Bipolar cell and preparation method thereof, battery module and electric equipment

Abstract

The invention relates to a bipolar battery cell and a preparation method thereof, a battery module and electric equipment, the bipolar battery cell comprises a plurality of bipolar plate units which are laminated, each bipolar plate unit comprises a first pole plate, a conductive adhesive layer and a second pole plate which are laminated in sequence, the first pole plate comprises a first current collector and a negative electrode coating, and the second pole plate comprises a second current collector and a negative electrode coating. The second pole piece comprises a second current collector and a positive electrode coating, the first current collector is close to the second current collector, and an isolating membrane is arranged between every two adjacent bipolar piece units. The bipolar battery cell disclosed by the invention is simple in structure, has improved electrical performance and structural stability, is beneficial to improving the coating quality and avoiding the problem that the yield of the pole pieces is influenced by bulge, wrinkling, warping and the like of the pole pieces by respectively preparing the first pole piece and the second pole piece and carrying out hot pressing after lamination, and is suitable for large-scale production.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium batteries, and in particular, to a bipolar battery cell, a preparation method thereof, a battery module, and an electrical device. Background Art

[0002] Lithium-ion batteries have been widely used in energy storage systems, electric vehicles, consumer electronics and other fields due to their high energy density and long cycle life. With the diversification of application scenarios, the requirements for battery systems in terms of assembly efficiency, space utilization, and performance stability are also continuously increasing. Traditional battery structural forms, including square cases, cylinders, soft-pack batteries, etc., usually require complex external circuits for series or parallel connection of battery cells, which not only increases the complexity of the battery system, but also limits the layout flexibility and space utilization of the battery to a certain extent.

[0003] A bipolar battery cell is a new type of battery cell structure. By optimizing the internal connection design, it is beneficial to simplify the series connection method of battery cells and improve the space utilization efficiency. The characteristics of this structure are that the positive and negative electrode plates are alternately laminated, and the series connection of battery cell units is realized through a conductive substrate, which shows potential advantages in high-efficiency energy transfer, layout flexibility, and system integration, and is suitable for a variety of complex application scenarios. However, the bipolar battery cell has its unique problems in the manufacturing process. For example, during the material coating process, due to the different material properties of the positive and negative electrodes, problems such as electrode plate cracking, uneven coating, or material contamination may occur; during the compaction process, due to the large difference in the extension of the positive and negative current collectors, problems such as electrode plate wrinkling and warping are likely to occur. In addition, due to the complexity of process control, the bipolar battery cells prepared by the existing processes still need to be improved in terms of performance such as energy density, consistency, and cycle life. These problems not only limit the production efficiency, but also affect the competitiveness of bipolar battery cell products in large-scale applications. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a bipolar battery cell with improved electrical performance, a preparation method thereof, a battery module, and an electrical device.

[0005] To achieve the above purpose, in the first aspect of the present disclosure, a bipolar battery cell is provided. The bipolar battery cell includes a plurality of bipolar plate units stacked. The bipolar plate unit includes a first electrode plate, a conductive adhesive layer, and a second electrode plate stacked in sequence. The first electrode plate includes a first current collector and a negative electrode coating, the second electrode plate includes a second current collector and a positive electrode coating, the first current collector is close to the second current collector, and an isolation film is provided between adjacent bipolar plate units.

[0006] Optionally, the material of the first current collector includes one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0007] Optionally, the material of the second current collector includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0008] Optionally, the negative electrode coating is prepared from an aqueous-based system slurry and / or an organic solvent-based system slurry; The positive electrode coating is prepared from an organic solvent-based system slurry.

[0009] Optionally, the material of the conductive adhesive layer includes a first conductive agent and a first binder, and the weight ratio of the first conductive agent to the first binder is 1:(0.1~1.5); the conductive adhesive layer is prepared from an organic solvent-based system slurry and / or an aqueous-based system slurry.

[0010] Optionally, the first conductive agent includes one or more of superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or, The first binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyacrylamide, and polyvinyl alcohol.

[0011] Optionally, the compaction density of the first electrode sheet is 1.4~1.8 g / cm 3 ; and / or, the compaction density of the second electrode sheet is 2.6~3.7 g / cm 3 .

