Alkaline total-iron flow battery negative electrode electrolyte and preparation method thereof

Abstract

The invention belongs to the technical field of flow battery energy storage, and particularly relates to an alkaline all-iron flow battery negative electrode electrolyte and a preparation method thereof. The negative electrode electrolyte is prepared from ferric salt, a chelating agent, supporting electrolyte and water at a certain temperature, the total iron concentration is 0.1-1.0 M, the molar ratio of the chelating agent to the ferric salt is 2.0-3.0, the concentration of the supporting electrolyte is 0-2.0 mol / L, and the pH value is 13.0-14.0. Pyridinol is adopted as a complexing agent in the negative electrode electrolyte and forms a stable six-coordination structure with iron ions, so that the stability of the negative electrode electrolyte is enhanced, generation of ferric hydroxide precipitates can be effectively inhibited, and the stability of the iron ions is improved; the iron pyridinol organic metal ligand is large in molecule size, a formed chelate is large in steric effect, the transmembrane migration degree of iron ions / ferrous ions is reduced, the cycle life of the total-iron flow battery is greatly prolonged, and the iron pyridinol organic metal ligand can be widely applied to various aqueous flow batteries.

Description

Technical Field

[0001] The invention relates to the technical field of liquid flow batteries, and in particular to an alkaline all-iron liquid flow battery negative electrode electrolyte and a preparation method thereof. Background Art

[0002] In recent years, alkaline all-iron flow batteries have developed rapidly. By the end of 2023, there will be commercial energy storage application demonstration projects, which are likely to surpass the development trend of acidic all-iron flow batteries. Gong et al. 6 3- / 4- The first fully soluble all-iron flow battery is made for the redox couple, and the battery energy efficiency has been greatly improved compared with the traditional acidic all-iron. The alkaline iron-based negative electrode electrolytes disclosed in patents such as CN118336062A, CN113764714B, CN114709459B and CN116259810A all use TEA or TEA derivatives as the main ligands, and use small molecule organic imidazoles, polysaccharide alcohols, malonic acid, citric acid or glycine as auxiliary ligands to form a stable six-coordinate complex with iron ions. However, during the long-life cycle of the battery, these small molecule organics are easy to fall off and penetrate the diaphragm, resulting in the conversion of Fe-TEA / TEA derivatives into five-coordinate complexes. Under strong alkaline conditions (pH greater than 14.0), iron hydroxide precipitation and iron element are easily formed, and the battery capacity decays quickly and the cycle life is short.

[0003] Although both acidic all-iron flow batteries and strongly alkaline all-iron flow batteries have commercial demonstration devices, the system still has problems such as hydrogen evolution, iron dendrites and iron hydroxide precipitation that are difficult to solve. Therefore, it is urgent to develop a new alkaline all-iron flow battery that can perfectly solve a series of problems existing under strong acid and strong alkaline conditions. In the present invention, there are at least two hydrophilic groups (-OH) and one pyridine ring in the pyridinol molecule. Under alkaline conditions, the N atom, -OH in the pyridinol and the iron ion are chelated with a 2:1 molar ratio to form a stable six-membered ring network structure. The pyridinol iron has a high complex constant and good chemical stability. Even under strong alkaline conditions (pH = 13.0 ~ 14.0), it will not dissociate metallic iron ions, forming iron hydroxide precipitation, which is an essential problem affecting the long-term operation of the battery, greatly extending the cycle life of the all-iron flow battery, and can be widely used in various aqueous flow batteries. Therefore, it is very beneficial to invent an alkaline all-iron flow battery negative electrode electrolyte and its preparation method. Summary of the invention

[0004] In order to solve the technical problems existing in the above-mentioned acidic or alkaline all-iron liquid flow batteries, the present invention provides a negative electrode electrolyte for an alkaline all-iron liquid flow battery and a preparation method thereof, which can effectively inhibit the formation of iron hydroxide precipitation, improve the stability of iron ions, and greatly extend the cycle life of the all-iron liquid flow battery.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0006] An alkaline all-iron liquid flow battery negative electrode electrolyte, characterized in that: the negative electrode electrolyte is an alkaline aqueous solution composed of iron salt, pyridinol, and supporting electrolyte, the total iron concentration is 0.1-1.0 mol / L, the molar ratio of pyridinol to iron is 2.0-3.0, the supporting electrolyte concentration is 0-2.0 mol / L, and the inorganic base is used to adjust the pH value to 13.0-14.0.

