A method for improving the circulation performance of positive electrode electrolyte of aqueous organic liquid flow battery

Abstract

The present invention belongs to the field of new energy, and in particular to a method for improving the cyclic performance of the positive electrolyte of an aqueous organic liquid flow battery. An oxidizing additive having good oxidizability and soluble reduction products, such as hydrogen peroxide, sodium peracetate or a trivalent cobalt salt, is added to the positive electrolyte after multiple charge and discharge cycles to oxidize 1-hydroxy-2,2,6,6-tetramethylpiperidine, a chemical disproportionation reaction product of a 2,2,6,6-tetramethylpiperidine oxide derivative, to improve its cyclic stability. The oxidizing additive used in the present invention can restore the capacity of the organic positive electrolyte, improve its cyclic stability, reduce polarization overpotential, and improve energy efficiency. The present invention has the advantages of simple process, low cost, energy saving and environmental protection, and can achieve long-term stable operation of the organic positive electrolyte in battery operation.

Description

Technical Field

[0001] The present invention belongs to the field of new energy, and in particular relates to a method for improving the circulation performance of a positive electrode electrolyte of an aqueous organic liquid flow battery. Background Art

[0002] With the depletion of fossil fuels like oil and a growing emphasis on environmental protection, the use of renewable energy sources, such as solar and wind power, is rapidly increasing worldwide. However, renewable energy sources are intermittent, regional, and unstable, necessitating the development of efficient, large-scale energy storage technologies to smooth and stabilize power output and improve efficiency.

[0003] Flow batteries have attracted much attention as an electrochemical energy storage technology with economic feasibility and long lifespan. In addition, flow batteries have the advantages of flexible design, fast response, safety, reliability, and easy maintenance.

[0004] Currently, the widely used all-vanadium redox flow battery (VFB) releases pentavalent vanadium ions as vanadium pentoxide (V2O5) when operated at relatively high temperatures (>40°C). However, the application of VFBs is constrained by the global scarcity of vanadium. Furthermore, the high toxicity of vanadium-based species and the corrosive nature of the strongly acidic electrolyte are significant disadvantages.

[0005] Aqueous organic flow batteries are one of the next-generation large-scale energy storage technologies that are expected to replace all-vanadium flow batteries due to their rich variety of organic molecules, tunable structure and properties, easy recycling, and environmental friendliness. Jena Battery, a startup company from the University of Jena in Germany, has pioneered the commercialization of viologen-TEMPO aqueous organic flow battery technology in collaboration with BASF. Quino Energy, a startup company from Harvard University in the United States, is developing aqueous organic flow batteries focused on the quinone-based electrolyte TEMPO. Viologen-TEMPO aqueous organic flow batteries can operate in neutral or near-neutral environments and feature high safety, low cost, and independent power-capacity design. They are expected to address bottlenecks that hinder the efficient use of clean energy and have broad application prospects. However, when operating at higher temperatures (35-60°C), these flow batteries exhibit poor cycling performance and rapid capacity decay. The reason is that TEMPO species are prone to chemical disproportionation reactions, one of the disproportionation products being an inactive product (1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH)). Furthermore, this disproportionation reaction can lead to increased cross-penetration of active substances, significantly accelerating the battery's capacity degradation. To further accelerate the commercialization of viologen-TEMPO aqueous organic flow batteries, it is necessary to research methods that can inhibit TEMPO disproportionation reactions and improve their cycling performance. Summary of the Invention

[0006] The purpose of the present invention is to solve the capacity decay problem of the positive electrode electrolyte of the viologen derivative / / TEMPO aqueous organic liquid flow battery. An oxidizing additive is added to the positive electrode electrolyte after capacity decay to restore the capacity of the viologen derivative / / TEMPO aqueous organic liquid flow battery, improve the efficiency, and promote the efficient and stable operation of the aqueous all-organic liquid flow battery.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] An oxidizing additive is added to the cathode electrolyte of an aqueous all-organic flow battery after charge and discharge cycles.

[0009] Among them, the oxidizing additives are hydrogen peroxide, sodium peracetate, trivalent cobalt salts, sodium dichromate, potassium dichromate, potassium permanganate, ammonium persulfate, sodium hypochlorite, sodium percarbonate, sodium perborate, potassium perborate, bromine, iodine, etc.;

[0010] The oxidizing additive may be added multiple times or in batches.