[0012] In a second aspect of the present disclosure, a method for preparing the bipolar battery cell described in the first aspect of the present disclosure is provided, and the method includes: Obtaining a first current collector and a second current collector respectively, and the first current collector and the second current collector each have opposite first and second surfaces; Coating a negative electrode slurry on the first surface of the first current collector, and then performing a first rolling to obtain a first electrode sheet; Coating a positive electrode slurry on the second surface of the second current collector, and then performing a second rolling to obtain a second electrode sheet; Coating a conductive adhesive slurry on the first surface of the second current collector to obtain a second electrode sheet covered with a conductive adhesive layer; Stacking the first electrode sheet, the second electrode sheet covered with the conductive adhesive layer, and the separator in sequence to obtain a stacked structure; Performing hot pressing on the stacked structure to obtain a bipolar battery cell.

[0013] Optionally, the conditions for the first rolling include: a pressure of 1 to 100 T, a temperature of 0 to 60 °C, and a rolling speed of 5 to 120 m / min.

[0014] Optionally, the conditions for the second rolling include: a pressure of 1 to 100 T, a temperature of 0 to 60 °C, and a rolling speed of 5 to 120 m / min.

[0015] Optionally, the conditions for the hot pressing include: a temperature of 25 to 150 °C, a pressure of 0.2 to 3 MPa, and a pressure holding time of 10 to 600 s.

[0016] In a third aspect of the present disclosure, a battery module is provided, including the bipolar electrode core described in the first aspect of the present disclosure.

[0017] In a fourth aspect of the present disclosure, an electrical device is provided, characterized by including the battery module described in the third aspect of the present disclosure.

[0018] Through the above technical solutions, the bipolar electrode core of the present disclosure has a simple structure. A conductive adhesive layer is provided between the first electrode sheet and the second electrode sheet to achieve mechanical bonding and electrical connection, which is beneficial to improving the electrical performance and structural stability of the electrode core. By separately preparing the first electrode sheet and the second electrode sheet and performing hot pressing after lamination, it is beneficial to improve the coating quality and avoid problems that affect the yield rate of the electrode sheet, such as electrode sheet protrusion, wrinkling, and warping, and is suitable for large-scale production.

[0019] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation section. Description of the Drawings

[0020] The drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific implementation, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings: Figure 1 is a schematic structural diagram of a bipolar electrode core in a specific implementation.

[0021] Description of the Reference Numerals in the Drawings 10 - First electrode sheet, 11 - First current collector, 12 - Negative electrode coating, 20 - Conductive adhesive layer, 30 - Second electrode sheet, 31 - Second current collector, 32 - Positive electrode coating, 40 - Separator film. Specific Implementation

[0022] The following will describe in detail the specific implementation of the present disclosure with reference to the drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure and is not used to limit the present disclosure.

[0023] In this disclosure, unless otherwise stated, the directional terms such as "upper", "lower", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing this disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this disclosure. In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0024] In the first aspect of this disclosure, a bipolar battery cell is provided. Referring to Figure 1 , the bipolar battery cell includes a plurality of bipolar plate units stacked together. The bipolar plate unit includes a first pole plate 10, a conductive adhesive layer 20, and a second pole plate 30 stacked in sequence.

[0025] By providing a conductive adhesive layer 20 between the first pole plate 10 and the second pole plate 30 of the bipolar plate unit in this disclosure, the dual functions of mechanical bonding and electrical connection are achieved. The conductive adhesive layer 20 can evenly cover the connection interface, reduce the contact resistance, and at the same time can avoid the poor connection problems caused by direct welding or mechanical crimping in the traditional design, significantly improving the conductivity and structural stability of the battery cell.

[0026] In one embodiment, the material of the conductive adhesive layer 20 may include a first conductive agent and a first binder, and the weight ratio of the first conductive agent to the first binder may be 1:(0.1 - 1.5), preferably 1:(0.1 - 1). The conductive adhesive layer 20 can be prepared from an organic solvent-based slurry and / or a water-based slurry.

[0027] Among them, the first conductive agent may include one or more of superconducting carbon, conductive carbon black (SP), conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (CNT), graphene, and carbon nanofibers. The first binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), and polyvinyl alcohol (PVA).

[0028] In one embodiment, the thickness of the conductive adhesive layer 20 may be 0.1 - 10 μm, preferably 0.5 - 2 μm, which is beneficial to improving the energy density and cycle life of the battery cell while ensuring the conductivity and bonding performance.

