Composite current collector, bipolar electrode sheet, and bipolar battery

Abstract

To overcome the risk of internal short circuits in existing bipolar batteries using liquid electrolytes, this invention provides a composite current collector, comprising a base film, a first conductive layer, and a second conductive layer. The base film is a polymer film, including a central region and an edge encapsulation region, with the edge encapsulation region surrounding the central region. The first conductive layer covers one surface of the central region, and the second conductive layer covers the other surface. In the initial state, the porosity of the central region is greater than that of the edge encapsulation region, the pores in the central region are at least partially through-holes, and the porosity of the edge encapsulation region is <5%. This invention also discloses a bipolar electrode and a bipolar battery incorporating the above composite current collector. This invention effectively reduces the risk of internal short circuits while maintaining low impedance, resulting in a bipolar battery with high energy density, low impedance, and high safety.

Description

Technical Field

[0001] This invention belongs to the field of energy storage electronic components technology, specifically relating to a composite current collector, a bipolar electrode, and a bipolar battery. Background Technology

[0002] The power density of single-cell lithium / sodium-ion batteries is limited due to their finite voltage plateau. To improve the power density of single-cell lithium / sodium-ion batteries, the positive and negative electrode materials can be coated onto the same current collector, thereby increasing the voltage plateau and thus the power density through an internal series connection. To restrict the free movement of lithium / sodium ions, solid electrolytes are typically used to limit their movement range and prevent internal short circuits. However, using solid electrolytes in bipolar battery systems still has certain limitations. On the one hand, because solid electrolytes have a higher density than organic electrolytes, the energy density of the battery system is sacrificed to some extent. On the other hand, current solid electrolytes still suffer from low ionic conductivity, resulting in lower battery performance compared to batteries using liquid electrolytes. However, using liquid electrolytes also presents certain problems. The main issue is that the penetration of liquid electrolytes between different layers, combined with the inherent structure of bipolar electrodes integrating positive and negative electrodes on the same electrode, can easily form a conductive galvanic cell inside the battery, causing internal short circuits. Therefore, in solutions that do not use solid electrolytes, reducing the risk of internal short circuits is a key problem that current bipolar battery technology needs to address. Summary of the Invention

[0003] To address the risk of internal short circuits in existing bipolar batteries using liquid electrolytes, this invention provides a composite current collector, bipolar electrodes, and a bipolar battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] On one hand, the present invention provides a composite current collector, comprising a base film, a first conductive layer and a second conductive layer, wherein the base film is a polymer film, the base film includes a central region and an edge encapsulation region, the edge encapsulation region surrounds the periphery of the central region; the first conductive layer covers one side surface of the central region, and the second conductive layer covers the other side surface of the central region;

[0006] In the initial state, the porosity of the intermediate region is greater than that of the edge encapsulation region, the pores in the intermediate region are at least partially through-holes, and the porosity of the edge encapsulation region is <5%;

[0007] After covering the first conductive layer and the second conductive layer, the first conductive layer and the second conductive layer fill and seal the pores in the intermediate region, and the first conductive layer and the second conductive layer are electrically connected through the through holes in the intermediate region.

[0008] Optionally, the porosity of the intermediate region is 50% to 95%.

[0009] Optionally, the pore size of the intermediate region is 5~1000nm.

[0010] Optionally, the middle area is a rectangular area with a side length of 10mm≤L1≤1500mm; the edge encapsulation area is a rectangular frame area with a border width of 2.0mm≤L3≤15mm.

[0011] Optionally, the base film further includes a transition region located between the middle region and the edge encapsulation region, the porosity of the transition region being 5%~50%, and the border width of the transition region being 0mm≤L2≤20mm.

[0012] Optionally, the first conductive layer completely covers the intermediate region, and the edge of the first conductive layer at least partially or completely covers the transition region; and / or,

[0013] The second conductive layer completely covers the projection area of ​​the first conductive layer on the base film, and the edge of the second conductive layer at least partially or completely covers the transition area.

[0014] Optionally, the first conductive layer is aluminum or its alloy, and the second conductive layer is copper or its alloy.

[0015] Optionally, the thickness of the first conductive layer is 0.1~5.0 μm; and / or,

[0016] The thickness of the second conductive layer is 0.1~5.0 μm.

[0017] Optionally, the base film includes one or more of polyethylene, polyethylene terephthalate, polyimide, polypropylene, polyamide, polyphenylene sulfide, polyethylene naphthalate, ethylene-vinyl acetate copolymer, and polylactic acid.

[0018] Optionally, the resistivity between the first conductive layer and the second conductive layer of the composite current collector is ρ≤5.5Ω·m.

[0019] In another aspect, the present invention provides a bipolar electrode, comprising a positive electrode material layer, a negative electrode material layer, and a composite current collector as described above; the positive electrode material layer is located on the surface of the first conductive layer opposite to the base film, and the negative electrode material layer is located on the surface of the second conductive layer opposite to the base film.

[0020] Optionally, a first empty foil area is provided on the first conductive layer at the position of the outer perimeter frame of the positive electrode material layer, and the width of the first empty foil area is 2mm≤L4≤10mm;

[0021] A second empty foil area is provided on the second conductive layer at the position of the outer perimeter frame of the negative electrode material layer, and the width of the second empty foil area is 0.5mm≤L5≤6mm.

