Electrolyte containing redox medium and preparation and application thereof

Abstract

The invention discloses an electrolyte containing a redox medium as well as preparation and application of the electrolyte. The positive electrode electrolyte and the negative electrode electrolyte comprise tetravalent or trivalent vanadium ions, mixed acid, an iron ion additive and water, the iron ion additive is composed of iron phthalocyanine and a second iron-containing compound, and the second iron-containing compound comprises at least one of ferric acetylacetonate, heme iron and iron trifluoromethanesulfonate. The preparation method comprises the following steps: activating vanadium pentoxide in mixed acid, adding water to obtain a mixed solution, and adding a reducing agent into the mixed solution to react to obtain an initial mother solution; adding an iron ion additive into the initial mother solution, and uniformly mixing to obtain a positive electrode electrolyte; and electrolyzing the initial mother liquor to obtain electrolyte containing trivalent vanadium ions, adding an iron ion additive into the electrolyte, and uniformly mixing to obtain the negative electrode electrolyte. The charge-discharge polarization is reduced by using a small amount of iron ion additive containing iron phthalocyanine; the capacity fading caused by pentavalent vanadium precipitation is released; and the energy efficiency and the cycling stability of the battery are improved.

Description

Technical Field

[0001] The invention relates to a vanadium liquid flow battery electrolyte, in particular to a vanadium liquid flow battery electrolyte containing a redox medium and the preparation and application thereof. Background Art

[0002] With the continuous growth of global energy demand and the rapid development of renewable energy, large-scale long-term energy storage technology is gradually becoming a rigid demand. All-vanadium liquid flow battery is a kind of energy storage technology with long life and high safety. It is considered to be one of the most suitable representative technologies for long-term energy storage. It is widely used in the storage of renewable energy, peak shaving and valley filling of power grid, emergency power supply in remote areas, etc.

[0003] The positive and negative electrolytes in the all-vanadium flow battery electrolyte are composed of a single vanadium element ion solution with different valence states. The positive electrode pair is VO 2+ / VO2 + , the negative electrode pair is V 3+ / V 2+ , avoiding cross contamination caused by different element ions penetrating through the membrane. Theoretically, vanadium electrolyte can be recycled indefinitely, however, high-valent VO2 + It is easy to hydrolyze to form V2O5 precipitate, which is difficult to dissolve and recover, making the battery irreversible.

[0004] To address this problem, the researchers increased the concentration of sulfuric acid to inhibit VO2 + The hydrolysis reaction of ions will lead to the problem of VOSO4 crystal precipitation; the researchers also stabilized VO2 by introducing phosphoric acid + ions, inhibiting their hydrolysis, but there will also be the problem of VOPO4 crystal precipitation. On the other hand, researchers introduced stabilizers into the positive electrode electrolyte, which were adsorbed on the surface of the V(V) initial particle core to inhibit or even eliminate the growth or continued formation of precipitated particles, but this would lead to increased polarization and damage its electrochemical performance. Therefore, in order to further improve the energy density and cycle life of all-vanadium liquid flow batteries, it is urgent to solve the problem of positive electrode VO 2+ / VO2 + Reversible transformation and elimination of VO2 + Capacity fade due to hydrolysis. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an electrolyte containing a redox medium to solve the problem of capacity attenuation of vanadium flow batteries. Another purpose of the present invention is to propose a method for preparing an electrolyte containing a redox medium to solve the problem of how to prepare an electrolyte containing a redox medium. The third purpose of the present invention is to propose the application of an electrolyte containing a redox medium in a vanadium flow battery to solve the problem of how to prepare a vanadium flow battery.

[0006] Technical solution: The electrolyte containing a redox medium described in the present invention includes a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte contains tetravalent vanadium ions, a mixed acid, an iron ion additive and water, and the negative electrode electrolyte contains trivalent vanadium ions, a mixed acid, an iron ion additive and water, wherein the iron ion additive is composed of iron phthalocyanine and a second iron-containing compound, and the second iron-containing compound includes at least one of acetylacetonate iron, heme iron, and iron trifluoromethanesulfonate.

