Preparation method of iron-based positive electrolyte and application thereof

Abstract

The application discloses a preparation method of an iron-based complex positive electrode material and application thereof. Specifically, the iron-based positive electrode electrolyte is a positive electrode active material based on an iron metal organic complex, and a complex structure of the iron metal organic complex is formed by pyridine nitrogen coordination of ferrous ions and tris(2-pyridylmethyl)amine. The complex has good solubility (0.62 M) in a neutral aqueous solution, and an oxidation-reduction potential is 0.55 V vs. SHE, and can be used as a positive electrode electrolyte for a neutral water-based flow battery. The iron-based positive electrode electrolyte used in the application has cheap and easily available raw materials and a simple preparation method, provides a solution for constructing an efficient water-based flow battery, and is favorable for promoting large-scale application of the water-based flow battery.

Description

Technical Field

[0001] This invention belongs to the field of large-scale energy storage flow battery technology, specifically relating to a method for preparing an iron-based cathode electrolyte and its application. Background Technology

[0002] With increasingly severe environmental pollution and energy crises, global energy transition has become an inevitable trend, gradually shifting from a traditional energy system dominated by fossil fuels to a new energy system dominated by clean energy. Among clean energy sources, wind and solar power will occupy a major position. However, wind and solar energy are intermittent and fluctuating, making it difficult to achieve supply-demand balance and directly connect to the grid. Therefore, energy storage technologies, especially large-scale, long-term energy storage technologies, are needed. Aqueous flow batteries, due to their intrinsic safety and capacity-power decoupling characteristics, are considered one of the preferred technologies.

[0003] Vanadium redox flow batteries are currently the most mature aqueous flow battery technology and have entered the early stages of commercialization. However, they still face challenges such as limited vanadium resources, high vanadium prices, and the need for use in acidic systems. Therefore, it is necessary to develop new battery systems with abundant reserves and lower costs. Iron ranks only after oxygen, silicon, and aluminum in the elemental distribution sequence, accounting for approximately 5.1% of the Earth's crust by mass, making it the second most abundant metal on Earth. Iron-based metal-organic complexes have advantages such as low cost and high designability, and have attracted widespread attention in recent years.

[0004] Due to the limited availability of cathode materials suitable for neutral aqueous conditions, the potential of iron-based complexes has gradually attracted attention. Xiang et al. reported an iron complex, Fe(Dcbpy)2(CN)2. 4- / 3- Compared to SHE, it exhibits a high redox potential of 0.86 V, excellent solubility (1.22 M), and a capacity decay rate of 0.22% per day. However, the generation of toxic gases during synthesis and the complexity of the chemical synthesis route may hinder the low-cost production of this molecule (X. Li, et al., Nat. Energy 2021, 6, 873). Therefore, it is crucial to provide an iron-based cathode material with a safe, simple, and low-cost synthesis route, which can achieve long-term stable cycling in a neutral aqueous environment and effectively suppress the formation of ferric hydroxide precipitation. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an iron-based positive electrode electrolyte.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an iron-based positive electrode electrolyte, characterized in that it includes, Ferrous chloride and tris(2-pyridylmethyl)amine (TPA) were dissolved separately in acetonitrile, mixed and stirred to react. Then, an antisolvent was added to the reaction solution to precipitate the precipitate. After filtration, washing and drying, the iron-based complex Fe(TPA) was obtained, which is the active material of the iron-based positive electrode electrolyte.

[0009] In a preferred embodiment of the preparation method described in this invention, the molar ratio of ferrous chloride to TPA is 1:1.

[0010] In a preferred embodiment of the preparation method described in this invention, the temperature of the stirring reaction is 25–90°C, and the stirring reaction time is 0.5–24 h.

[0011] In a preferred embodiment of the preparation method described in this invention, the antisolvent is selected from at least one of diethyl ether, acetone, ethyl acetate, chloroform, and dichloromethane.

[0012] In a preferred embodiment of the preparation method described in this invention, the drying is performed under vacuum at a temperature of 30–80°C.

[0013] Another objective of this invention is to overcome the shortcomings of the prior art and provide an iron-based complex positive electrode electrolyte, characterized in that the iron-based complex Fe(TPA) has the following structure: .

[0014] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of an iron-based complex cathode electrolyte in an aqueous flow battery, characterized in that: the iron-based complex cathode electrolyte is applied to a single cell or a stack of multiple single cells assembled together.