[0022] Optionally, the positive electrode material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; the positive electrode active material is selected from lithium positive electrode materials or sodium positive electrode materials, the lithium positive electrode material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials, the sodium positive electrode material includes one or more of sodium iron sulfate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron phosphate pyrophosphate, sodium vanadium phosphate, sodium copper iron manganese oxide, sodium iron nickel manganese oxide, and Prussian blue positive electrode; the positive electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal-organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets; the positive electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

[0023] Optionally, the negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder; the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxide; the negative electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal-organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets; the negative electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

[0024] In another aspect, the present invention provides a bipolar battery, including a separator, an electrolyte, and bipolar electrodes as described above, wherein a plurality of the bipolar electrodes are stacked sequentially, the separator is disposed between two adjacent bipolar electrodes, and the electrolyte is used for ion conduction between the bipolar electrodes.

[0025] Optionally, the electrolyte is a gel electrolyte or a liquid electrolyte.

[0026] Optionally, the edge encapsulation areas of multiple bipolar electrodes are stacked with the edge of the separator and then heat-fused to form a heat-sealed area. The heat-sealed area covers the edge of the first conductive layer and the edge of the second conductive layer to form a sealed space between two adjacent bipolar electrodes, and the electrolyte is contained in the sealed space.

[0027] Optionally, the base film further includes a transition region located between the intermediate region and the edge encapsulation region. The edge of the first conductive layer at least partially or completely covers the transition region, and the edge of the second conductive layer at least partially or completely covers the transition region. The heat-sealing region covers the edge encapsulation region, the transition region, the edge of the first conductive layer in the transition region, and the edge of the second conductive layer in the transition region.

[0028] Optionally, it also includes a first unipolar electrode and a second unipolar electrode, wherein the first unipolar electrode includes a first current collector and a first active material layer, and the second unipolar electrode includes a second current collector and a second active material layer.

[0029] The first unipolar electrode is located outside the outermost bipolar electrode, the first active material layer is located on the surface of the first current collector facing the bipolar electrode, and the diaphragm is disposed between the first unipolar electrode and the bipolar electrode.

[0030] The second unipolar electrode is located outside the outermost bipolar electrode, the second active material layer is located on the surface of the second current collector facing the bipolar electrode, and the diaphragm is disposed between the second unipolar electrode and the bipolar electrode.

[0031] Optionally, it also includes an aluminum-plastic film, in which the separator, the electrolyte and the bipolar electrode are encapsulated, and the edges of the aluminum-plastic film are stacked and hot-pressed in the edge encapsulation area to form the heat-sealed area.

[0032] According to the composite current collector provided by the present invention, a first conductive layer and a second conductive layer are disposed on both sides of a polymer film as a composite current collector. Compared with traditional metal current collectors, this composite current collector can effectively reduce the overall weight of the current collector, which is beneficial to improving the energy density of the battery. To address the problems of insufficient electronic conductivity and electrolyte permeation short circuit inherent in the polymer film itself, a middle region and an edge encapsulation region are disposed on the base film. The porosity of the middle region is defined to be greater than that of the edge encapsulation region. In the middle region, the first conductive layer and the second conductive layer on both sides are electrically connected by forming a middle region with high porosity through holes, thereby reducing the internal resistance. At the same time, the pores of the middle region are sealed by the first conductive layer and the second conductive layer. The edge encapsulation region is set to seal and form a sealed space for accommodating the electrolyte. By limiting the edge encapsulation region to a low porosity state, the probability of electrolyte permeation on both sides of the composite current collector can be effectively reduced. Thus, while ensuring low impedance, the risk of internal short circuit is effectively reduced. Combining the above factors, a bipolar battery with high energy density, low impedance, and high safety can be obtained. Attached Figure Description

[0033] Figure 1 This is a top view of the base film provided by the present invention;

[0034] Figure 2 This is a schematic diagram of the composite current collector provided by the present invention;

[0035] Figure 3 This is a schematic diagram of the structure of the bipolar electrode provided by the present invention;

[0036] Figure 4 This is a schematic diagram of the structure of the bipolar battery provided by the present invention.

[0037] The reference numerals in the accompanying drawings are as follows:

[0038] 1. Bipolar electrode; 11. Base film; 111. Intermediate region; 1111. Through hole; 112. Transition region; 113. Edge encapsulation region; 12. First conductive layer; 121. First empty foil region; 13. Second conductive layer; 131. Second empty foil region; 2. First unipolar electrode; 21. First current collector; 22. First active material layer; 3. Second unipolar electrode; 31. Second current collector; 32. Second active material layer; 4. Separator; 5. Heat-sealing region. Detailed Implementation

[0039] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0040] See Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a composite current collector, including a base film 11, a first conductive layer 12, and a second conductive layer 13. The base film 11 is a polymer film, and the base film 11 includes a central region 111 and an edge encapsulation region 113, with the edge encapsulation region 113 surrounding the periphery of the central region 111. The first conductive layer 12 covers one side surface of the central region 111, and the second conductive layer 13 covers the other side surface of the central region 111.

[0041] In the initial state, the porosity of the intermediate region 111 is greater than that of the edge encapsulation region 113, the pores in the intermediate region 111 are at least partially through holes 1111, and the porosity of the edge encapsulation region 113 is <5%;

[0042] After covering the first conductive layer 12 and the second conductive layer 13, the first conductive layer 12 and the second conductive layer 13 fill and seal the pores of the intermediate region 111, and the first conductive layer 12 and the second conductive layer 13 are electrically connected through the through hole 1111 of the intermediate region 111.

