Zinc-bromine flow battery electrolyte and application thereof

Abstract

The invention discloses a zinc-bromine flow battery electrolyte and application thereof. The electrolyte comprises a zinc salt, a supporting electrolyte salt, a solvent matrix and a bromine complexing agent, wherein the solvent matrix is composed of water and at least five organic solvents. According to the electrolyte, at least five organic solvents are introduced into a water-zinc salt system to form a high-entropy solvation structure, a hydrogen bond network of water is destroyed through high-configuration entropy, the freezing point is remarkably reduced, the water activity and a zinc ion solvation structure are regulated and controlled, and therefore high ionic conductivity and proper viscosity are achieved at the same time at the low temperature. According to the invention, the low-temperature anti-freezing performance of the electrolyte and the stability of an electrode interface are synergistically improved, and an effective solution is provided for long-acting operation of the zinc-bromine flow battery in a wide temperature range.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to zinc-bromine flow battery electrolyte and its applications. Background Technology

[0002] Large-scale energy storage is key to improving the utilization rate of renewable energy and the grid's regulation capacity, and flow batteries are one important direction. Zinc halide flow batteries are promising due to their low cost and good safety, but their performance is directly affected by the electrolyte.

[0003] The main challenge is that zinc anodes are prone to dendrite formation during cycling, leading to short circuits, side reactions, and reduced lifespan. The problem is exacerbated at low temperatures: ion diffusion slows down, polarization increases, dendrite growth is faster, and the electrolyte is prone to freezing, causing system failure.

[0004] Existing research focuses primarily on improving room-temperature performance, such as optimizing the separator and current collector, but it struggles to address the issue of electrolyte solidification at low temperatures. Low-temperature electrolyte research is still in its early stages, with two main approaches: one is to use novel complexing agents to suppress the phase transition of polybrominated species, but this has limited impact on improving the reversibility of the zinc anode; the other is to use high-concentration electrolytes to lower the freezing point, but this approach is mostly limited to small static batteries and is difficult to apply to practical fluid flow systems.

[0005] Therefore, developing an electrolyte that combines low-temperature freeze resistance with a highly reversible zinc anode is of great significance for promoting the application of zinc-bromine flow batteries in a wide temperature range, especially in frigid regions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a zinc-bromine flow battery electrolyte and its applications. This electrolyte introduces at least five organic solvents into a water-zinc salt system to form a "high-entropy solvation structure." By disrupting the hydrogen bond network of water through high configurational entropy, the freezing point is significantly lowered, and the water activity and zinc ion solvation structure are controlled, thereby achieving both high ionic conductivity and suitable viscosity at low temperatures. This invention synergistically improves the low-temperature antifreeze performance and electrode interface stability of the electrolyte, providing an effective solution for the long-term operation of zinc-bromine flow batteries over a wide temperature range.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a zinc-bromine flow battery electrolyte, the electrolyte comprising a zinc salt, a supporting electrolyte salt, a solvent matrix, and a bromine complexing agent; wherein the solvent matrix is ​​composed of water and not less than five organic solvents.

[0008] Furthermore, the zinc salt is zinc bromide with a concentration of 0.5-5 mol / L.

[0009] Furthermore, the supporting electrolyte salt is potassium chloride, with a concentration of 0.5-5 mol / L.

[0010] Furthermore, the composition of the solvent matrix satisfies the following: the water content is 100-180 parts by volume, the content of each individual organic solvent is 4-120 parts by volume, and the total content of all organic solvents is 140-400 parts by volume.

[0011] Furthermore, the organic solvent is selected from any five or more of the following: tetrahydrofuran, 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, acetone, propylene carbonate, glycerol, methanol, ethylene glycol dimethyl ether, N-methylpyrrolidone, tetraethylene glycol dimethyl ether, triethyl phosphate, N,N-dimethylacetamide, trimethyl phosphate, and dimethyl carbonate.

[0012] Furthermore, the organic solvent is selected from any five or more of 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, methanol, N-methylpyrrolidone, and dimethyl carbonate.

[0013] Furthermore, the content of each individual organic solvent is 4-100 parts by volume.

[0014] Further, the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide, with a concentration of 0.1-2 mol / L.

