Bipolar current collector, bipolar pole piece, electrochemical device and electronic device

Abstract

The invention discloses a bipolar current collector, a bipolar pole piece, an electrochemical device and an electronic device. The bipolar current collector comprises a negative current collector and a positive current collector, the negative current collector comprises a first polymer layer and a first metal layer, the first metal layer is arranged on the surface of one side of the first polymer layer along the thickness direction, and the first metal layer is a copper layer; the positive current collector comprises a second polymer layer and a second metal layer, the second metal layer is arranged on the surface of one side of the second polymer layer along the thickness direction, and the second metal layer is an aluminum layer; the first metal layer, the first polymer layer, the second polymer layer and the second metal layer are sequentially arranged in the thickness direction of the bipolar current collector, and the first polymer layer is connected to the second polymer layer; the thickness of the copper layer is A [mu] m, the thickness of the aluminum layer is B [mu] m, A and B meet the following conditions: 0.8 < = A < = 3.0, and 1.2 < = B / A < = 3.5. When the bipolar current collector is applied to an electrochemical device, the energy density and the cycle performance of the electrochemical device can be improved.

Description

Bipolar current collector, bipolar pole piece, electrochemical device and electronic device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a bipolar current collector, a bipolar pole piece, an electrochemical device, and an electronic device. Background Art

[0002] Electrochemical devices, such as lithium-ion batteries, have advantages such as high specific energy, high operating voltage, low self-discharge rate, compact size, and light weight, making them widely used in consumer electronics. Current collectors are an essential component of lithium-ion batteries, and bipolar current collectors are gaining increasing attention due to their high toughness and lightweight design. However, existing bipolar current collectors in lithium-ion batteries suffer from insufficient bonding strength with the active material layer and large differential expansion between the positive and negative electrodes, which compromises the electrochemical performance of lithium-ion batteries.

[0003] Summary of the Invention

[0004] The purpose of the present application is to provide a bipolar current collector, a bipolar pole piece, 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 in the invention content 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. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a bipolar current collector, which includes a negative electrode current collector and a positive electrode current collector; the negative electrode current collector includes a first polymer layer and a first metal layer, and along the thickness direction of the bipolar current collector, the first metal layer is arranged on one side surface of the first polymer layer, and the first metal layer is a copper layer; the positive electrode current collector includes a second polymer layer and a second metal layer, and along the thickness direction, the second metal layer is arranged 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 in sequence, and the first polymer layer is connected to the second polymer layer; the thickness of the copper layer is Aμm, the thickness of the aluminum layer is Bμm, and A and B satisfy: 0.8≤A≤3.0, 1.2≤B / A≤3.5.

[0007] In the present application, the negative electrode current collector and the positive electrode current collector are connected through the first polymer layer and the second polymer layer to form a bipolar current collector, and the thickness A of the copper layer and the value of B / A are regulated within the scope of the present application. This is beneficial to reducing the weight of the current collector in the electrochemical device and improving 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 the copper layer is beneficial to reducing the contact impedance 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, the application of the bipolar current collector of the present application in the electrochemical device is beneficial to improving the energy density and cycle performance of the electrochemical device.

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

[0009] In one embodiment of the present application, the bipolar current collector further includes an adhesive layer connecting the first polymer layer and the second polymer layer. The provision of the adhesive layer is beneficial for improving the strength of the bipolar current collector and the cycling performance of the electrochemical device using the bipolar current collector.

[0010] In one embodiment of the present application, the thickness of the first polymer layer is C μm, the thickness of the second polymer layer is D μm, and C and D satisfy the following conditions: 1.6 ≤ D ≤ 8.0, and 1.2 ≤ C / D ≤ 3.0. Controlling the thickness D of the second polymer layer and the C / D ratio within the above ranges can help reduce the volume expansion rate of the electrochemical device during cycling and improve its cycling performance.

[0011] In one embodiment of the present application, 2.0≤C≤10.0. Adjusting the thickness C of the first polymer layer within the above range is beneficial to reducing the volume expansion rate of the electrochemical device during cycling and improving the cycling performance of the electrochemical device.

[0012] In one embodiment of the present 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 the present application, the material of the first polymer layer and the material of the second polymer layer each independently include at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyethylene terephthalate. The use of these materials for the first and second polymer layers can improve the energy density and cycling performance of the electrochemical device.

[0014] In one embodiment of the present 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. Having good tensile strength in both the negative and positive electrode current collectors is beneficial for improving the cycling performance of the electrochemical device.

[0015] In one embodiment of the present application, the thickness of the adhesive layer is 1 μm to 4 μm. Adjusting the thickness of the adhesive layer within the above range is beneficial to improving the strength of the bipolar current collector, increasing the energy density of the electrochemical device and achieving good cycle performance.

[0016] In one embodiment of the present application, the adhesive layer comprises at least one of epoxy resin, polyacrylic acid, polyurethane, or polyvinyl chloride. The aforementioned adhesive layer materials have excellent bonding properties, which are beneficial for increasing the strength of the bipolar current collector and improving the cycling performance of the electrochemical device.

