A highly stable iron-based flow battery alkaline negative electrolyte

Abstract

The application discloses a high-stability iron-based negative electrolyte for a flow battery, and belongs to the technical field of flow battery energy storage. The main component of the negative electrolyte is a water solution of a coordination compound formed by coordination of a ferric salt and N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine (TETRA), N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine (EDTP) or a derivative chemical thereof. Compared with the ligand used in the prior art, TETRA and EDTP have more active coordination sites and are easier to chelate with iron to form a stable complex. In addition, the ligand has a large molecular size, and the chelate formed has a large steric hindrance effect, thereby reducing cross contamination. The flow battery disclosed by the application can solve the problems of metal iron deposition and battery capacity attenuation and poor stability caused by the metal iron deposition, improve the cycle life of the iron-based flow battery, and has low electrolyte cost and simple operation.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of liquid flow battery energy storage, in particular to a preparation method of a high-stability alkali negative electrolyte of an iron-based liquid flow battery. BACKGROUND

[0002] People pay more and more attention to the development and utilization of renewable energy, such as wind energy and light energy, however, renewable energy must be equipped with large-scale energy storage equipment due to its discontinuity. As a new large-scale energy storage technology, the liquid flow battery has the advantages of large energy storage capacity, high energy efficiency, safety and reliability, and can be used in the fields of power peak shaving and photovoltaic cell power generation as a large-scale energy storage system.

[0003] In the structure of the liquid flow battery, there are two storage tanks outside for storing positive and negative electrolytes. The electrolyte contains active substances, which can be transported to the electrode surface under the action of a pump to generate an oxidation-reduction reaction and realize energy conversion. In the charging and discharging process, the diaphragm between the positive and negative electrolytes not only conducts electricity, but also blocks the transmembrane penetration of the active molecules of the electrolyte. The unique structure of the liquid flow battery enables the energy and capacity to be independently controlled: the energy capacity is determined by the storage amount of the electrolyte, and the power density is related to the size of the electrode area.

[0004] Among them, the all-vanadium liquid flow battery has been commercialized, has the advantages of high efficiency, good stability, long cycle life and wide application prospect, but the cost of the active substance of the all-vanadium liquid flow battery is relatively high, which limits the larger-scale application of the all-vanadium liquid flow battery to some extent. In addition, the currently researched more are iron-chromium liquid flow batteries, iron-based liquid flow batteries, zinc-iron liquid flow batteries and zinc-bromine liquid flow batteries. Among them, the iron-based liquid flow battery uses iron ions as the active substance for the positive and negative electrodes, can avoid cross contamination, has low cost and rich resources, and is one of the most cost-effective energy storage systems.

[0005] The electrolyte contains active substances and is the most core part of the iron-based liquid flow battery, and should meet the following requirements: high solubility, good stability; large positive and negative electrode potential difference, good reversibility; fast reaction speed, small capacity loss. At present, the developed negative electrolyte ligand molecules are small in size, and most of them face the problems of transmembrane transport and cross contamination, and the battery operation is difficult to stabilize. Therefore, seeking new ligands with many active coordination sites and large molecular size and developing new negative electrolytes are one of the important paths for improving the practicability of the iron-based liquid flow battery. SUMMARY

[0006] The application adds appropriate ligands and adjusts the coordination environment, the ligands themselves have many active coordination sites, are more prone to chelation with iron ions, have large molecular sizes, reduce cross contamination, make them and Fe 3+ / Fe 2+The coordination to form a ligand compound can solve the problems of metal iron deposition and poor stability caused by the battery capacity attenuation, improve the battery life, and has low price, environmental friendliness and good application prospect.

[0007] The application adopts the following technical scheme:

[0008] The alkali negative electrolyte of the high-stability iron-based flow battery is characterized in that the negative electrolyte is a strong alkali aqueous solution, and the strong alkali aqueous solution contains a complex formed by trivalent iron ions and a complex ligand, a supporting electrolyte and an auxiliary electrolyte.

[0009] The negative electrolyte of the iron-based flow battery is characterized in that the negative electrolyte is composed of: the molar concentration of the trivalent iron ions is 0-1.0 mol / L and is not 0, and is preferably 0.1-0.5 mol / L; the molar concentration of the ligands TETRA and EDTP is 0-3.0 mol / L and is not 0, and is preferably 0.5-1.5 mol / L; the molar concentration of the supporting electrolyte is 0-8.0 mol / L and is not 0, and is preferably 1.0-4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0-3.0 mol / L and is not 0, and is preferably 0.5-1.5 mol / L; and deoxygenated deionized water is used as a solvent.

