Polycationic additive-containing viologen electrolyte and flow battery thereof

Abstract

The invention discloses viologen electrolyte containing a polycationic additive and a flow battery of the viologen electrolyte. Belongs to the field of flow batteries. According to the viologen electrolyte containing the polycationic additive, the polycationic additive is added into the viologen electrolyte, and the mass fraction of the polycationic additive in the viologen electrolyte is 0.01%-20%. The polycation additive forms dynamic association with a viologen molecule reduction state through multiple mechanisms such as electrostatic induction, cation-pi interaction and molecular chain coating, so that the aggregation and precipitation behaviors of the polycation additive in an aqueous solution are effectively interfered, the dispersion stability of the electrolyte is remarkably improved, and the cycle life of the battery is remarkably prolonged. The polycation additive has good water solubility and electrochemical inertness, and can stably exist in a system for a long time while the conductivity and reaction reversibility of the electrolyte are maintained. The additive is rich in source, simple and convenient to synthesize, low in cost and suitable for large-scale application of viologen flow batteries, and has a wide industrialization prospect and an energy storage market value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid flow battery, in particular to a viologen electrolyte containing polycationic additive and a liquid flow battery thereof. BACKGROUND

[0002] Liquid flow battery is widely concerned in the field of large-scale renewable energy grid connection due to its high safety, long cycle life and strong scalability. Water-based organic liquid flow battery uses water as solvent and organic molecules as active material, which is a potential green energy storage system. Viologen compounds are often used as negative active material. The one-electron reduced state (V + ) of viologen compounds is prone to π-π stacking in aqueous solution, leading to molecular aggregation and even precipitation, which reduces the stability of electrolyte, attenuates the capacity of battery, and limits its long-term performance and application life.

[0003] To inhibit the aggregation of viologen radicals, current researches introduce bulky substituents, hydrophobic segments and charge-regulated structures into the molecular structure to improve the steric hindrance and electrostatic repulsion between molecules, thereby blocking the formation of face-to-face stacking configuration and improving the stability of viologen compounds in aqueous solution. However, the current molecular structure modification strategy has obvious shortcomings, which often requires complex molecular design and multi-step synthesis process, making it difficult to balance electrochemical performance, solubility and cost control at the same time. This greatly limits the popularization and application of this scheme in practical engineering. SUMMARY

[0004] To solve the problem of poor electrical performance and short actual running life of liquid flow battery caused by the aggregation of viologen compounds during the dissolution process, which leads to the decline of electrolyte stability, the present application provides a viologen electrolyte containing polycationic additive and a liquid flow battery thereof. Without changing the structure of viologen, the polycationic additive is introduced to regulate the aggregation behavior of the reduced radical through non-covalent interaction between molecules, thereby significantly improving the cycle stability of water-based viologen liquid flow battery system.

[0005] To achieve the above purpose, the present application provides the following technical solutions: The present application provides a viologen electrolyte containing polycationic additive, which comprises a viologen electrolyte and a polycationic additive added to the viologen electrolyte. The mass fraction of the polycationic additive in the viologen electrolyte is 0.01% to 20%.

[0006] Further, the concentration of viologen derivative in the viologen electrolyte is 0.01M to 5M.

[0007] Further, the mass ratio of viologen derivative to polycationic additive is (1-30):1.

[0008] Further, the cationic group of the polycationic additive comprises one or more of quaternary ammonium group, imidazolium group, pyridinium group.

[0009] Further, the polycationic additive comprises one or more of polyquaternium-6, polyquaternium-7, polyquaternium-22, polyquaternium-37.

[0010] Further, the viologen derivative in the viologen electrolyte comprises one or more of alkyl-substituted viologen, quaternary ammonium cation-modified viologen, sulfonate-modified viologen, phosphate-modified viologen.

[0011] Further, the degree of polymerization of the polycationic additive is 5-2000.

[0012] Further, the electrolyte in the viologen electrolyte comprises one or more of alkali metal chloride, alkaline earth metal chloride, alkali metal sulfate, alkaline earth metal sulfate, alkali metal phosphate, alkaline earth metal phosphate, alkali metal sulfonate, alkaline earth metal sulfonate.

[0013] Further, the pH of the viologen electrolyte is 4-12.

[0014] The application also provides a flow battery, and the above-mentioned viologen electrolyte containing a polycationic additive is used as the electrolyte of the negative electrode of the flow battery.

