Bipolar current collector, preparation method and all-solid-state battery

Abstract

The invention discloses a bipolar current collector, a preparation method and an all-solid-state battery, the bipolar current collector comprises a stainless steel substrate, one side of the stainless steel substrate is a porous copper layer, and the other side of the stainless steel substrate is a graphene conductive layer. The stainless steel substrate is combined with the porous copper layer, so that the current distribution uniformity and the overall performance of the current collector are improved, the current is more effectively collected and transmitted, and the energy loss is reduced; the graphene conductive layer is arranged on the other side of the stainless steel substrate, so that the corrosion resistance of the current collector is improved, the service life is prolonged, the heat dissipation performance is enhanced, and the risk of thermal runaway in the battery is reduced. Through the combination effect of the porous copper layer and the graphene conductive layer, the energy density and conductivity of the battery can be remarkably improved, the charge and discharge performance of the battery is optimized, and meanwhile, the safety and stability of the battery in the operation process can be effectively guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a bipolar current collector, a preparation method and an all-solid-state battery. Background Art

[0002] As a key component in electrochemical energy storage devices, the performance of the current collector significantly impacts the overall efficiency of the battery. Traditionally, current collectors have been unipolar, consisting of a single layer of positive or negative electrode material deposited on the same substrate to collect and transmit current. However, with the continuous advancement of electrochemical technology and the increasing diversification of application requirements, bipolar current collectors have gradually attracted attention.

[0003] A bipolar current collector is a composite material with bipolar properties, formed by depositing positive and negative electrode materials on two different surfaces of a single substrate. This design not only simplifies the battery structure, reduces material usage and weight, but also improves the battery's energy and power density. Furthermore, bipolar current collectors enable more efficient use of space, shorten the current transmission path, and reduce internal resistance, thereby improving the battery's cycle stability and rate performance.

[0004] Stainless steel has demonstrated significant advantages as a current collector in various fields. Graphene, as a new material, possesses many unique physical and chemical properties, and its application has made significant progress, particularly in metal corrosion protection and heat dissipation. Summary of the Invention

[0005] The purpose of the present invention is to provide a bipolar current collector, a preparation method and an all-solid-state battery to optimize the performance of the battery, improve the energy density and conductivity, and ensure the safety and stability of the battery.

[0006] To achieve the above object, the technical solution provided by the present invention is:

[0007] A first aspect of the present application provides a bipolar current collector comprising a stainless steel substrate, wherein one side of the stainless steel substrate is a porous copper layer and the other side is a graphene conductive layer.

[0008] The thickness of the stainless steel substrate is 5 to 16 μm; the thickness of the porous copper layer is 0.8 to 1.5 μm, and the porosity is 89.8% to 92.6%; the thickness of the graphene conductive layer is 1 to 3 μm.

[0009] A second aspect of the present application provides a method for preparing a bipolar current collector, comprising the following steps: preparing a porous copper layer on one side of a stainless steel substrate and preparing a graphene conductive layer on the other side.

[0010] The stainless steel substrate is first pretreated, including decontamination treatment, rust removal treatment and activation treatment, and the activation treatment includes pickling and chemical reduction treatment.

[0011] The porous copper layer is prepared by water electroplating, specifically:

[0012] The stainless steel is placed on a DC temperature-controlled winding electroplating line for water electroplating and the electroplating temperature is controlled so that the stainless steel surface is in a cathode state. At the same time, copper ions are added to the anode and reduced to solid copper through electrolysis reaction and deposited on the stainless steel surface.

[0013] The porosity of the porous copper layer is controlled by the electroplating temperature and current density, and the thickness of the porous copper layer is controlled by the power-on time and current density. The electroplating temperature is 20-26°C, and the current density is 4-10A / dm 2 , the power-on time is 80 to 160 seconds.

[0014] The graphene conductive layer is prepared by a coating method, specifically:

[0015] A graphene conductive slurry is prepared and evenly coated on the other side of the stainless steel substrate opposite to the porous copper layer.

[0016] The preparation method of the graphene conductive slurry comprises the following steps: weighing graphene, hydroxyethyl cellulose and acetylene black, grinding them uniformly, and then adding polyvinyl alcohol and grinding them uniformly; wherein the mass ratio of graphene, hydroxyethyl cellulose, acetylene black and polyvinyl alcohol is 70-85:5-15:3-10:5-15.

