Low-cost neutral aqueous organic iron-cerium flow battery

Abstract

The invention discloses a low-cost neutral aqueous organic iron-cerium flow battery, and belongs to the field of electrochemical energy storage. The positive electrode electrolyte and the negative electrode electrolyte both adopt organic phosphine ligand chelating metals in a water system, and organic phosphine ligands are selected from 2-hydroxyphosphonoacetic acid, etidronic acid, diethylenetriaminepenta (methylene phosphonic acid), 2-phosphonobutane-1, 2, 4-tricarboxylic acid, polyhydric alcohol phosphate ester, hexamethylenediamine tetra (methylene phosphonic acid), polyamino polyether methylene phosphonic acid and bis (1, 2, 4-tricarboxylic acid. And one or more of 2, 6-hexylidene triamine penta (methylene phosphonic acid) and lithium, sodium, potassium and ammonium salt derivatives thereof. And the supporting electrolyte is used for adjusting and stabilizing the pH environment of the electrolyte. According to the invention, no additional auxiliary electrolyte is needed, high conductivity and stable performance can be achieved, and a new possibility is developed for development and application of a flow battery technology. The material has the characteristics of stable performance, low cost, wide raw material source and environmental friendliness, and is suitable for automobile power supplies, household energy storage, standby power supplies, large-scale energy storage devices and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow batteries, and specifically to a low-cost neutral aqueous organic iron cerium liquid flow battery, which can be widely used in automotive power supplies, household energy storage, backup power supplies, and large-scale energy storage devices such as wind energy and solar energy. Background Art

[0002] At present, in the field of large-scale energy storage, flow batteries have received extensive attention due to their intrinsic safety, while all-vanadium flow batteries face the challenges of high vanadium raw material costs and severe self-discharge, which largely hinder their further development. In this case, the development of low-cost, fully soluble flow batteries is expected to become a very attractive alternative to flow batteries. Among the existing low-cost routes, iron-based flow batteries are usually the main ones, but the negative electrode reaction of the traditional technical route is the deposition and stripping reaction of Fe on the electrode. The coordination structure of Fe ions and water easily induces hydrogen evolution reaction, which accelerates the failure and capacity loss of the battery and reduces the life of the flow battery. In addition, some ferrocyanide electrolytes on the positive electrode side also have the problem of precipitation of iron hydroxide. In order to solve the problems of iron precipitation at the negative electrode and precipitation at the positive electrode, the present invention prepares a low-cost neutral aqueous organic iron cerium flow battery by adopting a new type of organic phosphine ligand chelation method. It is worth noting that the organic phosphine ligands innovatively adopted in the present invention are all currently large-scale industrialized water additive products, which are usually used for sewage treatment and scale and corrosion inhibition of pipeline water. They are low-cost and widely available, and do not require the addition of additional auxiliary electrolytes, opening up new possibilities for the development and application of liquid flow battery technology. Summary of the invention

[0003] The purpose of the present invention is to provide a low-cost neutral aqueous organic iron-cerium flow battery with stable performance and environmental friendliness, overcome the problems of metal dendrites, hydrogen evolution reaction, severe self-discharge and high cost in existing flow battery technology, and expand the market for abundant cerium resources in China.

[0004] The low-cost neutral water-based organic iron-cerium flow battery described in the present invention is mainly improved on the basis of the existing flow battery. The key to the present invention is that the electrolyte, that is, the active component of the negative electrode electrolyte is a chelate of iron salt chemicals and organic phosphine ligands, and the active component of the positive electrode electrolyte is a chelate of cerium salt chemicals and organic phosphine ligands, and a supporting electrolyte is added to adjust the pH to a neutral environment.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A low-cost neutral aqueous organic iron-cerium liquid flow battery, comprising a positive electrode electrolyte and a negative electrode electrolyte, characterized in that: the active component of the negative electrode electrolyte is a stable chelate formed by an iron salt chemical and an organic phosphine ligand, the active component of the positive electrode electrolyte is a stable chelate formed by a cerium salt chemical and an organic phosphine ligand, and the reaction of the active substance of the electrolyte on the electrode surface during charging is as follows:

[0007] Negative electrode reaction: Fe 3+ +e→Fe 2+

[0008] Positive electrode reaction: Ce 3+ -e→Ce 4+

[0009] The total battery reaction is: Fe 3+ +Ce 3+ →Fe 2+ +Ce 4+

[0010] Discharging is the reverse reaction of the above reaction.