[0010] The alkali negative electrolyte of the iron-based flow battery is characterized in that: the active substance containing trivalent iron ions is one or more of iron chloride, iron sulfate and iron nitrate; the complex ligand is selected from N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine or a derivative chemical thereof; the supporting electrolyte is one or more of lithium hydroxide, potassium hydroxide and sodium hydroxide; and the auxiliary electrolyte is one or more of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, potassium nitrate and sodium nitrate, so as to improve the conductivity of the electrolyte.

[0011] The preparation method of the negative electrolyte of the iron-based flow battery is prepared according to the following process:

[0012] Nitrogen is introduced into the reactor to exhaust air, and trivalent iron ions, complex ligands, supporting electrolytes and auxiliary electrolytes are added, and then deionized water is added after mixing, and the mixture is fully stirred for 3-24 hours to form a uniform solution, and the solution is used after standing for 6 hours.

[0013] An iron-based flow battery includes the alkali negative electrolyte, and a corresponding positive electrolyte is a ferrocyanide aqueous solution, the ferrocyanide includes one or more of potassium ferrocyanide, sodium ferrocyanide, lithium ferrocyanide, ammonium ferrocyanide, magnesium ferrocyanide and calcium ferrocyanide, and the concentration is 0-6 mol / L and is not 0.

[0014] The positive electrolyte of the iron-based flow battery, characterized in that: the positive electrolyte further comprises an auxiliary electrolyte, the auxiliary electrolyte is one or more of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, potassium nitrate and sodium nitrate, so as to improve the conductivity of the electrolyte.

[0015] The positive electrolyte of the iron-based flow battery is prepared according to the following process: nitrogen is introduced into the reactor to remove air, one or more than two ferrocyanide is added into the reactor, the auxiliary electrolyte is added, and then deionized water is added to fully stir until completely dissolved.

[0016] The positive and negative electrolytes of the iron-based flow battery, characterized in that: the temperature suitable for operation of the electrolyte is 10-80 DEG C.

[0017] An iron-based flow battery, which is composed of electrodes, electrolytes, separators, storage tanks, pumps and pipelines, wherein the electrodes and electrolytes are separated by the separators into two chambers of positive and negative, and the electrolytes are circulated by the pumps.

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

[0019] 1. The complex of the ferric salt and TETRA, EDTP is used as the alkaline negative electrolyte of the flow battery, compared with the existing negative electrolyte, the N, O coordination sites of TETRA, EDTP are more, and the complex stability is better, so that the cross contamination is reduced and the stability is improved.

[0020] 2. The negative electrolyte provided by the present application and the ferrocyanide aqueous solution form the iron-based flow battery, which can be stably cycled for a long time, and the aqueous electrolyte is flame-retardant, so the safety is good.

[0021] 3. The negative electrolyte used in the present application is low in cost and easy to operate, TETRA, EDTP or its derivatives are generally low in price, and the additional cost of the iron-based flow battery is low. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The cyclic voltammogram of Example 1 in 2-100 mV·s -1

[0023] Figure 2 The charge and discharge efficiency-cycle curve of Example 1 in 900-1000 cycles.

[0024] Figure 3 The charge and discharge capacity-cycle curve of Example 1 in 900-1000 cycles.

[0025] Table 1 is a comparison of the battery test results of the first cycle of each example.

[0026] ​Table 2 is a comparison of the battery test results after 1000 cycles of each example. DETAILED DESCRIPTION

[0027] The application will be described in detail below through specific examples, but the purpose and purpose of these example embodiments are only used to exemplify the application, and do not constitute any form of any limitation on the actual protection scope of the application, nor limit the protection scope of the application.

[0028] Example 1

[0029] In this embodiment, the main components of the negative electrolyte include: ferric chloride, N,N,N',N'-tetra (2-hydroxyethyl) ethylenediamine (TETRA), sodium hydroxide as a supporting electrolyte, sodium chloride as an auxiliary electrolyte, and deoxygenated deionized water as a solvent. Among them, the concentration of ferric chloride is 0.2 mol / L, the concentration of TETRA is 1.0 mol / L, the concentration of sodium hydroxide is 3.0 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0030] The specific steps for configuring the negative electrolyte are as follows:

[0031] Nitrogen was introduced into the reactor to remove air, and 5.4 g of ferric chloride, 23.6 g of TETRA, 12.0 g of sodium hydroxide, and 2.9 g of sodium chloride were sequentially added. After mixing, deoxygenated deionized water was added, stirred for 6 hours to form a uniform solution, and then diluted to 100 mL. After standing for 24 hours, it was used.

[0032] The above negative electrolyte was subjected to electrochemical test, and the results are shown in Figure 1 The cyclic voltammetry curve was scanned at a scan rate of 2-100 mV / s, and had good reversibility.

