first polymer layer is denoted as the second surface.

[0113] The negative electrode active material is artificial graphite, the negative electrode active material is silicon, and the negative electrode binder is styrene-butadiene rubber (SBR, with a weight average molecular weight of 5×10⁻⁶). 6The conductive carbon and negative electrode conductive agent were mixed in a mass ratio of 74:20:5:1, and then deionized water was added as a solvent. The mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 50 wt% was obtained. The negative electrode slurry was uniformly coated onto the second surface of the copper layer, dried at 90°C, and then cold-pressed and slit to obtain negative electrode sheets with a size of 76 mm × 856 mm for later use. The compaction density of the negative electrode active material layer was 1.6 g / cm³. 3 .

[0114] <Preparation of the positive electrode>

[0115] A positive electrode current collector is obtained by vacuum evaporation depositing an aluminum layer on one surface of the second polymer layer. The thickness of the second polymer layer is D = 2.0 μm, and the material of the second polymer layer is PET (weight-average molecular weight = 3 × 10⁻⁶). 4 The thickness of the aluminum layer is B = 4.0 μm. The surface of the aluminum layer that is in contact with the second polymer layer is designated as the third surface, and the surface that is not in contact with the second polymer layer is designated as the fourth surface.

[0116] The positive electrode active material is lithium nickel cobalt manganese oxide (NCM811), the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight-average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was then uniformly coated onto the fourth surface of the aluminum layer, dried at 90°C, and subsequently cold-pressed and slit to obtain positive electrode sheets with dimensions of 74 mm × 851 mm. The compaction density of the positive electrode active material layer was 3.5 g / cm³. 3 .

[0117] <Preparation of Bipolar Electrodes>

[0118] The surfaces of the first polymer layer of the negative electrode that are not in contact with the copper layer and the surfaces of the second polymer layer of the positive electrode that are not in contact with the aluminum layer are overlapped and hot-pressed at 80°C and 5t for 15 minutes to bond the negative electrode and the positive electrode together to form a bipolar electrode.

[0119] <Preparation of the separating membrane>

[0120] A porous polyethylene (PE) film with a thickness of 8 μm was used as the separator.

[0121] <Preparation of Electrolyte>

[0122] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed thoroughly in a mass ratio of 20:30:40:10. Then, lithium hexafluorophosphate (LiPF6) was added and the mixture was stirred until homogeneous to obtain the electrolyte. The concentration of the lithium salt in the electrolyte was 1 mol / L.

[0123] <Preparation of Lithium-ion Batteries>

[0124] After stacking the separator and bipolar electrode sheets, they are wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film in a packaging bag, and after dehydration at 80°C, the electrolyte is injected and the assembly is sealed. After processes such as formation, degassing, and shaping, a lithium-ion battery is obtained.

[0125] Examples 1-2

[0126] <Preparation of Bipolar Electrodes>

[0127] In the first polymer layer of the negative electrode sheet, on the surface that is not in contact with the copper layer, an adhesive layer material of polyacrylic acid (weight average molecular weight = 8 × 10⁻⁶) is coated. 5 After overlapping the surfaces of the second polymer layer of the positive electrode that are not in contact with the aluminum layer, the electrode is rolled at 5t and then dried at 80℃. An adhesive layer is formed between the negative electrode and the positive electrode, and the two electrodes are bonded together to form a bipolar electrode.

[0128] The preparation of the negative electrode, positive electrode, separator, electrolyte, and lithium-ion battery are the same as in Examples 1-1.

[0129] Examples 1-3 to Examples 1-27

[0130] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-2.

[0131] Examples 2-1 to 2-7

[0132] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-2.

[0133] Examples 3-1 to 3-8

[0134] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-2.

[0135] Comparative Examples 1 to 3

[0136] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-2.

[0137] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0138] Table 1 Note: In Table 1, "\" indicates that there is no corresponding parameter.

