Hydrochloric-sulfuric acid mixed acid supporting electrolyte and its application in tin iron flow battery

Abstract

The application relates to a hydrochloric acid-sulfuric acid mixed acid supporting electrolyte and application thereof in a tin-iron liquid flow battery. The mixed acid supporting electrolyte is an acidic mixed aqueous solution containing chloride ions and sulfate ions, and the molar concentration ratio of the chloride ions to the sulfate ions is 5-7:1. On the basis of the mixed acid supporting electrolyte, tin sources and iron sources are dissolved to serve as negative and positive active materials respectively. The tin-iron liquid flow battery adopting the mixed acid supporting electrolyte of the application can be stably operated for more than 500 hours under an 80 mA cm −2 Current density. The deposited tin in the system presents uniformly distributed polyhedral particles, forms a dense and continuous covering layer on the surface of carbon fibers, has high nucleation density and uniform deposition. The application provides the mixed acid supporting electrolyte for the tin-iron liquid flow battery, the specific molar ratio of the chloride ions to the sulfate ions is accurately constructed, the coordination of the two at the electrode interface is realized, and thus the performance bottleneck is broken through.

Description

Technical Field

[0001] This invention relates to the field of aqueous metal-based flow battery technology, specifically to a hydrochloric acid-sulfuric acid mixed acid supported electrolyte and its application in tin-iron flow batteries. Background Technology

[0002] Tin-iron flow batteries possess advantages such as high theoretical capacity, abundant raw material resources, and high intrinsic safety, making them promising candidates for large-scale electrochemical energy storage. In tin-iron flow battery systems, the supporting electrolyte not only provides the necessary acidic environment for electrochemical reactions but also significantly influences electrode reaction kinetics and battery operational stability by affecting the coordination structure, solvation state, and ion distribution at the electrode interface of metal ions. Existing research indicates that the stability and deposition behavior of tin ions in acidic systems are closely related to the types of anions in the electrolyte. Currently, research on supporting electrolytes for acidic tin-iron flow batteries mainly focuses on single-acid systems, including chloride ion systems using hydrochloric acid (HCl) as the supporting electrolyte and sulfate ion systems using sulfuric acid (H₂SO₄) as the supporting electrolyte. Among these, the higher concentration of chloride ions in hydrochloric acid supporting electrolytes can react with Sn... 2+ Formation of stable chloride complexes, thereby improving Sn 2+ Hydrochloric acid is widely used in tin-based flow battery systems because it improves the solubility and stability of the electrolyte and promotes electrode deposition reactions. However, high chloride ion concentrations in the electrolyte enhance corrosion of the metal electrodes and exacerbate interfacial side reactions, thus adversely affecting the long-term cycle stability of the battery. In contrast, sulfate in sulfuric acid-supported electrolytes has weaker coordination ability and higher chemical stability; the introduction of sulfate helps reduce system corrosivity and improve electrolyte stability. However, due to the negative effects of sulfate on Sn... 2+ Due to weak complexation, pure sulfuric acid systems often exhibit poor performance in tin deposition kinetics. Therefore, single acid-supported electrolytes in tin-based electrochemical systems often fail to simultaneously meet the requirements of ion stability, deposition kinetics, and interfacial stability.

[0003] In the field of tin-based flow batteries, some studies have attempted to introduce hydrochloric acid-sulfuric acid mixed acids as supporting electrolytes, aiming to combine the advantages of both acids. However, these existing technologies merely treat the mixed acid as a simple combination of two acids, failing to recognize the synergistic coordination effect of chloride and sulfate ions at the electrode interface on the tin deposition process, and failing to disclose or suggest the existence of a specific ion molar ratio window that can simultaneously achieve high energy efficiency, uniform deposition morphology, and long cycle life. Therefore, existing technologies have consistently failed to overcome performance bottlenecks, and their cycle stability and energy efficiency are not ideal.