[0007] A better technical solution of the present invention is that the pyridinol is one or more of 2,6-pyridine dimethanol, 2,4,6-pyridinetrimethanol, 3-hydroxy-2,6-pyridine dimethanol, 2,6-bis(hydroxymethyl)-4-methoxypyridine, and 1-(6-(1-hydroxy-ethyl)-pyridin-2-yl)-ethanol.

[0008] The iron salt is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric carbonate and ferric hydroxide, wherein the total iron concentration is 0.1-1.0 mol / L.

[0009] The supporting electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate, wherein the supporting electrolyte concentration is 0 to 2.0 mol / L.

[0010] The inorganic base is one or more of ammonia water, sodium hydroxide, potassium hydroxide, and lithium hydroxide, wherein the inorganic base is used to adjust the pH value to 13.0-14.0.

[0011] The pyridinol is one or more of 2,6-pyridine dimethanol, 2,4,6-pyridinetrimethanol, 3-hydroxy-2,6-pyridine dimethanol, 2,6-bis(hydroxymethyl)-4-methoxypyridine, and 1-(6-(1-hydroxy-ethyl)-pyridin-2-yl)-ethanol, wherein the pyridinol / Fe molar ratio is 2.0 to 3.0.

[0012] The negative electrode electrolyte preparation method comprises the following steps: weighing a certain mass of iron salt, pyridine alcohol, and supporting electrolyte and dissolving them in an appropriate amount of distilled water, then adjusting the pH value of the above solution to 13.0-14.0 with an inorganic base, stirring at 40-60° C. for 24 hours, cooling to room temperature, and filtering to obtain the negative electrode electrolyte.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] (1) In the present invention, the pyridinol molecules have at least two hydrophilic groups (-OH) and one pyridine ring. Under alkaline conditions, the N atom, -OH and iron ions in the pyridinol are chelated with a molar ratio of 2:1 to form a stable six-membered ring network structure. The pyridinol iron has a high complex constant and good chemical stability. Even under strong alkaline conditions (pH = 13.0-14.0), the metal iron ions will not be dissociated, which greatly improves the cycle stability of the negative electrode electrolyte.

[0015] (2) The molecular size of the active substance pyridinol iron in the negative electrode electrolyte of the present invention is relatively large, and the permeability through the ion exchange membrane is greatly reduced. The ion exchange membrane can effectively block the migration of the active substance by only treating it with distilled water. The assembled battery has high coulombic efficiency, good stability, and low capacity attenuation rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The structure of the organometallic complex of iron-2,6-pyridine dimethanol

[0017] Figure 2 Cyclic voltammetry curves (CV curves) of 500 groups of negative electrode electrolytes in Example 1

[0018] Figure 3 Coulombic efficiency, energy efficiency and voltage efficiency of the alkaline all-iron flow battery composed of Example 1

[0019] Figure 4 Capacity retention rate of all-iron liquid flow batteries composed of Example 1 and Comparative Examples 1 to 3 DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the preferred implementation schemes of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0021] The present invention is further described in detail below through comparative examples and embodiments.

[0022] 1 Preparation process of all-iron liquid flow battery electrolyte

[0023] 1.1 Positive Electrolyte Preparation Process:

[0024] Weigh a certain mass of ferrocyanide and supporting electrolyte and dissolve them in an appropriate amount of distilled water, then adjust the pH value of the solution to 13.0-14.0 with alkali solution, stir at 40-60°C for 24 hours, and cool to room temperature to obtain a positive electrode electrolyte.

