Large-interlayer-spacing LDH carbon fiber electrode material and alkaline zinc-based flow battery thereof

Abstract

The invention discloses a large-interlayer-spacing LDH carbon fiber electrode material and an alkaline zinc-based flow battery thereof, and belongs to the field of zinc-based flow batteries. The preparation method disclosed by the invention is simple and efficient, and the prepared EDTA-coated LDH has a uniform layered structure with relatively large interlayer spacing and good chemical stability. According to the invention, the diffusion effect of Zn (OH) 4 < 2-> is enhanced, so that Zn (OH) 4 < 2-> can be rapidly conducted in the electrode material, and the effect of reducing a reaction energy barrier can also be achieved in the OH dissociation process. The method is applied to the zinc-based flow battery, the ion diffusivity can be obviously improved, the Zn deposition is more uniform, the concentration polarization of the battery is reduced, and the service life of the battery is effectively prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of zinc-based flow batteries, and particularly relates to a LDH carbon fiber electrode material with a large interlayer spacing and an alkaline zinc-based flow battery. Background Art

[0002] In recent years, in the energy field, with the growing demand for efficient and sustainable energy storage systems, flow battery technology has attracted much attention due to its unique advantages. In particular, alkaline zinc-based flow batteries show great application potential due to their high energy density, low cost, and environmental friendliness. However, the development of zinc-based flow batteries faces many challenges, and one of the most critical problems is the formation of zinc dendrites. Zinc dendrites not only cause internal short circuits in the battery but also lead to a rapid decline in battery performance, seriously affecting the cycle life and safety of the battery.

[0003] Layered double hydroxide (LDH) materials have become a very promising candidate material due to their unique layered structure and adjustable chemical composition. LDH materials have a large interlayer spacing, which can provide more deposition sites and transport channels for zinc ions, thus effectively inhibiting the formation of zinc dendrites. This study proposes an innovative electrode material design strategy, that is, by compounding LDH nanosheets with a large interlayer spacing on the surface of carbon felt, a new type of carbon fiber electrode material is prepared. This composite electrode material not only retains the high conductivity and porous structure of carbon felt but also significantly improves the transport and deposition behavior of zinc ions by virtue of the large interlayer spacing and abundant surface active sites of LDH nanosheets. In addition, by optimizing the synthesis method and composite process of LDH nanosheets, the performance and stability of the electrode material are further improved.

[0004] The formation of zinc dendrites is mainly due to the uneven deposition of zinc during the charge and discharge process, which results from the uneven distribution of zinc ions and the insufficient transport rate of zinc ions on the electrode surface. Existing electrode materials are difficult to achieve the rapid conduction and diffusion of Zn(OH) 4 2- Moreover, the ion transport path is complex, further exacerbating the insufficient supply of zinc ions on the electrode surface. In addition, due to the difference in the hydroxide dissociation energy barrier of different materials, their distribution is uneven. Therefore, modifying the interlayer spacing of the material, optimizing the interlayer structure, and utilizing the advantages of different-scale interlayers are of great significance for alleviating the zinc dendrite problem in zinc-based flow batteries, improving battery efficiency, extending service life, and enhancing safety. Summary of the Invention

[0005] The object of the present invention is to overcome the defects in the prior art, especially aiming at the imbalance between conductivity and ion diffusion efficiency in the prior art, and to provide a LDH carbon fiber electrode material with a large interlayer spacing and an alkaline zinc-based flow battery. The present invention can fully improve Zn(OH)4 2- The diffusion efficiency in the electrode is improved, the uniformity of ion distribution inside the electrode is enhanced, the hydrolysis energy barrier of hydroxide ions is reduced, and the mass transfer rate of zinc ions is increased. At the same time, the zinc nucleation sites are increased, the nucleation overpotential of zinc is reduced, the uniformity of zinc deposition is improved, the generation of zinc dendrites is inhibited, the efficiency of the zinc-based flow battery is enhanced, and its lifespan and safety are improved.