[0139] Table 2

[0140] As can be seen from Examples 1-1 to 1-10, the electrochemical devices in this application form a bipolar current collector by connecting the negative electrode current collector and the positive electrode current collector through a first polymer layer and a second polymer layer. The thickness A of the copper layer and the value of B / A are controlled within the range of this application. The negative electrode current collector has a high tensile strength Rm1, and the positive electrode current collector has a high tensile strength Rm2. The electrochemical device has a high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion rate. This indicates that the electrochemical devices in this application simultaneously possess high energy density and good cycle performance, meaning that the energy density and cycle performance of the electrochemical devices in this application are improved. In contrast, the electrochemical devices in Comparative Examples 1 to 3 have at least one of the copper layer thickness A or the value of B / A that is not within the range of this application. The comparative examples have lower energy density, higher internal resistance, or lower cycle capacity retention and higher cycle expansion rate, indicating that the electrochemical devices in the comparative examples of this application cannot simultaneously achieve high energy density and high cycle performance.

[0141] The placement of the adhesive layer in a bipolar current collector typically affects the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-1 and 1-2, the electrochemical device with the adhesive layer in the bipolar current collector within the scope of this application exhibits high tensile strength Rm1 in its negative electrode current collector and high tensile strength Rm2 in its positive electrode current collector. This results in a higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, demonstrating that the electrochemical device of this application possesses high energy density and excellent cycle performance.

[0142] The thickness A of the copper layer, the thickness B of the aluminum layer, and the B / A ratio typically affect the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2 to 1-12, Examples 1-21 to 1-23, and Comparative Examples 1 to 3, electrochemical devices with copper layer thickness A, aluminum layer thickness B, and B / A values ​​within the scope of this application exhibit higher tensile strength Rm1 in the negative electrode current collector and higher tensile strength Rm2 in the positive electrode current collector. These electrochemical devices also demonstrate higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, indicating that the electrochemical device of this application possesses both high energy density and good cycle performance. In Examples 1-2, 1-9 to 1-12, and especially in Examples 1-2, 1-10, and 1-11, the electrochemical devices balance high energy density and high cycle performance; therefore, 1.5 to 2.5 is a preferred range for B / A. Compared to Examples 1-5 and 1-6, Examples 1-8 have lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, but lower energy density. Examples 1-5 and 1-6 are better able to balance high energy density and high cycle performance of electrochemical devices.

[0143] The thickness C of the first polymer layer, the thickness D of the second polymer layer, and the C / D ratio typically affect the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2, 1-13 to 1-21 and 1-23, electrochemical devices with the thickness C of the first polymer layer, the thickness D of the second polymer layer, and the C / D ratio within the scope of this application exhibit higher tensile strength Rm1 in the negative electrode current collector and higher tensile strength Rm2 in the positive electrode current collector. These electrochemical devices also demonstrate higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, thus indicating that the electrochemical device of this application possesses higher energy density and better cycle performance. In Examples 1-13 to 1-21, although Example 1-17 has a higher cycle capacity retention rate and a lower cycle expansion rate compared to Examples 1-13 to 1-16 and Examples 1-18 to 1-21, its energy density is lower. Therefore, compared to Example 1-17, Examples 1-13 to 1-16 and Examples 1-18 to 1-21 can better balance the high energy density and high cycle performance of the electrochemical device.

[0144] The thickness of the adhesive layer typically affects the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2, 1-24 to 1-27, electrochemical devices with adhesive layer thicknesses within the scope of this application exhibit higher tensile strength Rm1 in the negative electrode current collector and higher tensile strength Rm2 in the positive electrode current collector. These electrochemical devices demonstrate higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, thus indicating that the electrochemical device of this application possesses higher energy density and better cycle performance.

[0145] Table 3 Note: "Mw" in Table 3 represents the weight-average molecular weight.

[0146] The material types of the first polymer layer and / or the second polymer layer typically affect the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2 and Examples 2-1 to 2-5, electrochemical devices whose first and / or second polymer layers are within the scope of this application exhibit higher tensile strength Rm1 in their negative electrode current collector and higher tensile strength Rm2 in their positive electrode current collector. These electrochemical devices demonstrate higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, thus indicating that the electrochemical device of this application possesses higher energy density and better cycle performance.

[0147] The type of material used in the adhesive layer typically affects the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2, 2-6, and 2-7, electrochemical devices with adhesive layer materials within the scope of this application exhibit higher tensile strength Rm1 in the negative electrode current collector and higher tensile strength Rm2 in the positive electrode current collector. These devices demonstrate higher energy density, lower internal resistance, higher cycle capacity retention, and lower cycle expansion rate, indicating that the electrochemical device of this application possesses both high energy density and excellent cycle performance.