[0025] 1.2 Negative electrolyte preparation process:

[0026] Weigh a certain mass of iron salt, pyridine alcohol, and supporting electrolyte and dissolve them in an appropriate amount of distilled water, then adjust the pH value of the above solution to 13.0-14.0 with an inorganic base, stir at 40-60°C for 24 hours, cool to room temperature, and filter to obtain a negative electrode electrolyte.

[0027] Example 1

[0028] An alkaline all-iron liquid flow battery negative electrode electrolyte: 0.1 mol ferric chloride, 0.3 mol 2,6-pyridine dimethanol, 1 mol potassium chloride, 1 mol sodium chloride, the pH value is adjusted to 13.0 with sodium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing 0.1M iron-2,6-pyridine dimethanol organic metal complex is prepared.

[0029] Example 2

[0030] An alkaline all-iron liquid flow battery negative electrode electrolyte: 0.2 mol ferric sulfate, 0.5 mol 2,4,6-pyridinetrimethanol, 0.5 mol ammonium chloride, 0.5 mol sodium sulfate, the pH value is adjusted to 13.5 with potassium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing 0.2M iron-2,4,6-pyridinetrimethanol is prepared.

[0031] Example 3

[0032] An alkaline all-iron liquid flow battery negative electrode electrolyte: 0.3 mol ferric nitrate, 0.8 mol 3-hydroxy-2,6-pyridine dimethanol, 0.5 mol potassium sulfate, 0.5 mol ammonium sulfate, the pH value is adjusted to 14.0 with lithium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing 0.3M iron-3-hydroxy-2,6-pyridine dimethanol is prepared.

[0033] Example 4

[0034] An alkaline all-iron liquid flow battery negative electrode electrolyte: 0.5 mol iron carbonate, 1.1 mol, 2, 6-bis(hydroxymethyl)-4-methoxypyridine, 0.25 mol sodium nitrate, 0.25 mol potassium nitrate, the pH value is adjusted to 13.0 with potassium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing 0.5M iron-6-bis(hydroxymethyl)-4-methoxypyridine is prepared.

[0035] Example 5

[0036] An alkaline all-iron flow battery negative electrode electrolyte: 0.8 mol ferric sulfate, 1.6 mol 1-(6-(1-hydroxy-ethyl-pyridin-2-yl)-ethanol, 0.5 mol ammonium chloride, the pH value is adjusted to 13.5 with ammonia water, the volume is fixed to 1L, and a negative electrode electrolyte containing 0.8M iron-1-(6-(1-hydroxy-ethyl-pyridin-2-yl)-ethanol is prepared.

[0037] Example 6

[0038] An alkaline all-iron liquid flow battery negative electrode electrolyte: 1.0 mol iron hydroxide, 2.0 mol 2,6-pyridine dimethanol, the pH value is adjusted to 13.0 with lithium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing 1.0M iron-2,6-pyridine dimethanol is prepared.

[0039] Comparative Example 1

[0040] Negative electrolyte: 0.1 mol ferric chloride, N,N'-ethylenebis-(o-hydroxyphenylglycine), 2 mol potassium chloride, adjust the pH to 13.0 with sodium hydroxide, and adjust the volume to 1 L to prepare a negative electrolyte containing 0.1 M iron-N,N'-ethylenebis-(o-hydroxyphenylglycine) organic metal complex.

[0041] Comparative Example 2

[0042] Negative electrode electrolyte: 0.5 mol ferric chloride, 1.0 mol triethanolamine (TEA), 4 mol KOH, 0.5 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1 L to prepare a negative electrode electrolyte containing 0.5 M Fe-TEA.

[0043] Comparative Example 3

[0044] The positive and negative electrolytes are both ferrous chloride (total iron concentration: 1.0M), hydrochloric acid concentration: 2.0M.