[0004] Therefore, developing a mixed-acid supported electrolyte suitable for tin-iron flow batteries, from the perspective of ion synergistic coordination, and precisely controlling the molar ratio of chloride ions to sulfate ions to make it fall within a specific synergistic window, thereby taking into account high conductivity, stable tin deposition morphology and excellent cycle life, has important academic value and application prospects. Summary of the Invention

[0005] Addressing the technical bottlenecks of existing tin-iron flow battery support electrolytes—the single hydrochloric acid system has high conductivity but strong corrosivity and poor long-term cycle stability; the single sulfuric acid system has weak corrosivity but poor tin deposition kinetics; and the existing tin-based mixed acid system simply mixes hydrochloric acid and sulfuric acid without addressing the control of the chloride to sulfate ratio, thus failing to simultaneously achieve high energy efficiency, uniform deposition morphology, and long cycle life—this invention provides a mixed acid support electrolyte for tin-iron flow batteries. By precisely constructing a specific molar ratio of chloride to sulfate, it achieves synergistic coordination of the two at the electrode interface, thereby overcoming the aforementioned performance bottlenecks.

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

[0007] A hydrochloric acid-sulfuric acid mixed-acid supported electrolyte, wherein the mixed-acid supported electrolyte is an acidic mixed aqueous solution containing chloride ions and sulfate ions, and the molar concentration ratio of chloride ions to sulfate ions is 5~7:1.

[0008] The hydrochloric acid-sulfuric acid mixed acid supporting electrolyte preferably has a chloride to sulfate molar ratio of 6:1.

[0009] The hydrochloric acid-sulfuric acid mixed acid supported electrolyte preferably has chloride ions and sulfate ions derived from hydrochloric acid and sulfuric acid, respectively.

[0010] The hydrochloric acid-sulfuric acid mixed acid supporting electrolyte is preferably provided with a hydrochloric acid concentration of 3.0 mol / L and a sulfuric acid concentration of 0.5 mol / L.

[0011] The application of the hydrochloric acid-sulfuric acid mixed acid supported electrolyte of the present invention in tin-iron flow batteries involves dissolving tin and iron sources on the basis of the mixed acid supported electrolyte, which are used as negative and positive electrode active materials, respectively.

[0012] Preferably, the tin source is a water-soluble tin salt, and the iron source is a water-soluble ferrous salt.

[0013] The preferred total concentration of tin source is 0.2 mol / L, and the preferred total concentration of iron source is 0.4 mol / L.

[0014] The specific invention is as follows:

[0015] The essential feature that distinguishes this invention from existing tin-based mixed acid systems is that existing technologies simply mix hydrochloric acid and sulfuric acid in any concentration ratio, while this invention is the first to discover that the molar ratio of chloride ions to sulfate ions must fall within a specific window of 5:1 to 7:1 in order to activate the synergistic coordination effect of the two anions.

[0016] In a preferred embodiment, the molar ratio of chloride ions to sulfate ions is 6:1. At this ratio, the synergistic coordination of the two anions reaches optimal equilibrium. SEM characterization results show that, as Figure 5 As shown in Figure a, in the 6:1 system, deposited tin exhibits uniformly distributed polyhedral particles, forming a dense and continuous capping layer on the carbon fiber surface, with high nucleation density and uniform deposition. When the ratio deviates from this window, the size of the deposited tin particles increases or local agglomeration occurs (e.g., Figure 6 As shown in the figure, the energy efficiency and cycle life of the corresponding system both decreased significantly.

[0017] To demonstrate that 5:1 to 7:1 is a consistently effective synergistic window, rather than being effective only at the isolated point of 6:1, this invention provides endpoint examples 2 (chloride-sulfur molar ratio 5:1) and 3 (chloride-sulfur molar ratio 7:1) in specific embodiments. Examples 1 to 3 collectively demonstrate that a synergistic effect can be continuously generated within the chloride-sulfate molar ratio range of 5:1 to 7:1, achieving the beneficial effects of this invention.

