Application of quaternary ammonium salt additive in zinc-bromine flow battery electrolyte

Abstract

The invention discloses application of a quaternary ammonium salt additive in a zinc-bromine flow battery electrolyte, and belongs to the technical field of electrochemical energy storage, the chemical name of the quaternary ammonium salt additive is N-(2-ethoxyl)-N-methyl-pyrrolidinium bromide, and the quaternary ammonium salt additive is added into the zinc-bromine flow battery electrolyte as a complexing agent of elemental bromine. According to the invention, the low-temperature range of operation of the zinc-bromine flow battery is widened, and the zinc-bromine flow battery added with the novel additive can work at-20 DEG C for more than 200 hours; the dynamic characteristics of the battery are improved, and the normal-temperature and low-temperature cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present application relates to the application of a quaternary ammonium salt additive in a zinc-bromine flow battery electrolyte, belonging to the technical field of electrochemical energy storage. Background Art

[0002] With the improvement of the level of human social development, human demand for energy is increasing day by day. Most of the energy consumed by humans is fossil energy represented by coal, natural gas, and oil, which has brought about global climate anomalies and serious environmental pollution. Increasing the proportion of renewable energy such as solar energy and wind energy is an effective way to reduce carbon emissions on the energy supply side. However, renewable energy has obvious discontinuous, unstable, and uncontrollable characteristics, which poses huge risks to the stable transmission of electricity by the power grid and the reliable operation of power load devices. Equipped with efficient energy storage devices, it can adjust the time difference contradiction between power generation and power supply; mobilize the load response capability and reduce the load's demand for regulation and support of large power grids. Energy storage facilities are divided into physical energy storage and electrochemical energy storage, and flow batteries have become one of the most promising technologies in large-scale electrochemical energy storage due to their good safety and long cycle life.

[0003] Due to the high abundance of zinc in the earth's crust, the compatibility of zinc metal with water, and the relatively stable existence of zinc metal in the air, the cost of assembling and processing aqueous zinc-based flow batteries is relatively low; at the same time, compared with other aqueous cation batteries, aqueous zinc-based flow batteries have a suitable working potential, which provides a relatively negative potential while avoiding significant side reactions. Zinc-bromine flow batteries have been developed earlier and have received extensive research attention due to their advantages such as high open circuit voltage and high energy density.

[0004] N-methyl-N-ethylpyrrolidine (MEP) is the most commonly used additive for zinc-bromine flow battery electrolyte for complexing bromine. It can form an oily ionic liquid with bromine that is separated from the water phase. During the low-temperature operation of zinc-bromine flow batteries, the oily ionic liquid solidifies and blocks the pipeline, causing the zinc-bromine flow battery to fail in low-temperature environments. Therefore, it is necessary to develop a new most commonly used additive for complexing bromine. The ionic liquid formed by this additive and bromine complexing remains liquid at low temperatures to ensure the long-term stable operation of the battery at low temperatures. Summary of the invention

[0005] According to one aspect of the present application, a quaternary ammonium salt additive is provided for use in a zinc-bromine flow battery electrolyte. The novel quaternary ammonium salt additive is used to broaden the low-temperature use range of the zinc-bromine flow battery, improve the stability of the battery system, and solve the problem in the prior art that the zinc-bromine flow battery electrolyte is prone to solidification in a low-temperature environment, resulting in poor stability of the battery at low temperatures and short cycle life.

[0006] This application adopts the following technical solutions:

[0007] A quaternary ammonium salt additive is used in a zinc-bromine flow battery electrolyte. The chemical name of the quaternary ammonium salt additive is N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and its structural formula is as follows:

[0008]

[0009] Optionally, the zinc-bromine flow battery electrolyte includes N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide (MEPOH).

[0010] Alternatively, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide (MEPOH) is used as a complexing agent for bromine in zinc-bromine flow battery electrolyte.

[0011] Optionally, the zinc-bromine flow battery electrolyte includes zinc bromide, a supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and water.

[0012] Optionally, the zinc-bromine flow battery electrolyte consists of zinc bromide, supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide and water.

[0013] Water is used as the solvent.

[0014] Optionally, the content of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide in the zinc-bromine flow battery electrolyte is x, wherein 0 mol / L<x≤2 mol / L.

[0015] Optionally, the content of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide in the zinc-bromine flow battery electrolyte is selected from any value among 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.2mol / L, 1.4mol / L, 1.6mol / L, 1.8mol / L, 2mol / L or any range value therebetween.

