Bipolar current collector, electrochemical device, and electronic device

Abstract

The present application provides a bipolar current collector, an electrochemical device, and an electronic device. The bipolar current collector comprises a copper layer, an aluminum layer, and a polymer layer. The polymer layer is located between the copper layer and the aluminum layer. The thickness of the copper layer is T1 μm, the thickness of the aluminum layer is T2 μm, the porosity of the copper layer is A1, and the porosity of the aluminum layer is A2, wherein T2(1-A2)>T1(1-A1). In the present application, T1, T2, A1 and A2 of the bipolar current collector are regulated to meet the described relationship, and structural optimization is performed for different features of the copper layer and the aluminum layer, thereby improving the energy density, power density and cycle performance of the electrochemical device.

Description

Bipolar current collector, electrochemical device and electronic device

[0001] This application claims priority to the Chinese patent application No. 202410881053.2, filed on July 2, 2024, and entitled “Bipolar current collector, electrochemical device and electronic device”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to a bipolar current collector, an electrochemical device and an electronic device. BACKGROUND

[0003] Electrochemical devices, such as lithium ion batteries, are widely used in the fields of smart phones, wearable devices, consumer drones and electric vehicles, due to their high energy density, long cycle life and no memory effect.

[0004] With the wide application of lithium ion batteries in the above fields, the market requires higher energy density of lithium ion batteries. The current collector is one of the indispensable components in lithium ion batteries, and its structural characteristics will affect the energy density and cycle performance of lithium ion batteries. SUMMARY

[0005] The purpose of the present application is to provide a bipolar current collector, an electrochemical device and an electronic device to improve the energy density and cycle performance of the electrochemical device. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a bipolar current collector, comprising a copper layer, an aluminum layer and a polymer layer, the polymer layer is located between the copper layer and the aluminum layer, the thickness of the copper layer is T1 μm, the thickness of the aluminum layer is T2 μm, the porosity of the copper layer is A1, the porosity of the aluminum layer is A2, and T2(1-A2) > T1(1-A1). By adjusting T1, T2, A1 and A2 of the bipolar current collector to meet the above relationship, the structure of the copper layer and the aluminum layer is optimized according to their different characteristics, which is beneficial to balance the contact resistance and mass difference of the copper layer and the aluminum layer, and is applied to the electrochemical device, which is beneficial to balance the expansion rate difference of the positive active material and the negative active material, thereby improving the energy density, power density and cycle performance of the electrochemical device.

[0007] In some embodiments of the present application, the bipolar current collector meets any one of the following characteristics: (1) T1 = T2, A1 > A2; (2) T1 < T2, A1 = A2; (3) T1 < T2, A1 > A2. The bipolar current collector meeting the above conditions is applied to the electrochemical device, which is beneficial to improve the energy density, power density and cycle performance of the electrochemical device.

[0008] In some embodiments of the present application, 5%≤A1≤45%, 0%≤A2≤30%. By regulating the values of A1 and A2 within the above ranges, the energy density and cycle performance of the electrochemical device are improved.

[0009] In some embodiments of the present application, 15%≤A1≤45%, 0%≤A2≤21%. By regulating the values of A1 and A2 within the above ranges, the energy density and cycle performance of the electrochemical device are improved, and the power density is also considered.

[0010] In some embodiments of the present application, 15%≤A1≤25%, 11%≤A2≤21%. By regulating the values of A1 and A2 within the above ranges, the energy density and cycle performance of the electrochemical device are further improved, and the power density is also considered.

[0011] In some embodiments of the present application, 0.5≤T1≤10, 0.5≤T2≤10. By regulating the values of T1 and T2 within the above ranges, the copper layer and the aluminum layer have high mechanical strength, the bipolar current collector is not prone to breakage, the volume of the bipolar current collector is reduced, and the copper layer and the aluminum layer have small contact impedance, which is beneficial to improve the energy density and the power density of the electrochemical device.

[0012] In some embodiments of the present application, 0.5≤T1≤5, 2≤T2≤8. By regulating the values of T1 and T2 within the above ranges, the energy density and the power density of the electrochemical device are further improved.

[0013] In some embodiments of the present application, 2≤T1≤5, 2≤T2≤7. By regulating the values of T1 and T2 within the above ranges, the energy density and the power density of the electrochemical device are further improved.

[0014] In some embodiments of the present application, 1≤T2 / T1≤4. By regulating the value of T2 / T1 within the above range, the thickness of the aluminum layer is greater than or equal to the thickness of the copper layer, which is beneficial to reduce the mass of the copper layer and the contact impedance of the aluminum layer, balance the mass and contact impedance difference between the copper layer and the aluminum layer, and thus improve the energy density and the power density of the electrochemical device.

[0015] In some embodiments of the present application, 1≤T2 / T1≤3.5. By regulating the value of T2 / T1 within the above range, the energy density of the electrochemical device is further improved.

[0016] In some embodiments of the present application, the average pore size of the copper layer is D1 pm, the average pore size of the aluminum layer is D2 pm, 20≤D1≤400, and 20≤D2≤400. By regulating the average pore size D1 of the copper layer and the average pore size D2 of the aluminum layer within the above range, the mass of the copper layer and the aluminum layer can be reduced, while the bipolar current collector has good ion conductivity and high mechanical strength, so that the bipolar current collector applied to the electrochemical device is conducive to improving the energy density and cycle performance of the electrochemical device.

[0017] In some embodiments of the present application, 150≤D1≤300, and 150≤D2≤300. By regulating the average pore size D1 of the copper layer and the average pore size D2 of the aluminum layer within the above range, the bipolar current collector applied to the electrochemical device is conducive to further improving the energy density and cycle performance of the electrochemical device, while the power density is also considered.

[0018] In some embodiments of the present application, the surface of the copper layer away from the polymer layer is a first surface, the surface of the aluminum layer away from the polymer layer is a second surface, the bipolar current collector comprises a plurality of first holes and a plurality of second holes, the first holes extend from the first surface along the thickness direction of the bipolar current collector, the second holes extend from the second surface along the thickness direction of the bipolar current collector, the depth of the first holes is H1 pm, the depth of the second holes is H2 pm, the thickness of the polymer layer is T3 pm, and the bipolar current collector satisfies any one of the following characteristics: (1) H1≤T1, and H2≤T2; (2) T1

[0019] In some embodiments of the present application, 0.1≤H1≤15, and 0.1≤H2≤15. By regulating the values of H1 and H2 within the above range, the energy density and cycle performance of the electrochemical device can be improved.