[0043] A composite current collector is constructed by setting a first conductive layer 12 and a second conductive layer 13 on both sides of a polymer film. Compared with traditional metal current collectors, this composite current collector can effectively reduce the overall weight of the current collector, which is beneficial to improving the energy density of the battery. To address the problems of insufficient electronic conductivity and electrolyte permeation short circuits inherent in polymer films, a central region 111 and an edge encapsulation region 113 are formed on the base film 11. The porosity of the central region 111 is defined to be greater than that of the edge encapsulation region 113. In the central region 111, high-porosity through-holes 1111 are formed to connect the two sides... The first conductive layer 12 and the second conductive layer 13 are electrically connected to each other, thereby reducing the internal resistance. At the same time, the first conductive layer 12 and the second conductive layer 13 seal the pores of the middle region 111, and the edge encapsulation region 113 is set to seal and form a sealed space for accommodating the electrolyte. By limiting the edge encapsulation region 113 to a low porosity state, the probability of electrolyte permeation on both sides of the composite current collector can be effectively reduced. Thus, while ensuring low impedance, the risk of internal short circuit is effectively reduced. Considering the above factors, a bipolar battery with high energy density, low impedance and high safety can be obtained.

[0044] In the description of this invention, unless otherwise specified, the term "initial state" refers to the state of the base film 11 before the deposition of the first conductive layer 12 and the second conductive layer 13; the term "porosity of the intermediate region 111" refers to the porosity of the intermediate region 111 of the base film 11 before the deposition of the first conductive layer 12 and the second conductive layer 13. It is understood that the porosity of the intermediate region 111 will decrease after the deposition of the first conductive layer 12 and the second conductive layer 13.

[0045] In some embodiments, the first conductive layer 12 and the second conductive layer 13 seal all the through holes 1111 of the intermediate region 111.

[0046] In some embodiments, in the initial state, the porosity of the edge encapsulation region 113 can be in the range of any two of 0.0%, 0.3%, 0.5%, 0.8%, 1.1%, 1.3%, 1.6%, 1.8%, 2.1%, 2.4%, 2.6%, 2.9%, 3.2%, 3.4%, 3.7%, 3.9%, 4.2%, 4.5%, 4.7%, 5.0%, or more.

[0047] If the porosity of the edge encapsulation region 113 is too high, there is a risk of electrolyte penetration.

[0048] In some embodiments, the porosity of the intermediate region 111 is 50% to 95% in the initial state.

[0049] In a specific embodiment, the porosity of the intermediate region 111 can be any two of the following: 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 93%, 95%, or more.

[0050] When the porosity of the intermediate region 111 is within the above range, it can provide sufficient filling space for the first conductive layer 12 and the second conductive layer 13, ensuring reliable electrical conduction between the two through the through hole 1111, effectively improving the electronic conductivity, while also ensuring the structural strength of the intermediate region 111 of the base film 11, avoiding easy damage to the base film 11 due to excessive porosity, thus balancing the conductivity and mechanical properties of the current collector.

[0051] In some embodiments, the pore size of the intermediate region 111 is 5~1000 nm.

[0052] In a specific embodiment, the pore size of the intermediate region 111 can be any two of the following: 5nm, 57nm, 109nm, 161nm, 213nm, 265nm, 317nm, 369nm, 421nm, 473nm, 525nm, 577nm, 629nm, 681nm, 733nm, 785nm, 837nm, 889nm, 941nm, 1000nm, or more.

[0053] The design of the pore size of the intermediate region 111, which is 5~1000nm, can be adapted to the filling requirements of the first conductive layer 12 and the second conductive layer 13 as well as the pore sealing requirements. If the pore size of the intermediate region 111 is too small, it will be difficult for the conductive layer to fully fill the pores, affecting the electrical conductivity and causing an increase in impedance. If the pore size of the intermediate region 111 is too large, the first conductive layer 12 and the second conductive layer 13 will be unable to completely seal the pores of the intermediate region 111, thus leaving a permeation path for electrolyte (especially electrolyte liquid) in the intermediate region 111, which will lead to an internal short circuit problem.

[0054] In some embodiments, the middle area 111 is a rectangular area with a side length of 10mm ≤ L1 ≤ 1500mm; the edge encapsulation area 113 is a rectangular frame area with a border width of 2.0mm ≤ L3 ≤ 15mm.

[0055] The intermediate region 111 and the edge encapsulation region 113 are based on the shape of the base film 11. In other embodiments, when the base film 11 is a circle, triangle or other shape, the intermediate region 111 and the edge encapsulation region 113 can also be adapted to the corresponding shape. In most embodiments, the shape of the intermediate region 111 is the same as the shape of the base film 11, and the edge encapsulation region 113 is a planar frame structure with the edge of the base film 11 as the outer edge.

[0056] In a specific embodiment, the border width of the edge encapsulation area 113 can be any two of the following: 2mm, 3mm, 3mm, 4mm, 5mm, 5mm, 6mm, 7mm, 7mm, 8mm, 9mm, 10mm, 10mm, 11mm, 12mm, 12mm, 13mm, 14mm, 14mm, 15mm.

[0057] Setting the border width of the edge encapsulation area 113 to 2.0mm≤L3≤15mm can balance the encapsulation sealing performance and battery energy density. If the border width of the edge encapsulation area 113 is too low, it will easily lead to insufficient sealing strength and electrolyte leakage. If the border width of the edge encapsulation area 113 is too high, it will increase the non-battery active area and lead to a decrease in battery energy density.

[0058] In some embodiments, the base film 11 further includes a transition region 112, which is located between the middle region 111 and the edge encapsulation region 113. The porosity of the transition region 112 is 5% to 50%, and the border width of the transition region 112 is 0 mm ≤ L2 ≤ 20 mm.