[0017] The second aspect of the present application provides a bipolar pole piece, the bipolar pole piece includes the bipolar current collector described in any of the above embodiments, wherein the bipolar pole piece further includes a negative electrode active material layer, the negative electrode active material layer is provided on the side 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 1.1g / cm 3 Up to 2.0g / cm 3 The bipolar electrode also includes a positive electrode active material layer, which is provided on the surface of the aluminum layer away from the second polymer layer along the thickness direction. The compaction density of the positive electrode active material layer is 2.5 g / cm 3 Up to 4.5g / cm 3 By regulating the compaction density of the negative electrode active material layer and the positive electrode active material layer within the above range, the electrochemical device has good cycle performance and high energy density.

[0018] In one embodiment of the present 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 the present application provides an electrochemical device comprising the bipolar current collector or the bipolar pole piece described in any of the aforementioned embodiments. Thus, the electrochemical device has good cycle performance and high energy density.

[0020] A fourth aspect of the present application provides an electrical device comprising the electrochemical device described in any of the aforementioned embodiments.

[0021] Beneficial effects of this application:

[0022] The present application provides a bipolar current collector, a bipolar pole piece, an electrochemical device and an electronic device, wherein the bipolar current collector is formed by connecting the negative electrode current collector and the positive electrode current collector in the present application through a first polymer layer and a second polymer layer, and the thickness A of the copper layer and the value of B / A are regulated within the scope of the present application. It is beneficial to reduce the weight of the bipolar current collector and improve 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 the copper layer is beneficial to reduce the contact impedance of the positive electrode current collector, reduce the internal resistance of the electrochemical device, and thus improve the cycle performance of the electrochemical device. Therefore, the application of the bipolar current collector of the present application in the electrochemical device is beneficial to improve the energy density and cycle performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0024] FIG1 is a schematic diagram of the cross-sectional structure of a bipolar current collector along its thickness direction in one embodiment of the present application;

[0025] FIG2 is a schematic diagram of the cross-sectional structure of a bipolar current collector along its thickness direction in another embodiment of the present application;

[0026] FIG3 is a schematic diagram of the cross-sectional structure of a bipolar pole piece along its thickness direction in one embodiment of the present application;

[0027] FIG4 is a schematic diagram of the cross-sectional structure of a bipolar pole piece along its thickness direction in another embodiment of the present application.

[0028] Figure markings: 1010 - bipolar current collector, 1020 - bipolar pole piece, 11 - first polymer layer, 12 - first metal layer, 101 - negative electrode current collector, 102 - negative electrode active material layer, 21 - second polymer layer, 22 - second metal layer, 201 - positive electrode current collector, 202 - positive electrode active material layer, 122 - first side, 222 - second side, 30 - bonding layer. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. 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 the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0031] The first aspect of the present application provides a bipolar current collector, which includes a negative electrode current collector and a positive electrode current collector; the negative electrode current collector includes a first polymer layer and a first metal layer, and along the thickness direction of the bipolar current collector, the first metal layer is arranged on one side surface of the first polymer layer, and the first metal layer is a copper layer; the positive electrode current collector includes a second polymer layer and a second metal layer, and along the thickness direction, the second metal layer is arranged 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 in sequence, and the first polymer layer is connected to the second polymer layer; the thickness of the copper layer is Aμm, the thickness of the aluminum layer is Bμm, and A and B satisfy: 0.8≤A≤3.0, 1.2≤B / A≤3.5.

[0032] For ease of understanding, in this application, the width direction of the bipolar current collector itself is defined as Y, and the thickness direction is defined as Z. It should be understood that the above definition of direction is for the purpose of convenient description of this application, and the direction defined in this application can be understood based on the relative position of the accompanying drawings and the actual product elements. It can be understood that the width direction, length direction and thickness direction of the positive and negative current collectors themselves 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 electrode 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 indicated by A. The positive electrode 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 indicated by 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 in sequence, 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 directly in contact and connected. In another embodiment, as shown in FIG2 , the first polymer layer 21 and the second polymer layer 22 are connected via an adhesive layer 30.

[0033] For example, A is 0.8, 1.0, 1.3, 1.6, 1.7, 1.9, 2, 2.2, 2.6, 2.9, 3.0, or any value between any two of the aforementioned numerical ranges. For example, B / A is 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 between any two of the aforementioned numerical ranges. If A is less than 0.8, the copper layer thickness is too small, and insufficient copper layer strength will cause the negative electrode current collector to easily break, affecting its normal use. If A is greater than 3.0, the copper layer thickness is too large, which will increase the volume of the negative electrode current collector. When the negative electrode current collector is used in an electrochemical device, it will reduce the energy density of the electrochemical device. The negative electrode current collector uses a copper layer as a conductive layer, and the positive electrode current collector uses an aluminum layer as a 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 will affect the contact impedance of the positive electrode current collector, and the magnitude of the positive electrode current collector's contact impedance will affect the cycling 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 will affect the weight of the negative electrode current collector and the positive electrode current collector, thereby affecting the energy density of the electrochemical device. If B / A is less than 1.2, the copper layer is relatively thick, and the negative electrode current collector is too heavy. When the negative electrode current collector is used in an electrochemical device, the increased weight of the electrochemical device will result in a loss in its energy density. If B / A is greater than 3.5, the aluminum layer is too thick relative to the copper layer, the contact impedance of the positive electrode current collector will be too high, and the ohmic polarization and concentration polarization of the electrochemical device will increase, thereby reducing the cycling performance of the electrochemical device.