[0006] The specific technical solution adopted in the present invention is as follows:

[0007] In the first aspect, the present invention provides a large-layer-spacing LDH carbon fiber electrode material, which is prepared by compounding LDH nanosheets intercalated with EDTA on the surface of carbon fibers.

[0008] Preferably, the carbon fiber includes graphite felt, carbon felt, carbon paper or carbon cloth, and the specific surface area is 1450.

[0009] Preferably, the layer spacing of the LDH nanosheets intercalated with EDTA is

[0010] Preferably, the preparation method of the large-layer-spacing LDH carbon fiber electrode material is specifically as follows:

[0011] Dissolve Mg(NO 3 ) 2 and Al(NO 3 ) 3 in water to obtain a mixed solution; in the mixed solution, the concentration of Mg 2+ is 0.1 - 0.8 M, and the concentration of Al 3+ is 0.05 - 0.4 M; adjust the pH of the mixed solution to 11 with NaOH, fully mix the reactants evenly, age at 80 °C for 2 hours to obtain a MgAl-LDH nanosheet solution; adjust the pH of the MgAl-LDH nanosheet solution to 5.5 with EDTA, then add carbon fibers, soak, and age at 60 - 100 °C for 6 - 20 h; wash the reacted carbon fibers with water and dry at 40 - 80 °C for 12 h to obtain the large-layer-spacing LDH carbon fiber electrode material.

[0012] Further, in the mixed solution, the concentration of Mg 2+ is 0.2 - 0.4 M, and the concentration of Al 3+ is 0.1 - 0.2 M.

[0013] Further, after adding the carbon fibers, soak in the solution for 3 - 12 h, and then react at a temperature of 80 - 100 °C for 8 - 10 h.

[0014] In a second aspect, the present invention provides an alkaline zinc-based flow battery, comprising a negative electrode, a positive electrode and a reference electrode. The negative electrode material uses the LDH carbon fiber electrode material with a large interlayer spacing as described in any one of claims 1 to 6. The positive electrode uses a carbon fiber material, and the reference electrode uses a saturated calomel electrode.

[0015] Preferably, the size of the negative electrode is 5 cm × 5 cm, the thickness is 2 - 6 mm, and the porosity is 75% - 98%; the size of the positive electrode is 5 cm × 5 cm.

[0016] Further, the thickness of the negative electrode is 3 mm, and the porosity is 90%.

[0017] Further, the negative electrode electrolyte includes 0.1 - 0.4 M zinc hydroxide, the positive electrode electrolyte includes 0.2 - 0.8 M potassium ferricyanide, and the separator uses Nafion 211.

[0018] The present invention has the following beneficial effects compared with the prior art:

[0019] 1) Improving the zinc ion transport rate: By optimizing the interlayer structure, the rapid conduction and diffusion of Zn(OH) 4 2- are achieved, reducing the insufficient supply of zinc ions on the electrode surface. Especially at a relatively high current density, the concentration polarization phenomenon originally limited by the mass transfer efficiency can be effectively alleviated. On the other hand, by optimizing Zn(OH) 4 2- Effectively reducing the formation of zinc dendrites: The modified electrode material can evenly distribute zinc ions, reduce the formation of zinc dendrites, and improve the long-term stability of the battery. In the performance test of the battery, it is found that the optimized interlayer structure and rapid ion transport improve the charge and discharge efficiency of the battery.

[0020] 2) The technology of the present invention has low difficulty, simple process, and cheap raw materials, which can provide a reliable solution for the large-scale application of zinc-based flow batteries, and promote the application and development of zinc-based flow batteries in the energy storage field. Description of the Drawings

[0021] Figure 1 is the SEM electron microscope scanning image of EDTA@LDH-CF;

[0022] Figure 2 is the SEM electron microscope scanning image of EDTA@LDH-CF after zinc deposition;

[0023] Figure 3 is the Fourier transform infrared spectroscopy (FTIR) spectrum of LDH-CF and EDTA@LDH-CF;

[0024] Figure 4It is a comparative curve of the voltage efficiency varying with the current density of different negative electrode materials in an alkaline zinc-iron flow battery. Specific Embodiments

[0025] The present invention will be further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment in the present invention can be combined correspondingly on the premise of no mutual conflict.