[0017] The third aspect of the present application provides a solid-state battery comprising the above-mentioned bipolar current collector.

[0018] A positive electrode material and a solid polymer electrolyte are added to the surface of the graphene conductive layer of the bipolar current collector to form a solid-state battery unit; the solid-state battery contains one solid-state battery unit or two or more solid-state battery units stacked in the same direction.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention uses stainless steel as the current collector matrix. Stainless steel has good electrical conductivity and stability and can withstand chemical erosion by weak corrosive media such as air, steam, and water and strong corrosive media such as acid, alkali, and salt.

[0021] The present invention combines a stainless steel substrate with a porous copper layer, which not only enhances the conductivity of the current collector, but also increases the surface area due to the porous structure of the copper layer, thereby improving the current distribution uniformity and overall performance of the current collector; specifically, the porous structure is conducive to increasing the contact area between the solid polymer electrolyte and the electrode material, promoting the deposition of lithium ions, thereby improving the charge and discharge performance of the battery. The porous copper plating can also more effectively collect and transmit current, reduce energy loss, and is particularly suitable for electrochemical systems such as batteries with high requirements for energy density and cycle stability.

[0022] The present invention sets a graphene conductive layer on the other side of the stainless steel substrate, which is beneficial to reducing the interface resistance during the battery charge and discharge cycle. The graphene conductive layer can not only significantly improve the corrosion resistance of the current collector and extend the service life, but also enhance the heat dissipation performance, play a role in metal corrosion protection and heat dissipation, reduce the risk of thermal runaway inside the battery, and further improve the performance of the battery.

[0023] The graphene conductive layer of the present invention is made of graphene, hydroxyethyl cellulose and acetylene carbon black. The electrical properties under a certain ratio form an advantageous combination with the porous copper layer of a certain thickness, which significantly improves the energy density and conductivity of the battery, optimizes the battery's charge and discharge performance, and effectively ensures the safety and stability of the battery during operation.

[0024] The porous copper layer and the graphene conductive layer also produce a synergistic effect with the solid polymer electrolyte and the positive electrode material. For example, for the composite positive electrode material constructed with a polyethylene oxide (PEO)-based solid polymer electrolyte and a PEO-containing material, the pore structure of the porous copper layer can accommodate the flexible filling of the PEO electrolyte, expand the solid-solid contact area, and reduce the interface impedance; the flexibility of PEO combined with the mechanical properties of porous copper can alleviate the stress concentration problem caused by the volume change of the electrode during charging and discharging; the PEO electrolyte is easily oxidized and decomposed under high voltage, and the chemical inertness of the graphene conductive layer can reduce the side reactions at the high-voltage interface and improve the battery cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : Schematic diagram of the structure of the bipolar current collector of the present invention.

[0026] Figure 2 : Schematic diagram of the preparation of the solid-state battery of the present invention. DETAILED DESCRIPTION

[0027] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0028] The experimental methods used in the following examples are conventional methods unless otherwise specified, and the reagents, methods and equipment used are conventional reagents, methods and equipment in the art unless otherwise specified.

[0029] For the sake of simplicity, this document only specifically discloses some numerical values ​​and optional ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range. Similarly, any upper limit can be combined with any other upper limit to form an unspecified range; the optional items in the optional range can also be combined arbitrarily.

[0030] Unless otherwise specified, the terms used in this application have the commonly known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art.

[0031] The present application provides a bipolar current collector, comprising a stainless steel substrate, one side of the stainless steel substrate is a porous copper layer, and the other side is a graphene conductive layer, such as Figure 1 As shown. The solution of this application makes the best use of the advantages of combining stainless steel with porous copper and graphene:

[0032] A porous copper layer is prepared on one side of a stainless steel substrate, and a graphene conductive layer is prepared on the other side; the stainless steel substrate provides structural stability and mechanical strength, maintains stable performance in high-temperature environments, and is not prone to deformation or melting; stainless steel contains elements such as nickel, molybdenum, titanium, niobium, copper, and iron, and has excellent conductive properties, allowing current to be efficiently transmitted in the current collector, reducing energy loss.