[0034] In general, in the present application, the negative electrode current collector and the positive electrode current collector are connected through the first polymer layer and the second polymer layer to form a bipolar current collector, and the thickness A of the copper layer and the value of B / A are regulated within the scope of the present application, which is conducive to reducing the weight of the current collector in the electrochemical device and improving 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 the copper layer is conducive to reducing the contact impedance 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, the application of the bipolar current collector of the present application in the electrochemical device is conducive to improving the energy density and cycle performance of the electrochemical device.

[0035] In one embodiment of the present 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 regulating the thickness B of the aluminum layer within the above range, the aluminum layer has higher strength, the risk of fracture 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 the present 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 foregoing ranges. Controlling the B / A value within the range of 1.5 to 2.5 is beneficial for further improving the energy density and cycling performance of the electrochemical device.

[0037] In one embodiment of the present application, the bipolar current collector further comprises an adhesive layer, which connects the first polymer layer and the second polymer layer. As shown in FIG2 , the bipolar current collector 1010 comprises 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 provision of the adhesive layer is conducive to improving the bonding performance between the positive electrode current collector and the negative electrode current collector, and improving the strength of the bipolar current collector, thereby helping to increase the service life of the bipolar current collector, so that the electrochemical device using the bipolar current collector has good cycle performance.

[0038] In one embodiment of the present 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 the following: 1.6 ≤ D ≤ 8.0, 1.2 ≤ C / D ≤ 3.0. For example, D is 1.6, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, or any value between any two of the aforementioned numerical ranges. For example, C / D is 1.2, 1.5, 1.7, 1.9, 2.0, 2.1, 2.3, 2.6, 2.8, 3.0, or any value between any two of the aforementioned numerical 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 aforementioned ranges facilitates the first polymer layer to absorb the expansion of the negative electrode active material, thereby reducing the volume expansion rate of the electrochemical device during cycling. As a result, the electrochemical device can further improve its cycling performance while maintaining a higher energy density.

[0039] In one embodiment of the present 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 foregoing ranges. Controlling the thickness C of the first polymer layer within the foregoing range facilitates the first polymer layer absorbing 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 cycling performance of the electrochemical device.

[0040] In one embodiment of the present 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 regulating the C / D value within the above range, the electrochemical device can have better cycling performance while having a higher energy density.

[0041] In one embodiment of the present 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 aforementioned numerical 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 aforementioned numerical ranges. Simultaneously regulating B / A and C / D within the aforementioned ranges can further improve the energy density and cycling performance of the electrochemical device.

[0042] In one embodiment of the present application, the material of the first polymer layer and the material of the second polymer layer each independently include at least one of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) or polyethylene terephthalate (PET). The above-mentioned types of materials have the characteristics of low density, light weight, high temperature resistance, and not easily corroded by electrolyte. The selection of the above-mentioned types of materials as the materials for the first polymer layer and the second polymer layer is conducive to making the bipolar current collector have a lighter weight, good stability during use in the electrochemical device, and can also better absorb the expansion and deformation of the positive electrode active material and the negative electrode active material. Therefore, the application of the bipolar current collector in the electrochemical device is conducive to improving the energy density and cycle performance of the electrochemical device.

[0043] In one embodiment of the present application, the material of the first polymer layer is the same as or different from the material of the second polymer layer. For example, 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 polymer layer and the second polymer layer facilitates adhesion between the first polymer layer and the second polymer layer, and helps reduce production costs and increase production efficiency during the preparation of the bipolar current collector.

[0044] In one embodiment of the present application, the tensile strength of the negative electrode current collector is 150 MPa to 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 numerical ranges. The negative electrode current collector has good tensile strength. Using the negative electrode current collector to prepare a bipolar current collector is beneficial for making the bipolar current collector have a higher tensile strength. Further, when applied to an electrochemical device, it is beneficial to have good impact resistance when the electrochemical device is subjected to an impact or other working conditions, thereby improving the safety performance of the electrochemical device while having a higher energy density and good cycle performance.

[0045] In one embodiment of the present application, the tensile strength of the positive electrode current collector is 150MPa to 240MPa. For example, the tensile strength of the positive electrode current collector is 150MPa, 161MPa, 168MPa, 179MPa, 190MPa, 200MPa, 209MPa, 214MPa, 224MPa, 230MPa, 236MPa, 240MPa or any value between any two of the above numerical ranges. This shows that the positive electrode current collector has good tensile strength. Using the positive electrode current collector to prepare a bipolar current collector is beneficial for making the bipolarity have a higher tensile strength, and then applied to electrochemical devices, which is beneficial for having good impact resistance when the electrochemical device is impacted, thereby improving the safety performance of the electrochemical device while having a higher 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 particularly limit the method for regulating 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 regulating 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, and the tensile strength of the negative current collector can be achieved by regulating 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 the present application, as shown in FIG2 , the thickness T of the adhesive layer 30 is 30 The thickness of the adhesive layer is 1 μm to 4 μm. For example, the thickness of the adhesive layer is 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 the above ranges helps ensure that the bipolar current collector has an appropriate thickness while also exhibiting good bonding properties. Consequently, when the bipolar current collector is used in an electrochemical device, the electrochemical device has a higher energy density and good cycling performance.