[0033] In the battery test, the electrolyte of the positive electrode was a solution of 0.5 mol / L sodium ferrocyanide and 0.5 mol / L sodium chloride.

[0034] The positive electrolyte was prepared according to the following process: nitrogen was introduced into the reactor to remove air, 24.0 g of sodium ferrocyanide was added to the reactor, 2.9 g of sodium chloride was added, and then deionized water was added and stirred until completely dissolved. Stir for 6 hours to form a uniform solution, dilute to 100 mL, and stand for 24 hours before use.

[0035] The single cell components include aluminum end plate, polytetrafluoroethylene gasket, current collector plate, graphite bipolar plate, graphite felt electrode, fluororubber gasket, and proton exchange membrane. Assemble the single cell, and form a battery test system with the positive and negative electrolyte tanks, positive and negative peristaltic pumps, and circulation pipeline.

[0036] Before the test, the battery system is circulated with inert gas to avoid the deactivation of active material and the deactivation of alkaline electrolyte.

[0037] The volume of positive and negative electrolyte is 30ml, and the positive and negative electrode is 3*3cm 2 The porous carbon felt electrode, the proton membrane is Nafion 117 membrane. Charge to 1.5V at 80mA / cm 2 The discharge to 0.8V at 80mA / cm 2 The charge and discharge is still stable after 1000 cycles. As shown in the following table, in 900-1000 cycles, the CE of the battery is about 95%, and the VE and EE are about 65%, which is basically consistent with the battery efficiency of the first cycle and the battery after 1000 cycles. Figure 2 As shown in the following table, in 900-1000 cycles, the charge and discharge capacity is still stable at about 0.1Ah. Figure 3

[0038] Example 2

[0039] In this embodiment, the main components of the negative electrolyte include: iron sulfate, N, N, N', N'-tetra(2-hydroxypropyl)ethylenediamine (EDTP), supporting electrolyte is lithium hydroxide, auxiliary electrolyte is potassium chloride, and solvent is oxygen-free deionized water. Among them, the concentration of iron sulfate is 0.3mol / L, the concentration of EDTP is 1.2mol / L, the concentration of lithium hydroxide is 2.5mol / L, and the concentration of potassium chloride is 0.5mol / L.

[0040] The specific steps of preparing the negative electrolyte are as follows:

[0041] Nitrogen is introduced into the reactor to remove air, and 12.0g of iron sulfate, 35.1g of EDTP, 6.0g of lithium hydroxide and 3.7g of potassium chloride are sequentially added. After mixing, deoxygenated ion water is added, stirred for 6 hours to form a uniform solution, and then diluted to 100mL. After standing for 24 hours, it is used.

[0042] The above negative electrolyte is subjected to electrochemical test.

[0043] In the battery test, the electrolyte of the positive electrode is 0.5mol / L lithium ferrocyanide and 0.5mol / L sodium chloride solution, and the preparation process is as described in Example 1.

[0044] Before the test, the battery system is circulated with inert gas to avoid the deactivation of active material and the deactivation of alkaline electrolyte.

[0045] The volume of positive and negative electrolyte is 30ml, and the positive and negative electrode is 2*2cm 2 ​Porous carbon felt electrode, proton membrane is Nafion 212 membrane. Charge to 1.5V at 80mA / cm 2 Discharge to 0.8V at 80mA / cm 2 .

[0046] Example 3:

[0047] In this embodiment, the main components of the negative electrolyte include: ferric nitrate, TETRA, supporting electrolyte is potassium hydroxide, auxiliary electrolyte is potassium chloride, and the solvent is oxygen-free deionized water. Among them, the concentration of ferric nitrate is 0.4mol / L, the concentration of TETRA is 1.5mol / L, the concentration of potassium hydroxide is 3.0mol / L, and the concentration of potassium chloride is 0.5mol / L.

[0048] The specific steps of configuring the negative electrolyte are as follows:

[0049] Nitrogen was introduced into the reactor to exhaust air, and 9.6g of ferric nitrate, 35.0g of TETRA, 17.0g of potassium hydroxide, and 3.7g of potassium chloride were added in turn. After mixing, oxygen-free deionized water was added, stirred for 6 hours to form a uniform solution, and then diluted to 100mL. After standing for 24 hours, it was used.

[0050] The above negative electrolyte was subjected to electrochemical test.

[0051] In the battery test, the electrolyte of the positive electrode was 0.5mol / L potassium ferrocyanide and 0.5mol / L potassium chloride solution, and the configuration process referred to Example 1.

[0052] Before testing, inert gas was circulated in the battery system to avoid inactivation of active substances and deterioration of alkaline electrolyte.