[0020] In some embodiments of the present application, 1.5≤H1≤5, and 1.5≤H2≤5. By regulating the values of H1 and H2 within the above range, the energy density and cycle performance of the electrochemical device can be further improved, while the power density is also considered.

[0021] In some embodiments of the present application, the thickness of the polymer layer is T3 μm, 1≤T3≤20. By regulating the value of T3 within the above range, the volume and mass of the bipolar current collector are reduced, while the bipolar current collector has high mechanical strength and is not prone to breakage, thereby facilitating the improvement of the energy density of the electrochemical device.

[0022] In some embodiments of the present application, 1≤T3≤4. By regulating the value of T3 within the above range, the energy density of the electrochemical device is further improved.

[0023] In some embodiments of the present application, the material of the polymer layer comprises at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride or polyethylene terephthalate. The selection of the above-mentioned materials for the polymer layer facilitates the improvement of the energy density and cycle performance of the electrochemical device.

[0024] The second aspect of the present application provides an electrochemical device comprising a bipolar electrode sheet, wherein the bipolar electrode sheet comprises the bipolar current collector provided by the first aspect of the present application. The electrochemical device provided by the present application has high energy density and power density and good cycle performance.

[0025] The third aspect of the present application provides an electronic device comprising the electrochemical device provided by the second aspect of the present application. The electrochemical device provided by the present application has high energy density and power density and good cycle performance, thereby the electronic device provided by the present application has a long service life and good performance.

[0026] Advantages of the embodiments of the present application:

[0027] The embodiments of the present application provide a bipolar current collector, an electrochemical device and an electronic device. The bipolar current collector comprises a copper layer, an aluminum layer and a polymer layer, the polymer layer is located between the copper layer and the aluminum layer, the thickness of the copper layer is T1 μm, the thickness of the aluminum layer is T2 μm, the porosity of the copper layer is A1, the porosity of the aluminum layer is A2, and T2(1-A2)>T1(1-A1). By regulating T1, T2, A1 and A2 of the bipolar current collector to satisfy the above relationship, the structure of the copper layer and the aluminum layer is optimized according to the different characteristics of the copper layer and the aluminum layer, which is conducive to balancing the contact resistance and mass difference of the copper layer and the aluminum layer, thereby facilitating the balancing of the expansion rate difference between the positive active material and the negative active material when the bipolar current collector is applied to the electrochemical device, and improving the energy density, power density and cycle performance of the electrochemical device.

[0028] Of course, implementing any product or method of the present application does not necessarily require all the advantages described above to be achieved at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0030] Fig. 1 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to an embodiment of the present application;

[0031] Fig. 2 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to another embodiment of the present application;

[0032] Fig. 3 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to another embodiment of the present application;

[0033] Fig. 4 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to another embodiment of the present application;

[0034] Fig. 5 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to a fifth embodiment of the present application;

[0035] Fig. 6 is a schematic diagram of the cross-sectional structure of a bipolar current collector along the thickness direction of itself according to a sixth embodiment of the present application.

[0036] Reference signs: bipolar current collector 10, copper layer 11, aluminum layer 12, polymer layer 13, first surface 11a, second surface 12a, first hole 11b, second hole 12b. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some embodiments of the present application, and all other embodiments obtained by those skilled in the art based on the present application also fall within the scope of protection of the present application.

[0038] It should be noted that in the following content, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery. The specific technical solutions are as follows:

[0039] The first aspect of the present application provides a bipolar current collector, comprising a copper layer, an aluminum layer and a polymer layer, the polymer layer being located between the copper layer and the aluminum layer, the thickness of the copper layer being T1 μm, the thickness of the aluminum layer being T2 μm, the porosity of the copper layer being A1, the porosity of the aluminum layer being A2, and T2(1-A2) > T1(1-A1).

[0040] For the convenience of understanding, in the present application, the length direction of the bipolar current collector is defined as Y, and the thickness direction of the bipolar current collector is defined as Z. The bipolar current collector usually has a long side and a short side after being unfolded, and the length direction is the extension direction of the long side of the bipolar current collector after being unfolded. It should be understood that the above definitions of directions are for the purpose of conveniently describing the present application. As shown in FIG. 1, the bipolar current collector 10 includes a copper layer 11, an aluminum layer 12, and a polymer layer 13 between the copper layer 11 and the aluminum layer 12. T1 is the thickness of the copper layer 11, T2 is the thickness of the aluminum layer 12, and T3 is the thickness of the polymer layer 13.

[0041] Compared with using a positive electrode current collector and a negative electrode current collector respectively in an electrochemical device, the use of the bipolar current collector of the present application is beneficial to reduce the mass of the current collector in the electrochemical device, reduce the loss of the energy density of the electrochemical device caused by the increase in mass, and thus improve the energy density of the electrochemical device. At the same time, the use of the bipolar electrode tab prepared from the bipolar current collector of the present application in the electrochemical device is beneficial to save the amount of separator, reduce the volume of the electrochemical device, reduce the loss of the energy density of the electrochemical device caused by the increase in volume, and thus improve the energy density of the electrochemical device. The bipolar current collector of the present application is provided with pores, which is beneficial to reduce the mass of the bipolar current collector, and thus further improve the energy density of the electrochemical device. At the same time, the pores are also beneficial to embed the positive electrode active material and the negative electrode active material, and absorb the expansion of the positive electrode active material and the negative electrode active material, and thus improve the cycle performance of the electrochemical device.

[0042] The bipolar current collector of the present application includes a copper layer and an aluminum layer. From the perspective of contact resistance, the resistivity of the copper layer is 1.68 x 10 -8 Ω / m, and the resistivity of the aluminum layer is 2.65 x 10 -8 Ω / m. The resistivity of the copper layer is 0.6 times the resistivity of the aluminum layer. The thickness relationship and the porosity relationship of the copper layer and the aluminum layer will affect the contact resistance of the bipolar current collector. The smaller the thickness, the greater the contact resistance. The greater the porosity, the greater the contact resistance. T1 < T2 and / or A1 > A2 are beneficial to balance the difference in contact resistance between the copper layer and the aluminum layer, reduce the internal resistance of the electrochemical device, and thus improve the power density of the electrochemical device. If the thickness of the aluminum layer is smaller and / or the porosity is greater, i.e., T1 > T2 and / or A1 < A2, or the copper layer and the aluminum layer have the same thickness and porosity, i.e., T1 = T2 and A1 = A2, the contact resistance of the aluminum layer will be too high, which will affect the power density of the electrochemical device. From the perspective of mass, the density of the copper layer is 8.96 g / cm 3 , and the density of the aluminum layer is 2.7 g / cm 3The thickness relationship and porosity relationship of the copper layer and the aluminum layer affect the quality of the bipolar current collector. The greater the thickness, the greater the quality. The smaller the porosity, the greater the quality. T1

[0043] In the present application, appropriate T1, T2, A1 and A2 can be set according to the product characteristics of the electrochemical device. For example, for an electrochemical device requiring high energy density, the bipolar current collector can be selected to have smaller T1 and T2 and larger A1 and A2 to reduce its mass; for an electrochemical device requiring high power density, the bipolar current collector can be selected to have larger T1 and T2 and smaller A1 and A2 to reduce its contact resistance; for an electrochemical device requiring good cycle performance, the bipolar current collector can be selected to have larger A1 to improve the problem of large expansion rate of the negative active material.