[0059] In a specific embodiment, the porosity of the transition region 112 can be any two of the following: 5.0%, 7.4%, 9.8%, 12.2%, 14.6%, 17.0%, 19.4%, 21.8%, 24.2%, 26.6%, 29.0%, 31.4%, 33.8%, 36.2%, 38.6%, 41.0%, 43.4%, 45.8%, 48.2%, 50.0%, or more.

[0060] In a specific embodiment, the border width of the transition area 112 can be 0.0mm, 1.1mm, 2.2mm, 3.3mm, 4.4mm, 5.5mm, 6.6mm, 7.7mm, 8.8mm, 9.9mm, 11.0mm, 12.1mm, 13.2mm, 14.3mm, 15.4mm, 16.5mm, 17.6mm, 18.7mm, 19.8mm, 20.0mm, or any two of the above.

[0061] The setting of the transition zone 112 and the porosity design of 5%~50% can avoid the stress concentration of the base film 11 structure caused by the sudden change in porosity between the middle zone 111 and the edge zone, and improve the overall mechanical stability of the base film 11. At the same time, the cooperation between the transition zone 112 and the first conductive layer 12 and the second conductive layer 13 can play the role of gradient barrier of electrolyte, further reducing the risk of electrolyte penetration. The width design of 0mm≤L2≤20mm can flexibly adapt to different sealing and structural requirements.

[0062] In some embodiments, the porosity of the intermediate region 111, the transition region 112, and the edge encapsulation region 113 can be obtained by testing the following methods:

[0063] The sample to be tested was pre-baked at 105℃ for 4 hours. 0.3g~1.0g of the sample was placed in the sample tube of the mercury porosimeter and then placed in the mercury porosimeter. The sample mass was recorded. The test temperature was set to 20±1℃, the mercury injection pressure was 0.10 to 61,000.00psia, and the contact angle was 130.0°. The test was started, and the mercury volume Vm before pressure impregnation and the mercury volume Vs after pressure impregnation were recorded. The porosity is then (Vm-Vs) / Vm*100%.

[0064] In some embodiments, the first conductive layer 12 completely covers the intermediate region 111, and the edge of the first conductive layer 12 at least partially or completely covers the transition region 112.

[0065] By ensuring that the first conductive layer 12 completely covers the intermediate region 111, the adsorption of electrolyte by the pores in the intermediate region 111 can be effectively avoided, reducing the risk of internal short circuits.

[0066] In some embodiments, the second conductive layer 13 completely covers the projection area of ​​the first conductive layer 12 on the base film 11, and the edge of the second conductive layer 13 at least partially or completely covers the transition region 112.

[0067] The first conductive layer 12 is used to set the positive electrode material layer, and the second conductive layer 13 is used to set the negative electrode material layer, so that the second conductive layer 13 completely covers the projection area of ​​the first conductive layer 12 on the base film 11. This is mainly used to ensure that the negative electrode material layer has a setting area that can completely cover and exceed the positive electrode material layer, ensuring that the N / P ratio is greater than 1, which can effectively reduce the risk of lithium plating on the negative electrode.

[0068] During the subsequent hot-press sealing process, the transition zone 112 and the edge encapsulation zone 113 are both located in the heat-sealing area 5. By at least partially or completely covering the transition zone 112 with the edges of the first conductive layer 12 and the second conductive layer 13, the first conductive layer 12 and the second conductive layer 13 themselves have good electrolyte barrier properties, thereby forming a continuous encapsulation between the first conductive layer 12 and the second conductive layer 13 and the heat-sealing area 5, ensuring sealing performance and reducing electrolyte penetration between different layers.

[0069] In some embodiments, the first conductive layer 12 and the second conductive layer 13 each independently include one or more elements or alloys selected from copper, aluminum, gold, silver, iron, nickel, etc.

[0070] In some embodiments, the first conductive layer 12 is aluminum or its alloy, and the second conductive layer 13 is copper or its alloy.

[0071] In some embodiments, the thickness of the first conductive layer 12 is 0.1~5.0 μm.

[0072] In some embodiments, the thickness of the second conductive layer 13 is 0.1~5.0 μm.

[0073] If the thickness of the first conductive layer 12 and the second conductive layer 13 is too low, it will be difficult to ensure complete sealing of the pores in the intermediate region 111, and the intermediate region 111 will be at risk of permeation. If the thickness of the first conductive layer 12 and the second conductive layer 13 is too high, it will lead to an increase in the overall weight of the composite current collector, losing its weight advantage compared to conventional metal fluids and affecting the energy density of the battery.

[0074] In some embodiments, the base film 11 comprises one or more of polyethylene, polyethylene terephthalate, polyimide, polypropylene, polyamide, polyphenylene sulfide, polyethylene naphthalate, ethylene-vinyl acetate copolymer, and polylactic acid.

[0075] In some embodiments, the resistivity between the first conductive layer 12 and the second conductive layer 13 of the composite current collector is ρ≤5.5Ω·m.

[0076] like Figure 3 As shown, another embodiment of the present invention provides a bipolar electrode 1, including a positive electrode material layer, a negative electrode material layer, and a composite current collector as described above; the positive electrode material layer is located on the surface of the first conductive layer 12 away from the base film 11, and the negative electrode material layer is located on the surface of the second conductive layer 13 away from the base film 11.

[0077] Because of the composite current collector used as described above, the high-porosity middle region 111 can ensure electrical conductivity between the positive electrode material layer and the negative electrode material layer, reducing series impedance, while the low-porosity edge encapsulation region 113 can prevent electrolyte from penetrating to both sides of the composite current collector, avoiding the occurrence of internal short circuits between the positive electrode material layer and the negative electrode material layer.

