Negative electrode electrolyte and acidic tin-bromine flow battery

Abstract

The invention discloses a negative electrode electrolyte and an acidic tin-bromine flow battery, and belongs to the technical field of energy storage. The negative electrode electrolyte provided by the invention comprises an active substance and a supporting electrolyte, the active substance comprises tetravalent tin salt; the tetravalent tin salt is selected from at least one of tin tetrachloride, tin sulfate, tin bromide and stannate; the supporting electrolyte is selected from at least one of sulfuric acid, hydrochloric acid, perchloric acid, methanesulfonic acid, hydrobromic acid and hydriodic acid. According to the acidic tin-bromine flow battery provided by the invention, a proper tin ion ligand is selected in the negative electrode electrolyte, and the formed tin-based complex can effectively improve the redox kinetics of Sn < 4 + > / Sn < 2 + > and improve the efficiency of the tin-bromine flow battery. Besides, the modification of the negative electrode can further improve the adsorption of reactive active substances and improve the electron transfer rate, and the high specific surface area can provide more active sites, so that the reaction polarization is reduced and the battery performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and particularly relates to a negative electrode electrolyte and an acidic tin-bromine flow battery. Background Art

[0002] Under the background of the "dual carbon" goal, it has become an inevitable trend to develop an energy structure dominated by renewable energy. However, renewable energy such as wind energy, solar energy, and tidal energy has defects such as unstable and discontinuous output, making it difficult to be incorporated into the national power grid on a large scale. Therefore, the development of matching large-scale energy storage devices has become a research hotspot at present and for a long time to come. Among them, flow batteries have become one of the energy storage technologies with good development prospects due to their high safety, long cycle life, independent design of power and capacity, and insensitivity to geographical restrictions.

[0003] The energy density of a flow battery depends on the concentration of the electrolyte, the number of electron transfers of the active substance, and the battery voltage. In traditional flow battery systems, such as all-vanadium flow batteries, due to the limited concentration of the electrolyte and the electrochemical process of single-electron transfer, their energy density is low. Therefore, it has become an inevitable trend to develop a new flow battery system with high solubility and multi-electron transfer. The Sn 4+ / Sn negative electrode couple can achieve four-electron transfer, and the active substance has high solubility (SnCl 4 >4M). At the same time, there is no obvious dendrite problem during the tin metal deposition process, making it a promising negative electrode couple. However, the redox reversibility and kinetics of the high-valent tin electrode couple are poor (Sn 4+ / Sn 2+ ) and the battery efficiency is low. Summary of the Invention

[0004] In view of this, the present invention provides a negative electrode electrolyte and an acidic tin-bromine flow battery, and the main purpose is to solve the technical problems of poor redox reversibility and kinetics of the high-valent tin electrode couple (Sn 4+ / Sn 2+ ) and low battery efficiency.

[0005] On the one hand, the present invention provides a negative electrode electrolyte, and the negative electrode electrolyte includes an active substance and a supporting electrolyte;

[0006] Wherein, the active substance includes a tetravalent tin salt;

[0007] The tetravalent tin salt is selected from at least one of tin tetrachloride, tin sulfate, tin bromide, and stannate;

[0008] The supporting electrolyte is selected from at least one of sulfuric acid, hydrochloric acid, perchloric acid, methanesulfonic acid, hydrobromic acid, and hydroiodic acid.

[0009] The acidic multi-electron transfer tin-bromine flow battery provided by the present invention uses a salt solution containing Sn 4+ as the negative electrode active material. It has the electrochemical property of four-electron transfer and is expected to construct a battery system with high energy density. Moreover, there are no obvious dendrite and hydrogen evolution problems in the tin metal negative electrode. However, Sn 4+ / Sn 2+ exhibits poor redox kinetics and serious polarization. Usually, the tin metal negative electrode is based on the two-electron transfer of Sn 2+ / Sn. Therefore, in the present invention, by changing the types of anions in the negative electrode electrolyte, different tin-based complex structures are constructed, and the electron transfer rate is accelerated by optimizing the bridging adsorption effect of complex ions on the electrode surface, thereby reducing the polarization of the reaction. In addition, by introducing a carbon-based catalyst modification on the electrode surface, the reversibility and electrochemical activity of the negative electrode reaction can be further improved, so as to construct a high-performance, multi-electron transfer tin-bromine flow battery.

