Modified graphite felt, preparation method and application thereof, and flow battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a modified graphite felt, a preparation method and application thereof and a flow battery. According to the preparation method of the modified graphite felt, the modified graphite felt is prepared by combining an impregnation method and heat treatment. The modified graphite felt obtained by loading the transition metal oxide on the graphite felt by utilizing the metal salt with low price and combining an impregnation method and heat treatment shows good performance in an iron-based flow battery negative electrode electrolyte alkaline environment, and the performance is obviously improved compared with that of an original graphite felt.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a modified graphite felt, its preparation method and application, and flow batteries. Background Technology

[0002] With the continuous development of human society, the constant consumption of non-renewable energy sources such as oil and coal has constrained the sustainable development of human society. Vigorously developing clean and renewable energy is an important way to solve the energy problem. Among them, flow battery technology is widely regarded as an important direction for large-scale energy storage technology due to its high capacity, long life, high safety, and large-scale deployment capabilities.

[0003] Electrodes, as key components of flow batteries, significantly impact their overall performance. Polyacrylonitrile-based graphite felt, made from polyacrylonitrile through high-temperature carbonization and graphitization, is widely used in flow batteries due to its high strength and oxidation resistance. However, its poor hydrophilicity and limited catalytic activity negatively affect the overall battery performance. Therefore, it is necessary to modify polyacrylonitrile-based graphite felt to improve its hydrophilicity and catalytic activity, thereby enhancing battery performance.

[0004] A common modification method involves using metal salts and a hydrothermal approach to load transition metal oxides onto graphite felt. For example, graphite felt and a solution prepared with a metal salt are placed in a high-pressure vessel, which is then placed in a heating chamber and heated to a specific temperature and held for a certain duration. By controlling the reaction temperature, time, and solvent concentration, transition metal oxides are loaded onto the surface of the graphite felt. However, the hydrothermal method for loading transition metal oxides onto graphite felt is costly and cannot be applied on a large scale. Furthermore, the hydrothermal method can damage the mechanical properties of the graphite felt itself. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified graphite felt, its preparation method and application, as well as a flow battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing modified graphite felt, which is prepared by a combination of impregnation and heat treatment.

[0008] The specific steps are as follows: 1) Pretreatment of graphite felt; 2) Immersion of the graphite felt obtained in step 1) in a salt solution containing transition metals; 3) Heat treatment of the graphite felt obtained in step 2).

[0009] The transition metal mentioned in step 2) is one or a mixture of iron, copper, and nickel.

[0010] 4. The method for preparing modified graphite felt according to claim 2, characterized in that step 2) specifically involves: adding a transition metal salt to deionized water to prepare a solution, and then completely immersing the graphite felt in the prepared solution; preferably, ultrasonic treatment is performed.

[0011] Preferably, the transition metal salt is one or a mixture of ferric chloride, copper nitrate hexahydrate, and nickel nitrate hexahydrate;

[0012] Preferably, the solution concentration is 0.01-0.5 mol / L.

[0013] The graphite felt obtained in step 2) is placed in a resistance furnace and heated to 600-800℃ at a heating rate of 5-20℃ / min and held for 1-12 hours. It is then removed after cooling to room temperature.

[0014] The graphite felt is completely immersed in the etching solution for chemical treatment, and then washed with deionized water and dried. Preferably, the etching solution is one or a mixture of hydrogen peroxide, sulfuric acid, and nitric acid.

[0015] The present invention also includes a modified graphite felt obtained by the preparation method described above.

[0016] The present invention also includes an application of the modified graphite felt described herein.

[0017] The present invention also includes a flow battery comprising the modified graphite felt.

[0018] The modified graphite felt is used as an electrode, a positive electrolyte, a negative electrolyte, and a diaphragm.

[0019] Preferably, the negative electrode electrolyte includes FeCl3, NaOH, and TEOA; the positive electrode electrolyte includes K4[Fe(CN)6] and NaOH; and the separator is a SPEEK membrane.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This application utilizes inexpensive metal salts, combined with impregnation and heat treatment, to load transition metal oxides onto graphite felt, resulting in modified graphite felt that exhibits excellent performance in the alkaline environment of the negative electrode electrolyte of iron-based flow batteries, showing a significant improvement in performance compared to the original graphite felt. Attached Figure Description

[0022] Figure 1 The figure shows the CV curves of the graphite felt before and after modification in the electrolyte in Example 1.

[0023] Figure 2 (a) is an SEM image of the graphite felt before modification, and (b) is an SEM image of the graphite felt after modification in Example 1. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0025] Example 1

[0026] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0027] (1) Take a piece of graphite felt measuring 3cm*3cm*5mm and immerse it completely in concentrated nitric acid (68%) for 2 hours. After removing it, wash it with deionized water and dry it. Figure 2 (a) is the SEM image of the unmodified graphite felt from this step, corresponding to... Figure 1 (modified graphite felt in the middle).

