Three-dimensional porous current collector, preparation method and application thereof

Abstract

The application discloses a kind of three-dimensional porous current collector and its preparation method and application, belong to sodium metal battery current collector technical field, solve the problem that the electrochemical performance of anode metal sodium battery in prior art is not ideal enough.The three-dimensional porous current collector includes copper substrate and bismuth nanosheet vertically grown on the surface of copper substrate;Among them, the copper substrate is a reticular structure, and the bismuth nanosheet is a three-dimensional honeycomb structure.The three-dimensional porous current collector provided by the application has super-stable sodium deposition stripping performance and excellent long cycle stability.

Description

Technical Field

[0001] This invention relates to the field of sodium metal battery current collector technology, and more specifically to a three-dimensional porous current collector, its preparation method and application. Background Technology

[0002] With the continuous development of electric vehicles and smart grids, there has been a strong interest in large-scale energy storage devices. Sodium is abundant in nature, and sodium-ion batteries have become a viable energy storage solution. Among various negative electrode materials for sodium-ion batteries, metallic sodium has significant advantages due to its high specific capacity, low potential, and abundant availability, making sodium metal batteries a promising candidate for high-energy applications.

[0003] However, the commercialization of sodium metal batteries is hampered by persistent challenges, including severe dendrite growth, continuous side reactions, and significant volume expansion at the electrode / electrolyte interface. Sodium dendrite growth can lead to membrane permeation, causing short circuits. Furthermore, side reactions and continuous volume expansion promote the decomposition and reconstruction of the solid electrolyte interphase (SEI), exacerbating dendrite growth and resulting in the stripping of large amounts of "dead sodium," further reducing sodium activity and accelerating battery degradation. Simultaneously, directly using metallic sodium as the negative electrode may lead to excessive thickness, reducing energy density and posing potential risks.

[0004] These challenges hinder the realization of sodium metal as a high-energy-density battery. In an ideal state, anode-free sodium metal battery can achieve 100% sodium utilization during charge and discharge. However, anode-free sodium metal batteries place more stringent demands on materials, requiring higher coulombic efficiency, virtually no dendrites, and no "dead sodium," which can lead to faster capacity decay and more serious problems such as side reactions during actual charge and discharge and shorter cycle life. Therefore, more optimization methods are needed to tune the electrode / electrolyte interface to improve its electrochemical performance. Summary of the Invention

[0005] This invention provides a three-dimensional porous current collector, its preparation method, and its application, in order to solve the problem that the electrochemical performance of non-negative electrode sodium metal batteries is not ideal in the prior art.

[0006] In a first aspect, the present invention provides a three-dimensional porous current collector, comprising a copper substrate and bismuth nanosheets vertically grown on the surface of the copper substrate; wherein the copper substrate has a mesh structure and the bismuth nanosheets have a three-dimensional honeycomb structure.

[0007] As one possible implementation, the copper substrate has a mesh pore size of 40–50 μm; the copper substrate has a thickness of 100–150 μm; and the bismuth nanosheets have a honeycomb pore size of 50–300 nm.

[0008] In a second aspect, the present invention provides a method for preparing a three-dimensional porous current collector according to any possible implementation of the first aspect, comprising the following steps: placing the copper substrate in an N,N-dimethylformamide solution of bismuth ions and heating it at 37-43°C for 11-13 hours to obtain a crude product; and sequentially washing and vacuum drying the crude product to obtain the three-dimensional porous current collector.

[0009] As one possible implementation, the cleaning agent used in the cleaning is either ethanol or deionized water; and / or, the vacuum drying operation is vacuum drying at a temperature of 55-65°C for 8-12 hours.

[0010] As one possible implementation, in the N,N-dimethylformamide solution of bismuth ions, the donor of the bismuth ions is bismuth chloride.

[0011] As one possible implementation, the molar ratio of copper element in the copper substrate to bismuth ions is 3:1.5 to 2.5; and / or, the concentration of the organic solution of bismuth ions is 0.018 to 0.022 M.

[0012] One possible implementation includes the following steps: placing the copper substrate in a 0.02 mol / L bismuth chloride N,N-dimethylformamide solution and heating it at 40°C for 12 h to obtain the crude product; washing the crude product with ethanol and then vacuum drying it at 60°C for 8 h in a vacuum drying oven to obtain the three-dimensional porous current collector.

[0013] Thirdly, the present invention provides an application of a three-dimensional porous current collector prepared by any possible implementation of the first aspect or by any possible implementation of the second aspect in a negative electrode-free sodium metal battery.