[0048] In one embodiment of the present application, the bonding layer material includes at least one of epoxy resin, polyacrylic acid, polyurethane, or polyvinyl chloride. The bonding layer materials of the aforementioned types have good bonding properties, which facilitates bonding the positive electrode current collector and the negative electrode current collector to form a bipolar current collector with good performance.

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

[0050] It should be noted that the positive and negative active material layers have the same width, length, and thickness as the bipolar current collector. As shown in Figures 3 and 4, bipolar pole piece 1020 includes bipolar current collector 1010, negative active material layer 102, and positive active material layer 202. Negative active material layer 102 is disposed on first side 122 of first metal layer 12, where first side 122 is the side of first metal layer 12 away from first polymer layer 11 along the thickness direction Z. Positive active material layer 202 is disposed on second side 222 of second metal layer 22, where second side 222 is the side of second metal layer 22 away from 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 / cm 3 Up to 2.0g / cm 3 For example, the compaction density of the negative electrode active material layer is 1.1 g / cm 3 , 1.2g / cm 3, 1.3g / 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 numerical ranges mentioned above. For example, the compacted density of the positive electrode active material layer is 2.5 g / cm 3 Up to 4.5g / cm 3 For example, the compaction density of the positive electrode active material layer is 2.5 g / cm 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 numerical ranges mentioned above.

[0052] By regulating the compaction density of the negative electrode active material layer within the above range, the risk of the negative electrode active material rupture is low, the negative electrode active material particles also have good contact, the surface of the negative electrode active material particles has good interfacial stability, and the negative electrode active material layer has a relatively low thickness while having more negative electrode active material. By regulating the compaction density of the positive electrode active material layer within the above range, the risk of the positive electrode active material rupture is low, the positive electrode active material particles also have good contact, the surface of the positive electrode active material particles has good interfacial stability, and the positive electrode active material layer has a relatively low thickness while having more positive electrode active material. In this way, the bipolar pole piece is applied to the electrochemical device, which can enable the electrochemical device to have good cycle performance and high energy density.

[0053] The present application does not particularly limit the method for controlling the compaction density of the positive electrode active material layer and the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, this can be achieved by controlling the pressure of cold pressing the positive electrode sheet and the negative electrode sheet.

[0054] In one embodiment of the present 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 foregoing ranges. Thus, the bipolar electrode sheet can be used in an electrochemical device to provide the electrochemical device with excellent cycling performance.

[0055] In one embodiment of the present application, the peel strength between the positive electrode active material layer and the aluminum layer is 12 N / m to 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 foregoing ranges. Thus, the bipolar electrode sheet is applied to an electrochemical device, thereby enabling the electrochemical device to have excellent cycling performance.

[0056] The present application does not particularly limit the method for regulating the peel strength between the negative electrode active material layer and the copper layer, and the peel strength between the positive electrode active material layer and the aluminum layer, as long as the purpose of the present application can be achieved. For example, the peel strength between the negative electrode active material layer and the copper layer can be achieved by regulating 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 regulating 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 restrictions on the positive electrode active material layer, as long as the objectives of this application can be achieved. For example, the positive electrode active material layer of this application comprises a positive electrode active material. This application does not impose any particular restrictions on the type of positive electrode active material, as long as the objectives of this application can be achieved. For example, the positive electrode active material may comprise at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. In this application, the positive electrode active material may also comprise non-metallic elements, which may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive electrode active material. This application does not impose any particular restrictions on the thickness of the positive electrode active material layer, as long as the objectives of this application can be achieved. 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 further comprise at least one of a positive electrode conductive agent or a positive electrode binder. This application does not impose any particular restrictions on the type of positive electrode conductive agent or positive electrode binder in the positive electrode active material layer, as long as the objectives of this application can be achieved. The present application does not particularly limit the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer. Those skilled in the art can select the mass ratio according to actual needs as long as the purpose of the present application can be achieved.

[0058] There is no particular limitation on the negative electrode active material layer in this application, as long as the object of this application can be achieved. For example, the negative electrode active material layer in this application contains a negative electrode active material. There is no particular limitation on the type of the negative electrode active material in this application, as long as the object of this application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, mesophase microcarbon beads (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 metallic lithium. There is no particular limitation on the thickness of the negative electrode active material layer in this application, as long as the object of this 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. There is no particular limitation on the types of the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer in this application, as long as the object of this application can be achieved. There is no particular limitation 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 in this application, as long as the object of this application can be achieved.

[0059] There is no particular limitation on the preparation method of the bipolar electrode in this application, as long as the object of this application can be achieved. In one embodiment of this application, the preparation method of the bipolar electrode 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 slurry 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 slurry 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, the first polymer layer is connected to the second polymer layer to form a bipolar electrode.

