A solid-state battery and its preparation method, and a battery module

Abstract

This invention discloses a solid-state battery and its fabrication method, as well as a battery module. The solid-state battery includes several stacked battery cells connected by a shared bipolar current collector. The bipolar current collector includes a three-dimensional cross-linked carbon fiber film, which has a first surface and a second surface arranged opposite to each other. A composite positive electrode layer is formed on the first surface, comprising a positive electrode active material layer and a positive electrode protective layer. A composite negative electrode layer is formed on the second surface, comprising a negative electrode active material layer and a conductive buffer layer. The positive electrode protective layer comprises Li3PO4, and the conductive buffer layer comprises PEDOT-PSS. By using the three-dimensional cross-linked carbon fiber film as the bipolar current collector and setting the positive electrode protective layer and conductive buffer layer on the positive and negative electrode active material layers respectively, the energy density of the solid-state battery can be improved while reducing the interface impedance, thereby improving safety performance and extending cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a solid-state battery and its preparation method, as well as a battery module. Background Technology

[0002] In batteries, the current collector is one of the core components. Its core function is to act as a conductive carrier for the active materials, collecting electrons generated / consumed by the active materials during charging and discharging to form a complete current path; at the same time, it provides physical support for the active materials and fixes the electrode coating structure. The commonly used current collector in batteries is the unipolar current collector. Unipolar current collectors require independent encapsulation of the positive and negative electrodes, resulting in a high proportion of inactive materials (about 40%) and limited energy density. To overcome this limitation, the bipolar current collector was proposed. Its core is to construct conductive layers adapted to the positive and negative electrodes on two opposite surfaces of a single substrate. The positive and negative active materials can be coated on both sides respectively. This structure allows the current collector to serve as a common conductive substrate for two adjacent cell units, realizing internal series connection of the cells, thereby simplifying the battery structure, improving packaging efficiency, and significantly increasing energy density and power density.

[0003] However, the practical application of bipolar current collectors still faces a series of key technical challenges: First, the substrate must withstand both the high-voltage oxidation environment on the positive electrode side and the electrochemical stability requirements on the negative electrode side, which places extremely stringent demands on the selection of material systems; Second, after coating different active materials on both sides, problems such as substrate warping, coating delamination, or interface peeling can easily occur due to differences in thermal expansion and mechanical properties; Third, and most importantly, how to achieve systematic synergy between the current collector substrate and the positive and negative electrode active material layers on both sides in terms of mechanical support, electrochemical compatibility, and interfacial ion / electron transport, so as to improve energy density while ensuring long-term interface stability and cycle life, remains a core problem that urgently needs to be solved in this field. Summary of the Invention

[0004] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a bipolar electrode, a method for preparing the same, and a battery.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a solid-state battery comprising a plurality of stacked battery cells, wherein the battery cells are connected to each other by a common bipolar current collector.

[0007] The bipolar current collector includes a three-dimensional cross-linked carbon fiber film (3D-CF), and the three-dimensional cross-linked carbon fiber film has a first surface and a second surface disposed opposite to each other;

[0008] A composite positive electrode layer is formed on the first surface, the composite positive electrode layer including a positive electrode active material layer and a positive electrode protective layer covering the positive electrode active material layer;

[0009] A composite negative electrode layer is formed on the second surface, the composite negative electrode layer including a negative electrode active material layer and a conductive buffer layer covering the negative electrode active material layer;

[0010] The solid-state battery also includes a solid electrolyte membrane, which is located between the positive electrode protective layer and the conductive buffer layer. The battery cell is composed of a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked in sequence.

[0011] The positive electrode protective layer includes Li3PO4, and the conductive buffer layer includes PEDOT-PSS.

[0012] In the solid-state battery of the present invention, when both sides of the bipolar current collector contain battery cells, the bipolar current collector is shared by two adjacent battery cells.

[0013] In some embodiments, the three-dimensional cross-linked carbon fiber film satisfies at least one of the following conditions:

[0014] (1) The porosity of the three-dimensional cross-linked carbon fiber film is 5%~20%;

[0015] (2) The tensile strength of the three-dimensional cross-linked carbon fiber film is 300MPa~800MPa;

[0016] (3) The thickness of the three-dimensional cross-linked carbon fiber film is 5μm~20μm.

[0017] In some embodiments, the carbon source of the three-dimensional cross-linked carbon fiber film is selected from at least one of polyacrylonitrile, polyimide, and lignin.

[0018] In some embodiments, the thickness of the positive electrode protective layer is 3 μm to 12 μm.

[0019] In some embodiments, the thickness of the conductive buffer layer is 5 μm to 15 μm.

[0020] In a second aspect, the present invention provides a method for preparing the solid-state battery described in the first aspect, the method comprising the following steps:

[0021] S1. Prepare a spinning solution containing a carbon source, prepare a precursor fiber membrane by electrospinning, and then perform pre-oxidation, pre-calendering of the pre-oxidized fiber membrane, and carbonization in sequence to obtain a three-dimensional cross-linked carbon fiber film as a bipolar current collector. The three-dimensional cross-linked carbon fiber film has a first surface and a second surface arranged opposite to each other.

[0022] S2. A positive electrode slurry is coated on the first surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the positive electrode active material layer is formed; a solution containing Li3PO4 is coated on the surface of the positive electrode active material layer, and after drying, the positive electrode protective layer is formed.

[0023] S3. A negative electrode slurry is coated on the second surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the negative electrode active material layer is formed; a solution containing PEDOT-PSS is coated on the surface of the negative electrode active material layer, and after drying, the conductive buffer layer is formed, thus obtaining an integrated positive and negative electrode.

[0024] S4. A first solid electrolyte film is stacked on the surface of the positive electrode protective layer of the integrated positive and negative electrode, and a second solid electrolyte film is stacked on the surface of the conductive buffer layer of the integrated positive and negative electrode.

[0025] S5. A first composite structure is stacked on the surface of the first solid electrolyte membrane. Along the direction away from the first solid electrolyte membrane, the first composite structure includes a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked sequentially. A second composite structure is stacked on the surface of the second solid electrolyte membrane. Along the direction away from the second solid electrolyte membrane, the second composite structure includes a positive electrode protective layer, a positive electrode active material layer, and a bipolar current collector stacked sequentially, to obtain a battery cell.

[0026] S6. The battery cell is encapsulated in a housing, an impregnating agent is added, and the opening is sealed to obtain a solid-state battery;

[0027] The solid-state battery includes several stacked battery cells, each battery cell comprising a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector arranged in sequence.