[0029] According to the present disclosure, the first electrode tab 10 and the second electrode tab 30 serve as the negative electrode tab and the positive electrode tab, respectively. The first electrode tab 10 includes a first current collector 11 and a negative electrode coating 12. The first current collector 11 may have opposite first surfaces (or upper surfaces) and second surfaces (or lower surfaces), and the negative electrode coating 12 may be disposed on the first surface of the first current collector 11. The second electrode tab 30 includes a second current collector 31 and a positive electrode coating 32. The second current collector 31 may have opposite first surfaces (or upper surfaces) and second surfaces (or lower surfaces), and the positive electrode coating 32 may be disposed on the second surface of the second current collector 31 so that the first current collector 11 is close to the second current collector 31. A conductive adhesive layer 20 is disposed between the first current collector 11 and the second current collector 31.

[0030] The first current collector 11 and the second current collector 31 may employ substrates with different extension characteristics. In one embodiment, the material of the first current collector 11 may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, preferably including copper and / or nickel. The material of the second current collector 31 may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, preferably including aluminum and / or nickel.

[0031] The first current collector 11 and the second current collector 31 each have a certain thickness. Specifically, the thickness of the first current collector 11 may be 2 to 15 μm, and the thickness of the second current collector 31 may be 3 to 20 μm.

[0032] The negative electrode coating 12 and the positive electrode coating 32 may be prepared using the same or different solvent system slurries, preferably using different solvent system slurries. In a specific embodiment, the negative electrode coating 12 may be prepared from an aqueous-based system slurry and / or an organic solvent-based system slurry, preferably prepared from an aqueous-based system slurry; the positive electrode coating 32 may be prepared from an organic solvent-based system slurry.

[0033] The material of the negative electrode coating 12 includes a negative electrode active material, and in addition, a second conductive agent, a second binder, and a dispersant may be further included. The contents of the above components can be adjusted within a certain range. Specifically, based on the total weight of the negative electrode coating 12, the content of the second conductive agent can be ≤5% by weight, the content of the second binder can be ≤5% by weight, and the content of the dispersant can be ≤5% by weight. Among them, the negative electrode active material can be a negative electrode active material for battery monomers well-known in the art, such as but not limited to natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.; the second conductive agent can include one or more of superconducting carbon, conductive carbon black (SP), conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (CNT), graphene, and carbon nanofibers; the second binder can include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), and polyvinyl alcohol (PVA); the dispersant can include sodium carboxymethyl cellulose (CMC-Na) and / or sodium carboxymethyl cellulose (CMC-Li).

[0034] The material of the positive electrode coating 32 includes a positive electrode active material, and in addition, a third conductive agent and a third binder may be further included. The contents of the above components can be adjusted within a certain range. Specifically, based on the total weight of the positive electrode coating 32, the content of the third conductive agent can be ≤5% by weight, and the content of the third binder can be ≤5% by weight. Among them, the positive electrode active material can be a positive electrode active material for battery monomers well-known in the art, such as but not limited to lithium phosphate compounds, lithium-containing transition metal oxides, sodium-containing phosphate compounds, and sodium-containing transition metal oxides, etc.; the third conductive agent can include one or more of superconducting carbon, conductive carbon black (SP), conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (CNT), graphene, and carbon nanofibers; the third binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0035] The negative electrode coating 12 and the positive electrode coating 32 can respectively have a certain thickness. Specifically, the thickness of the negative electrode coating 12 can be 50 - 200 μm, preferably 70 - 150 μm; the thickness of the positive electrode coating 32 can be 40 - 180 μm, preferably 60 - 120 μm.

[0036] The first electrode 10 and the second electrode 20 may have different compaction densities to better adapt to the characteristics of the anode and cathode materials and their different requirements in electrochemical performance, and improve the energy density, cycle life, and overall performance of the battery cell. Specifically, the compaction density of the first electrode may be 1.4 - 1.8 g / cm 3 ; and / or, the compaction density of the second electrode may be 2.6 - 3.7 g / cm 3 .

[0037] According to the present disclosure, the number of the bipolar electrode units is not particularly limited and can be flexibly adjusted according to specific application requirements. The multiple bipolar electrode units are closely arranged, which is beneficial to improving the energy density of the battery cell and reducing the need for additional connection components. The stacking order of the electrodes in the multiple bipolar electrode units is the same. That is, in adjacent bipolar electrode units, the second electrode 30 of the previous unit is close to the first electrode 10 of the next unit. An isolation film 40 is provided between adjacent bipolar electrode units to achieve effective isolation between the first electrode 10 and the second electrode 30, prevent short circuits, and improve the safety, ion transport efficiency, and overall electrochemical performance of the battery cell.

