An aqueous flow battery electrolyte, its preparation method and application

Abstract

This invention belongs to the field of electrochemical energy storage technology, and discloses an aqueous flow battery electrolyte, its preparation method, and its application. The aqueous flow battery electrolyte of this invention comprises organic polysulfides; the general formula of the organic polysulfides is R-S. x ‑ Wherein, 2≤x≤6; R is an organic group containing at least one hydrophilic functional group; the hydrophilic functional group includes hydroxyl, amino, carboxyl, sulfonic acid, phosphate, quaternary ammonium, amide, guanidine, and at least one of the metal salts corresponding to the above groups. The electrolyte of this invention not only endows sulfur-based flow batteries with extremely high charge-discharge reversibility and near-zero-attenuation long-cycle stability, but also, through the rational design of the organic polysulfide molecular structure, precisely controls the redox potential, reaction kinetics, and dissolution behavior of the active material, demonstrating enormous industrial application potential and market prospects in demanding fields such as large-scale energy storage power stations and industrial waste heat recovery-electrochemical coupling systems.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to an aqueous flow battery electrolyte, its preparation method, and its application. Background Technology

[0002] Aqueous flow batteries are considered one of the most competitive energy storage technologies due to their inherent safety, long cycle life, and energy-power decoupling advantages, showing broad application prospects in areas such as grid peak shaving, renewable energy consumption, and distributed energy storage. Among these, vanadium redox flow batteries are the most mature, but the high cost and volatile price of vanadium resources severely restrict their commercialization in large-scale, long-term energy storage scenarios. In contrast, sulfur is abundant and widely distributed on Earth, with extremely low raw material costs and no heavy metal pollution risk, making it an ideal active material for constructing clean, low-cost energy storage systems. Sulfur-based flow battery systems, such as sulfur-iron flow batteries, sulfur-iodine flow batteries, and sulfur-bromine flow batteries, are expected to become the mainstream technology in the next generation of long-term energy storage due to their inherent safety, low cost, and environmental friendliness.

[0003] However, existing sulfur-based flow batteries still face many key technological bottlenecks in practical applications, which severely limit their performance improvement and commercialization process. Specifically, these bottlenecks are mainly reflected in the following aspects: First, traditional inorganic polysulfides (such as K2S)... x Na2S xThe small size of inorganic polysulfides makes them prone to crossing ion exchange membranes during charge-discharge cycles, leading to cross-contamination with the positive electrode active material and causing a severe shuttle effect. This results in reduced coulombic efficiency, rapid capacity decay, and shortened cycle life. Although some studies have attempted to suppress the shuttle effect by controlling the consistency between auxiliary ions and active material cations or by using specific membrane types, these methods have not fundamentally solved the diffusion problem caused by the small ion size of inorganic polysulfides. Secondly, although organic sulfides have larger molecular sizes and are expected to reduce the shuttle effect, their electrochemical performance has significant defects. For example, the sulfur in benzenesulfonic acid mentioned in Chinese invention patent CN115000480A is in its highest oxidation state, and its reduction reaction is irreversible and accompanied by harmful side reactions, making it impossible to form a stable redox couple. Therefore, it cannot be used as an active material in flow batteries. For thioethers, thiols, or thiophenols with sulfur atoms in their lowest reduction state (-2 valence), the oxidation of thioethers to sulfoxides and sulfones is highly irreversible, making it difficult to construct reversible redox couples. Q. Chen et al. in "J" Am. Chem. Soc. 2026, 148, 3, 3392–3400, DOI:10.1021 / jacs.5c18379 and Chinese invention patent CN121726459A attempt to convert thiols or thiophenols (R-SH) into disulfides (structure: RSSR) through a reversible dimerization reaction. However, the reaction kinetics are extremely slow, and the oxidation state of sulfur can only increase from -2 to -1. Each sulfur atom contributes only one electron, resulting in a lower theoretical specific capacity of the battery.