[0026] The present invention provides a large interlayer spacing LDH carbon fiber electrode material, which is mainly prepared by compounding LDH nanosheets (EDTA@LDH) intercalated with EDTA on the surface of carbon fiber. Among them, the EDTA@LDH nanosheets are synthesized by ion exchange, and the EDTA@LDH grows vertically on the surface of the carbon fiber, forming a flaky surface layer on the surface of the carbon fiber.

[0027] As a relatively preferred embodiment of the present invention, the carbon fiber includes graphite felt, carbon felt, carbon paper or carbon cloth, and carbon felt is preferably used, and the specific surface area can be 1450.

[0028] As a relatively preferred embodiment of the present invention, the interlayer spacing of the LDH nanosheets intercalated with EDTA can be

[0029] As a relatively preferred embodiment of the present invention, the preparation method of the large interlayer spacing LDH carbon fiber electrode material is specifically as follows:

[0030] Dissolve Mg(NO 3 ) 2 and Al(NO 3 ) 3 in water to obtain a mixed solution. In this mixed solution, the concentration of Mg 2+ is 0.1 - 0.8 M, and the concentration of Al 3+ is 0.05 - 0.4 M. In actual use, in the mixed solution, the concentration of Mg 2+ can be 0.2 - 0.4 M, and the concentration of Al 3+ can be 0.1 - 0.2 M.

[0031] Adjust the pH of the above mixed solution to 11 with NaOH, fully mix the reactants evenly, and age at 80 °C for 2 hours to obtain a MgAl-LDH nanosheet solution.

[0032] Adjust the pH of the above MgAl-LDH nanosheet solution to 5.5 with EDTA, then add carbon fiber, soak it, and age at 60 - 100 °C for 6 - 20 h. In actual use, after adding carbon fiber, it can be soaked in the solution for 3 - 12 h, and then react at a temperature of 80 - 100 °C for 8 - 10 h.

[0033] Finally, wash the reacted carbon fiber with water and dry it at 40 - 80 °C for 12 h to obtain the LDH carbon fiber electrode material with large interlayer spacing of the present invention.

[0034] That is to say, the preparation method of the LDH carbon fiber electrode material with large interlayer spacing includes the following steps:

[0035] 1) Solution preparation: Using deionized water as the solvent, prepare a salt solution of strong acid and weak base of magnesium and aluminum (i.e., the mixed solution, including Mg(NO 3 ) 2 and Al(NO 3 ) 3 ). Among them, the concentration of Mg 2+ is 0.1 - 0.8 M, preferably 0.2 - 0.4 M; the concentration of Al 3+ is 0.05 - 0.4 M, preferably 0.1 - 0.2 M. Then, mix the mixed solution with sodium hydroxide solution to adjust the pH of the solution to 11.

[0036] 2) Preparation of MgAl-LDH: After mixing evenly in a magnetic stirrer, age at 80 °C for 2 hours to form MgAl-LDH nanosheets.

[0037] 3) Intercalation of EDTA molecules into MgAl-LDH: Adjust the pH of the solution to 5.5 with EDTA, and adjust at this solution pH so that EDTA intercalates into the LDH structure to form EDTA@LDH.

[0038] 4) Formation of carbon fiber-supported EDTA@LDH electrode material: Cut the carbon fiber into dimensions and shapes suitable for the battery, and soak it in the solution of step 3) for 3 - 12 h. Subsequently, place the carbon fiber and the solution in a hydrothermal reaction kettle, and react at a temperature of 60 - 100 °C (preferably 80 - 100 °C) for 6 - 20 h (preferably 8 - 10 h).

[0039] 5) After the reaction is completed, wash the carbon fiber with deionized water and dry it at 40 - 80 °C (preferably 50 - 70 °C) for 12 h to obtain the EDTA@LDH-CF electrode material (i.e., the LDH carbon fiber electrode material with large interlayer spacing).