[0028] As a preferred technical solution for the solid-state battery of the present invention, the following steps are performed after step S4:

[0029] (a) At least one integrated positive and negative electrode and a third solid electrolyte membrane are sequentially stacked on the surface of a first solid electrolyte membrane, wherein two sides of the first solid electrolyte membrane and the third solid electrolyte membrane are in contact with the positive electrode protective layer and the conductive buffer layer, respectively; and / or,

[0030] (b) At least one integrated positive and negative electrode and a fourth solid electrolyte membrane are sequentially stacked on the surface of the second solid electrolyte, wherein the two sides of the second solid electrolyte membrane and the fourth solid electrolyte are in contact with the positive electrode protective layer and the conductive buffer layer, respectively.

[0031] In some embodiments, the amount of wetting agent added is 0.5 wt.% to 5 wt.%, based on the total mass of the solid-state battery (100%).

[0032] In some implementations, step S1 satisfies at least one of the following conditions:

[0033] (1) In the spinning solution, the mass fraction of the carbon source is 7%~16%;

[0034] (2) The electrospinning voltage is 10kV~25kV, the propulsion rate is 0.5mL / h~1.5mL / h, and the receiving distance is 10cm~20cm;

[0035] (3) The pre-oxidation temperature is 250℃~300℃;

[0036] (4) The pre-calendering pressure is 2MPa~10MPa;

[0037] (5) The carbonization temperature is 700℃~1200℃.

[0038] In some embodiments, the solid content of the Li3PO4-containing solution in step S2 is 10% to 20%.

[0039] In some embodiments, the solid content of the PEDOT-PSS-containing solution in step S3 is 10% to 20%.

[0040] Thirdly, the present invention provides a battery module, the battery module comprising the solid-state battery provided in the first aspect.

[0041] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a partial structure of a solid-state battery according to one embodiment of the present invention, wherein 1 is a battery cell, 11 is a bipolar current collector, 12 is a composite positive electrode layer, 121 is a positive electrode active material layer, 122 is a positive electrode protective layer, 13 is a composite negative electrode layer, 131 is a negative electrode active material layer, 132 is a conductive buffer layer, and 14 is a solid electrolyte membrane. Detailed Implementation

[0043] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms “comprising” or “including” and similar terms used herein mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “and / or” or “and / or” as used herein include any and all combinations of one or more of the associated listed items.

[0045] The following describes some preferred embodiments of this application. It should be noted that the following description is for illustrative purposes only and is not intended to limit the scope of protection of this application. The steps involved in this application may be performed precisely in sequence, or various steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0046] In a first aspect, the present invention provides a solid-state battery comprising a plurality of stacked battery cells, wherein the battery cells are connected to each other by a common bipolar current collector.

[0047] The bipolar current collector includes a three-dimensional cross-linked carbon fiber film (3D-CF), and the three-dimensional cross-linked carbon fiber film has a first surface and a second surface disposed opposite to each other;

[0048] A composite positive electrode layer is formed on the first surface, the composite positive electrode layer including a positive electrode active material layer and a positive electrode protective layer covering the positive electrode active material layer;

[0049] A composite negative electrode layer is formed on the second surface, the composite negative electrode layer including a negative electrode active material layer and a conductive buffer layer covering the negative electrode active material layer;

[0050] The solid-state battery also includes a solid electrolyte membrane, which is located between the positive electrode protective layer and the conductive buffer layer. The battery cell is composed of a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked in sequence.

[0051] The positive electrode protective layer includes Li3PO4, and the conductive buffer layer includes PEDOT-PSS.

[0052] In this invention, the three-dimensional cross-linked carbon fiber film refers to a three-dimensional porous network structure film formed by the cross-linking and entanglement of carbon fibers, which is obtained by electrospinning and subsequent heat treatment processes.

[0053] In the solid-state battery of the present invention, a three-dimensional cross-linked carbon fiber film (3D-CF) is used as a bipolar current collector, and a positive electrode protective layer containing Li3PO4 and a conductive buffer layer containing PEDOT-PSS are respectively constructed on both sides of it, forming an integrated electrode system with deep synergy in mechanical, electrochemical and interfacial transport.

[0054] Three-dimensional cross-linked carbon fiber film is used as a bipolar current collector and an integrated conductive framework, providing a stable, lightweight, and highly adaptable support for the functional layers on both sides of the interface. It combines high strength, high temperature resistance, and good flexibility, which can significantly reduce the thickness of the electrode and reduce its weight. Its three-dimensional network structure can effectively suppress lithium dendrite growth and buffer electrode volume changes, thereby improving the mechanical and thermal stability of the interface.

[0055] Furthermore, this invention introduces a Li3PO4-containing positive electrode protective layer on the outer surface of the positive electrode active material layer, which mainly solves the problem of chemical and electrochemical compatibility under high voltage. It can effectively suppress interfacial side reactions, provide low-impedance migration channels for lithium ions, thereby significantly reducing the positive electrode interfacial impedance. At the same time, it has a certain mechanical stability and works synergistically with the 3D-CF framework to alleviate the volume change stress in the positive electrode material during cycling and reduce particle pulverization.

[0056] However, during battery cycling, both the positive and negative electrode active materials undergo volume changes, leading to physical contact failure. To address this issue, this invention adds a conductive buffer layer containing PEDOT-PSS to the outer side of the negative electrode active material layer (i.e., the side furthest from the bipolar current collector). This layer possesses excellent flexibility and viscoelasticity, effectively absorbing and dispersing stress during cycling, improving rigid solid-solid contact, filling micro-gaps, solving physical contact and stress buffering problems, maintaining tight interfacial contact, preventing interfacial separation due to volume changes, and dispersing internal stress generated during cell cycling. Furthermore, as a conductive polymer, PEDOT-PSS' conductivity ensures that electrons can be smoothly collected onto the three-dimensional cross-linked carbon fiber film, and its porous structure provides channels for ion transport. The conductive buffer layer containing PEDOT-PSS also plays a positive role in reducing interfacial impedance. More importantly, the buffer layer complements the 3D-CF framework in terms of conductivity and ion transport: the 3D-CF provides an efficient electron current collection network, while the porous structure of PEDOT-PSS provides an auxiliary channel for ion transport. Together, they further optimize the charge transport dynamics at the interface.