[0004] Furthermore, B. Yang et al., in *Energy Mater Adv. 2022; 2022, DOI:10.34133 / 2022 / 9795675*, attempted to conduct an exchange reaction between organic disulfides (RSSRs) and inorganic disulfides, hoping to obtain a composite system that combines the advantages of both. However, while this method integrates the properties of both, it inevitably compromises their respective disadvantages. The resulting product is a complex mixture rather than a single compound, which leads to its electrochemical reaction kinetics and anti-shuttle performance being inferior to either single-component system. At the same time, the reaction conditions of this exchange reaction are demanding to control, the reaction process is difficult to precisely regulate, the product stability is poor, and it is difficult to achieve large-scale preparation and application, thus failing to fundamentally solve the core shortcomings of existing sulfur-based active materials.

[0005] Therefore, how to develop a sulfur-based electrolyte active material that combines high energy density, low shuttle effect, good reaction reversibility and fast kinetic characteristics, and controllable cost remains a core technical challenge that urgently needs to be overcome in the field of sulfur-based flow batteries. It is the key to promoting the practical application and industrialization of sulfur-based flow batteries, and has important practical significance and significant industrial value for reducing the cost of large-scale long-term energy storage, promoting the efficient use of renewable energy, and promoting the high-quality development of the energy storage industry. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an aqueous flow battery electrolyte, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an aqueous flow battery electrolyte, wherein the aqueous flow battery electrolyte comprises an organic polysulfide; the general formula of the organic polysulfide is RS. x - Wherein, 2≤x≤6; R is an organic group containing at least one hydrophilic functional group; the hydrophilic functional group includes at least one of hydroxyl, amino, carboxyl, sulfonic acid, phosphate, quaternary ammonium, amide, guanidine, and the metal salt corresponding to the above groups.

[0008] The aqueous flow battery electrolyte of this invention achieves near 100% coulombic efficiency, while maintaining cycle stability, and exhibits excellent energy efficiency and volumetric capacity by introducing organic polysulfides with specific structures. Furthermore, through the rational design of the organic polysulfide molecular structure, the redox potential, reaction kinetics, and dissolution behavior of the active material can be precisely controlled. This overcomes the technical bottleneck of traditional inorganic polysulfide systems, which struggle to balance "low shuttle effect" and "fast kinetics," demonstrating enormous industrial application potential and market prospects in demanding fields such as large-scale energy storage power stations and industrial waste heat recovery-electrochemical coupling systems.

[0009] In a preferred embodiment of the aqueous flow battery electrolyte of the present invention, the concentration of the organic polysulfide in the aqueous flow battery electrolyte is 0.1 mol / L-6 mol / L.

[0010] In the electrolyte of the aqueous flow battery of this invention, the concentration of organic polysulfides is controlled within the above-mentioned range, which not only provides excellent energy efficiency and volumetric capacity, but also maintains low viscosity and good hydrodynamic properties, ensuring long-term stable operation of the battery under high current density.

[0011] Preferably, the concentration of the organic polysulfide in the electrolyte of the aqueous flow battery is 1 mol / L.

[0012] In a preferred embodiment of the aqueous flow battery electrolyte of the present invention, the value of x is a range of one or both of 2, 3, 4, 5, and 6.

[0013] In the aqueous flow battery electrolyte of this invention, the chain length of organic polysulfides is controlled within the above-mentioned range, which can effectively improve the solubility of active materials and sulfur equivalent per unit volume, so that the electrolyte has high redox potential, excellent energy efficiency and volumetric capacity, as well as good solubility and stability.

[0014] In a preferred embodiment of the aqueous flow battery electrolyte of the present invention, R is a C1-C6 alkyl group containing at least one hydrophilic functional group; and / or, the hydrophilic functional group includes at least one of hydroxyl, carboxyl, and sulfonic acid groups.