[0018] The chloride and sulfate ions mentioned above preferably originate from hydrochloric acid and sulfuric acid, respectively. When the concentration of hydrochloric acid is 3.0 mol / L and the concentration of sulfuric acid is 0.5 mol / L, the optimal ion molar ratio of 6:1 is satisfied, which is the best embodiment of the present invention.

[0019] Based on the aforementioned mixed acid supported electrolyte, tin and iron sources are further dissolved to serve as the negative and positive electrode active materials, respectively. The tin source is a water-soluble tin salt, and the iron source is a water-soluble ferrous salt. It should be noted that the function of the active materials is to provide the metal ions required for the electrochemical reaction, a basic function identical to that of existing tin-iron flow batteries. However, what truly determines the difference in battery performance is the anion composition and ratio of the supporting electrolyte, as the latter directly regulates the Sn content. 2+ The coordination structure, interfacial mass transfer behavior, and tin deposition morphology of the material are analyzed. This invention achieves significantly superior performance compared to existing technologies by precisely controlling the anion ratio.

[0020] In one specific implementation (Example 1), the total concentration of tin source was 0.2 mol / L and the total concentration of iron source was 0.4 mol / L. Experiments showed that within a reasonable range of fluctuation around these concentrations, there was no significant difference in battery performance, indicating that the technical effect of this invention is mainly determined by the ion ratio of the supporting electrolyte, rather than the concentration of the non-active material.

[0021] Compared with the prior art, the inventive contribution of this invention lies in the first discovery and definition of the co-coordination molar ratio window (5~7:1) of chloride ions and sulfate ions in tin-iron flow batteries, which brings the following beneficial effects:

[0022] (1) Significantly improves energy efficiency and cycle life. The tin-iron flow battery using the mixed-acid supported electrolyte of this invention achieves a cycle life of 80 mA cm⁻¹. −2 The system can operate stably for over 500 hours at current density. Example 1 (chlorine-sulfur molar ratio 6:1) operated stably for over 500 hours, with a coulombic efficiency exceeding 99% and an energy efficiency exceeding 87% over 1500 cycles; Examples 2 (5:1) and 3 (7:1) both showed energy efficiencies exceeding 85%. The charge-discharge voltage-time curves maintained a stable voltage plateau in the early, middle, and late stages of the cycle, without significant decay. Comparative experiments show that the overall performance of the system of this invention is significantly better than that of a single hydrochloric acid system, a single sulfuric acid system, and a mixed acid system outside the window.

[0023] (2) Effectively improves the morphology of tin deposition. In the systems of all embodiments of the present invention, the deposited tin exhibits uniformly distributed polyhedral particles, forming a dense and continuous coating layer on the carbon fiber surface, with high nucleation density and uniform deposition. In single hydrochloric acid or sulfuric acid systems, the deposited tin exhibits large-sized blocky agglomerates with uneven distribution; in the mixed acid ratio system outside the window, irregular particles and local agglomerates coexist. Statistical particle size analysis further quantitatively confirms that the average particle size distribution of the deposited tin in the system of the present invention is concentrated and dense, significantly better than that of the comparative examples.

[0024] (3) Revealing the synergistic coordination mechanism and optimizing crystal growth orientation. The chloride and sulfur characteristic spectra of the deposited tin in the system of this invention show broadened peaks, which directly confirms that there is dynamic synergistic coordination between chloride ions and sulfate ions at the electrode interface. This elevates the mixed acid design from empirical "trial and error" to rational control based on the theory of ion coordination chemistry. This synergistic coordination enables the tin crystal to preferentially grow along the (200) low surface energy direction, which is conducive to the formation of a dense and uniform deposition layer.

