Titanium-chlorine flow battery electrolyte, application thereof and titanium-chlorine flow battery

Abstract

The invention discloses a titanium-chlorine flow battery electrolyte, application thereof and a titanium-chlorine flow battery, and belongs to the field of flow batteries. Titanium salt, chlorine salt and amine compounds are adopted as main active components of the electrolyte. The amine compound used in the electrolyte can rapidly react with chlorine gas generated in the positive electrode side chlorine salt charging process to generate a chloro amine compound, a stable charging product is formed, and reversible discharging is carried out. The titanium chlorine redox flow battery composed of titanium salt on the negative electrode side can perform cyclic charging and discharging at coulombic efficiency close to 98%, almost does not release harmful chlorine, has the advantages of environmental friendliness, low price, high energy density and the like, and is suitable for large-scale energy storage.

Description

Technical Field

[0001] This application relates to a titanium chloride flow battery electrolyte and its application, and to a titanium chloride flow battery, belonging to the field of flow batteries. Background Technology

[0002] In modern energy systems, renewable energy has gradually become an important component due to its clean, pollution-free, and sustainable characteristics. However, renewable energy sources such as wind and solar power suffer from discontinuity and instability, limiting their further development. Energy storage technology can address these issues through peak shaving and frequency regulation, enabling the grid integration and consumption of renewable energy. Flow batteries, as an emerging energy storage technology, have attracted significant attention in recent years due to their high safety, independently designable storage capacity and power, and lack of geographical limitations. Flow batteries can use different elements as active materials, with halogens often used as positive electrode active elements due to their suitable redox electrode potentials, high electrochemical activity, and low price. Among halogens, bromine and iodine are particularly widely used, such as in zinc-bromine and zinc-iodine flow batteries. However, chlorine, another element with higher abundance, is rarely used as an active element, mainly because it produces chlorine gas during charging. Chlorine gas has extremely low solubility in water and is easily released into the air, making reversible discharge impossible. Furthermore, chlorine gas poses a significant health hazard if released into the environment, greatly compromising the safety of chlorine-based batteries. To address the solubility issue of chlorine, common practices include cryogenic cooling or using organic solvents such as carbon tetrachloride to form low-temperature hydrates with chlorine or dissolve it in an organic solvent. While these methods can immobilize chlorine to some extent, they also significantly increase the complexity and cost of the system. Therefore, it is necessary to develop alternative methods that use elemental chlorine instead of chlorine gas as the active material to fundamentally solve the problems associated with chlorine-based flow batteries. Summary of the Invention

[0003] To address the above technical problems, this invention aims to provide a titanium chloride flow battery electrolyte, its application, and a titanium chloride flow battery.

[0004] This invention employs both chloride salts and amine compounds as positive electrode active materials in the electrolyte. The amine compounds selected in this invention exhibit high chemical reactivity with chlorine gas. During battery charging, the chlorine gas generated by the chloride salts quickly reacts with the amine compounds in the solution to form chloroamine compounds (such as chlorothioamide), preventing harmful chlorine gas from escaping from the solution. The electron-withdrawing groups surrounding the amino group give the amino group a certain ability to dissociate hydrogen atoms into protons. During electrochemical oxidation, the charged chlorine can undergo an electrophilic substitution reaction with the amino group, thereby generating stable chloroamine compounds. The entire reaction is a proton-coupled electron transfer reaction process that can proceed smoothly under acidic conditions. The generated chloroamine compounds are electrochemically active and can reversibly discharge, enabling the battery to stably cycle through charge and discharge. This method converts the active material generated during positive electrode charging from chlorine gas into chloroamine compounds, fundamentally solving the problem of chlorine gas release. Using titanium salts as the negative electrode active material, and adding a certain amount of supporting electrolyte, it can serve as a component of the electrolyte in a titanium-chlorine flow battery. Titanium chloride flow batteries using this electrolyte can perform long charge-discharge cycles with high coulombic efficiency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The electrolyte contains chloride salts;

[0007] The chloride salt is at least one or more of sodium chloride, potassium chloride, ammonium chloride, hydrochloric acid, magnesium chloride, calcium chloride, and other chloride-containing salts, preferably sodium chloride.

[0008] The chloride ion concentration is 0.01-6 mol / L. -1 Preferably 1-3 mol L -1 .

[0009] The electrolyte contains titanium salts;

[0010] The titanium salt is at least one or more of titanium sulfate, titanium tetrachloride, titanium bromide, and potassium fluorotitanate, preferably titanium sulfate.