[0011] The amount of additive added to the positive electrode electrolyte is Among them, n ad is the amount of additive added to the positive electrode electrolyte (mol); C i is the initial capacity (mAh); C f is the capacity after cycling (mAh); F is the Faraday constant (96485 C / mol).

[0012] Since 1 mol of hydrogen peroxide or sodium peracetate can oxidize 2 mol of the disproportionation reaction product 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH), 50% is the amount of oxidant that is just enough for the reaction according to the reaction equation, while 100% is an excess of twice the oxidant.

[0013] The working temperature of the positive electrode electrolyte using the additive is 15 to 60° C. The preferred working temperature is 25 to 45° C.

[0014] The reduction products of the additive are water-soluble metal salts, water or weak acids;

[0015] The oxidizing additive is added to the positive electrode electrolyte after the capacity decays after charge and discharge cycles, and is added multiple times or in batches.

[0016] The redox active substances suitable for the negative electrode electrolyte of the aqueous all-organic liquid flow battery of the present invention are: methyl viologen dichloride (MV), 1,1'-bis(3-sulfopropyl)-4,4'-bipyridine ((SPr)2V), (1-methyl-1'-[3-(trimethylamino)propyl]-4,4'-trichlorobipyridinium ([(Me)(NPr)V]Cl3)), (1,1'-bis[3-(trimethylamino)propyl]4,4'-bipyridinium tetrabromide ([(NPr)2V]Br4)), (1-[3-(trimethylamino)propyl]1'-(3-sulfopropyl)-4,4'-bipyridinium dibromide ([(NPr)(SPr)V]Br2)) or a mixture thereof. The concentration of the viologen derivative in the aqueous solution of the negative electrode electrolyte is 0.2 to 3.0 mol / L.

[0017] The redox substance used in the positive electrolyte of the aqueous all-organic flow battery of the present invention is a TEMPO derivative. The positive electrolyte is an aqueous solution, and the TEMPO derivative is 1-methylimidazole-2,2,6,6-tetramethylpiperidinium (MTTEMPO), 2,2,6,6-tetramethylpiperidinium oxide-4-sulfate potassium (TEMPOSP), or a mixture thereof. The concentration of the TEMPO derivative in the aqueous positive electrolyte solution is 0.2 to 2.0 mol / L.

[0018] The beneficial results of the present invention are:

[0019] The additive used in the present invention, when added to the cathode electrolyte after capacity decay, can oxidize 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH), the chemical disproportionation product of TEMPO, thereby partially restoring the capacity of the cathode electrolyte, improving the stability of the cathode electrolyte, reducing the polarization overpotential, and improving energy efficiency. The present invention has the advantages of simple process, low cost, energy conservation and environmental protection, and can achieve long-term stable operation of the cathode electrolyte in battery operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a graph of the discharge capacity of the aqueous organic liquid flow battery of Example 1 (hydrogen peroxide additive was added at the 129th cycle).

[0021] Figure 2 Graph showing the charge and discharge curves of the aqueous organic flow battery of Example 1 before and after the addition of hydrogen peroxide.

[0022] Figure 3 This is a graph of the discharge capacity of the aqueous organic liquid flow battery of Example 2 (sodium peracetate additive was added at the 129th cycle).

[0023] Figure 4 This is a graph of the discharge capacity of the aqueous organic liquid flow battery of Example 3 (CoF3 additive was added at the 129th cycle).

[0024] Figure 5 This is a graph showing the discharge capacity of the aqueous organic liquid flow battery of Example 4 (ammonium persulfate additive was added at cycle 129). DETAILED DESCRIPTION

[0025] The following examples are provided to further illustrate the present invention, but are not intended to limit the scope of the present invention.

[0026] Example 1

[0027] The constructed aqueous organic liquid flow battery uses an aqueous solution containing 1.5 mol / L TEMPO (1-methylimidazole-2,2,6,6-tetramethylpiperidine (MTTEMPO)) and 1.5 mol / L NaCl as the positive electrode electrolyte, an aqueous solution containing 1.5 mol / LMV and 1 mol / L NaCl as the negative electrode electrolyte, and a DSV anion exchange membrane as the separator. Both the positive and negative electrodes use hydrophilic treated carbon felt electrodes. During the experiment, the positive and negative electrolytes were protected by nitrogen, the flow rate of the electrolyte was 60 mL / min, and the temperature of the battery was controlled at 25°C. The charge and discharge experiments were carried out in constant current and constant voltage charging + constant current discharge mode, and the charge and discharge current density was 80 mA cm -2 , the charging cut-off voltage is 1.5V and the discharging cut-off voltage is 0.4V.