[0010] Optionally, the concentration of tin ions in the tetravalent tin salt is 0.1 - 3 mol / L -1 .

[0011] Optionally, the concentration of tin ions in the tetravalent tin salt is 1 - 3 mol / L -1 .

[0012] Optionally, the concentration of tin ions in the tetravalent tin salt is selected from any value of 0.1, 0.5, 1, 1.5, 2, 2.5, 3 or the range value between any two of them, and the unit is mol / L -1 .

[0013] Optionally, the concentration of the supporting electrolyte is 0.1 - 4 mol / L -1 .

[0014] Optionally, the concentration of the supporting electrolyte is 2 - 3 mol / L -1 .

[0015] Optionally, the concentration of the supporting electrolyte is selected from any value of 0.1, 0.5, 1.0, 1.5, 2, 2.5, 3, 3.5, 4 or the range value between any two of them, and the unit is mol / L -1 .

[0016] Optionally, the molar ratio of the concentration of the supporting electrolyte to the concentration of tin ions in the tetravalent tin salt is 0.1 - 30.

[0017] Optionally, the molar ratio of the concentration of the supporting electrolyte to the concentration of tin ions in the tetravalent tin salt is 1 - 6.

[0018] Optionally, the molar ratio of the concentration of the supporting electrolyte to the concentration of tin ions in the stannic salt is any value among 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or a range value between any two of them.

[0019] Optionally, the negative electrode electrolyte further includes an additive; the additive is selected from at least one of sulfosalicylic acid, iodide, ethylenediaminetetraacetate (EDTA), propylenediaminetetraacetate (PDTA), caprolactam, fluoride, amino acids, and phosphates.

[0020] Optionally, the molar ratio of the concentration of the additive to the concentration of tin ions in the stannic salt is 0.1 to 10.

[0021] Optionally, the molar ratio of the concentration of the additive to the concentration of tin ions in the stannic salt is 0.1 to 2.

[0022] Optionally, the molar ratio of the concentration of the additive to the concentration of tin ions in the stannic salt is any value among 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range value between any two of them.

[0023] Optionally, the negative electrode electrolyte further includes a complexing agent; the complexing agent includes a bromine complexing agent; the bromine complexing agent is selected from at least one of choline chloride, 1-ethyl-2-methylpyridinium bromide (BCA), and N-methyl-N-ethylpyrrolidinium bromide (MEP).

[0024] Optionally, the concentration of the bromine complexing agent is 0.1 to 1 mol / L -1 。

[0025] Optionally, the concentration of the bromine complexing agent is 0.1 to 0.2 mol / L -1 。

[0026] Optionally, the concentration of the bromine complexing agent is any value among 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or a range value between any two of them.

[0027] In a second aspect, the present invention provides an acidic tin-bromine flow battery, including a positive electrode electrolyte, a negative electrode electrolyte, a positive electrode, a negative electrode, a separator, a storage tank, and a pump; the negative electrode electrolyte includes the above-mentioned negative electrode electrolyte.

[0028] Optionally, the negative electrode carbon felt is a raw carbon felt or a carbon felt modified by an in-situ grown carbon-based catalyst; the thickness of the carbon felt is 4 to 6 mm; preferably 5 mm.

[0029] Optionally, the deposition temperature of the in-situ grown carbon-based catalyst modified carbon felt is 600-800 °C.

[0030] Optionally, the deposition temperature of the in-situ grown carbon-based catalyst modified carbon felt is 600-700 °C.

[0031] Optionally, the preparation process of the in-situ grown carbon-based catalyst modified carbon felt includes: soaking the pretreated carbon felt in an ethanol solution in which one or more nickel salts such as nickel chloride, nickel acetate, nickel nitrate or nickel sulfate are dissolved and stirring, followed by ultrasonic treatment for 0.5-6 h, and then drying; the obtained carbon felt is subjected to CVD (chemical vapor deposition) modification treatment in a tubular furnace. First, the catalyst nickel is reduced at 600 °C using a hydrogen-argon mixed gas, and then the mixed gas is turned off and an acetylene-argon balance gas is introduced. The time for introducing acetylene gas is 10-30 min, and the gas introduction temperature is 600-800 °C; the obtained modified carbon felt is soaked and heated in an acidic solution to remove metallic nickel; the acid solution is one of hydrochloric acid, sulfuric acid, and hydroiodic acid, and the concentration of the acid solution is 0.1-4 mol / L -1 , and the heating temperature is 40-100 °C; then it is soaked in clean water until the pH is 7.

