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

Abstract

The application 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-hydroxyethyl)-N-methyl-pyrrolidinium bromide, which is added into the zinc-bromine flow battery electrolyte as a complexing agent of bromine. The application widens the low-temperature range of the zinc-bromine flow battery operation, and the zinc-bromine flow battery with the novel additive can work for more than 200 hours at-20 DEG C; the application improves the kinetic characteristics of the battery and prolongs the cycle life of the battery at normal temperature and low temperature.

Description

TECHNICAL FIELD

[0001] The application relates to application of a quaternary ammonium salt additive in a zinc-bromine flow battery electrolyte and belongs to the technical field of electrochemical energy storage. BACKGROUND

[0002] With the improvement of the development level of human society, the demand for energy of human beings is increasing day by day. Most of the energy consumed by human beings is represented by fossil energy such as coal, natural gas and oil, which has brought 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, but renewable energy has obvious characteristics of discontinuity, instability and uncontrollability, which brings great risks to the stable power transmission of the power grid and the reliable work of the power load device. A high-efficiency energy storage device can adjust the time difference between power generation and power supply; mobilize the load response capability and reduce the demand for load adjustment support of the power grid. Energy storage facilities are divided into physical energy storage and electrochemical energy storage, and among large-scale electrochemical energy storage technologies, the aqueous zinc-based flow battery has become one of the most promising technologies due to its 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, the relatively stable existence of zinc metal in air and other advantages, the aqueous zinc-based flow battery has low assembly and processing cost; at the same time, compared with other aqueous cation batteries, the aqueous zinc-based flow battery has a suitable working potential, can provide a relatively negative potential and avoid significant side reactions. The zinc-bromine flow battery has been developed early and has received extensive attention due to its high open-circuit voltage and high energy density.

[0004] N-methyl-N-ethyl pyrrolidine (MEP) is the most commonly used additive for complexing bromine monomer in the electrolyte of the zinc-bromine flow battery, which can form an oil-like ionic liquid in a water phase with bromine monomer. In the process of low-temperature operation of the zinc-bromine flow battery, the oil-like ionic liquid solidifies and blocks the pipeline, causing the failure of the zinc-bromine flow battery in a low-temperature environment. Therefore, a new commonly used additive for complexing bromine monomer needs to be developed, and the ionic liquid formed by the complexing of the additive with bromine monomer remains in a liquid state at low temperature to ensure the long-term stable operation of the battery at low temperature. SUMMARY

[0005] According to one aspect of the application, application of a quaternary ammonium salt additive in a zinc-bromine flow battery electrolyte is provided, a new quaternary ammonium salt additive is used, the low-temperature use range of the zinc-bromine flow battery is widened, the stability of the battery system is improved, and the problem of poor stability and short cycle life of the battery at low temperature caused by the solidification of the zinc-bromine flow battery electrolyte in a low-temperature environment in the prior art is solved.

[0006] The application adopts the following technical scheme:

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

[0008]

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

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

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

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

[0013] Wherein water is used as a 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 or a range value between any two of 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L.

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

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

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

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

[0020] Optionally, the supporting electrolyte is selected from at least one of ammonium chloride, potassium chloride, sodium chloride, magnesium chloride, lithium chloride.

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

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

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

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

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

[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-ethyl pyrrolidinium bromide (MEP), N-methyl-N-ethyl morpholinium bromide (MEM), choline bromide, choline chloride, tetra-pentyl ammonium bromide, 1-ethyl-2-methyl pyridinium bromide, 1-butyl-3-methyl pyridinium bromide, sodium acetate, potassium acetate, sodium formate, potassium formate, potassium bromide, sodium bromide, lithium bromide, magnesium bromide, calcium bromide, ethylene glycol, N-N dimethylamide, dimethyl sulfoxide.

[0029] Optionally, the structural formulae of the N-methyl-N-ethyl pyrrolidinium bromide (MEP) and the N-methyl-N-ethyl morpholinium bromide (MEM) are as follows, respectively.