[0044] In some embodiments of the present application, the bipolar current collector satisfies: T1=T2, A1>A2. In the case of the same thickness of the copper layer and the aluminum layer, the porosity A1 of the copper layer is greater than the porosity A2 of the aluminum layer. Since the aluminum layer has a higher resistivity, the smaller porosity of the aluminum layer is conducive to reducing the contact impedance of the aluminum layer, making the difference in contact impedance between the aluminum layer and the copper layer smaller, reducing the internal resistance of the electrochemical device, and thus being conducive to improving the power density of the electrochemical device. At the same time, since the copper layer has a greater density, the greater porosity of the copper layer is conducive to reducing the mass of the copper layer, making the difference in mass between the aluminum layer and the copper layer smaller, and thus being conducive to improving the energy density of the electrochemical device. The expansion rate of the negative active material is often greater than that of the positive active material, and the greater porosity of the copper layer is also conducive to embedding more negative active material in the pores of the copper layer, improving the problem of the greater expansion rate of the negative active material, and thus being conducive to improving the cycle performance of the electrochemical device. Therefore, the bipolar current collector satisfying the above conditions is applied to the electrochemical device, which is conducive to improving the energy density, power density and cycle performance of the electrochemical device.

[0045] In some embodiments of the present application, the bipolar current collector satisfies: T1<T2, A1=A2. In the case of the same porosity of the copper layer and the aluminum layer, the thickness of the copper layer is smaller than that of the aluminum layer. Since the aluminum layer has a higher resistivity, the greater thickness of the aluminum layer is conducive to reducing the contact impedance of the aluminum layer, making the difference in contact impedance between the aluminum layer and the copper layer smaller, reducing the internal resistance of the electrochemical device, and thus being conducive to improving the power density of the electrochemical device. At the same time, since the copper layer has a greater density, the smaller thickness of the copper layer is conducive to reducing the mass of the copper layer, making the difference in mass between the aluminum layer and the copper layer smaller, and thus being conducive to improving the energy density of the electrochemical device. Therefore, the bipolar current collector satisfying the above conditions is applied to the electrochemical device, which is conducive to improving the energy density and power density of the electrochemical device.

[0046] In some embodiments of the present application, the bipolar current collector satisfies: T1 < T2, A1 > A2. The thickness of the copper layer is less than the thickness of the aluminum layer, and the porosity of the copper layer is greater than the porosity of the aluminum layer. Due to the higher resistivity of the aluminum layer, the greater thickness and smaller porosity of the aluminum layer are conducive to further reducing the contact impedance of the aluminum layer, reducing the impedance difference between the aluminum layer and the copper layer, and reducing the internal resistance of the electrochemical device, thereby being applied to the electrochemical device to further improve the power density thereof. At the same time, due to the greater density of the copper layer, the smaller thickness and greater porosity of the copper layer are conducive to further reducing the mass of the copper layer, reducing the mass difference between the aluminum layer and the copper layer, and thereby being applied to the electrochemical device to further improve the energy density thereof. The expansion rate of the negative active material is often greater than that of the positive active material, and the greater porosity of the copper layer is also conducive to embedding more negative active material in the pores of the copper layer, improving the problem of the greater expansion rate of the negative active material, and thereby being applied to the electrochemical device to improve the cycle performance thereof. Thus, the bipolar current collector satisfying the above conditions is applied to the electrochemical device, which is conducive to further improving the energy density, power density and cycle performance of the electrochemical device.

[0047] In some embodiments of the present application, 5%≤A1≤45%, 0%≤A2≤30%, optionally, 15%≤A1≤45%, 0%≤A2≤21%, further, 15%≤A1≤25%, 11%≤A2≤21%. For example, A1 can be 5%, 10%, 14%, 15%, 20%, 25%, 26%, 30%, 35%, 40%, 45%, or a range consisting of any two of the above values, and A2 can be 0%, 5%, 10%, 11%, 16%, 20%, 21%, 24%, 30%, or a range consisting of any two of the above values. By adjusting the values of A1 and A2 within the above range, the bipolar current collector has high mechanical strength and is not prone to breakage, and is also conducive to reducing the mass of the copper layer and the aluminum layer, thereby being applied to the electrochemical device to improve the energy density thereof. In addition, the pores of the copper layer are conducive to embedding the negative active material and absorbing the expansion of the negative active material, and the pores of the aluminum layer are conducive to embedding the positive active material and absorbing the expansion of the positive active material, thereby being applied to the electrochemical device to improve the cycle performance thereof. Thus, the bipolar current collector satisfying the above conditions is applied to the electrochemical device, which is conducive to improving the energy density and cycle performance of the electrochemical device.

[0048] In some embodiments, as shown in FIG. 2, the aluminum layer 12 does not include pores, and A2 = 0%. Due to the lower density of the aluminum layer, the aluminum layer does not include pores, which is conducive to improving the mechanical strength of the bipolar current collector and reducing the contact impedance of the aluminum layer, thereby being applied to the electrochemical device to improve the power density and cycle performance thereof.

[0049] In some embodiments of the present application, 0.5≤T1≤10, 0.5≤T2≤10, optionally, 0.5≤T1≤5, 2≤T2≤8, further, 2≤T1≤5, 2≤T2≤7. For example, T1 can be 0.5, 2, 3.2, 4, 5, 6, 7.1, 8, 9.3, 10, or a range defined by any two of the above values, and T2 can be 0.5, 2, 3.4, 4, 5, 6, 7, 7.2, 8, 9.1, 10, or a range defined by any two of the above values. By regulating the values of T1 and T2 within the above ranges, the copper layer and the aluminum layer have high mechanical strength, the bipolar current collector is less likely to break, and the volume of the bipolar current collector is reduced, and the copper layer and the aluminum layer have small contact impedance, and the electrochemical device has small internal resistance, thereby being applied to the electrochemical device to improve the energy density and the power density of the electrochemical device.

