An aqueous all-organic flow battery electrolyte containing a quaternary ammonium salt additive

Abstract

The application belongs to the field of new energy, and particularly relates to a kind of water-based all-organic liquid flow battery electrolyte containing quaternary ammonium salt additive, the quaternary ammonium salt additive is one or several of tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, methyltriethylammonium chloride, propyltrimethylammonium chloride, phenyltrimethylammonium chloride, choline chloride, bis (2-hydroxyethyl) dimethylammonium chloride, benzyltrimethylammonium chloride or benzyltriethylammonium chloride: the concentration of quaternary ammonium salt additive is 1mmol / L~1.5mol / L. Using quaternary ammonium salt as electrolyte additive can improve the stability of electrolyte, reduce viscosity, reduce the polarization overpotential of water-based all-organic liquid flow battery, improve energy efficiency, effectively inhibit the capacity decay problem of battery during long-term charge and discharge cycle, realize the stable operation of battery. The electrolyte additive of the application has low cost, energy saving and environmental protection, and can realize the long-term stable operation of electrolyte in the battery.

Description

Technical Field

[0001] This invention belongs to the field of new energy, specifically relating to an aqueous all-organic flow battery electrolyte containing quaternary ammonium salt additives. Background Technology

[0002] In recent years, with the continuous depletion of fossil fuels and the increasing awareness of environmental protection, the electricity generated by renewable energy sources such as solar, wind, biomass, geothermal, and tidal energy has grown rapidly worldwide. However, because these renewable energy sources are typically intermittent and unstable, efficient large-scale energy storage technologies must be developed to smooth and stabilize electricity output.

[0003] Flow batteries have become one of the most promising energy storage technologies for large-scale energy storage in renewable energy power generation due to their outstanding advantages such as decoupling of energy and power output, fast response, environmental friendliness, safety and reliability, ease of maintenance, and long cycle life.

[0004] Vanadium redox flow batteries are severely constrained by the scarcity of vanadium. Furthermore, the high toxicity of vanadium-based compounds and the strong corrosiveness of acidic electrolytes are also significant disadvantages. Compared to the limited number of inorganic redox active materials, organic materials offer a wide variety and greater selection. Organic materials possess high structural designability; key properties such as potential, kinetic parameters, and solubility can be easily controlled through "parent material" selection and functional group reduction. In addition, organic materials are easy to recycle and process, meeting green environmental protection requirements. Therefore, aqueous organic redox flow batteries using organic redox active materials have become an important branch of current electrochemical energy storage technology. And with in-depth research, their technological maturity is increasing.

[0005] Electrolyte is a crucial component of flow batteries, and its effective concentration of active species directly determines the system's energy density. In aqueous all-organic flow batteries, the effective concentration of redox active species in the electrolyte is generally no greater than 2 mol / L. When the concentration increases further, the electrolyte is prone to a sudden increase in viscosity or precipitation of active species, leading to decreased stability, increased polarization overpotential, and rapid capacity decay. Therefore, to achieve improved energy density, the stability of high-concentration electrolytes must be ensured. One effective approach is to add a small amount of additives to the electrolyte to stabilize it. For example, Orita et al. added a small amount of nicotinamide to the negative electrode electrolyte of organic flow batteries, enhancing the water solubility of the electroactive species sodium flavin mononucleotide (FMN-Na) by strengthening intermolecular hydrogen bonding (Nat. Commun. 2016, 7, 13230). Furthermore, the addition of complexing agents (CN 202011455858.9) or small hydrophilic organic molecules (CN 201711094327.X) to the electrolyte of vanadium redox flow batteries has been shown to stabilize vanadium species through coordination, thereby improving electrolyte stability and long-term battery performance. However, these additives are typically non-ionizable organic molecules, and large additions will significantly reduce the ionic conductivity of the electrolyte. Summary of the Invention

[0006] The purpose of this invention is to solve the electrolyte stability problem pointed out in the background section, and to provide an aqueous all-organic flow battery electrolyte containing quaternary ammonium salt additives, so as to achieve the goal of efficient and stable operation of aqueous all-organic flow batteries.