[0015] In a preferred embodiment of the application described in this invention, the aqueous flow battery comprises a positive electrolyte, a negative electrolyte, positive and negative electrodes, a current collector, a separator, and a supporting electrolyte; the active material of the positive electrolyte is an iron-based complex Fe(TPA), and the active material of the negative electrolyte is a water-soluble viologen compound.

[0016] In a preferred embodiment of the application described in this invention, the supporting electrolyte is a mixed electrolyte solution of potassium chloride and potassium sulfate, the concentration of the supporting electrolyte in the electrolyte is 1.0 to 2.0 mol / L, and the mixing ratio of potassium chloride and potassium sulfate is 0:10 to 10:0.

[0017] In a preferred embodiment of the application described in this invention, the concentration of the iron-based complex Fe(TPA) in the positive electrode electrolyte is 0.01–0.62 mol / L.

[0018] Beneficial effects of this invention: (1) This invention provides a novel positive electrode active material—iron-based organometallic complex Fe(TPA), which uses ferrous chloride and TPA ligand as starting materials to synthesize the target product through a simple antisolvent method. It has good solubility (0.62 M) in water and good redox potential (~0.55 V vs. SHE).

[0019] (2) The TPA ligand provided by the present invention can chelate with the iron center to form a coordination sphere. The combination of the four coordination atoms in TPA with the metal ions can avoid the generation of iron hydroxide during the charging and discharging process of the battery.

[0020] (3) By combining the present invention with viologen-based negative electrode electrolyte to assemble a neutral aqueous flow battery, the present invention can effectively solve the problems of low molecular potential and low solubility of existing neutral positive electrode molecules, and provides a new solution for constructing a neutral aqueous flow battery with high voltage, high power density and high efficiency.

[0021] (4) The iron-based complex used in this invention is simple to prepare, the raw materials are cheap and readily available, and it has strong scalability, which helps to promote the further commercialization of neutral aqueous flow batteries. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The image shows the XRD pattern of Fe(TPA) obtained in Example 2 of this application.

[0023] Figure 2 The TGA spectrum of Fe(TPA) obtained in Example 2 of this application is shown.

[0024] Figure 3 The images show the ultraviolet absorption spectra of different concentrations of Fe(TPA) used in Example 13 of this application.

[0025] Figure 4 According to Embodiment 13 of this application Figure 3 The resulting solubility standard curve.

[0026] Figure 5 This is the cyclic voltammetry curve of the Fe(TPA) solution used in Example 14 of this application.

[0027] Figure 6 This is a cycle stability diagram of the flow battery in Embodiment 15 of this application.

[0028] Figure 7 This is a cycle stability diagram of the flow battery in Embodiment 16 of this application.

[0029] Figure 8 This is a cycle stability diagram of the flow battery in Embodiment 17 of this application. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] The raw materials used in this invention are: FeCl2 (99.0%), tris(2-pyridylmethyl)amine (TPA, 98%), methanol, acetonitrile, ethyl acetate, acetone, diethyl ether, dichloromethane, chloroform, potassium chloride (99.5%), potassium sulfate (99.0%), and dichloromethyl viologen (98.0%), all of which are analytical grade reagents and were purchased from Beijing Innocare Technology Co., Ltd. The graphite felt was purchased from Liaoning Jingu Carbon Materials Co., Ltd., and the DSV anion exchange membrane was manufactured by AGC Engineering Co., Ltd.

[0034] The instruments used in this invention embodiment are as follows: Electronic analytical balance (FA2104N) manufactured by Shanghai Jingqi Instrument Co., Ltd.; constant temperature magnetic stirrer (SZCL-3B), circulating water pump (SHZ-D(Ⅲ)) and electric heating oil bath (SZCL-3B) manufactured by Gongyi Yuhua Instrument Co., Ltd.; forced air drying oven (XHDHG) and rotary evaporator (XHRE-2000B) manufactured by Shanghai Xiaohan Industrial Development Co., Ltd.; ultrapure water system (Smart2Pure) manufactured by Thermo Fisher Scientific, Inc., USA; ultrasonic instrument (KQ5200DE) manufactured by Kunshan Ultrasonic Instrument Co., Ltd.; ultraviolet-visible spectrometer (Hitachi UV-5700) manufactured by Hitachi High Technology Co., Ltd., Japan; electrochemical workstation (CHI 630 E) manufactured by Shanghai Chenhua Instrument Co., Ltd.; battery testing system (Neware BTS 3000, 5 V 6 A) manufactured by Shenzhen Xinwei Electronics Co., Ltd.; glassy carbon electrode (3 The micrometer (mm) was manufactured by Wuhan Gaoshi Ruilian Technology Co., Ltd.; the X-ray powder diffractometer (Miniflex 600C) was manufactured by Rigaku, Japan; the thermogravimetric analyzer (TGA550) was manufactured by Waters Group, USA; and the elemental analyzer (Vario EL cube) was manufactured by Elementar, Germany.