[0011] The organic phosphine ligand is selected from 2-hydroxyphosphonoacetic acid (HPAA), hydroxyethylidene diphosphonic acid (HEDP), diethylene triamine penta (methylene phosphonic acid) (DTPMPA), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), polyol phosphate (PAPE), hexamethylene diamine tetra (methylene phosphonic acid) (HDTMPA), polyamino polyether methylene phosphonic acid (PAPEMP), bis (1,6-hexamethylene triamine penta (methylene phosphonic acid) (BHMTPMPA) and lithium, sodium, potassium, ammonium salt derivative chemicals thereof or a mixture of several thereof.

[0012] In addition to active substances and ligands, the positive and negative electrolytes also contain a pH supporting electrolyte for stabilizing the chelating structure of the active substances for adjusting the pH, which is selected from one or more of potassium carbonate, sodium carbonate, lithium carbonate, potassium tetraborate, sodium tetraborate, potassium hydroxide, and sodium hydroxide.

[0013] The iron salt active material used in the negative electrode electrolyte is selected from one or more of ferric chloride, ferric nitrate, ferric acetate, ammonium ferric sulfate, and ferric sulfate; the cerium salt chemicals used in the positive electrode are selected from one or more of cerium trichloride, cerium oxalate, cerium sulfate, cerium acetate, and cerium nitrate.

[0014] The positive electrode electrolyte is an aqueous solution composed of a stable chelate formed by iron salt chemicals and organic phosphine ligands and a pH supporting electrolyte.

[0015] The negative electrode electrolyte is an aqueous solution composed of a stable chelate formed by cerium salt chemicals and organic phosphine ligands and a pH supporting electrolyte.

[0016] The concentration of the positive electrode cerium active material in the electrolyte is 0 to 2 mol / L and not 0, preferably in the range of 0.5 to 1.5 mol / L; the concentration of the negative electrode iron active material in the electrolyte is 0 to 2 mol / L and not 0, preferably in the range of 0.5 to 1.5 mol / L; the ratio of cerium to iron active material is 1.2:1 to 1:1, preferably 1.05:1. The ratio of the concentration of the organic phosphine ligand to the active material is 2:1 to 1:1. An appropriate pH adjuster is added to adjust the pH of the electrolyte to a neutral range of 5 to 9, preferably pH=7.

[0017] The low-cost neutral aqueous organic ferrocerium liquid flow battery comprises positive and negative electrodes, a battery separator, and a current collector.

[0018] The positive and negative electrode materials are selected from one of the inert materials of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth. One of Nafion117, Nafion115, Nafion212, and Nafion211 is used as the battery separator. The current collector is a metal plate or a carbon bipolar plate. The operating temperature is 10 to 90°C, and the electrolyte is circulated by a pump.

[0019] Compared with the prior art, the present invention has the following significant advantages and beneficial effects:

[0020] 1. The positive and negative electrolytes of the present invention form stable compounds with iron salts, cerium salts and organic phosphine ligands by chelating and coordinating, which not only avoids the problems of iron generating metal dendrites and hydrogen evolution reaction in traditional processes, but also improves the life of the liquid flow battery and reduces the operating cost of the liquid flow battery system.

[0021] 2. The organic phosphine ligand contains multiple P, N, and O groups. The introduction of the ligand can break the original solvation structure of iron and cerium in H2O, and iron and cerium form new coordination with O and N in the ligand. At the same time, the presence of P further enhances the electron donation of O and enhances the coordination stability with the active substance.

[0022] 3. The molecular volume of the chelate itself is relatively large, which enhances the steric effect, eliminates the capacity and energy loss caused by the transmembrane transport of the ligand, improves the stability of the battery, and reduces the loss of active substances caused by side reactions.

[0023] 4. The active substance, chelating agent and supporting electrolyte used in the present invention are all industrial chemicals widely used in the current market, with simple production process, low cost, easy scale-up and no environmental safety hazards.

[0024] 5. The rare earth metal elements used in the present invention are domestic advantageous resources, providing new options for comprehensive, circular and green utilization, and have broad application prospects and potential.