[0016] Optionally, the content of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide in the zinc-bromine flow battery electrolyte is 0.5 to 0.7 mol / L.

[0017] Optionally, the content of zinc bromide in the zinc-bromine flow battery electrolyte is 0.5 to 5 mol / L.

[0018] Optionally, the content of zinc bromide in the zinc-bromine flow battery electrolyte is 1.5 to 3 mol / L.

[0019] Optionally, the supporting electrolyte is selected from at least one of ammonium chloride, potassium chloride, sodium chloride, magnesium chloride and lithium chloride.

[0020] Optionally, at room temperature, the supporting electrolyte is selected from ammonium chloride or potassium chloride.

[0021] Optionally, at room temperature, the supporting electrolyte is ammonium chloride, and the concentration of ammonium chloride in the zinc-bromine flow battery electrolyte is 1 to 6 mol / L.

[0022] Optionally, at room temperature, the supporting electrolyte is ammonium chloride, and the concentration of ammonium chloride in the zinc-bromine flow battery electrolyte is 4 to 4.5 mol / L.

[0023] Optionally, at room temperature, the supporting electrolyte is ammonium chloride, and the concentration of ammonium chloride in the zinc-bromine flow battery electrolyte is 4 to 4.2 mol / L.

[0024] Optionally, at room temperature, the supporting electrolyte is potassium chloride, and the concentration of ammonium chloride in the zinc-bromine flow battery electrolyte is 1 to 6 mol / L.

[0025] Optionally, at room temperature, the supporting electrolyte is potassium chloride, and the concentration of ammonium chloride in the zinc-bromine flow battery electrolyte is 2.5-4 mol / L.

[0026] Optionally, the content of the supporting electrolyte in the zinc-bromine flow battery electrolyte is y, wherein 0 mol / L<y≤5 mol / L.

[0027] Optionally, the zinc-bromine flow battery electrolyte further comprises other additives.

[0028] Optionally, the other additives are selected from at least one of N-methyl-N-ethylpyrrolidinium bromide (MEP), N-methyl-N-ethylmorpholinium bromide (MEM), choline bromide, choline chloride, tetrapentylammonium bromide, 1-ethyl-2-methylpyridinium bromide, 1-butyl-3-methylpyridinium bromide, sodium acetate, potassium acetate, sodium formate, potassium formate, potassium bromide, sodium bromide, lithium bromide, magnesium bromide, calcium bromide, ethylene glycol, NN dimethylamide, and dimethyl sulfoxide;

[0029] Optionally, the structural formulas of the N-methyl-N-ethylpyrrolidinium bromide (MEP) and N-methyl-N-ethylmorpholinium bromide (MEM) are as follows:

[0030]

[0031] Optionally, the content of other additives in the zinc-bromine flow battery electrolyte is z, 0mol / L<z≤4mol / L.

[0032] Optionally, the zinc-bromine flow battery comprises a single cell or a battery pack consisting of two or more single cells connected in series or / and in parallel;

[0033] The single cell includes a positive terminal plate, a positive current collector, a positive electrode frame, a positive electrode, a separator, a negative electrode, a negative electrode frame, a negative current collector, and a negative terminal plate stacked in sequence;

[0034] The diaphragm is a porous ion-conducting membrane.

[0035] Optionally, the cavity between the current collector and the separator is filled with electrolyte and electrodes.

[0036] Optionally, the zinc-bromine flow battery electrolyte is located in the chambers where the positive and negative electrodes are located on both sides of the diaphragm.

[0037] Optionally, the electrolyte added into the chambers on both sides of the diaphragm before charging has the same composition.

[0038] Optionally, the positive terminal plate and the negative terminal plate are both acid corrosion-resistant metal plates.

[0039] Optionally, the metal end plate is selected from an aluminum alloy plate and a stainless steel plate, preferably a stainless steel plate, and the positive end plate and the negative end plate are made of the same material.

[0040] Optionally, the porous ion conducting membrane has an average pore size of 0.01 to 0.1 μm and a porosity of 20 to 60%.

[0041] Optionally, the positive electrode current collector and the negative electrode current collector are independently selected from at least one of a graphite plate, a titanium plate, and a carbon composite plate.

[0042] Optionally, the positive electrode current collector and the negative electrode current collector are made of the same material.

[0043] Optionally, the positive electrode current collector and the negative electrode current collector are both graphite plates.