[0078] In some embodiments, a first empty foil area 121 is provided on the first conductive layer 12 at the position of the outer perimeter frame of the positive electrode material layer, and the width of the first empty foil area 121 is 2mm≤L4≤10mm.

[0079] In a specific embodiment, the width of the first empty foil area 121 can be any two of the following: 2.0mm, 2.4mm, 2.8mm, 3.2mm, 3.6mm, 4.0mm, 4.4mm, 4.8mm, 5.2mm, 5.6mm, 6.0mm, 6.4mm, 6.8mm, 7.2mm, 7.6mm, 8.0mm, 8.5mm, 9.0mm, 9.5mm, 10.0mm.

[0080] In some embodiments, a second empty foil area 131 is provided on the second conductive layer 13 at the position of the outer perimeter frame of the negative electrode material layer, and the width of the second empty foil area 131 is 0.5mm≤L5≤6mm.

[0081] In a specific embodiment, the width of the second empty foil area 131 can be any two of the following: 0.5mm, 0.8mm, 1.1mm, 1.4mm, 1.7mm, 2.0mm, 2.3mm, 2.6mm, 2.9mm, 3.2mm, 3.5mm, 3.8mm, 4.1mm, 4.4mm, 4.7mm, 5.0mm, 5.3mm, 5.6mm, 5.8mm, 6.0mm.

[0082] The first empty foil area 121 and the second empty foil area 131 are used to form the heat-sealing area 5 in the future, to ensure the encapsulation continuity between the first conductive layer 12 and the second conductive layer 13 and the heat-sealing area 5, and to avoid the formation of electrolyte penetration sites at the edge of the composite current collector.

[0083] In some embodiments, the positive electrode material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; the positive electrode active material is selected from lithium positive electrode materials or sodium positive electrode materials, the lithium positive electrode material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials, the sodium positive electrode material includes one or more of sodium iron sulfate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron phosphate pyrophosphate, sodium vanadium phosphate, sodium copper iron manganese oxide, sodium iron nickel manganese oxide, and Prussian blue positive electrode; the positive electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal-organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets; the positive electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

[0084] In some embodiments, the negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder; the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxide; the negative electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal-organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets; the negative electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

[0085] like Figure 4 As shown, another embodiment of the present invention provides a bipolar battery, including a separator 4, an electrolyte and a bipolar electrode 1 as described above. A plurality of the bipolar electrodes 1 are stacked sequentially, and the separator 4 is disposed between two adjacent bipolar electrodes 1. The electrolyte is used for ion conduction between the bipolar electrodes 1.

[0086] Stacking multiple bipolar electrodes 1 together with a separator 4 enables an internal series design for the battery, improving the voltage platform and power density. At the same time, the electrolyte barrier structure of the composite current collector and electrodes solves the internal short circuit problem under liquid electrolyte, eliminating the need for solid electrolyte and balancing battery performance and energy density.

[0087] In some embodiments, the electrolyte is a gel electrolyte or a liquid electrolyte.

[0088] When the electrolyte is a gel electrolyte, polymeric monomers can be added to the liquid electrolyte to polymerize and form a gel-like framework to adsorb and fix the liquid electrolyte. Compared with liquid electrolyte, gel electrolyte can limit the penetration of electrolyte on both sides of the composite current collector, thus having higher safety. At the same time, since it adsorbs some liquid electrolyte inside, gel electrolyte has higher ion conduction efficiency than solid electrolyte.

[0089] In some embodiments, the polymeric monomers include one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, methyl methacrylate, acrylonitrile, pentaerythritol tetraacrylate, 1,3-dioxolane, ethoxylated trimethylolpropane triacrylate, and 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0090] In some embodiments, the edge encapsulation areas 113 of a plurality of bipolar electrodes 1 are stacked with the edges of the separator 4 and then heat-sealed to form a heat-sealed area 5. The heat-sealed area 5 covers the edges of the first conductive layer 12 and the second conductive layer 13 to form a sealed space between two adjacent bipolar electrodes 1, and the electrolyte is contained in the sealed space.

[0091] The heat-sealing region 5 has a frame-like structure, which can seal the electrolyte in the sealed space and restrict the flow of the electrolyte. At the same time, based on the setting of the low porosity edge encapsulation region 113, the risk of electrolyte permeation in the heat-sealing region 5 can be reduced, thereby improving the safety of the bipolar battery.

[0092] In some embodiments, the base film 11 further includes a transition region 112 located between the intermediate region 111 and the edge encapsulation region 113. The edge of the first conductive layer 12 at least partially or completely covers the transition region 112, and the edge of the second conductive layer 13 at least partially or completely covers the transition region 112. The heat-sealing region 5 covers the edge encapsulation region 113, the transition region 112, the first conductive layer 12 located at the edge of the transition region 112, and the second conductive layer 13 located at the edge of the transition region 112.

[0093] By having the heat-sealed area 5 cover the edge encapsulation area 113, the transition area 112, the first conductive layer 12 located at the edge of the transition area 112, and the second conductive layer 13 located at the edge of the transition area 112, the first conductive layer 12, the second conductive layer 13 and the heat-sealed area 5 can form a continuous encapsulation, preventing the electrolyte from penetrating into the heat-sealed area 5.