[0030]

[0031] Optionally, the content of the other additives in the zinc-bromine flow battery electrolyte is z, wherein 0 mol / L < z≤4 mol / 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 comprises, in sequence, a positive end 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 end plate.

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

[0035] Optionally, the cavities between the current collectors and the separator are filled with electrolyte and electrodes.

[0036] Optionally, the electrolyte of the zinc-bromine flow battery is in the cavities on both sides of the separator.

[0037] Optionally, the electrolyte added in the cavities on both sides of the separator before charging is the same.

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

[0039] Optionally, the metal end plate is selected from one of 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 average pore size of the porous ion-conducting membrane is 0.01-0.1 μm, and the porosity is 20-60%.

[0041] Optionally, the positive current collector and the negative 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 current collector and the negative current collector are made of the same material.

[0043] Optionally, the positive current collector and the negative 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 is selected from one of a perfluorosulfonic acid membrane, a porous polyolefin membrane, a sulfonated polyether ether ketone membrane, and a polybenzimidazole membrane.

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

[0049] Optionally, the zinc-bromine flow battery has a use temperature of -20-40℃.

[0050] Optionally, the zinc-bromine flow battery has a use temperature of -20-0℃ in a low-temperature environment or a normal-temperature environment.

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

[0052] The application can produce beneficial effects, including:

[0053] (1) The application provides the use of the quaternary ammonium salt additive in the electrolyte of the zinc-bromine flow battery, which widens the temperature use 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 temperature. The specific performance is as follows:

[0054] a. Stability of the oil-like ionic liquid: the oil-like ionic liquid formed by the complexation of the novel quaternary ammonium salt additive and bromine can maintain a liquid state at -40℃;

[0055] b. Overall stability of the positive electrolyte (aqueous phase and oil-like ionic liquid): the positive electrolyte added with the novel quaternary ammonium salt additive can keep the aqueous phase and the oil-like ionic liquid phase in a liquid state at -20℃ when the charge depth is 50% (charge depth = actual capacity / maximum theoretical capacity, ), so that the battery system can be stably operated for more than 140 hours in a -20℃ environment.

[0056] (1) Promotes the rapid diffusion of bromine and bromide ions in the electrolyte, and the rapid kinetics reduces the accumulation of products, prolonging the cycle life of the battery at low temperature and normal temperature. The zinc-bromine flow battery using the novel quaternary ammonium salt additive can be stably operated for more than 1400 hours under deep (> 77.3%) charging. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 It is the molecular structure of the quaternary ammonium salt additive N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide of the application.

[0058] Figure 2 It is the battery performance at -20℃ in Example 1 of the application.

[0059] Figure 3 It is the time-voltage curve of the battery operated at -20℃ in Example 1 of the application.

[0060] Figure 4 It is the battery performance at -20℃ in Comparative Example 1 of the application.

[0061] Figure 5 It is the battery performance at -20℃ in Comparative Example 2 of the application.

[0062] Figure 6 Battery performance at 25 °C for the battery in Example 2 of the present application.

[0063] Figure 7 Battery performance at 25 °C for the battery in Comparative Example 3 of the present application.

[0064] Figure 8 Battery performance at 25 °C for the battery in Example 3 of the present application.

[0065] Figure 9 Time-voltage curve for the battery at 25 °C for the battery in Example 3 of the present application. DETAILED DESCRIPTION

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

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

[0068] Unless otherwise specified, the test methods are all conventional methods, and the instrument settings are all factory-recommended settings, wherein the battery performance test uses a new Wei charge-discharge instrument or an Arbin 2000 charge-discharge 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 to the magnetically stirred N-methylpyrrole, and after 48 hours of reaction, the reaction solution is poured into diethyl ether, and the separated solid is separated, washed, and recrystallized for use, which specifically includes:

[0071] At room temperature, N-methylpyrrolidine and acetonitrile are mixed in a three-necked flask with a reflux device under nitrogen protection, and magnetic stirring is used to mix thoroughly. A constant-pressure dropping funnel is used to slowly drop 2-bromoethanol into the three-necked flask, and the dropping is completed within a certain time, and the reaction is fully mixed and contacted while dropping. After the dropping of 2-bromoethanol is completed, N2 protection and reflux of water can be stopped, and the solution is kept stirring. After 48 hours of dropping of 2-bromoethanol, the magnetic stirring is stopped, and the three-necked flask is still a uniform solution. In the case of using mechanical stirring, a large amount of solid is precipitated after adding diethyl ether into the three-necked flask at one time. The solid product is separated by filtration. The solid product obtained by washing at room temperature is dried in a vacuum oven, and finally a beige N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide solid powder is obtained.

[0072] Preparation Example 1

[0073] N-methylpyrrolidine 1 mol, acetonitrile 60 mL were mixed in a three-neck flask with reflux device under nitrogen protection at room temperature, and the mixture was stirred well with a magnetic stirrer. A constant pressure dropping funnel was used to slowly drop 2-bromoethanol 1 mol into the three-neck flask, and the dropping was completed within 1 hour. The reaction was stirred well while the dropping was in progress. After 2 hours of dropping of 2-bromoethanol, the N2 protection and the reflux of condensed water were stopped, and the solution was kept stirring. After 48 hours of dropping of 2-bromoethanol, the magnetic stirring was stopped, and the three-neck flask still contained a homogeneous solution. With the use of mechanical stirring, 150 mL of ether was added into the three-neck flask at one time, and a large amount of solid was precipitated. The solid was separated by filtration. The obtained solid product was washed with 100 mL of ether at room temperature, and the washing was repeated 5 times. The product was dried in a vacuum oven at 40°C for 8 hours, and finally a beige solid powder of N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide was obtained.

[0074] Example 1

[0075] The battery was operated at -20°C, and the electrolyte of the battery was 2 mol / L ZnBr2+4.2 mol / L NH4Cl+0.6 mol / L MEPOH. The single cell was sequentially a positive end plate, a positive electrode 6x6 cm 2 graphite plate, positive electrode frame, carbon felt, Daramic 900 μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6 cm 2 graphite plate, negative end plate. The volume of electrolyte on each side was 25 mL, and the flow rate of electrolyte was controlled by a peristaltic pump at 50 mL / min -1 , the charge and discharge current density was 40 mA / cm 2 , the surface capacity was 25 mA cm -2 , the discharge cut-off voltage was 0.3 V, and the charge depth was 33.6%.

[0076] Example 2

[0077] The battery was operated at 25°C, and the electrolyte of the battery was 2 mol / L ZnBr2+3 mol / L KCl+0.6 mol / L MEPOH. The single cell was sequentially a positive end plate, a positive electrode 6x6 cm 2 graphite plate, positive electrode frame, carbon felt, Daramic 900 μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6 cm 2 graphite plate, negative end plate. The volume of electrolyte on each side was 40 mL, and the flow rate of electrolyte was controlled by a magnetic pump at 70 mL / min -1 , the charge and discharge current density was 40 mA / cm 2 , the surface capacity was 80 mA cm -2 , the discharge cut-off voltage was 0.3 V, and the charge depth was 67.3%.

[0078] Example 3

[0079] The battery was operated at 25℃, the battery electrolyte was 2mol / L ZnBr2+4.2mol / L NH4Cl+0.6mol / L MEPOH, and the single cell was in turn a positive end plate, a positive electrode 6x6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative end plate. The electrolyte volume on each side was 50mL, and the magnetic pump controlled the electrolyte flow rate at 70mL / min -1 , the charge and discharge current density was 40mA / cm 2 , the surface capacity was 115mA / cm -2 , the discharge cut-off voltage was 0.3V, and the charge depth was 77.4%.

[0080] Example 4

[0081] The prepared simulated 50% charged electrolyte had an electrolyte composition of 1M ZnBr2+4.2M NH4Cl+0.6M MEPOH+1M Br2, and the electrolyte was divided into an aqueous phase layer and an oil phase layer. The aqueous phase layer was mainly an aqueous solution and was located in the upper layer of the electrolyte; the oil phase layer was mainly a quaternary ammonium salt polybromide ionic liquid, and the elemental bromine was mainly concentrated in the oil phase layer. The oil phase layer had a relatively large density and was located in the lower layer of the electrolyte.