[0044] Optionally, the positive electrode and the negative electrode are independently graphite felt or carbon felt.

[0045] Optionally, the positive electrode and the negative electrode are made of the same material.

[0046] Optionally, the positive electrode and the negative electrode are both carbon felt.

[0047] Optionally, the separator may be selected from one of a perfluorosulfonic acid membrane, a porous polyolefin membrane, a sulfonated polyetheretherketone membrane, and a polybenzimidazole membrane.

[0048] Optionally, the separator is a Daramic 900 μm polyethylene porous membrane.

[0049] Optionally, the operating temperature of the zinc-bromine flow battery is -20 to 40°C.

[0050] Optionally, the zinc-bromine flow battery is used in a low temperature environment of -20 to 0°C or a normal temperature environment.

[0051] The energy density at the use temperature is 6.5 to 400Wh / L.

[0052] The beneficial effects of this application include:

[0053] (1) The application of the quaternary ammonium salt additive in the zinc-bromine flow battery electrolyte provided by the present application broadens the temperature range of the zinc-bromine flow battery, improves the stability of the zinc-bromine flow battery in a low temperature environment, and improves the energy density of the battery at low temperatures. Specifically,

[0054] a. Stability of oily ionic liquid: The oily ionic liquid formed by the complexation of the new quaternary ammonium salt additive and bromine can maintain liquid state at -40°C;

[0055] b. Co-stabilization of the positive electrolyte as a whole (aqueous phase and oily ionic liquid): The positive electrolyte with the addition of the new quaternary ammonium salt additive has a charge depth of 50% (charge depth = actual capacity / maximum theoretical capacity, ) when the water phase and the oily ionic liquid phase can remain in liquid state at -20°C, allowing the battery system to operate stably for more than 140 hours in a -20°C environment.

[0056] (1) It promotes the rapid diffusion of bromine and bromide ions in the electrolyte, and the rapid kinetics reduces the accumulation of products, extending the cycle life of the battery at low and room temperatures. The zinc-bromine flow battery using the new quaternary ammonium salt additive can operate stably for more than 1400 hours under deep (>77.3%) charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The present invention discloses a molecular structure of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, a quaternary ammonium salt additive.

[0058] Figure 2 This is the battery performance in Example 1 of the present application when operated at -20°C.

[0059] Figure 3 This is the time-voltage curve of the battery operated at -20°C in Example 1 of the present application.

[0060] Figure 4 This is the battery performance of Comparative Example 1 of the present application when operated at -20°C.

[0061] Figure 5 This is the battery performance in Comparative Example 2 of the present application when operated at -20°C.

[0062] Figure 6 This is the battery performance in Example 2 of the present application when operated at 25°C.

[0063] Figure 7 This is the battery performance of Comparative Example 3 of the present application when operated at 25°C.

[0064] Figure 8 This is the battery performance in Example 3 of the present application when operated at 25°C.

[0065] Fig. 9 This is the time-voltage curve of the battery operated at 25° C. in Example 3 of the present application. DETAILED DESCRIPTION

[0066] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0067] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0068] Unless otherwise specified, conventional methods were used for testing, and instrument settings were all those recommended by the manufacturer. The battery performance test was performed using a Xinwei charging and discharging instrument or an Arbin2000 charging and discharging instrument.

[0069] In the present application, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide (MEPOH) is prepared by the following method:

[0070] Under the premise of reflux condensation, 2-bromoethanol is slowly added dropwise to magnetically stirred N-methylpyrrole, and after reacting for 48 hours, ether is poured into the reaction solution, and the precipitated solid is separated, washed, and recrystallized for use, which specifically includes:

[0071] At room temperature, mix N-methylpyrrolidine and acetonitrile in a three-necked flask with a reflux device under nitrogen protection, and use a magnetic stirrer to mix thoroughly. Slowly drip 2-bromoethanol into the three-necked flask using a constant pressure dropping funnel, and complete the addition within a certain period of time. Stir thoroughly while adding, so that the reactants are fully mixed and contacted. After the addition of 2-bromoethanol is completed, you can stop N 2 Protect and reflux the condensed water to keep the solution in a stirring state. 48 hours after the addition of 2-bromoethanol is completed, stop the magnetic stirring, and the three-necked flask is still a uniform solution. While using mechanical stirring, add ether to the three-necked flask at one time, and a large amount of solid precipitates. Use filtration to separate the solid. Use the solid product obtained by washing at room temperature, and then dry it in a vacuum oven after washing to finally obtain a beige N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide solid powder.