[0094] In some embodiments, the device further includes a first unipolar electrode 2 and a second unipolar electrode 3. The first unipolar electrode 2 includes a first current collector 21 and a first active material layer 22, and the second unipolar electrode 3 includes a second current collector 31 and a second active material layer 32.

[0095] The first unipolar electrode 2 is located outside the outermost bipolar electrode 1, the first active material layer 22 is located on the side surface of the first current collector 21 facing the bipolar electrode 1, the diaphragm 4 is disposed between the first unipolar electrode 2 and the bipolar electrode 1, and the polarity of the first active material layer 22 is opposite to that of the opposite side of the bipolar electrode 1.

[0096] The second unipolar electrode 3 is located outside the outermost bipolar electrode 1, the second active material layer 32 is located on the side surface of the second current collector 31 facing the bipolar electrode 1, the diaphragm 4 is disposed between the second unipolar electrode 3 and the bipolar electrode 1, and the polarity of the second unipolar electrode 3 is opposite to that of the opposite bipolar clip.

[0097] The combination of the unipolar electrode, the bipolar electrode 1, and the separator 4 forms a complete stacked battery structure, ensuring the stability and continuity of the battery current output and improving the overall electrochemical performance of the battery.

[0098] In some embodiments, the first current collector 21 and the second current collector 31 are selected from the composite current collector.

[0099] In some embodiments, the first active material layer 22 is a negative electrode layer, and the second active material layer 32 is a positive electrode layer. The selection of the negative electrode layer is the same as that of the negative electrode material layer described above, and the selection of the positive electrode layer is the same as that of the positive electrode material layer described above, which will not be repeated here.

[0100] In some embodiments, the first current collector 21 has a negative electrode tab and the second current collector 31 has a positive electrode tab, which facilitates the connection of the battery to an external circuit.

[0101] In some embodiments, an aluminum-plastic film is also included, in which the separator 4, the electrolyte and the bipolar electrode 1 are encapsulated, and the edges of the aluminum-plastic film are stacked and hot-pressed in the edge encapsulation area 113 to form the heat-sealed area 5.

[0102] The aluminum-plastic film encapsulates the battery and forms a heat-sealing area 5 together with the edge area. The aluminum-plastic film has excellent water and oxygen barrier properties, which can isolate the influence of the external environment on the battery interior and delay battery aging. At the same time, the heat sealing with the edge area further enhances the overall sealing of the battery, prevents electrolyte leakage and external water vapor and oxygen from entering the battery interior, and improves battery storage and cycle life.

[0103] The present invention will be further illustrated by the following examples.

[0104] Example 1

[0105] This embodiment illustrates the bipolar battery disclosed in this invention, which includes a separator, an electrolyte, a first unipolar electrode, a second unipolar electrode, and a bipolar electrode. Multiple bipolar electrodes are stacked sequentially, and the separator is disposed between two adjacent bipolar electrodes.

[0106] The bipolar electrode includes a positive electrode material layer, a negative electrode material layer, and a composite current collector; the composite current collector includes a base film, a first conductive layer, and a second conductive layer, wherein the first conductive layer is aluminum, the second conductive layer is copper, the base film is a polyethylene terephthalate film, and the base film includes an intermediate region, a transition region, and an edge encapsulation region, wherein the edge encapsulation region surrounds the periphery of the intermediate region, and the transition region is located between the intermediate region and the edge encapsulation region; the first conductive layer covers the intermediate region and the transition region, and the second conductive layer covers the other side surface of the intermediate region; after covering the first conductive layer and the second conductive layer, the first conductive layer and the second conductive layer fill and seal the pores of the intermediate region, and the first conductive layer and the second conductive layer are electrically conductive through the through-holes of the intermediate region.

[0107] In the initial state, the porosity of the intermediate region is greater than that of the edge packaging region. The pores in the intermediate region are at least partially through-holes. The porosity of the edge packaging region is 1%, the porosity of the intermediate region is 72%, the pore diameter of the intermediate region is 10~800nm, and the porosity of the transition region is 24%.

[0108] The positive electrode material layer is located on the surface of the first conductive layer away from the base film. A first empty foil area is provided on the first conductive layer at the outer perimeter frame position of the positive electrode material layer. The negative electrode material layer is located on the surface of the second conductive layer away from the base film. A second empty foil area is provided on the second conductive layer at the outer perimeter frame position of the negative electrode material layer. The positive electrode active material of the positive electrode material layer is lithium iron phosphate, and the negative electrode active material of the negative electrode material layer is graphite.

[0109] The first unipolar electrode includes a first current collector and a negative electrode layer, and the second unipolar electrode includes a second current collector and a positive electrode layer;

[0110] The first unipolar electrode is located outside the outermost bipolar electrode, the negative electrode layer is located on the surface of the first current collector facing the bipolar electrode, and the diaphragm is disposed between the first unipolar electrode and the bipolar electrode.

[0111] The second unipolar electrode is located outside the outermost bipolar electrode, the positive electrode layer is located on the surface of the second current collector facing the bipolar electrode, and the diaphragm is disposed between the second unipolar electrode and the bipolar electrode.

[0112] The edges of the first unipolar electrode, the edges of the second unipolar electrode, the transition area of ​​multiple bipolar electrodes, the edge encapsulation area, and the edge of the separator are stacked and heat-fused together to form a heat-sealed area. The heat-sealed area covers the edges of the first empty foil area and the edges of the second empty foil area, so that a sealed space is formed on both sides of the bipolar electrode, and the electrolyte is contained in the sealed space.

