An alkaline zinc-bromine flow battery

Abstract

The present invention discloses an alkaline zinc-bromine flow battery, belonging to the technical field of flow batteries. The alkaline zinc-bromine flow battery of the present invention mainly includes a positive electrode, a separator, a negative electrode and an electrolyte. The positive and negative electrolytes include ZnBr2, an alkali and a complexing agent. The complexing agent is one or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, and tetrabutylammonium bromide. The positive electrode of the battery undergoes a bromine redox reaction, and the negative electrode undergoes a deposition and dissolution reaction of metallic zinc. The complexing agent in the electrolyte can complex the bromine into a solid complex, thereby inhibiting the disproportionation reaction of bromine in the alkaline zinc-bromine flow battery. The electrolyte of the present invention is easy to prepare and does not require the positive and negative electrodes to be prepared separately. By complexing the bromine generated during the charging process into a solid state, the disproportionation of bromine is reduced, the battery performance is improved, and the battery self-discharge is reduced. The electrolyte has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow batteries, and in particular relates to an alkaline zinc-bromine liquid flow battery. Background Art

[0002] With the increasing depletion of fossil energy, the development and utilization of renewable energy sources such as wind and solar energy has become a focus of global attention. Because wind and solar energy are intermittent and unstable due to factors such as weather, they can impact the power grid during the integration of renewable energy generation, affecting power supply quality and grid stability. Energy storage technology can address this issue, ensuring the efficient and stable operation of integrated renewable energy generation. Energy storage technologies are primarily categorized as physical and chemical. Chemical energy storage, represented by flow batteries, offers the greatest advantages for large-scale energy storage due to their many advantages, including independent power and capacity, rapid response, simple structure, ease of design, long cycle life, and environmental friendliness. Currently, the main flow battery systems include all-vanadium flow batteries, zinc-bromine flow batteries, and iron-chromium flow batteries. Among them, all-vanadium flow batteries use ions of the same element with different valence states in the positive and negative electrolyte active materials, greatly reducing cross-contamination between the positive and negative electrolytes. However, the cost of the electrolyte and separator in this battery system is relatively high. The main advantage of iron-chromium flow batteries is their low price, but their most prominent problem is severe cross-contamination between ions. The main advantages of zinc-bromine flow batteries are their high open-circuit voltage, low price, and broad application prospects. However, they are plagued by problems such as self-discharge caused by the direct reaction of bromine and zinc, and the dense zinc deposition morphology that limits the battery's areal capacity. How to suppress self-discharge and increase the battery's areal capacity in zinc-bromine flow batteries has become an important research topic. Summary of the Invention

[0003] In view of this, an object of the present invention is to provide an electrolyte for an alkaline zinc-bromine flow battery and an alkaline zinc-bromine flow battery obtained by assembling the electrolyte.

[0004] The object of the present invention is to achieve the following goals:

[0005] The present invention provides an electrolyte for a liquid flow battery, comprising ZnBr2, an alkali, and a complexing agent, wherein the complexing agent is one or a combination of two or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0006] Furthermore, the alkali is one or both of sodium hydroxide and potassium hydroxide.

[0007] Furthermore, the complexing agent is tetraethylammonium bromide.

[0008] Furthermore, the electrolyte is an aqueous electrolyte.

[0009] Furthermore, the concentration of ZnBr2 in the electrolyte is 0.5-2M, OH - The concentration is 2-6M, the complexing agent concentration is 0.4-0.8M, and the concentration ratio of ZnBr2 to the complexing agent is 4:1-1:1.

[0010] Furthermore, the concentration of ZnBr2 in the electrolyte is 0.5-0.8M, OH - The concentration is 2-4M and the complexing agent concentration is 0.4-0.6M.

[0011] Another aspect of the present invention provides an alkaline zinc-bromine flow battery, which mainly includes a positive electrode, a separator, a negative electrode and an electrolyte. The electrolytes of the positive and negative electrodes are both the above-mentioned electrolytes. The positive electrode of the battery undergoes a bromine redox reaction, and the negative electrode undergoes a deposition and dissolution reaction of metallic zinc. The complexing agent in the electrolyte can complex bromine into a solid complex, thereby inhibiting the disproportionation reaction of bromine in the alkaline zinc-bromine flow battery.

[0012] Furthermore, the diaphragm is selected from an ion conducting membrane and a Nafion membrane, preferably a sulfonated polyetheretherketone ion conducting membrane.

[0013] Furthermore, the electrode materials of the positive electrode and the negative electrode are selected from graphite felt or carbon felt, preferably carbon felt.