[0045] 2 Electrochemical performance test of all-iron liquid flow battery

[0046] 2.1 Cyclic voltammetry curve (CV curve)

[0047] Experimental conditions: Cyclic voltammetry curve (CV curve): three-electrode mode (electrochemical workstation: Shanghai Chenhua Instrument Co., Ltd. CHI660E), working electrode: glassy carbon electrode (diameter 6mm), counter electrode: platinum wire electrode (15*15*0.1mm), reference electrode: Ag / AgCl, scanning voltage range: -0.6~-1.2V; scanning voltage: 50mv / s, number of cycles: 500 groups, the electrolyte changes after 500 groups of CV curves of the negative electrode electrolyte in Examples 1~6 and Comparative Examples 1~3 are as follows Table 1, and the 500 groups of CV curves of the negative electrode electrolyte in Example 1 are as follows Figure 2 .

[0048] Table 1 Electrochemical experimental phenomena of negative electrode electrolyte

[0049]

[0050] Note: The total iron concentration in Examples 1 to 6 and Comparative Examples 1 to 3 was diluted to 0.1 mol / L with deoxygenated distilled water.

[0051] It can be clearly seen from Table 1 above that after 500 sets of cyclic voltammetry curves (CV curves) of the negative electrode electrolyte in Examples 1 to 6, no iron element was generated on the working electrode, no bubbles were generated, and no red flocculent precipitation was present in the electrolyte; however, in Comparative Example 1, the negative electrode electrolyte had a small amount of iron element on the working electrode, and the electrolyte became slightly turbid; in Comparative Example 2, the negative electrode electrolyte had obvious iron element on the working electrode, accompanied by a large amount of bubbles, and the electrolyte became obviously turbid; in Comparative Example 3, the negative electrode electrolyte had a large amount of iron element on the working electrolyte. Figure 2 It can be seen that the CV curves of 500 groups of negative electrode electrolytes in Example 1 have very good coincidence, which indicates that the negative electrode electrolyte in Example 1 has very good stability.

[0052] In summary, this shows that Examples 1 to 6 have good stability, while the cycle stability of the negative electrode electrolytes in Comparative Examples 1 to 3 is poor.

[0053] 2.2 All-iron flow battery performance test

[0054] (1) Assembly of all-iron flow battery

[0055] The single cell was assembled in the following order: positive electrode aluminum end plate, gold-plated copper plate, graphite current collector, positive electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), ion exchange membrane Nafion212 (soaked in the negative electrode electrolyte for 1 day and then repeatedly washed with distilled water before use), negative electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), graphite current collector, gold-plated copper plate and negative electrode aluminum end plate.

[0056] Liquid flow battery: It is composed of the above-mentioned positive electrode electrolyte and negative electrode electrolyte, positive electrode electrolyte tank, negative electrode electrolyte tank, circulation pump, circulation pipeline and single battery circuit connected in series.

[0057] (2) All-iron flow battery test conditions

[0058] Charge and discharge tester: CT-4008T from Dongguan Xinwei Testing Technology Co., Ltd., charge and discharge mode: constant current charging mode, the volume of the positive and negative electrolytes is 35ml, the flow rate of the positive and negative electrolytes is 150ml / min, nitrogen is introduced for deoxygenation before charge and discharge, current density: 100mA / cm 2 , temperature: 35°C, charge and discharge cut-off voltages are 1.65V and 0.8V respectively, and the number of charge and discharge times is 500. Table 2 shows the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1-6 and Comparative Examples 1-3. Figure 3The coulombic efficiency, voltage efficiency and energy efficiency of the alkaline flow battery of Example 1 are shown. Figure 4 The capacity retention rate of the all-iron liquid flow batteries composed of Example 1 and Comparative Examples 1-3 is shown.

[0059] Table 2 All-iron flow battery performance

[0060]

[0061]

[0062] It can be clearly seen from Table 2 above that the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1-6 are significantly higher than those of Comparative Examples 1-3.

[0063] from Figure 4 It can be seen that the capacity retention rate of the all-iron liquid flow battery composed of Example 1 is still higher than 90% after 500 charge and discharge cycles, and the capacity retention rate is relatively high; however, the capacity retention rate of the all-iron liquid flow battery composed of Comparative Examples 1 to 3 is relatively low after 500 charge and discharge cycles, and the capacity decay is fast, especially the all-iron liquid flow battery composed of Comparative Examples 2 to 3, the capacity decay has decayed by more than 60% after 500 cycles.