[0060] In another embodiment of the present application, the preparation method of the bipolar electrode sheet includes but is not limited to the following steps: (i) plating a first metal layer on one surface of a first polymer layer to obtain a negative electrode current collector; uniformly coating a negative electrode slurry on the surface of the first metal layer away from the first polymer layer in the thickness direction, drying, cold pressing, and cutting to obtain a negative electrode sheet; (ii) plating a second metal layer on one surface of a second polymer layer to obtain a positive electrode current collector; uniformly coating a positive electrode slurry on the surface of the second metal layer away from the second polymer layer in the thickness direction, drying, cold pressing, and cutting to obtain a positive electrode sheet; (iii) coating an adhesive layer material on one of the other surface of the first polymer layer not in contact with the first metal layer and the other surface of the second polymer layer not in contact with the second metal layer, overlapping the other, first rolling and then drying, so that an adhesive layer is formed between the negative electrode current collector and the positive electrode 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 preparation method prepares the positive electrode sheet and the negative electrode sheet separately, and then recombines the positive electrode sheet and the negative electrode sheet to form a bipolar electrode sheet. The process is simple and the layers of the bipolar electrode sheet have good adhesion, which greatly reduces the probability of delamination of the layers. The positive active material layer and the negative active material layer of the present application are both set on one side, and are cold-pressed separately and then recombined to form a bipolar electrode sheet. This is conducive to controlling the compaction density of the positive active material layer and the negative active material layer, so that both the positive active material layer and the negative active material layer have a suitable compaction density. The bipolar electrode sheet thus prepared is used in an electrochemical device, so that the electrochemical device has good cycle performance and high energy density.

[0062] The present application has no particular restrictions on the method of plating the first metal layer in the above steps (1) and (i), as long as the purpose of the present application can be achieved. For example, the first metal layer can be plated on the surface of the first polymer layer by electroplating. The present application has no 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 the present application can be achieved. The present application has no particular restrictions on the process parameters of drying and cold pressing in the above steps (1) and (i), and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the method of plating the second metal layer in the above steps (2) and (ii), as long as the purpose of the present application can be achieved. For example, the second metal layer can be plated on the surface of the second polymer layer by vacuum evaporation. The present application has no 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 the present application can be achieved. The present application has no particular restrictions on the process parameters of drying and cold pressing in the above steps (2) and (ii), and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. The present application does not particularly limit the process parameters of the hot pressing treatment in the above step (3). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the temperature of the hot pressing is 70°C to 90°C, the pressure is 4t to 6t, and the time is 5min to 20min. The present application does not particularly limit the process parameters of the rolling and drying in the above step (iii). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the pressure of the rolling is 4t to 6t, and the temperature of the drying is 70°C to 90°C.

[0063] A third aspect of the present application provides an electrochemical device comprising the bipolar current collector or the bipolar pole piece described in any of the aforementioned embodiments. Thus, the electrochemical device has good cycle performance and high energy density.

[0064] In one embodiment of the present application, the electrochemical device further comprises a diaphragm. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. The material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE) and polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) films), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. The present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved.

[0065] The electrochemical device of the present application also includes a packaging bag and an electrolyte. The present application has no particular restrictions on the packaging bag and the electrolyte, and can be any packaging bag and electrolyte known in the art, as long as they can achieve the purpose of the present application.

[0066] The electrochemical device of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0067] This application does not particularly limit the preparation method of the electrochemical device, as long as the objectives of this application can be achieved. For example, the preparation method of the electrochemical device includes, but is not limited to, the following steps: stacking a separator and bipolar pole pieces, winding to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device; or stacking a separator and bipolar pole pieces, then securing the four corners of the entire stack to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device.

[0068] A fourth aspect of the present application provides an electrical device comprising the electrochemical device described in any of the aforementioned embodiments.

[0069] The electrical equipment of the present application is not particularly limited and can be any electrical equipment known in the prior art. For example, the electrical equipment can include, but is not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0070] Example

[0071] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0072] Test methods and equipment:

[0073] Tensile strength test:

[0074] At an ambient temperature of 25°C, the lithium-ion battery is discharged to 2V at 0.2C and then disassembled. The bipolar pole piece is removed and soaked in dimethyl carbonate (DMC) for 20 minutes. The bipolar pole piece is then placed in an oven and dried at 80°C for 12 hours. After removing the negative active material layer and the positive active material layer on the surface of the bipolar pole piece, it is soaked in N,N-dimethylformamide (DMF) for 1 hour. The edges of the first polymer layer and the second polymer layer are separated by a cutter, and the first polymer layer and the second polymer layer are separated by a clamp. If an adhesive layer is contained, the edges of the adhesive layer and the first polymer layer and the adhesive layer and the second polymer layer are separated by a cutter, and the first polymer layer and the second polymer layer are separated from the adhesive layer respectively by a clamp to obtain a negative current collector and a positive current collector. The negative current collector and the positive current collector are then placed in an oven and dried at 80°C for 12 hours for use.

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

[0076] Cut the negative electrode current collector into a sample with a size of width × length = 15 mm × 200 mm, measure the thickness h1 (μm) of the sample with a micrometer, and perform a tensile test using a high-speed rail tensile tester at room temperature and pressure. Set the initial position and make the sample 50 mm long between the clamps. Stretching is carried out at a speed of 50 mm / min, and record the load L1 (N) until it breaks. The tensile strength Rm1 = L1 / (15×h1)×1000.

