A neutral iron-bromine flow battery

Abstract

The present invention discloses a neutral iron-bromine liquid flow battery, which belongs to the technical field of liquid flow batteries. The neutral iron-bromine liquid flow battery of the present invention comprises a single cell or a battery stack composed of two or more single cells, including a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the active substances of the positive electrode electrolyte are bromide ions and bromine element, and the active substances of the negative electrode electrolyte are complexes of divalent iron ions and trivalent iron ions with ethylenediaminetetramethylenephosphonic acid. The neutral iron-bromine liquid flow battery of the present invention does not involve a deposition-dissolution reaction, and the power and density can be designed independently. At 40 mA cm ‑2 Under the constant current charge and discharge conditions, the coulomb efficiency is 99.5%, the energy efficiency is 81.0%, and it can be stably charged and discharged for more than 300 times. Moreover, the energy density of the iron-bromine liquid flow battery in this invention is as high as 27.5Ah L ‑1 The cost is far lower than that of all-vanadium liquid flow battery, showing good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid flow batteries, and in particular relates to a neutral iron-bromine liquid flow battery with high energy density. Background Art

[0002] Liquid flow battery is a new electrochemical energy storage technology. Compared with other energy storage technologies, it has the advantages of flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety and environmental protection, and low maintenance cost. It can be widely used in wind power, solar energy and other renewable energy power generation and storage, emergency power supply systems, backup power stations and power system peak shaving and valley filling. All-vanadium liquid flow battery (VFB) is considered to have good application prospects due to its high safety, good stability, high efficiency, and long life (lifespan>15 years). However, the price of VFB electrolyte is relatively high, which to a certain extent limits its large-scale application.

[0003] In addition to all-vanadium flow batteries, zinc-based flow batteries are currently more mature, mainly zinc-bromine, zinc-iron and zinc-nickel battery systems. During the operation of zinc-based flow batteries, zinc deposition and dissolution occur at the negative electrode, causing problems such as uneven deposition and zinc dendrites, which in turn cause dendrites to pierce the diaphragm and eventually short-circuit the battery. At the same time, the zinc deposition process limits the energy density of the battery to the surface capacity, hindering the further development of zinc-based flow batteries. Research and development of high-energy-density flow batteries has become an important topic that needs to be studied urgently. Summary of the invention

[0004] In order to solve the above technical problems, an object of the present invention is to provide a neutral iron-bromine flow battery with high energy density.

[0005] The object of the present invention is achieved by the following methods:

[0006] A high-energy-density neutral iron-bromine liquid flow battery, wherein the active material of the negative electrode electrolyte of the neutral iron-bromine liquid flow battery is a complex of iron ions, and the active material of the positive electrode electrolyte is bromide ions and bromine element.

[0007] Furthermore, the complex is a complex of iron ions and EDTMPA, the iron ions include divalent iron ions and trivalent iron ions, and the complexing molar ratio of the iron ions to EDTMPA is 1:1 to 1:2.

[0008] Furthermore, the concentration of the complex is 0.1-1.2M, preferably 0.5-1M.

[0009] Furthermore, the source of bromide ions includes one or more of sodium bromide, potassium bromide, lithium bromide, ammonium bromide, magnesium bromide or zinc bromide, wherein the molar concentration of bromide ions is 0.1 to 8M, preferably 2 to 4M.

[0010] Furthermore, the source of the divalent iron ions is ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous fluoride, ferrous iodide, ferrous bromide, and ammonium ferrous sulfate; the source of the trivalent iron ions is ferric chloride, ferric bromide, ferric sulfate, ferric nitrate, ferric acetate, and ferric fluoride.

[0011] Furthermore, supporting electrolytes are added to the positive and negative electrolytes, including one or more of soluble salts of lithium chloride, potassium chloride, sodium chloride, ammonium chloride, lithium sulfate, potassium sulfate, sodium sulfate, ammonium sulfate, lithium bromide, sodium bromide, potassium bromide, and ammonium bromide to improve the conductivity of the electrolyte; the molar concentration of the supporting electrolyte is 0.1 to 5M, preferably 1 to 2M.

[0012] Furthermore, the supporting electrolyte is potassium chloride with a molar concentration of 0.5 to 5M, preferably 1 to 3M.

[0013] Furthermore, the neutral iron-bromine liquid flow battery comprises a positive electrode current collecting plate, a positive electrode, an ion conducting membrane, a negative electrode, and a negative electrode current collecting plate stacked in sequence.

[0014] Furthermore, the electrode materials of the positive and negative electrodes are both one of carbon materials such as carbon felt, carbon cloth or carbon paper, preferably carbon felt.

[0015] Furthermore, the ion conducting membrane is a Nafion membrane produced by DuPont, preferably Nafion212.

[0016] Furthermore, the positive and negative electrode current collecting plates are graphite plates or copper plates, preferably graphite plates.

[0017] Furthermore, the neutral iron-bromine liquid flow battery is provided with a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a circulation pump and a circulation pipeline.