[0113] Example 2

[0114] This embodiment is used to illustrate the bipolar battery disclosed in this invention, including most of the structure in Embodiment 1, with the difference being:

[0115] The porosity of the edge encapsulation region is 0.1%, the porosity of the middle region is 90%, and the porosity of the transition region is 5%.

[0116] Example 3

[0117] This embodiment is used to illustrate the bipolar battery disclosed in this invention, including most of the structure in Embodiment 1, with the difference being:

[0118] The porosity of the edge encapsulation region is 4%, the porosity of the middle region is 60%, and the porosity of the transition region is 20%.

[0119] Example 4

[0120] This embodiment is used to illustrate the bipolar battery disclosed in this invention, including most of the structure in Embodiment 1, with the difference being:

[0121] The pore size in the intermediate region is >2μm.

[0122] Example 5

[0123] This embodiment is used to illustrate the bipolar battery disclosed in this invention, including most of the structure in Embodiment 1, with the difference being:

[0124] The edges of the first unipolar electrode, the second unipolar electrode, and the edges of multiple bipolar electrodes are stacked and heat-fused together with the edges of the separator to form a heat-sealing area. The heat-sealing area does not cover the edges of the first empty foil area and the second empty foil area. A gap is left between the edge of the first empty foil area and the heat-sealing area, and a gap is left between the edge of the second empty foil area and the heat-sealing area, which is located in the transition zone.

[0125] Comparative Example 1

[0126] This comparative example is used to illustrate the bipolar battery disclosed in this invention, including most of the structures in Example 1, with the following differences:

[0127] The porosity of the edge encapsulation area, the middle area, and the transition area is all 72%.

[0128] Performance testing

[0129] The bipolar battery prepared above was subjected to the following performance tests:

[0130] Energy density: The battery under test is charged at 1.0C to 3.6×n V, where n is the number of internal cells in series. After resting for 10 minutes, it is discharged at 1.0C to 2.7×n V. The discharge energy E is recorded. The discharge energy E / battery mass m is recorded as the energy density, with the unit being Wh / kg.

[0131] Power density: The battery under test is charged at 1.0C to 3.6×n V, where n is the number of internal cells in series. After resting for 10 minutes, it is discharged at 20.0C to 2.7×n V. The discharge power W is recorded. The discharge power W / battery mass m is recorded as the power density, with the unit being kW / kg.

[0132] Cycle capacity retention: The battery under test is charged at 1.0C to 3.6×n V, where n is the number of internal battery cells in series. After resting for 10 minutes, it is discharged at 1.0C to 2.7×n V. The initial discharge capacity C1 is recorded. The test procedure is repeated for 500 cycles, and the discharge capacity Cn of each single cycle is recorded. C500 / C1*100% is the capacity retention rate after 500 cycles, in % or less. If the capacity retention rate is lower than 60%, the test is stopped, and the corresponding number of cycles n1 is recorded. During the cycle, it is observed whether the battery exhibits phenomena such as gas swelling.

[0133] DC impedance: When the battery under test is adjusted to 20% SOC, it is discharged at a current of 3.0C for 10s. The voltages V1 and V2 before and after discharge are recorded. The ratio of the voltage difference to the current, i.e. (V1-V2) / 3.0C, is recorded as the DC impedance, and the unit is mΩ.

[0134] The test results are entered into Table 1.

[0135] Table 1

[0136]

[0137] The test results of Examples 1-5 and Comparative Example 1 show that the design of the base film with a higher porosity in the middle region than in the edge encapsulation region can significantly improve the energy density and power density of the bipolar battery, improve the cycle capacity retention rate, reduce DC resistance, effectively reduce battery gas generation, and improve the overall performance and safety of the battery. However, in Comparative Example 1, which did not differentiate the porosity regions of the base film, internal self-discharge caused by electrolyte permeation exacerbated the battery side reactions, resulting in capacity reduction and gas generation, and also posed a safety risk.

[0138] The test results of Examples 1-3 and Example 4 show that when the pore size in the middle region is controlled within a suitable range, the battery can maintain excellent energy density, power density and cycle stability, with low impedance and less gas generation. However, in Example 4, the pore size is too large, and the conductive layer cannot completely seal the pores, which makes it easy for the electrolyte to penetrate into the middle region and trigger side reactions. This will lead to a significant decrease in various battery performances, a decrease in cycle capacity retention, an increase in impedance, and a slight gas generation.

[0139] As can be seen from the test results of Examples 1-3 and Example 5, when the heat-sealed area covers the edge encapsulation area, the transition area, and the edges of the first and second conductive layers, a continuous sealed space is formed, which can effectively restrict the flow of electrolyte, thereby improving energy density, power density, and cycle capacity retention, and reducing impedance and gas generation. However, in Example 5, the heat-sealed area does not completely cover the relevant areas, and the electrolyte is prone to leakage or penetration to the edge of the conductive layer, which will lead to a significant decline in battery performance, a significant decrease in cycle capacity retention, a significant increase in impedance, and severe gas generation.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that, It includes a base film, a first conductive layer, and a second conductive layer. The base film is a polymer film and includes a central region and an edge encapsulation region, with the edge encapsulation region surrounding the periphery of the central region. The first conductive layer covers one side surface of the central region, and the second conductive layer covers the other side surface of the central region. In the initial state, the porosity of the intermediate region is greater than that of the edge encapsulation region, the pores in the intermediate region are at least partially through-holes, and the porosity of the edge encapsulation region is <5%; After covering the first conductive layer and the second conductive layer, the first conductive layer and the second conductive layer fill and seal the pores in the intermediate region, and the first conductive layer and the second conductive layer are electrically connected through the through holes in the intermediate region.