[0064] After the experiment was completed, the all-iron liquid flow battery stacks composed of Examples 1 to 6 and Comparative Examples 1 to 3 were disassembled. We found that the ion exchange membranes and graphite felts in the liquid flow batteries composed of Examples 1 to 6 were clean, no iron hydroxide precipitation, no iron element was generated, and the electrolyte was still clear and transparent; however, in the liquid flow batteries composed of Comparative Examples 1 to 3, there were obvious iron elements or red flocculent precipitation of iron hydroxide on the graphite felt, and obvious red flocculent precipitation on the ion exchange membrane, and the positive and negative electrolytes were turbid. This shows that the charge and discharge performance of the alkaline all-iron liquid flow battery composed of Examples 1 to 6 is significantly better than that of Comparative Examples 1 to 3, and the positive and negative electrolytes of the present invention have high charge and discharge activity, few side reactions, low ion permeability, and good cycle stability.

[0065] In summary, the present invention provides an alkaline all-iron flow battery negative electrode electrolyte, using iron-pyridinol as the negative electrode electrolyte active material, with multiple hydrophilic groups (-OH) and 1 pyridine ring, under alkaline conditions, the N atom, -OH and iron ions in pyridinol chelate with a 2: 1 molar ratio to form a stable six-membered ring network structure, pyridinol iron has a high complex constant and good chemical stability, even under strong alkaline (pH = 13.0 ~ 14.0) conditions, it will not dissociate metal iron ions, greatly improving the cycle stability of the negative electrode electrolyte. In the present invention, the molecular size of the negative electrode electrolyte active material pyridinol iron is relatively large, and the permeability through the ion exchange membrane is greatly reduced. The ion exchange membrane can effectively block the migration of active substances by only treating with distilled water. The alkaline all-iron flow battery composed of the alkaline positive electrode electrolyte (ferrocyanate, etc.) has high coulombic efficiency, good stability, and low capacity attenuation rate.

Claims

1. An alkaline all-iron liquid flow battery negative electrode electrolyte, characterized in that: The negative electrode electrolyte is an alkaline aqueous solution composed of iron salt, pyridinol and supporting electrolyte, the total iron concentration is 0.1-1.0 mol / L, the molar ratio of pyridinol to iron is 2.0-3.0, the supporting electrolyte concentration is 0-2.0 mol / L, and the inorganic base is used to adjust the pH value to 13.0-14.

0.

2. The negative electrode electrolyte of an alkaline all-iron liquid flow battery according to claim 1, characterized in that: The pyridinol is one or more of 2,6-pyridine dimethanol, 2,4,6-pyridinetrimethanol, 3-hydroxy-2,6-pyridine dimethanol, 2,6-bis(hydroxymethyl)-4-methoxypyridine, and 1-(6-(1-hydroxy-ethyl)-pyridin-2-yl)-ethanol.

3. The negative electrode electrolyte of an alkaline all-iron liquid flow battery according to claim 1, characterized in that: The iron salt is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric carbonate and ferric hydroxide.

4. The negative electrode electrolyte of an alkaline all-iron liquid flow battery according to claim 1, characterized in that: The supporting electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate.

5. The negative electrode electrolyte of an alkaline all-iron liquid flow battery according to claim 1, characterized in that: The inorganic base is one or more of ammonia water, sodium hydroxide, potassium hydroxide and lithium hydroxide.

6. A method for preparing a negative electrolyte for an alkaline all-iron flow battery according to claim 1, characterized in that: The negative electrode electrolyte preparation method comprises the following steps: weighing iron salt, pyridinol, and supporting electrolyte and dissolving them in an appropriate amount of distilled water, then adjusting the pH value of the solution to 13.0-14.0 with an inorganic base, stirring at 40-60° C. for 24 hours, cooling to room temperature, and filtering to obtain the negative electrode electrolyte.

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