[0032] Optionally, the positive electrode electrolyte includes bromide (HBr) which serves as both an active substance and a supporting electrolyte.

[0033] Optionally, the concentration of bromide ions in the positive electrode electrolyte is 0.1-4 mol / L -1 .

[0034] Optionally, the concentration of bromide ions in the positive electrode electrolyte is 1-3 mol / L - ;

[0035] Optionally, the concentration of bromide ions in the positive electrode electrolyte is selected from any value or the range value between any two of 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, with the unit mol / L -1 .

[0036] Optionally, the positive electrode electrolyte further includes a complexing agent; the complexing agent includes a bromine complexing agent; the bromine complexing agent is selected from at least one of choline chloride, 1-ethyl-2-methylpyridinium bromide (BCA), and N-methyl-N-ethylpyrrolidinium bromide (MEP).

[0037] Optionally, the concentration of the bromine complexing agent is 0.1-1 mol / L -1 .

[0038] The concentration of the bromine complexing agent is 0.1-0.5 mol / L -1 .

[0039] Optionally, the concentration of the bromine complexing agent is 0.1 to 0.2 mol / L -1 .

[0040] Optionally, the concentration of the bromine complexing agent is selected from any value among 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or the range value between any two of them.

[0041] Optionally, the positive electrode is the original carbon felt.

[0042] Optionally, the solutions of the positive electrode electrolyte and the negative electrode electrolyte are both aqueous solutions; the diaphragm is an untreated cation exchange membrane for separating the positive electrode active material, the negative electrode active material and conducting protons.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) For the acidic tin-bromine flow battery provided by the present invention, a suitable tin ion ligand is selected in the negative electrode electrolyte, and the formed tin-based complex can effectively improve the redox kinetics of Sn 4+ / Sn 2+ , and improve the efficiency of the tin-bromine flow battery. In addition, the modification of the negative electrode can further improve the adsorption of the reactive substances and increase the electron transfer rate, and the high specific surface area can also provide more active sites, thereby reducing the reaction polarization and improving the battery performance.

[0045] 2) For the tin-bromine flow battery constructed by the present invention, since there is no obvious dendrite problem in the deposition / dissolution of the tin negative electrode, a very high deposition surface capacity can be obtained. At the same time, the electrolyte components mainly include halogens, tin salts and complexing agents, and the composition is relatively simple, having better battery stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is the time-voltage curve of the battery in Example 1 of the present invention;

[0047] Figure 2 is the charge-discharge curve of the battery in Example 1 of the present invention;

[0048] Figure 3 is the time-voltage curve of the battery in Example 2 of the present invention;

[0049] Figure 4 is the charge-discharge curve of the battery in Example 3 of the present invention;

[0050] Figure 5 is the battery efficiency diagram of the battery cycle in Comparative Example 1 of the present invention;

[0051] Figure 6It is the time-voltage curve of the battery in Comparative Example 2 of the present invention;

[0052] Figure 7 It is the charge-discharge curve graph of the battery in Comparative Example 3 of the present invention;

[0053] Figure 8 It is the battery efficiency graph of the battery cycle in Comparative Example 4 of the present invention;

[0054] Figure 9 It is the charge-discharge curve of the battery in Comparative Example 4 of the present invention;

[0055] Figure 10 It is the time-voltage curve of the battery in Comparative Example 5 of the present invention;

[0056] Figure 11 It is the charge-discharge curve of the battery in Comparative Example 5 of the present invention;

[0057] Figure 12 It is the schematic diagram of the flow battery provided by the present invention. Detailed implementation manners

[0058] The following further elaborates the present application in combination with specific embodiments. The following descriptions are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed in the following preferred embodiments, it is not intended to limit the present application. Any person skilled in the relevant art can make some changes or modifications within the scope of the technical solution of the present application by using the disclosed technical content above, which are all equivalent to equivalent implementation cases and fall within the scope of the technical solution.