[0007] Preferably, the mixed acid includes at least two of hydrochloric acid, sulfuric acid, phosphoric acid, perchloric acid, methanesulfonic acid, and hydrogen bromide.

[0008] Preferably, the final concentration of hydrogen ions in the positive electrode electrolyte is 1-10 mol / L, and the final concentration of hydrogen ions in the negative electrode electrolyte is 1-10 mol / L.

[0009] Preferably, the final concentration of tetravalent vanadium ions in the positive electrode electrolyte is 1-2.2 mol / L, and the final concentration of trivalent vanadium ions in the negative electrode electrolyte is 1-2.2 mol / L.

[0010] Preferably, the final concentration of iron ions in the positive electrode electrolyte is 0.02-1 mol / L, and the final concentration of iron ions in the negative electrode electrolyte is 0.02-1 mol / L.

[0011] Another aspect of the present invention discloses a method for preparing the above-mentioned electrolyte containing a redox medium, comprising the following steps:

[0012] (1) activating vanadium pentoxide in a mixed acid to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding a reducing agent to the mixed solution to react to obtain an initial mother solution;

[0013] (2) adding an iron ion additive to the initial mother solution and mixing well to obtain a positive electrode electrolyte;

[0014] (3) electrolyzing the initial mother liquor to obtain an electrolyte containing trivalent vanadium ions, adding an iron ion additive to the electrolyte containing trivalent vanadium ions and mixing well to obtain a negative electrode electrolyte.

[0015] Specifically, in step (1), the activation condition is 50-100° C. for 1-12 h under magnetic stirring at 200-800 rpm. The reducing agent can be oxalic acid, and the amount of oxalic acid used is the same as the molar amount of V2O5 used.

[0016] Preferably, the iron ion additive consists of iron phthalocyanine and heme iron in a molar ratio of 1:0.1-2.

[0017] Preferably, the final concentration of iron phthalocyanine in the positive electrode electrolyte is at least 0.01 mol / L, and the positive electrode electrolyte contains sulfuric acid with a final concentration of 1-3 mol / L and hydrochloric acid with a final concentration of 0.1-3 mol / L; the final concentration of iron phthalocyanine in the negative electrode electrolyte is at least 0.01 mol / L, and the negative electrode electrolyte contains sulfuric acid with a final concentration of 1-3 mol / L and hydrochloric acid with a final concentration of 0.1-3 mol / L.

[0018] Preferably, in step (3), the method for electrolyzing the initial mother solution is: placing equal volumes of the initial mother solution on the positive and negative electrodes of the battery respectively, and applying power at 10-400 mA / cm 2 An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions are respectively prepared by electrolysis under electric current.

[0019] The third aspect of the present invention discloses the use of the above-mentioned electrolyte containing redox mediator in a vanadium redox flow battery.

[0020] The present invention also provides a vanadium flow battery with a redox medium, wherein both the positive and negative electrodes use carbon felt as electrodes, and the carbon felt electrode has a large active area, which is beneficial to the cycle performance at a high rate; the carbon felt used in the vanadium flow battery has an area of ​​2×2 cm 2 The battery separator uses the commercial Nafion 117 proton membrane commonly used in liquid flow batteries. The area of ​​the proton exchange membrane is also 3.5×3.5cm 2 , to ensure that the positive and negative electrolytes are completely physically separated. The electrolyte uses the above-mentioned electrolyte containing redox medium;