[0015] In a second aspect, the present invention also provides a zinc-bromine flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, a separator disposed between the positive electrode electrolyte and the negative electrode electrolyte, a positive electrode, a negative electrode, and a bipolar plate, wherein the positive electrode electrolyte and / or the negative electrode electrolyte are zinc-bromine flow battery electrolytes as described in any of the first aspects above.

[0016] Furthermore, the positive electrode electrolyte and the negative electrode electrolyte have the same composition.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Excellent low temperature performance: By constructing a "high entropy solvation structure" composed of water and no less than five organic solvents that are mutually soluble and chemically complementary, the high configurational entropy effect effectively destroys the regular hydrogen bond network of water, significantly reducing the freezing point of the electrolyte, so that it can still maintain good fluidity and pumpability in deep low temperature environment, ensuring the normal operation of the flow battery system under severe cold conditions. (2) High anode stability: Multi-component solvents synergistically regulate water activity and zinc ion solvation structure, reduce desolvation energy barrier, promote uniform and dense zinc deposition, effectively suppress dendrite growth and hydrogen evolution side reaction, and improve anode cycle life. (3) Integrated system solution: Starting from the essence of electrolyte medium, it simultaneously solves the two major problems of low temperature solidification and negative electrode interface deterioration, provides a systematic solution, and breaks through the limitations of existing technology. (4) Strong engineering adaptability: The formulation system can adjust key parameters such as ionic strength, conductivity and viscosity within a wide range, and is compatible with different battery architectures and commercial separators, with good potential for engineering and large-scale application. Attached Figure Description

[0018] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below. For those skilled in the art, other related drawings can be obtained from the above drawings without any creative effort.

[0019] Figure 1 Comparative optical photographs of Comparative Example 1 and Example 1 taken at 25°C / -50°C; Figure 2 The graphs show the ionic conductivity of Comparative Example 1 and Example 1 at different temperatures; Figure 3 Thermogravimetric analysis (TGA) results for Comparative Example 1 and Example 1; Figure 4 This is a schematic diagram of the cycling of Example 1 in a zinc-bromine flow battery at -30°C. Detailed Implementation

[0020] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] This invention provides a zinc-bromine flow battery electrolyte, which includes a zinc salt, a supporting electrolyte salt, a solvent matrix, and a bromine complexing agent; wherein the solvent matrix is ​​composed of water and no less than five organic solvents.

[0022] In this invention, the core design of the zinc-bromine flow battery electrolyte lies in constructing a high-entropy solvation structure system formed by "water + ≥5 kinds of organic solvents". This system utilizes the synergistic effect of multiple components to effectively suppress the formation of ordered hydrogen bond networks of water molecules at low temperatures by increasing configurational entropy, thereby significantly enhancing the low-temperature flow performance of the electrolyte. Simultaneously, the multi-component solvents, through synergistic regulation of water activity and zinc ion solvation structure, can effectively suppress hydrogen evolution side reactions, optimize zinc deposition kinetics, and inhibit dendrite formation, thereby systematically improving the reversibility of the negative electrode. Compared to the traditional approach that mainly relies on bromine complexing agents to regulate the positive electrode reaction, this invention starts from the electrolyte medium level, simultaneously improving the two key challenges of "freezing resistance" and "negative electrode dendrite / hydrogen evolution suppression" through the high-entropy solvation structure.

[0023] In addition, the system is based on "water + multiple solvents + supporting electrolyte salt + bromine complexing agent" to build an adjustable formulation platform that can be adapted to different battery architectures and commercial separators, and has good engineering adaptability and transfer potential.

[0024] In some embodiments, the zinc salt is zinc bromide with a concentration of 0.5-5 mol / L. In exemplary cases, the concentrations can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L.

[0025] In some embodiments, the supporting electrolyte salt is potassium chloride with a concentration of 0.5-5 mol / L. In exemplary cases, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L.

[0026] In some embodiments, the composition of the solvent matrix satisfies the following: the water content is 100-180 parts by volume, the content of each individual organic solvent is 4-120 parts by volume, and the total content of all organic solvents is 140-400 parts by volume.