[0050] In some embodiments of the present application, 1≤T2 / T1≤4, optionally, 1≤T2 / T1≤3.5. For example, T2 / T1 can be 1, 1.2, 1.8, 2.0, 2.3, 2.6, 2.8, 3.0, 3.3, 3.5, 4, or a range defined by any two of the above values. By regulating the value of T2 / T1 within the above range, the thickness of the aluminum layer is greater than or equal to the thickness of the copper layer, and due to the higher resistivity of the aluminum layer, the greater thickness of the aluminum layer is conducive to reducing the contact impedance of the aluminum layer, reducing the difference in contact impedance between the aluminum layer and the copper layer, and reducing the internal resistance of the electrochemical device, thereby being applied to the electrochemical device to improve the power density of the electrochemical device. At the same time, due to the greater density of the copper layer, the smaller thickness of the copper layer is conducive to reducing the mass of the copper layer, reducing the difference in mass between the aluminum layer and the copper layer, and thereby being applied to the electrochemical device to improve the energy density of the electrochemical device. Thus, the bipolar current collector satisfying the above conditions is applied to the electrochemical device to improve the energy density and the power density of the electrochemical device.

[0051] In some embodiments of the present application, the average pore diameter of the copper layer is D1 μm, the average pore diameter of the aluminum layer is D2 μm, 20≤D1≤400, 20≤D2≤400, optionally, 150≤D1≤300, 150≤D2≤300. For example, D1 can be 20, 60, 100, 150, 170, 200, 240, 300, 350, 400, or a range defined by any two of the above values, and D2 can be 20, 50, 100, 150, 160, 200, 250, 300, 340, 400, or a range defined by any two of the above values. By regulating the average pore diameter D1 of the copper layer and the average pore diameter D2 of the aluminum layer within the above ranges, the mass of the copper layer and the aluminum layer is reduced, and the transmission of lithium ions is facilitated, so that the bipolar current collector has good ion conduction capability and high mechanical strength, and thereby being applied to the electrochemical device to improve the energy density and the cycle performance of the electrochemical device.

[0052] The shape of the holes in the copper layer and the aluminum layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the shape of the holes in the copper layer and the aluminum layer can include, but is not limited to, at least one of a circular shape, a square shape, a triangular shape, or a slot shape. In the present application, the average pore diameter refers to the diameter of the circumscribed circle of the hole shape, which can be measured after the outline of the hole is drawn using a Keyence IM8000.

[0053] In FIGS. 1 to 6, the surface of the copper layer 11 away from the polymer layer 13 is a first surface 11a, the surface of the aluminum layer 12 away from the polymer layer 13 is a second surface 12a, the bipolar current collector 10 includes a plurality of first holes 11b and a plurality of second holes 12b, the first holes 11b extend from the first surface 11a in the thickness direction of the bipolar current collector 10, the second holes 12b extend from the second surface 12a in the thickness direction of the bipolar current collector 10, the depth of the first holes 11b is H1 μm, the depth of the second holes 12b is H2 μm, and the thickness of the polymer layer 13 is T3 μm.

[0054] In some embodiments of the present application, the bipolar current collector satisfies H1≤T1 and H2≤T2. Specifically, in some embodiments, as shown in FIG. 1, H1

[0055] In some embodiments of the present application, the bipolar current collector satisfies T1

[0056] In some embodiments of the present application, as shown in FIG. 6, the bipolar current collector satisfies: T1

[0057] In some embodiments, 0.1≤H1≤15, 0.1≤H2≤15, and optionally, 1.5≤H1≤5, 1.5≤H2≤5. For example, H1 can be 0.1, 1, 1.5, 2.5, 4, 5, 7.5, 9, 10, 12, 15, or a range defined by any two of the above values, and H2 can be 0.1, 1, 1.5, 2.5, 4, 5, 7.5, 9, 10, 12, 15, or a range defined by any two of the above values. The bipolar current collector satisfying the above conditions is conducive to improving the energy density and cycle performance of the electrochemical device.

[0058] In some embodiments of the present application, the thickness of the polymer layer is T3μm, 1≤T3≤20, and optionally, 1≤T3≤4. For example, T3 can be 1, 3, 4, 5, 8, 10, 12, 15, 18, 20, or a range defined by any two of the above values. By regulating the value of T3 within the above range, it is conducive to reducing the volume and mass of the bipolar current collector, while making the bipolar current collector have high mechanical strength and not prone to breakage, so that the application in the electrochemical device is conducive to improving the energy density thereof.

[0059] In some embodiments of the present application, the material of the polymer layer comprises at least one of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) or polyethylene terephthalate (PET). The polymer materials of the above-mentioned kinds have the characteristics of small density, light mass, high temperature resistance and corrosion resistance to electrolyte. The bipolar current collector has a light mass and good stability during use of the electrochemical device, and is also conducive to absorbing the expansion of the positive active material and the negative active material. Therefore, the bipolar current collector meeting the above conditions is applied to the electrochemical device, which is conducive to improving the energy density and cycle performance of the electrochemical device.

[0060] The present application does not have special restrictions on the preparation method of the bipolar current collector, as long as the purpose of the present application can be achieved. For example, the preparation method of the bipolar current collector can include but is not limited to the following steps: (1) forming a copper layer on one surface of the polymer layer; (2) forming an aluminum layer on the other surface of the polymer layer; (3) punching the copper layer and the aluminum layer respectively to obtain the bipolar current collector.

[0061] The present application does not have special restrictions on the way of forming the copper layer in the above-mentioned step (1) and the way of forming the aluminum layer in the above-mentioned step (2), as long as the purpose of the present application can be achieved. For example, the way of forming the copper layer and / or the aluminum layer can be chemical deposition, magnetron sputtering or vacuum evaporation. The present application does not have special restrictions on the process parameters of chemical deposition, magnetron sputtering or vacuum evaporation, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. The present application does not have special restrictions on the way of punching the copper layer and the aluminum layer in the above-mentioned step (3), as long as the purpose of the present application can be achieved. For example, the way of punching the copper layer and the aluminum layer can be chemical etching, laser punching or mechanical punching, respectively. The way of chemical etching can include but is not limited to: after the bipolar current collector is subjected to oil removal treatment, hydrochloric acid is used as an etching liquid, and the concentration of the hydrochloric acid, the etching time and the etching temperature are adjusted to etch holes on the surfaces of the copper layer and the aluminum layer, respectively. The way of laser punching can include but is not limited to: using femtosecond laser technology to process the bipolar current collector to obtain a porous bipolar current collector. The way of mechanical punching can include but is not limited to: using a die or a punch to stamp or punch the bipolar current collector to obtain a porous bipolar current collector. The present application does not have special restrictions on the distribution of the holes in the copper layer and the aluminum layer, as long as the purpose of the present application can be achieved. For example, the distribution of the holes in the copper layer and the aluminum layer can be average distribution or uneven distribution.