[0021] The present invention adopts iron ion additives to catalyze and accelerate the electrolysis process of tetravalent vanadium and pentavalent vanadium, reduce the polarization of charge and discharge; release the capacity decay caused by pentavalent vanadium precipitation; improve the energy efficiency and cycle stability of the battery. Its working principle is that divalent iron / trivalent iron has a lower redox potential (0.771V vs. SHE), while the redox potential of tetravalent vanadium / pentavalent vanadium is 0.991V vs. SHE, which means that divalent iron ions can reduce pentavalent vanadium including precipitated vanadium pentoxide solid to tetravalent vanadium ions through spontaneous chemical reactions, which are themselves oxidized to trivalent iron ions; at the same time, since divalent / trivalent iron ions are both present in the electrolyte in a liquid state, trivalent iron ions can flow to the surface of the positive electrode through the positive electrode peristaltic pump to undergo an electrochemical reaction, and are reduced to divalent iron ions again during the discharge process, and flow back to the positive electrode electrolyte storage tank again, and react chemically with the precipitated vanadium pentoxide solid. The specific reaction principles of the positive and negative electrodes during charging and discharging are shown as follows (1), (2), (3) and (4):

[0022] positive electrode:

[0023]

[0024]

[0025] negative electrode:

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0027] The present invention uses a small amount of iron ion additive containing iron phthalocyanine as a redox medium to catalyze and accelerate the electrolysis process of tetravalent vanadium and pentavalent vanadium, reduce the polarization of charge and discharge, release the capacity decay caused by pentavalent vanadium precipitation, and improve the energy efficiency and cycle stability of the battery. The iron salt additive of the present invention is pollution-free, safe and reliable, and has price and resource advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The specific capacity and voltage curves of the vanadium liquid flow battery of Example 1 at different current densities;

[0029] Figure 2 The specific capacity and voltage curves of the vanadium liquid flow battery of Example 2 at different current densities;

[0030] Figure 3 The vanadium redox flow battery in Comparative Example 1 and Example 1 at 180 mA / cm 2 Below, the comparison curve of energy density and discharge median voltage;

[0031] Figure 4 The vanadium redox flow battery in Comparative Example 1 and Example 1 at 180 mA / cm 2 Below is the comparison of the charge and discharge curves of the 30th cycle. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0033] Embodiment 1: An electrolyte containing a redox medium comprises a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte comprises tetravalent vanadium ions with a final concentration of 1.5 mol / L, sulfuric acid with a final concentration of 1.5 mol / L, hydrochloric acid with a final concentration of 1 mol / L, iron phthalocyanine with a final concentration of 0.05 mol / L, heme iron with a final concentration of 0.05 mol / L and water, and the negative electrode electrolyte comprises trivalent vanadium ions with a final concentration of 1.5 mol / L, sulfuric acid with a final concentration of 1.5 mol / L, hydrochloric acid with a final concentration of 1 mol / L, iron phthalocyanine with a final concentration of 0.05 mol / L, heme iron with a final concentration of 0.05 mol / L and water.

[0034] The preparation method of the above-mentioned electrolyte containing redox medium is as follows:

[0035] (1) placing vanadium pentoxide in a mixed acid of sulfuric acid and hydrochloric acid at a molar ratio of V2O5:H2SO4:HCl of 1.5:1.5:1, maintaining activation at 80°C for 8 h under magnetic stirring at 500 rpm to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding oxalic acid with the same molar amount of V2O5 to the mixed solution to react and obtain an initial mother solution;

[0036] (2) adding iron phthalocyanine and heme iron in a molar ratio of 1:1 to the initial mother solution, and mixing them to obtain a positive electrode electrolyte;

[0037] (3) Place equal volumes (100 mL) of the initial mother solution at the positive and negative electrodes of the battery and apply power at 250 mA / cm 2 An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions were prepared by electrolysis for 16 hours under electric current, and iron phthalocyanine and heme iron in a molar ratio of 1:1 were added to the electrolyte containing trivalent vanadium ions and mixed to obtain a negative electrode electrolyte.

[0038] Example 2: An electrolyte containing a redox medium, comprising a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte comprises tetravalent vanadium ions with a final concentration of 2 mol / L, sulfuric acid with a final concentration of 1 mol / L, hydrochloric acid with a final concentration of 3 mol / L, iron phthalocyanine with a final concentration of 0.01 mol / L, heme iron with a final concentration of 0.02 mol / L, and water, and the negative electrode electrolyte comprises trivalent vanadium ions with a final concentration of 2 mol / L, sulfuric acid with a final concentration of 1 mol / L, hydrochloric acid with a final concentration of 3 mol / L, iron phthalocyanine with a final concentration of 0.01 mol / L, acetylacetonate iron with a final concentration of 0.02 mol / L, and water.