[0033] The porous copper layer is a non-negative electrode material. Its porous structure helps to increase the contact area between the electrode and the polymer electrolyte, promote the deposition of lithium, slow down the growth of lithium dendrites, and is beneficial to improve the discharge capacity of the battery and extend the cycle life of the battery.

[0034] Graphene's excellent electrical conductivity helps reduce interfacial resistance during battery charge and discharge cycles, improving battery performance and lifespan. Graphene also demonstrates remarkable effectiveness in metal corrosion protection and heat dissipation. Incorporating its properties into battery configurations aims to optimize battery performance across the board: by increasing energy density and electrical conductivity, significantly boosting battery power output.

[0035] The present application can significantly improve the energy density and conductivity of the battery through the combination of the porous copper layer and the graphene conductive layer, thereby optimizing the battery's charge and discharge performance, and effectively ensuring the safety and stability of the battery during operation.

[0036] Preferably, the thickness of the stainless steel substrate is 5 to 16 μm; the thickness of the porous copper layer is 0.8 to 1.5 μm, and the porosity is 89.8% to 92.6%; and the thickness of the graphene conductive layer is 1 to 3 μm.

[0037] More preferably, the thickness of the porous copper layer is 1 to 1.2 μm.

[0038] In some embodiments, the stainless steel substrate is first pretreated, including decontamination, rust removal and activation. The activation includes pickling and chemical reduction, and the stainless steel is treated with a chemical reducing agent to increase its surface activity.

[0039] In some embodiments, the porous copper layer is prepared by water electroplating, specifically:

[0040] The stainless steel is placed on a DC temperature-controlled winding electroplating line for water electroplating and the electroplating temperature is controlled so that the stainless steel surface is in a cathode state. At the same time, copper ions are added to the anode and reduced to solid copper through electrolysis reaction and deposited on the stainless steel surface.

[0041] The porosity of the porous copper layer is controlled by the electroplating temperature and current density, and the thickness of the porous copper layer is controlled by the power-on time and current density. Preferably, the electroplating temperature is 20-26°C and the current density is 4-10A / dm 2 , the power-on time is 80 to 160 seconds.

[0042] In some embodiments, the graphene conductive layer is prepared by a coating method, specifically:

[0043] A graphene conductive slurry is prepared and evenly coated on the other side of the stainless steel substrate opposite to the porous copper layer.

[0044] The preparation method of the graphene conductive slurry comprises the following steps: weighing graphene, hydroxyethyl cellulose and acetylene black, grinding them uniformly, and then adding polyvinyl alcohol and grinding them uniformly; wherein the mass ratio of the graphene, hydroxyethyl cellulose, acetylene black and polyvinyl alcohol is 70-85:5-15:3-10:5-15.

[0045] Further preferably, the mass ratio of graphene, hydroxyethyl cellulose, acetylene black and polyvinyl alcohol is 75:10:5:10.

[0046] The present application also provides a solid-state battery comprising the above-mentioned bipolar current collector.

[0047] A positive electrode material and a solid polymer electrolyte are added to the surface of the graphene conductive layer of the bipolar current collector to form a solid-state battery cell.

[0048] In some embodiments, the solid-state battery of the present application comprises one solid-state battery unit or two or more stacked solid-state battery units, such as Figure 2 shown.

[0049] The present invention is further described in detail below with reference to specific embodiments:

[0050] Example 1

[0051] 1. Cleaning and decontamination: First, thoroughly clean and decontaminate the stainless steel surface to remove oil, dust and other impurities to ensure that the surface is clean and free of dirt.

[0052] 2. Rust removal: If there is rust or corrosion on the stainless steel surface, rust removal is required to ensure a smooth surface, which is conducive to the adhesion of the electroplating layer.

[0053] 3. Activation treatment: Before electroplating, the stainless steel surface is activated. The activation treatment methods include pickling and chemical treatment. Pickling is performed with 100mL / L H2SO4. The chemical treatment agent is Na2CO3 28g / L, Na2SiO3·9H2O 8g / L, and Na3PO4·12H2O 23g / L to improve its surface activity so that the electroplating layer can better adhere to the surface.