[0025] (4) Achieving unexpected comprehensive technical effects with a specific ratio window. Existing tin-based mixed acid systems simply mix hydrochloric acid and sulfuric acid, remaining at the level of arbitrary acid concentration ratios, and have never recognized the existence of a synergistic window determined by the ion molar ratio. Comparative Examples 3 (chlorine-sulfur molar ratio 2:1) and 4 (0.67:1) of this invention both use mixed acids, but because the ion ratio falls outside the window, their cycle life and energy efficiency are significantly inferior to those of the embodiments of this invention; Examples 2 and 3 verify the effectiveness of the window endpoints 5:1 and 7:1, proving that this window is a continuous and stable synergistic effect range, rather than existing only at the isolated point of 6:1. The above effects are not achieved by any of the comparative example systems, constituting direct evidence that the synergistic effect brings unexpected technical effects. Attached Figure Description

[0026] Figure 1 Example 1 of the present invention: constant current charge and discharge voltage-time curve of battery: (a) initial stage; (b) middle stage; (c) final stage.

[0027] Figure 2 Comparison of (a) coulombic efficiency and (b) energy efficiency of constant current charge and discharge of batteries in Examples 1, 2 and 3 of this invention (data point interval: 10 cycles).

[0028] Figure 3 Comparison of (a) coulombic efficiency and (b) energy efficiency of constant current charge and discharge of batteries in Example 1 of this invention with Comparative Examples 1 and 2 (data point interval: 10 cycles).

[0029] Figure 4 Comparison of (a) coulombic efficiency and (b) energy efficiency of constant current charge and discharge of batteries in Example 1 of this invention with Comparative Examples 3 and 4 (data point interval: 10 cycles).

[0030] Figure 5 Scanning electron microscope (SEM) images of tin deposited on the carbon felt electrode surface after battery charging according to embodiments of the present invention: (a) Example 1; (b) Example 2; (c) Example 3.

[0031] Figure 6 Scanning electron microscope (SEM) images of tin deposited on the carbon felt electrode surface after charging of the present invention and comparative examples: (a) Example 1; (b) Comparative Example 1; (c) Comparative Example 2; (d) Comparative Example 3; (e) Comparative Example 4.

[0032] Figure 7 X-ray diffraction (XRD) images of tin deposited on the carbon felt electrode surface after charging of the battery in the embodiments and comparative examples of this invention.

[0033] Figure 8 (a) X-ray photoelectron spectroscopy (XPS) Cl 2p spectra of tin deposited on the carbon felt electrode surface after charging of the batteries of Example 1 and Comparative Example 1 of the present invention; (b) X-ray photoelectron spectroscopy (XPS) S 2p spectra of tin deposited on the carbon felt electrode surface after charging of the batteries of Example 1 and Comparative Example 2 of the present invention. Detailed Implementation

[0034] To make the above-mentioned objectives, features and advantages of the present invention clearer and easier to understand, the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0035] Example 1 (Chlorine-sulfur molar ratio 6:1 system)

[0036] This embodiment provides a mixed acid supported electrolyte for tin-iron flow batteries, with the following composition: hydrochloric acid (HCl): 3.0 mol / L; sulfuric acid (H2SO4): 0.5 mol / L.

[0037] Dissolved in the above mixed acid supported electrolyte:

[0038] Tin source: stannous chloride (SnCl2), concentration 0.15 mol / L, stannous sulfate (SnSO4), concentration 0.05 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.3 mol / L, ferrous sulfate (FeSO4), concentration 0.1 mol / L. Calculations show that the total chloride ion concentration introduced by hydrochloric acid and metal salts is 3.9 mol / L, and the total sulfate ion concentration introduced by sulfuric acid and metal salts is 0.65 mol / L. The actual molar ratio of chloride ions to sulfate ions in the electrolyte is 6:1, consistent with the designed ratio of the supporting electrolyte.

[0039] Preparation method:

[0040] The negative electrode electrolyte is prepared as follows: First, concentrated hydrochloric acid and concentrated sulfuric acid are diluted with deionized water to prepare a 3.0 M HCl - 0.5 M H2SO4 mixed acid supported electrolyte.

[0041] Weigh out specific amounts of SnCl2 and SnSO4, FeCl2 and FeSO4 respectively, and dissolve them in the above mixed acid supported electrolyte. Stir until completely dissolved to obtain the negative electrode electrolyte (containing 0.2 mol / L Sn). 2+ ) and positive electrode electrolyte (containing 0.4 mol / L Fe) 2+ ).