[0015] The application adds a polycationic additive to the viologen electrolyte, and such an additive can form a stable complex or association state with V + · The free radicals form a stable complex or association state through cation-π interaction, electrostatic induction or dipole induction, etc., thereby effectively weakening the motivation for further face-to-face stacking aggregation; at the same time, unlike low-molecular cations, the polycation has higher molecular flexibility and chain segment freedom, and can simultaneously form multi-point association with multiple viologen radicals, forming a "chain-molecule-chain" or "wrapping-isolation" structure. This complex state similar to supramolecular self-assembly effectively improves the dispersibility of viologen radicals in the electrolyte, reduces the collision frequency and effective contact area of viologen radicals in the solution, thereby inhibiting the aggregation-induced precipitation or degradation behavior; the polycation is easy to form a swollen state or charge-coated state structure in an aqueous solution, which further enhances the dispersion stability of viologen molecules through intermolecular physical barrier and charge barrier, slows down the kinetics of spontaneous nucleation and precipitation. At the same time, part of the polycation has hydrophilic side chains or auxiliary groups, which helps to improve the solvation capacity and diffusion efficiency of the whole system, thereby maintaining the reversible conversion behavior of the free radical state viologen. Through the above-mentioned multi-mechanism synergistic regulation, the polycationic additive of the application significantly improves the electrochemical stability of viologen molecules in an aqueous solution, delays the capacity decay rate of the battery, and improves the cycle life, and its structure design is simple, the synthesis process is mature, the raw material cost is low, and it is suitable for large-scale preparation and long-term operation of industrialized energy storage electrolyte.

[0016] The present application uses such viologen electrolyte containing polycation additives in the field of flow batteries, which can effectively improve the stability and reliability of the battery charging and discharging process, greatly reduce the capacity decay degree in the battery cycle process, and significantly prolong the service life of the battery. At the same time, the battery can still maintain excellent coulomb efficiency in long-term cycle operation, showing excellent cycle performance and long-term operation ability, and having practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 The cyclic voltammetry test graph of the methyl viologen electrolyte added with polyquaternary ammonium salt-6 in the embodiment 1 of the present application; Figure 2 The cyclic voltammetry test graph of the methyl viologen electrolyte without adding polyquaternary ammonium salt-6 in the comparative example 1 of the present application; Figure 3 The charge-discharge curve graph of the MVCl2 / 4-(NMe3 + )-TEMPO battery assembled in the embodiment 2 of the present application and added with polyquaternary ammonium salt-6 additive; Figure 4 The charge-discharge curve graph of the MVCl2 / 4-(NMe3 + )-TEMPO battery assembled in the comparative example 2 of the present application; Figure 5 The long cycle capacity-coulomb efficiency graph of the MVCl2 / 4-(NMe3 + )-TEMPO battery assembled in the embodiment 2 of the present application and added with polyquaternary ammonium salt-6 additive.

[0019] Figure 6 The long cycle capacity-coulomb efficiency graph of the MVCl2 / 4-(NMe3 + )-TEMPO battery assembled in the comparative example 2 of the present application; DETAILED DESCRIPTION In order to make the technical problems, technical solutions and beneficial effects of the present application more clearly understood, the following will further describe the present application in combination with embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0020] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0021] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of the items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0022] It should be understood that the size of the sequence number of the above-mentioned processes in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0023] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass in the specification of the embodiments of the present application can be μg, mg, g, kg, etc. mass units commonly known in the chemical industry.

[0025] Aqueous organic flow battery uses water as solvent and designable organic molecules as electrolyte active substances, which not only has advantages in material acquisition and environmental compatibility, but also has the characteristics of adjustable electrochemical performance and controllable cost, and is a new generation of green energy storage system with great development potential. In such systems, viologen compounds are widely used in the development of negative active materials due to their simple structure, easy synthesis and excellent redox performance. In particular, the formation and transformation of one-electron reduced state (V + •) occupies a core position in viologen batteries. However, V +• Vi state molecules have a strong π-π stacking tendency in aqueous solution, which easily leads to molecular aggregation and even precipitation, resulting in decreased electrolyte stability, rapid battery capacity decay, and severely limiting long-term operation performance and practical application life in flow batteries.

[0026] To solve the problem of poor battery performance caused by the aggregation of viologen compounds in aqueous organic flow batteries, the present application proposes a solution strategy based on polycationic electrolyte additives, wherein the polycationic additive is a water-soluble polymer containing repeating positive charge groups.