[0018] Another aspect of the present invention provides a battery module, wherein the battery module is formed by connecting two or more neutral iron-bromine flow batteries in series and / or in parallel.

[0019] During the operation of the battery of the present invention, the positive and negative electrolytes are pumped from the positive and negative electrolyte storage tanks into the positive and negative electrodes through the pipelines. The operating principle of the battery is as follows:

[0020] Positive electrode reaction:

[0021] Negative electrode reaction:

[0022] The beneficial effects of the present invention compared with the prior art are as follows:

[0023] 1. The present invention has discovered a new iron complexing agent EDTMPA, which has a redox potential of -0.46V vs. SCE after complexing iron. When paired with a bromine electrode, the open circuit voltage of the battery is 1.27V.

[0024] 2. The battery system of the present invention does not have a deposition-dissolution reaction, and the power and energy of the battery can be designed independently, which has broad prospects for large-scale applications.

[0025] 3. The battery electrolyte of the present invention is neutral, with a pH value between 7 and 8, and is environmentally friendly.

[0026] 4. The electrolyte discharge capacity of the battery of the present invention is up to 27.5Ah L -1 ;Battery at 40mA cm -2 The coulombic efficiency (CE) is higher than 99% and the energy efficiency (EE) is 81%, which has high performance in the field of bromine-based and iron-based flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0028] Figure 1 Molecular structural formula of ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetramethylenephosphonic acid (EDTMPA).

[0029] Figure 2 Comparison of cyclic voltammetry curves of Fe-EDTA and Fe-EDTMPA.

[0030] Figure 3 Schematic diagram of the structure of the neutral iron-bromine flow battery of the present invention.

[0031] Figure 4 CV diagrams of the positive and negative electrode pairs of the neutral iron-bromine flow battery of the present invention; (a) CV test of the negative electrode active material, the electrolyte composition is a mixed aqueous solution of 0.1M FeCl3, 0.1M EDTMPA and 2M KCl; (b) CV test of the positive electrode active material, the electrolyte composition is a mixed aqueous solution of 0.2M KBr and 2M KCl.

[0032] Figure 5 (a) Single-cycle charge and discharge curve of neutral iron-bromine flow battery; (b) Cyclic charge and discharge curve of neutral iron-bromine flow battery; the positive electrode electrolyte composition is 4M KBr and 2M KCl, and the negative electrode electrolyte composition is a mixed aqueous solution of 1M FeCl3, 1MEDTMPA and 2M KCl.

[0033] Figure 6 This is a battery performance diagram of the neutral iron-bromine flow battery in Example 1 at different current densities.

[0034] Figure 7 (a) Cycle life and efficiency diagram of neutral iron-bromine flow battery; (b) Discharge capacity diagram corresponding to the cycle life of neutral iron-bromine flow battery.

[0035] Figure 8 Comparative Example 1 shows the cycle performance of a neutral iron-bromine flow battery assembled using EDTA as an iron chelating agent. DETAILED DESCRIPTION

[0036] 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 partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0037] Example 1

[0038] (1) Single cell assembly: The single cell is assembled in the following order: positive terminal plate, graphite current collector, positive electrode carbon felt, Nafion212, negative electrode carbon felt, graphite current collector, negative terminal plate. The area of ​​the positive and negative electrode carbon felts is 6x8 cm 2 , the battery structure is as follows Figure 3 .

[0039] (2) The negative electrode electrolyte composition is a mixed aqueous solution of 1M FeCl3, 1M EDTMPA and 2M KCl, and the pH of the aqueous solution is adjusted to 8; for the CV test of the positive electrode active material, the electrolyte composition is a mixed aqueous solution of 4M KBr and 2M KCl.

[0040] (3) Both the positive and negative electrolytes were in liquid flow form, with an electrolyte volume of 60 mL and a flow rate of 80 ml / min.

[0041] Battery test conditions: Electrode effective area: 48cm 2 The battery adopts constant current charge and discharge mode, the charge cut-off condition is capacity cut-off, the discharge cut-off condition is voltage cut-off, and the cut-off voltage is 0.1V; the volume of positive and negative electrolytes is 60mL each, the positive and negative electrodes are porous carbon felt electrodes, and the graphite plate is used as the current collector; the diaphragm is Nafion 212. The experimental conditions and battery performance are shown in Table 1.

[0042] Example 2

[0043] The other experimental conditions were the same as those in Example 1, except that the current density of the battery test condition was 60 mA cm -2 .

[0044] Example 3

[0045] The other experimental conditions were the same as those in Example 1, except that the current density of the battery test condition was 80 mA cm -2 .

[0046] Comparative Example 1

[0047] The other experimental conditions are the same as those in Example 1, except that the chelating agent of the negative electrode electrolyte is EDTA, the molar concentration of the negative electrode active substance FeCl3 is 0.5M (due to the low solubility of the complex, the concentration cannot be increased), and the test conditions of the battery performance are the same as those in Example 1.