[0007] The electrolyte for an aqueous all-organic flow battery includes positive and negative electrode electrolytes. This electrolyte contains quaternary ammonium salt additives, specifically quaternary ammonium chloride salts, including one or more of tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, methyltriethylammonium chloride, propyltrimethylammonium chloride, phenyltrimethylammonium chloride, choline chloride, bis(2-hydroxyethyl)dimethylammonium chloride, benzyltrimethylammonium chloride, or benzyltriethylammonium chloride.

[0008] The additive can be added alone to the positive electrode electrolyte, alone to the negative electrode electrolyte, or simultaneously to both the positive and negative electrode electrolytes.

[0009] The concentration of the additive in the electrolyte is 1 mmol / L to 1.5 mol / L.

[0010] Furthermore, the preferred concentration of the additive in the electrolyte is 0.1 mol / L to 0.5 mol / L.

[0011] Furthermore, the additive is preferably tetramethylammonium chloride, tetraethylammonium chloride, or choline chloride.

[0012] The redox substance of the negative electrode electrolyte of the aqueous all-organic flow battery applicable to the present invention is a viologen derivative, wherein the viologen derivative is methyl viologen dichloride (MV), 1,1′-di(2-propanol)-4,4′-bipyridine dichloride (BHOP-Vi), 1,1′-bis(3-(trimethylamino)propyl)-4,4′-bipyridine tetrachloride (BTMAP-Vi) or a mixture thereof.

[0013]

[0014] The concentration of redox substances in the negative electrode electrolyte is 0.5–4 mol / L, and the concentration of the supporting electrolyte (sodium chloride or potassium chloride) is 0–2 mol / L.

[0015] The preferred concentration of redox substances in the negative electrode electrolyte is 1–3 mol / L, and the preferred concentration of the supporting electrolyte is 0–1.5 mol / L.

[0016] The redox material of the positive electrode electrolyte of the aqueous all-organic flow battery applicable to the present invention is a TEMPO derivative, wherein the TEMPO derivative is 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide (4-HO-TEMPO), N,N,N-2,2,6,6-heptamethylpiperidineoxy-4-ammonium chloride (TEMPTMA), 4-[3-(trimethylamino)propoxy]-2,2,6,6-tetramethylpiperidine-1-oxychloride (TMAP-TEMPO) or a mixture thereof.

[0017]

[0018] The concentration of redox substances in the positive electrode electrolyte is 0.5–5 mol / L, and the concentration of the supporting electrolyte (sodium chloride or potassium chloride) is 0–2 mol / L.

[0019] The preferred concentration of redox substances in the positive electrode electrolyte is 1–3 mol / L, and the preferred concentration of the supporting electrolyte is 0–1.5 mol / L.

[0020] The beneficial results of this invention are as follows: The quaternary ammonium salt additive used in this invention can not only partially replace the supporting electrolyte (such as NaCl or KCl) and provide sufficient ionic conductivity, but also reduce the cross-permeation of redox substances between the positive and negative electrodes, inhibit the capacity decay of the electrolyte during charge-discharge cycles, and improve battery performance. Simultaneously, it can reduce electrolyte viscosity, increase the solubility of redox substances, and improve battery energy density. This invention features a simple process, low cost, energy saving, and environmental friendliness, while also enabling long-term stable operation of the electrolyte in the battery. Attached Figure Description

[0021] Figure 1 This is a comparison chart of the discharge capacity of the negative electrode electrolyte containing tetraethylammonium chloride additive in Example 1 and the blank negative electrode electrolyte (the negative electrode active material is MV).

[0022] Figure 2 This is a comparison chart of the discharge capacity and energy efficiency of the positive electrode electrolyte containing tetramethylammonium chloride additive and the blank positive electrode electrolyte in Example 2.

[0023] Figure 3 This is a comparison chart of the discharge capacity of the negative electrode electrolyte containing tetraethylammonium chloride additive in Example 3 and the blank negative electrode electrolyte (the negative electrode active material is BHOP-Vi).