[0015] In the aqueous flow battery electrolyte of this invention, the structure of the R group of the organic polysulfide has a significant impact on the overall performance of the active material. When R is selected as a C1-C6 alkyl chain, on the one hand, it can provide appropriate steric hindrance for the organic polysulfide, effectively increasing the effective size of the active molecule, thereby more effectively suppressing its shuttle behavior across the separator and reducing the risk of cross-contamination. On the other hand, the shorter alkyl chain avoids the negative impact of excessive molecular volume on solubility and reaction kinetics, further improving the high dispersibility and rapid mass transfer capability of the active material in the aqueous electrolyte. Furthermore, introducing hydrophilic functional groups such as hydroxyl, carboxyl, or sulfonic acid groups into the R group can significantly enhance the interaction between the organic polysulfide molecules and water molecules, greatly improving its solubility stability in the aqueous phase and preventing precipitation due to insufficient solubility during long-cycle operation. Simultaneously, these hydrophilic functional groups can effectively regulate the electron cloud density of sulfur atoms on the polysulfide chain through inductive or conjugation effects, thereby precisely controlling the redox potential of the organic polysulfide and achieving better voltage matching with the positive electrode active material. In addition, some hydrophilic functional groups (such as carboxyl groups and sulfonic acid groups) can also dissociate in water to form charged groups, which can further inhibit the non-specific adsorption between active materials and membranes and electrodes by utilizing electrostatic repulsion, thereby reducing membrane fouling and electrode passivation, and thus synergistically improving the coulombic efficiency, energy efficiency and cycle life of the battery.

[0016] Preferably, R is an ethyl group containing at least one hydrophilic functional group.

[0017] Preferably, the hydrophilic functional group includes a hydroxyl group.

[0018] As a preferred embodiment of the aqueous flow battery electrolyte of the present invention, the aqueous flow battery electrolyte further comprises an additive; the concentration of the additive in the aqueous flow battery electrolyte is 0.01 mmol / L-50 mmol / L; the additive is a homogeneous catalyst for the electrolyte; the additive includes at least one of cyanocobalamin or its derivative, hematoxylin or its derivative, cobalt tetraaminophthalocyanine or its derivative, and zinc tetrasulfonate phthalocyanine or its derivative.

[0019] Through experiments conducted by the inventors, it was discovered that the aqueous flow battery electrolyte of this invention achieves excellent electrochemical performance even without the addition of additives, exhibiting good charge-discharge reversibility and cycle stability, meeting the basic application requirements of sulfur-based flow batteries. However, with the introduction of additives, the activation energy of the electrochemical reaction is significantly reduced by promoting the breaking and formation of SS bonds in organic polysulfides, thereby accelerating the redox kinetics of the active material during charge and discharge, effectively reducing electrode polarization losses, improving energy efficiency, and maintaining higher capacity output at high current densities without affecting the intrinsic low shuttle effect and long cycle characteristics of the electrolyte, thus further optimizing the overall performance of the electrolyte. Preferably, the concentration of the additive in the aqueous flow battery electrolyte is 0.1 mmol / L-25 mmol / L.

[0020] In the aqueous flow battery electrolyte of this invention, by controlling the concentration of additives within the above-mentioned range, the effect of catalyzing the breaking and formation of SS bonds with high efficiency and stability can be further improved, the activation energy of the reaction can be significantly reduced, the charge transfer process can be accelerated, and the interference of excessive additives on the intrinsic properties of the electrolyte can be avoided. This synergistically improves the energy efficiency, rate performance and cycle stability of the battery, thereby achieving a balance between catalytic effect and system stability.

[0021] More preferably, the concentration of the additive in the aqueous flow battery electrolyte is 1 mmol / L.

[0022] Preferably, the additive includes at least one of cyanocobalamin, hematoxylin, cobalt tetraaminophthalocyanine, and zinc tetrasulfonate phthalocyanine.

[0023] Through experiments conducted by the inventors, it was discovered that when the additives in the electrolyte of the aqueous flow battery of this invention are selected from the above-mentioned compounds, they can more effectively catalyze the electron transfer process of organic polysulfide redox couples, reduce polarization loss, and thus significantly improve energy efficiency and cycle stability.

[0024] Secondly, the present invention provides a method for preparing the electrolyte of the aqueous flow battery, comprising the following steps: S1. Dissolve the organic sulfide precursor and alkali in water, then add sulfur to react and generate organic polysulfides. S2. Add additives to the organic polysulfide to obtain the aqueous flow battery electrolyte.