[0059] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels and used directly without any special treatment.

[0060] Embodiment 1

[0061] Composition of the electrolyte of the acidic tin-bromine flow battery:

[0062] The positive and negative electrolyte solutions are aqueous solutions composed of 1 mol / L -1 crystalline tin tetrachloride (SnCI 4 ), 0.3 mol / L -1 choline chloride, 1 mol / L -1 HBr and 1 mol / L -1 KBr;

[0063] Assembly of the acidic tin-bromine flow battery:

[0064] The structure of the battery includes a stainless - steel end plate, a graphite plate current collector, two original carbon felts with an area of 3×3 cm and a thickness of 5 mm as the positive and negative electrodes, untreated Nafion115 as the separator, a ring - shaped silica gel pad, a ring - shaped flow frame, an electrolyte storage tank, a pump, and pipelines. The battery is assembled according to the conventional flow - battery structure and assembly process.

[0065] Performance test of the acidic tin - bromine flow battery:

[0066] The volumes of the positive and negative electrolyte solutions used for the battery performance test are 8 mL and 50 mL respectively, and the flow rate of the electrolyte solution is about 60 mL min -1 . The cyclic stability test of the battery is all carried out in a constant - current charge - discharge mode. The current density adopted in the cyclic performance test is 40 mA cm -2 , and the SOC of all tests is about 70%. During the test, the protection voltage for charging is set to 1.5 V, and the cut - off condition for discharging adopts voltage cut - off, and the cut - off voltage is 0.5 V. The Coulombic efficiency, voltage efficiency, energy efficiency, and discharge capacity at different cycle numbers are recorded by a Neware charge - discharge instrument.

[0067] Control Example 1

[0068] Treatment of the negative - electrode carbon felt:

[0069] The high - temperature pretreated carbon felt is soaked in an ethanol solution of nickel chloride, stirred, and then ultrasonically treated for 2 h, and then dried. The obtained carbon felt is subjected to CVD treatment in a tubular furnace. First, the catalyst nickel is reduced at 600 °C using a hydrogen - argon mixed gas, and then the mixed gas is turned off, and an acetylene - argon balance gas is introduced. The time for introducing acetylene gas is 15 min, and the gas - passing temperature is 700 °C. The obtained modified carbon felt is soaked and heated in an acidic solution for a period of time to remove metallic nickel. The acid solution is sulfuric acid with a concentration of 3 mol L -1 , and the heating temperature is 50 °C; then it is soaked in a large amount of clear water until the pH is 7, and dried for standby.

[0070] The composition of the electrolyte of the acidic tin - bromine flow battery is the same as that in Table 1, and the other battery accessories, the assembly process, and the cyclic performance test are exactly the same as those in Example 1.

[0071] The other examples and comparative examples are shown in Table 1 in detail, where the battery assembly process, the battery performance test, and the rate performance test are exactly the same as those in Example 1.

[0072] Table 1. Flow batteries and battery efficiency of Examples 1 - 8

[0073]

[0074] As can be seen from Example 1, by introducing halogen bromine anions into the negative electrolyte, complexes can be formed with tin ions, and a relatively stable tin-bromine dual-flow battery can be assembled. The introduction of the bromine complexing agent can reduce the generation of bromine vapor and inhibit the corrosion of elemental bromine on battery devices, etc. Choline chloride has good solubility.

[0075] In Example 2, by introducing a chloride ion medium to change the anion species of the negative electrolyte and adjusting the coordination structure of tin and halogen ions, keeping the positive and negative electrolytes consistent is to alleviate the influence caused by the intermixing of positive and negative ions during the long-cycle stability test of the battery, and the initial state can be restored by intermixing the electrolytes. Compared with Example 1, when chloride ions are used as the main anion medium in Example 2, the battery efficiency is lower than that of the bromide ion medium (such as Figure 1 and Figure 3 ).

[0076] As can be seen from Example 3, when an iodide ion additive is added to the negative electrode, even if its concentration is the same as that of the supporting electrolyte bromic acid and it is not the main anion medium, it greatly improves the battery efficiency. This shows that the metal-halogen ion complex structure formed by iodide ions and tin ions has a much higher activation effect on the electrode reaction than the bromide ion complex, and the bromide anion medium is higher than the halogen chloride ion complex structure.