[0014] The present invention has the following beneficial effects compared to the prior art:

[0015] 1. Compared with existing zinc-bromine flow batteries, the alkaline zinc-bromine flow battery of the present invention has a loose and porous zinc deposition morphology in an alkaline environment, which has a stronger mass transfer capacity and is more conducive to the electrolyte reaction on the surface close to the diaphragm, so the battery can obtain a higher surface capacity.

[0016] 2. The alkaline zinc-bromine flow battery of the present invention has zinc bromide as the active material of both the positive and negative electrodes. The electrolyte can be easily prepared without the need to prepare the positive and negative electrodes separately, and the operation is simple.

[0017] 3. The present invention complexes the bromine generated during the charging process into a solid state. Compared with the conventional MEP liquid complexing agent, it can solve the disproportionation problem of bromine in the alkaline electrolyte system and improve battery performance.

[0018] 4. The present invention complexes the bromine generated during the charging process into a solid state and deposits it on the electrode surface. Compared with the conventional zinc-bromine liquid flow battery system, the positive electrode liquid phase is transformed into a liquid-solid phase transformation, which significantly reduces the self-discharge of the battery. The alkaline zinc-bromine liquid flow battery of the present invention has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0020] Figure 1 This is the cyclic voltammetry test diagram of the electrolyte in Example 1.

[0021] Figure 2 This is a cycle performance diagram of the alkaline zinc-bromine flow battery in Example 2.

[0022] Figure 3 This is the zinc deposition morphology in the alkaline zinc-bromine flow battery in Example 2.

[0023] Figure 4 Alkaline zinc-bromine flow battery with a surface capacity of 240 mAh cm -2 Charge and discharge curves.

[0024] Figure 5 Alkaline zinc-bromine flow battery with a surface capacity of 240 mAh cm -2 Cycle performance.

[0025] Figure 6 Morphology of zinc deposition in conventional zinc-bromine flow battery. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0027] Example 1

[0028] 1*1cm 2 Carbon felt is the working electrode, Ag / AgCl electrode is the reference electrode, 3*3cm 2 The graphite plate was used as the counter electrode for cyclic voltammetry test. The electrolyte was 0.5 mol L -1 ZnBr2+0.4mol L -1 (C2H5)4NBr+2mol L -1 NaOH, scan range 0-0.7 V, 10 mV / s.

[0029] from Figure 1 As can be seen in the figure, bromine has a clear redox peak under alkaline conditions, and the couple is reversible, which also indicates that the bromine couple can be used as the positive electrode couple in the alkaline electrolyte system. In addition, the bromine couple's oxidation and reduction peak currents under alkaline conditions are not much different, which also shows that the solid-state complexation of bromine effectively suppresses the occurrence of disproportionation reaction.

[0030] Example 2

[0031] An alkaline zinc-bromine flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4mol L -1 (C2H5)4NBr+2mol L -1 NaOH; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; at 80mA cm -2 The charge was carried out for 15 min at a current density of 80 mA cm -2 The discharge current density is 0.8V, and the results are as follows Figure 2 shown.

[0032] The cycling data of alkaline zinc-bromine flow battery show that the cycling performance of alkaline zinc-bromine flow battery is stable, with battery CE reaching 98%, VE reaching 90%, and EE reaching 87%. The high battery CE also indicates that the disproportionation reaction of bromine under alkaline conditions and battery self-discharge are effectively suppressed by complexing bromine into a solid state. In addition, Figure 3 Scanning electron microscopy shows that after charging, the zinc deposition morphology in the alkaline zinc-bromine flow battery is a loose porous structure, which will be beneficial for the electrolyte inside the battery to be transferred to the electrode surface for reaction, thereby increasing the battery surface capacity.

[0033] Example 3

[0034] An alkaline zinc-bromine flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4mol L -1 (C2H5)4NBr+2mol L -1 NaOH; positive electrode electrolyte volume 200 mL; negative electrode electrolyte volume 200 mL; at 40 mA cm -2 The battery is charged for 6 hours under the current density condition, the upper limit of the battery charging voltage is 2.2V, and the battery is charged at 40mA cm -2 After discharging to 0.8 V under the current density of 10 mA cm -2 The discharge was continued to 0.8V under the condition of current density. Figure 4 、 Figure 5 As shown. The battery surface capacity can reach 240mAh cm -2 , the battery cycle performance is stable.

[0035] Comparative Example 1

[0036] An alkaline zinc-bromine flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+2mol L-1 NaOH; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; at 80mA cm -2 The charge was carried out for 15 min at a current density of 80 mA cm -2 The battery was discharged to 0.8 V under the condition of current density.

[0037] Without the addition of a complexing agent, the battery CE is only 60%, indicating poor performance. This is mainly due to the direct reaction of bromine with zinc, which causes battery self-discharge, and the disproportionation of bromine in alkali.