[0025] The organic polysulfide in the electrolyte of the aqueous flow battery of this invention is an active material with a stable structure and controllable chain length, constructed in situ through a nucleophilic addition-chain growth reaction between a water-soluble organic sulfide precursor and elemental sulfur. Specifically, the sulfur anion generated by the dissociation of the organic sulfide precursor (structure R-SH) in the aqueous phase acts as a nucleophile, launching a nucleophilic attack on the sulfur atoms in elemental sulfur, initiating a ring-opening insertion reaction, thereby achieving precise and controllable growth of the polysulfide chain length. In the resulting organic polysulfide molecule, the organic group R is covalently linked to the end of the polysulfide chain, and the hydrophilic functional group carried on R endows the molecule with high solubility and dispersibility in the aqueous electrolyte.

[0026] In a preferred embodiment of the preparation method of the electrolyte for an aqueous flow battery according to the present invention, in step S1, the organic sulfide precursor includes at least one of the following: mercaptoethanol, mercaptoformic acid, mercaptoethanol, mercaptoacetic acid, mercaptopropanol, mercaptopropionic acid, 3-mercapto-1-propanesulfonic acid, trimercaptotriazine, dimercaptosuccinic acid, dimercaptopropanol, 2,3-dimercaptopropanesulfonic acid, and the metal salt corresponding to the above compounds; and / or, in step S1, the alkali includes at least one of potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonia water.

[0027] Preferably, the organosulfur precursor includes mercaptoethanol.

[0028] Preferably, the alkali includes potassium hydroxide.

[0029] In a preferred embodiment of the preparation method of the aqueous flow battery electrolyte of the present invention, in step S1, the concentration of the organic sulfide precursor in the reaction system is 0.01 mol / L-6 mol / L; and / or, in step S1, the concentration of the alkali in the reaction system is 0.1 mol / L-5 mol / L; and / or, in step S1, the molar ratio of thiol groups to sulfur in the organic sulfide precursor is 1:(1-5).

[0030] Preferably, in step S1, the concentration of the organosulfur precursor in the reaction system is 2 mol / L.

[0031] Preferably, in step S1, the concentration of the alkali in the reaction system is 4 mol / L.

[0032] Preferably, in step S1, the molar ratio of thiol groups to sulfur in the organosulfur precursor is one or both of the following: 1:1, 1:2, 1:3, 1:4, and 1:5.

[0033] This invention controls the molar ratio of thiol groups and sulfur in the organic sulfide precursor within the aforementioned range, enabling precise regulation of the sulfur chain length of the organic polysulfide. This, in turn, synergistically optimizes the redox potential, reaction kinetics, and dissolution behavior of the active material. Consequently, when the aqueous flow battery electrolyte is used in sulfur-based flow batteries, it exhibits high charge-discharge reversibility and excellent long-cycle stability, thus overcoming the technical bottleneck of traditional inorganic polysulfide systems that struggle to balance low shuttle effect and rapid kinetics.

[0034] Thirdly, the present invention provides a sulfur-based flow battery, the sulfur-based flow battery comprising a positive electrode electrolyte, a negative electrode electrolyte and a separator; the negative electrode electrolyte comprises the aqueous flow battery electrolyte described above.

[0035] As a preferred embodiment of the sulfur-based flow battery of the present invention, the sulfur-based flow battery is any one of the following: sulfur-iron flow battery, sulfur-iodine flow battery, sulfur-manganese flow battery, zinc-sulfur flow battery, sulfur-bromine flow battery, or sulfur-organic flow battery.

[0036] Preferably, the sulfur-based flow battery is a sulfur-iron flow battery; the positive electrode electrolyte is an aqueous solution containing ferrocyanide; and the concentration of ferrocyanide in the positive electrode electrolyte is 0.5 mol / L-1.6 mol / L.

[0037] More preferably, the concentration of ferrocyanide in the positive electrode electrolyte is 1 mol / L.