[0027] The viologen electrolyte containing the polycationic additive provided by the present application includes a viologen electrolyte, a polycationic additive is added to the viologen electrolyte, and the mass fraction of the polycationic additive in the viologen electrolyte is 0.01% to 20%.

[0028] The present application provides a kind of viologen electrolyte containing polycationic additive, polycationic additive is added in electrolyte, the additive molecule is rich in multiple positive charged functional groups, with high charge density, good water-solubility, chemical stability and water phase swelling performance and hydration behavior. On the one hand, the polycationic additive can form a non-covalent association structure with the one-electron reduced state (Vi + ) free radical of viologen molecule through electrostatic induction, electronic coupling and electrostatic induction and cation-π interaction, reduce the effective approach and face-to-face stacking probability between free radicals, thereby effectively interfering with the π-π stacking behavior of the reduced state molecule of viologen, and alleviating the spontaneous aggregation behavior of its thermodynamic tendency; on the other hand, its good water phase swelling performance and hydration behavior can form a covering hydration shell, enhance the solvation ability of the system, provide intermolecular barrier in the physical level, and enhance the stability of the free radical state of viologen in the chemical level. The additive can significantly improve the dispersion stability and reversibility of viologen molecules during discharge, improve the reversible conversion efficiency during the cycle process, and further improve the chemical stability of the electrolyte and the cycle life of the battery.

[0029] In some embodiments of the present application, the concentration of viologen derivatives in the viologen electrolyte is 0.01M to 5M. The mass ratio of viologen derivatives to polycationic additive is (1-30):1. Within this ratio range, the synergistic effect of the two can be fully exerted, effectively ensuring the charge-discharge performance and cycle stability of the battery, reducing capacity decay, and prolonging the service life of the battery.

[0030] In some embodiments of the present application, the cationic groups of the polycationic additive include one or more of quaternary ammonium groups, imidazolium groups, pyridinium groups. The provided polycationic additive is an organic polycationic compound with linear or branched structure, or is an inorganic polycationic compound with a clear structure, and the polycationic additive containing these cationic groups can stabilize the positive charge and form multiple interaction sites in aqueous solution.

[0031] In some embodiments of the present application, the polycationic additive includes one or more of polyquaternium-6, polyquaternium-7, polyquaternium-22, polyquaternium-37. The molecular chain of these polycationic additives has a certain molecular flexibility and expandability, and can simultaneously form multiple point electrostatic adsorption or dipole association with multiple viologen molecules in a "wrapping" manner in solution, to construct a stable molecular association network structure.

[0032] In some embodiments of the present application, the viologen derivatives in the viologen electrolyte include alkyl-substituted viologen, quaternary ammonium cation-modified viologen, sulfonate-modified viologen, phosphate-modified viologen. For example, dichloromethyl viologen, dibromoethyl viologen, 1,1'-bis(3-(trimethylammonium)propyl)-[4,4'-bipyridine]-1,1'-diium-tetrabromide (quaternary ammonium salt modified viologen), 3,3'-([4,4'-bipyridine]-1,1'-diium-1,1'-diyl) bis(propane-1-sulfonate), 1,1'-bis(3-phosphonopropyl)-[4,4'-bipyridine]-1,1'-diium (phosphate viologen), etc. The polycationic additive is applicable to these structural types of viologen derivatives, and the polycationic additive is suitable for regulating the solubility and aggregation tendency of the reduced viologen radical (Vi + •), and significantly improves the chemical life of the viologen in the electrolyte.

[0033] In some embodiments of the present application, the polycationic additive has a degree of polymerization of 5-2000, and the polycationic additive has good molecular flexibility and sufficient chain segment freedom at this degree of polymerization, and can be associated with multiple viologen radicals.

[0034] In some embodiments of the present application, the electrolyte in the viologen electrolyte includes one or more of alkali metal chlorides, alkaline earth metal chlorides, alkali metal sulfates, alkaline earth metal sulfates, alkali metal phosphates, alkaline earth metal phosphates, alkali metal sulfonates, alkaline earth metal sulfonates. For example, sodium chloride, potassium chloride, lithium chloride, sodium sulfate, potassium sulfate, lithium sulfate, lithium potassium phosphate, etc.

[0035] In some embodiments of the present application, the pH of the viologen electrolyte is 4-12; the polycationic additive is a water-soluble material, which has good chemical stability and electrochemical inertness under neutral or weak acid-base conditions, and can stably exist in the aqueous electrolyte at a higher concentration without easy self-polymerization or precipitation, and will not significantly negatively affect the ionic conductivity and mass transfer performance of the electrolyte.