[0035] The structure of the viologen compound used in the embodiments of this invention is as follows: The battery assembly method and characterization method in this embodiment of the invention are as follows: (1) The positive and negative electrodes are made of graphite felt with a side length of 3×3cm and a thickness of 4 mm.

[0036] (2) The diaphragm is a DSV anion exchange membrane with a thickness of 95~100μm; the current collector is a 2 mm thick titanium plate.

[0037] (3) Electrolyte preparation: The active material of the negative electrode electrolyte is viologen compound with the structure of compound (2), and the concentration is 0.1 to 1.0 mol / L; the active material of the positive electrode electrolyte is Fe(TPA), and the concentration range is 0.01 to 0.62 mol / L.

[0038] (4) The electrolyte is a mixed electrolyte solution of potassium chloride and potassium sulfate. Specifically, the mixing ratio of potassium chloride and potassium sulfate is 0:10 to 10:0. The concentration of the electrolyte in the electrolyte is 1.0 to 2.0 mol / L. The distilled water used is deoxygenated.

[0039] (5) Battery assembly: In a glove box filled with Ar atmosphere, the end plate, current collector, electrode frame, positive and negative electrodes, separator, supporting electrolyte, positive and negative electrolyte, flow pipe, storage tank and peristaltic pump are assembled according to a specific process.

[0040] (6) Battery testing and electrochemical characterization: The battery was tested using a battery testing system for charge-discharge cycles and rate capability, with a current density range of 20–120 mA / cm². 2 Its electrochemical properties were characterized by cyclic voltammetry.

[0041] Example 1 TPA (10 mmol, 2.90 g) and FeCl2 (10 mmol, 1.27 g) were dissolved in 15 mL of methanol, respectively. The TPA methanol solution was then slowly added dropwise to the FeCl2 methanol solution. The mixture was stirred at room temperature for 12 h, and a small amount of yellow precipitate was obtained. The precipitate was filtered, washed, and dried under vacuum at 60 °C to obtain the target Fe(TPA) product with a yield of 30%.

[0042] Example 2 (1) Dissolve TPA (10 mmol, 2.90 g) and FeCl2 (10 mmol, 1.27 g) in 10 mL of acetonitrile, then slowly add the TPA acetonitrile solution to the FeCl2 acetonitrile solution, stir for 12 h at room temperature, and then filter to obtain a clear filtrate.

[0043] (2) 500 mL of ethyl acetate antisolvent was added dropwise to the obtained filtrate, and a large amount of pale yellow precipitate was precipitated. The precipitate was filtered, washed, and dried under vacuum at 60°C to obtain the Fe(TPA) target product with a yield of 80%.

[0044] like Figure 1 The image shows the XRD pattern of the obtained sample. Figure 2 The thermogravimetric spectrum of the obtained sample is shown in the figure. Table 1 shows the elemental analysis results of the obtained sample.

[0045] Table 1 Elemental Analysis Results

[0046] Example 3 The difference between this embodiment and Example 2 is that the ethyl acetate antisolvent in step (2) is replaced with diethyl ether antisolvent, resulting in the precipitation of a pale yellow precipitate. The precipitate is then filtered, washed, and dried under vacuum at 60°C to obtain the Fe(TPA) target product with a yield of 40%.

[0047] Example 4 The difference between this embodiment and Example 2 is that the ethyl acetate antisolvent in step (2) is replaced with acetone antisolvent, resulting in the precipitation of a pale yellow precipitate. The precipitate is then filtered, washed, and dried under vacuum at 60°C to obtain the Fe(TPA) target product with a yield of 30%.

[0048] Example 5 The difference between this embodiment and Example 2 is that the ethyl acetate antisolvent in step (2) is replaced with chloroform antisolvent, a small amount of pale yellow precipitate is precipitated, filtered, washed, and dried under vacuum at 60°C to obtain the Fe(TPA) target product with a yield of 10%.

[0049] Example 6 The difference between this embodiment and Example 2 is that the ethyl acetate antisolvent in step (2) is replaced with dichloromethane antisolvent, and no precipitate is formed.

[0050] According to Examples 2-6, the preferred antisolvent is ethyl acetate.