[0039] The preparation method of the above-mentioned electrolyte containing redox medium is as follows:

[0040] (1) placing vanadium pentoxide in a mixed acid of sulfuric acid and hydrochloric acid at a molar ratio of V2O5:H2SO4:HCl of 2:1:3, maintaining activation at 50°C for 12 h under magnetic stirring at 200 rpm to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding oxalic acid with the same molar amount of V2O5 to the mixed solution to react and obtain an initial mother solution;

[0041] (2) adding iron phthalocyanine and heme iron in a molar ratio of 1:2 to the initial mother solution, and mixing them to obtain a positive electrode electrolyte;

[0042] (3) Place equal volumes (100 mL) of the initial mother solution at the positive and negative electrodes of the battery and apply power at 400 mA / cm 2An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions were prepared by electrolysis for 12 hours under electric current, and iron phthalocyanine and iron acetylacetonate in a molar ratio of 1:2 were added to the electrolyte containing trivalent vanadium ions and mixed to obtain a negative electrode electrolyte.

[0043] Example 3: An electrolyte containing a redox medium, comprising a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte comprises tetravalent vanadium ions with a final concentration of 1 mol / L, phosphoric acid with a final concentration of 3 mol / L, perchloric acid with a final concentration of 0.1 mol / L, iron phthalocyanine with a final concentration of 0.5 mol / L, iron trifluoromethanesulfonate with a final concentration of 0.05 mol / L and water, and the negative electrode electrolyte comprises trivalent vanadium ions with a final concentration of 1 mol / L, phosphoric acid with a final concentration of 3 mol / L, perchloric acid with a final concentration of 0.1 mol / L, iron phthalocyanine with a final concentration of 0.5 mol / L, heme iron with a final concentration of 0.05 mol / L and water.

[0044] The preparation method of the above-mentioned electrolyte containing redox medium is as follows:

[0045] (1) placing vanadium pentoxide in a mixed acid of phosphoric acid and perchloric acid at a molar ratio of V2O5:phosphoric acid:perchloric acid of 1:3:0.1, maintaining the mixture at 100°C for 1 hour under magnetic stirring at 800 rpm to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding oxalic acid having the same molar amount of V2O5 to the mixed solution to obtain an initial mother solution;

[0046] (2) adding iron phthalocyanine and iron trifluoromethanesulfonate in a molar ratio of 1:0.1 to the initial mother solution, and mixing them to obtain a positive electrode electrolyte;

[0047] (3) Place equal volumes (100 mL) of the initial mother solution at the positive and negative electrodes of the battery and apply power at 100 mA / cm 2 An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions were prepared by electrolysis for 14 hours under electric current, and iron phthalocyanine and heme iron in a molar ratio of 1:0.1 were added to the electrolyte containing trivalent vanadium ions and mixed to obtain a negative electrode electrolyte.

[0048] Example 4: An electrolyte containing a redox medium, comprising a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte comprises tetravalent vanadium ions with a final concentration of 2.2 mol / L, methanesulfonic acid with a final concentration of 2 mol / L, hydrogen bromide with a final concentration of 1 mol / L, iron phthalocyanine with a final concentration of 0.1 mol / L, heme iron with a final concentration of 0.05 mol / L, and water, and the negative electrode electrolyte comprises trivalent vanadium ions with a final concentration of 2.2 mol / L, methanesulfonic acid with a final concentration of 2 mol / L, hydrogen bromide with a final concentration of 1 mol / L, iron phthalocyanine with a final concentration of 0.1 mol / L, heme iron with a final concentration of 0.05 mol / L, and water.