[0038] The isolation film 40 may be a substrate commonly used in the art with good chemical stability and mechanical stability. In a specific embodiment, the material of the isolation film 40 may include one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene, and polyvinylidene fluoride. The above types have excellent thermal stability, electrochemical stability, and mechanical strength, which is beneficial to improving the comprehensive performance of the battery cell. The thickness of the isolation film 40 may be 3 - 20 μm, preferably 5 - 12 μm. The bipolar battery cell of the present disclosure simplifies the internal structure and electrical connection method of the battery cell, reduces the complex welding points and external connection components in the traditional design, reduces the difficulty and cost of the manufacturing process. The compact layout of the stacked arrangement has both flexibility and high safety, enabling the bipolar battery cell to achieve a higher energy density in a limited space, and performing excellently in vibration resistance, thermal management, and long-term use stability. It is widely applicable to various application scenarios, especially suitable for energy storage systems with strict requirements on battery volume and weight, and can meet the requirements for high performance and high reliability in fields such as electric vehicles, renewable energy storage systems, and consumer electronics.

[0039] In the second aspect of the present disclosure, a method for preparing the bipolar battery cell described in the first aspect of the present disclosure is provided. The method includes the following steps S101 - S106: S101. Obtain a first current collector and a second current collector respectively. The first current collector and the second current collector each have opposite first surfaces (or upper surfaces) and second surfaces (or lower surfaces); S102. Coat the negative electrode slurry on the first surface of the first current collector, and then perform the first rolling to obtain the first electrode sheet; Among them, the negative electrode slurry can be an aqueous-based system slurry and / or an organic solvent-based system slurry. Specifically, the negative electrode slurry includes the negative electrode active material described above, an optional second conductive agent, an optional second binder, an optional dispersant, and a first solvent. The first solvent can include, but is not limited to, N-methylpyrrolidone (NMP), deionized water, and its dosage can be adjusted within a certain range. For example, the weight ratio of the total weight of the negative electrode active material, the optional second conductive agent, the optional second binder, and the optional dispersant to the weight of the first solvent can be 1:(0.25 - 2.3), preferably 1:(0.54 - 1.22). Relative to the first surface of the first current collector per unit area of 1540 mm 2 The coating amount of the negative electrode slurry can be 80 - 250 mg. After the coating of the negative electrode slurry is completed, it can be dried at a temperature of 50 - 150 °C to remove the first solvent, and then the first rolling is performed. The conditions of the first rolling can include: the pressure is 1 - 100 T, preferably 1 - 20 T; the temperature is 0 - 60 °C, preferably 1 - 30 °C; the rolling speed is 5 - 120 m / min, preferably 10 - 30 m / min; the number of rolling times can be one or more. In the obtained first electrode sheet, the negative electrode coating is formed on the first surface (or the upper surface) of the first current collector.

[0040] S103. Coat the positive electrode slurry on the second surface of the second current collector, and then perform the second rolling to obtain the second electrode sheet; Among them, the positive electrode slurry can be an organic solvent-based system slurry. Specifically, the positive electrode slurry includes the positive electrode active material described above, an optional third conductive agent, an optional third binder, and a second solvent. The second solvent can include, but is not limited to, N-methylpyrrolidone (NMP), and its dosage can be adjusted within a certain range. For example, the weight ratio of the total weight of the positive electrode active material, the optional third conductive agent, and the optional third binder to the weight of the second solvent can be 1:(0.1 - 2.3), preferably 1:(0.3 - 0.55). Relative to the second surface of the second current collector per unit area of 1540 mm 2 The coating amount of the positive electrode slurry can be 100 - 400 mg. After the coating of the positive electrode slurry is completed, it can be dried at a temperature of 50 - 150 °C to remove the second solvent, and then the second rolling is performed. The conditions of the second rolling can include: the pressure is 1 - 100 T, preferably 35 - 50 T; the temperature is 0 - 60 °C, preferably 1 - 30 °C; the rolling speed is 5 - 120 m / min, preferably 10 - 50 m / min; the number of rolling times can be one or more. In the obtained second electrode sheet, the positive electrode coating is formed on the second surface (or the lower surface) of the second current collector.