[0051] Example 7 The difference between this embodiment and embodiment 2 is that the stirring temperature in step (1) is replaced with 50°C, while the rest of the steps are the same as in embodiment 2, and the Fe(TPA) target product is obtained with a yield of 78%.

[0052] Example 8 The difference between this embodiment and Example 2 is that the stirring temperature in step (1) is replaced with 70°C, while the rest of the steps are the same as in Example 2, and the Fe(TPA) target product is obtained with a yield of 78%.

[0053] Example 9 The difference between this embodiment and embodiment 2 is that the stirring temperature in step (1) is replaced with 90°C, while the rest of the steps are the same as in embodiment 2, and the Fe(TPA) target product is obtained with a yield of 77%.

[0054] According to Examples 7-9, the preferred stirring temperature is room temperature.

[0055] Example 10 The difference between this embodiment and embodiment 2 is that the stirring time in step (1) is replaced with 30 min, while the rest of the steps are the same as in embodiment 2, and the Fe(TPA) target product is obtained with a yield of 20%.

[0056] Example 11 The difference between this embodiment and embodiment 2 is that the stirring time in step (1) is replaced with 2 h, while the rest of the steps are the same as in embodiment 2, and the Fe(TPA) target product is obtained with a yield of 30%.

[0057] Example 12 The difference between this embodiment and embodiment 2 is that the stirring time in step (1) is replaced with 24 h, while the rest of the steps are the same as in embodiment 2, and the Fe(TPA) target product is obtained with a yield of 76%.

[0058] According to Examples 10-12, the stirring time is preferably 12 hours.

[0059] Example 13 Dissolve 1.04 g of Fe(TPA) in deionized water and bring the volume to 25 mL to obtain a 0.1 mol / L Fe(TPA) solution. The Fe(TPA) solution was successively diluted to 0.01, 0.03, 0.05, 0.07, and 0.09 mmol / L for UV testing. Figure 3 ), and obtained the standard curve of Fe(TPA) solution absorption spectrum ( Figure 4 ).

[0060] Take 2.5 μL of saturated Fe(TPA) solution, dilute to 25 mL, and perform UV testing. Figure 4 The standard curve calculation yielded a saturated solubility of Fe(TPA) of 0.62 M.

[0061] Example 14 0.417 g of Fe(TPA) was dissolved in a 1 mol / L potassium chloride aqueous solution, and the resulting solution was subjected to cyclic voltammetry testing. The results are as follows: Figure 5 As shown.

[0062] Depend on Figure 5 It can be seen that Fe(TPA) exhibits good electrochemical properties, with a redox potential of ~0.55 V vs. SHE.

[0063] Example 15: Construction of a flow battery using 0.1 mol / L Fe(TPA) compound and viologen compound Dissolve 1.04 g Fe(TPA) and 1.86 g potassium chloride in deionized water and bring the volume to 25 mL to obtain a 0.1 mol / L Fe(TPA) positive electrode electrolyte. Dissolve 1.28 g of viologen compound and 1.86 g of potassium chloride in deionized water and bring the volume to 25 mL to obtain a 0.2 mol / L viologen compound negative electrode electrolyte.

[0064] The battery was then assembled in an argon-filled glove box. Specifically, 6 mL of positive electrolyte and 10 mL of negative electrolyte were used. A titanium plate was used as the current collector, and a 3 mm thick graphite felt was used as the electrode. An anion exchange membrane (DSV) was used to separate the positive and negative electrolytes. The electrolyte was pumped into the battery assembly using a peristaltic pump at a flow rate of 60 mL / min. The positive and negative electrodes of the battery were then connected to the battery testing system, and a current density of 20 mA / cm² was applied. 2 Perform constant current charge and discharge tests on the battery.

[0065] Battery cycle performance such as Figure 6 As shown, at 20 mA / cm 2 Under these conditions, the battery can provide a capacity of ~12 Ah / L, while the battery energy efficiency remains stable at ~70%. After 60 cycles, the capacity retention is close to 90%, and the coulombic efficiency per cycle is close to 100%, demonstrating good cycle stability.

[0066] Example 16: Construction of a flow battery using 0.1 mol / L Fe(TPA) compound and viologen compound Dissolve 1.04 g Fe(TPA) and 3.55 g sodium sulfate in deionized water and bring the volume to 25 mL to obtain a 0.1 mol / L Fe(TPA) positive electrode electrolyte. Dissolve 1.28 g of viologen compound and 3.55 g of sodium sulfate in deionized water and bring the volume to 25 mL to obtain a 0.2 mol / L viologen compound negative electrode electrolyte.