[0042] Battery assembly and testing:

[0043] The main components of the flow battery used in the experiment include end plates, gold-plated copper plates, current collectors, and carbon felt electrodes (4 cm² in area). 2 The battery cell was assembled using Nafion 115 membrane and sealing gaskets, etc. 15 mL of each of the positive and negative electrolytes was injected into the corresponding storage tanks, and the assembled battery cell was connected to the electrolyte circulation system. During the experiment, the electrolyte circulation pump speed was set to 40 mL / min. −1 At a current density of 80 mA cm⁻¹ −2 Under constant current charge-discharge conditions, the capacity of a single charge was 13.33 mAh cm⁻¹. −2 (corresponding to 4 cm) 2The charging capacity of the tin-iron flow battery is 53.3 mAh, and the discharge cutoff voltage is 0.5 V. Constant current charge-discharge cycle tests were performed on the tin-iron flow battery, and the changes in coulombic efficiency and energy efficiency with the number of cycles were recorded and analyzed. The results are as follows: Figure 1 , Figure 2 As shown.

[0044] The resulting battery was at 80 mA cm⁻¹ −2 At current densities, it can operate stably for over 500 hours (e.g., Figure 1 As shown); in 1500 cycles, the coulombic efficiency exceeds 99%, and the energy efficiency exceeds 87% (as shown). Figure 2 As shown), no significant energy efficiency degradation was observed. After charging, the tin-deposited surface of the carbon felt electrode exhibited uniformly distributed polyhedral particles, forming a relatively dense and continuous capping layer on the carbon fiber surface, indicating increased nucleation density and a more uniform deposition process (as shown). Figure 5 (as shown in a). Statistical analysis of particle size was performed on deposited particles from different supported electrolyte systems, and the results are shown in Table 1. XRD analysis indicates (as shown in a). Figure 7 As shown), after charging, the tin crystals deposited on the carbon felt electrode preferentially grow along the (200) low surface energy direction, which is beneficial for forming a dense and uniform deposition layer. XPS analysis shows (as shown) Figure 8 As shown in the figure, the Cl 2p and S 2p spectra of tin deposited on the carbon felt electrode after charging exhibit characteristic broadened peaks, directly confirming the dynamic cooperative coordination between chloride ions and sulfate ions at the electrode interface.

[0045] Example 2 (5:1 chlorine-sulfur molar ratio system)

[0046] The difference from Example 1 is as follows:

[0047] Supporting electrolytes: hydrochloric acid (HCl): 2.86 mol / L; sulfuric acid (H2SO4): 0.57 mol / L.

[0048] Tin source: stannous chloride (SnCl2), concentration 0.143 mol / L, stannous sulfate (SnSO4), concentration 0.057 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.286 mol / L, ferrous sulfate (FeSO4), concentration 0.114 mol / L.

[0049] The preparation and testing methods are the same as in Example 1.

[0050] Test results: at 80 mA cm −2 At current density, this battery can operate stably for over 500 hours (corresponding to over 1500 cycles), with a coulombic efficiency exceeding 99% and an energy efficiency exceeding 85% during cycling (e.g., Figure 2As shown). SEM images of the carbon felt electrode after charging show that the deposited tin exhibits uniform and dense polyhedral particles (as shown). Figure 5 (as shown in b). This embodiment confirms that the 5:1 ratio is at the boundary of the synergistic effect window and has excellent results.

[0051] Example 3 (Chlorine-sulfur molar ratio 7:1 system)

[0052] The difference from Example 1 is as follows:

[0053] Supporting electrolytes: hydrochloric acid (HCl): 3.11 mol / L; sulfuric acid (H2SO4): 0.44 mol / L.

[0054] Tin source: stannous chloride (SnCl2), concentration 0.156 mol / L, stannous sulfate (SnSO4), concentration 0.044 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.312 mol / L, ferrous sulfate (FeSO4), concentration 0.088 mol / L.

[0055] The preparation and testing methods are the same as in Example 1.

