Modified foamed nickel three-dimensional current collector and preparation method and application thereof

Abstract

The invention provides a preparation method of a modified foamed nickel three-dimensional current collector, which comprises the following steps: S1, cutting commercial foamed nickel into wafers, soaking the wafers in a 0.1 M HCl solution for 6-12 hours, and then drying the wafers; s2, measuring an MXene solution, and adding deionized water to prepare a 40mL solution; s3, zinc nitrate hexahydrate is weighed and dissolved in 10 mL of deionized water, and after zinc nitrate hexahydrate is completely dissolved, the solution in the step S2 is added; s4, transferring the solution in the step S3 into a PTFE lining, and adding the foamed nickel wafer in the step S1; s5, sealing the lining into a stainless steel shell, and performing hydro-thermal treatment at 80-120 DEG C for 12-24 hours; and S6, the foamed nickel is taken out, washed with deionized water and then subjected to vacuum drying at the temperature of 80 DEG C. According to the foamed nickel three-dimensional current collector provided by the invention, the potential non-uniformity of the surface of traditional commercial foamed nickel is relieved, the lithium affinity of the modified current collector is improved and a stable lithium ion migration channel is provided due to the adhesion of zinc elements in zinc nitrate on nanosheets, so that lithium ions can be induced to deposit from bottom to top in the migration process, and the lithium ion conductivity is improved. And the space utilization rate of the current collector is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of battery negative electrodes, and in particular to a preparation method of a modified nickel foam three-dimensional current collector and a lithium metal battery. Background Art

[0002] Currently, commercial lithium-ion batteries primarily use commercial graphite as anode material. Limited by the theoretical capacity of graphite (372 mAh / g), conventional lithium-ion batteries have been unable to break the 300Wh / kg upper limit. Compared to commercial graphite anodes, lithium metal has garnered widespread attention due to its highest theoretical specific capacity (3860 mAh / g) and lowest standard redox potential (-3.04V vs. SHE), earning it the nickname "the holy grail" of lithium-ion batteries. Lithium metal batteries using lithium metal as anodes have seen rapid development.

[0003] In order to further improve the performance of batteries and deepen the understanding of the modification of lithium metal negative electrodes, in addition to constructing an artificial protective layer on the surface of lithium metal, constructing a three-dimensional current collector that is lithiophilic and can induce lithium ion deposition from the bottom up is also an important method. Traditional commercial current collectors such as copper foam, nickel foam and carbon skeletons will hinder the electroplating and stripping process of lithium ions due to their high nucleation overpotential and unevenly distributed surface potential, inhibiting the transformation of active lithium and accelerating the growth of lithium dendrites on the surface of the current collector. In addition, depositing lithiophilic sites on the surface of the current collector or increasing the specific surface area of ​​the current collector can promote the bottom-up deposition of lithium metal and improve the volume utilization of the current collector.

[0004] Research and development has revealed that modified nickel foam with a single-layer nanosheet of MXene material on its surface is a promising current collector for lithium anodes. This three-dimensional current collector skeleton with a single-layer nanosheet significantly increases its specific surface area, alleviating the potential non-uniformity of the surface of traditional commercial nickel foam. At the same time, the adhesion of zinc elements in zinc nitrate to the nanosheets increases the lithium affinity of the modified current collector and provides a stable lithium ion migration channel, which can induce lithium ions to deposit from bottom to top during migration and increase the spatial utilization of the current collector. When assembled into a symmetrical battery for cycling, the stable single-layer nanosheets and zinc ions on the surface can also effectively improve the strength and stability of the surface SEI film, which can greatly enhance the electrochemical performance of the battery. Therefore, a method for preparing a modified three-dimensional nickel foam current collector has been proposed. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a modified nickel foam three-dimensional current collector. This nickel foam skeleton has a uniform and controllable single-layer MXene nanosheet on its surface. A one-step hydrothermal method is used, with MXene material as solute and zinc nitrate hexahydrate as initiator, to prepare a modified nickel foam with a single-layer nanosheet of MXene material on its surface. This solves the problem of uncontrollable disordered growth of lithium metal when traditional commercial nickel foam is used as a lithium deposition skeleton. As far as the deposition process is concerned, the MNF skeleton (more preferably the MNF2 skeleton) modified by the one-step hydrothermal method, after SEM characterization, it can be found that lithium metal is uniformly deposited inside it, the overall space is well utilized, and the lithium metal deposition on the surface is smooth and flat.