[0040] Based on the above LDH carbon fiber electrode material with large interlayer spacing, the present invention also provides an alkaline zinc-based flow battery, which mainly includes a negative electrode, a positive electrode and a reference electrode. Among them, the negative electrode material uses the above LDH carbon fiber electrode material with large interlayer spacing of the present invention, the positive electrode uses a carbon felt material, and the reference electrode uses a saturated calomel electrode (SCE), and the reference electrode is used for potential measurement and calibration.

[0041] As a preferred embodiment of the present invention, the negative electrode has a size of 5 cm × 5 cm (i.e., length × width), a thickness of 2 - 6 mm (preferably 3 mm), and a porosity of 75% - 98% (preferably 90%). The positive electrode has a size of 5 cm × 5 cm (i.e., length × width).

[0042] As a preferred embodiment of the present invention, the electrolyte of the negative electrode is a solution containing zinc ions. The zinc concentration in the electrolyte is 0.1 - 0.4 M, which exists in the form of zinc hydroxide and is provided by ZnO for the zinc deposition and dissolution reactions of the negative electrode.

[0043] As a preferred embodiment of the present invention, the electrolyte of the positive electrode includes potassium ferricyanide with a concentration of 0.2 - 0.8 M, which is provided by K 3 Fe(CN) 6 for the redox reaction of the positive electrode.

[0044] As a preferred embodiment of the present invention, Nafion 211 is used as the diaphragm of the battery. It has good ion selectivity and conductivity, can effectively separate the positive and negative electrode electrolytes, and allows ions to pass through at the same time.

[0045] Next, the materials of the present invention, as well as the preparation methods and performances of its batteries, will be specifically described through examples and comparative examples.

[0046] Example

[0047] This example provides a preparation method for a large interlayer spacing LDH carbon fiber electrode material. The specific implementation is as follows:

[0048] First, Mg(NO 3 ) 2 and Al(NO 3 ) 3 are dissolved in deionized water at a molar ratio of 2:1. The pH is adjusted to 11 with NaOH. After mixing evenly, it is aged at 80°C for 2 hours to form MgAl-LDH nanosheets. Then, the pH of the solution is adjusted to 5.5 with EDTA, and the carbon felt is added to the solution for an 8-hour ion exchange reaction to allow EDTA to intercalate into the LDH structure. After the reaction is completed, it is washed with deionized water and vacuum dried at 40°C for 12 hours to obtain a large interlayer spacing LDH carbon fiber electrode material (i.e., EDTA@LDH-CF).

[0049] Using the prepared EDTA@LDH-CF, an alkaline zinc-iron flow battery was also prepared as follows:

[0050] The as-prepared EDTA@LDH-CF was used as the negative electrode with a size of 5 cm * 5 cm. The positive electrode was a square commercial carbon felt with a thickness of 4 mm, a size of 5 cm * 5 cm, and a porosity of 85%. A 0.4 M zinc oxide solution and a 0.8 M sodium ferrocyanide solution were used as the negative electrode electrolyte and the positive electrode electrolyte, respectively. A Nafion211 cation exchange membrane was used as the separator to assemble a zinc-based flow battery.

[0051] The test results showed that EDTA@LDH-CF significantly improved the energy efficiency of the battery, especially at high current densities, with more obvious effects, effectively reducing the formation of zinc dendrites and prolonging the service life of the battery.

[0052] Comparative example

[0053] An alkaline zinc-iron flow battery was assembled according to the method described in the example. The difference was that the negative electrode materials were respectively changed to untreated ordinary carbon felt (CF) and unmodified initial LDH (LDH-CF).

