An all-iron flow battery electrode and method of making the same

Abstract

The application belongs to the technical field of electrochemical energy storage, and more particularly relates to a full-iron flow battery electrode and a preparation method thereof. The application aims at the problem of low battery efficiency and short service life caused by large initial reaction overpotential of the negative electrode of the full-iron flow battery and uneven iron deposition, and proposes in-situ limited growth of active sites with metal iron and tin atomic dispersion on the surface of carbon electrodes such as carbon fiber felt, carbon fiber cloth, carbon fiber paper, etc., for use in the negative electrode of the full-iron flow battery. The method is simple to operate, can be prepared on a large scale, and is low in cost. The electrode can serve as a nucleation site for the deposition of the negative electrode metal iron during the charging process, reduce the polarization of the negative electrode of the full-iron flow battery during the charging process, and at the same time make the deposited iron uniformly distributed on the electrode surface, avoid the generation of iron dendrites, and greatly improve the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to the field of flow batteries, and in particular to a full-iron flow battery electrode and a method for preparing the same. BACKGROUND

[0002] With the development of society, the demand for energy has surged, and primary energy represented by oil and natural gas is facing the problem of limited reserves and easy pollution to the environment. These problems force people to seek renewable clean energy such as wind and solar energy. In order to improve the discontinuous and unstable characteristics of such energy, developing new energy storage technology and improving the tolerance of the power system to the intermittency of new energy are considered as effective measures to increase the share of new clean energy power in China's energy consumption.

[0003] Full-iron flow batteries are a new type of large-scale energy storage battery that stores electrical energy in electrolyte with redox reaction activity. Compared with lithium-ion batteries and all-vanadium flow batteries, full-iron flow batteries have the advantages of low cost, high safety, and abundant raw materials. The electrode is one of the key components of the full-iron flow battery, and its performance directly affects the electrochemical reaction rate, the internal resistance of the battery, and the state of the electrolyte solution distribution. The currently widely used electrode materials are carbon fiber felt, carbon fiber cloth, and carbon fiber paper, but if these porous carbon electrodes are used directly, it will cause the electrode to have varying degrees of activation polarization, concentration polarization, and ohmic polarization, ultimately affecting the energy conversion efficiency and power density of the battery. At the same time, the dendrites caused by iron deposition in the charging process of the negative electrode are one of the key factors that directly affect the service life of the battery.

[0004] In view of the dendrite problem of deposition-type flow batteries, the Hong Kong University of Science and Technology (CN111509234A) discloses a gradient electrode for deposition-type flow battery negative electrode and application, by setting the gradient change of the porosity and the number of deposition sites of the gradient electrode along the electrode surface, promoting the uniform deposition of active substances to the bipolar plate side during the charging process of the deposition-type flow battery, inhibiting the growth of dendrites, and improving the charging capacity and cycle stability of the battery, but this method has the problems of narrow application range and high processing cost.

[0005] Zhejiang University (CN115172774A) discloses a cyanogroup modified Zr-Fe MOF protective layer for zinc-based flow battery zinc negative electrode and a preparation method thereof. The cyanogroup modified Zr-Fe MOF nanosheet is coated on the surface of a zinc-bromine flow zinc negative electrode to construct a protective layer. The Zr and Fe metal nodes can homogenize the zinc surface electric field, reduce the surface electric field fluctuation of the zinc negative electrode during the charging process, homogenize the surface current density of the zinc negative electrode, increase the Zn affinity of the substrate, reduce the energy barrier of Zn nucleation, inhibit the growth of zinc dendrites, and improve the cycle life of the zinc-based flow battery, but still has the problem of difficult scale preparation.

[0006] The Chinese Academy of Sciences Dalian Institute of Chemical Physics (CN114628715A) discloses a certain thickness of glass fiber membrane placed between the separator and the negative carbon felt electrode, leaving sufficient space for zinc deposition, effectively preventing the generation of zinc dendrites, and improving the surface capacity and cycle stability of the zinc-bromine flow battery. However, this method increases the volume of the battery, increases the difficulty of assembling the battery, and reduces the power density of the system.