[0057] In summary, the 3D-CF framework not only provides a uniform and robust substrate for the functional layers on both sides, but its three-dimensional structure also helps guide the uniform distribution of lithium ions at the interface. This, together with the Li3PO4-containing positive electrode protective layer and the PEDOT-PSS-containing conductive buffer layer, suppresses lithium plating or side reactions caused by excessively high local current density. This complementary interface structure enables the battery to achieve high energy density while also possessing extremely low interfacial impedance, excellent interfacial contact stability, and long cycle life.

[0058] In some embodiments, the porosity of the three-dimensional cross-linked carbon fiber film is 5% to 20%, for example, it can be 5%, 6%, 7%, 8%, 10%, 12%, 13%, 14%, 15%, 16%, 18% or 20%.

[0059] If the porosity is too high, the mechanical strength will decrease, and the tape will easily break during high-tension stretching; if the porosity is too low, the active material will not be firmly bonded to the current collector, and it will easily fall off.

[0060] In some embodiments, the tensile strength of the three-dimensional cross-linked carbon fiber film is 300MPa to 800MPa, for example, it can be 300MPa, 320MPa, 340MPa, 350MPa, 375MPa, 400MPa, 425MPa, 450MPa, 470MPa, 500MPa, 525MPa, 550MPa, 580MPa, 600MPa, 630MPa, 660MPa, 680MPa, 700MPa, 720MPa, 740MPa, 760MPa, 780MPa, or 800MPa, etc.

[0061] If the tensile strength is too high, the flexibility of the current collector will decrease and the brittleness will increase, which is not conducive to subsequent winding processes; if the tensile strength is too low, subsequent processes such as tape feeding will lead to tape breakage.

[0062] In some embodiments, the thickness of the three-dimensional cross-linked carbon fiber film is 5μm to 20μm, for example, it can be 5μm, 7μm, 9μm, 10μm, 12μm, 13μm, 14μm, 16μm, 18μm or 20μm.

[0063] If the thickness is too large, the battery's gravimetric and volumetric energy densities will decrease, the electron transport path will become longer, and the interface impedance will increase. If the thickness is too small, the mechanical properties will deteriorate, the stability and uniformity of electron conduction will be affected, and uneven current distribution will occur in different parts of the electrode.

[0064] In some embodiments, the carbon source of the three-dimensional cross-linked carbon fiber film is selected from at least one of polyacrylonitrile (PAN), polyimide, and lignin. These provide different carbon structures and properties, with PAN exhibiting good fiber-forming properties and high carbonization yield.

[0065] In some embodiments, the thickness of the positive electrode protective layer is 3μm to 12μm, for example, it can be 3μm, 5μm, 7μm, 8μm, 10μm or 12μm.

[0066] Preferably, the thickness of the conductive buffer layer is 5μm to 15μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 13μm or 15μm.

[0067] Preferably, the positive electrode active material layer includes a positive electrode active material, a first solid electrolyte, a first binder, and a first conductive agent. The mass ratio of the positive electrode active material, the first solid electrolyte, the first binder, and the first conductive agent is (70~80):(15~20):(1~4):(1~4). The positive electrode active material is selected from a range of "70~80", for example, 70, 72, 73, 75, 77, 78, or 80. The first solid electrolyte is selected from a range of "15~20", for example, 15, 16, 17, 18, 19, or 20. The first binder is selected from a range of "1~4", for example, 1, 1.5, 2, 2.5, 3, 3.5, or 4. The first conductive agent is selected from a range of "1~4", for example, 1, 1.5, 2, 2.5, 3, 3.5, or 4.

[0068] The present invention does not particularly limit the types of positive electrode active material, first solid electrolyte, first binder and first conductive agent, and those skilled in the art can select them as needed.

[0069] In some embodiments, the positive electrode active material may be at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0070] In some embodiments, the first solid electrolyte may be one or more of an oxide solid electrolyte, a sulfide solid electrolyte, or a polymer solid electrolyte.

[0071] In some embodiments, the first binder includes at least one of polyvinylidene fluoride (PVDF) and nitrile rubber (NBR).

[0072] In some embodiments, the first conductive agent is at least one selected from Super P, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber.

[0073] In some embodiments, the thickness of the positive electrode active material layer is 30μm to 100μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm.

[0074] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a second solid electrolyte, a second binder, and a second conductive agent. The mass ratio of the negative electrode active material, the second solid electrolyte, the second binder, and the second conductive agent is (55~70):(25~40):(1~4):(1~4). The negative electrode active material is selected from a range of "55~70", for example, 55, 57, 60, 62, 64, 66, 68, or 70. The second solid electrolyte is selected from a range of "25~40", for example, 25, 26, 28, 30, 32, 35, 37, or 40. The second binder is selected from a range of "1~4", for example, 1, 1.5, 2, 2.5, 3, 3.5, or 4. The second conductive agent is selected from a range of "1~4", for example, 1, 1.5, 2, 2.5, 3, 3.5, or 4.

[0075] The present invention does not particularly limit the types of negative electrode active material, second solid electrolyte, second binder and second conductive agent, and those skilled in the art can select them as needed.

[0076] In some embodiments, the negative electrode active material may be at least one of graphite, elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

[0077] In some embodiments, the second solid electrolyte may be one or more of an oxide solid electrolyte, a sulfide solid electrolyte, or a polymer solid electrolyte.

[0078] In some embodiments, the second adhesive is at least one of styrene-butadiene rubber (SBR) and nitrile rubber (NBR).

[0079] In some embodiments, the second conductive agent is at least one selected from Super P, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber.

[0080] Preferably, the thickness of the negative electrode active material layer is 10μm to 60μm, for example, it can be 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm or 60μm, etc.

[0081] In a second aspect, the present invention provides a method for preparing a bipolar electrode as described in the first aspect, the method comprising the following steps:

[0082] S1. Prepare a spinning solution containing a carbon source, prepare a precursor fiber membrane by electrospinning, and then perform pre-oxidation, pre-calendering of the pre-oxidized fiber membrane, and carbonization in sequence to obtain a three-dimensional cross-linked carbon fiber film as a bipolar current collector. The three-dimensional cross-linked carbon fiber film has a first surface and a second surface arranged opposite to each other.

[0083] S2. A positive electrode slurry is coated on the first surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the positive electrode active material layer is formed; a solution containing Li3PO4 is coated on the surface of the positive electrode active material layer, and after drying, the positive electrode protective layer is formed.