[0062] The method for regulating the porosity A1 of the copper layer and the porosity A2 of the aluminum layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, it can be obtained by regulating the number of pores per unit area of the copper layer and the aluminum layer. When other conditions remain unchanged, the number of pores per unit area of the copper layer increases, A1 increases, the number of pores per unit area of the copper layer decreases, A1 decreases; the number of pores per unit area of the aluminum layer increases, A2 increases, the number of pores per unit area of the aluminum layer decreases, A2 decreases. For example, it can be obtained by regulating the average pore diameter D1 of the copper layer and the average pore diameter D2 of the aluminum layer. When other conditions remain unchanged, D1 increases, A1 increases, D2 increases, A2 increases; D1 decreases, A1 decreases, D2 decreases, A2 decreases. For example, it can be obtained by regulating the depth H1 of the first pore and the depth H2 of the second pore. When other conditions remain unchanged, H1 increases, A1 increases, H2 increases, A2 increases; H1 decreases, A1 decreases, H2 decreases, A2 decreases.

[0063] The method for regulating the thickness T1 of the copper layer and the thickness T2 of the aluminum layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, it can be obtained by regulating the deposition time during the preparation of the copper layer and the aluminum layer. When other conditions remain unchanged, the deposition time during the preparation of the copper layer increases, T1 increases, the deposition time during the preparation of the aluminum layer increases, T2 increases; the deposition time during the preparation of the copper layer decreases, T1 decreases, the deposition time during the preparation of the aluminum layer decreases, T2 decreases.

[0064] The second aspect of the present application provides an electrochemical device, which comprises a bipolar electrode sheet comprising the bipolar current collector provided by the first aspect of the present application. The electrochemical device provided by the present application has high energy density and power density and good cycle performance. The surface of the aluminum layer of the bipolar current collector is provided with a positive electrode material layer, and the surface of the copper layer of the bipolar current collector is provided with a negative electrode material layer. It should be noted that the "surface" herein can be the entire area of the bipolar current collector, or can be part of the area of the bipolar current collector, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0065] The coating area density of the positive electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the coating area density of the positive electrode material layer can be 8 mg / cm 2 to 20 mg / cm 2 The coating area density of the negative electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the coating area density of the negative electrode material layer can be 4 mg / cm 2 to 15 mg / cm 2 The compaction density of the positive electrode material layer and the negative electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the compaction density of the positive electrode material layer can be 1 g / cm3 to 5 g / cm 3 The compacted density of the negative material layer can be 0.5 g / cm 3 to 2 g / cm 3 .

[0066] The positive material layer of the present application includes a positive active material, which includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive material layer can be one layer or multiple layers, and each layer in the multiple positive material layers can include the same or different positive active materials. The positive active material of the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the positive active material can include but is not limited to at least one of nickel cobalt manganese lithium (e.g., NCM811, NCM622, NCM523, NCM111), nickel cobalt aluminum lithium, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The chemical formula of the above-mentioned lithium-rich manganese-based material is γLi2MnO3·(1-γ)LiGO2, 0<γ<1, and G is a transition metal nickel, cobalt, manganese, or iron, etc. In the present application, the surface of the positive active material can be attached with a substance different from its composition, and the surface-attached substance can include but is not limited to at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate, or carbon. By attaching the above-mentioned substance to the surface of the positive active material, it is beneficial to inhibit the oxidation reaction of the electrolyte on the surface of the positive active material, thereby improving the service life of the electrochemical device.

[0067] The positive electrode material layer can further include a positive electrode conductive agent and a positive electrode binder. The type of the positive electrode conductive agent and the positive electrode binder is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the positive electrode binder can include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, an epoxy resin, or nylon. The positive electrode conductive agent can include, but is not limited to, at least one of a carbon-based material, a metal-based material, or a conductive polymer. For example, the carbon-based material can include at least one of natural graphite, artificial graphite, conductive carbon black (Super P), or carbon fiber, the metal-based material can include, but is not limited to, at least one of metal powder, metal fiber, copper, nickel, aluminum, or silver, and the conductive polymer can include, but is not limited to, a polyphenylene derivative. The mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer is not particularly limited in the present application, and can be selected as needed as long as the purpose of the present application can be achieved.

[0068] The negative electrode material layer of the present application includes a negative electrode active material. The negative electrode material layer can be one layer or multiple layers. Each layer of the multiple layers of the negative electrode material layer can include the same or different negative electrode active material. The negative electrode active material is any material capable of reversibly intercalating and deintercalating active ions such as lithium ions. The negative electrode active material can include, but is not limited to, at least one of graphite, meso-carbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0 < x ≤ 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate spinel structure Li4Ti5O12, Li-Al alloy, and metallic lithium. 12

[0069] The negative electrode material layer of the present application can further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode material layer can further include a negative electrode binder, a negative electrode conductive agent, or a thickening agent. The type of the negative electrode binder and the negative electrode conductive agent is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the negative electrode binder can include, but is not limited to, at least one of the positive electrode binders described above, and the negative electrode conductive agent can include, but is not limited to, at least one of the positive electrode conductive agents described above. The type of the thickening agent is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. The mass ratio of the negative electrode active material, the negative electrode conductive agent, the thickening agent, and the negative electrode binder in the negative electrode material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0070] ​The electrochemical device of the present application further includes an electrolyte including a lithium salt and a nonaqueous solvent. The lithium salt can include various lithium salts commonly used in the art, for example, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluorophosphate. The concentration of the lithium salt in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved. The nonaqueous solvent is not particularly limited in the present application, as long as the object of the present application is achieved, for example, can include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents. The carbonate compound described above can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The chain carbonate compound described above can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or methyl ethyl carbonate (EMC). The cyclic carbonate described above can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound described above can include, but is not limited to, at least one of fluorinated ethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The carboxylate compound described above can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound described above can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents described above can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0071] In the present application, the electrochemical device further includes a separator for separating the bipolar electrode sheet, preventing internal short circuit of the electrochemical device, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. The separator of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; and the type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaid film. For example, the separator can include a base layer and a surface treatment layer. The base layer can be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited in the present application and can include, for example, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder in the inorganic layer is not particularly limited in the present application and can be, for example, at least one of the positive electrode binders described above. The polymer layer includes a polymer, and the polymer is not particularly limited in the present application and can include, for example, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved, and for example, the thickness of the separator can be 5 μm to 30 μm.