[0048] Table 1. Experimental conditions and battery performance

[0049]

[0050] The results in Table 1 show that the active substance of the negative electrode electrolyte is a complex of iron ions and EDTMPA, and the active substance of the positive electrode electrolyte is bromide ions and bromine element. The discharge energy density of the electrolyte of the neutral iron-bromine flow battery is as high as 27.5AhL -1 ;Battery at 40mA cm -2 The coulombic efficiency (CE) is higher than 99%, and the energy efficiency (EE) is 81%, which has high performance in the field of liquid flow batteries. In addition, the battery system of the present invention does not have a deposition dissolution reaction, and both the positive and negative electrodes are liquid-liquid phase reactions. The power and energy of the battery can be designed independently, and the cost is much lower than that of all-vanadium liquid flow batteries, which has broad prospects for large-scale applications.

[0051] Figure 2 It can be seen that the redox potential of FeEDTMPA has obviously shifted toward the negative direction by about 300 mV compared with FeEDTA, and the assembled battery has a higher open circuit voltage and energy density.

[0052] Figure 4 It can be seen that the redox potential after complexing iron is -0.46V vs. SCE. When paired with bromine electrodes, the open circuit voltage of the battery is about 1.27V.

[0053] Figure 6 It can be seen that when the current density of the neutral iron-bromine flow battery of the present invention is increased to 80 mA cm -2 When the battery is charged, the energy efficiency still reaches over 70%.

[0054] Figure 7 It can be seen that the capacity of the battery of the present invention remains stable after 300 consecutive charge and discharge cycles; and there is no obvious attenuation of the battery performance.

[0055] Depend on Figure 8 It can be seen that when conventional EDTA is used as a chelating agent, the assembled iron-bromine flow battery has unstable charging and discharging after FeEDTA is paired with bromine, and the battery performance fluctuates greatly.

[0056] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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. A neutral iron-bromine flow battery, characterized in that: The active substance of the negative electrode electrolyte of the neutral iron-bromine flow battery is a complex of iron ions, and the active substance of the positive electrode electrolyte is bromide ions or bromine element; The complex is a complex of iron ions and EDTMPA, wherein the iron ions include divalent iron ions and trivalent iron ions, and the complexing molar ratio of the iron ions to EDTMPA is 1:1 to 1:

2.

2. The neutral iron-bromine flow battery according to claim 1, characterized in that: The concentration of the complex is 0.1-1.2M.

3. The neutral iron-bromine flow battery according to claim 2, characterized in that: The concentration of the complex is 0.5-1M.

4. The neutral iron-bromine flow battery according to claim 1, characterized in that: The source of bromide ions includes one or more of sodium bromide, potassium bromide, lithium bromide, ammonium bromide, magnesium bromide or zinc bromide, wherein the molar concentration of bromide ions is 0.1-16M; the source of divalent iron ions is ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous fluoride, ferrous iodide, ferrous bromide, and ammonium ferrous sulfate; the source of trivalent iron ions is ferric chloride, ferric bromide, ferric sulfate, ferric nitrate, ferric acetate, and ferric fluoride.

5. The neutral iron-bromine flow battery according to claim 4, characterized in that: The molar concentration of the bromide ions is 1-6M.

6. The neutral iron-bromine flow battery according to claim 1, characterized in that: Supporting electrolytes are also added to the positive and negative electrode electrolytes, including one or more of lithium chloride, potassium chloride, sodium chloride, ammonium chloride, lithium sulfate, potassium sulfate, sodium sulfate, ammonium sulfate, lithium bromide, sodium bromide, potassium bromide, and ammonium bromide; the molar concentration of the supporting electrolyte is 0.1 to 5M.

7. The neutral iron-bromine flow battery according to claim 6, characterized in that: The molar concentration of the supporting electrolyte is 2-3M.

8. The neutral iron-bromine flow battery according to any one of claims 1 to 7, characterized in that: The neutral iron-bromine liquid flow battery comprises a positive electrode current collecting plate, a positive electrode, an ion conducting membrane, a negative electrode and a negative electrode current collecting plate which are stacked in sequence.

9. The neutral iron-bromine flow battery according to claim 8, characterized in that: The electrode materials of the positive and negative electrodes are one of carbon felt, carbon cloth or carbon paper.

10. The neutral iron-bromine flow battery according to claim 9, characterized in that: The electrode materials for both the positive and negative electrodes are carbon felt.

11. The neutral iron-bromine flow battery according to claim 8, characterized in that: The ion conduction membrane is Nafion membrane produced by DuPont; the positive and negative current collecting plates are graphite plates or copper plates.

12. The neutral iron-bromine flow battery according to claim 11, characterized in that: The ion conduction membrane is Nafion212; the positive and negative current collecting plates are graphite plates.

13. The neutral iron-bromine flow battery according to claim 1, characterized in that: The neutral iron-bromine liquid flow battery is provided with a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a circulation pump and a circulation pipeline.

14. A battery module, characterized in that: The battery module is formed by connecting two or more neutral iron-bromine flow batteries according to any one of claims 1 to 13 in series and / or in parallel.

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