[0084] S3. A negative electrode slurry is coated on the second surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the negative electrode active material layer is formed; a solution containing PEDOT-PSS is coated on the surface of the negative electrode active material layer, and after drying, the conductive buffer layer is formed, thus obtaining an integrated positive and negative electrode.

[0085] S4. A first solid electrolyte film is stacked on the surface of the positive electrode protective layer of the integrated positive and negative electrode, and a second solid electrolyte film is stacked on the surface of the conductive buffer layer of the integrated positive and negative electrode.

[0086] S5. A first composite structure is stacked on the surface of the first solid electrolyte membrane. Along the direction away from the first solid electrolyte membrane, the first composite structure includes a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked sequentially. A second composite structure is stacked on the surface of the second solid electrolyte membrane. Along the direction away from the second solid electrolyte membrane, the second composite structure includes a positive electrode protective layer, a positive electrode active material layer, and a bipolar current collector stacked sequentially, to obtain a battery cell.

[0087] S6. The battery cell is encapsulated in a housing, an impregnating agent is added, and the opening is sealed to obtain a solid-state battery;

[0088] The solid-state battery includes a plurality of stacked battery cells, each battery cell comprising a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector, which are sequentially stacked. As a preferred embodiment of the solid-state battery of the present invention, the following steps are performed after step S4:

[0089] (a) At least one integrated positive and negative electrode and a third solid electrolyte membrane are sequentially stacked on the surface of a first solid electrolyte membrane, wherein two sides of the first solid electrolyte membrane and the third solid electrolyte membrane are in contact with the positive electrode protective layer and the conductive buffer layer, respectively; and / or,

[0090] (b) At least one integrated positive and negative electrode and a fourth solid electrolyte membrane are sequentially stacked on the surface of the second solid electrolyte, wherein the two sides of the second solid electrolyte membrane and the fourth solid electrolyte are in contact with the positive electrode protective layer and the conductive buffer layer, respectively.

[0091] In the method of the present invention, when step (a) is performed after step S4, in step S5, a first composite structure is stacked on the surface of a third solid electrolyte membrane as a base.

[0092] In the method of the present invention, when step (b) is performed after step S4, in step S5, a second composite structure is stacked on the surface of the fourth solid electrolyte membrane as a base.

[0093] In the method of the present invention, the terms "first", "second", "third" and "fourth" in the first solid electrolyte membrane, second solid electrolyte membrane, third solid electrolyte membrane and fourth solid electrolyte membrane are only distinguished by name, and the composition of the solid electrolyte membranes can be the same.

[0094] In one embodiment, the method for forming the first composite structure may refer to step S3.

[0095] In one embodiment, the method for forming the second composite structure may refer to step S2.

[0096] In some embodiments, the amount of wetting agent added is 0.5 wt.% to 5 wt.%, based on the total mass of the solid-state battery (100%). For example, it can be 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, or 5 wt.%. The function of the wetting agent is to wet the interface, allowing for more sufficient interface contact, without affecting the battery's electrical and safety performance.

[0097] The method of this invention is simple, easy to operate, and suitable for industrial production.

[0098] This invention does not specifically limit the preparation methods of the positive electrode slurry and the negative electrode slurry. Those skilled in the art can refer to the methods disclosed in the prior art to perform homogenization.

[0099] In some embodiments, the method for preparing the positive electrode slurry includes: mixing the positive electrode active material, the first solid electrolyte, the first binder, the first conductive agent and the first solvent evenly to obtain the positive electrode slurry.

[0100] In some embodiments, the first solvent includes at least one of cyclohexane, hexane, heptane, butyl butyrate, and isobutyl isobutyrate.

[0101] In some embodiments, the method for preparing the negative electrode slurry includes: mixing the negative electrode active material, the second solid electrolyte, the second binder, the second conductive agent, and the second solvent evenly to obtain the positive electrode slurry.

[0102] In some embodiments, the second solvent includes at least one of cyclohexane, hexane, heptane, butyl butyrate, and isobutyl isobutyrate.

[0103] In the spinning solution described in step S1, the carbon source has a mass fraction of 7% to 16%, for example, it can be 7%, 8%, 10%, 12%, 13%, 14%, 15%, or 16%. If the mass fraction of the carbon source is too low, continuous fibers cannot be formed; if the mass fraction of the carbon source is too high, spinning will be difficult.

[0104] The present invention does not specifically limit the type of solvent used in preparing the spinning solution. For example, it can be at least one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), ethylene carbonate (EC), and N-methylpyrrolidone (NMP), but is not limited to the above types. Other organic solvents commonly used in the art that can fully dissolve carbon sources are also applicable to the present invention.

[0105] In some embodiments, during the electrospinning process described in step S1, the spinning voltage is 10kV to 25kV, for example, it can be 10kV, 12kV, 14kV, 16kV, 18kV, 20kV, 22kV, 23kV, or 25kV. If the spinning voltage is too low, it will prevent the formation of a Taylor cone, thus preventing the acquisition of spun fibers; if the spinning voltage is too high, it will cause jet instability and affect the spinning effect.

[0106] In some embodiments, the feed rate is 0.5 mL / h to 1.5 mL / h, for example, it can be 0.5 mL / h, 0.7 mL / h, 0.8 mL / h, 1 mL / h, 1.2 mL / h, 1.3 mL / h, or 1.5 mL / h. The feed rate is matched with the spinning voltage to maintain a stable jet.

[0107] In some implementations, the receiving distance is 10cm to 20cm, for example, it can be 10cm, 12cm, 14cm, 16cm, 18cm, or 20cm. The receiving distance affects the electric field strength and the solvent evaporation rate, which in turn affects the quality of the spun fibers.

[0108] In some embodiments, the ambient humidity is 40% to 60%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. In the method of the present invention, the ambient humidity should not be too high, otherwise it will inhibit solvent evaporation and cause fiber adhesion.

[0109] This invention does not impose strict limitations on the ambient temperature for electrospinning; generally, it can be carried out at 25℃±5℃.

[0110] In some embodiments, the electrospinning process described in step S1 further includes using a roller rotating at a speed of 500 rpm to 1000 rpm (e.g., 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, or 1000 rpm, etc.) to collect fibers with a certain degree of orientation, thereby obtaining a precursor fiber membrane. The fibers having a certain degree of orientation can affect the mechanical and electrical properties of the current collector in different directions.

[0111] In some embodiments, the pre-oxidation temperature in step S1 is 250°C to 300°C, for example, it can be 250°C, 260°C, 270°C, 280°C, 290°C or 300°C.