[0028] Figure 1 This is the discharge capacity diagram of the aqueous organic liquid flow battery (0.7 mL of 3% hydrogen peroxide solution was added at the 129th cycle). Figure 1 It can be seen that when no oxidant was added to the positive electrolyte, the battery's first cycle capacity was 133.6mAh, and the capacity at the 128th cycle was 95.2mAh, decreasing at a rate of 0.2244% per cycle for the first 128 cycles. After adding hydrogen peroxide (no oxidant was added in the above content), the battery's charge capacity increased from 95.2mAh to 101.8mAh, an increase of about 6.9%. The discharge capacity increased from 94.8mAh to 100.1mAh, an increase of about 5.6%. Before adding hydrogen peroxide, the battery's capacity decay rate was 0.2244% per cycle. After adding hydrogen peroxide, the capacity decay rate was reduced to 0.0760% per cycle.

[0029] Figure 2 The charge and discharge curves of the aqueous organic flow battery before and after the addition of hydrogen peroxide are shown. As can be seen, the addition of hydrogen peroxide slightly decreases the battery's charging platform, while the discharge platform voltage increases, and the average energy efficiency increases from 77.0% to 78.1%.

[0030] Example 2

[0031] The assembly and testing methods of the aqueous organic liquid flow battery are the same as those in Example 1. The temperature of the battery is controlled at 45°C. After 128 cycles of charge and discharge of the aqueous organic liquid flow battery, 0.75mL of 1mol / L sodium peracetate aqueous solution is added to the positive electrode electrolyte, and the charge and discharge cycle experiment is continued. Before the addition of sodium peracetate, the capacity decay rate of the battery was 0.3125% per cycle. After the addition of sodium peracetate, the capacity decay rate was reduced to 0.0892% per cycle. After the addition of sodium peracetate, the average energy efficiency increased from 78.9% to 80.4%. The discharge capacity increased from 80.3mAh to 118.1mAh, an increase of about 47.1%.

[0032] Example 3

[0033] The aqueous organic flow battery was assembled and tested in the same manner as in Example 1. The battery temperature was controlled at 25°C. After 128 charge-discharge cycles, 0.1g of CoF3 was added to the positive electrolyte, and the charge-discharge cycle experiment was continued. Before the addition of CoF3, the battery's capacity fade rate was 0.2245% per cycle. After the addition of CoF3, the capacity fade rate decreased to 0.0623% per cycle. The discharge capacity increased from 94.8mAh to 109.9mAh, an increase of approximately 15.9%.

[0034] Example 4

[0035] The aqueous organic flow battery was assembled and tested in the same manner as in Example 1. The battery temperature was controlled at 60°C. After 128 charge-discharge cycles, 0.1g of ammonium persulfate was added to the positive electrolyte, and the charge-discharge cycle experiment was continued. Before the addition of ammonium persulfate, the battery's capacity fade rate was 0.1754% per cycle. After the addition of ammonium persulfate, the capacity fade rate decreased to 0.0415% per cycle. The discharge capacity increased from 103.9mAh to 123.9mAh, an increase of approximately 19.2%.

[0036] Example 5

[0037] The assembly and testing methods of the aqueous organic flow battery were the same as those in Example 1. The battery temperature was controlled at 60°C. After 128 charge and discharge cycles, 0.1g of sodium hypochlorite was added to the positive electrolyte, and the charge and discharge cycle experiment was continued. Before the addition of sodium hypochlorite, the battery's capacity fade rate was 0.1754% per cycle. After the addition of sodium hypochlorite, the capacity fade rate decreased to 0.0706% per cycle. The discharge capacity increased from 103.9mAh to 109.8mAh, an increase of approximately 5.7%.