[0007] The Chinese Academy of Sciences Institute of Chemistry and Physics (CN114583182A) discloses a nitrogen-doped porous carbon felt material in a zinc-based flow battery. The porous structure increases the pore volume, specific surface area and hydrophilicity of the carbon felt, while enhancing the adsorption capacity of zinc atoms, providing more zinc deposition sites, promoting uniform zinc deposition, and ultimately inhibiting the generation and growth of zinc dendrites. The zinc-based flow battery assembled with this material has high voltage efficiency, energy efficiency and cycle stability.

[0008] Currently disclosed applications for deposition-type flow battery negative dendrites mainly control the total amount of deposited active material or reserve a certain space between the negative electrode and the separator to provide space for dendrite growth. However, these methods reduce the battery capacity, increase the battery ohmic loss, limit the improvement of battery performance, and are mainly applied to zinc-based flow batteries. There are few reports on full-iron flow battery negative dendrites.

[0009] In addition, zinc-based flow batteries and full-iron flow batteries differ in negative deposition mechanism, nucleation energy barrier and nucleation site selectivity, so the solution strategy for zinc-based flow batteries cannot be directly applied to full-iron flow batteries. Iron monatomic atoms can act as nucleation sites for metal iron deposition, and tin monatomic atoms can accelerate iron nucleation, promoting uniform deposition of iron on the electrode surface.

[0010] Based on the above two points, the patent in-situ limits the growth of atomic-level iron and tin active sites on the surface of carbon fiber felt, carbon fiber cloth, carbon fiber paper and other carbon electrodes, which is used as the negative electrode of the full iron flow battery. This electrode can act as a nucleation site for metal iron deposition, reduce the polarization during the charging process of the negative electrode of the full iron flow battery, and make the metal iron evenly distributed on the electrode surface to avoid the occurrence of dendrites, greatly improving the cycle life of the battery. SUMMARY

[0011] To solve the above technical problems, the atomic-level dispersed iron and tin modified electrode is used in the full iron flow battery, which can not only reduce the polarization during the charging process of the negative electrode, but also avoid the generation of dendrites, improve the energy conversion efficiency and cycle life of the battery.

[0012] To achieve the above purpose, the specific technical scheme adopted by the present application is as follows:

[0013] Step 1) prepare a mixed acid solution, wherein the mixed acid is a mixture of sulfuric acid and nitric acid, the ratio of the two is 1:3-3:1, and the total acid concentration is 2-10 mol / L;

[0014] Step 2) immerse the original porous carbon electrode in the prepared mixed acid solution, the treatment time is 2-20 hours, and the temperature is maintained at 20-80℃, so that the mixed acid can fully soak the original carbon electrode;

[0015] Step 3) configure an aqueous solution containing iron ions and tin ions, the concentration of iron ions in the configured aqueous solution is 0.05-1, preferably 0.1-0.2 mol / L, the concentration of tin ions is 0.05-1.0 mol / L, preferably 0.1-0.2 mol / L, and the concentration ratio of iron ions to tin ions is 1:5-5:1;

[0016] Step 4) immerse the pretreated carbon electrode in the aqueous solution containing iron ions and tin ions, and the adsorption process is carried out in an ice water bath under the assistance of ultrasonic waves, and the standing adsorption time is 2-100 hours, preferably 4-8 hours;

[0017] Step 5) place the adsorbed carbon electrode in a drying box, dry at 60-120℃ for 2-12 hours, and the preferred condition is to dry at 60℃ for 4 hours;

[0018] Step 6) place the carbon electrode in a high-temperature tube furnace and protect it with inert gas; the first process is to heat to 100-200℃, then keep the temperature for 1-2 hours, then heat to 300-500℃, then keep the temperature for 1-2 hours, and then heat to 800-1000℃, then keep the temperature for 1-2 hours; the heating rate of each stage is 1-20℃ / min.