[0025] 6. Thanks to the characteristics of the organic phosphine ligand, the electrolyte of the present invention can work normally within a relatively high temperature range, and the working temperature range is extended to 90°C (the limit temperature of the prior art flow battery is 60-70°C, while the temperature of the present invention exceeds the above limit temperature and can even operate at a temperature of (60-70)-90°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the iron cerium liquid flow battery.

[0027] Figure 2 Schematic diagram of the molecular structure of the organophosphine ligand.

[0028] Figure 3 This is the charge and discharge curve of the iron-cerium liquid flow battery in Example 1.

[0029] Figure 4 This is the cycle efficiency result of the iron-cerium liquid flow battery in Example 1.

[0030] Figure 5 This is the cycle efficiency result of the iron-cerium liquid flow battery in Example 2.

[0031] Figure 6 This is the cycle efficiency result of the iron-cerium liquid flow battery in Example 3.

[0032] Figure 7 The cycle efficiency results of the iron-cerium liquid flow battery of Example 4 operating at 90°C.

[0033] Table 1 shows the average CE, VE and EE of different electrolytes in battery tests. DETAILED DESCRIPTION

[0034] The present invention is described in detail below through specific examples, but the use and purpose of these exemplary embodiments are only used to illustrate the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to these.

[0035] Embodiment 1:

[0036] like Figure 1 The schematic diagram of the structure of the iron-cerium liquid flow battery shown in the figure mainly includes a single cell, positive and negative electrode storage tanks, a peristaltic pump, and an anti-corrosion circulation pipeline. The components of the single cell include: aluminum end plates, polytetrafluoroethylene gaskets, collector plates, graphite bipolar plates, fluororubber gaskets, proton exchange membranes, and graphite felt electrodes. During the test, the positive and negative electrolytes flow into the single cell through the pump, and return to the electrolyte tank after the redox reaction. The active component of the negative electrode electrolyte is a chelate of iron salt chemicals and organic phosphine ligands, and the active component of the positive electrode electrolyte is a chelate of cerium salt chemicals and organic phosphine ligands, and the supporting electrolyte is added to adjust the pH to a neutral environment.

[0037] Figure 2 The figure is a schematic diagram of the molecular structure of the organophosphine ligand. The organophosphine ligand contains multiple N, P, and O groups. The introduction of the ligand can break the original solvation structure of iron and cerium in H2O, and iron and cerium form new coordination with O and N in the ligand. At the same time, the presence of P further enhances the electron-donating property of O and enhances the coordination stability with the active substance.

[0038] In this embodiment, the negative electrode electrolyte iron salt is ferric sulfate, the chelating agent is the organic phosphine ligand HPAA, potassium tetraborate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the iron ion concentration is 0.5 mol / L, the concentration of the organic phosphine ligand HPAA is 1 mol / L, and potassium tetraborate is added to adjust the final pH of the solution to 7.

[0039] In this embodiment, the cerium salt of the positive electrode electrolyte is cerium sulfate, the chelating agent is the organic phosphine ligand HPAA, potassium tetraborate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of cerium ions is 0.5 mol / L, the concentration of the organic phosphine ligand HPAA is 1 mol / L, and potassium tetraborate is added to adjust the final pH of the solution to 7.

[0040] After the battery components are assembled, the system is filled with inert gas to prevent the loss of active substances and pH changes. The above-prepared electrolyte is added to the electrolyte storage tank at a volume ratio of 1:1. The electrode material is a 5mm thick graphite felt electrode with a compression ratio of 40%. The ion exchange membrane is Nafion 212. The operating temperature of the battery is 25°C.

[0041] The above-mentioned iron-cerium liquid flow battery was tested for 1000 charge-discharge cycles, and the charge-discharge current was set to 80 mA / cm 2 The upper and lower limits of charge and discharge are 1.2V and 0.01V respectively. The charge and discharge curve results are as follows Figure 3 As shown, Fe / Ce HPAA has very excellent performance. Figure 4 The efficiency results of the flow battery in the embodiment within 1000 cycles at 100% state of charge (SOC) are shown. At the beginning of the cycle, the coulombic efficiency (CE) is ~93%, which gradually increases as the cycle progresses and finally stabilizes at around ~99%. Its energy efficiency (EE) is ~77% after stabilization after a certain number of cycles, which fully demonstrates the cycle stability of the battery.