[0011] The concentration of titanium salt is 0.1-3 mol / L. -1 Preferably 1-2 mol L -1 Titanium salts are mainly used as negative electrode active materials to match the positive electrode, and are not the main innovation of this invention. The main innovation of this invention lies in the combined use of chloride salts and amine compounds on the positive electrode side.

[0012] The electrolyte contains amine compounds;

[0013] The amine compound is at least one or more of thioamide, methanesulfonamide, N-methylmethanesulfonamide, succinimide, and acetamide, preferably thioamide.

[0014] The concentration of amine compounds was 0.01-6 mol / L. -1 Preferably 1-4.5 mol L -1 Amine compounds are mainly used to stabilize the charging products of chloride ions on the positive electrode side, forming stable and reversible chloroamine compounds.

[0015] The electrolyte contains a supporting electrolyte;

[0016] The supporting electrolyte can be at least two or more of the following: sulfuric acid, hydrochloric acid, acetic acid, potassium acetate, sodium chloride, potassium chloride, sodium acetate, and sodium sulfate. Sulfuric acid is preferred. The supporting electrolyte is mainly selected from commonly used substances with high conductivity. Among them, hydrochloric acid, sodium chloride, and potassium chloride, while having high conductivity, also contain chloride ions and can be used as chloride salts.

[0017] According to another aspect of this application, the above-mentioned flow battery electrolyte is provided for use in a single cell.

[0018] The single cell includes a metal end plate, a current collector, a flow frame, activated carbon felt or graphite felt as electrodes, a separator for separating the positive and negative electrodes, and a rubber gasket for sealing. The cavity between the positive current collector and the separator is filled with positive graphite felt or carbon felt and positive electrolyte, and the cavity between the negative current collector and the separator is filled with negative graphite felt or carbon felt and negative electrolyte. The electrolyte is circulated between the cavity and the storage tank by a magnetic centrifugal pump or a peristaltic pump. The positive electrolyte may not circulate and is sealed in the cavity, thus serving as a single-flow battery.

[0019] Specifically, the metal end plate can be selected from any one of aluminum alloy plate, stainless steel plate and other acid corrosion resistant metal plates, preferably stainless steel plate; the current collector can be selected from any one of graphite plate and titanium plate, and the positive current collector is preferably titanium plate; the diaphragm can be selected from any one of perfluorosulfonic acid membrane, porous polyolefin membrane, sulfonated polyether ether ketone membrane, polybenzimidazole membrane, preferably perfluorosulfonic acid membrane.

[0020] The electrolyte used in the titanium chloride flow battery comprises chloride salts, titanium salts, amine compounds, and a supporting electrolyte. The titanium chloride flow battery system using this electrolyte can be reversibly charged and discharged with virtually no release of harmful chlorine gas.

[0021] The amine compounds used in the electrolyte can rapidly react with chlorine gas generated during the charging process of the chloride salt on the positive electrode side to form chloroamine compounds, creating stable charging products and enabling reversible discharge. The titanium chloride flow battery, composed of titanium salt on the negative electrode side, can cycle with a coulombic efficiency approaching 98% and releases almost no harmful chlorine gas. It boasts advantages such as environmental friendliness, low cost, and high energy density, making it suitable for large-scale energy storage.

[0022] The beneficial effects that this application can produce include:

[0023] The electrolyte provided in this application can be used as an electrolyte in titanium chloride flow batteries and is suitable for low-cost flow battery systems for large-scale energy storage.

[0024] 1) The flow battery electrolyte provided in this application utilizes the electrochemical + chemical reaction mechanism between chlorine and specific amine compounds, which allows chlorine gas generated on the electrode surface during charging to react with amine compounds through a rapid chemical reaction to generate highly soluble chloroamine compounds, thereby preventing chlorine gas from escaping from the electrolyte, effectively improving the stability of the battery, and greatly enhancing the safety of the battery.

[0025] 2) The titanium chloride flow battery based on the electrolyte of this application exhibits high coulombic efficiency and long cycle stability. Even at 10 mA / cm², it maintains high efficiency. 2 It still achieves a coulombic efficiency of 98% at current densities. The battery can cycle stably for more than 300 cycles, exhibiting long-term cycle stability and making it suitable for large-scale energy storage.

[0026] 3) The amine compounds used in this application are all composed of sulfur, oxygen, nitrogen, hydrogen and carbon elements, all of which are elements with high abundance, and can have low cost after large-scale application; chloride salts and titanium salts can be made of inexpensive substances, such as sodium chloride, which has the advantage of low price.