[0024] Figure 4 This is a comparison chart of the discharge capacity of the positive and negative electrode electrolytes containing choline chloride additive and the blank electrolyte in Example 4. Detailed Implementation

[0025] The following embodiments are further illustrations of the present invention, but not limitations on the scope of the invention. Any modifications or alterations made by those skilled in the art using the disclosed technical content without departing from the scope of the technical solution of this application are equivalent to equivalent implementations and fall within the scope of the technical solution.

[0026] Example 1

[0027] A flow battery experiment was conducted using an aqueous solution containing 1.5 mol / L TEMPTMA (a redox agent) and 1.5 mol / L NaCl as the supporting electrolyte, and an aqueous solution containing 1.5 mol / L MV (a redox agent) and 1 mol / L NaCl as the supporting electrolyte. Nitrogen gas was used for electrolyte protection during the experiment, carbon felt electrodes were used, and the electrolyte flow rate was 60 mL / min. The negative electrode electrolyte in group A did not contain a stabilizer, while the negative electrode electrolyte in group B contained 0.5 mol / L tetraethylammonium chloride. The charge-discharge experiment was conducted using a constant current / constant voltage charging + constant current discharging mode. Figure 1 This chart compares the discharge capacity retention of two groups of batteries: one without additives and one with tetraethylammonium chloride additive. From... Figure 1 It can be seen that the battery containing tetraethylammonium chloride additive has a significantly higher capacity retention rate than the battery without the additive. Furthermore, the average energy efficiency of the battery containing tetraethylammonium chloride additive is 78.2%, while the average energy efficiency of the battery without the additive is only 69.1%.

[0028] Example 2

[0029] A flow battery experiment was conducted using an aqueous solution containing 1 mol / L TEMPTMA and 1 mol / L NaCl as the positive electrode electrolyte and an aqueous solution containing 1 mol / L MV and 1.5 mol / L NaCl as the negative electrode electrolyte. The positive electrode electrolyte in group C batteries did not contain a stabilizer, while the positive electrode electrolyte in group D batteries contained 0.5 mol / L tetramethylammonium chloride. Charge-discharge experiments were performed using a constant current / constant voltage charging + constant current discharging mode. Other experimental conditions were the same as in Example 1. Figure 2 The graph compares the discharge capacity and energy efficiency of batteries using cathode electrolytes without additives and those containing 0.5 mol / L tetramethylammonium chloride. It can be seen that the discharge capacity degradation of the battery using the tetramethylammonium chloride cathode electrolyte is significantly lower than that of the battery using the additive-free cathode electrolyte. Furthermore, the average energy efficiency of the battery using the tetramethylammonium chloride cathode electrolyte is 78.3%, while the average energy efficiency of the battery using the additive-free cathode electrolyte is only 74.6%.

[0030] Example 3

[0031] A flow battery experiment was conducted using an aqueous solution containing 1 mol / L TEMPTMA and 1.5 mol / L NaCl as the positive electrode electrolyte and an aqueous solution containing 0.5 mol / L LHOP-Vi and 1 mol / L NaCl as the negative electrode electrolyte. The negative electrode electrolyte in group E batteries did not contain a stabilizer, while the negative electrode electrolyte in group F batteries contained 0.25 mol / L tetraethylammonium chloride. Charge-discharge experiments were conducted using a constant current / constant voltage charging + constant current discharging mode. Other experimental conditions were the same as in Example 1. Figure 3 This chart compares the discharge capacity of batteries using negative electrode electrolytes without additives and those containing 0.25 mol / L tetraethylammonium chloride (NAC) (NAC active material BHOP-Vi). The battery using the NAC with additives exhibits significantly less capacity decay than the battery without additives. The battery with the NAC containing tetraethylammonium chloride has an average energy efficiency of 77.4%, while the battery without additives has an average energy efficiency of only 65.2%.