2. The composite current collector according to claim 1, characterized in that, The porosity of the intermediate region is 50% to 95%.

3. The composite current collector according to claim 1, characterized in that, The pore size of the intermediate region is 5~1000nm.

4. The composite current collector according to claim 1, characterized in that, The middle area is a rectangular area with a side length of 10mm ≤ L1 ≤ 1500mm; the edge encapsulation area is a rectangular frame area with a border width of 2.0mm ≤ L3 ≤ 15mm.

5. The composite current collector according to claim 1, characterized in that, The base film also includes a transition region located between the middle region and the edge encapsulation region. The porosity of the transition region is 5% to 50%, and the border width of the transition region is 0mm ≤ L2 ≤ 20mm.

6. The composite current collector according to claim 5, characterized in that, The first conductive layer completely covers the intermediate region, and the edge of the first conductive layer at least partially or completely covers the transition region; and / or, The second conductive layer completely covers the projection area of ​​the first conductive layer on the base film, and the edge of the second conductive layer at least partially or completely covers the transition area.

7. The composite current collector according to claim 6, characterized in that, The first conductive layer is aluminum and its alloys, and the second conductive layer is copper and its alloys.

8. The composite current collector according to claim 1, characterized in that, The thickness of the first conductive layer is 0.1~5.0 μm; and / or, The thickness of the second conductive layer is 0.1~5.0 μm.

9. The composite current collector according to claim 1, characterized in that, The base film includes one or more of polyethylene, polyethylene terephthalate, polyimide, polypropylene, polyamide, polyphenylene sulfide, polyethylene naphthalate, ethylene-vinyl acetate copolymer, and polylactic acid.

10. The composite current collector according to claim 1, characterized in that, The resistivity between the first and second conductive layers of the composite current collector is ρ≤5.5Ω·m.

11. A bipolar electrode, characterized in that, It includes a positive electrode material layer, a negative electrode material layer, and a composite current collector as described in any one of claims 1 to 10; the positive electrode material layer is located on the surface of the first conductive layer opposite to the base film, and the negative electrode material layer is located on the surface of the second conductive layer opposite to the base film.

12. The bipolar electrode according to claim 11, characterized in that, A first empty foil area is provided on the first conductive layer at the position of the outer perimeter frame of the positive electrode material layer, and the width of the first empty foil area is 2mm≤L4≤10mm; A second empty foil area is provided on the second conductive layer at the position of the outer perimeter frame of the negative electrode material layer, and the width of the second empty foil area is 0.5mm≤L5≤6mm.

13. The bipolar electrode according to claim 11, characterized in that, The positive electrode material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; the positive electrode active material is selected from lithium positive electrode materials or sodium positive electrode materials, the lithium positive electrode material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials, the sodium positive electrode material includes one or more of sodium iron sulfate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron phosphate pyrophosphate, sodium vanadium phosphate, sodium copper iron manganese oxide, sodium iron nickel manganese oxide, and Prussian blue positive electrode; the positive electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, three-dimensional conductive metal-organic framework, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets; the positive electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

14. The bipolar electrode according to claim 11, characterized in that, The negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder; the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxide; the negative electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, three-dimensional conductive metal-organic framework, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite flakes; the negative electrode binder includes one or more of styrene-butadiene rubber, modified rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polypropylene, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, and polyacrylonitrile.

15. A bipolar battery, characterized in that, The device includes a diaphragm, an electrolyte, and a bipolar electrode as described in any one of claims 11 to 14. A plurality of the bipolar electrodes are stacked sequentially, and the diaphragm is disposed between two adjacent bipolar electrodes. The electrolyte is used for ion conduction between the bipolar electrodes.

16. The bipolar battery according to claim 15, characterized in that, The electrolyte is a gel electrolyte or a liquid electrolyte.

17. The bipolar battery according to claim 15, characterized in that, Multiple bipolar electrodes are stacked on the edge of the encapsulation area and the edge of the separator and then heat-sealed together to form a heat-sealed area. The heat-sealed area covers the edge of the first conductive layer and the edge of the second conductive layer to form a sealed space between two adjacent bipolar electrodes, and the electrolyte is contained in the sealed space.

18. The bipolar battery according to claim 17, characterized in that, The base film also includes a transition region located between the intermediate region and the edge encapsulation region. The edge of the first conductive layer at least partially or completely covers the transition region, and the edge of the second conductive layer at least partially or completely covers the transition region. The heat-sealing region covers the edge encapsulation region, the transition region, the edge of the first conductive layer in the transition region, and the edge of the second conductive layer in the transition region.

19. The bipolar battery according to claim 15, characterized in that, It also includes a first unipolar electrode and a second unipolar electrode. The first unipolar electrode includes a first current collector and a first active material layer, and the second unipolar electrode includes a second current collector and a second active material layer. The first unipolar electrode is located outside the outermost bipolar electrode, the first active material layer is located on the surface of the first current collector facing the bipolar electrode, and the diaphragm is disposed between the first unipolar electrode and the bipolar electrode. The second unipolar electrode is located outside the outermost bipolar electrode, the second active material layer is located on the surface of the second current collector facing the bipolar electrode, and the diaphragm is disposed between the second unipolar electrode and the bipolar electrode.

20. The bipolar battery according to claim 17, characterized in that, It also includes an aluminum-plastic film, in which the separator, the electrolyte and the bipolar electrode are encapsulated, and the edges of the aluminum-plastic film are stacked and hot-pressed in the edge encapsulation area to form the heat-sealed area.

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