[0027] 4) The titanium chloride flow battery electrolyte used in this application has a high energy density on the positive electrode side. Amine compounds such as thioamide and chloride salts such as sodium chloride on the positive electrode side both have high solubility. The solubility of thioamide can reach 7.83 mol / L. -1 Sodium chloride can also reach 5.43.

[0028] mol L -1 Furthermore, the positive electrode reaction exhibits the characteristic of a two-electron transfer reaction, therefore the theoretical capacity on the positive electrode side can reach 227 Ah / L. -1 .

[0029] 5) All active materials used in this application are dissolved in aqueous solution, and the electrolyte remains a homogeneous aqueous solution during charging and discharging without any other phase separation. This allows for easy expansion based on capacity, making it suitable for large-scale, long-term energy storage. Attached Figure Description

[0030] Figure 1 The charge-discharge curves of the batteries in Example 1 and Comparative Example 1 are shown in the figure. The dashed line is the charge-discharge curve of Comparative Example 1, and the solid line is the charge-discharge curve of Example 1.

[0031] Figure 2 Example 5 shows the charge / discharge curves, where the solid line represents the charging process and the dashed line represents the discharging process. Figure 3 Example 1: Long cycle graph. The left side of the graph shows the efficiency during the battery charging and discharging process, and the right side shows the discharge capacity during the battery charging and discharging process. Detailed Implementation

[0032] The following embodiments are further illustrations of this application, but not limitations on its scope. Unless otherwise specified, the materials used in the embodiments and comparative examples of this application were all purchased commercially. Battery performance testing was performed using a Newway charge-discharge instrument.

[0033] Example 1

[0034] Assemble a flow battery:

[0035] The positive and negative electrode electrolytes have the same composition, both consisting of 2.0 mol L. -1 Sodium chloride, 1.0 mol L -1 Titanium sulfate, 1.0 mol L -1 Thionamide and 1.0 mol L -1 Its sulfuric acid composition.

[0036] Assembly of a single battery:

[0037] The structure of a single cell includes an end plate, a graphite plate as a current collector, and a diameter of 6×8cm. 2 The system consists of carbon felt as the positive and negative electrodes, Nafion membrane as the perfluorosulfonic acid diaphragm, flow frame, gaskets, end plates, positive and negative electrode electrolyte storage tanks, pumps, and pipelines.

[0038] The structure of a single cell includes, in sequence, an end plate, a silicone pad, a current collector, a silicone pad, an annular liquid flow frame with the positive electrode placed in a central through hole, a silicone pad, a diaphragm, a silicone pad, an annular liquid flow frame with the negative electrode placed in a central through hole, a silicone pad, and an end plate; the electrolyte in the positive and negative electrolyte storage tanks flows through pipelines via pumps through the electrode chambers in the annular liquid flow frame of the positive electrode and the electrode chambers in the annular liquid flow frame of the negative electrode, respectively, and returns to the positive and negative electrolyte storage tanks.

[0039] Battery test:

[0040] A constant current charge-discharge mode was adopted, with an electrolyte flow rate of 70 mL / min. -1 The charging and discharging current density is 10 mA cm⁻¹ -2 The charging cutoff voltage is 1.7V, and the discharging cutoff voltage is 0.1V. Coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are the average values ​​obtained from the tests.

[0041] Other examples and comparative examples of flow batteries assembled differ only in electrolyte composition from Example 1. Examples 1-5 and Examples 10-11 are mainly examples of titanium chloride flow batteries based on thioamide as an amine compound, while Examples 6-9 are examples of titanium chloride flow batteries with the addition of other amine compounds, as detailed in Table 1.

[0042] Table 1. Battery composition and performance of different embodiments and comparative examples.

[0043]

[0044]

[0045] The battery performance data from Examples 1-5 show that the coulombic efficiency of the titanium chloride flow battery with an electrolyte composed of chloride salt, titanium salt, thioamide, and supporting electrolyte can be above 98%, indicating that this method can stabilize the charging products of chlorine on the positive electrode side and enable the battery to be reversibly charged and discharged.

[0046] As can be seen from Examples 1 and 2, the cations in chloride salts have little effect on the coulombic efficiency of the battery. The main component in chloride salts is chloride ions, which play a redox role on the positive electrode side of the battery.

[0047] As can be seen from Examples 1 and 3, increasing the concentration of thioamide can further increase the coulombic efficiency of the battery. This is mainly because thioamide can combine with the oxidation products of chlorine to form stable chlorothioamides; the higher the concentration of thioamide, the more it is generated, thus increasing the coulombic efficiency.