[0112] In some embodiments, the heating rate of the pre-oxidation in step S1 is 1°C / min to 5°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, or 5°C / min. Slow heating can ensure the stability of the fiber structure and avoid melting.

[0113] In some embodiments, the heat preservation time for pre-oxidation in step S1 is 1 hour to 3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. The purpose of pre-oxidation is to stabilize the structure of the membrane.

[0114] In some embodiments, the pre-calendering pressure in step S1 is 2MPa to 10MPa, for example, it can be 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa.

[0115] In one embodiment, during the pre-calendering process described in step S1, the linear speed of the calendering roller is 1m / min to 10m / min, for example, it can be 1m / min, 2m / min, 3m / min, 4m / min, 5m / min, 6m / min, 7m / min, 8m / min, 9m / min or 10m / min, etc.

[0116] In some embodiments, the carbonization temperature in step S1 is 700℃~1200℃, for example, it can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃.

[0117] In some embodiments, the carbonization holding time in step S1 is 0.5h to 2h, for example, it can be 0.5h, 0.7h, 1h, 1.2h, 1.5h, 1.8h or 3h.

[0118] In some embodiments, the carbonization described in step S1 is carried out under the protection of nitrogen and / or an inert gas.

[0119] In some embodiments, the heating rate of carbonization in step S1 is 2℃ / min to 5℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc.

[0120] Through the carbonization step, fibers can be transformed into carbon materials. The higher the temperature, the better the degree of graphitization and conductivity, but the fiber shrinkage may be more pronounced. Therefore, the preferred carbonization temperature is 700℃~1200℃.

[0121] In some embodiments, after the slurry is coated and dried during the preparation of the positive and negative active material layers, a pressing process is required. In this invention, "pressing" refers to a smoothing process performed under low pressure, and its specific implementation may include, but is not limited to, rolling, flat pressing, etc. Its main purpose is to improve the surface smoothness and uniformity of the coating to facilitate the subsequent coating of functional layers.

[0122] In some embodiments, the pressing pressure is typically controlled within the range of 0.1 MPa to 2 MPa, for example, it can be 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa, or 2 MPa. This pressure is significantly lower than the pressure (2 MPa to 10 MPa) used for pre-calendering the pre-oxidized fiber membrane in step S1. This lower pressure is sufficient to achieve surface leveling without causing the network structure of the three-dimensional cross-linked carbon fiber film to collapse, nor does it subject the active material layer to high-pressure densification compaction in the traditional sense, thus fully preserving the porosity and elastic buffering function of the three-dimensional skeleton.

[0123] In some embodiments, the solid content of the Li3PO4-containing solution in step S2 is 10% to 20%, for example, it can be 10%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0124] In step S2 of the present invention, by adjusting the areal density of the coated solution containing Li3PO4, Li3PO4 protective layers of different thicknesses can be obtained.

[0125] In some embodiments, the solid content of the PEDOT-PSS-containing solution in step S3 is 10% to 20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0126] In some embodiments, the preparation method of the PEDOT-PSS-containing solution in step S3 includes the following steps: mixing water, PSS aqueous solution and EDTO monomer to obtain a buffer layer precursor solution; adding an oxidant to the buffer layer precursor solution under stirring to carry out an oxidative polymerization reaction; after the reaction is completed, separating the reaction product; and mixing the reaction product with an organic solvent to obtain the buffer layer precursor solution.

[0127] In some embodiments, the mass ratio of the water, the PSS aqueous solution, and the EDTO monomer is (80~95):(5~15):1, wherein the water is selected from the range of "80~95", for example, it can be 80, 82, 83, 85, 88, 90, 92, 93, or 95, etc.; the PSS aqueous solution is selected from the range of "5~15", for example, it can be 5, 7, 8, 10, 12, 13, 14, or 15, etc.

[0128] In some embodiments, the concentration of the PSS aqueous solution is 1wt% to 3wt%, for example, it can be 1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, or 3wt%, etc.

[0129] In some embodiments, the buffer layer precursor solution further includes an emulsifier, which includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and Triton X-100.

[0130] In some embodiments, the emulsifier accounts for 0.5% to 5% of the mass of the EDTO monomer, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0131] Adding emulsifiers helps EDOT monomers disperse in water to form an emulsion.

[0132] In some embodiments, the catalyst includes at least one of ferric sulfate, ferric chloride, and ferric nitrate.

[0133] In some embodiments, the catalyst accounts for 1% to 10% of the mass of the EDTO monomer, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0134] In some embodiments, the oxidant includes ammonium persulfate and / or potassium persulfate.

[0135] In some embodiments, the oxidant accounts for 100% to 300% of the mass of the EDTO monomer, for example, it can be 100%, 120%, 150%, 170%, 200%, 220%, 240%, 260%, 280%, or 300%.

[0136] In some embodiments, the temperature of the oxidative polymerization reaction is 5°C to 30°C, for example, it can be 5°C, 10°C, 15°C, 20°C, 25°C or 30°C.

[0137] In some embodiments, the oxidative polymerization reaction takes 5 to 24 hours, for example, 5 hours, 7 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0138] In step S3 of the present invention, by adjusting the areal density of the coated solution containing PEDOT-PSS, Li3PO4 protective layers of different thicknesses can be obtained.

[0139] Thirdly, the present invention provides a battery module, the battery module comprising the solid-state battery described in the first aspect.

[0140] In the solid-state battery of the present invention, a separator is provided between adjacent bipolar electrodes, and the separator is a solid electrolyte membrane.

[0141] In some embodiments, the method for preparing a solid electrolyte membrane includes: wet homogenizing a third solid electrolyte and a third binder to obtain a solid electrolyte slurry; coating the solid electrolyte slurry onto a base membrane; drying and rolling the base membrane before peeling it off to obtain a solid electrolyte membrane.

[0142] In some embodiments, the third solid electrolyte is a sulfide solid electrolyte, which has good flexibility.

[0143] In some embodiments, the third adhesive is nitrile rubber (NBR).