[0041] By separately preparing the first electrode sheet and the second electrode sheet, it is possible to ensure that the solvents of the positive and negative electrode slurries do not mix and contaminate, improve the coating quality, and at the same time facilitate the recovery of solvents (especially organic solvents); the independent rolling process can effectively avoid a series of problems such as electrode sheet protrusion, wrinkling, and warping caused by inconsistent ductility of the current collector, and can optimize the compaction density of the first electrode sheet and the second electrode sheet respectively, select appropriate rolling conditions according to their respective electrochemical characteristics, and improve the energy density and cycle performance of the battery cell.

[0042] S104. Coating a conductive adhesive slurry on the first surface of the second current collector to obtain a second electrode sheet covered with a conductive adhesive layer; Among them, the conductive adhesive slurry can be an organic solvent system slurry and / or a water-based system slurry. Specifically, the conductive adhesive slurry can include the first conductive agent, the first binder, and the third solvent described above. The third solvent can include but is not limited to N-methylpyrrolidone (NMP), deionized water, and its dosage can be adjusted within a certain range. For example, the weight ratio of the total weight of the first conductive agent and the first binder to the weight of the third solvent can be 1:(0.2 - 8). The coating method of the conductive adhesive slurry is flexible, and processes such as spraying, printing, or roll coating can be selected to adapt to the manufacturing requirements of battery cells of different scales and shapes, improving the process compatibility and production efficiency. Relative to the first surface of the second current collector per unit area of 1540mm 2 The coating amount of the conductive adhesive slurry can be 0.5 - 50 mg.

[0043] S105. Stacking the first electrode sheet, the second electrode sheet covered with the conductive adhesive layer, and the separator in sequence to obtain a stacked structure; Among them, the stacked structure includes a plurality of bipolar sheet units described in the first aspect of the present disclosure, and adjacent bipolar sheet units are separated by a separator.

[0044] S106. Thermally pressing the stacked structure to obtain a bipolar battery cell.

[0045] Among them, the conditions of the thermal pressing can include: the temperature is 25 - 150 °C, preferably 80 - 95 °C; the pressure is 0.2 - 3 MPa, preferably 0.7 - 0.9 MPa; the pressure holding time is 10 - 600 s, preferably 90 - 120 s. Through thermal pressing, the conductive adhesive layer can be cured to form a tight bonding interface with the first electrode sheet and the second electrode sheet, improving the structural stability of the battery cell.

[0046] The method of the present disclosure can effectively improve the production efficiency and product yield of bipolar battery cells and has the potential for large-scale industrial production.

[0047] In the third aspect of the present disclosure, a battery module is provided, which includes the bipolar electrode core described in the first aspect of the present disclosure. There is no special limitation on the specific structure of the battery module, and it may include other common structures in the art, such as electrolyte and packaging shell, etc.

[0048] By adopting the bipolar electrode core, the battery module provided by the present disclosure has the characteristics of high energy density, high voltage platform and modular design, can better meet the application requirements of high power and long endurance, and is widely applicable to energy storage systems and power equipment.

[0049] In the fourth aspect of the present disclosure, an electrical device is provided, which is characterized by including the battery module described in the third aspect of the present disclosure.

[0050] The present disclosure will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are not used to limit the present disclosure.

[0051] The test and calculation method for the compaction density of the electrode sheet is as follows: Weigh the coating weight per unit area, measure the thickness of the electrode sheet after rolling, and the ratio of the weight to the thickness is the compaction density.

[0052] Example 1 (1) A copper foil with a thickness of 6 μm is selected as the negative electrode current collector. The negative electrode active material graphite, conductive agent SP, binder SBR, dispersant CMC-Na, and solvent deionized water are mixed according to a weight ratio of 0.96:0.01:0.02:0.01:0.54, and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on one side surface of the copper foil, and the coating amount of the negative electrode slurry is 180 mg / 1540 mm 2 , and dried at a temperature of 105 °C until the solvent is completely removed to form a negative electrode coating with a thickness of 90 μm. Then, it is rolled at 20 T, 30 m / min, and 25 °C to obtain a negative electrode sheet, and its compaction density is detected and listed in Table 1.