[0067] The battery was then assembled in an argon-filled glove box. Specifically, 5 mL of positive electrolyte and 10 mL of negative electrolyte were used. A titanium plate was used as the current collector, and a 3 mm thick graphite felt was used as the electrode. An anion exchange membrane (DSV) was used to separate the positive and negative electrolytes. The electrolyte was pumped into the battery assembly using a peristaltic pump at a flow rate of 60 mL / min. The positive and negative electrodes of the battery were then connected to the battery testing system, and a current density of 10 mA / cm² was applied. 2 Perform constant current charge and discharge tests on the battery.

[0068] Battery cycle performance such as Figure 7 As shown, at 10 mA / cm 2 The battery provides a capacity of ~6 Ah / L, while maintaining a stable energy efficiency of ~68%. After 30 cycles, the capacity retention is close to 90%, and the coulombic efficiency per cycle is close to 100%.

[0069] Example 17: Construction of a flow battery using 0.4 mol / L Fe(TPA) compound and viologen compound Dissolve 4.16 g Fe(TPA) and 1.86 g potassium chloride in deionized water and bring the volume to 25 mL to obtain a 0.4 mol / L Fe(TPA) positive electrode electrolyte. Dissolve 6.40 g of viologen compound and 1.86 g of potassium chloride in deionized water and bring the volume to 25 mL to obtain a 0.5 mol / L viologen compound negative electrode electrolyte.

[0070] The battery was then assembled in an argon-filled glove box. Specifically, 5 mL of positive electrolyte and 10 mL of negative electrolyte were used. A titanium plate was used as the current collector, and a 3 mm thick graphite felt was used as the electrode. An anion exchange membrane (DSV) was used to separate the positive and negative electrolytes. The electrolyte was pumped into the battery assembly using a peristaltic pump at a flow rate of 60 mL / min. The positive and negative electrodes of the battery were then connected to the battery testing system, and a current density of 10 mA / cm² was applied. 2 Perform constant current charge and discharge tests on the battery.

[0071] Battery cycle performance such as Figure 8 As shown, 10 mA / cm 2 Under these conditions, the battery can provide a capacity of ~20 Ah / L, while maintaining a stable energy efficiency of ~67%. After 10 cycles, the capacity retention is close to 90%, and the coulombic efficiency per cycle is close to 100%.

[0072] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing an iron-based positive electrode electrolyte, characterized in that: include, Ferrous chloride and tris(2-pyridylmethyl)amine (TPA) were dissolved separately in acetonitrile, mixed and stirred to react. Then, an antisolvent was added to the reaction solution to precipitate the precipitate. After filtration, washing and drying, the iron-based complex Fe(TPA) was obtained, which is the active material of the iron-based positive electrode electrolyte.

2. The preparation method according to claim 1, characterized in that: The molar ratio of ferrous chloride to TPA is 1:

1.

3. The preparation method according to claim 1, characterized in that: The temperature of the stirring reaction is 25–90°C; the time of the stirring reaction is 0.5–24 h.

4. The preparation method according to claim 1, characterized in that: The antisolvent is selected from at least one of diethyl ether, acetone, ethyl acetate, chloroform, and dichloromethane.

5. The preparation method according to claim 1, characterized in that: The drying process is vacuum drying, and the drying temperature is 30–80°C.

6. The iron-based complex positive electrode electrolyte prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The structure of the iron-based complex Fe(TPA) is as follows: 。 7. The application of the iron-based complex cathode electrolyte as described in claim 6 in an aqueous flow battery, characterized in that: The iron-based complex cathode electrolyte is used in single cells or in stacks of multiple single cells.

8. The application as described in claim 7, characterized in that: The aqueous flow battery includes a positive electrolyte, a negative electrolyte, positive and negative electrodes, a current collector, a separator, and a supporting electrolyte; the active material of the positive electrolyte is an iron-based complex Fe(TPA), and the active material of the negative electrolyte is a water-soluble viologen compound.

9. The application as described in claim 8, characterized in that: The supporting electrolyte is a mixed electrolyte solution of potassium chloride and potassium sulfate, and the concentration of the supporting electrolyte in the electrolyte is 1.0 to 2.0 mol / L; the mixing ratio of potassium chloride and potassium sulfate is 0:10 to 10:

0.

10. The application as described in claim 8, characterized in that: The concentration of the iron-based complex Fe(TPA) in the positive electrode electrolyte is 0.01–0.62 mol / L.

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