[0072] The electrochemical device of the present application further includes a packaging bag for containing the bipolar electrode sheet, the separator, and the electrolyte, and other components in the electrochemical device known in the art, and the other components are not particularly limited in the present application. The packaging bag is not particularly limited in the present application and can be a packaging bag known in the art as long as the purpose of the present application can be achieved. For example, an aluminum-plastic film packaging bag can be used.

[0073] The electrochemical device of the present application is not particularly limited, and can include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device can include, but is not limited to, a lithium ion battery, a sodium ion battery, a lithium polymer electrochemical device, or a lithium ion polymer electrochemical device, etc.

[0074] The method for preparing the electrochemical device of the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the method for preparing the electrochemical device includes, but is not limited to, the following steps: stacking the separator film and the bipolar electrode sheet, winding to obtain an electrode assembly of a wound structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing, to obtain the electrochemical device; or stacking the separator film and the bipolar electrode sheet, and then fixing the four corners of the entire stack structure to obtain an electrode assembly of a stack structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing, to obtain the electrochemical device.

[0075] The third aspect of the present application provides an electronic device comprising the electrochemical device provided by the second aspect of the present application. The electrochemical device provided by the present application has high energy density and power density and good cycle performance, so that the electronic device provided by the present application has a long service life and good performance.

[0076] The electronic device of the present application is not particularly limited, and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor.

[0077] Examples

[0078] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0079] Test methods and apparatus:

[0080] Sampling method of bipolar current collector

[0081] After disassembling the lithium ion battery of each example and comparative example after discharging at 0.1C to 2.5V, the bipolar electrode sheet was obtained, and then the positive electrode material layer and the negative electrode material layer were scraped off to obtain the bipolar current collector. After cleaning the bipolar current collector with dimethyl carbonate (DMC), the bipolar current collector sample was obtained by drying at 60°C. The bipolar current collector sample was cut along the direction of the plane defined parallel to the thickness direction and the width direction, and along the direction of the plane defined parallel to the thickness direction and the length direction to obtain a cuboid sample with a length of 20 mm and a width of 10 mm. The following tests of porosity, average pore size, thickness, and depth of the first and second holes can use the above sampling method to obtain the cuboid sample.

[0082] Test of porosity

[0083] The cuboid sample was tomographically scanned using an industrial CT (Zeiss Xradia 620 Versa) to obtain a three-dimensional image of the cuboid sample. The outer contour volume of the copper layer X1, the volume of the pores in the copper layer Y1, and the outer contour volume of the aluminum layer X2, and the volume of the pores in the aluminum layer Y2 in the cuboid sample were obtained by image analysis. The porosity A1 of the copper layer was calculated by the following formula: A1 (%) = Y1 / X1 x 100%. The porosity A2 of the aluminum layer was calculated by the following formula: A2 (%) = Y2 / X2 x 100%.

[0084] Test of average pore size

[0085] The cuboid sample was tomographically scanned using an industrial CT (Zeiss Xradia 620 Versa) to obtain a three-dimensional image of the cuboid sample. The diameter of the circumscribed circle of the hole shape was obtained by image analysis, and the average value of the above 10 circumscribed circle diameters was calculated as the average pore size D1 of the copper layer. The diameter of the circumscribed circle of the hole shape was obtained by image analysis, and the average value of the above 10 circumscribed circle diameters was calculated as the average pore size D2 of the aluminum layer.

[0086] Test of thickness

[0087] The cuboid sample was tomographically scanned using an industrial CT (Zeiss Xradia 620 Versa) to obtain a three-dimensional image of the cuboid sample. Ten unperforated areas were selected, and the thicknesses of the copper layer, the aluminum layer, and the polymer layer of the above 10 unperforated areas were obtained by image analysis, and the average values were calculated as the thickness T1 of the copper layer, the thickness T2 of the aluminum layer, and the thickness T3 of the polymer layer, respectively.

[0088] Test of depth of the first and second holes

[0089] The cuboid sample is tomographically scanned using an industrial CT (Zeiss Xradia 620 Versa) to obtain a three-dimensional image of the cuboid sample. Optionally, the depths of 10 first holes are obtained by image analysis, and the average value is calculated as the depth H1 of the first hole. Optionally, the depths of 10 second holes are obtained by image analysis, and the average value is calculated as the depth H2 of the second hole.

[0090] Test of energy density

[0091] The lithium ion battery is charged at 0.2 C to a voltage of 4.30 V at 25°C, and then charged at 4.30 V to a current of 0.05 C, and then rested for 15 min; then discharged at 0.2 C to a voltage of 2.5 V. The discharge energy at this time is tested and recorded by a battery tester (Neware CTE-4016-5V-200A), and is recorded as the energy E of the lithium ion battery; and the mass of the lithium ion battery is measured and recorded as m. The energy density is calculated by the following formula: energy density (Wh / kg) = E / m.

[0092] Test of internal resistance

[0093] The lithium ion batteries of each example and the comparative example are placed in a 25°C constant temperature box and rested for 30 min, and then the lithium ion batteries are charged at 0.2 C to a voltage of 4.30 V, and then charged at 4.30 V to a current of 0.05 C, and then rested for 15 min, and then discharged at 0.2 C to 2.5 V, and then an internal resistance tester is used to apply an alternating current signal of 1 kHz to the lithium ion battery. The internal resistance of the lithium ion battery is calculated by the following formula: internal resistance R = ΔU / I, wherein ΔU is the voltage change of the lithium ion battery under the alternating current signal, and I is the alternating current passing through the lithium ion battery at the same time. The power density of the lithium ion battery is evaluated by the internal resistance of the lithium ion battery. The greater the internal resistance of the lithium ion battery, the smaller the power density, and the smaller the internal resistance, the greater the power density.

[0094] Test of cycle performance

[0095] (1) Test of cycle capacity retention rate

[0096] The lithium ion battery was charged at 1.0C constant current to 4.30V, then charged at 4.30V constant voltage to 0.05C, and rested for 15 min at 25℃. Then it was discharged at 4.0C constant current to 2.5V, and rested for 15 min. The above was one charge-discharge cycle. The discharge capacity was tested by a battery tester (Neware CTE-4016-5V-200A) and recorded as the initial capacity Q0. According to the above charge-discharge method, 500 cycles were performed. The discharge capacity of the 500th cycle was recorded as the capacity after 500 cycles Q1. The cycle capacity retention rate was calculated by the following formula: cycle capacity retention rate (%) = Q1 / Q0x100%.