[0028] (2) Weigh 0.16g of ferric chloride and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0029] (3) Remove the graphite felt and place it in a box-type resistance furnace. Heat the furnace to 600℃ at a rate of 10℃ / min and maintain the temperature for 6 hours. Remove the furnace after the equipment has cooled down. Figure 2 (b) is the SEM image of the modified graphite felt in this step, corresponding to... Figure 1 (Example in the text)

[0030] Three-electrode testing was employed (working electrode: graphite felt, counter electrode: graphite rod, reference electrode: Hg / HgO; electrolyte: 0.1 mol / L Fe2(SO4)3, 0.2 mol / L FeSO4·7H2O, 1.5 mol / L NaOH, 0.5 mol / L N,N-bis(2-hydroxyethyl)glycine).

[0031] Figure 1 The figures show the CV curves of the modified graphite felt in the aforementioned electrolyte. The peak current of the redox peak of the modified graphite felt is more than twice that of the unmodified graphite felt. Furthermore, the potential difference between the oxidation and reduction peaks of the modified graphite felt is significantly smaller than that of the unmodified one. When assembled into a flow battery (the negative electrode electrolyte was prepared with 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared with 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), the CV curves were measured at 100 mA / cm². 2At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 75.3%.

[0032] like Figure 1 As shown, the graphite felt prepared using the method of Example 1 showed that the peak value of the redox peak was more than twice that of the unmodified graphite felt, proving that the modified graphite felt has stronger catalytic activity.

[0033] Example 2

[0034] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0035] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in concentrated nitric acid (68%) for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0036] (2) Weigh 0.38g of copper nitrate hexahydrate and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0037] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 600℃ at 10℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0038] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 100 mA / cm². 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 74.3%.

[0039] Example 3

[0040] A modified polyacrylonitrile graphite felt is prepared by first soaking it in hydrogen peroxide, then washing it with clean water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0041] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in concentrated nitric acid (68%) for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0042] (2) Weigh 0.87g of nickel nitrate hexahydrate and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1h.

[0043] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 600℃ at 10℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0044] It was assembled into a flow battery (the negative electrode electrolyte consisted of 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the separator was a SPEEK membrane), and tested at 50 mA / cm². 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 76.8%.

[0045] Example 4

[0046] A modified polyacrylonitrile graphite felt is prepared by first soaking it in hydrogen peroxide, then washing it with clean water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0047] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in hydrogen peroxide (15%) for chemical treatment for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0048] (2) Weigh 2g of ferric chloride and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0049] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 600℃ at 5℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0050] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 50 mA / cm 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 73.5%.

[0051] Example 5

[0052] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0053] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in hydrogen peroxide (15%) for chemical treatment for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0054] (2) Weigh 2g of ferric chloride and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0055] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 700℃ at 5℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0056] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 100 mA / cm 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 71.4%.

[0057] Example 6

[0058] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0059] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in hydrogen peroxide (15%) for chemical treatment for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0060] (2) Weigh 2g of ferric chloride and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0061] (3) Take out the graphite felt and put it into a box-type resistance furnace to heat it to 800℃ at 5℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0062] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 100 mA / cm 2 At a current density of 1.6V and 0.7V respectively, after 100 cycles, the energy efficiency reaches 72.5%.

[0063] Example 7

[0064] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0065] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in concentrated sulfuric acid (68%) for 6 hours for chemical corrosion. After taking it out, wash it with deionized water and then dry it.

[0066] (2) Weigh 0.38g of copper nitrate hexahydrate and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1 hour.

[0067] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 600℃ at 10℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0068] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 100 mA / cm 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 68.3%.

[0069] Example 8

[0070] A modified polyacrylonitrile graphite felt is prepared by first soaking it in a strong acid, then washing it with water and drying it, and then loading a transition metal oxide onto its surface using an impregnation method and heat treatment. The process involves the following steps:

[0071] (1) Take a piece of graphite felt with a diameter of 3cm*3cm*5mm and immerse it completely in hydrogen peroxide (15%) for chemical treatment for 2 hours. After taking it out, wash it with deionized water and then dry it.

[0072] (2) Weigh 0.87g of nickel nitrate hexahydrate and add it to 100ml of deionized water. Stir mechanically until the solid is completely dissolved to obtain a mixed solution. Place the graphite felt into the mixed solution and sonicate for 1h.

[0073] (3) Take out the graphite felt and put it into the box-type resistance furnace. Heat it to 600℃ at 10℃ / min and keep it at that temperature for 6 hours. Take it out after the equipment cools down.

[0074] It was assembled into a flow battery (the negative electrode electrolyte was prepared from 0.2 mol / L FeCl3, 2 mol / L NaOH, and 0.3 mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared from 0.2 mol / L K4[Fe(CN)6] and 2 mol / L NaOH; the separator was a SPEEK membrane), at 50 mA / cm 2 At a current density of 1.6V and 0.7V respectively, after 100 cycles, the energy efficiency reaches 70.4%.