[0038] Fourthly, the present invention provides the aqueous flow battery electrolyte and the sulfur-based flow battery in the field of energy storage.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: First, in the aqueous flow battery electrolyte of the present invention, the molecular size of the organic polysulfides generated in situ is significantly larger than that of traditional inorganic polysulfide ions. This significantly increases the free volume required for them to cross the membrane and the difficulty in overcoming steric hindrance, thereby reducing cross-contamination of active materials from the source. This allows for extremely high coulombic efficiency and long-term cycle stability even when using ordinary ion exchange membranes or even ultra-thin membranes. Second, in the aqueous flow battery electrolyte of the present invention, the electrochemical activity of the organic polysulfides originates from the S–S bond, which has a low dissociation energy and good reaction reversibility, inheriting the advantages of inorganic polysulfides. The rapid charge-discharge characteristics of organic polysulfides result in significantly higher voltage and energy efficiencies compared to simple organic disulfide systems. Furthermore, the aqueous flow battery electrolyte of this invention improves the solubility of active materials and sulfur equivalent per unit volume by precisely controlling the sulfur chain length and organic framework structure of the organic polysulfides, thereby achieving high volumetric energy density to meet the requirements of compact energy storage systems. Simultaneously, the aqueous flow battery electrolyte of this invention employs a one-step direct chemical reaction, eliminating the need for complex separation or purification steps, and the raw materials involve only inexpensive and readily available elemental sulfur powder and common organic thiols, greatly reducing the cost and technical barriers to large-scale production. Moreover, the aqueous flow battery electrolyte of this invention, through flexible molecular-level design of the types, quantities, and charge states of hydrophilic functional groups in the R group, can simultaneously achieve multiple optimization goals such as reducing permeability, increasing potential, and enhancing solubility, providing a rich molecular toolbox and broad technical expansion space for the rational development of subsequent high-performance aqueous flow batteries. Attached Figure Description

[0040] Figure 1 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 1 of the present invention. Figure 2 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 2 of the present invention. Figure 3 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 3 of the present invention. Figure 4 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 4 of the present invention. Figure 5 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 5 of the present invention. Figure 6The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 6 of the present invention. Figure 7 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Example 7 of the present invention. Figure 8 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Comparative Example 1 of this invention are shown. Figure 9 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Comparative Example 2 of the present invention are shown. Figure 10 The voltage-capacity difference curve and long-cycle capacity-efficiency stability test graph of the sulfur-based flow battery prepared with the aqueous flow battery electrolyte of Comparative Example 3 of this invention are shown. Figure 11 This is a schematic diagram of the electrolyte in the aqueous flow battery of Embodiments 5, 6 and Comparative Example 5 of the present invention. Detailed Implementation

[0041] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0042] The following description, in conjunction with specific embodiments, illustrates the practical effects of the present invention.

[0043] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0044] Example 1: This embodiment provides an aqueous flow battery electrolyte, the preparation method of which includes the following steps: (1) Add 7.9 g (0.1 mol) mercaptoethanol and 11.2 g (0.2 mol) potassium hydroxide (KOH) to 50 mL of deionized water and stir thoroughly until completely dissolved; (2) Add 9.6g (0.3mol) of sulfur powder to the solution obtained in step (1) and stir thoroughly until completely dissolved; (3) Add 135 mg of cyanocobalamin as a homogeneous catalyst to the solution obtained in step (2), stir until it is completely dissolved, and then make up to 100 mL with deionized water to obtain the electrolyte for the aqueous flow battery.

[0045] Example 2: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (1), 7.9 g (0.1 mol) of mercaptoethanol was replaced with 9.4 g (0.1 mol) of mercaptoacetic acid; The remaining components and steps are the same as in Example 1.

[0046] Example 3: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (1), 7.9 g (0.1 mol) of mercaptoethanol was replaced with 10.72 g (0.1 mol) of 3-mercaptopropionic acid; The remaining components and steps are the same as in Example 1.

[0047] Example 4: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (1), 7.9 g (0.1 mol) of mercaptoethanol was replaced with 17.99 g (0.1 mol) of sodium 3-mercapto-1-propanesulfonate; The remaining components and steps are the same as in Example 1.