[0014] As one possible implementation, the fabrication process of the negative electrode-free sodium metal battery includes the following steps: using the three-dimensional porous current collector as the current collector, assembling it with a sodium sheet, electrolyte, and separator to form a sodium-copper half-cell, and depositing sodium on the three-dimensional porous current collector according to the positive / negative electrode N / P=1 to form a composite current collector; using the composite current collector as the negative electrode, assembling it with a positive electrode, electrolyte, and separator to obtain the negative electrode-free sodium metal battery.

[0015] As one possible implementation, the positive electrode is sodium titanium phosphate, the electrolyte is an ether-based electrolyte, and the diaphragm is a polypropylene diaphragm.

[0016] This invention provides a three-dimensional porous current collector (Bi-NAs@Cu) that exhibits ultra-stable sodium deposition stripping performance and can cycle stably for over 1000 hours. This is because during the initial electrochemical reaction, an electroplating process occurs on the electrode surface, causing the protective metal layer on the electrode surface to alloy with the electroplated sodium, thereby forming an alloy layer. This alloy layer on the electrode surface also serves as a composite material that reduces sodium nucleation resistance and induces uniform sodium deposition.

[0017] The method for preparing a three-dimensional porous current collector provided by this invention uses N,N-dimethylformamide as the solvent for bismuth chloride. N,N-dimethylformamide and bismuth chloride achieve an aggregate structure through a chlorine bridge, providing a stable and uniform electrochemical environment during the redox process of bismuth ions and copper. This results in bismuth nanosheets of the obtained three-dimensional porous current collector having a moderate thickness, a uniform and stable honeycomb distribution, and a honeycomb pore size of appropriate size.

[0018] This invention provides the application of a three-dimensional porous current collector in a negative electrode-free sodium metal battery, demonstrating ultra-stable sodium deposition stripping performance and excellent long-cycle stability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The images shown are cross-sectional SEM images of Bi-NAs@Cu-A provided in the embodiments of the present invention, where (a) is a 100 μm scale image and (b) is a magnified view at the 500 nm scale.

[0021] Figure 2 The images shown are SEM images of the longitudinal section of Bi-NAs@Cu-A provided in the embodiments of the present invention, where (a) is a 100 μm level image and (b) is a magnified view at the 500 nm level.

[0022] Figure 3 The image shows a TEM image of Bi-NAs@Cu-A provided in an embodiment of the present invention.

[0023] Figure 4 The image shows the XRD pattern of Bi-NAs@Cu-A provided in an embodiment of the present invention, where Intensity represents the intensity.

[0024] Figure 5 The image shows a SEM image of Bi-NAs@Cu-B provided in an embodiment of the present invention.

[0025] Figure 6 The image shown is a SEM image of Bi-NAs@Cu-C provided in an embodiment of the present invention, wherein Dimethyl sulfoxide represents dimethyl sulfoxide.

[0026] Figure 7 The image shown is a SEM image of Bi-NAs@Cu-D provided in an embodiment of the present invention, wherein N-methyl pyrrolidone represents N-methylpyrrolidone.

[0027] Figure 8 The image shown is a SEM image of Bi-NAs@Cu-E provided in an embodiment of the present invention, where Ethylene glycol represents ethylene glycol.

[0028] Figure 9 The image shown is a SEM image of Bi-NAs@Cu-F provided in an embodiment of the present invention, where Ethanol represents ethanol.

[0029] Figure 10 Half-cells fabricated using Bi-NAs@Cu-A, Pure Cu-mesh, and Pure Cu-foil, respectively, according to embodiments of the present invention, at 1 mA·cm⁻¹ -2 and 1mAh·cm -2 The graph shows the cyclic performance under the given conditions, where Coulombicefficiency represents the Coulomb efficiency and Cycle number represents the number of cycles.

[0030] Figure 11 The half-cell fabricated from Bi-NAs@Cu-B provided in this embodiment of the invention operates at 1 mA·cm⁻¹. -2 and 1mAh·cm -2 The graph shows the cyclic performance under the given conditions, where Coulombic efficiency represents the Coulombic efficiency and Cycle number represents the number of cycles.

[0031] Figure 12 The half-cell fabricated from Bi-NAs@Cu-C provided in this embodiment of the invention operates at 1 mA·cm⁻¹. -2 and 1mAh·cm -2 The graph shows the cyclic performance under the given conditions, where Coulombic efficiency represents the Coulombic efficiency and Cycle number represents the number of cycles.