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

[0078] Cut the positive electrode current collector into a sample with a size of width × length = 15 mm × 200 mm, measure the thickness h2 (μm) of the sample with a micrometer, and 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 50 mm long between the clamps. Stretching is carried out at a speed of 50 mm / min, and record the load L2 (N) until it breaks. The tensile strength Rm2 = L2 / (15×h2)×1000.

[0079] Compaction density test:

[0080] At an ambient temperature of 25°C, the lithium-ion battery was discharged to 2V at 0.2C and then disassembled. The bipolar pole piece was taken out and soaked in dimethyl carbonate (DMC) for 20 minutes. The bipolar pole piece was then placed in an oven and dried at 80°C for 12 hours before the following test.

[0081] (1) Test of compaction density of negative electrode active material layer:

[0082] The thickness of the negative electrode active material layer was measured with a micrometer. The negative electrode active material layer was cut into 1 mm × 1 mm slices. The weight of the slices was measured with a balance. The negative electrode active material layer on the surface of the slices was removed. The remaining weight of the slices was measured with a balance. The compacted density of the negative electrode active material layer was PD1 (g / cm 3 )=(m1-m2) / ((T1×1×1)×10 -6 ).

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

[0084] The thickness of the positive electrode active material layer was measured with a micrometer. The positive electrode active material layer was cut into 1 mm × 1 mm slices. The weight of the slices was measured with a balance. The positive electrode active material layer on the surface of the slices was removed. The remaining weight of the slices was measured with a balance. The compacted density of the positive electrode active material layer was PD2 (g / cm 3 )=(m3-m4) / ((T2×1×1)×10 -6 ).

[0085] Peel strength test:

[0086] At an ambient temperature of 25°C, the lithium-ion battery was discharged to 2V at 0.2C and then disassembled. The bipolar pole piece was taken out and soaked in dimethyl carbonate (DMC) for 20 minutes. The bipolar pole piece was then placed in an oven and dried at 80°C for 12 hours before the following test.

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

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

[0089] 2) Clamping method: Use a clamp to clamp the sample and 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 appropriate for the sample size into the instrument. Then, peel the negative electrode active material layer and copper layer at a constant speed (100 mm / min) until they are completely separated. The applied force, L1, is recorded during the peeling process.

[0091] 4) Data recording and analysis: The force L1 applied during the peeling process was recorded, and the peel strength was calculated using the formula F1 = L1 / A, where A is the peeling 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 the bipolar pole piece obtained above into a sample with a width of 30 mm and a length of 150 mm. Ensure that the surface of the sample is clean and flat.

[0094] 2) Clamping method: Use a clamp to clamp the sample and 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 appropriate for the sample size into the instrument. Then, peel the positive electrode active material layer and aluminum layer at a constant speed (typically 100 mm / min) until they are completely separated. The applied force, L2, is recorded during the peeling process.

[0096] 4) Data recording and analysis: The force L2 applied during the peeling process was recorded, and the peel strength was calculated using the formula F2 = L2 / A, where A is the peeling length of the sample.

[0097] Energy density test:

[0098] At 25°C, charge a lithium-ion battery to 4.30V at a constant current of 0.2C, then charge it to 0.05C at a constant voltage of 4.30V and let it rest for 5 minutes. Then, discharge it to 2.0V at a constant current of 0.2C and let it rest for 5 minutes. Take the discharge energy at this point as the energy E of the lithium-ion battery. Measure the weight of the lithium-ion battery as m and calculate the energy density of the lithium-ion battery.

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

[0100] Cycle performance test:

[0101] (1) Capacity retention rate test:

[0102] At 25°C, charge a lithium-ion battery to 4.3V at a constant current of 1C, then charge it to 0.05C at a constant voltage of 4.3V, rest for 10 minutes, and then discharge it to 2.0V at a constant current of 4C, rest for 15 minutes. This constitutes one cycle. Repeat this cycle for 1000 times. Record the discharge capacity at the first cycle as the initial capacity Q0, and the discharge capacity at the 1000th cycle as Q2. Calculate the capacity retention of the lithium-ion battery.

[0103] The calculation formula of the capacity retention rate is: capacity retention rate (%) = Q2 / Q0×100%.

[0104] (2) Cyclic expansion rate test:

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

[0106] At 25°C, charge the lithium-ion battery to 4.3V at a constant current of 1C, then charge it to 0.05C at a constant voltage of 4.3V, and let it rest for 10 minutes; then discharge it to 2.0V at a constant current of 4C, and let it rest for 15 minutes. The above is one cycle, and the above cycle is repeated 1000 times. Then charge the lithium-ion battery to 4.3V at a constant current of 1C, then charge it to 0.05C at a constant voltage of 4.3V, and let it rest for 10 minutes. Test the thickness of the lithium-ion battery, which is recorded as T2.

[0107] The calculation formula of the cycle expansion ratio is: cycle expansion ratio (%) = (T2-T0) / T0×100%.