[0144] Example 1

[0145] This embodiment provides a solid-state battery, and a schematic diagram of part of its structure is shown below. Figure 1The device includes several stacked battery cells 1, which are connected by a common bipolar current collector 11. The bipolar current collector is a three-dimensional cross-linked carbon fiber film with a porosity of 10%, a tensile strength of 550 MPa, and a thickness of 8 μm. The bipolar current collector 11 has a first surface and a second surface disposed opposite to each other. A composite positive electrode layer 12 is formed on the first surface. The composite positive electrode layer 12 includes a positive electrode active material layer 121 in contact with the bipolar current collector 11 and a positive electrode protective layer 122 covering the positive electrode active material layer. The thickness of the positive electrode active material layer 121 is 50 μm, and the thickness of the positive electrode protective layer 122 is a Li3PO4 protective layer. A composite negative electrode layer 13 is formed on the second surface with a thickness of 0 μm. The composite negative electrode layer 13 includes a negative electrode active material layer 131 in contact with the bipolar current collector 11 and a conductive buffer layer 132 covering the negative electrode active material layer 131. The thickness of the negative electrode active material layer 131 is 30 μm, and the conductive buffer layer 132 is a PEDOT-PSS buffer layer with a thickness of 8 μm. The solid-state battery also includes a solid electrolyte membrane 14, which is located between the positive electrode protection layer 122 and the conductive buffer layer 132. The bipolar current collector 11, the positive electrode active material layer 121, the positive electrode protection layer 122, the solid electrolyte membrane 14, the conductive buffer layer 132, the negative electrode active material layer 131, and the bipolar current collector 11 are stacked in sequence to form the battery cell 1.

[0146] This embodiment also provides a method for preparing the above-mentioned solid-state battery, including the following steps:

[0147] (1) Preparation of bipolar current collectors

[0148] a. Preparation of spinning solution

[0149] Polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) were mixed to obtain a spinning solution with a mass fraction of 10%.

[0150] b. Electrospinning process

[0151] Electrospinning was performed using the aforementioned spinning solution, with the following parameters controlled:

[0152] Spinning voltage: 15kV;

[0153] Propulsion rate: 1.0 mL / h;

[0154] Reception distance: 15cm;

[0155] Ambient temperature: 25℃;

[0156] Ambient humidity: 40%;

[0157] Receiving device: uses a high-speed rotating drum at 700 rpm.

[0158] c. Pre-oxidation

[0159] The electrospun membrane prepared in step b was pre-oxidized at a temperature of 280℃, a heating rate of 2℃ / min, and a holding time of 2h.

[0160] d. Pre-calendering

[0161] The electrospun film after pre-oxidation in step c is pre-calcined, with the pressure controlled at 4 MPa and the linear speed of the calcining rollers at 2 m / min.

[0162] e. Carbonization

[0163] The film obtained by pre-calendering in step d is heated to 800℃ at 2℃ / min and held for 2h in a N2 atmosphere to obtain a three-dimensional cross-linked carbon fiber film, also known as a bipolar current collector. The two sides of the bipolar current collector are the positive electrode side and the negative electrode layer, respectively. The surface of the positive electrode side is denoted as the first surface, and the surface of the negative electrode side is denoted as the second surface.

[0164] (2) Fabrication of integrated positive and negative electrodes:

[0165] According to LiNi 0.8 Co 0.1 Mn 0.1 O2:Li6PS5Cl:NBR:Super P (mass ratio) = 75:20:3:2. The above raw materials are added to cyclohexane and homogenized to obtain a positive electrode slurry. The positive electrode slurry is coated on the first surface of the bipolar current collector, dried and rolled (pressure of 2MPa) to form a positive electrode active material layer with a thickness of 50μm.

[0166] According to the ratio of graphite, Li6PS5Cl, conductive carbon black, and NBR (mass ratio) = 65:30:3:2, the above raw materials are added to cyclohexane and homogenized to obtain a negative electrode slurry. The negative electrode slurry is coated on the second surface of a bipolar current collector, dried and rolled to form a negative electrode active material layer with a thickness of 30μm.

[0167] Preparation of the positive electrode protective layer on the positive electrode side:

[0168] Li3PO4 and cyclohexane were mixed to obtain a Li3PO4 solution with a solid content of 15%. The Li3PO4 solution was coated on the surface of the positive electrode active material layer. After drying, a positive electrode protective layer (Li3PO4 protective layer) with a thickness of 10 μm was obtained on the positive electrode side.

[0169] Fabrication of the conductive buffer layer on the negative electrode side:

[0170] A mixed solution was prepared by mixing deionized water, polystyrene sulfonic acid aqueous solution (concentration 2wt%), EDOT monomer, and sodium dodecyl sulfate, wherein the mass ratio of deionized water to polystyrene sulfonic acid aqueous solution (concentration 2wt%) to EDOT monomer was 90:9:1, and the amount of sodium dodecyl sulfate added was 2% of the mass of EDOT.

[0171] Under stirring conditions, ammonium persulfate (200% of the mass of EDOT) and ferric sulfate (5% of the mass of EDOT) were added to the mixed solution to initiate the oxidative polymerization reaction of EDOT. The reaction temperature was controlled at 20℃ and the reaction time was 15h. After filtration and drying, PEDOT-PSS was obtained. PEDOT-PSS was added to cyclohexane to form a PEDOT-PSS solution with a solid content of 15%. The PEDOT-PSS solution was coated on the surface of the negative electrode active material layer. After drying, a conductive buffer layer (PEDOT-PSS buffer layer) with a thickness of 8μm was obtained on the negative electrode side, thus obtaining an integrated positive and negative electrode.

[0172] (3) Preparation of solid-state batteries:

[0173] Preparation of solid electrolyte membranes:

[0174] Li 10 GeP2S 12 LGPS and NBR are mixed at a mass ratio of 95:5, and cyclohexane is added for wet homogenization to obtain a solid electrolyte slurry. The solid electrolyte slurry is coated onto a polyethylene terephthalate (PET) film, dried, rolled, and then the PET film is peeled off to prepare a solid electrolyte membrane.

[0175] Preparation of the first composite structure:

[0176] Following the same method as in step (2), a negative electrode slurry was prepared, coated, dried, and rolled to prepare a negative electrode active material layer on the surface of the three-dimensional cross-linked carbon fiber film. Following the same method as in step (2), a PEDOT-PSS solution was prepared, coated, and dried to form a conductive buffer layer on the surface of the negative electrode active material layer, thus obtaining the first composite structure.

[0177] Preparation of the second composite structure:

[0178] Following the same method as in step (2), a positive electrode active material layer was prepared on the surface of the three-dimensional cross-linked carbon fiber film by preparing a positive electrode slurry, coating the positive electrode slurry, drying and rolling. Following the same method as in step (2), a Li3PO4 solution was prepared, coated with the Li3PO4 solution and dried to form a positive electrode protective layer on the surface of the positive electrode active material layer, thus obtaining the second composite structure.