[0053] The volume of the positive and negative electrolyte was 30ml respectively, and the positive and negative electrodes were both 3x3cm 2 Porous carbon felt electrode, proton membrane is Nafion 212 membrane. Charge to 1.5V at 80mA / cm 2 Discharge to 0.8V at 80mA / cm 2 .

[0054] Table 1 Comparison of battery test results of each example in the first cycle

[0055]

[0056] Table 2 Comparison of battery test results of each example after 1000 cycles

[0057]

Claims

1. An iron-based flow battery, characterized in that, The negative electrode electrolyte consists of: ferric chloride, N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine (TETRA), with sodium hydroxide as the supporting electrolyte, sodium chloride as the auxiliary electrolyte, and deionized water as the solvent; wherein the concentration of ferric chloride is 0.2 mol / L, the concentration of TETRA is 1.0 mol / L, the concentration of sodium hydroxide is 3.0 mol / L, and the concentration of sodium chloride is 0.5 mol / L. The specific steps for preparing the negative electrode electrolyte are as follows: Nitrogen gas was introduced into the reactor to purge the air. 5.4 g ferric chloride, 23.6 g TETRA, 12.0 g sodium hydroxide, and 2.9 g sodium chloride were added in sequence. After mixing, deionized water was added and the mixture was stirred for 6 hours to make a homogeneous solution. The solution was then brought to a final volume of 100 mL and allowed to stand for 24 hours before use. In battery testing, the electrolyte for the positive electrode was a solution of 0.5 mol / L sodium ferrocyanide and 0.5 mol / L sodium chloride. The positive electrode electrolyte is prepared according to the following process: nitrogen gas is introduced into the reactor to purge the air, 24.0 g of sodium ferrocyanide is added to the reactor, followed by 2.9 g of sodium chloride, and then deionized water is added and stirred thoroughly until completely dissolved; the solution is stirred for 6 hours to form a homogeneous solution, and then brought to a final volume of 100 mL. After standing for 24 hours, it is used. The single cell components include aluminum end plates, polytetrafluoroethylene gaskets, current collectors, graphite bipolar plates, graphite felt electrodes, fluororubber gaskets, and proton exchange membranes; the single cell is assembled and combined with positive and negative electrode storage tanks, positive and negative electrode peristaltic pumps, and circulation pipelines to form a battery. Inert gas is circulated within the battery system to prevent deactivation of active materials and alkaline electrolyte; The electrolyte volume for both positive and negative electrodes is 30 ml, and both electrodes are 3 × 3 cm. 2 Porous carbon felt electrode, proton exchange membrane is Nafion 117 membrane; at 80 mA / cm 2 Charged to 1.5 V at a current density of 80 mA / cm² 2 It can be discharged to 0.8 V at a current density; after 1000 cycles, the charge and discharge remain stable; in 900 to 1000 cycles, the battery's CE is 95%, and VE and EE are 65%, which is basically consistent with the battery efficiency after the first cycle and 1000 cycles; in 900 to 1000 cycles, the charge and discharge capacity remains stable at 0.1 Ah.

2. An iron-based flow battery, characterized in that, The negative electrode electrolyte consists of: ferric sulfate, N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine (EDTP), with lithium hydroxide as the supporting electrolyte, potassium chloride as the auxiliary electrolyte, and deionized water as the solvent; wherein the concentration of ferric sulfate is 0.3 mol / L, the concentration of EDTP is 1.2 mol / L, the concentration of lithium hydroxide is 2.5 mol / L, and the concentration of potassium chloride is 0.5 mol / L. The specific steps for preparing the negative electrode electrolyte are as follows: Nitrogen gas was introduced into the reactor to purge the air. 12.0 g of ferric sulfate, 35.1 g of EDTP, 6.0 g of lithium hydroxide and 3.7 g of potassium chloride were added in sequence. After mixing, deionized water was added and the mixture was stirred for 6 hours to make a homogeneous solution. The solution was then brought to a final volume of 100 mL and allowed to stand for 24 hours before use. The electrolyte for the positive electrode is a 0.5 mol / L lithium ferrocyanide and a 0.5 mol / L sodium chloride solution; Inert gas is circulated within the battery system to prevent deactivation of active materials and deterioration of alkaline electrolyte; The electrolyte volume for both positive and negative electrodes is 30 ml, and both electrodes are 2 × 2 cm. 2 Porous carbon felt electrode, proton exchange membrane is Nafion 212 membrane; at 80 mA / cm 2 Charged to 1.5 V at a current density of 80 mA / cm² 2 Discharged to 0.8V at a current density; CE was 96.6% after 1000 cycles.

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