[0072] Preparation Example 1

[0073] At room temperature, mix 1 mol of N-methylpyrrolidine and 60 mL of acetonitrile in a three-necked flask with a reflux device under nitrogen protection, and use a magnetic stirrer to mix thoroughly. Slowly drip 1 mol of 2-bromoethanol into the three-necked flask using a constant pressure dropping funnel, and complete the addition within 1 hour. Stir thoroughly while adding, so that the reactants are fully mixed and contacted. Stop the addition of 2-bromoethanol 2 hours after the end of the addition. 2 Protect and reflux the condensed water to keep the solution in a stirring state. 48 hours after the addition of 2-bromoethanol was completed, stop the magnetic stirring, and the three-necked flask was still a uniform solution. While using mechanical stirring, add 150mL of ether to the three-necked flask at one time, and a large amount of solid precipitates. Use filtration to separate the solid matter. Wash the solid product with 100mL of ether at room temperature, wash 5 times, and then dry it in a vacuum oven at 40°C for 8 hours to obtain a beige N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide solid powder.

[0074] Example 1

[0075] The battery was operated at -20°C and the battery electrolyte was 2 mol / L ZnBr 2 +4.2mol / L NH 4 Cl+0.6mol / LMEPOH, the single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 25mL, and the peristaltic pump controls the electrolyte flow rate to 50mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 25mA cm -2 , discharge cut-off voltage is 0.3V, and charging depth is 33.6%.

[0076] Example 2

[0077] The battery was operated at 25°C and the battery electrolyte was 2 mol / L ZnBr 2 +3mol / L KCl+0.6mol / L MEPOH, the single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 40mL, and the magnetic pump controls the electrolyte flow rate to 70mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 80mA cm-2 , discharge cut-off voltage is 0.3V, and charging depth is 67.3%.

[0078] Example 3

[0079] The battery was operated at 25°C and the battery electrolyte was 2 mol / L ZnBr 2 +4.2mol / L NH 4 Cl+0.6mol / L MEPOH, the single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 50mL, and the magnetic pump controls the electrolyte flow rate to 70mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 115mA cm -2 , discharge cut-off voltage is 0.3V, and charging depth is 77.4%.

[0080] Example 4

[0081] The prepared simulated 50% charge electrolyte contains 1M ZnBr 2 +4.2M NH 4 Cl+0.6M MEPOH+1MBr 2 The electrolyte is divided into an aqueous phase layer and an oil phase layer. The aqueous phase layer is mainly an aqueous solution and is located in the upper layer of the electrolyte; the oil phase layer is mainly a quaternary ammonium polybromide ionic liquid, and the bromine element is mainly concentrated in the oil phase layer. The oil phase layer has a larger density and is located in the lower layer of the electrolyte.

[0082] Comparative Example 1

[0083] The battery was operated at -20°C and the battery electrolyte was 2 mol / L ZnBr 2 +4.2mol / L NH 4 Cl+0.6mol / L MEP, the single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 25mL, and the peristaltic pump controls the electrolyte flow rate to 50mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 25mAcm -2 , discharge cut-off voltage is 0.3V, and charging depth is 33.6%.

[0084] Comparative Example 2

[0085] The battery was operated at -20°C and the battery electrolyte was 2 mol / L ZnBr 2 +4.2mol / L NH 4 Cl+0.6mol / L MEM, single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 25mL, and the peristaltic pump controls the electrolyte flow rate to 50mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 25mAcm -2 , discharge cut-off voltage is 0.3V, and charging depth is 33.6%.

[0086] Comparative Example 3

[0087] The battery was operated at 25°C and the battery electrolyte was 2 mol / L ZnBr 2 +3mol / L KCl+0.6mol / L MEP, the single cell is positive terminal plate, positive electrode 6×6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6×6cm 2 Graphite plate, negative terminal plate. The electrolyte volume on each side is 40mL, and the magnetic pump controls the electrolyte flow rate to 70mL min -1 , charge and discharge current density 40mA / cm 2 , surface capacity 80mA cm -2 , discharge cut-off voltage is 0.3V, and charging depth is 67.3%.