[0075] Comparative Example 1

[0076] A 3cm*3cm*5mm piece of raw graphite felt was assembled into a flow battery (the negative electrode electrolyte was prepared with 0.2mol / L FeCl3, 2mol / L NaOH, and 0.3mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared with 0.2mol / L K4[Fe(CN)6] and 2mol / L NaOH; the separator was a SPEEK membrane), and the flow rate was 50mA / cm. 2 At a current density of 1.6V and 0.7V respectively, after 100 cycles, the energy efficiency is 67.3%. Figure 2 (a) is a SEM image of the original graphite felt.

[0077] Comparative Example 2

[0078] A 3cm*3cm*5mm piece of raw graphite felt was assembled into a flow battery (the negative electrode electrolyte was prepared with 0.2mol / L FeCl3, 2mol / L NaOH, and 0.3mol / L N,N-bis(2-hydroxyethyl)glycine; the positive electrode electrolyte was prepared with 0.2mol / L K4[Fe(CN)6] and 2mol / L NaOH; the separator was a SPEEK membrane). The flow rate was 100mA / cm. 2 At a current density of 1.6V and 0.7V respectively, and after 100 cycles, the energy efficiency reaches 63.2%.

[0079] The main parameter results of each embodiment and comparative example are shown in Table 1.

[0080] Table 1

[0081] Metal salts temperature Treatment fluid Energy efficiency Example 1 Ferric chloride Heat to 600℃ at a rate of 10℃ / min and hold for 6 hours. concentrated nitric acid 75.3％ Example 2 Copper nitrate hexahydrate Heat to 600℃ at a rate of 10℃ / min and hold for 6 hours. concentrated nitric acid 74.3％ Example 3 Nickel nitrate hexahydrate Heat to 600℃ at a rate of 10℃ / min and hold for 6 hours. concentrated nitric acid 76.8％ Example 4 Ferric chloride Heat to 600℃ at a rate of 5℃ / min and hold for 6 hours. hydrogen peroxide 73.5％ Example 5 Ferric chloride Heat to 700℃ at a rate of 5℃ / min and hold for 6 hours. hydrogen peroxide 71.4％ Example 6 Ferric chloride Heat to 800℃ at a rate of 5℃ / min and hold for 6 hours. hydrogen peroxide 72.5％ Example 7 Copper nitrate hexahydrate Heat to 600℃ at a rate of 10℃ / min and hold for 6 hours. concentrated sulfuric acid 68.3％ Example 8 Nickel nitrate hexahydrate Heat to 600℃ at a rate of 10℃ / min and hold for 6 hours. hydrogen peroxide 70.4％ Comparative Example 1 / / / 67.3％ Comparative Example 2 / / / 63.2％

[0082] In summary, this application utilizes inexpensive metal salts, combined with impregnation and heat treatment, to load transition metal oxides onto graphite felt, resulting in modified graphite felt that exhibits excellent performance in the alkaline environment of the negative electrode electrolyte of iron-based flow batteries, showing a significant improvement in performance compared to the original graphite felt.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing modified graphite felt, characterized in that, It was prepared by a combination of impregnation and heat treatment.

2. The method for preparing modified graphite felt according to claim 1, characterized in that, The specific steps are as follows: 1) Pretreatment of graphite felt; 2) Immersion of the graphite felt obtained in step 1) in a salt solution containing transition metals; 3) Heat treatment of the graphite felt obtained in step 2).

3. The method for preparing modified graphite felt according to claim 2, characterized in that, The transition metal mentioned in step 2) is one or a mixture of iron, copper, and nickel.

4. The method for preparing modified graphite felt according to claim 2, characterized in that, Step 2) involves the following steps: adding a transition metal salt to deionized water to prepare a solution, then immersing the graphite felt completely in the prepared solution; preferably, ultrasonic treatment is then performed. Preferably, the transition metal salt is one or a mixture of ferric chloride, copper nitrate hexahydrate, and nickel nitrate hexahydrate; Preferably, the solution concentration is 0.01-0.5 mol / L.

5. The method for preparing modified graphite felt according to claim 2, characterized in that, The specific steps of step 3) are as follows: Place the graphite felt obtained in step 2) in a resistance furnace, heat it to 600-800℃ at a heating rate of 5-20℃ / min and keep it at that temperature for 1-12 hours. Take it out after it cools down to room temperature.

6. The method for preparing modified graphite felt according to claim 2, characterized in that, The specific steps of step 1) are as follows: the graphite felt is completely immersed in the etching solution for chemical treatment, and after being taken out, it is washed with deionized water and then dried; preferably, the etching solution is one or a mixture of hydrogen peroxide, sulfuric acid and nitric acid.

7. A modified graphite felt obtained by the preparation method according to any one of claims 1-6.

8. An application of the modified graphite felt according to claim 6.

9. A flow battery, characterized in that, Including the modified graphite felt as described in claim 7.

10. The flow battery according to claim 9, characterized in that, The device includes the modified graphite felt as described in claim 7 as an electrode, a positive electrode electrolyte, a negative electrode electrolyte, and a separator; preferably, the negative electrode electrolyte includes FeCl3, NaOH, and TEOA; the positive electrode electrolyte includes K4[Fe(CN)6] and NaOH; and the separator is a SPEEK membrane.

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