[0108] Internal resistance test:

[0109] The lithium-ion battery was placed in a 25°C environment and charged to 4.3V at a constant current of 1C. It was then charged to 0.05C at a constant voltage of 4.3V and left to rest for 10 minutes. The lithium-ion battery was then discharged to 3.6V at a constant current of 4C. An internal resistance tester (HIOKI Co., Ltd., BT3554) was used to apply a 1kHz AC signal to the lithium-ion battery and measure its AC voltage drop to obtain the internal resistance of the lithium-ion battery at this time.

[0110] Example 1-1

[0111] <Preparation of negative electrode sheet>

[0112] A copper layer is plated on one surface of the first polymer layer by electroplating to obtain a negative electrode current collector. 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 4 The copper layer had a thickness of A = 2.0 μm. The surface of the copper layer in contact with the second polymer layer was designated as the first surface, and the surface not in contact with the first polymer layer was designated as the second surface.

[0113] The negative electrode active material artificial graphite, the negative electrode active material silicon, the negative electrode binder styrene butadiene rubber (SBR, weight average molecular weight 5×10 6), the negative electrode conductive agent conductive carbon is mixed in a mass ratio of 74:20:5:1, and then deionized water is added as a solvent. The mixture is stirred under the action of a vacuum mixer until the solid content is 50wt% and the system is uniform. The negative electrode slurry is evenly coated on the second surface of the copper layer, dried at 90°C, and then cold pressed and cut to obtain a negative electrode sheet with a specification of 76mm×856mm for use. The compaction density of the negative electrode active material layer is 1.6g / cm 3 .

[0114] <Preparation of positive electrode sheet>

[0115] An aluminum layer is deposited on one surface of the second polymer layer by vacuum evaporation to obtain a positive electrode current collector. 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 4 The thickness of the aluminum layer was B = 4.0 μm. The surface of the aluminum layer in contact with the second polymer layer was designated as the third surface, and the surface not in contact with the second polymer layer was 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 5 ) were mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) was added as a solvent, and stirred in a vacuum mixer until a solid content of 75wt% and a uniform positive electrode slurry was obtained. The positive electrode slurry was evenly coated on the fourth surface of the aluminum layer, dried at 90°C, and then cold pressed and cut to obtain a positive electrode sheet with a size of 74mm×851mm for use. The compacted density of the positive electrode active material layer was 3.5g / cm 3 .

[0117] <Preparation of bipolar pole piece>

[0118] The surface of the first polymer layer of the negative electrode sheet that is not in contact with the copper layer and the surface of the second polymer layer of the positive electrode sheet that is not in contact with the aluminum layer are overlapped and placed, and hot pressing treatment is performed at a temperature of 80°C and a pressure of 5t for 15 minutes to bond the negative electrode sheet to the positive electrode sheet to form a bipolar electrode sheet.

[0119] <Preparation of Separator>

[0120] A polyethylene (PE) porous 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 ethyl methyl carbonate (EMC) were mixed in a mass ratio of 20:30:40:10. The electrolyte was then added with lithium hexafluorophosphate and stirred evenly to prepare 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 form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, injected with the aforementioned electrolyte, and packaged. After a series of processes including formation, degassing, and shaping, a lithium-ion battery is obtained.

[0125] Example 1-2

[0126] <Preparation of bipolar pole piece>

[0127] The surface of the first polymer layer of the negative electrode sheet that is not in contact with the copper layer is coated with an adhesive layer material polyacrylic acid (weight average molecular weight = 8×10 5 ), after the surface of the second polymer layer of the positive electrode sheet that is not in contact with the aluminum layer is overlapped and placed, it is rolled at 5t and then dried at 80°C to form an adhesive layer between the negative electrode sheet and the positive electrode sheet, and the bipolar electrode sheet is formed by bonding them together through the adhesive layer.

[0128] <Preparation of negative electrode sheet>, <Preparation of positive electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those in Example 1-1.

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

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

[0131] Example 2-1 to Example 2-7

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

[0133] Example 3-1 to Example 3-8

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

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

[0138] Table 1 Note: “\” in Table 1 indicates no corresponding parameter.

[0139] Table 2

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

[0141] The placement of an adhesive layer in a bipolar current collector typically affects the energy density and cycling performance of an electrochemical device. As can be seen from Examples 1-1 and 1-2, electrochemical devices with an adhesive layer within the scope of this application exhibit a high negative electrode current collector tensile strength Rm1 and a high positive electrode current collector tensile strength Rm2. These electrochemical devices also exhibit high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion. This demonstrates that the electrochemical devices of this application exhibit both high energy density and good cycling performance.

[0142] The thickness A of the copper layer, the thickness B of the aluminum layer, and the value of B / A generally affect the energy density and cycle performance of the electrochemical device. From Examples 1-2 to 1-12, Examples 1-21 to 1-23, and Comparative Examples 1 to 3, it can be seen that the electrochemical device with the thickness A of the copper layer, the thickness B of the aluminum layer, and the value of B / A within the scope of the present application has a higher tensile strength Rm1 of the negative electrode current collector and a higher tensile strength Rm2 of the positive electrode current collector, and the electrochemical device has a higher energy density, a lower internal resistance, a higher cycle capacity retention rate, and a lower cycle expansion rate, thereby indicating that the electrochemical device of the present application has a higher energy density and good cycle performance. Among Examples 1-2, 1-9 to 1-12, the electrochemical devices of Examples 1-2, 1-10, and 1-11 take into account both high energy density and high cycle performance, and therefore, 1.5 to 2.5 is the preferred range of B / A. Compared with Examples 1-5 and 1-6, Example 1-8 has lower internal resistance, higher cycle capacity retention rate, and lower cycle expansion rate, but its energy density is lower. Examples 1-5 and 1-6 can better take into account the high energy density and high cycle performance of the electrochemical device.