[0179] A solid electrolyte membrane prepared in step (3) is stacked on the surface of the positive electrode protective layer of the integrated positive and negative electrode as a first solid electrolyte membrane. A first composite structure is stacked on the surface of the first solid electrolyte membrane (wherein, the conductive buffer layer in the first composite structure is in contact with the first solid electrolyte membrane). A solid electrolyte membrane prepared in step (3) is stacked on the surface of the conductive buffer layer of the integrated positive and negative electrode as a second solid electrolyte membrane. A second composite structure is stacked on the surface of the second solid electrolyte membrane (wherein, the positive electrode protective layer in the second composite structure is in contact with the second solid electrolyte membrane), thus obtaining a battery cell.

[0180] The battery cell is encapsulated in a housing, a wetting agent is added, and the housing is sealed to obtain a solid-state battery.

[0181] Example 2

[0182] The difference from Example 1 is that the thickness of the three-dimensional cross-linked carbon fiber film is 12 μm.

[0183] Example 3

[0184] The difference from Example 1 is that the thickness of the three-dimensional cross-linked carbon fiber film is 5 μm.

[0185] Example 4

[0186] The difference from Example 1 is that the thickness of the three-dimensional cross-linked carbon fiber film is 20 μm.

[0187] Example 5

[0188] The difference from Example 1 is that the thickness of the three-dimensional cross-linked carbon fiber film is 3 μm.

[0189] Example 6

[0190] The difference from Example 1 is that the thickness of the three-dimensional cross-linked carbon fiber film is 40 μm.

[0191] Example 7

[0192] The difference from Example 1 is that the thickness of the Li3PO4 protective layer on the positive electrode side is 5 μm.

[0193] Example 8

[0194] The difference from Example 1 is that the thickness of the Li3PO4 protective layer on the positive electrode side is 3μm.

[0195] Example 9

[0196] The difference from Example 1 is that the thickness of the Li3PO4 protective layer on the positive electrode side is 12μm.

[0197] Example 10

[0198] The difference from Example 1 is that the thickness of the Li3PO4 protective layer on the positive electrode side is 1 μm.

[0199] Example 11

[0200] The difference from Example 1 is that the thickness of the Li3PO4 protective layer on the positive electrode side is 20 μm.

[0201] Example 12

[0202] The difference from Example 1 is that the thickness of the PEDOT-PSS buffer layer on the negative electrode side is 6 μm.

[0203] Example 13

[0204] The difference from Example 1 is that the thickness of the PEDOT-PSS buffer layer on the negative electrode side is 5 μm.

[0205] Example 14

[0206] The difference from Example 1 is that the thickness of the PEDOT-PSS buffer layer on the negative electrode side is 15 μm.

[0207] Example 15

[0208] The difference from Example 1 is that the thickness of the PEDOT-PSS buffer layer on the negative electrode side is 2 μm.

[0209] Example 16

[0210] The difference from Example 1 is that the thickness of the PEDOT-PSS buffer layer on the negative electrode side is 25 μm.

[0211] Comparative Example 1

[0212] The difference from Example 1 is that, instead of using a three-dimensional cross-linked carbon fiber film as the bipolar current collector, separate positive and negative current collectors are used. Specifically:

[0213] Aluminum foil is used as the positive current collector, and copper foil is used as the negative current collector. The positive active material layer and the Li3PO4 protective layer are sequentially disposed on the surface of the positive current collector, and the negative active material layer and the PEDOT-PSS buffer layer are sequentially disposed on the surface of the negative current collector.

[0214] Comparative Example 2

[0215] The difference from Example 1 is that, instead of using a three-dimensional cross-linked carbon fiber film as the bipolar current collector, a PET film with a double-sided metallized layer is used. Specifically:

[0216] One side of the PET film is coated with an aluminum layer, and the other side of the PET film is coated with a copper layer.

[0217] Comparative Example 3

[0218] The difference from Example 1 is that no Li3PO4 protective layer is provided in the solid-state battery.

[0219] Comparative Example 4

[0220] The difference from Example 1 is that the solid-state battery does not have a PEDOT-PSS buffer layer.

[0221] Performance testing:

[0222] (1) Energy density test: Weigh the solid-state battery to obtain its weight, and perform charge-discharge tests on the solid-state battery. Under the condition of 25℃, charge at 0.1C to the cutoff voltage of 4.2V, charge at constant voltage to the cutoff current of 0.05C, and let stand for 30min; discharge at 0.1C to the cutoff voltage of 3.0V, record the discharge capacity, and obtain the discharge capacity (C, in Ah). Calculate the average working voltage (U, in V) according to the discharge curve. Calculate the mass energy density of the solid-state battery according to the formula energy density = C × U / m, and its unit is Wh / kg.

[0223] (2) Cyclic performance test: Under 25℃ conditions, charge at 0.1C to the cutoff voltage of 4.2V, charge at constant voltage to the cutoff current of 0.05C, and let stand for 30min; discharge at 0.1C to the cutoff voltage of 3.0V, record the discharge capacity (this is the first discharge capacity, denoted as C1), and let stand for 30min; cycle charge and discharge at 0.1C for 500 times, and record the discharge capacity C on the 500th cycle. 500 Calculate the capacity retention rate after 500 cycles using the following formula: Capacity retention rate after 500 cycles = C 500 / C1×100%.

[0224] (3) Electrochemical impedance spectroscopy (EIS) test: The solid-state battery is tested to obtain the interfacial impedance per unit area.

[0225] The results are shown in Table 1.

[0226]

[0227] As shown in Table 1, the present invention utilizes a three-dimensional cross-linked carbon fiber film as a bipolar current collector, and sets a Li3PO4 protective layer and a PEDOT-PSS buffer layer on the outer side of the positive and negative electrode active material layers, which can improve the energy density of the battery, reduce the interface impedance, and improve the long cycle life.

[0228] As can be seen from Examples 1 to 6, a thickness of 5 μm to 20 μm in a three-dimensional cross-linked carbon fiber film can better reduce interfacial impedance and improve cycle performance.

[0229] By comparing Examples 1 with Examples 7-11 and Comparative Example 3, it can be seen that the setting of the Li3PO4 protective layer plays a very important role in reducing interface resistance and improving cycle performance. Moreover, its thickness is in the range of 3μm to 12μm, which can better reduce interface impedance and improve cycle performance.