[0032] Figure 13 The diagram shows the cycle performance of a symmetric cell fabricated with Bi-NAs@Cu-A according to an embodiment of the present invention at a depth of discharge of 75%, where Voltage represents voltage.

[0033] Figure 14 The graphs show the cycle stability test results of the Bi-NAs@Cu-A and Pure Cu-mesh sodium metal batteries without negative electrodes provided in the embodiments of the present invention. In the graphs, Discharge capacity represents the discharge capacity and Coulombicefficiency represents the coulombic efficiency. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To address the issue of suboptimal electrochemical performance in existing negative electrode-less sodium metal batteries, this invention provides a preparation experiment and morphology characterization experiment of a three-dimensional porous current collector. It is evident that this invention successfully prepared the target product, and the provided three-dimensional porous current collector possesses a porous substrate and a three-dimensional honeycomb-like surface, with a thickness of approximately 10 nm, a spacing of 50–300 nm, and a lateral dimension of 100–500 nm. Furthermore, in the preparation of the three-dimensional porous current collector, when the solvent for bismuth chloride is DMSO, NMP, ethylene glycol, or ethanol, the resulting bismuth nanosheets all exhibit high thickness and uneven honeycomb shape and size distribution.

[0036] Furthermore, this invention provides an electrochemical performance testing experiment for a three-dimensional porous current collector. It is shown that Bi-NAs@Cu-A exhibits ultra-stable sodium deposition stripping performance and can cycle stably for over 1000 hours. Moreover, in symmetric cell testing, at a DOD of 75%, Bi-NAs@Cu-A can maintain stable long-term cycling for over 1000 hours and retain a small nucleation overpotential.

[0037] Furthermore, this invention provides an application performance test experiment for a three-dimensional porous current collector. It shows that at a current density of 1C, the sodium metal battery involving Bi-NAs@Cu-A can stably cycle for 267 cycles, confirming that Bi-NAs@Cu-A has great application potential in anode-free sodium metal batteries.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Example 1

[0040] This embodiment provides an experimental method for preparing a three-dimensional porous current collector.

[0041] The size is 4×4cm 2 The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate A. Bismuth chloride was dissolved in N,N-dimethylformamide (DMF) and ultrasonically dispersed for 5 minutes to form solution A with a final concentration of 0.02 mol / L. Copper substrate A was placed in solution A and heated in a water bath at 40°C for 12 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector A, named Bi-NAs@Cu-A.

[0042] The size is 4×4cm 2 The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate B. Bismuth chloride was dissolved in DMF and ultrasonically dispersed for 5 minutes to form solution B with a final concentration of 0.02 mol / L. Copper substrate B was placed in solution B and heated in a water bath at 40°C for 24 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector B, named Bi-NAs@Cu-B.

[0043] The size is 1×1cm 2 The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate C. Bismuth chloride was dissolved in dimethyl sulfoxide (DMSO) and ultrasonically dispersed for 5 minutes to form solution C with a final concentration of 0.02 mol / L. Copper substrate C was placed in solution C and heated in a water bath at 20°C for 12 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector C, named Bi-NAs@Cu-C.

[0044] The size is 1×1cm 2 The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate D. Bismuth chloride was dissolved in N-methylpyrrolidone (NMP) and ultrasonically dispersed for 5 minutes to form solution D with a final concentration of 0.02 mol / L. Copper substrate D was placed in solution D and heated in a water bath at 20°C for 24 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector D, named Bi-NAs@Cu-D.

[0045] The size is 1×1cm 2The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate E. Bismuth chloride was dissolved in ethylene glycol and ultrasonically dispersed for 5 minutes to form solution E with a final concentration of 0.02 mol / L. Copper substrate E was placed in solution E and heated in a water bath at 20°C for 24 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector E, named Bi-NAs@Cu-E.

[0046] The size is 1×1cm 2 The copper mesh was sequentially cleaned with dilute hydrochloric acid and deionized water, then dried to obtain copper substrate F. Bismuth chloride was dissolved in ethanol and ultrasonically dispersed for 5 minutes to form solution F with a final concentration of 0.02 mol / L. Copper substrate F was placed in solution F and heated in a water bath at 20°C for 24 hours. It was then removed, cleaned with ethanol, and placed in a vacuum drying oven at 60°C for 8 hours to obtain a three-dimensional porous current collector F, named Bi-NAs@Cu-F.

[0047] The size is 4×4cm 2 The copper mesh was cleaned sequentially with dilute hydrochloric acid and deionized water, then dried, and used as the current collector G, named Pure Cu-mesh.