[0027] In this embodiment of the invention, the solvent matrix of the electrolyte is constructed as a multi-component system consisting of water and no fewer than five miscible organic solvents. This "miscibility" characteristic is the prerequisite and foundation for the high-entropy solvation structure design, and its significance is mainly reflected in three aspects: First, it ensures uniform dispersion of the solvent at the molecular scale, achieving high configurational entropy and effectively disrupting the low-temperature hydrogen bond network to guarantee the low-temperature fluidity of the electrolyte; second, it enables water and various organic solvents to form a uniform intermolecular interaction network, synergistically inhibiting low-temperature solidification; and third, it provides a consistent chemical environment for zinc ions, enabling multiple solvents to synergistically regulate the ion solvation structure, achieving interface optimization such as suppressing side reactions and promoting uniform deposition. Therefore, solvent miscibility is a necessary condition for constructing a high-entropy homogeneous system and achieving the integrated function of "antifreeze-interface stability".

[0028] In some embodiments, the organic solvent is selected from any five or more of the following: tetrahydrofuran, 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, acetone, propylene carbonate, glycerol, methanol, ethylene glycol dimethyl ether, N-methylpyrrolidone, tetraethylene glycol dimethyl ether, triethyl phosphate, N,N-dimethylacetamide, trimethyl phosphate, and dimethyl carbonate.

[0029] In a preferred embodiment, the organic solvent is selected from any five or more of 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, methanol, N-methylpyrrolidone, and dimethyl carbonate.

[0030] In a preferred embodiment, the content of each individual organic solvent is 4-100 parts by volume.

[0031] In some embodiments, the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide with a concentration of 0.1-2 mol / L. In exemplary cases, it can be 0.1 mol / L, 0.3 mol / L, 0.6 mol / L, 0.9 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L.

[0032] In a preferred embodiment, the preparation of the electrolyte of the present invention includes the following steps: taking 53 μL of pure water and mixing it with 100 μL of electrolyte containing 3 mol·L⁻¹ -1 ZnBr2, 3 mol·L -1 KCl and 0.3 mol·L -1 An aqueous solution of 1-methyl-1-ethylpyrrolidone bromide was mixed, followed by the sequential addition of 23 μL ethylene glycol, 12 μL N,N-dimethylformamide, 93 μL methanol, 15 μL N-methylpyrrolidone, and 4 μL 1,4-dioxane. After thorough mixing, a high-entropy electrolyte with a total volume of 300 μL was obtained. The final composition of this electrolyte was: 1 mol·L⁻¹ -1 ZnBr2, 1 mol·L -1 KCl, 0.1 mol·L -1 1-Methyl-1-ethylpyrrolidine bromide, and a variety of organic solvents.

[0033] Furthermore, this application also provides a zinc-bromine flow battery, including a positive electrode electrolyte, a negative electrode electrolyte, a separator disposed between the positive electrode electrolyte and the negative electrode electrolyte, a positive electrode, a negative electrode, and a bipolar plate, wherein the positive electrode electrolyte and / or the negative electrode electrolyte is the zinc-bromine flow battery electrolyte described in any of the above embodiments.

[0034] In some embodiments, the positive electrode electrolyte and the negative electrode electrolyte have the same composition.

[0035] To further illustrate the technical effects of the present invention, the following specific embodiments are also provided.

[0036] Example 1 The neutral zinc-bromine flow battery uses a neutral zinc-bromine flow electrolyte with a positive and negative electrode composition of 1 mol / L ZnBr2 + 1 mol / L KCl + 0.1 mol / L 1-methyl-1-ethylpyrrolidone bromide, and solvents of water, ethylene glycol, N,N-dimethylformamide, methanol, N-methylpyrrolidone, and 1,4-dioxane. The example used a high-entropy electrolyte, abbreviated as HEE.

[0037] Comparative Example 1 The neutral zinc-bromine flow battery uses a neutral zinc-bromine flow electrolyte with a positive and negative electrode composition of 1 mol / L ZnBr2 + 1 mol / L KCl + 0.1 mol / L 1-methyl-1-ethylpyrrolidine bromide, and water as the solvent. Comparative Example 1 is used as the reference electrolyte, abbreviated as BE.

[0038] Freeze-thaw test: The electrolytes prepared in Example 1 and Comparative Example 1 were placed in a freezer at -50°C, and the results are as follows. Figure 1 As shown, after 7 days of freezing, the electrolyte HEE in Example 1 remained liquid, while the electrolyte BE in Comparative Example 1 was clearly frozen.