[0048] Example 5: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (2), the amount of sulfur powder used is 3.2g (0.1mol); The remaining components and steps are the same as in Example 1.

[0049] Example 6: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (2), the amount of sulfur powder used is 16g (0.5mol); The remaining components and steps are the same as in Example 1.

[0050] Example 7: This embodiment provides an aqueous flow battery electrolyte, which differs from Embodiment 1 only in that: In step (3), 135 mg of cyanocobalamin is replaced with 65 mg of hematoxylin; The remaining components and steps are the same as in Example 1.

[0051] Comparative Example 1: This comparative example provides an aqueous flow battery electrolyte, the preparation method of which includes the following steps: (1) Add 11.3g (0.1mol) K2S and 11.2g (0.1mol) potassium hydroxide (KOH) to 50mL of deionized water and stir thoroughly until completely dissolved; (2) Add 3.2g (0.1mol) of sulfur powder to the solution obtained in step (1) and stir thoroughly until completely dissolved; (3) Add 135 mg of cyanocobalamin as a homogeneous catalyst to the solution obtained in step (2), stir until it is completely dissolved, and then make up to 100 mL with deionized water to obtain an aqueous flow battery electrolyte containing inorganic polysulfides.

[0052] Comparative Example 2: This comparative example provides an aqueous flow battery electrolyte, the preparation method of which includes the following steps: s (1) Add 15.43 g (0.1 mol) of 2,2'-dithiodiethanol (HEDS) and 11.2 g (0.2 mol) of potassium hydroxide (KOH) to 50 mL of deionized water and stir thoroughly until completely dissolved; (2) Add 135 mg of cyanocobalamin as a homogeneous catalyst to the solution obtained in step (1), stir until it is completely dissolved, and then dilute to 100 mL with deionized water to obtain an aqueous flow battery electrolyte containing organic disulfide.

[0053] Comparative Example 3: This comparative example provides an aqueous flow battery electrolyte, the preparation method of which includes the following steps: (1) Add 11.3g (0.1mol) K2S, 15.43g (0.1mol) 2,2'-dithiodiethanol (HEDS) and 11.2g (0.2mol) potassium hydroxide (KOH) to 50mL of deionized water and stir thoroughly until completely dissolved; (2) Add 135 mg of cyanocobalamin as a homogeneous catalyst to the solution obtained in step (1), stir until it is completely dissolved, and then make up to 100 mL with deionized water to obtain an aqueous flow battery electrolyte containing an organic disulfide-inorganic disulfide complex.

[0054] Comparative Example 4: This comparative example provides an aqueous flow battery electrolyte, which differs from Example 1 only in that: In step (2), the amount of sulfur powder used is 0g; The remaining components and steps are the same as in Example 1; The product obtained is RS - (Thiols), in which sulfur is in the -2 valence state, the lowest reduction state, and cannot be further reduced, meaning the battery cannot be charged and cannot be used as an active material in flow batteries.

[0055] Comparative Example 5: This comparative example provides an aqueous flow battery electrolyte, which differs from Example 1 only in that: In step (2), the amount of sulfur powder used is 19.2g; The remaining components and steps are the same as in Example 1; The product obtained is R-S7 - Structure, however, as Figure 11 As shown on the right, a large amount of undissolved sulfur powder precipitates in the solution after the reaction, and obvious solid residues are visible at the bottom of the solution. This indicates that the sulfur chains are too long, resulting in insufficient solubility and posing a risk of clogging the flow battery pipes and stack, making it unsuitable as a practical electrolyte.

[0056] Test example: Test method: The aqueous flow battery electrolytes prepared in Examples 1-7 and Comparative Examples 1-3 were used as negative electrode electrolytes, and an aqueous solution of potassium ferrocyanide (K4[Fe(CN)6]) and sodium ferrocyanide (Na4[Fe(CN)6]) with a concentration of 0.5 mol / L was used as positive electrode electrolytes. A Nafion 115 cation exchange membrane was used as the separator to assemble a sulfur-iron flow battery.