[0056] Test results: at 80 mA cm −2 At current density, this battery can operate stably for over 500 hours (corresponding to over 1500 cycles), with a coulombic efficiency exceeding 99% and an energy efficiency exceeding 85% during cycling (e.g., Figure 2 As shown in the image). SEM images of the carbon felt electrode after charging show that the deposited tin also exhibits uniform and dense polyhedral particles (as shown in the image). Figure 5 (As shown in c). This embodiment confirms that a 7:1 ratio can still maintain a synergistic effect.

[0057] Comparative Example 1 (Single Hydrochloric Acid System)

[0058] The difference from Example 1 is as follows:

[0059] Supporting electrolyte: Hydrochloric acid (HCl): 4.0 mol / L. The concentration of 4.0 mol / L was chosen to ensure that the total hydrogen ion concentration of the system was similar to that in Example 1 (approximately 4.0 MH). + To keep them at the same level, thus eliminating the interference of acidity differences on performance comparison.

[0060] Tin source: stannous chloride (SnCl2), concentration 0.2 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.4 mol / L.

[0061] The preparation and testing methods are the same as in Example 1.

[0062] Test results: at 80 mA cm −2At current density, the energy efficiency of the comparative system drops below 80% after approximately 170 cycles (e.g., Figure 3 As shown), the deposited tin exhibits a large, blocky agglomerate structure with clear but unevenly distributed particle boundaries, easily accumulating in localized areas. This indicates a low nucleation density, significant diffusion control during growth, and poor uniformity in the deposition process (e.g.). Figure 6 (As shown in b). The XRD and XPS results of the tin deposited on the carbon felt electrode after charging are compared with those of Example 1 as shown in Figure 1. Figure 7 , Figure 8 As shown.

[0063] Comparative Example 2 (Single Sulfuric Acid System)

[0064] The difference from Example 1 is as follows:

[0065] Supporting electrolyte: Sulfuric acid (H₂SO₄): 2.0 mol / L. The concentration of 2.0 mol / L was chosen to ensure that the total hydrogen ion concentration of the system was similar to that in Example 1 (approximately 4.0 MH). + To keep them at the same level, thus eliminating the interference of acidity differences on performance comparison.

[0066] Tin source: stannous sulfate (SnSO4), concentration 0.2 mol / L; Iron source: ferrous sulfate (FeSO4), concentration 0.4 mol / L.

[0067] The preparation and testing methods are the same as in Example 1.

[0068] Test results: at 80 mA cm −2 At current density, the energy efficiency of the comparative system drops below 80% after approximately 130 cycles (e.g., Figure 3 As shown), the deposited tin exhibits a large, blocky structure with uneven distribution, indicating that the deposition process is limited in the pure sulfuric acid system, making it difficult to form a uniform and dense deposition layer (as shown). Figure 6 (As shown in c). The XRD and XPS results of the tin deposited on the carbon felt electrode after charging are compared with those of Example 1 as follows: Figure 7 , Figure 8 As shown.

[0069] Comparative Example 3 (Chlorine-sulfur molar ratio 2:1 system)

[0070] The difference from Example 1 is as follows:

[0071] Supporting electrolytes: hydrochloric acid (HCl): 2.0 mol / L; sulfuric acid (H2SO4): 1.0 mol / L.

[0072] Tin source: stannous chloride (SnCl2), concentration 0.1 mol / L, stannous sulfate (SnSO4), concentration 0.1 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.2 mol / L, ferrous sulfate (FeSO4), concentration 0.2 mol / L.

[0073] The preparation and testing methods are the same as in Example 1.

[0074] Test results: at 80 mA cm −2 At current density, the energy efficiency of the comparative system drops below 80% after approximately 240 cycles (e.g., Figure 4 As shown), deposited tin exhibits characteristics of both irregular particles and localized agglomerations (e.g. Figure 6 (As shown in d). The XRD results of the carbon felt electrode deposited with tin after charging are compared with those of Example 1 as shown in d). Figure 7 As shown.