[0048] The size is 4×4cm 2 The copper foil was washed sequentially with dilute hydrochloric acid and deionized water, then dried, and used as the current collector H, named Pure Cu-foil.

[0049] Example 2

[0050] This embodiment provides a morphology characterization experiment for a three-dimensional porous current collector.

[0051] The Bi-NAs@Cu-A prepared in Example 1 was observed by SEM and TEM. SEM morphology analysis of its cross-section and longitudinal section at different magnifications was performed, and the results are as follows: Figure 1 , Figure 2 and Figure 3 The results are shown. It can be seen that the prepared three-dimensional porous current collector has a porous substrate and a three-dimensional honeycomb surface; the bismuth nanosheets attached to the substrate have a thickness of approximately 10 nm, a honeycomb pore size of 50–300 nm, and a radial length of 100–500 nm.

[0052] XRD analysis was performed on the Bi-NAs@Cu-A prepared in Example 1, and the results were compared with the XRD standard cards for copper and bismuth. Figure 4 The results shown are from Figure 4It can be seen that Bi-NAs@Cu-A not only has the characteristic peak of bismuth (012) but also the characteristic peak of copper (111), which further indicates that the target product was successfully prepared.

[0053] The Bi-NAs@Cu-B prepared in Example 2 was observed by SEM, and the morphology was as follows: Figure 5 The results are shown. It can be seen that the bismuth nanosheets on Bi-NAs@Cu-B are relatively thick, and the shape and size of the honeycomb are non-uniform.

[0054] The Bi-NAs@Cu-C prepared in Example 3 was observed by SEM, and the morphology was as follows. Figure 6 The results are shown. It can be seen that the bismuth nanosheets on Bi-NAs@Cu-C are relatively thick, and the shape and size of the honeycomb are non-uniform.

[0055] The Bi-NAs@Cu-D prepared in Example 4 was observed by SEM, and the morphology was as follows. Figure 7 The results are shown. It can be seen that the bismuth nanosheets on Bi-NAs@Cu-D are relatively thick, and the shape and size of the honeycomb are non-uniform.

[0056] The Bi-NAs@Cu-E prepared in Example 5 was observed by SEM, and the morphology was as follows. Figure 8 The results are shown. It can be seen that the bismuth nanosheets on Bi-NAs@Cu-E are relatively thick, and the shape and size of the honeycomb are non-uniform.

[0057] The Bi-NAs@Cu-F prepared in Example 6 was observed by SEM, and the results were as follows: Figure 9 The results are shown. It can be seen that the bismuth nanosheets on Bi-NAs@Cu-F are relatively thick, and the shape and size of the honeycomb are non-uniform.

[0058] Example 3

[0059] This embodiment provides an experiment for testing the electrochemical performance of a three-dimensional porous current collector.

[0060] The current collector to be tested is punched into a sheet and cut into electrode sheets with a diameter of not less than 10 mm to serve as the working electrode. A sodium sheet is used as the negative electrode to assemble a sodium||copper half-cell. The sodium||copper half-cell is used as the working electrode in symmetrical and full-cell tests using a composite sodium metal negative electrode formed by electrodeposition. A 1M sodium hexafluorophosphate solution in diethylene glycol dimethyl ether is used as the electrolyte. The working electrode, separator (Celgard PP 2325), and electrolyte are assembled into a battery device. In this embodiment, Bi-NAs@Cu-A to Bi-NAs@Cu-F, Pure Cu-mesh, and Pure Cu-foil from Example 1 are used as current collectors to assemble half-cells A to H, and symmetrical cells A to H are assembled using half-cells A to H.

[0061] For half-cells A, G, and H at 1 mA·cm -2 and 1mAh·cm -2 Under these conditions, asymmetric cells were tested, and the results were as follows: Figure 10 The results show that Bi-NAs@Cu-A exhibits ultra-stable sodium deposition stripping performance and can cycle stably for over 1000 hours. This is because during the initial electrochemical reaction, an electroplating process occurs on the electrode surface, causing the protective layer metal on the electrode surface to alloy with the electroplated sodium, thus forming an alloy layer. This alloy layer on the electrode surface also serves as a composite material to reduce sodium nucleation resistance and induce uniform sodium deposition. Pure Cu-foil also shows some sodium deposition stripping performance, but it is far inferior to Bi-NAs@Cu. Meanwhile, Pure Cu-mesh exhibits unstable and fluctuating coulombic efficiency, indicating poor sodium deposition stripping performance, possibly due to dendrite formation during the process.