[0019] The electrode can be used as the negative electrode of the full iron flow battery.

[0020] The porous carbon electrode is one of carbon fiber felt, carbon fiber cloth and carbon fiber paper.

[0021] The soluble salt of iron used can be one or two or more of ferric chloride, ferric nitrate, ferric sulfate and ferric acetate; the soluble salt of tin used is one or two or more of stannous chloride, stannic chloride, stannic acetate, stannous sulfate and stannic nitrate.

[0022] The electrode is applied as a negative electrode in a full-iron flow battery.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1) The carbon electrode modified by atomically dispersed iron and tin has high conductivity, reduces the polarization of the electrode, and enables the full-iron flow battery to have high energy efficiency at high current density.

[0025] 2) The active sites with atomically dispersed iron and tin grown in situ on the electrode surface have the effect of catalyzing the full-iron negative electrode reaction, greatly improving the reaction activity of the full-iron negative electrode reaction.

[0026] 3) The iron and tin are atomically dispersed on the electrode surface, have high electrochemical specific surface area, and can provide more nucleation sites for iron deposition, so that the deposited iron is uniformly distributed on the electrode surface, avoiding the generation of dendrites, and greatly improving the cycle life of the battery.

[0027] 4) The preparation method is simple, can be scaled up, and has low cost.

[0028] The present application grows atomically dispersed iron and tin on the electrode surface by an in-situ confinement method, provides nucleation sites for iron deposition, enables the deposited iron to be uniformly distributed on the electrode surface, avoids the generation of dendrites, and improves the cycle life of the battery. The preparation method of the high-stability electrode provided by the present application is simple, easy to control, has excellent cycle stability, and is expected to realize large-scale commercial production. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of the molecular structure of the carbon electrode;

[0030] Figure 2 is an X-ray crystal diffraction picture of the single-atom iron and tin loaded carbon electrode prepared in Example 1 of the present application;

[0031] Figure 3 is a spherical aberration correction transmission electron microscope photo of the single-atom iron and tin loaded carbon electrode prepared in Example 1 of the present application;

[0032] from Figure 2It can be seen that there is no diffraction peak of nanocrystal related to iron, tin and its compounds, which indicates that the metal iron and tin exist in the carbon electrode in the form of single atom. Figure 3 It is also proved again that the metal iron and tin exist in the carbon electrode in the form of single atom. DETAILED DESCRIPTION

[0033] The application will be described in detail below with examples, but the embodiments of the application are not limited thereto, and it is obvious that the examples described below are only some of the embodiments of the application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0034] Example 1

[0035] 1) Preparation of carbon electrode loaded with iron and tin single atoms:

[0036] (1) Pretreatment of carbon electrode: the specific operation of pretreatment is that the porous carbon fiber felt with square side length of 3 cm x 3 cm is soaked in mixed acid (nitric acid: sulfuric acid = 1:2.5) solution with total acid concentration of 6 mol / L at 25℃ for 5 hours.

[0037] (2) The specific operation of adsorption treatment is that the pretreated carbon fiber felt is soaked in 0.1 mol / L iron chloride solution and 0.1 mol / L stannous chloride solution, and is placed in an ice water bath under the assistance of ultrasonic wave for adsorption for 5 hours.

[0038] (3) The specific operation of drying treatment is that the carbon fiber felt after adsorption is placed in a vacuum drying box and dried at 60℃ for 4 hours.

[0039] (4) The specific operation of high-temperature heat treatment is that the dried carbon fiber felt is placed in a high-temperature tube furnace, and is heated to 200℃ at a heating rate of 5℃ / min under the protection of inert gas, and is kept at constant temperature for 1.5 hours; then it is heated to 400℃ at a heating rate of 7.5℃ / min, and is kept at constant temperature for 1 hour; finally it is heated to 950℃ at a heating rate of 5℃ / min, and is kept at constant temperature for 2 hours.