[0148] Table 4

[0149] The compaction density of the negative electrode active material layer typically affects the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2 and 3-1 to 3-4, for electrochemical devices with a compaction density of the negative electrode active material layer within the scope of this application, the peel strength F1 between the negative electrode active material layer and the copper layer in the bipolar electrode is within the scope of this application. The negative electrode current collector has a high tensile strength Rm1, and the positive electrode current collector has a high tensile strength Rm2. The electrochemical device exhibits a high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion rate, thus demonstrating that the electrochemical device of this application possesses high energy density and good cycle performance.

[0150] The compaction density of the positive electrode active material layer typically affects the energy density and cycle performance of an electrochemical device. As can be seen from Examples 1-2, 3-5 to 3-8, for electrochemical devices where the compaction density of the negative electrode active material layer falls within the scope of this application, the peel strength F2 between the positive electrode active material layer and the aluminum layer in the bipolar electrode is also within the scope of this application. The negative electrode current collector exhibits high tensile strength Rm1, and the positive electrode current collector exhibits high tensile strength Rm2. The electrochemical device demonstrates high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion rate, thus indicating that the electrochemical device of this application possesses high energy density and good cycle performance.

[0151] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0152] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0153] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A bipolar current collector, comprising: a negative current collector comprising a first polymer layer and a first metal layer, the first metal layer being disposed on one side surface of the first polymer layer along a thickness direction of the bipolar current collector, the first metal layer being a copper layer; a positive current collector comprising a second polymer layer and a second metal layer, the second metal layer being disposed on one side surface of the second polymer layer along the thickness direction, the second metal layer being an aluminum layer; the first metal layer, the first polymer layer, the second polymer layer and the second metal layer are sequentially arranged along the thickness direction, the first polymer layer being connected to the second polymer layer; a thickness of the copper layer is A μm, a thickness of the aluminum layer is B μm, A and B satisfy: 0.8≤A≤3.0, 1.2≤B / A≤3.

5.

2. The bipolar current collector of claim 1, wherein, 1.0≤B≤8.0。 3. The bipolar current collector of claim 1 or 2, wherein, The bipolar current collector further comprises a bonding layer connecting the first polymer layer and the second polymer layer.

4. The bipolar current collector of any one of claims 1 to 3, wherein, a thickness of the first polymer layer is C μm, a thickness of the second polymer layer is D μm, C and D satisfy: 1.6≤D≤8.0, 1.2≤C / D≤3.

0.

5. The bipolar current collector of claim 4, wherein, 2.0≤C≤10.0。 6. The bipolar current collector of claim 4, wherein, The bipolar current collector satisfies at least one of the following: (1) 1.5≤B / A≤2.5; (2) 1.5≤C / D≤2.

5.

7. The bipolar current collector of any one of claims 1 to 6, wherein, The material of the first polymer layer and the material of the second polymer layer each independently comprise at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride or polyethylene terephthalate.

8. The bipolar current collector of any one of claims 1 to 7, wherein, a tensile strength of the negative current collector is 150 MPa to 220 MPa; and / or, a tensile strength of the positive current collector is 150 MPa to 240 MPa.

9. The bipolar current collector of claim 3, wherein, a thickness of the bonding layer is 1 μm to 4 μm.

10. The bipolar current collector of claim 3, wherein, The material of the bonding layer comprises at least one of epoxy resin, polyacrylic acid, polyurethane or polyvinyl chloride.

11. A bipolar electrode tab comprising the bipolar current collector of any one of claims 1 to 10, wherein, The bipolar electrode sheet further includes a negative electrode active material layer provided on a side surface of the copper layer away from the first polymer layer in the thickness direction, the negative electrode active material layer having a compaction density of 1.1 g / cm 3 to 2.0 g / cm 3 ; The bipolar electrode sheet further includes a positive electrode active material layer provided on a side surface of the aluminum layer away from the second polymer layer in the thickness direction, the positive electrode active material layer having a compaction density of 2.5 g / cm 3 to 4.5 g / cm 3 .

12. The bipolar pole piece of claim 11, wherein, a peeling strength between the negative active material layer and the copper layer is 10 N / m to 20 N / m, and a peeling strength between the positive active material layer and the aluminum layer is 12 N / m to 20 N / m. 13.An electrochemical device comprising the bipolar current collector according to any one of claims 1 to 10 or the bipolar electrode according to claim 11 or 12.

14. An electrical device, comprising: The electric device comprises the electrochemical device according to claim 13.

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