[0032] Example 4

[0033] A flow battery experiment was conducted using an aqueous solution containing 0.3 mol / L 4-HO-TEMPO + 0.3 mol / L TEMPTMA and 1.5 mol / L NaCl as the positive electrolyte and an aqueous solution containing 0.5 mol / L MV and 1.5 mol / L NaCl as the negative electrolyte. The positive electrolyte in group G batteries contained no additives, while both the positive and negative electrolytes in group H batteries contained 0.1 mol / L choline chloride. Charge-discharge experiments were conducted using a constant current / constant voltage charging + constant current discharging mode. Other experimental conditions were the same as in Example 1. Figure 4This chart compares the discharge capacity of batteries using additive-free and choline chloride-containing positive and negative electrode electrolytes. The battery using the additive-containing electrolyte shows less capacity decay than the additive-free battery. The average energy efficiency of the battery using choline chloride-containing positive and negative electrode electrolytes is 76.9%. The average energy efficiency of the battery using additive-free positive and negative electrode electrolytes is 77.3%.

[0034] Furthermore, after adding 0.1 mol / L choline chloride, the viscosity of the negative electrode electrolyte rapidly decreased from ~100 mPas to approximately 10 mPas after several charge-discharge cycles at room temperature. In the negative electrode electrolyte containing 0.2 mol / L choline chloride, the effective concentration of the active species MV could be increased to 2 mol / L. In contrast, the effective concentration of the active species MV in the negative electrode electrolyte without choline chloride was no higher than 1.5 mol / L.

[0035] Example 5

[0036] The negative electrode electrolyte contained 0.5 mol / L phenyltrimethylammonium chloride, and other experimental conditions were the same as in Example 1. After 30 cycles, the battery with the phenyltrimethylammonium chloride negative electrode electrolyte exhibited an average energy efficiency of 77.3%, significantly higher than the average energy efficiency (69.1%) of the battery without additives. Its discharge capacity retention rate was 98.5%, significantly higher than the discharge capacity retention rate (approximately 96.8%) of the battery without the phenyltrimethylammonium chloride negative electrode electrolyte.

[0037] Example 6

[0038] The negative electrode electrolyte contained 1.5 mol / L tetraethylammonium chloride, and other experimental conditions were the same as in Example 1. After 50 cycles, the battery with the negative electrode electrolyte containing 1.5 mol / L tetraethylammonium chloride had an average energy efficiency of 70.3%, lower than the average energy efficiency (78.2%) of the battery with the negative electrode electrolyte containing 0.5 mol / L tetraethylammonium chloride. Its discharge capacity retention rate was 93.6%, lower than the discharge capacity retention rate (approximately 99%) of the battery with the negative electrode electrolyte containing 0.5 mol / L tetraethylammonium chloride.

[0039] Compare with Example 1

[0040] The negative electrode electrolyte contained 0.5 mol / L tetraethylammonium bromide, and other experimental conditions were the same as in Example 1. The battery containing tetraethylammonium bromide additive had an average energy efficiency of 67.9% after 50 cycles, which was significantly lower than the average energy efficiency (78.2%) of the battery containing tetraethylammonium chloride.

Claims

1. An aqueous all-organic flow battery electrolyte containing quaternary ammonium salt additives, characterized in that, The electrolyte contains a quaternary ammonium salt additive, which can be added alone to the positive or negative electrode electrolyte, or simultaneously to both the positive and negative electrode electrolytes; the quaternary ammonium salt additive is a quaternary ammonium chloride, and its concentration in the electrolyte is 1 mmol / L to 1.5 mol / L; The quaternary ammonium salt additive is tetramethylammonium chloride, tetraethylammonium chloride, or choline chloride. The negative electrode electrolyte is an aqueous solution containing one or more viologen derivatives as redox active substances. The positive electrode electrolyte is an aqueous solution containing one or more 2,2,6,6-tetramethylpiperidine oxide (TEMPO) derivatives as redox active substances; the concentration of the TEMPO derivatives in the positive electrode electrolyte is 0.5–5 mol / L, and the supporting electrolyte is sodium chloride or potassium chloride with a concentration of 0–2 mol / L. TEMPO derivatives have the following structural formula: ； The viologen derivative has the following structural formula: 。 2. The aqueous all-organic flow battery electrolyte according to claim 1, characterized in that, The concentration of viologen derivative in the negative electrode electrolyte is 0.5–4 mol / L, and the supporting electrolyte is sodium chloride or potassium chloride with a concentration of 0–2 mol / L.

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