[0054] 4. Electroplating of porous copper: put the treated stainless steel into the DC temperature-controlled winding electroplating line for water electroplating. The thickness of the stainless steel substrate is 8μm, the electroplating temperature is 22℃, and the surface of the stainless steel substrate is in the cathode state; at the same time, copper ions are added to the anode and the electrolytic reaction is carried out at 6A / dm 2 The current density was controlled and the power was applied for 100s to reduce the copper ions into solid copper and deposit it on the stainless steel surface. The thickness of the copper deposition was adjusted by controlling the current density, and the thickness of the electrodeposited porous copper layer was 1μm.

[0055] 5. Post-processing: After electroplating is completed, the stainless steel workpiece is removed from the electroplating tank and cleaned and dried to remove residual electroplating solution and other impurities on the surface.

[0056] 6. Graphene coating: Graphene, hydroxyethyl cellulose, and acetylene black were weighed in a mass ratio of 70:10:10, mixed evenly, and placed in a zirconia ball mill for ball milling at a speed of 300 rpm. After ball milling for 3 hours, polyvinyl alcohol was added and continued to grind for 0.5 hours to obtain a uniform graphene conductive slurry; the non-electroplated copper side of the stainless steel foil was placed close to the coating platform, the graphene conductive slurry was measured, and evenly coated with a scraper to a coating thickness of 2 μm. The stainless steel after single-side coating was transferred to an 80°C drying oven for rapid drying for 15 minutes, and then vacuum dried at 85°C for 10 hours to obtain a bipolar current collector.

[0057] The present invention provides a method for manufacturing a bipolar current collector comprising the following steps:

[0058] Coating the positive electrode material: dissolve the positive electrode active material lithium iron phosphate (LFP), solid polymer electrolyte polyethylene oxide (PEO), conductive agent, and binder in the organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 60:20:10:10, coat it on the coated graphene surface of the bipolar current collector, and then dry it.

[0059] Preparation of a solid polymer electrolyte: Polyethylene oxide (PEO) and lithium bis(fluorosulfonyl)imide (LIFSI) were dissolved in an organic solvent, N,N-dimethylformamide (DMF), and then heated at 90°C in a vacuum-dried environment for 12 hours before cooling to room temperature; the molar ratio of polyethylene oxide (PEO) to lithium bis(fluorosulfonyl)imide (LIFSI) was 20:1.

[0060] The above materials are stacked to form a solid-state battery unit; then the two solid-state battery units are stacked in the same direction and hot-pressed at 80°C for 10 minutes to make all surfaces fit tightly; finally, the compacted solid-state battery unit is encapsulated in a button battery to obtain a high-voltage bipolar all-solid-state battery.

[0061] Example 2

[0062] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1 μm, and the ratio of the graphene coating is 75:10:10:5.

[0063] Example 3

[0064] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1 μm, and the ratio of the graphene coating is 75:10:5:10.

[0065] Example 4

[0066] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1 μm, and the ratio of the graphene coating is 75:5:10:10.

[0067] Example 5

[0068] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1 μm, and the ratio of the graphene coating is 85:5:5:5.

[0069] Example 6

[0070] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 0.5 μm, and the ratio of the graphene coating is 75:10:5:10.

[0071] Example 7

[0072] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 0.8 μm, and the ratio of the graphene coating is 75:10:5:10.

[0073] Example 8

[0074] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1.2 μm, and the ratio of the graphene coating is 75:10:5:10.

[0075] Example 9

[0076] This embodiment relates to a bipolar current collector, a preparation method, and an all-solid-state battery. The only difference from Example 1 is that the thickness of the electrodeposited porous copper layer is 1.5 μm, and the ratio of the graphene coating is 75:10:5:10.

[0077] Comparative Example

[0078] Compared with Example 1, the copper layer of this comparative example does not contain pores, and a copper layer with the same thickness of 1 μm is directly plated by magnetron sputtering technology, and the ratio of the graphene coating is 70:10:10:10.

[0079] The examples and comparative examples were tested and the results are shown in Table 1.

[0080] Table 1 Bipolar current collector composition and battery performance of each embodiment and comparative example

[0081]

[0082]

[0083] From the comparison of Examples 1-5, it can be seen that when the thickness of the porous copper layer and the graphene conductive layer remains unchanged, when the raw material composition of the graphene conductive layer prepared in Example 3 is graphene, hydroxyethyl cellulose, acetylene carbon black and polyvinyl alcohol in a mass ratio of 75:10:5:10, the battery prepared has a significantly higher first-cycle discharge specific capacity, and this composition ratio is the preferred option.