[0040] 2) Preparation of iron flow battery electrolyte:

[0041] (1) First, 0.1 mol / L HCl solution is added to deionized water to adjust the solution pH≈3.5, and 80 ml of weak acid solution 1 is prepared.

[0042] (2) 0.1 mol FeSO4 is weighed and slowly added into solution 1, and the pH value of the solution is monitored by a pH meter during the addition process. The pH value of the solution is adjusted to 3.5 by adding deionized water and a small amount of 0.1 mol / L HCl, and an acidic solution 2 is obtained.

[0043] (3) Solution 2 was transferred to a 100ml volumetric flask, and then diluted to the mark with a small amount of deionized water to obtain 100ml of 1mol / L FeSO4 electrolyte, which can be used as the electrolyte for both the positive and negative electrodes.

[0044] 3) Full iron flow battery assembly:

[0045] The single cell was assembled in the following order: positive end plate, graphite current collector, positive 6mm x 3cm x 3cm carbon felt, Naifion 115 prepared as the separator, carbon electrode prepared as the negative electrode, graphite current collector, and negative end plate.

[0046] 4) Evaluation of the performance of the full iron flow battery:

[0047] During the operation of the battery, the flow rates of the positive and negative electrolytes were both 100mL / min, and the charge and discharge tests were performed at 80mA / cm 2 The charge and discharge cutoff voltages were set to 1.65V and 0.8V, respectively.

[0048] From Figure 2 and Figure 3 it can be concluded that iron and tin are dispersed at the atomic level on the surface of the carbon fiber felt, and no metal characteristic peaks are observed, which provides abundant nucleation sites for the deposition of metallic iron and avoids dendrites, thereby improving the cycle stability.

[0049] Example 2

[0050] To simplify the description and enhance the contrast effect, the preparation method and process of Example 2 are the same as those of Example 1, except that the ratio of mixed acid during pretreatment is adjusted to nitric acid:sulfuric acid = 2.5:1.

[0051] Example 3

[0052] To simplify the description and enhance the contrast effect, the preparation method and process of Example 2 are the same as those of Example 1, except that the ratio of mixed acid during pretreatment is adjusted to nitric acid:sulfuric acid = 1:1.

[0053] Example 4

[0054] To simplify the description and enhance the contrast effect, the preparation method and process of Example 4 are the same as those of Example 1, except that the total acid concentration is 8mol / L.

[0055] Example 5

[0056] To simplify the description and enhance the contrast effect, the preparation method and process of Example 5 are the same as those of Example 1, except that during the adsorption of iron and tin ions, the iron ion solution is 0.2mol / L and the tin ion solution is 0.1mol / L.

[0057] Example 6

[0058] For the purpose of simplifying the description and enhancing the contrast effect, the preparation method and process of Example 6 are the same as those of Example 1, except that the iron ion solution is 0.1 mol / L and the tin ion solution is 0.2 mol / L when adsorbing iron and tin ions.

[0059] Example 7

[0060] For the purpose of simplifying the description and enhancing the contrast effect, the preparation method and process of Example 7 are the same as those of Example 1, except that the temperature of the third stage is 900°C when high-temperature calcination.

[0061] Example 8

[0062] For the purpose of simplifying the description and enhancing the contrast effect, the preparation method and process of Example 8 are the same as those of Example 1, except that the temperature of the third stage is 1000°C when high-temperature calcination.

[0063] Comparative Example 1

[0064] 1) The carbon fiber felt electrode was pretreated; the process and conditions were the same as those of step 1) of Example 1.

[0065] 2) After the end of step 1), the drying and high-temperature heat treatment operations were the same as those of Example 1.