[0048] As can be seen from Examples 1 and 4, the electrolyte can be replaced as needed without fundamentally affecting the battery efficiency. Its impact on the battery is mainly reflected in the change of battery polarization caused by the change in conductivity.

[0049] As can be seen from Examples 1 and 5, the concentrations of both sodium chloride and thioamide can reach 4.2 mol / L. -1Since the reaction on the positive electrode side is a two-electron transfer reaction, the oxidation of one chloride ion or the reduction of one chlorothioamide corresponds to the conversion of two electrons, and its theoretical capacity can reach 227.3 Ah L. -1 This is at a relatively high level in flow batteries.

[0050] As can be seen from Examples 1 and 6-9, the titanium chloride flow batteries with added thioamide, methanesulfonamide, N-methylmethanesulfonamide, succinimide, and acetamide all achieve a coulombic efficiency exceeding 98%, indicating that these five amine compounds can react with chloride ions during charging to generate the corresponding chloroamine compounds and undergo reversible discharge. The difference lies in the fact that the voltage and energy efficiencies of the titanium chloride flow batteries based on methanesulfonamide, N-methylmethanesulfonamide, succinimide, and acetamide are not as high as those of the titanium chloride flow batteries with added thioamide. This is mainly because thioamide has a stronger binding force with chloride ions on the electrode surface, enabling a faster electrochemical reaction and resulting in lower electrochemical polarization, thus exhibiting higher voltage and energy efficiencies. Therefore, among the five amine compounds selected in this invention, thioamide is the preferred option.

[0051] As can be seen from Examples 1 and 10, adding a low concentration of thioamide can also result in a high coulombic efficiency for the titanium chloride flow battery. However, the battery capacity depends on the concentrations of chloride ions and thioamide; too low a concentration of thioamide will also lead to a low battery capacity. Adding 0.01 mol L... -1 The capacity of the thioamide-based titanium chloride flow battery is only 0.536 Ah / L. -1 In practical applications, the capacity is relatively small. Therefore, in this invention, the preferred low concentration of amine compounds is 1 mol / L. -1 This ensures that the battery capacity reaches 53.6 Ah / L. -1 This is more in line with practical applications.

[0052] As can be seen from Examples 1 and 11, adding 6 mol L... -1 The concentration of thioamide compared to adding 1 mol / L -1 A higher concentration of thioamide can achieve a slightly higher coulombic efficiency, mainly because more thioamide can react more quickly with chloride ion charging products to form more stable chlorothioamide, reducing battery self-discharge and thus achieving higher coulombic efficiency. However, the battery voltage efficiency is also lower, mainly because excessive thioamide leads to an overly concentrated electrolyte. An overly concentrated electrolyte slows down the diffusion of active materials, increases concentration polarization, and reduces battery voltage efficiency. Therefore, in this invention, the preferred high concentration of amine compounds is 4.5 mol / L. -1 This allows the battery to have high capacity without excessively reducing its voltage efficiency.

[0053] A comparison of Example 1 with Comparative Examples 1, 2, and 3 shows that chloride salts, titanium salts, and thioamides are all necessary conditions for the stable operation of titanium chloride flow batteries. The absence of any one of them will lead to a significant decrease in the battery's coulombic efficiency. Specifically, chlorine in chloride salts is the center for electron gain and loss during redox reactions on the positive electrode side; without chlorine, an irreversible oxygen evolution reaction will occur on the positive electrode side. Thiamides are mainly used to stabilize the oxidation products of chlorine; without thioamides, an irreversible chlorine evolution reaction will occur on the negative electrode side. Similarly, titanium in titanium salts is the center for electron gain and loss during redox reactions on the negative electrode side; without titanium, an irreversible hydrogen evolution reaction will occur on the negative electrode side.

[0054] A comparison of Example 1 with Comparative Examples 4, 5, and 6 shows that the amine compounds in the comparative examples cannot react with chlorine to form stable chloroamine compounds. Therefore, the reaction still primarily releases chlorine gas, resulting in a very low coulombic efficiency of the flow battery, essentially the same as that of the battery in Comparative Example 1 without added amine compounds. This is mainly because the amino group in the amine compounds of the comparative examples is an electron-donating group, which cannot ionize hydrogen atoms into protons. Consequently, during charging, the oxidized chlorine cannot undergo an electrophilic substitution reaction with the amino group, thus failing to form stable chloroamine compounds. In contrast, the thioamide in Example 1 can undergo an electrophilic substitution reaction with chlorine through electron-withdrawing interactions. The entire reaction is a proton-coupled electron transfer process, which can generate stable chlorothioamide.