[0006] The technical solutions of the present invention are as follows: A method for preparing a modified nickel foam three-dimensional current collector comprises the following steps: S1. Use a punch to cut commercial nickel foam into discs with a diameter of 12 mm, soak them in 0.1 M HCl solution for 6-12 h, and then remove them and dry them for later use; S2. Measure a certain amount of MXene solution and add appropriate amount of deionized water to make a 40mL solution; S3. Weigh an appropriate amount of zinc nitrate hexahydrate, dissolve it in 10mL of deionized water, and add it to the solution in step S2 after complete dissolution; S4. The solution obtained in step S3 is transferred to the PTFE liner and the nickel foam disc dried in step S1 is added; S5. Seal the liner into a stainless steel shell and treat at 80-120°C for 12-24h; S6. Remove the nickel foam, rinse it with deionized water three times, and then dry it in a vacuum at 80°C.

[0007] Preferably, the concentration of the MXene solution in step S2 is controlled at 3-10 mg / mL, preferably 5 mg / mL.

[0008] Preferably, the treatment temperature in step S5 is 80-120°C, preferably 80°C.

[0009] Preferably, the processing time of step S5 is 12-24 hours, preferably 12 hours.

[0010] Preferably, the diameter of the disc in step S1 is preferably 12 mm.

[0011] Preferably, the amount of zinc nitrate hexahydrate weighed is 10 mg.

[0012] The present invention also provides a modified nickel foam three-dimensional current collector, which is prepared by the above-mentioned preparation method. The surface of the current collector is attached with MXene single-layer nanosheets, and zinc elements are attached to the nanosheets.

[0013] Preferably, the size of the MXene single-layer nanosheets is 200 nm, and the growth direction is consistent and evenly distributed.

[0014] Copper foil, blank nickel foam (BNF), and modified nickel foam (MNF) were used as the positive electrode and the bright lithium metal sheet to assemble into a half-cell. After the battery was left idle for two hours, it was connected to the blue power test system. The discharge current density was set to 2 mAh cm -2 , the discharge time is 10 h to obtain a current collector with a lithium deposition capacity of 20 mAh, which is used as a lithium metal negative electrode for subsequent tests to evaluate the effect of modification on the nickel foam current collector.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a modified nickel foam three-dimensional current collector. This three-dimensional current collector skeleton with a single-layer nanosheet has a significantly increased specific surface area, alleviates the potential non-uniformity of the surface of traditional commercial nickel foam, and at the same time, due to the attachment of zinc elements in zinc nitrate to the nanosheets, increases the lithium affinity of the modified current collector and provides a stable lithium ion migration channel, which can induce lithium ions to deposit from bottom to top during the migration process, thereby increasing the space utilization of the current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0017] Figure 1 XRD spectra of BNF and MNF.

[0018] Figure 2 This is the SEM image of the sample obtained in Example 1.

[0019] Figure 3 This is the SEM image of the sample obtained in Example 2.

[0020] Figure 4 Nucleation overpotential test of different current collectors.

[0021] Figure 5 EIS comparison test of different current collectors.

[0022] Figure 6 This is a comparison chart of the long cycle tests of Example 2, Example 3 and Example 4. DETAILED DESCRIPTION

[0023] The present invention is further illustrated below by way of examples, but is not intended to be limiting. Experimental procedures not specifically specified in the examples generally followed conventional conditions, those described in manuals, or those recommended by the manufacturers. The general equipment, materials, and reagents used were all commercially available unless otherwise specified. The raw materials required for the following examples were all commercially available.

[0024] Example 1 Commercial nickel foam was cut into 12 mm diameter discs using a punch, soaked in 0.1 M HCl solution for 6-12 h, removed, and dried for later use. A certain amount of MXene solution (5 mg / mL) was measured and added with an appropriate amount of deionized water to prepare 40 mL of solution. The solution obtained in the previous step was transferred to a PTFE liner and the dried nickel foam discs were added. The liner was sealed in a stainless steel shell and treated at 80°C for 12 h. The nickel foam was removed, rinsed with deionized water three times, and then vacuum-dried at 80°C. It was recorded as MNF1.