[0088] Comparative Example 4

[0089] The prepared simulated 50% charge electrolyte contains 1M ZnBr 2 +4.2M NH 4 Cl+0.6M MEP+1MBr 2 The electrolyte is divided into an aqueous phase layer and an oil phase layer. The aqueous phase layer is mainly an aqueous solution and is located in the upper layer of the electrolyte; the oil phase layer is mainly a quaternary ammonium polybromide ionic liquid, and the bromine element is mainly concentrated in the oil phase layer. The oil phase layer has a larger density and is located in the lower layer of the electrolyte.

[0090] Test Example 1

[0091] The battery performance was tested using a constant current charge and discharge method with a charge and discharge current density of 40 mA / cm 2, surface capacity 25mAcm -2 , discharge cut-off voltage 0.3V, charge depth 33.6%, test temperature -20℃, the results are as follows Figures 2 to 5 shown.

[0092] The battery cycle life comparison of Example 1 and Comparative Examples 1 and 2 is shown in Table 1. When the energy efficiency is reduced to 40%, it is considered that the battery is completely ineffective, and the battery cycle life is judged based on this. The battery cycle life using MEPOH (Example 1) as a bromine complexing agent is the longest, greater than 100 cycles, while the cycle life of the battery using MEP (Comparative Example 1) and MEM (Comparative Example 2) as a bromine complexing agent is less than 10 cycles, indicating that the battery using MEPOH as a bromine complexing agent can operate stably under -20°C, and MEPOH is superior to MEP and MEM in terms of low-temperature battery cycle life.

[0093] Table 1 Cycle life comparison

[0094] Operating temperature / ℃ Complexing agent Depth of charge / % Cycle life Example 1 -20 MEPOH 33.6 >100 Example 2 25 MEPOH 67.3 >400 Comparative Example 1 -20 MEP 33.6 <10 Comparative Example 2 -20 MEM 33.6 <10 Comparative Example 3 25 MEP 67.3 <80

[0095] The battery performance comparison of Example 1 and Comparative Examples 1 and 2 is shown in Table 2. The coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) are all averaged over the cycle life. The average energy efficiency of the battery with MEPOH (Example 1) as a bromine complexing agent is greater than 60.4% over a cycle life of 120 cycles, while the average energy efficiency of the battery with MEP (Comparative Example 1) as a bromine complexing agent is only 42.6% over 10 cycles, and the average energy efficiency of the battery with MEM (Comparative Example 2) as a bromine complexing agent is only 49.1% over 10 cycles, and the batteries of MEP (Comparative Example 1) and MEM (Comparative Example 2) fail after 10 cycles, indicating that MEPOH is superior to MEP and MEM in terms of low-temperature battery performance.

[0096] Table 2 Battery performance comparison

[0097]

[0098]

[0099] Note: Coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) are all averaged over the cycle life.

[0100] Test Example 2

[0101] The battery performance was tested using a constant current charge and discharge method with a charge and discharge current density of 40 mA / cm 2 , surface capacity 80mAcm -2 , discharge cut-off voltage 0.3V, charge depth 67.3%, test temperature 25℃, the results are as follows Figure 6 , 7 shown.

[0102] The battery cycle life comparison of Example 2 and Comparative Example 3 is shown in Table 3. When the energy efficiency drops to 40%, the battery is considered to be completely failed, and the battery cycle life is determined based on this.

[0103] The battery with (Example 2) as a bromine complexing agent has the longest cycle life, greater than 400 cycles, while the battery with MEP (Comparative Example 3) as a bromine complexing agent has a cycle life of less than 80 cycles, indicating that MEPOH is superior to MEP in terms of the cycle life of the battery at room temperature.

[0104] Table 3 Comparison of cycle life at room temperature

[0105] Operating temperature / ℃ Complexing agent Depth of charge / % Cycle life Example 2 25 MEPOH 67.3 >400 Comparative Example 3 25 MEP 67.3 <80

[0106] The battery performance comparison of Example 2 and Comparative Example 3 is shown in Table 4. The coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) are all averaged over the cycle life.

[0107] (Example 2) The average energy efficiency of the battery using bromine as a complexing agent within a cycle life of 400 cycles is greater than 74.4%, and the average energy efficiency within 80 cycles is greater than 77.2%. The average energy efficiency of the battery using MEP (Comparative Example 3) as a complexing agent for bromine is 76.0% within 80 cycles, indicating that MEPOH is superior to MEP in terms of room temperature battery performance.