[0039] Conductivity and thermogravimetric analysis: The electrolytes prepared in Example 1 and Comparative Example 1 were subjected to ionic conductivity and thermogravimetric analysis, and the results are as follows: Figure 2 and Figure 3 As shown. Example 1 exhibited good ionic conductivity and antifreeze properties, while Comparative Example 1 showed a sharp decrease in ionic conductivity. Combined with... Figure 3 Thermogravimetric analysis suggests that the cause may be that the electrolyte froze at -7.9℃.

[0040] Performance testing: A zinc-bromine flow battery was assembled using the electrolyte prepared in Example 1. The positive electrode was a carbon felt, the negative electrode was a carbon felt with a zinc sheet, the bipolar plate was a graphite plate, and the separator was a commercially available microporous membrane for zinc-bromine flow batteries with an effective area of ​​4 cm². 2 The current density is 10 mA cm⁻¹ -2 The surface area capacity is 5 mAh cm⁻¹ -2 The result is as follows Figure 4 As shown, the zinc-bromine flow battery assembled at -30℃ has a coulombic efficiency (CE) of 98.62%, an energy efficiency (EE) of 48.63%, and a battery life of >280 cycles.

[0041] Compared to existing technologies, this invention offers significant improvements in low-temperature performance, anode stability, system integration, and engineering adaptability. By constructing a high-entropy solvation structure formed by water and various miscible organic solvents, the high configurational entropy effect breaks the hydrogen bond network of water, significantly lowering the electrolyte's freezing point. This allows the electrolyte to maintain good fluidity and pumpability even in cryogenic environments, ensuring stable operation of the flow battery under extreme cold conditions. Simultaneously, the multi-component solvents synergistically regulate water activity and zinc ion solvation structure, reducing the desolvation energy barrier, promoting uniform and dense zinc deposition, effectively suppressing dendrite growth and hydrogen evolution side reactions, and improving the anode cycle life. This invention addresses the two key issues of low-temperature solidification and anode interface deterioration from the perspective of electrolyte fundamentals, providing an integrated system solution. Furthermore, the key parameters of this electrolyte system, such as ionic strength, conductivity, and viscosity, can be adjusted within a wide range, making it compatible with various battery architectures and commercial separators, and possessing excellent potential for engineering and large-scale application.

[0042] The specific embodiments of the present invention have been described above. It should be understood that the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A zinc-bromine flow battery electrolyte, characterized in that, The electrolyte comprises a zinc salt, a supporting electrolyte salt, a solvent matrix, and a bromine complexing agent; wherein the solvent matrix is ​​composed of water and no fewer than five organic solvents.

2. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The zinc salt is zinc bromide, with a concentration of 0.5-5 mol / L.

3. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The supporting electrolyte salt is potassium chloride, with a concentration of 0.5-5 mol / L.

4. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The composition of the solvent matrix satisfies the following: the water content is 100-180 parts by volume, the content of each individual organic solvent is 4-120 parts by volume, and the total content of all organic solvents is 140-400 parts by volume.

5. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The organic solvent is selected from any five or more of the following: tetrahydrofuran, 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, acetone, propylene carbonate, glycerol, methanol, ethylene glycol dimethyl ether, N-methylpyrrolidone, tetraethylene glycol dimethyl ether, triethyl phosphate, N,N-dimethylacetamide, trimethyl phosphate, and dimethyl carbonate.

6. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The organic solvent is selected from any five or more of 1,4-dioxane, dimethyl sulfoxide, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol, N,N-dimethylformamide, acetonitrile, methanol, N-methylpyrrolidone, and dimethyl carbonate.

7. The zinc-bromine flow battery electrolyte according to claim 6, characterized in that, The content of each of the individual organic solvents is 4-100 parts by volume.

8. The zinc-bromine flow battery electrolyte according to claim 1, characterized in that, The bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide, with a concentration of 0.1-2 mol / L.

9. A zinc-bromine flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, a separator disposed between the positive electrode electrolyte and the negative electrode electrolyte, a positive electrode, a negative electrode, and a bipolar plate, characterized in that, The positive electrode electrolyte and / or the negative electrode electrolyte are zinc-bromine flow battery electrolytes as described in any one of claims 1-6.

10. The zinc-bromine flow battery according to claim 9, characterized in that, The positive electrode electrolyte and the negative electrode electrolyte have the same composition.

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