[0053] (2) An aluminum foil with a thickness of 13 μm is selected as the positive electrode current collector. The positive electrode active material NCM, binder PVDF, conductive agent SP, and solvent NMP are mixed according to a weight ratio of 0.97:0.01:0.02:0.45, and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on one side surface of the aluminum foil, and the coating amount of the positive electrode slurry is 278 mg / 1540 mm 2 , and dried at 105 °C until the solvent is completely removed to form a positive electrode coating with a thickness of 65 μm. Then, it is rolled at 40 T, 50 m / min, and 25 °C to obtain a positive electrode sheet, and its compaction density is detected and listed in Table 1.

[0054] (3) Mix the conductive agent SP, binder PVDF, and solvent NMP in a weight ratio of 1:1:12, stir evenly to prepare a conductive adhesive paste. Using the doctor blade coating process, evenly coat the conductive adhesive paste on the other side (the side without the positive electrode coating) surface of the positive electrode sheet, and the coating amount of the conductive adhesive paste is 10 mg / 1540 mm 2 , to form a conductive adhesive layer with a thickness of 2 μm.

[0055] (4) Select a PE separator with a thickness of 7 μm, stack the negative electrode sheet, conductive adhesive layer, positive electrode sheet, and separator in sequence to form a stacked structure of 5 bipolar sheet units.

[0056] (5) Put the stacked structure into a hot pressing device, and perform hot pressing under the conditions of a temperature of 95 °C, a pressure of 0.9 MPa, and a holding pressure time of 120 s to obtain a bipolar battery cell.

[0057] Example 2 Prepare a bipolar battery cell according to the method of Example 1, the difference is that in step (3), the weight ratio of SP, PVDF, and solvent NMP is 1:1.5:12.

[0058] Example 3 Prepare a bipolar battery cell according to the method of Example 1, the difference is that in step (3), use the conductive agent CNT to replace SP, and use the binder SBR to replace PVDF.

[0059] Example 4 Prepare a bipolar battery cell according to the method of Example 1, the difference is that in step (3), the coating amount of the conductive adhesive paste is 15 mg / 1540 mm 2 , to form a conductive adhesive layer with a thickness of 3 μm.

[0060] Example 5 Prepare a bipolar battery cell according to the method of Example 1, the difference is that in step (1), the rolling conditions are: 25 T, 60 m / min, 25 °C, and in step (2), the rolling conditions are: 30 T, 70 m / min, 25 °C.

[0061] Example 6 Prepare a bipolar battery cell according to the method of Example 1, the difference is that in step (5), the hot pressing conditions are: 100 °C, 1 MPa, 150 s.

[0062] Comparative Example 1 Prepare a bipolar battery cell using the method in the prior art. The specific steps are as follows: (1)Select a copper-aluminum composite foil with a thickness of 25 μm as the current collector of the bipolar battery cell. Mix the negative electrode active material graphite, conductive agent SP, binder SBR, dispersant CMC-Na, and solvent deionized water in a weight ratio of 0.96:0.01:0.02:0.01:0.54, and stir evenly to obtain the negative electrode paste. Uniformly coat the negative electrode paste on one side surface of the copper foil of the aluminum composite foil, and the coating amount of the negative electrode paste is 180 mg / 1540 mm 2 , and dry it at a temperature of 105 °C until the solvent is completely removed to form a negative electrode coating with a thickness of 90 μm. Then, roll it at 25 T, 30 m / min, and 25 °C to obtain a negative electrode sheet, and detect its compaction density, which is listed in Table 1.

[0063] (2)After obtaining the above negative electrode sheet, mix the positive electrode active material NCM, binder PVDF, conductive agent SP, and solvent NMP in a weight ratio of 0.97:0.01:0.02:0.45, and stir evenly to obtain the positive electrode paste. Uniformly coat the positive electrode paste on one side surface of the aluminum foil of the aluminum composite foil, and the coating amount of the positive electrode paste is 278 mg / 1540 mm 2 , and dry it at 105 °C until the solvent is completely removed to form a positive electrode coating with a thickness of 65 μm. Then, roll it at 40 T, 50 m / min, and 25 °C to obtain a pole piece composed of a positive electrode and a negative electrode, and detect the compaction density of the positive electrode sheet part, which is listed in Table 1.

[0064] (3)Select a PE separator with a thickness of 7 μm, and stack the negative electrode sheet, positive electrode sheet, and separator in sequence to form a stacked structure of 5 bipolar sheet units.

[0065] (4)Put the stacked structure into a hot pressing device, and perform hot pressing at a temperature of 95 °C, a pressure of 0.9 MPa, and a holding time of 120 s to obtain a bipolar battery cell.