[0230] By comparing Example 1 with Examples 12-16 and Comparative Example 4, it can be seen that the setting of the PEDOT-PSS buffer layer plays a very important role in reducing interface resistance and improving cycle performance. Moreover, its thickness is in the range of 5μm to 15μm, which can better reduce interface impedance and improve cycle performance.

[0231] A comparison of Example 1 with Comparative Examples 1 and 2 reveals that Comparative Example 1, employing traditional positive and negative current collectors, suffers from low energy density, high interfacial resistance, and poor cycle performance. Comparative Example 2, using metal plating on both sides of a PET film to construct a bipolar current collector, while improving energy density, reducing interfacial resistance, and enhancing cycle performance compared to Comparative Example 1, still exhibits drawbacks such as low energy density, high interfacial resistance, and the need for further improvement in cycle performance. This invention utilizes a three-dimensional cross-linked carbon fiber film as the bipolar current collector and constructs the bipolar electrode, significantly improving energy density, reducing interfacial resistance, and enhancing cycle performance compared to Comparative Example 2.

[0232] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A solid-state battery, characterized in that, It includes several stacked battery cells, which are connected by a common bipolar current collector; The bipolar current collector includes a three-dimensional cross-linked carbon fiber film, and the three-dimensional cross-linked carbon fiber film has a first surface and a second surface disposed opposite to each other. A composite positive electrode layer is formed on the first surface, the composite positive electrode layer including a positive electrode active material layer in contact with the bipolar current collector and a positive electrode protective layer covering the positive electrode active material layer; A composite negative electrode layer is formed on the second surface. The composite negative electrode layer includes a negative electrode active material layer in contact with the bipolar current collector and a conductive buffer layer covering the negative electrode active material layer. The solid-state battery also includes a solid electrolyte membrane, which is located between the positive electrode protective layer and the conductive buffer layer. The battery cell is composed of a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked in sequence. The positive electrode protective layer includes Li3PO4, and the conductive buffer layer includes PEDOT-PSS.

2. The solid-state battery according to claim 1, characterized in that, The three-dimensional cross-linked carbon fiber film satisfies at least one of the following conditions: (1) The porosity of the three-dimensional cross-linked carbon fiber film is 5%~20%; (2) The tensile strength of the three-dimensional cross-linked carbon fiber film is 300MPa~800MPa; (3) The thickness of the three-dimensional cross-linked carbon fiber film is 5μm~20μm.

3. The solid-state battery according to claim 1, characterized in that, The carbon source of the three-dimensional cross-linked carbon fiber film is selected from at least one of polyacrylonitrile, polyimide and lignin.

4. The solid-state battery according to claim 1, characterized in that, The thickness of the positive electrode protective layer is 3μm~12μm.

5. The solid-state battery according to claim 1, characterized in that, The thickness of the conductive buffer layer is 5μm~15μm.

6. A method for preparing a solid-state battery as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: S1. Prepare a spinning solution containing a carbon source, prepare a precursor fiber membrane by electrospinning, and then perform pre-oxidation, pre-calendering of the pre-oxidized fiber membrane, and carbonization in sequence to obtain a three-dimensional cross-linked carbon fiber film as a bipolar current collector. The three-dimensional cross-linked carbon fiber film has a first surface and a second surface arranged opposite to each other. S2. A positive electrode slurry is coated on the first surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the positive electrode active material layer is formed; a solution containing Li3PO4 is coated on the surface of the positive electrode active material layer, and after drying, the positive electrode protective layer is formed. S3. A negative electrode slurry is coated on the second surface of the three-dimensional cross-linked carbon fiber film, and after drying and pressing, the negative electrode active material layer is formed; a solution containing PEDOT-PSS is coated on the surface of the negative electrode active material layer, and after drying, the conductive buffer layer is formed, thus obtaining an integrated positive and negative electrode. S4. A first solid electrolyte film is stacked on the surface of the positive electrode protective layer of the integrated positive and negative electrode, and a second solid electrolyte film is stacked on the surface of the conductive buffer layer of the integrated positive and negative electrode. S5. A first composite structure is stacked on the surface of the first solid electrolyte membrane. Along the direction away from the first solid electrolyte membrane, the first composite structure includes a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector stacked sequentially. A second composite structure is stacked on the surface of the second solid electrolyte membrane. Along the direction away from the second solid electrolyte membrane, the second composite structure includes a positive electrode protective layer, a positive electrode active material layer, and a bipolar current collector stacked sequentially, to obtain a battery cell. S6. The battery cell is encapsulated in a housing, an impregnating agent is added, and the opening is sealed to obtain a solid-state battery; The solid-state battery includes several stacked battery cells, each battery cell comprising a bipolar current collector, a positive electrode active material layer, a positive electrode protective layer, a solid electrolyte membrane, a conductive buffer layer, a negative electrode active material layer, and a bipolar current collector arranged in sequence.

7. The method for preparing a solid-state battery according to claim 6, characterized in that, After step S4, the following steps are performed: (a) At least one integrated positive and negative electrode and a third solid electrolyte membrane are sequentially stacked on the surface of a first solid electrolyte membrane, wherein two sides of the first solid electrolyte membrane and the third solid electrolyte membrane are in contact with the positive electrode protective layer and the conductive buffer layer, respectively; and / or, (b) At least one integrated positive and negative electrode and a fourth solid electrolyte membrane are sequentially stacked on the surface of the second solid electrolyte, wherein the two sides of the second solid electrolyte membrane and the fourth solid electrolyte are in contact with the positive electrode protective layer and the conductive buffer layer, respectively.

8. The method for preparing a solid-state battery according to claim 6, characterized in that, Step S1 satisfies at least one of the following conditions: (1) In the spinning solution, the mass fraction of the carbon source is 7%~16%; (2) The electrospinning voltage is 10kV~25kV, the propulsion rate is 0.5mL / h~1.5mL / h, and the receiving distance is 10cm~20cm; (3) The pre-oxidation temperature is 250℃~300℃; (4) The pre-calendering pressure is 2MPa~10MPa; (5) The carbonization temperature is 700℃~1200℃.

9. The method for preparing a solid-state battery according to claim 6, characterized in that, The solid content of the Li3PO4-containing solution described in step S2 is 10%~20%; The solid content of the PEDOT-PSS-containing solution in step S3 is 10%~20%.

10. A battery module, characterized in that, The battery module includes the solid-state battery as described in any one of claims 1-5.

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