[0036] The present application also provides a flow battery, the above-mentioned viologen electrolyte containing a polycationic additive is used as the electrolyte of the negative electrode of the flow battery; and a TEMPO solution is used as the positive electrode.

[0037] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. Furthermore, it should be understood that after reading the description of the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0038] The following examples use the conventional apparatus in the art. The experimental methods in the following examples, if not specified, are usually carried out according to the conventional conditions, or according to the conditions suggested by the manufacturers. The following examples use various raw materials, unless otherwise specified, and the conventional commercially available products are used, which are of the conventional specifications in the art.

[0039] Example 1 A flow battery system using a viologen electrolyte with polyquaternary ammonium salt-6 (poly (dimethyl diallyl ammonium chloride)) as a polycationic additive is prepared, and the electrochemical performance of the negative electrode viologen electrolyte is tested.

[0040] 0.77 g of MVCl2 (dichloromethyl viologen) is weighed and dissolved in 30 mL of 1 mol / L potassium chloride solution, and oscillation stirring is carried out to prepare a 0.1 mol / L methyl viologen solution, at this time the pH of the electrolyte is 7, and 0.3 g of 1% wt equivalent polyquaternary ammonium salt-6 is added and stirred uniformly to obtain a methyl viologen electrolyte with added polyquaternary ammonium salt-6.

[0041] Comparative Example 1 0.77 g of MVCl2 is weighed and dissolved in 30 mL of 1 mol / L potassium chloride solution, and oscillation stirring is carried out to prepare a 0.1 mol / L methyl viologen solution.

[0042] The above-prepared electrolyte is subjected to cyclic voltammetry test using a three-electrode system, a glassy carbon electrode is used as the working electrode, an Ag / AgCl electrode is used as the reference electrode, and a platinum electrode is used as the counter electrode. As shown in Figure 1 and Figure 2As shown, the redox potential and redox peak difference of the two electrolytes are basically the same, proving that adding polyquaternary ammonium salt-6 as an additive will not bring side reactions to the MV system, and the electrolyte system has good electrochemical reversibility.

[0043] Example 2: A redox flow battery system of a viologen electrolyte with polyquaternary ammonium salt-6 as a polycation additive was prepared, and full cell performance test was carried out.

[0044] 0.385 g of MVCl2 was weighed and dissolved in 15 ml of 1 mol / L potassium chloride solution, oscillated and stirred to prepare a 0.1 mol / L MVCl2 solution, and 0.15 g of 1% wt equivalent polyquaternary ammonium salt-6 was added and stirred uniformly to obtain a methyl viologen electrolyte with polyquaternary ammonium salt-6 as the negative electrode; 0.498 g of TEMPO derivative 4- (NMe3 + )-TEMPO was weighed and dissolved in 20 ml of 1 mol / L potassium chloride solution, oscillated and stirred to prepare a 0.1 mol / L 4- (NMe3 + )-TEMPO solution as the positive electrode.

[0045] Comparative Example 2 0.385 g of MVCl2 was weighed and dissolved in 15 ml of 1 mol / L potassium chloride solution, oscillated and stirred to prepare a 0.1 mol / L methyl viologen electrolyte as the negative electrode; 0.498 g of TEMPO derivative 4- (NMe3 + )-TEMPO was weighed and dissolved in 20 ml of 1 mol / L potassium chloride solution, oscillated and stirred to prepare a 0.1 mol / L 4- (NMe3 + )-TEMPO solution as the positive electrode.

[0046] After the above electrolyte was deoxygenated by nitrogen, the positive electrolyte and the negative electrolyte were respectively stored in liquid storage tanks and were propelled and conducted by pumps. The two electrolytes were respectively circulated through pipelines and met at both sides of the diaphragm, and oxidation-reduction reactions occurred at the electrodes on both sides of the diaphragm. The positive and negative electrodes were connected to the power supply load, the circuit transferred electrons, and the diaphragm transferred positive and negative ions to form a loop. Copper plates were used as current collectors, 2 pieces of graphite plates with serpentine flow channels were used as flow field plates for the positive and negative electrolytes, and graphite felt or carbon paper was used as the reaction electrode. A copolymer film of polyvinylidene chloride, polyacrylonitrile and butadiene-styrene rubber was used as an ion exchange membrane to separate the positive and negative reaction electrodes.