[0054] The results are as follows:

[0055] Figure 1 The specific morphology of the obtained EDTA@LDH-CF in the example was shown. It could be seen from the figure that the surface of the carbon fiber was densely covered with a layer of material. These materials presented a flaky structure, and most of the flaky structures were intertwined with each other and grew perpendicular to the surface of the carbon fiber. These flaky structures were LDH nanosheets intercalated with EDTA. They formed a structure similar to a "forest" on the surface of the carbon fiber. The nanosheets interlaced with each other, forming a rich pore structure. It could be seen from the image that the coverage of the LDH nanosheets was very dense, and almost no bare carbon fiber surface was exposed, indicating that the preparation process of EDTA@LDH-CF was very successful, and the nanosheets grew uniformly and densely on the carbon fiber. The arrangement of the nanosheets indicated that they had a certain directionality during the growth process, and most of the nanosheets grew perpendicular to the surface of the carbon fiber. This arrangement was helpful to improve the specific surface area and ion transport performance of the material.

[0056] Figure 2 It clearly showed the significant advantages of the obtained EDTA@LDH-CF electrode material during the zinc deposition process. It could be seen from the figure that the zinc deposition experiment was carried out at a constant current density (10 mA cm -2 ), and the duration was 10 minutes. The zinc deposition showed a relatively uniform distribution on the surface of EDTA@LDH-CF. Zinc was mainly deposited in the gaps between the vertically arranged LDH nanosheets, and the deposition layer was relatively flat. This uniform distribution indicated that the EDTA@LDH-CF electrode could effectively guide the zinc ion deposition process, reduce the local supersaturation phenomenon, and thus inhibit the formation of zinc dendrites.

[0057] Figure 3 shows the Fourier transform infrared spectroscopy (FTIR) spectra of two different electrode materials as the negative electrode (i.e., LDH-CF and EDTA@LDH-CF) in the examples and comparative examples. As can be seen from the figure, in the spectrum of LDH, the broad peak (3456 cm -1 ) is mainly attributed to the stretching vibration of the hydroxyl group (-OH) in the interlayer of LDH and water molecules, and the strong peak (1354 cm -1 ) can be attributed to the characteristic vibration of nitrate ions (NO 3 - ) in the interlayer of LDH. Among the characteristic peaks shown by EDTA@LDH (1608 cm -1 , 1404 cm -1 and 924 cm -1 ), these peaks are respectively attributed to the stretching vibrations of the C═C double bond and C-O single bond in the EDTA molecule. These characteristic peaks only appear in the EDTA@LDH-CF sample, indicating that the EDTA molecule has successfully inserted into the interlayer structure of LDH. This result confirms the effectiveness of the ion exchange process, and the presence of the EDTA molecule significantly changes the interlayer chemical environment of LDH. The EDTA molecule has successfully entered the interlayer structure of LDH through ion exchange, replacing part or all of the nitrate ions. This is confirmed by the presence of the EDTA characteristic peak and the weakening or disappearance of the nitrate ion characteristic peak in the FTIR spectrum. Despite the insertion of EDTA, the basic structure of LDH is not destroyed, and the characteristic peak of the hydroxyl group (-OH) still exists, indicating that the layered structure of LDH is retained.

[0058] Figure 4The comparative curves of the voltage efficiency of different negative electrode materials varying with the current density in an alkaline zinc-iron flow battery are shown. It can be seen from the figure that the test objects include CF: untreated original carbon felt; LDH-CF: carbon felt coated with ordinary LDH nanosheets on the surface; and EDTA@LDH-CF: carbon felt coated with EDTA-intercalated LDH nanosheets on the surface (i.e., the example). At low current densities, the voltage efficiency differences among the three materials are small. This is because the influence of concentration polarization is small at this time, and the performance of the battery is mainly affected by the intrinsic electrochemical properties of the electrode materials. As the current density increases, the influence of concentration polarization gradually becomes significant, and at this time, the differences in the ion transport ability of the electrode materials begin to appear. The voltage efficiency of EDTA@LDH-CF is significantly higher than that of CF and LDH-CF, and as the current density increases, its advantage becomes more obvious. This indicates that after EDTA intercalation, the layer spacing of LDH expands (0.95 nm), which can effectively accelerate the transport of zincate ions, reduce concentration polarization, and thus improve the voltage efficiency. At 320 mA cm-2, the voltage efficiency of EDTA@LDH-CF is 8.2% higher than that of CF, which fully demonstrates the significant improvement effect of EDTA@LDH-CF on the battery performance at high current densities.