[0025] Example 2 Commercial nickel foam was cut into 12 mm diameter discs using a punch, soaked in 0.1 M HCl solution for 6-12 h, removed, and dried for later use. A certain amount of MXene solution (5 mg / mL) was measured and an appropriate amount of deionized water was added to prepare 40 mL of solution. 10 mg of zinc nitrate hexahydrate was weighed and dissolved in 10 mL of deionized water. After complete dissolution, it was added to the aforementioned solution. The solution obtained in the previous step was transferred to a PTFE liner and the dried nickel foam disc was added. The liner was sealed in a stainless steel shell and treated at 80°C for 12 h. The nickel foam was removed, rinsed with deionized water three times, and then vacuum-dried at 80°C, which was recorded as MNF2.

[0026] Example 3 Commercial nickel foam was cut into 12 mm diameter discs using a punch, soaked in 0.1 M HCl solution for 6-12 h, removed, and dried for later use. A certain amount of MXene solution (8 mg / mL) was measured and an appropriate amount of deionized water was added to prepare 40 mL of solution. 10 mg of zinc nitrate hexahydrate was weighed and dissolved in 10 mL of deionized water. After complete dissolution, it was added to the aforementioned solution. The solution obtained in the step was transferred to a PTFE liner and the dried nickel foam disc was added. The liner was sealed in a stainless steel shell and treated at 80°C for 12 h. The nickel foam was removed, rinsed with deionized water three times, and then vacuum-dried at 80°C, which was recorded as MNF3.

[0027] Example 4 Commercial nickel foam was cut into 12 mm diameter discs using a punch, soaked in 0.1 M HCl solution for 6-12 h, removed, and dried for later use. A certain amount of MXene solution (12 mg / mL) was measured and an appropriate amount of deionized water was added to prepare 40 mL of solution. 10 mg of zinc nitrate hexahydrate was weighed and dissolved in 10 mL of deionized water. After complete dissolution, it was added to the aforementioned solution. The solution obtained in the step was transferred to a PTFE liner and the dried nickel foam disc was added. The liner was sealed in a stainless steel shell and treated at 80°C for 12 h. The nickel foam was removed, rinsed with deionized water three times, and then vacuum-dried at 80°C, which was recorded as MNF4.

[0028] Figure 1 The XRD spectra of BNF and MNF were obtained. The crystal structures of various nickel foams were verified by X-ray diffraction (XRD) experiments. As can be seen from the figure, the crystal structure of the blank nickel foam (BNF) before hydrothermal treatment closely corresponds to the characteristic peaks of the Ni (JCPDS 01-070-0989) standard card. After hydrothermal treatment with zinc nitrate initiator for 12 hours, MNF2 exhibited distinct characteristic peaks corresponding to Ti₃AlC₂ (JCPDS 00-052-0875) and ZnNO₃ (03-065-5973), respectively. Although the peak positions shifted significantly after hydrothermal treatment, the XRD results still indicate that the MXene material adhered to the surface of the nickel foam after hydrothermal treatment.

[0029] Figure 2 and Figure 3 The SEM images of the samples obtained in Example 1 and Example 2. It can be seen from the figure that although some nanosheet materials are deposited on the surface of the nickel foam without the addition of zinc nitrate initiator, they are obviously in a scattered, disordered and unevenly distributed form and the overall size is uneven, indicating that under the condition of simply adding MXene material, it is not possible to uniformly grow nanosheets on the surface of the nickel foam. Ultra-thin nanosheets with a size of 200nm are uniformly grown on the surface of MNF2. The ultra-thin nanosheets show a single-layer morphology in the figure and the growth direction is almost consistent. The uniform ultra-thin nanosheets appearing in MNF2 indicate that it is impossible to uniformly grow complete nanosheets on the surface of the nickel foam by hydrothermal treatment under the condition of simply adding MXene material, but after adding zinc nitrate initiator, ultra-thin nanosheets with complete morphology, uniform size and consistent growth direction can be grown on the surface of the nickel foam under the same conditions.