[0077] It can be inferred from this that among the three different halogen anion species, the order of the battery kinetic performance of the tin negative electrode is I - >Br - >CI - . At the same time, it can be seen from the charge-discharge curve that the potential of the first charging platform in the iodine medium is lower ( Figure 2 and Figure 4 ), and this platform represents the reduction of Sn 4+ to Sn 2+ , which means that the polarization of its electrode reaction is smaller. The "ion bridge" effect exerted by halogen ions at the electrode and electrolyte interface can not only adsorb on the electrode surface but also form surface complexes, thereby activating the cathode reaction, reducing the reaction activation energy, and its activation order is I - >Br - >CI - .

[0078] Example 4 is to explore whether the battery performance of the tin negative electrode has good performance when other inorganic acids are used as the supporting electrolyte. It can be seen from the battery cycle data ( Figure 5 ) that in the sulfuric acid medium, the tin-bromine flow battery can also operate stably. However, when the carbon felt is modified with a catalyst, compared with Example 1, the improvement of its battery efficiency is not obvious. This can indirectly confirm the advantages of halogen anions for the tin-based electrode reaction.

[0079] Example 5 is to select an organic additive to explore the battery performance of a tin negative electrode. It can be seen from the experimental data that the addition of caprolactam can improve the battery energy efficiency to a certain extent ( Figure 6 ).

[0080] Example 6 mainly explores the influence of the type of complexing agent on the performance of a tin-bromine flow battery. MEP has a relatively wide application in bromine-based flow batteries and has a strong complexing ability for bromine. However, on the premise of using a catalyst-modified carbon felt, its battery efficiency is lower than that of the battery using choline chloride in Example 1, indicating that the use of choline chloride as a bromine complexing agent has a smaller impact on the tin-bromine flow battery ( Figure 7 ).

[0081] It can be seen from the above experiments that when bromide anions or iodide ions are added to the negative electrolyte as the coordinating halogen ions of the tin complex, better battery performance can be obtained. Therefore, in order to further improve the battery performance and reduce the polarization of the electrochemical reaction; by modifying the negative carbon felt, the electrode is an important place where the electrode reaction occurs, and its conductivity, specific surface area, etc. greatly affect the ion adsorption at the interface and the speed of electron transfer.

[0082] Example 7 is to use a catalyst carbon felt in the negative electrode under a bromine medium. Compared with Example 1, its battery performance has been greatly improved, and the battery can operate stably ( Figure 8 and Figure 9 ).

[0083] Example 8 is to use iodide ions as an additive in the negative electrolyte and a catalyst carbon felt at the same time. Its battery efficiency has an obvious gap compared with the bromine medium. The higher battery efficiency indicates that the type of additive and the negative modified carbon felt play a synergistic role. Therefore, the improved tin-bromine flow battery has a higher reaction kinetics of the tin negative electrode ( Figure 10 and Figure 11 ). Among them, the presence of the negative carbon catalyst not only improves the conductivity of the electrode and avoids the accumulation of surface charges on the electrode, but also improves the reversibility of the electrochemical reaction. At the same time, the in-situ grown carbon fiber / carbon nanotube material represents a higher specific surface area, provides more reaction sites, and reduces the electrochemical polarization.

[0084] Based on the above analysis, the acidic tin-bromine flow battery in this application has a high energy density, areal capacity, good cycle stability, and high battery efficiency.

[0085] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are all equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A negative electrode electrolyte, characterized in that, the negative electrode electrolyte comprises an active material and a supporting electrolyte; wherein, the active material comprises a tetravalent tin salt; the supporting electrolyte is selected from at least one of sulfuric acid, hydrochloric acid, perchloric acid, methanesulfonic acid, hydrobromic acid and hydroiodic acid.

2. The negative electrode electrolyte according to claim 1, characterized in that, the tetravalent tin salt is selected from at least one of tin tetrachloride, tin sulfate, tin bromide and stannate; Preferably, the concentration of tin ions in the stannic salt is 0.1 to 3 mol / L -1 ; Preferably, the concentration of tin ions in the stannic salt is 1 to 3 mol / L -1 ; Preferably, the concentration of the supporting electrolyte is 0.1 to 4 mol L -1 ; Preferably, the concentration of the supporting electrolyte is 2 to 3 mol / L -1 .