[0066] Table 1

[0067] Test Example After assembling the bipolar battery cells of the examples and comparative examples into batteries according to the conventional methods in the art, perform performance tests, and the results are listed in Table 2.

[0068] The test method for energy density is as follows: Charge to 100% SOC at 1 / 3C, let it stand for 5 min, discharge to 0% SOC at 1 / 3C, let it stand for 5 min, obtain the actual discharge energy W0 of the battery cell, and calculate the weight energy density WED = W0 / m according to the weight m of the battery cell, with the unit of Wh / kg. Here, 1 / 3C represents the current magnitude of 1 / 3 of the battery cell capacity. For example, for a 10 Ah battery cell, 1 / 3C = 1 / 3 × 10 A.

[0069] The test method for the number of cycling circles is as follows: Charge at 1C to 100% SOC, rest for 5 minutes, discharge at 1C to 0% SOC, rest for 5 minutes, and repeat the above steps until the capacity retention rate reaches 80%. Here, 1C represents the current magnitude of the cell capacity. For example, for a 10Ah cell, 1C = 10A.

[0070] Table 2

[0071] As can be seen from Table 2, the bipolar cells of the embodiments can improve the energy density and cycle life of the battery, showing excellent performance.

[0072] The preferred embodiments of the present disclosure have been described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0073] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, without conflict, they can be combined in any appropriate manner. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination methods.

[0074] Furthermore, any combination can be made between various different embodiments of the present disclosure, as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A bipolar battery cell, characterized in that: The bipolar battery cell includes a plurality of bipolar sheet units stacked together, each bipolar sheet unit including a first pole sheet, a conductive adhesive layer, and a second pole sheet stacked in sequence, the first pole sheet including a first current collector and a negative electrode coating, the second pole sheet including a second current collector and a positive electrode coating, the first current collector being close to the second current collector, and an isolation membrane being arranged between adjacent bipolar sheet units.

2. The bipolar battery cell according to claim 1, wherein: The material of the first current collector includes one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy; and / or, The material of the second current collector includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

3. The bipolar battery cell according to claim 1, wherein: The negative electrode coating is prepared from a water-based system slurry and / or an organic solvent system slurry; The positive electrode coating is prepared from an organic solvent system slurry.

4. The bipolar battery cell according to claim 1, wherein: The conductive adhesive layer is made of a first conductive agent and a first adhesive, wherein the weight ratio of the first conductive agent to the first adhesive is 1:(0.1-1.5); the conductive adhesive layer is prepared from an organic solvent system slurry and / or a water-based system slurry.

5. The bipolar battery cell according to claim 4, wherein: The first conductive agent includes one or more of superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; and / or, The first binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylic resin, styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyacrylamide and polyvinyl alcohol.

6. The bipolar battery cell according to claim 1, wherein: The compaction density of the first pole piece is 1.4-1.8 g / cm 3 ; and / or, the compaction density of the second pole piece is 2.6~3.7g / cm 3 .

7. A method for preparing a bipolar battery cell according to any one of claims 1 to 6, characterized in that: The method includes: Obtaining a first current collector and a second current collector, respectively, wherein the first current collector and the second current collector each have a first surface and a second surface opposite to each other; Applying the negative electrode slurry to the first surface of the first current collector, and then performing a first roll pressing to obtain a first electrode sheet; Applying the positive electrode slurry to the second surface of the second current collector, and then performing a second roll pressing to obtain a second electrode sheet; Coating a conductive adhesive slurry on the first surface of the second current collector to obtain a second pole piece covered with a conductive adhesive layer; The first pole piece, the second pole piece covered with the conductive adhesive layer, and the isolation film are stacked in sequence to obtain a stacked structure; The laminate structure is hot pressed to obtain a bipolar battery cell.

8. The method according to claim 7, wherein: The first rolling conditions include: a pressure of 1-100T, a temperature of 0-60°C, and a rolling speed of 5-120m / min; The second rolling conditions include: a pressure of 1-100T, a temperature of 0-60°C, and a rolling speed of 5-120m / min.

9. The method according to claim 7, wherein: The hot pressing conditions include: temperature of 25-150° C., pressure of 0.2-3 MPa, and holding time of 10-600 s.

10. A battery module, characterized in that: A bipolar battery cell comprising any one of claims 1 to 6.

11. An electrical device, characterized in that: A battery module comprising the battery module according to claim 10.

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