[0057] The battery performance was tested at room temperature using a constant current charge-discharge test system with a current density of 40 mA / cm². 2 The voltage window is 0.5-1.6V. The balance voltage, coulombic efficiency, energy efficiency, volumetric specific capacity, and capacity retention rate after 100 cycles of each battery during the first charge and discharge are recorded.

[0058] The test results are shown in Table 1: Table 1. Performance test results of aqueous flow battery electrolytes in Examples 1-7 and Comparative Examples 1-3. As shown in Table 1 and Figure 1-11As shown, the aqueous flow battery electrolyte containing organic polysulfides prepared in this embodiment of the invention, when used as the negative electrode active material in a sulfur-iron flow battery, exhibits significant comprehensive performance advantages. Specifically, the sulfur-iron flow battery prepared with the aqueous flow battery electrolyte of this embodiment of the invention maintains a capacity retention rate of no less than 99.23% after 100 cycles of constant current charge-discharge testing, which is much higher than that of the comparative examples (94.01% for Comparative Example 1 and 97.17% for Comparative Example 3). This indicates that the introduction of the organic framework in this invention effectively suppresses the polysulfide shuttle effect and side reactions, and significantly reduces irreversible side reactions on the negative electrode side (such as sulfur precipitation and disproportionation reactions). Furthermore, thanks to the steric hindrance effect and possible electrostatic repulsion of the organic groups, the electrolyte exhibits excellent performance during long-term cycling. The excellent chemical and electrochemical structural stability was maintained, laying the foundation for the construction of long-life flow battery systems. Secondly, the coulombic efficiencies of the sulfur-iron flow batteries prepared with the aqueous flow battery electrolyte in the embodiments of this invention are all above 99.9%, reaching a maximum of 99.99%, significantly better than Comparative Example 1 (98.1%) and Comparative Examples 2-3 (approximately 99.0%). Furthermore, from the perspective of coulombic efficiency loss, the maximum coulombic efficiency loss in the embodiments of this invention is only 0.08% (Example 5, 99.92%), while the minimum coulombic efficiency in the comparative examples has reached 0.9% (…). Comparative Example 2 (99.1%) shows that the aqueous flow battery electrolyte of the present invention achieves more than ten times the optimization of coulombic efficiency loss. This further illustrates that the redox reaction of the organic polysulfides constructed in this invention on the negative electrode side has excellent reversibility, with almost no irreversible capacity loss or cross-contamination of active materials. Furthermore, the ultra-high coulombic efficiency not only means extremely low shuttle current but also reduces the stringent requirements on the selectivity of the ion exchange membrane, providing a technical possibility for using low-cost, high-conductivity membranes. In addition, the sulfur-iron mixture prepared by the aqueous flow battery electrolyte of this embodiment of the present invention... The equilibrium voltage of the flow battery (0.945-1.022V) is generally higher than that of the comparative example (0.913-0.985V), and its higher equilibrium voltage helps to directly improve the energy density and power density of the battery. In terms of energy efficiency, the embodiments of the present invention can achieve an energy efficiency of 72.31%-78.69%, which is significantly better than that of the comparative example (61.8%-66.3%), and its volumetric specific capacity can reach up to 26.42Ah / L, which is better than the best value in the comparative example (26.17Ah / L), and is maintained above 25.5Ah / L overall. The above results show that the aqueous flow battery electrolyte constructed in this invention has significant advantages in terms of comprehensive electrochemical performance.In contrast, Comparative Examples 1-3 failed to achieve the comprehensive performance level of the organic polysulfide system of this invention due to shuttle effect, structural instability, or solubility issues. Comparative Example 4 completely lacked energy storage functionality. Comparative Example 5 generated excessively long sulfur chains, resulting in insufficient solubility and the formation of large amounts of precipitates, posing a risk of clogging the flow battery pipelines and stack, making it unsuitable for practical application. This fully demonstrates the enormous potential of the aqueous flow battery electrolyte containing organic polysulfides of this invention as a next-generation high-stability, high-reversibility aqueous flow battery anode material.