[0066] Comparative Example 2

[0067] 1) The carbon fiber felt electrode was pretreated; the process and conditions were the same as those of step 1) of Example 1.

[0068] 2) The adsorption solution was replaced with a 0.1 mol / L iron chloride solution, and the specific adsorption treatment operation was the same as that of step 2) of Example 1.

[0069] 3) The drying and high-temperature heat treatment operations were the same as those of Example 1.

[0070] Comparative Example 3

[0071] 1) The carbon fiber felt electrode was pretreated; the process and conditions were the same as those of step 1) of Example 1.

[0072] 2) The adsorption solution was replaced with a 0.1 mol / L stannous chloride solution, and the specific adsorption treatment operation was the same as that of step 2) of Example 1.

[0073] 3) The drying and high-temperature heat treatment operations were the same as those of Example 1.

[0074] Comparative Example 4

[0075] Commercial carbon felt was directly used as the electrode without any treatment and was directly applied to the full iron flow battery negative electrode. The battery evaluation method was the same as that of Example 1.

[0076] The electrodes prepared in each example and the comparative example were applied to a full iron flow battery, and the coulombic efficiency, voltage efficiency, energy efficiency, cycle number required for 30% capacity decay, and the like of the battery were listed in Table 1. As can be seen from Table 1, compared with the commercial carbon felt commonly used for the negative electrode of the full iron flow battery, the electrode prepared in the present patent increased the coulombic efficiency of the battery by more than 10%, the energy efficiency by more than 10%, and the cycle number required for 30% capacity decay by more than 2 times, which fully demonstrates that the electrode prepared in the present patent has excellent performance.

[0077] Table 1. Comparison table of full iron flow battery performance of different carbon fiber felt electrodes

[0078]

Claims

1. A method for preparing an all-iron flow battery electrode, characterized in that, Active sites with atomic-level dispersion of metallic iron and tin are grown in situ on the surface of a carbon electrode. Carbon atoms and doped oxygen atoms in the carbon material serve as rivet atoms for the iron and tin atoms. The specific synthesis process includes the following steps: 1) Treat the surface of the carbon electrode with mixed acid to enrich it with oxygen functional groups; the carbon electrode used is one of carbon fiber felt, carbon fiber cloth, or carbon fiber paper; the mixed acid used is a mixture of sulfuric acid and nitric acid with a concentration ratio of 1:3-3:1 and a total acid concentration of 2-10 mol / L; the treatment time is 2-20 hours; the treatment temperature is 20-80℃. 2) Place the carbon electrode in an aqueous solution containing iron and tin ions. The iron-containing substance in the aqueous solution is one or more of ferric chloride, ferric nitrate, ferric sulfate, and ferric acetate, with a concentration of 0.05-1.0 mol / L; the tin-containing substance in the aqueous solution is one or more of stannous chloride, stannous chloride, stannous acetate, stannous sulfate, and stannous nitrate, with a concentration of 0.05-1.0 mol / L; the iron ion to tin ion concentration ratio is 1:5-5:1; let stand for 2-100 hours. 3) Dry the above carbon electrode at 60-120℃ for 2-12 hours; 4) Subsequently, the carbon electrode is subjected to high-temperature treatment under an inert atmosphere to obtain atomically dispersed carbon electrodes of metallic iron and tin.

2. The method for preparing an all-iron flow battery electrode as described in claim 1, characterized in that, Step 2, the adsorption process, is carried out in an ice-water bath and is supplemented with ultrasound.

3. The method for preparing an all-iron flow battery electrode as described in claim 1, characterized in that, Step 4, the high-temperature treatment process, is carried out in an inert gas at a heating rate of 1-20℃ / min. It consists of three heating processes: the first process involves heating to 100-200℃ and holding the temperature for 1-2 hours; the second process involves heating to 300-500℃ and holding the temperature for 1-2 hours; and the third process involves heating to 800℃-1000℃ and holding the temperature for 1-2 hours.

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