[0038] Example 6

[0039] The assembly and testing methods of the aqueous organic flow battery were the same as those in Example 1. The battery temperature was controlled at 60°C. After 128 charge and discharge cycles, 0.1g of sodium perborate was added to the positive electrolyte, and the charge and discharge cycle experiment was continued. Before the addition of sodium perborate, the battery's capacity fade rate was 0.1754% per cycle. After the addition of sodium perborate, the capacity fade rate decreased to 0.0656% per cycle. The discharge capacity increased from 103.9mAh to 111.6mAh, an increase of approximately 7.4%.

[0040] Example 7

[0041] The aqueous organic flow battery was assembled and tested in the same manner as in Example 1. The battery temperature was maintained at 60°C. After 128 charge-discharge cycles, 0.1g of bromine was added to the positive electrolyte, and the charge-discharge cycle experiment was continued. Before the addition of bromine, the battery's capacity fade rate was 0.1754% per cycle. After the addition of bromine, the capacity fade rate decreased to 0.0866% per cycle. The discharge capacity increased from 103.9mAh to 106.8mAh, an increase of approximately 2.8%.

[0042] Example 8

[0043] The assembly and testing methods of the aqueous organic liquid flow battery are the same as those in Example 1. The temperature of the battery is controlled at 25°C. After 128 cycles of charge and discharge of the aqueous organic liquid flow battery, 0.75mL of 1mol / L sodium peracetate aqueous solution is added to the positive electrode electrolyte, and the charge and discharge cycle experiment is continued. Before the addition of sodium peracetate, the capacity decay rate of the battery was 0.3125% per cycle. After the addition of sodium peracetate, the capacity decay rate was reduced to 0.1176% per cycle. After the addition of sodium peracetate, the average energy efficiency increased from 78.9% to 80.1%. The discharge capacity increased from 80.3mAh to 106.9mAh, an increase of about 33.1%. Compared with Example 2, at higher temperatures, the oxidant sodium peracetate has a better effect on capacity recovery and improving stability.

[0044] Example 9

[0045] The constructed aqueous organic liquid flow battery uses an aqueous solution containing 1.5 mol / L 2,2,6,6-tetramethylpiperidinyl oxide-4-potassium sulfate (TEMPOSP) and 1.5 mol / L NaCl as the positive electrode electrolyte, an aqueous solution containing 1.5 mol / L MV and 1 mol / L NaCl as the negative electrode electrolyte, and a DSV anion exchange membrane as the separator. Both the positive and negative electrodes use hydrophilic treated carbon felt electrodes. During the experiment, the positive and negative electrolytes were protected by nitrogen, the flow rate of the electrolyte was 60 mL / min, and the temperature of the battery was controlled at 25 ° C. The charge and discharge experiments were carried out in constant current and constant voltage charging + constant current discharge mode, and the charge and discharge current density was 80 mA cm -2, the charging cut-off voltage is 1.5V and the discharging cut-off voltage is 0.4V.

[0046] Without an oxidant added to the positive electrolyte, the battery's first-cycle capacity was 158.6 mAh, reaching 115.4 mAh at cycle 128, decreasing at a rate of 0.2128% per cycle for the first 128 cycles. After adding hydrogen peroxide, the battery's discharge capacity increased from 115.4 mAh to 136.6 mAh, an improvement of approximately 18.4%. Before adding hydrogen peroxide, the battery's capacity faded at a rate of 0.2128% per cycle. After adding hydrogen peroxide, the capacity fade rate decreased to 0.0642% per cycle.

[0047] Example 10

[0048] The constructed aqueous organic flow battery uses an aqueous solution containing 1.5 mol / L 2,2,6,6-tetramethylpiperidinium oxide-4-potassium sulfate (TEMPOSP) and 1.5 mol / L NaCl as the positive electrode electrolyte, an aqueous solution containing 1.5 mol / L 1,1'-bis(3-sulfopropyl)-4,4'bipyridine ((SPr)2V) and 1 mol / L NaCl as the negative electrode electrolyte, and a DSV anion exchange membrane as the separator. Both the positive and negative electrodes use hydrophilic treated carbon felt electrodes. During the experiment, the positive and negative electrolytes were protected by nitrogen, the flow rate of the electrolyte was 60 mL / min, and the temperature of the battery was controlled at 25°C. The charge and discharge experiments were carried out in constant current and constant voltage charging + constant current discharge mode, and the charge and discharge current density was 80 mA cm -2 , the charging cut-off voltage is 1.5V and the discharging cut-off voltage is 0.4V.