[0059] In summary, the aqueous flow battery electrolyte containing organic polysulfides of this invention achieves near 100% coulombic efficiency, over 99.2% capacity retention per 100 cycles, and excellent energy efficiency (72.31%-78.69%) and volumetric specific capacity (25.5 Ah / L-26.42 Ah / L) through precise control of the type of mercapto compound, sulfur content, and homogeneous catalyst. This electrolyte not only endows sulfur-based flow batteries with extremely high charge-discharge reversibility and near-attenuation long-cycle stability, but also precisely controls the redox potential, reaction kinetics, and dissolution behavior of active materials through the rational design of the organic polysulfide molecular structure. This overcomes the technical bottleneck of traditional inorganic polysulfide systems, which struggle to balance "low shuttle effect" and "fast kinetics," demonstrating enormous industrial application potential and market prospects in demanding fields such as large-scale energy storage power stations and industrial waste heat recovery-electrochemical coupling systems.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An aqueous flow battery electrolyte, characterized in that, The electrolyte of the aqueous flow battery includes organic polysulfides; the general formula of the organic polysulfides is RS. x - ; Wherein, 2≤x≤6; R is a C1-C6 alkyl group containing at least one hydrophilic functional group; the hydrophilic functional group includes at least one of hydroxyl, carboxyl, sulfonic acid, and metal salts corresponding to the above groups; The electrolyte of the aqueous flow battery also contains additives; the additives include at least one of cyanocobalamin or its derivatives, hematoxylin or its derivatives, tetraaminophthalocyanine cobalt or its derivatives, and tetrasulfonated phthalocyanine zinc or its derivatives. The preparation method of the electrolyte for the aqueous flow battery includes the following steps: S1. Dissolve the organic sulfide precursor and alkali in water, then add sulfur to react and generate organic polysulfides. S2. Add additives to the organic polysulfide to obtain the aqueous flow battery electrolyte; In step S1, the organosulfur precursor includes at least one of the following: mercaptoethanol, mercaptoformic acid, mercaptoethanol, mercaptoacetic acid, mercaptopropanol, mercaptopropionic acid, 3-mercapto-1-propanesulfonic acid, trimercaptotriazine, dimercaptosuccinic acid, dimercaptopropanol, 2,3-dimercaptopropanesulfonic acid, and the metal salts corresponding to the above compounds. In step S1, the alkali includes at least one of potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonia water.

2. The aqueous flow battery electrolyte as described in claim 1, characterized in that, The concentration of the additive in the electrolyte of the aqueous flow battery is 0.01 mmol / L-50 mmol / L.

3. The aqueous flow battery electrolyte as described in claim 1, characterized in that, In step S1, the concentration of the organosulfur precursor in the reaction system is 0.01 mol / L-6 mol / L; and / or, in step S1, the concentration of the base in the reaction system is 0.1 mol / L-5 mol / L; and / or, in step S1, the molar ratio of thiol groups to sulfur in the organosulfur precursor is 1:(1-5).

4. A sulfur-based flow battery, characterized in that, It includes a positive electrode electrolyte, a negative electrode electrolyte, and a separator, wherein the negative electrode electrolyte includes the aqueous flow battery electrolyte according to any one of claims 1-3.

5. The sulfur-based flow battery as described in claim 4, characterized in that, The sulfur-based flow battery is any one of the following: sulfur-iron flow battery, sulfur-iodine flow battery, sulfur-manganese flow battery, zinc-sulfur flow battery, sulfur-bromine flow battery, or sulfur-organic flow battery.

6. The sulfur-based flow battery as described in claim 5, characterized in that, The sulfur-based flow battery is a sulfur-iron flow battery; the positive electrode electrolyte is an aqueous solution containing ferrocyanide; the concentration of ferrocyanide in the positive electrode electrolyte is 0.5 mol / L-1.6 mol / L.

7. The application of the aqueous flow battery electrolyte according to any one of claims 1-3 and the sulfur-based flow battery according to any one of claims 4-6 in the field of energy storage.

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