[0038] Comparative Example 2

[0039] An alkaline zinc-bromine flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4M 1-methyl-1-ethylpyrrolidone bromide (MEP)+2mol L -1 NaOH; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; at 80mA cm -2 Charge to 15min under the current density of 80mAcm -2 The battery was discharged to 0.8 V under the condition of current density.

[0040] Alkaline zinc-bromine flow batteries using MEP as a complexing agent had a CE of 70%, indicating poor performance. This may be because the complexing agents used in traditional zinc-bromine flow batteries do not effectively address the bromine disproportionation problem in alkaline zinc-bromine flow batteries.

[0041] Comparative Example 3

[0042] A zinc-bromine flow battery was assembled using PE film as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4MMEP+3mol L -1 KCl; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; at 80mA cm -2 The charge was carried out for 15 min at a current density of 80 mA cm -2 The battery is discharged to 0.8V under the condition of current density. The zinc deposition morphology after charging is as follows Figure 6 As shown. Figure 6 It can be seen that the zinc deposition morphology in traditional zinc-bromine flow batteries is dense, with fewer surface voids, which affects the transfer of electrolyte to the electrode surface. As the surface capacity increases, the concentration polarization of the battery gradually increases until the battery fails.

[0043] Comparative Example 4

[0044] A zinc-bromine flow battery was assembled using PE film as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4M1-methyl-1-ethylpyrrolidone bromide (MEP)+3mol L -1 KCl; positive electrode electrolyte volume 200 mL; negative electrode electrolyte volume 200 mL; at 40 mA cm -2 The battery is charged for 6 hours under the current density condition, the upper limit of the battery charging voltage is 2.2V, and the battery is charged at 40mA cm -2 After discharging to 0.8 V under the current density of 10 mA cm -2 The battery was discharged to 0.8 V under the condition of current density.

[0045] The battery capacity during charging reaches 160 mAh cm -2 When the battery voltage reaches the protection voltage, the system cannot continue to charge. This is mainly because the zinc deposition morphology is dense and there are fewer surface voids, which affects the transfer of electrolyte solution to the electrode surface. As the surface capacity increases, the concentration polarization of the battery gradually increases and the battery reaches the protection voltage.

[0046] Comparative Example 5

[0047] An alkaline zinc-bromine flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane as the separator. The electrolyte compositions of both the positive and negative electrodes were 0.5 mol L -1 ZnBr2+0.4mol L -1 (C2H5)4NBr+7mol L -1 NaOH; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; at 80mA cm -2 The charge was carried out for 15 min at a current density of 80 mA cm -2 The battery was discharged to 0.8 V under the condition of current density.

[0048] When the alkali concentration increases to 7M, the cell CE is only 90%, which is mainly due to the intensification of the bromine disproportionation reaction caused by the increase in alkali concentration.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte for a flow battery, characterized in that: The invention comprises ZnBr2, a base and a complexing agent, wherein the complexing agent is one or a combination of two or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide; The alkali is one or both of sodium hydroxide and potassium hydroxide; The concentration of ZnBr2 in the electrolyte is 0.5-2M, OH - The concentration is 2-6M, the complexing agent concentration is 0.4-0.8M, and the concentration ratio of ZnBr2 to the complexing agent is 4:1-1:

1.

2. The electrolyte according to claim 1, characterized in that The complexing agent is tetraethylammonium bromide.

3. The electrolyte according to claim 1, characterized in that The electrolyte is an aqueous electrolyte.

4. The electrolyte according to claim 1, characterized in that The concentration of ZnBr2 in the electrolyte is 0.5-0.8M, OH - The concentration is 2-4M and the complexing agent concentration is 0.4-0.6M.

5. An alkaline zinc-bromine flow battery, characterized in that The invention mainly comprises a positive electrode, a diaphragm, a negative electrode and an electrolyte. The positive and negative electrolytes are both the electrolytes according to any one of claims 1 to 4. The complexing agent in the electrolyte can complex bromine into a solid complex to inhibit the disproportionation reaction of bromine in the alkaline zinc-bromine flow battery.

6. The alkaline zinc-bromine flow battery according to claim 5, characterized in that The diaphragm is selected from an ion conducting membrane and a Nafion membrane.

7. The alkaline zinc-bromine flow battery according to claim 6, characterized in that The diaphragm is selected from sulfonated polyetheretherketone ion conductive membrane.

8. The alkaline zinc-bromine flow battery according to claim 5, characterized in that The electrode materials of the positive electrode and the negative electrode are selected from graphite felt or carbon felt.

9. The alkaline zinc-bromine flow battery according to claim 8, characterized in that The electrode materials of the positive electrode and the negative electrode are carbon felt.

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