[0047] The long cycle charge-discharge performance test was carried out on the battery, and the current size of 100 mA / cm 2 was used for charge and discharge. As Figures 3-6As shown, it can be seen that in the 100 cycles, the weekly capacity fade rate of the control sample without the addition of polyquaternary ammonium salt-6 is 0.03%, and the average coulombic efficiency is maintained above 99.70%. The weekly capacity fade rate of the experimental sample with the addition of polyquaternary ammonium salt-6 is only 0.01%, and the average coulombic efficiency is maintained above 99.70%, showing excellent cycle performance.

[0048] Example 3 Take 2.02g 1,1'-bis(3-(trimethylammonium)propyl)-[4,4'-bipyridine]-1,1'-dium dissolved in 30ml 1 mol / L sodium chloride solution, oscillation stirring to make 0.1 mol / L viologen solution, and add 0.3g, 1% wt equivalent of polyquaternary ammonium salt-7 to stir evenly to obtain polyquaternary ammonium salt-7 added viologen electrolyte.

[0049] Example 4 Take 1.67g 1,1'-bis(3-phosphine propyl)-[4,4'-bipyridine]-1,1'-dium-dibromide (phosphorus-modified viologen derivative) dissolved in 30ml 1 mol / L potassium sulfate solution, oscillation stirring to make 0.1 mol / L viologen solution, and add 0.3g, 1% wt equivalent of polyquaternary ammonium salt-6 to stir evenly to obtain polyquaternary ammonium salt-6 added viologen electrolyte.

[0050] Example 5 Take 0.77g MVCl2 (dichloromethyl viologen) dissolved in 30ml 1 mol / L potassium chloride solution, oscillation stirring to make 0.1 mol / L methyl viologen solution, and add 0.3g, 1% wt equivalent of polyquaternary ammonium salt-22 to stir evenly to obtain polyquaternary ammonium salt-22 added methyl viologen electrolyte.

[0051] Example 6 Take 0.77g MVCl2 (dichloromethyl viologen) dissolved in 30ml 1 mol / L potassium chloride solution, oscillation stirring to make 0.1 mol / L methyl viologen solution, and add 0.3g, 1% wt equivalent of polyquaternary ammonium salt-37 to stir evenly to obtain polyquaternary ammonium salt-37 added methyl viologen electrolyte.

[0052] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A viologen electrolyte containing a polycationic additive, characterized in that, The purple electrolyte comprises a poly-cationic additive, and the mass fraction of the poly-cationic additive in the purple electrolyte is 0.01%-20%.

2. The poly cationic additive containing viologen electrolyte according to claim 1, characterized in that, The concentration of the purple derivative in the purple electrolyte is 0.01M-5M.

3. The poly cationic additive-containing viologen electrolyte according to claim 2, characterized by The mass ratio of the purple derivative to the poly-cationic additive is (1-30):

1.

4. The poly cationic additive-containing viologen electrolyte according to claim 1, characterized by The cationic group of the poly-cationic additive comprises one or more of quaternary ammonium group, imidazolium group and pyridinium group.

5. The viologen electrolyte containing a polycationic additive according to claim 1, characterized in that, The poly-cationic additive comprises one or more of polyquaternium-6, polyquaternium-7, polyquaternium-22 and polyquaternium-37.

6. The poly cationic additive-containing viologen electrolyte according to claim 1, characterized by The purple derivative in the purple electrolyte comprises one or more of alkyl-substituted purple, quaternary ammonium cation-modified purple, sulfonate-modified purple and phosphate-modified purple.

7. The poly cationic additive-containing viologen electrolyte according to claim 1, characterized by The poly-cationic additive has a polymerization degree of 5-2000.

8. The poly cationic additive-containing viologen electrolyte according to claim 1, characterized by The electrolyte in the purple electrolyte comprises one or more of alkali metal chloride, alkali earth metal chloride, alkali metal sulfate, alkali earth metal sulfate, alkali metal phosphate, alkali earth metal phosphate, alkali metal sulfonate and alkali earth metal sulfonate.

9. The poly cationic additive-containing viologen electrolyte according to claim 1, characterized by, The pH of the purple electrolyte is 4-12.

10. A flow battery, characterized in that, The poly-cationic additive-containing purple electrolyte according to any one of claims 1-9 is used as an electrolyte for a negative electrode of a flow battery.

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