[0097] (2) Test of cycle expansion rate

[0098] The lithium ion battery was placed in an environment of 25℃, and charged at 1.0C constant current to 3.60V, i.e. half-state, to test the initial thickness of the lithium ion battery, recorded as T0. The lithium ion battery was charged at 1.0C constant current to 4.30V, then charged at 4.30V constant voltage to 0.05C, and rested for 15 min. Then it was discharged at 4.0C constant current to 2.5V, and rested for 15 min. The above was one charge-discharge cycle. After 500 cycles according to the above charge-discharge method, the lithium ion battery was charged at 1.0C constant current to 4.30V, then charged at 4.30V constant voltage to 0.05C, to reach the full state, and the thickness of the lithium ion battery was tested, recorded as T1. The cycle expansion rate was calculated by the following formula: cycle expansion rate (%) = (T1-T0) / T0x100%.

[0099] Example 1-1

[0100] Preparation of bipolar current collector

[0101] A copper layer with a thickness T1 of 2μm was formed on one surface of a polymer layer PET (weight average molecular weight Mw = 2x10 4 ) sheet with a thickness T3 of 4μm by vacuum evaporation, and an aluminum layer with a thickness T2 of 2μm was formed on the other surface of the polymer layer PET sheet by vacuum evaporation. Laser punching was used to punch holes in the copper layer and the aluminum layer, respectively. The porosity A1 of the copper layer and the porosity A2 of the aluminum layer are shown in Table 1, and the average pore diameter D1 of the copper layer, the average pore diameter D2 of the aluminum layer, the depth H1 of the first hole, and the depth H2 of the second hole are shown in Table 2.

[0102] Preparation of bipolar electrode sheet

[0103] The positive electrode active material lithium nickel cobalt manganese oxide NCM811, the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride (PVDF, Mw = 7x10 6) were mixed in a weight ratio of 95:3:2, N-methylpyrrolidone (NMP) was added as a solvent, and an anode slurry with a solid content of 65 wt% was prepared and uniformly stirred.

[0104] The negative electrode active material artificial graphite, the negative electrode active material silicon, the negative electrode conductive agent conductive carbon black (Super P), the negative electrode binder styrene-butadiene rubber (SBR, Mw = 5 x 10 6 ) were mixed in a weight ratio of 74:20:1:5, deionized water was added as a solvent, and an anode slurry with a solid content of 70 wt% was prepared and uniformly stirred.

[0105] The positive electrode slurry was uniformly coated on the aluminum layer of the bipolar current collector, dried at 85°C, and a positive electrode material layer was formed. The coating surface density of the positive electrode material layer after drying was 13 mg / cm 2 The negative electrode slurry was uniformly coated on the copper layer of the bipolar current collector, dried at 110°C, and a negative electrode material layer was formed. The coating surface density of the negative electrode material layer after drying was 8 mg / cm 2 , and the bipolar electrode sheet with a size of 50 mm x 80 mm was obtained. The compaction density of the positive electrode material layer was 3.5 g / cm 3 , and the compaction density of the negative electrode material layer was 1.6 g / cm 3 . Subsequent auxiliary processes such as tab welding and adhesive tape pasting were performed, and the preparation process of the bipolar electrode sheet was completed.

[0106] <Preparation of electrolyte>

[0107] In a dry argon atmosphere, first, non-aqueous solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC: EMC: DEC = 30:50:20, then lithium salt lithium hexafluorophosphate (LiPF6) was added to the non-aqueous solvent to dissolve and mix uniformly, and an electrolyte with a lithium salt concentration of 1.15 mol / L was obtained.

[0108] <Preparation of separator>

[0109] A porous polyethylene (PE) film with a thickness of 8 μm (provided by Celgard) was used as the separator.

[0110] <Preparation of lithium ion battery>

[0111] The isolation film and the bipolar electrode plate were alternately stacked, and the isolation film was 21 layers and the bipolar electrode plate was 22 layers. Then, the electrode assembly was obtained by fixing the four corners of the entire stack structure. The electrode assembly was placed in an aluminum plastic film packaging bag, and after drying, the electrolyte was injected, and after vacuum packaging, standing, formation (0.02C constant current charging to 3.3V, and then 0.1C constant current charging to 4.0V), shaping and other processes, a lithium ion battery was obtained.

[0112] Examples 1-2 to 1-14

[0113] Except that the relevant preparation parameters in <Preparation of the bipolar current collector> were adjusted according to Table 1, the rest was the same as Example 1-1. Among them, the thickness T1 of the copper layer was adjusted by adjusting the deposition time during the preparation of the copper layer, and the thickness T2 of the aluminum layer was adjusted by adjusting the deposition time during the preparation of the aluminum layer. The porosity A1 of the copper layer was adjusted by adjusting the punching density of the copper layer, and the porosity A2 of the aluminum layer was adjusted by adjusting the punching density of the aluminum layer.

[0114] Examples 2-1 to 2-14

[0115] Except that the relevant preparation parameters in <Preparation of the bipolar current collector> were adjusted according to Table 2, the rest was the same as Example 1-1. Among them, in Example 2-10, the projection of the first hole and the projection of the second hole were outside along the thickness direction of the bipolar current collector.

[0116] Comparative Example 1

[0117] Except that the copper layer and the aluminum layer were not punched in <Preparation of the bipolar current collector>, the rest was the same as Example 1-1.

[0118] Comparative Examples 2 to 5

[0119] Except that the relevant preparation parameters in <Preparation of the bipolar current collector> were adjusted according to Table 1, the rest was the same as Example 1-1. Among them, the thickness T1 of the copper layer was adjusted by adjusting the deposition time during the preparation of the copper layer, and the thickness T2 of the aluminum layer was adjusted by adjusting the deposition time during the preparation of the aluminum layer. The porosity A1 of the copper layer was adjusted by adjusting the punching density of the copper layer, and the porosity A2 of the aluminum layer was adjusted by adjusting the punching density of the aluminum layer.

[0120] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 2.