[0059] For the EDTA@LDH-CF prepared in the present invention, by observing its surface morphology through scanning electron microscopy (SEM), it is found that the LDH nanosheets after EDTA intercalation have a uniform layered structure, and the layer spacing is significantly increased, which is beneficial to the rapid conduction and diffusion of Zn(OH) 4 2- The energy efficiency test results show that the zinc-based flow battery using the modified electrode material exhibits higher energy efficiency at different current densities. Especially at high current densities, the improvement in energy efficiency is more obvious. This indicates that the modified electrode material can significantly increase the transport rate of zinc ions, reduce the formation of zinc dendrites, and extend the service life of the battery. Through the comparison of the above examples and comparative examples, the application of the modified electrode material of the present invention in the zinc-based flow battery shows a significant performance improvement, providing a new technical solution for the large-scale application of zinc-based flow batteries.

[0060] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A LDH carbon fiber electrode material with a large interlayer spacing, characterized in that: The nanosheets were prepared by composite EDTA intercalated LDH nanosheets on the surface of carbon fibers.

2. The LDH carbon fiber electrode material with large interlayer spacing according to claim 1, characterized in that: The carbon fiber includes graphite felt, carbon felt, carbon paper or carbon cloth, and has a specific surface area of ​​1450.

3. The LDH carbon fiber electrode material with large interlayer spacing according to claim 1, characterized in that: The interlayer spacing of the EDTA-intercalated LDH nanosheets is 4. The LDH carbon fiber electrode material with large interlayer spacing according to claim 1, characterized in that: The preparation method of the LDH carbon fiber electrode material with large interlayer spacing is as follows: Mg(NO3)2 and Al(NO3)3 are dissolved in water to obtain a mixed solution; in the mixed solution, Mg 2+ The concentration is 0.1-0.8M, Al 3+ The concentration is 0.05-0.4M; the pH value of the mixed solution is adjusted to 11 with NaOH, the reactants are fully mixed and aged at 80°C for 2 hours to obtain a MgAl-LDH nanosheet solution; the pH value of the MgAl-LDH nanosheet solution is adjusted to 5.5 with EDTA, and then carbon fiber is added, immersed and aged at 60-100°C for 6-20 hours; the reacted carbon fiber is washed with water and dried at 40-80°C for 12 hours to obtain the LDH carbon fiber electrode material with a large interlayer spacing.

5. The LDH carbon fiber electrode material with large interlayer spacing according to claim 4, characterized in that: In the mixed solution, Mg 2+ The concentration is 0.2-0.4M, Al 3+ The concentration is 0.1-0.2M.

6. The LDH carbon fiber electrode material with large interlayer spacing according to claim 4, characterized in that: After adding the carbon fiber, soak in the solution for 3-12 hours, and then react at a temperature of 80-100° C. for 8-10 hours.

7. An alkaline zinc-based flow battery, comprising a negative electrode, a positive electrode and a reference electrode, characterized in that: The negative electrode material is the LDH carbon fiber electrode material with a large interlayer spacing as described in any one of claims 1 to 6, the positive electrode is made of carbon fiber material, and the reference electrode is a saturated calomel electrode.

8. The alkaline zinc-based flow battery according to claim 7, characterized in that: The negative electrode has a size of 5cm×5cm, a thickness of 2-6mm, and a porosity of 75%-98%; the positive electrode has a size of 5cm×5cm.

9. The alkaline zinc-based flow battery according to claim 8, characterized in that: The thickness of the negative electrode is 3 mm, and the porosity is 90%.

10. The alkaline zinc-based flow battery according to claim 7, characterized in that: The negative electrode electrolyte includes 0.1-0.4M zinc hydroxide, the positive electrode electrolyte includes 0.2-0.8M potassium ferrocyanide, and the diaphragm is Nafion 211.

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