[0062] Half-cell B at 1 mA·cm -2 and 1mAh·cm -2 Under these conditions, asymmetric cells were tested, and the results were as follows: Figure 11 The results are shown. It can be seen that the coulombic efficiency of thicker and unevenly sized bismuth nanosheets fluctuates greatly. This is because a large number of dendrites are formed during the deposition and exfoliation process, which leads to the collapse of the nanosheet structure during charging and discharging, resulting in poor sodium deposition and exfoliation performance.

[0063] The half-cell C at 1 mA·cm -2 and 1mAh·cm -2 Under these conditions, asymmetric cells were tested, and the results were as follows: Figure 12 The results are shown. It can be seen that the coulombic efficiency of bismuth nanosheets with uneven size fluctuates greatly. This is because a large number of dendrites are formed during the deposition and exfoliation process, which leads to the collapse of the nanosheet structure during charging and discharging, resulting in poor sodium deposition and exfoliation performance.

[0064] The symmetrical cell A was tested, and its cycle performance at 75% depth of discharge (DOD) is compared as shown in the figure. Figure 13 As shown, Bi-NAs@Cu-A can maintain stable long-term cycling for over 1000 hours and retain a small nucleation overpotential at a DOD of 75%.

[0065] Example 4

[0066] This embodiment provides an application performance test experiment for a three-dimensional porous current collector.

[0067] Using Bi-NAs@Cu-A and Pure Cu-mesh from Example 1 as current collectors, sodium titanium phosphate as the positive electrode, ether-based electrolyte, and PP (polypropylene) as the separator, negative electrode-free sodium metal batteries were assembled. The cycle stability of the two sodium metal batteries was tested, and the results were as follows: Figure 14 The results are shown. (By...) Figure 14 It can be seen that at a current density of 1C, the sodium metal battery involving Bi-NAs@Cu-A can cycle stably for 267 cycles, confirming that Bi-NAs@Cu-A has great application potential in anode-free sodium metal batteries.

[0068] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0069] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A three-dimensional porous current collector, characterized by, The three-dimensional porous current collector comprises a copper substrate and bismuth nanosheets vertically grown on the surface of the copper substrate. The copper substrate is in a net structure, and the bismuth nanosheets are in a three-dimensional honeycomb structure. The net pore size of the copper substrate is 40-50 μm, and the thickness is 100-150 μm. The honeycomb pore size of the bismuth nanosheets is 50-300 nm. The preparation method of the three-dimensional porous current collector comprises the following steps: The copper substrate is placed in a bismuth ion N,N-dimethylformamide solution and heated at 37-43 ℃ for 11-13 h to obtain a crude product. The donor of the bismuth ion is bismuth chloride, and the concentration of the bismuth ion N,N-dimethylformamide solution is 0.018-0.022 M. The crude product is sequentially subjected to cleaning and vacuum drying to obtain the three-dimensional porous current collector. The cleaning agent used in the cleaning is ethanol, and the vacuum drying is performed at 55-65 ℃ for 8-12 h.

2. The three-dimensional porous manifold of claim 1, wherein, The molar ratio of copper elements in the copper substrate to the bismuth ion is 3:1.5-2.

5.

3. The three-dimensional porous manifold of claim 1, wherein, The preparation method comprises the following steps: The copper substrate is placed in a bismuth chloride N,N-dimethylformamide solution with a concentration of 0.02 mol / L and heated at 40 ℃ for 12 h to obtain the crude product. The crude product is cleaned with ethanol and vacuum dried in a vacuum drying oven at 60 ℃ for 8 h to obtain the three-dimensional porous current collector.

4. The three-dimensional porous current collector of claim 1 is applied in a negative electrode-free sodium metal battery.

5. Use according to claim 4, characterized in that, The preparation process of the negative electrode-free sodium metal battery comprises the following steps: The three-dimensional porous current collector is used as a current collector, combined with a sodium sheet, an electrolyte and a separator to assemble a sodium-copper half battery, and sodium is deposited on the three-dimensional porous current collector according to the positive-negative electrode N / P=1 to form a composite current collector. The composite current collector is used as a negative electrode, combined with a positive electrode, an electrolyte and a separator to obtain the negative electrode-free sodium metal battery.

6. Use according to claim 5, characterized in that, The positive electrode is a sodium titanium phosphate electrode, the electrolyte is an ether electrolyte, and the separator is a polypropylene separator.

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