[0084] According to Example 3 and the comparison of Examples 6-9, when the thickness of the graphene conductive layer and the composition of the raw materials for preparing the graphene conductive layer remain unchanged, the first-cycle discharge specific capacity of the battery is examined. As the thickness of the porous copper layer increases, the first-cycle discharge specific capacity of the battery first increases and then decreases. A porous copper layer that is too thick or too thin is not conducive to the optimization of battery performance. A porous copper layer that is too thick has a certain influence on the overall current distribution of the current collector. A porous copper layer that is too thin weakens the optimization effect of the reaction of the solid polymer electrolyte and the deposition of lithium, and is not conducive to forming an optimization scheme for improving battery performance with the graphene conductive layer. After testing, the optimal thickness of the porous copper layer is 1 to 1.2 μm.

[0085] Comparing Example 1 with the comparative example shows that porous copper foil has a higher specific surface area and better ion conductivity than solid copper. Its porous structure increases the contact area between the electrode and the electrolyte, enabling more efficient ion transmission, thereby improving the battery's charge and discharge efficiency. It also enhances battery safety, reducing safety risks caused by short circuits or overheating. With its unique structure and excellent performance, porous copper foil provides a crucial guarantee for the efficient and stable operation of solid-state batteries.

[0086] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent replacement and improvement made by any technician familiar with the profession to the above embodiment without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A bipolar current collector, characterized in that: It comprises a stainless steel substrate, one side of the stainless steel substrate is a porous copper layer, and the other side is a graphene conductive layer.

2. The bipolar current collector according to claim 1, wherein: The thickness of the stainless steel substrate is 5 to 16 μm; the thickness of the porous copper layer is 0.8 to 1.5 μm, and the porosity is 89.8% to 92.6%; the thickness of the graphene conductive layer is 1 to 3 μm.

3. A method for preparing a bipolar current collector, characterized in that: The method comprises the following steps: preparing a porous copper layer on one side of a stainless steel substrate, and preparing a graphene conductive layer on the other side.

4. The method for preparing a bipolar current collector according to claim 3, wherein: The stainless steel substrate is first pretreated, including decontamination treatment, rust removal treatment and activation treatment, and the activation treatment includes pickling and chemical reduction treatment.

5. The method for preparing a bipolar current collector according to claim 3, wherein: The porous copper layer is prepared by water electroplating, specifically: The stainless steel is placed on a DC temperature-controlled winding electroplating line for water electroplating and the electroplating temperature is controlled so that the stainless steel surface is in a cathode state. At the same time, copper ions are added to the anode and reduced to solid copper through electrolysis reaction and deposited on the stainless steel surface.

6. The method for preparing a bipolar current collector according to claim 5, characterized in that: The porosity of the porous copper layer is controlled by the electroplating temperature and current density, and the thickness of the porous copper layer is controlled by the power-on time and current density. The electroplating temperature is 20-26°C, and the current density is 4-10A / dm 2 , the power-on time is 80 to 160 seconds.

7. The method for preparing a bipolar current collector according to claim 2, wherein: The graphene conductive layer is prepared by a coating method, specifically: A graphene conductive slurry is prepared and evenly coated on the other side of the stainless steel substrate opposite to the porous copper layer.

8. The method for preparing a bipolar current collector according to claim 7, wherein: The preparation method of the graphene conductive slurry comprises the following steps: weighing graphene, hydroxyethyl cellulose and acetylene black, grinding them uniformly, and then adding polyvinyl alcohol and grinding them uniformly; wherein the mass ratio of graphene, hydroxyethyl cellulose, acetylene black and polyvinyl alcohol is 70-85:5-15:3-10:5-15.

9. A solid-state battery, characterized in that: A bipolar current collector prepared by the method according to claim 1 or 2 or any one of claims 3 to 8.

10. The solid-state battery according to claim 9, characterized in that: A positive electrode material and a solid polymer electrolyte are added to the surface of the graphene conductive layer of the bipolar current collector to form a solid-state battery unit; the solid-state battery contains one solid-state battery unit or two or more solid-state battery units stacked in the same direction.

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