[0082] Comparative Example 1

[0083] The battery was operated at -20℃, the battery electrolyte was 2mol / L ZnBr2+4.2mol / L NH4Cl+0.6mol / L MEP, and the single cell was in turn a positive end plate, a positive electrode 6x6cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900μm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative end plate. The electrolyte volume on each side was 25mL, and the peristaltic pump controlled the electrolyte flow rate at 50mL / min -1 , the charge and discharge current density was 40mA / cm 2 , the surface capacity was 25mA / cm -2 , the discharge cut-off voltage was 0.3V, and the charge depth was 33.6%.

[0084] Comparative Example 2

[0085] The battery was operated at -20℃, the battery electrolyte was 2mol / L ZnBr2+4.2mol / L NH4Cl+0.6mol / L MEM, and the single cell was in turn a positive end plate, a positive electrode 6x6cm 2Graphite plate, positive electrode frame, carbon felt, Daramic 900 pm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6 cm 2 Graphite plate, negative electrode end plate. The electrolyte volume on each side is 25 mL, and the peristaltic pump controls the electrolyte flow rate at 50 mL / min -1 , the charge and discharge current density is 40 mA / cm 2 , the surface capacity is 25 mA cm -2 , the discharge cut-off voltage is 0.3 V, and the charge depth is 33.6%.

[0086] Comparative Example 3

[0087] The battery is operated at 25°C, and the battery electrolyte is 2 mol / L ZnBr2+3 mol / L KCl+0.6 mol / L MEP. The single cell is sequentially a positive electrode end plate, a positive electrode 6x6 cm 2 Graphite plate, positive electrode frame, carbon felt, Daramic 900 pm polyethylene porous membrane, carbon felt, negative electrode frame, negative electrode 6x6 cm 2 Graphite plate, negative electrode end plate. The electrolyte volume on each side is 40 mL, and the magnetic pump controls the electrolyte flow rate at 70 mL / min -1 , the charge and discharge current density is 40 mA / cm 2 , the surface capacity is 80 mA cm -2 , the discharge cut-off voltage is 0.3 V, and the charge depth is 67.3%.

[0088] Comparative Example 4

[0089] The prepared simulated 50% charged electrolyte has an electrolyte composition of 1M ZnBr2+4.2M NH4Cl+0.6M MEP+1M Br2, and 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 salt polybromide ionic liquid, and elemental bromine 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 is tested by a constant current charge and discharge method, the charge and discharge current density is 40 mA / cm 2 , the surface capacity is 25 mA cm -2 , the discharge cut-off voltage is 0.3 V, the charge depth is 33.6%, and the test temperature is -20°C. The results are shown in Figures 2 to 5 .

[0092] The cycle life of the batteries of Example 1 and Comparative Examples 1 and 2 is shown in Table 1. The energy efficiency is reduced to 40% to be considered as the complete failure of the battery, and the cycle life of the battery is determined based on this. The battery using MEPOH (Example 1) as the bromine elemental complexing agent has the longest cycle life, more than 100 cycles, while the batteries using MEP (Comparative Example 1) and MEM (Comparative Example 2) as the bromine elemental complexing agent have cycle lives of less than 10 cycles, indicating that the battery using MEPOH as the bromine elemental complexing agent can be stably operated at -20°C, and MEPOH is superior to MEP and MEM in terms of the cycle life of the low-temperature battery.

[0093] Table 1. Comparison of cycle life

[0094] Operating temperature / °C Complexing agent Depth of charge / % Cycle life / cycles 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 performance of the batteries 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 from the cycle life. The average energy efficiency of the battery using MEPOH (Example 1) as the bromine elemental complexing agent is greater than 60.4% over the cycle life of 120 cycles, while the average energy efficiency of the battery using MEP (Comparative Example 1) as the bromine elemental complexing agent is only 42.6% over 10 cycles, and the average energy efficiency of the battery using MEM (Comparative Example 2) as the bromine elemental complexing agent is only 49.1% over 10 cycles, and the batteries using 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 the performance of the low-temperature battery.