[0049] The preparation method of the above-mentioned electrolyte containing redox medium is as follows:

[0050] (1) placing vanadium pentoxide in a mixed acid of methanesulfonic acid and hydrogen bromide at a molar ratio of V2O5:methanesulfonic acid:hydrogen bromide of 2.2:2:1, maintaining the mixture at 70°C for 6 h under magnetic stirring at 600 rpm to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding oxalic acid having the same molar amount of V2O5 to the mixed solution to obtain an initial mother solution;

[0051] (2) adding iron phthalocyanine and heme iron in a molar ratio of 2:1 to the initial mother solution, and mixing them to obtain a positive electrode electrolyte;

[0052] (3) Place equal volumes (100 mL) of the initial mother solution at the positive and negative electrodes of the battery and apply power at 300 mA / cm 2 An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions were prepared by electrolysis for 16 hours under electric current, and iron phthalocyanine and heme iron in a molar ratio of 2:1 were added to the electrolyte containing trivalent vanadium ions and mixed to obtain a negative electrode electrolyte.

[0053] Comparative Example 1: The rest is the same as Example 1, except that:

[0054] The iron phthalocyanine with a final concentration of 0.05 mol / L and the heme iron with a final concentration of 0.05 mol / L in the positive and negative electrolytes were replaced with ferrous sulfate with a final concentration of 0.1 mol / L.

[0055] Comparative Example 2: The rest is the same as Example 1, except that:

[0056] The final concentration of 0.05 mol / L iron phthalocyanine and the final concentration of 0.05 mol / L heme iron in the positive and negative electrolytes were replaced with a final concentration of 0.1 mol / L ferrocene.

[0057] Comparative Example 3: The rest is the same as Example 1, except that:

[0058] The iron phthalocyanine with a final concentration of 0.05 mol / L and the heme iron with a final concentration of 0.05 mol / L in the positive and negative electrolytes were replaced with ammonium ferrous sulfate with a final concentration of 0.1 mol / L.

[0059] Comparative Example 4: The rest is the same as Example 1, except that:

[0060] The iron phthalocyanine with a final concentration of 0.05 mol / L and the heme iron with a final concentration of 0.05 mol / L in the positive and negative electrolytes were replaced with iron acetylacetonate with a final concentration of 0.1 mol / L.

[0061] Comparative Example 5: The rest is the same as Example 1, except that:

[0062] The iron phthalocyanine with a final concentration of 0.05 mol / L and the heme iron with a final concentration of 0.05 mol / L in the positive and negative electrolytes were replaced with iron trifluoromethanesulfonate with a final concentration of 0.1 mol / L.

[0063] Comparative Example 6: The rest is the same as Example 1, except that:

[0064] The iron phthalocyanine in both the positive and negative electrolytes was replaced with heme iron.

[0065] Comparative Example 7: The rest is the same as Example 1, except that:

[0066] The iron phthalocyanine in both the positive and negative electrolytes was replaced with iron trifluoromethanesulfonate.

[0067] Comparative Example 8: The rest is the same as Example 1, except that:

[0068] The iron phthalocyanine in both the positive and negative electrolytes was replaced with iron acetylacetonate.

[0069] Comparative Example 9: The rest is the same as Example 1, except that:

[0070] The heme iron in both the positive and negative electrolytes was replaced with iron phthalocyanine.

[0071] Comparative Example 10: The rest is the same as Example 1, except that:

[0072] The heme iron in both the positive and negative electrolytes was replaced with ferrocene.

[0073] Comparative Example 11: The rest is the same as Example 1, except that:

[0074] The heme iron in both the positive and negative electrolytes is replaced with ferrous sulfate.

[0075] Comparative Example 12: The rest is the same as Example 1, except that:

[0076] Iron phthalocyanine and heme iron were not added.

[0077] The positive and negative electrolytes prepared in Examples 1-4 and Comparative Examples 1-12 were respectively applied to the assembly of flow batteries, using carbon felt as electrodes and Nafion 117 proton membrane as diaphragm. The electrode projected area was 4 cm 2 .