[0049] Without the addition of an oxidant to the positive electrolyte, the battery's first-cycle capacity was 145.8 mAh, reaching 108.4 mAh at cycle 128, decreasing at a rate of 0.2004% per cycle for the first 128 cycles. After adding hydrogen peroxide, the battery's discharge capacity increased from 108.4 mAh to 119.8 mAh, a 10.5% improvement. Before adding hydrogen peroxide, the battery's capacity faded at a rate of 0.2004% per cycle. After adding hydrogen peroxide, the rate decreased to 0.0703% per cycle.

[0050] Example 11

[0051] The assembly and testing methods of the aqueous organic liquid flow battery are the same as those in Example 1. The temperature of the battery is controlled at 45°C. After 128 cycles of charge and discharge of the aqueous organic liquid flow battery, 1.5mL of 1mol / L sodium peracetate aqueous solution is added to the positive electrode electrolyte, and the charge and discharge cycle experiment is continued. Before the addition of sodium peracetate, the capacity decay rate of the battery was 0.3125% per cycle. After the addition of sodium peracetate, the capacity decay rate was reduced to 0.0706% per cycle. After the addition of sodium peracetate, the average energy efficiency increased from 78.9% to 81.2%. The discharge capacity increased from 80.3mAh to 129.6mAh, an increase of about 61.4%, but the cost increased.

Claims

1. A method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery, characterized in that: The method comprises: placing an oxidizing additive in a cathode electrolyte of an aqueous organic liquid flow battery after long-term operation, wherein the oxidizing additive oxidizes 1-hydroxy-2,2,6,6-tetramethylpiperidine, a chemical disproportionation reaction product of a TEMPO derivative, and the amount of the oxidizing additive added to the cathode electrolyte is Among them, n ad is the amount of additive added to the positive electrode electrolyte, its unit is mol; C i is the initial capacity; C f is the capacity after cycling; F is the Faraday constant 96485C / mol, and the amount of additive added is 0-100% more than the theoretically calculated amount; The redox active substance in the positive electrode electrolyte of the aqueous organic liquid flow battery is a 2,2,6,6-tetramethylpiperidinium oxide TEMPO derivative, and the redox active substance contained in the negative electrode electrolyte is a viologen derivative; the TEMPO derivative is specifically 1-methylimidazole-2,2,6,6-tetramethylpiperidinium MTTEMPO, 2,2,6,6-tetramethylpiperidinium oxide-4-potassium sulfate TEMPOSP or a mixture thereof.

2. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The oxidizing additive is one or more of hydrogen peroxide, sodium peracetate, trivalent cobalt salt, sodium dichromate, potassium dichromate, potassium permanganate, ammonium persulfate, sodium hypochlorite, sodium percarbonate, sodium perborate, potassium perborate, bromine, and iodine.

3. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The oxidizing additive is added to the positive electrode electrolyte after capacity decay after charge and discharge cycles, and is added multiple times or in batches.

4. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The working temperature of the positive electrode electrolyte using the additive is 15 to 60°C.

5. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The reduction product of the additive is a water-soluble metal salt, water or a weak acid.

6. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The concentration of the redox active substance in the aqueous solution of the positive electrode electrolyte is 0.2 to 2.0 mol / L.

7. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 1, characterized in that: The redox active substances contained in the negative electrode electrolyte of the aqueous organic liquid flow battery are methyl viologen dichloride (MV), 1,1'-bis(3-sulfopropyl)-4,4'-bipyridyl (SPr)2V, (1-methyl-1'-[3-(trimethylamino)propyl]-4,4'-trichlorobipyridyl[(Me)(NPr)V]Cl3, (1,1'-bis[3-(trimethylamino)propyl]4,4'-bipyridyl tetrabromide[(NPr)2V]Br4, (1-[3-(trimethylamino)propyl]1'-(3-sulfopropyl)-4,4'-bipyridyl dibromide[(NPr)(SPr)V]Br2 or a mixture thereof.

8. The method for improving the circulation performance of the positive electrode electrolyte of an aqueous organic liquid flow battery according to claim 7, characterized in that: The concentration of the redox active substance in the negative electrode electrolyte is 0.2 to 3.0 mol / L.

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