[0143] The thickness C of the first polymer layer, the thickness D of the second polymer layer, and the C / D ratio generally affect the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2, 1-13, 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 range of the present application have a negative electrode current collector with a high tensile strength Rm1 and a positive electrode current collector with a high tensile strength Rm2, and the electrochemical device has a high energy density, a low internal resistance, a high cycle capacity retention rate, and a low cycle expansion rate, thereby demonstrating that the electrochemical device of the present application has a high energy density and good cycle performance. Among Examples 1-13 to 1-21, Example 1-17 has a higher cycle capacity retention rate and a lower cycle expansion rate than Examples 1-13 to 1-16 and Examples 1-18 to 1-21, but its energy density is lower. Therefore, compared with Example 1-17, Examples 1-13 to 1-16 and Examples 1-18 to 1-21 can better take into account the high energy density and high cycle performance of the electrochemical device.

[0144] The thickness of the adhesive layer generally affects the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2, 1-24, and 1-27, electrochemical devices having adhesive layer thicknesses within the ranges of this application have negative electrode current collectors with high tensile strength Rm1 and positive electrode current collectors with high tensile strength Rm2, and the electrochemical devices have high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion rate. This demonstrates that the electrochemical devices of this application have high energy density and good cycle performance.

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

[0146] The material type of the first polymer layer and / or the second polymer layer generally affects the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2 and 2-1 to 2-5, electrochemical devices whose first polymer layer and / or the second polymer layer are made of materials within the scope of this application have a negative electrode current collector with a high tensile strength Rm1 and a positive electrode current collector with a high tensile strength Rm2. The electrochemical device has a high energy density, a low internal resistance, a high cycle capacity retention rate, and a low cycle expansion rate. This indicates that the electrochemical device of the present application has a high energy density and good cycle performance.

[0147] The type of material used in the adhesive layer generally affects the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2, 2-6, and 2-7, electrochemical devices using adhesive layer materials within the scope of this application have negative electrode current collectors with high tensile strength Rm1 and positive electrode current collectors with high tensile strength Rm2. The electrochemical devices also have high energy density, low internal resistance, high cycle capacity retention, and low cycle expansion rate. This demonstrates that the electrochemical devices of this application have high energy density and good cycle performance.

[0148] Table 4

[0149] The compaction density of the negative electrode active material layer generally affects the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2, 3-1, and 3-4, the compaction density of the negative electrode active material layer is 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 sheet 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 has a high energy density, a low internal resistance, a high cycle capacity retention rate, and a low cycle expansion rate. This shows that the electrochemical device of the present application has a high energy density and good cycle performance.

[0150] The compaction density of the positive electrode active material layer generally affects the energy density and cycle performance of the electrochemical device. As can be seen from Examples 1-2, 3-5, and 3-8, the compaction density of the negative electrode active material layer is within the scope of the present application, the peel strength F2 between the positive electrode active material layer and the aluminum layer in the bipolar electrode sheet is within the scope of the present 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, a low internal resistance, a high cycle capacity retention rate, and a low cycle expansion rate. This shows that the electrochemical device of the present application has a high energy density and good cycle performance.

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

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

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

Claims

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

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2. The bipolar current collector according to claim 1, wherein 1.0≤B≤8.0。 3. The bipolar current collector according to claim 1 or 2, wherein: The bipolar current collector further includes an adhesive layer connecting the first polymer layer and the second polymer layer.

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

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

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7. The bipolar current collector according to 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 include at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyethylene terephthalate.

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

9. The bipolar current collector according to claim 3, wherein: The thickness of the adhesive layer is 1 μm to 4 μm.

10. The bipolar current collector according to claim 3, wherein: The material of the adhesive layer includes at least one of epoxy resin, polyacrylic acid, polyurethane or polyvinyl chloride.

11. A bipolar pole piece comprising the bipolar current collector according to any one of claims 1 to 10, wherein: The bipolar pole piece further includes a negative electrode active material layer, which is provided on a 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 / cm 3 Up to 2.0g / cm 3 ; The bipolar pole piece further includes a positive electrode active material layer, which is provided on a surface of the aluminum layer away from the second polymer layer along the thickness direction, and the compaction density of the positive electrode active material layer is 2.5 g / cm 3 Up to 4.5g / cm 3 .

12. The bipolar pole piece according to claim 11, wherein: 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.

13. An electrochemical device comprising the bipolar current collector according to any one of claims 1 to 10 or the bipolar pole piece according to claim 11 or 12.

14. An electrical device, wherein: The electrical equipment includes the electrochemical device according to claim 13.

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