[0078] The assembled liquid flow battery was subjected to charge and discharge tests under constant current density conditions, with 1.75 V and 0.8 V as the charge cutoff condition and discharge cutoff condition, respectively.

[0079] like Figure 1 and Figure 2 As shown, the liquid flow battery assembled using the present invention has excellent electrochemical performance at different current densities.

[0080] like Figure 3 As shown, in Example 1, a specific iron-containing organic compound is used as a redox medium, and the lower redox potential of divalent iron ions is used to reduce the pentavalent vanadium precipitated during the discharge process. At the same time, the divalent iron ions are oxidized to trivalent iron, transported back to the electrode through a pipeline and reduced to divalent iron ions to reduce the pentavalent vanadium again. The attenuation of energy density caused by the precipitation of pentavalent vanadium during the discharge process is avoided, and the discharge median voltage is stabilized during the cycle process, thereby improving the cycle life of the vanadium liquid flow battery. By comparing the vanadium liquid flow battery in Comparative Example 1 and Example 1 at 180mA / cm 2 The energy density and the median discharge voltage under the current density show that the vanadium flow battery assembled by the electrolyte in Example 1 still maintains an energy density of 22.7Wh / L after 70 cycles. The energy density of the vanadium flow battery assembled by the electrolyte in Comparative Example 1 is already lower than 20Wh / L after 50 cycles, and the median discharge voltage is significantly lower than that in Example 1. The main reason for this result is that the donors of iron ions are different. Although the inorganic iron salt in Comparative Example 1 can also provide ferrous ions, it cannot solve the capacity decay problem of the flow battery. The combination of iron phthalocyanine and heme iron in Example 1 successfully solves the capacity decay problem of the flow battery and effectively improves the cycle life of the flow battery. The specific organic groups in iron phthalocyanine and heme iron play an important role in the generation of this effect.

[0081] like Figure 4 As shown, by comparing the vanadium redox flow battery in Comparative Example 1 and Example 1 at 180 mA / cm 2 Voltage curve after 30 cycles at the current density. The introduction of iron phthalocyanine and heme iron can catalyze and accelerate the conversion process of tetravalent vanadium and pentavalent vanadium, significantly reduce the precipitation and accumulation of pentavalent vanadium during discharge, inhibit the increase of discharge voltage polarization, and significantly improve the energy efficiency of the battery.

[0082] The electrochemical performance of the flow batteries assembled using Examples 1-4 and Comparative Examples 1-12 after 100 cycles of charge and discharge was further tested and statistically analyzed, and the results are as follows:

[0083] Table 1 Effects of different electrolytes on the cycle performance of flow batteries

[0084] Group Energy density (Wh / L) Discharge median voltage (V) Example 1 21.8 1.17 Example 2 20.3 1.12 Example 3 20.1 1.11 Example 4 20.7 1.14 Comparative Example 1 15.4 1.03 Comparative Example 2 15.7 1.05 Comparative Example 3 14.9 1.01 Comparative Example 4 15.5 1.04 Comparative Example 5 15.8 1.05 Comparative Example 6 15.7 1.05 Comparative Example 7 15.6 1.04 Comparative Example 8 15.3 1.04 Comparative Example 9 15.4 1.05 Comparative Example 10 15.0 1.04 Comparative Example 11 14.8 1.01 Comparative Example 12 15.1 1.03

[0085] In the results of Table 1, the energy density and median discharge voltage of Comparative Examples 1-8 are significantly lower than those of Example 1. After 100 cycles, a large capacity decay occurs, and the cycle performance of the battery is significantly inferior to that of Example 1. It can be seen that in the absence of iron phthalocyanine, a variety of organic or inorganic compounds containing iron ions, whether added alone or in combination to the electrolyte of a vanadium flow battery, cannot significantly improve the cycle performance of the flow battery, and the capacity decay problem of the battery is more prominent. Iron phthalocyanine is a key additive to improve the cycle performance of flow batteries. However, it can be seen from Comparative Example 9 that the improvement of the cycle performance of flow batteries by iron phthalocyanine when added alone is relatively limited, and the addition of iron phthalocyanine alone cannot solve the capacity decay problem of vanadium flow batteries. However, when specific iron-containing organic compounds such as heme iron are used in combination with iron phthalocyanine, the two synergistically improve the cycle performance of the flow battery and successfully avoid the substantial capacity decay of the battery. Of course, it can be seen from Comparative Examples 10-11 that only some iron-containing organic compounds can assist in improving the effect of iron phthalocyanine, while inorganic ferrous salts do not have a synergistic effect.