[0121] Table 1

[0122] As can be seen from Examples 1-1 to 1-14, Comparative Examples 1 to 5, the lithium ion battery in the embodiments of the present application has a higher energy density and cycle capacity retention rate, and a lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has a higher energy density and power density and good cycle performance, by regulating T1, T2, A1, A2 of the bipolar current collector to satisfy T2(1-A2) > T1(1-A1). The lithium ion batteries of Comparative Examples 1 to 5 cannot simultaneously have a higher energy density and cycle capacity retention rate, and a lower internal resistance and cycle expansion rate, indicating that the lithium ion battery cannot have a higher energy density and power density and good cycle performance, because the T1, T2, A1, A2 of the bipolar current collector do not satisfy the above relationship.

[0123] The values of T1 and T2 generally affect the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Examples 1-1 to 1-10, when the values of T1 and T2 are within the range of the present application, the lithium ion battery has a higher energy density and cycle capacity retention rate, and a lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has a higher energy density and power density and good cycle performance.

[0124] The value of T2 / T1 generally affects the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Examples 1-1, 1-3, 1-8 to 1-10, when the value of T2 / T1 is within the range of the present application, the lithium ion battery has a higher energy density and cycle capacity retention rate, and a lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has a higher energy density and power density and good cycle performance.

[0125] The values of A1 and A2 generally affect the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Examples 1-1, 1-2, 1-11 to 1-14, when the values of A1 and A2 are within the range of the present application, the lithium ion battery has a higher energy density and cycle capacity retention rate, and a lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has a higher energy density and power density and good cycle performance.

[0126] Table 2

[0127] Note: T1 = 2 pm, T2 = 2 pm in Examples 2-1 to 2-14 in Table 2, Mw of PE in Example 2-13 = 3 x 10 4 , Mw of PS in Example 2-14 = 6 x 10 4 .

[0128] The values of D1 and D2 generally affect the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-1 to Example 2-5, when the values of D1 and D2 are within the range of the present application, the lithium ion battery has higher energy density and cycle capacity retention rate, and lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has higher energy density and power density and good cycle performance.

[0129] The size relationship between H1 and T1, T3, the size relationship between H2 and T2, T3, and the size relationship between H1+H2 and T1+T2+T3 generally affect the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-6 to Example 2-10, when the size relationship between H1 and T1, T3, the size relationship between H2 and T2, T3, and the size relationship between H1+H2 and T1+T2+T3 are within the range of the present application, the lithium ion battery has higher energy density and cycle capacity retention rate, and lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has higher energy density and power density and good cycle performance.

[0130] The value of T3 generally affects the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-11 to Example 2-12, when the value of T3 is within the range of the present application, the lithium ion battery has higher energy density and cycle capacity retention rate, and lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has higher energy density and power density and good cycle performance.

[0131] The material of the polymer layer generally affects the energy density, power density and cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-13 to Example 2-14, when the material of the polymer layer within the range of the present application is selected, the lithium ion battery has higher energy density and cycle capacity retention rate, and lower internal resistance and cycle expansion rate, indicating that the lithium ion battery has higher energy density and power density and good cycle performance.

[0132] It should be noted that the terms "comprising", "containing" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods or articles including a series of elements not only include those elements, but also include other elements not explicitly listed, or inherent to such processes, methods or articles.

[0133] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0134] The above description is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A bipolar current collector, comprising a copper layer, an aluminum layer, and a polymer layer, the polymer layer being between the copper layer and the aluminum layer, the copper layer having a thickness of T1 μm, the aluminum layer having a thickness of T2 μm, the copper layer having a porosity of A1, the aluminum layer having a porosity of A2, T2(1-A2)>T1(1-A1).

2. The bipolar current collector of claim 1, wherein, The bipolar current collector satisfies any one of the following characteristics: (1) T1=T2, A1>A2; (2) T1<T2, A1=A2; (3) T1<T2, A1>A2.

3. The bipolar current collector of claim 1 or 2, wherein, 5%≤A1≤45%, 0%≤A2≤30%.

4. The bipolar current collector of claim 3, wherein, 15%≤A1≤45%, 0%≤A2≤21%.

5. The bipolar current collector of claim 4, wherein, 15%≤A1≤25%, 11%≤A2≤21%.

6. The bipolar current collector of any one of claims 1 to 5, wherein, 0.5≤T1≤10, 0.5≤T2≤10.

7. The bipolar current collector of claim 6, wherein, 0.5≤T1≤5, 2≤T2≤8.

8. The bipolar current collector of claim 7, wherein, 2≤T1≤5, 2≤T2≤7.

9. The bipolar current collector of claim 6, wherein, 1≤T2 / T1≤4.

10. The bipolar current collector of claim 9, wherein, 1≤T2 / T1≤3.

5.

11. The bipolar current collector of any one of claims 1 to 10, wherein, The copper layer has an average pore size of D1 μm, the aluminum layer has an average pore size of D2 μm, 20≤D1≤400, 20≤D2≤400.

12. The bipolar current collector of claim 11, wherein, 150≤D1≤300, 150≤D2≤300.

13. The bipolar current collector of any one of claims 1 to 12, wherein, The surface of the copper layer away from the polymer layer is a first surface, the surface of the aluminum layer away from the polymer layer is a second surface, the bipolar current collector comprises a plurality of first holes and a plurality of second holes, the first holes extend from the first surface along the thickness direction of the bipolar current collector, the second holes extend from the second surface along the thickness direction of the bipolar current collector, the first holes have a depth of H1 μm, the second holes have a depth of H2 μm, the polymer layer has a thickness of T3 μm, the bipolar current collector satisfies any one of the following characteristics: (1) H1≤T1, H2≤T2; (2) T1<H1<T1+T3 and / or T2<H2<T2+T3, and H1+H2<T1+T2+T3; (3) T1<H1<T1+T3, T2<H2<T2+T3, H1+H2≥T1+T2+T3, the projection of the first hole and the projection of the second hole are outside away from each other along the thickness direction of the bipolar current collector.

14. The bipolar current collector of claim 13, wherein, 0.1≤H1≤15, 0.1≤H2≤15.

15. The bipolar current collector of claim 14, wherein, 1.5≤H1≤5, 1.5≤H2≤5.

16. The bipolar current collector of any one of claims 1 to 15, wherein, The polymer layer has a thickness of T3 μm, 1≤T3≤20.

17. The bipolar current collector of claim 16, wherein, 1≤T3≤4。 18. The bipolar current collector of any one of claims 1 to 17, wherein, The material of the polymer layer comprises at least one of polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyethylene terephthalate.

19. An electrochemical device, wherein, The electrochemical device comprises the bipolar current collector of any one of claims 1 to 18.

20. An electronic device, wherein, The electronic device comprises the electrochemical device of claim 19.

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