[0030] Figure 4Figure 2 is a schematic diagram of the nucleation overpotential. It can be seen that the nucleation overpotential of BNF is approximately 35 mV. In comparison, the nucleation overpotential of MXene-modified MNF1 and MNF2 is significantly reduced. This is because the three-dimensional porous structure with uniformly arranged single-layer nanosheets on the surface can effectively reduce the local current density, thereby reducing the nucleation overpotential. Subsequently, by comparing the potential difference between MNF1 and MNF2, it was found that the nucleation overpotential of MNF1 is higher at 24 mV, compared to 16 mV for MNF2. This may be due to the disordered deposition of lithium metal during the deposition process caused by the uneven surface of MNF1, resulting in a slight increase in the nucleation overpotential. Through nucleation overpotential testing, it was found that the nickel foam skeleton with uniformly arranged single-layer nanosheets on the surface can better deposit lithium.

[0031] pass Figure 5 As can be seen, at open-circuit voltage, the charge transfer resistance of the blank skeleton is 84.6 Ω. Both MNF1 and MNF2 show significantly lower charge transfer resistances compared to BNF. Comparing MNF1 and MNF2, it is found that due to the smooth and dense surface of MNF2 after lithium deposition, its interfacial transfer resistance is lower than that of MNF1, at 54.3 Ω and 42.6 Ω, respectively. Furthermore, MNF2 has the highest slope in the low-frequency region, indicating higher ion mobility.

[0032] pass Figure 6 It can be seen that excessive MXene modification has a significant impact on electrochemical performance. The presence of too many nanosheets has a negative effect on uniform lithium deposition, resulting in increased uneven lithium deposition and further reduced current distribution uniformity.

[0033] The above content is a preferred embodiment in combination with the preferred embodiments, but it cannot be considered that the specific implementation of the present invention is limited to the embodiments. For those skilled in the art who understand the field to which the present invention belongs, a number of variations and substitutions can be made without departing from the research ideas of the present invention, and these deductions and substitutions are all included in the scope defined by the present invention.

Claims

1. A method for preparing a modified nickel foam three-dimensional current collector, characterized in that: The following steps are involved: S1. Cut commercial nickel foam into discs, soak them in 0.1M HCl solution for 6-12 hours and then dry them; S2. Measure the MXene solution and add deionized water to make a 40 mL solution; S3. Weigh zinc nitrate hexahydrate and dissolve it in 10 mL of deionized water. After it is completely dissolved, add the solution from step S2. S4, transferring the solution from step S3 to the PTFE liner, and adding the nickel foam disc from step S1; S5. Seal the lining into the stainless steel shell and perform hydrothermal treatment at 80-120°C for 12-24h; S6. Take out the nickel foam, rinse it with deionized water, and then dry it in vacuum at 80°C.

2. The preparation method according to claim 1, characterized in that The concentration of the MXene solution in step S2 is 3-10 mg / mL.

3. The preparation method according to claim 2, characterized in that The concentration of the MXene solution in step S2 is 5 mg / mL.

4. The preparation method according to claim 1, characterized in that The hydrothermal treatment temperature in step S5 is 80°C.

5. The preparation method according to claim 1, characterized in that The hydrothermal treatment time in step S5 is 12 hours.

6. The preparation method according to claim 1, characterized in that The diameter of the disc in step S1 is 12 mm.

7. A modified nickel foam three-dimensional current collector, characterized in that: Prepared by the preparation method according to any one of claims 1-6, the current collector surface is attached with MXene single-layer nanosheets.

8. The modified nickel foam three-dimensional current collector according to claim 7, characterized in that: The size of the MXene single-layer nanosheet is 200 nm.

9. A lithium metal battery, characterized in that: The modified nickel foam three-dimensional current collector according to any one of claims 7 to 8 is used as a negative electrode.

10. The lithium metal battery according to claim 9, characterized in that The battery was evaluated for performance using a blue-electric test system, with the test conditions including a discharge current density of 2 mAh·cm-2, a discharge time of 10 h, and a lithium deposition amount of 20 mAh.

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