[0108] Table 4 Comparison of battery performance at room temperature

[0109] Complexing agent Sampling range / cycles Average CE / % Average VE / % Average EE / % Example 2 MEPOH 1-400 90.6 82.1 74.4 Example 2 MEPOH 1-80 90.4 85.4 77.2 Comparative Example 3 MEP 1-80 90.5 83.4 76.0

[0110] Test Example 3

[0111] The battery performance was tested using a constant current charge and discharge method with a charge and discharge current density of 40 mA / cm 2 , charge and discharge current density 40mA / cm 2 , surface capacity 115mA cm -2 , discharge cut-off voltage 0.3V, charge depth 77.4%, test temperature 25℃, the results are as follows Figure 8 , 9 shown.

[0112] Example 3 Battery life and battery performance are shown in Table 5. When the energy efficiency drops to 40%, the battery is considered to be completely ineffective. The cycle life of the battery is determined based on this. The battery cycle life using MEPOH (Example 3) as a bromine complexing agent is greater than 265 cycles, with an average energy efficiency of 70.9% in 1-100 cycles, 68.4% in 1-200 cycles, and 66.0% in 1-265 cycles. The battery operates stably for more than 1400 hours ( Fig. 9 ), which illustrates the excellent ability of MEPOH as a bromine complexing agent in batteries to operate stably during deep charge and discharge.

[0113] Table 5 Battery performance of deep charge and discharge at room temperature

[0114]

[0115] Test Example 4

[0116] The temperature was controlled using a high and low temperature box, and the solidification state of the electrolyte was observed. The results are shown in Table 6, which records the solidification states of the water phase layer and the oil phase layer at different temperatures.

[0117] Table 6 Electrolyte coagulation state

[0118]

[0119]

[0120] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. Application of a quaternary ammonium salt additive in zinc-bromine flow battery electrolyte, It is characterized in that The chemical name of the quaternary ammonium salt additive is N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and its structural formula is as follows:

2. The use according to claim 1, It is characterized in that The zinc-bromine flow battery electrolyte comprises zinc bromide, a supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and water; Preferably, the zinc-bromine flow battery electrolyte consists of zinc bromide, supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide and water.

3. The use according to claim 2, It is characterized in that The content of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide in the zinc-bromine flow battery electrolyte is x, wherein 0 mol / L<x≤2 mol / L.

4. The use according to claim 2, It is characterized in that The content of zinc bromide in the zinc-bromine flow battery electrolyte is 0.5-5 mol / L.

5. The use according to claim 2, It is characterized in that The supporting electrolyte is selected from at least one of ammonium chloride, potassium chloride, sodium chloride, magnesium chloride and lithium chloride; Preferably, the content of the supporting electrolyte in the zinc-bromine flow battery electrolyte is y, wherein 0 mol / L<y≤5 mol / L.

6. The use according to claim 2, It is characterized in that The zinc-bromine flow battery electrolyte further includes other additives; Preferably, the other additives are selected from at least one of N-methyl-N-ethylpyrrolidinium bromide, N-methyl-N-ethylmorpholinium bromide, choline bromide, choline chloride, tetrapentylammonium bromide, 1-ethyl-2-methylpyridinium bromide, 1-butyl-3-methylpyridinium bromide, sodium acetate, potassium acetate, sodium formate, potassium formate, potassium bromide, sodium bromide, lithium bromide, magnesium bromide, calcium bromide, ethylene glycol, NN dimethylamide, and dimethyl sulfoxide; Preferably, the content of other additives in the zinc-bromine flow battery electrolyte is z, 0 mol / L<z≤4 mol / L.

7. The use according to claim 1, It is characterized in that The zinc-bromine flow battery comprises a single cell or a battery pack consisting of two or more single cells connected in series or / and in parallel; The single cell includes a positive terminal plate, a positive current collector, a positive electrode frame, a positive electrode, a separator, a negative electrode, a negative electrode frame, a negative current collector, and a negative terminal plate stacked in sequence; The diaphragm is a porous ion-conducting membrane.

8. The use according to claim 7, It is characterized in that The average pore size of the porous ion conducting membrane is 0.01-0.1 μm, and the porosity is 20-60%.

9. The use according to claim 7, It is characterized in that The positive electrode current collector and the negative electrode current collector are independently selected from at least one of a graphite plate, a titanium plate, and a carbon composite plate; Preferably, the positive electrode and the negative electrode are independently graphite felt or carbon felt.

10. The use according to claim 7, It is characterized in that The operating temperature of the zinc-bromine flow battery is -20 to 40°C; The energy density at the use temperature is 6.5 to 400Wh / L.

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