[0075] Comparative Example 4 (chlorine-sulfur molar ratio 0.67:1 system)

[0076] The difference from Example 1 is as follows:

[0077] Supporting electrolytes: hydrochloric acid (HCl): 1.0 mol / L; sulfuric acid (H2SO4): 1.5 mol / L.

[0078] Tin source: stannous chloride (SnCl2), concentration 0.05 mol / L, stannous sulfate (SnSO4), concentration 0.15 mol / L; Iron source: ferrous chloride (FeCl2), concentration 0.1 mol / L, ferrous sulfate (FeSO4), concentration 0.3 mol / L.

[0079] The preparation and testing methods are the same as in Example 1.

[0080] Test results: at 80 mA cm −2 At current density, the energy efficiency of the comparative system drops below 80% after approximately 250 cycles (e.g., Figure 4 As shown in the figure, the deposited tin exhibits a combination of irregular particles and localized agglomerations. The particles are relatively small but show some disordered accumulation, indicating a decrease in deposition uniformity (e.g., Figure 6 (As shown in e). The XRD results of the carbon felt electrode with tin deposition after charging are compared with those of Example 1 as follows. Figure 7 As shown.

[0081] Table 1. Statistical distribution of tin deposition particles in different supporting electrolyte systems (100 particles were counted).

[0082] Example 1 26.76 13.61 Uniform and dense Example 2 27.34 11.56 Uniform and dense Example 3 26.95 12.47 Uniform and dense Comparative Example 1 48.41 18.78 Large particles Comparative Example 2 36.04 13.26 Large particles Comparative Example 3 33.51 13.21 Local reunion Comparative Example 4 22.19 8.41 Local reunion

[0083] As shown in Table 1, the deposited tin particles in Examples 1-3 of this invention exhibit a concentrated size distribution, with small average particle size and uniform, dense characteristics. This indicates that the mixed acid supporting electrolyte effectively optimizes the tin deposition morphology throughout the entire molar ratio window from 5:1 to 7:1. In contrast, the average particle size of the deposited tin particles in Comparative Examples 1 and 2 is relatively large; the average particle size of the deposited tin particles in Comparative Example 3 is medium, but irregular particles and local agglomerations coexist; the average particle size of the deposited tin particles in Comparative Example 4 is the smallest, but irregular particles and local agglomerations coexist, and the disordered particle accumulation affects uniformity. This result further confirms the optimizing effect of the preferred mixed acid supporting electrolyte on the tin deposition morphology of this invention.

Claims

1. A hydrochloric acid-sulfuric acid mixed acid supported electrolyte, characterized in that, The mixed acid supporting electrolyte is an acidic mixed aqueous solution containing chloride ions and sulfate ions, and the molar concentration ratio of chloride ions to sulfate ions is 5~7:

1.

2. The hydrochloric acid-sulfuric acid mixed acid supported electrolyte as described in claim 1, characterized in that, The molar ratio of chloride ions to sulfate ions is 6:

1.

3. The hydrochloric acid-sulfuric acid mixed acid supported electrolyte as described in claim 1, characterized in that, Chloride ions and sulfate ions originate from hydrochloric acid and sulfuric acid, respectively.

4. The hydrochloric acid-sulfuric acid mixed acid supported electrolyte as described in claim 3, characterized in that, The concentration of hydrochloric acid is 3.0 mol / L and the concentration of sulfuric acid is 0.5 mol / L.

5. The application of the hydrochloric acid-sulfuric acid mixed-acid supported electrolysis of claim 1 in a tin-iron flow battery, characterized in that, Based on the mixed acid-supported electrolyte, tin and iron sources are dissolved to serve as the negative and positive electrode active materials, respectively.

6. The application as described in claim 5, characterized in that, The tin source is a water-soluble tin salt, and the iron source is a water-soluble ferrous salt.

7. The application as described in claim 5, characterized in that, The total concentration of tin source was 0.2 mol / L, and the total concentration of iron source was 0.4 mol / L.

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