[0055] Figure 1 The graphs show the charge-discharge curves of batteries from Example 1 and Comparative Example 1. As can be seen from the graphs, Comparative Example 1, lacking the addition of thioamide, although capable of charging, exhibits very low discharge capacity, with a coulombic efficiency of only 35%. This is primarily because without thioamide, the oxidation product of chloride ions is chlorine gas, which has very low solubility in water. Numerous bubbles are observed being generated and escaping into the environment, preventing discharge. However, the addition of thioamide converts the charging products into chlorothioamide, which has extremely high solubility in water, allowing for reversible discharge.

[0056] Figure 2 This is the charge-discharge curve for Example 5. In Example 5, the concentrations of the active materials sodium chloride and thioamide on the positive electrode side both reached 4.2 mol / L. -1 Since the reaction occurring on the positive electrode side involves the transfer of two electrons, the charge and discharge specific capacities of the battery both exceed 200 Ah / L. -1 Compared to other flow battery systems, its specific capacity is at a relatively high level.

[0057] Figure 3This is a long-cycle diagram of Example 1. As can be seen from the diagram, the titanium chloride flow battery powered by the electrolyte prepared according to this invention can stably cycle for over 300 cycles with virtually no efficiency degradation. The coulombic efficiency can be maintained at 98%, and the energy efficiency can be maintained above 80%, making it suitable for large-scale energy storage as a flow battery.

[0058] In summary, the electrolyte composition of this application enables reversible charge-discharge of titanium chloride flow batteries, exhibiting advantages such as high coulombic efficiency and high specific capacity, making them suitable for large-scale, long-term energy storage. Furthermore, the above descriptions are merely several embodiments and comparative examples of this application and do not constitute any limitation on the application. Although preferred embodiments are shown above, they are not intended to limit the scope of this application. Any modifications or alterations made by those skilled in the art, without departing from the scope of the technical solution presented above, are equivalent to equivalent implementations and fall within the scope of the technical solution.

Claims

1. A titanium-chlorine flow battery electrolyte, characterized in that, The electrolyte comprises chloride ions, titanium ions, amine compounds and a supporting electrolyte.

2. The titanium chloride flow battery electrolyte of claim 1, wherein: The chloride ions in the electrolyte are provided by added chloride salts, which are at least one or more than two of sodium chloride, potassium chloride, ammonium chloride, hydrochloric acid, magnesium chloride, calcium chloride.

3. The titanium chloride flow battery electrolyte of claim 1, wherein: The titanium ions in the electrolyte are provided by added titanium salts, which are at least one or more than two of titanium sulfate, titanium tetrachloride, titanium bromide, potassium fluorotitanate.

4. The titanium chloride flow battery electrolyte of claim 1, wherein: The amine compounds in the electrolyte are at least one or more than two of sulfamide, methylsulfonamide, N-methylmethanesulfonamide, succinimide, acetamide.

5. The titanium chloride flow battery electrolyte of claim 1, wherein: The supporting electrolyte in the electrolyte is at least one or more than two of sulfuric acid, hydrochloric acid, acetic acid, potassium acetate, sodium chloride, potassium chloride, sodium acetate, sodium sulfate.

6. The electrolyte of the titanium-chlorine flow battery according to claim 1, wherein: The electrolyte is an aqueous solution. wherein the concentration of the chloride salt is 0.01-6 mol L -1 , preferably 1-3 mol L -1 ; titanium salt concentration is 0.1-3 mol L -1 , preferably 1-2 mol L -1 ; The amine compound concentration is 0.01-6 mol L -1 , preferably 1-4.5 mol L -1 ; Support electrolyte concentration 0.1-3 mol L -1 , preferably 1-2 mol L -1 Support electrolyte concentration 0.1-3 mol L -1 , preferably 1-2 mol L -1 7. Use of the electrolyte of any one of claims 1-6 as an electrolyte in a titanium-chlorine flow battery.

8. A titanium-chlorine flow battery, characterized in that, The flow battery comprises a positive electrode, a negative electrode and a separator for separating the positive and negative electrodes, the positive electrode is placed in a positive electrode side cavity, the negative electrode is placed in a negative electrode side cavity, and at least one or more than two of the electrolyte according to any one of claims 1-6 is filled or flowed through in the positive and negative electrode side cavities.

Images