[0096] Table 2. Comparison of battery performance

[0097]

[0098]

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

[0100] Test Example 2

[0101] The battery performance is tested by the constant current charge and discharge method, the charge and discharge current density is 40 mA / cm 2 , the surface capacity is 80 mA cm -2 , the discharge cut-off voltage is 0.3 V, the charge depth is 67.3%, and the test temperature is 25°C, and the results are shown in Figure 6 , 7 .

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

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

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

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

[0106] The battery performance 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 from the cycle life. MEPOH

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

[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 test was carried out by constant current charge and discharge method, the charge and discharge current density was 40 mA / cm 2 , the charge and discharge current density was 40 mA / cm 2 , the surface capacity was 115 mA cm -2 , the discharge cut-off voltage was 0.3 V, the charge depth was 77.4%, and the test temperature was 25°C. The results are shown in Figure 8 , 9 .

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

[0113] Table 5 Performance of deep charge-discharge battery at room temperature

[0114]

[0115] Test Example 4

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

[0117] Table 6 Solidification state of electrolyte

[0118]

[0119]

[0120] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the above is disclosed as a preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and such changes or modifications are equivalent to equivalent embodiments, and are within the scope of the technical solution.

Claims

1. Use of a quaternary ammonium salt additive in a zinc-bromine flow battery electrolyte, 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. Use according to claim 1, characterized in that, the zinc-bromine flow battery electrolyte comprises zinc bromide, a supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and water.

3. Use according to claim 1, characterized in that, the zinc-bromine flow battery electrolyte is composed of zinc bromide, a supporting electrolyte, N-(2-hydroxyethyl)-N-methyl-pyrrolidinium bromide, and water.

4. Use according to claim 2, 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.

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

6. Use according to claim 2, characterized in that, the supporting electrolyte is selected from at least one of ammonium chloride, potassium chloride, sodium chloride, magnesium chloride, and lithium chloride.

7. Use according to claim 2, characterized in that, the content of the supporting electrolyte in the zinc-bromine flow battery electrolyte is y, wherein 0 mol / L < y ≤ 5 mol / L.

8. Use according to claim 2, characterized in that, the zinc-bromine flow battery electrolyte further comprises other additives.

9. Use according to claim 8, characterized in that, the other additives are selected from at least one of N-methyl-N-ethyl pyrrolidinium bromide, N-methyl-N-ethyl morpholinium bromide, choline bromide, choline chloride, tetraamylammonium bromide, 1-ethyl-2-methyl pyridinium bromide, bromide-1-butyl-3-methyl pyridine, sodium acetate, potassium acetate, sodium formate, potassium formate, potassium bromide, sodium bromide, lithium bromide, magnesium bromide, calcium bromide, ethylene glycol, N-N dimethylamide, and dimethyl sulfoxide.

10. Use according to claim 8, characterized in that, the content of the other additives in the zinc-bromine flow battery electrolyte is z, wherein 0 mol / L < z ≤ 4 mol / L.

11. Use according to claim 1, characterized in that, the zinc-bromine flow battery comprises a single cell or a battery pack composed of two or more single cells connected in series or / and in parallel. the single cell comprises, in sequence, a positive end 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 end plate. the separator is a porous ion-conducting membrane.

12. Use according to claim 11, 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%.

13. The use according to claim 11, characterized in that, the positive current collector and the negative current collector are independently selected from at least one of a graphite plate, a titanium plate, and a carbon composite plate.

14. The use according to claim 11, characterized in that, the positive electrode and the negative electrode are independently graphite felt or carbon felt.

15. The use according to claim 11, characterized in that, the use temperature of the zinc-bromine flow battery is -20-40℃. the energy density at the use temperature is 6.5-400 Wh / L.

Images