Claims

1. An electrolyte containing a redox medium, characterized in that: The invention comprises a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte comprises tetravalent vanadium ions, a mixed acid, an iron ion additive and water, and the negative electrode electrolyte comprises trivalent vanadium ions, a mixed acid, an iron ion additive and water, wherein the iron ion additive comprises iron phthalocyanine and a second iron-containing compound, and the second iron-containing compound comprises at least one of ferric acetylacetonate, heme iron and iron trifluoromethanesulfonate.

2. The electrolyte containing a redox medium according to claim 1, characterized in that: The mixed acid includes at least two of hydrochloric acid, sulfuric acid, phosphoric acid, perchloric acid, methanesulfonic acid, and hydrogen bromide.

3. The electrolyte containing a redox medium according to claim 1, characterized in that: The final concentration of hydrogen ions in the positive electrode electrolyte is 1-10 mol / L, and the final concentration of hydrogen ions in the negative electrode electrolyte is 1-10 mol / L.

4. The electrolyte containing a redox medium according to claim 1, characterized in that: The final concentration of tetravalent vanadium ions in the positive electrode electrolyte is 1-2.2 mol / L, and the final concentration of trivalent vanadium ions in the negative electrode electrolyte is 1-2.2 mol / L.

5. The electrolyte containing a redox medium according to claim 1, characterized in that: The final concentration of iron ions in the positive electrode electrolyte is 0.02-1 mol / L, and the final concentration of iron ions in the negative electrode electrolyte is 0.02-1 mol / L.

6. The method for preparing an electrolyte containing a redox medium according to any one of claims 1 to 5, characterized in that: The steps include: (1) activating vanadium pentoxide in a mixed acid to obtain a vanadium activation solution, adding water to the vanadium activation solution to obtain a mixed solution, and adding a reducing agent to the mixed solution to react to obtain an initial mother solution; (2) adding an iron ion additive to the initial mother solution and mixing well to obtain a positive electrode electrolyte; (3) electrolyzing the initial mother liquor to obtain an electrolyte containing trivalent vanadium ions, adding an iron ion additive to the electrolyte containing trivalent vanadium ions and mixing well to obtain a negative electrode electrolyte.

7. The method for preparing an electrolyte containing a redox medium according to claim 6, characterized in that: The iron ion additive consists of iron phthalocyanine and heme iron in a molar ratio of 1:0.1-2.

8. The method for preparing an electrolyte containing a redox medium according to claim 6, characterized in that: The final concentration of iron phthalocyanine in the positive electrode electrolyte is at least 0.01 mol / L, and the positive electrode electrolyte contains sulfuric acid with a final concentration of 1-3 mol / L and hydrochloric acid with a final concentration of 0.1-3 mol / L; the final concentration of iron phthalocyanine in the negative electrode electrolyte is at least 0.01 mol / L, and the negative electrode electrolyte contains sulfuric acid with a final concentration of 1-3 mol / L and hydrochloric acid with a final concentration of 0.1-3 mol / L.

9. The method for preparing an electrolyte containing a redox medium according to claim 8, characterized in that: In step (3), the method of electrolyzing the initial mother solution is as follows: placing equal volumes of the initial mother solution on the positive and negative electrodes of the battery respectively, and applying power at 10-400 mA / cm 2 An electrolyte containing pentavalent vanadium ions and an electrolyte containing trivalent vanadium ions are respectively prepared by electrolysis under electric current.

10. Use of the electrolyte containing a redox medium according to any one of claims 1 to 5 in a vanadium redox flow battery.

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