3. The negative electrode electrolyte according to claim 1, characterized in that, the molar ratio of the concentration of the supporting electrolyte to the concentration of tin ions in the tetravalent tin salt is 0.1 to 30; preferably, the molar ratio of the concentration of the supporting electrolyte to the concentration of tin ions in the tetravalent tin salt is 1 to 6.

4. The negative electrode electrolyte according to claim 1, characterized in that, the negative electrode electrolyte further comprises an additive; the additive is selected from at least one of sulfosalicylic acid, iodide, ethylenediaminetetraacetate, propylenediaminetetraacetate, caprolactam, fluoride, amino acids and phosphates; preferably, the molar ratio of the concentration of the additive to the concentration of tin ions in the tetravalent tin salt is 0.1 to 10; preferably, the molar ratio of the concentration of the additive to the concentration of tin ions in the tetravalent tin salt is 0.1 to 2.

5. The negative electrode electrolyte according to claim 1, characterized in that, the negative electrode electrolyte further comprises a complexing agent; the complexing agent comprises a bromine complexing agent; the bromine complexing agent is selected from at least one of choline chloride, 1-ethyl-2-methylpyridinium bromide and N-methyl-N-ethylpyrrolidinium bromide; Preferably, the concentration of the bromine complexing agent is 0.1 to 1 mol / L -1 ; Preferably, the concentration of the bromine complexing agent is 0.1 to 0.2 mol / L -1 .

6. An acidic tin-bromine flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, a positive electrode, a negative electrode, a separator, a storage tank and a pump; characterized in that, the negative electrode electrolyte comprises the negative electrode electrolyte according to any one of claims 1 to 5.

7. The acidic tin-bromine flow battery according to claim 6, characterized in that, the negative electrode carbon felt is a raw carbon felt or a carbon felt modified by an in-situ grown carbon-based catalyst; the thickness of the carbon felt is 4 to 6 mm; preferably, the deposition temperature of the carbon felt modified by the in-situ grown carbon-based catalyst is 600 to 800 °C; preferably, the deposition temperature of the carbon felt modified by the in-situ grown carbon-based catalyst is 600 to 700 °C.

8. The acidic tin-bromine flow battery according to claim 7, characterized in that, The preparation process of the in-situ grown carbon-based catalyst modified carbon felt includes: soaking the pretreated carbon felt in an ethanol solution in which one or more nickel salts such as nickel chloride, nickel acetate, nickel nitrate or nickel sulfate are dissolved and stirring, followed by ultrasonic treatment for 0.5 to 6 h, and then drying treatment; the obtained carbon felt is subjected to CVD treatment in a tubular furnace. First, the catalyst nickel is reduced at 600 °C using a hydrogen-argon mixed gas, and then the mixed gas is turned off and an acetylene-argon balance gas is introduced. The time for introducing acetylene gas is 10 to 30 min, and the gas introduction temperature is 600 to 800 °C; the obtained modified carbon felt is soaked and heat-treated in an acidic solution to remove metallic nickel; the acid solution is one of hydrochloric acid, sulfuric acid, and hydroiodic acid, and the concentration of the acid solution is 0.1 to 4 mol / L -1 , and the heating temperature is 40 to 100 °C; then it is soaked in clean water until the pH is 7.

9. The acidic tin-bromine flow battery according to claim 6, characterized in that, the positive electrode electrolyte comprises a bromide as an active material and also as a supporting electrolyte and a complexing agent; the positive electrode is a raw carbon felt; Preferably, the concentration of bromide ions in the positive electrode electrolyte is 0.1 to 4 mol / L - ; the complexing agent includes a bromine complexing agent; the concentration of the bromine complexing agent is 0.1 to 1 mol / L -1 ; Preferably, the concentration of bromide ions in the positive electrode electrolyte is 1 to 3 mol / L -1 ; the concentration of the bromine complexing agent is 0.1 to 0.5 mol / L -1 .

10. The acidic tin-bromine flow battery according to claim 6, characterized in that, the solutions of the positive electrode electrolyte and the negative electrode electrolyte are both aqueous solutions; the separator is an untreated cation exchange membrane for separating the positive electrode active material, the negative electrode active material and conducting protons.

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