[0042] Embodiment 2:

[0043] In this embodiment, the negative electrode electrolyte iron salt is ferric chloride, the chelating agent is the organic phosphine ligand HEDP, potassium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the iron ion concentration is 0.5 mol / L, the concentration of the organic phosphine ligand HEDP is 1 mol / L, and potassium carbonate is added to adjust the final pH of the solution to 7.

[0044] In this embodiment, the positive electrode electrolyte cerium salt uses cerium chloride, the chelating agent is the organic phosphine ligand HEDP, potassium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of cerium ions is 0.5 mol / L, the concentration of the organic phosphine ligand HEDP is 1 mol / L, and potassium carbonate is added to adjust the final pH of the solution to 7.

[0045] The remaining steps are the same as those in Example 1. Figure 5 The results of the battery cycle efficiency (200 cycles) of the electrolyte in Example 2 above show that its coulombic efficiency is always close to 100%, and the battery performance increases slightly with the progress of the cycle. This is due to the incompatibility of the membrane material and the electrolyte at the beginning of the cycle. As the cycle progresses and the electrolyte and the membrane material are activated and infiltrated, the battery effect is gradually improved.

[0046] Embodiment 3:

[0047] In this embodiment, the negative electrode electrolyte iron salt is ferric chloride, the chelating agent is the organic phosphine ligand DTPMPA, lithium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the iron ion concentration is 0.5 mol / L, the concentration of the organic phosphine ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to 7.

[0048] In this embodiment, the positive electrode electrolyte cerium salt uses cerium chloride, the chelating agent is the organic phosphine ligand DTPMPA, potassium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of cerium ions is 0.5 mol / L, the concentration of the organic phosphine ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to 7.

[0049] The remaining steps are the same as those in Example 1. Figure 6 This is the battery cycle efficiency result of the electrolyte of Example 3. The results show that compared with Examples 1 and 2, after the N element is introduced into the main chain of the organic phosphine ligand and more phosphonic acid is added, its stability is further improved, and the amount of organic phosphine ligand used is reduced. Within 500 cycles, it showed better stability than the above electrolyte, and the CE and EE were always greater than 97% and 78% (EE was basically maintained at around 80%).

[0050] Embodiment 4:

[0051] In this embodiment, the negative electrode electrolyte iron salt is ferric chloride, the chelating agent is the organic phosphine ligand DTPMPA, lithium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the iron ion concentration is 0.5 mol / L, the concentration of the organic phosphine ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to 7.

[0052] In this embodiment, the positive electrode electrolyte cerium salt uses cerium chloride, the chelating agent is the organic phosphine ligand DTPMPA, potassium carbonate is the supporting electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of cerium ions is 0.5 mol / L, the concentration of the organic phosphine ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to 7.

[0053] The test conditions were as follows: the room temperature was raised to 90° C., and the remaining steps were the same as those in Example 3. Figure 7 The cycle efficiency results of the iron-cerium liquid flow battery in Example 4 at 90°C are shown. Within 80 cycles, CE and EE are slightly reduced compared with those at room temperature. This is because the molecular thermal motion is accelerated at high temperature, resulting in enhanced membrane permeability, intensified self-discharge and side reactions, but generally maintained a stable EE>70%.

[0054] The remaining ligands were configured in the same proportions as in Examples 1 and 2. The battery test results are the average efficiency values ​​within 100 cycles, which are summarized in Table 1.

[0055] Table 1 Average CE, VE and EE of different electrolytes in battery tests (room temperature)

[0056] Electrolyte CE / % VE / % EE / % Fe / Ce HPAA 98.6 75.7 74.6 Fe / Ce HEDP 99.2 79.8 79.2 Fe / Ce DTPMPA 98.0 80.4 78.8 Fe / Ce PBTCA 95.1 80.5 76.6 Fe / Ce PAPE 93.9 77.0 72.3 Fe / Ce HDTMPA 97.3 76.7 74.6 Fe / Ce PAPEMP 90.7 78.5 71.2 Fe / Ce BHMTPMPA 92.4 77.8 71.9 .

Claims

1. A low-cost neutral aqueous organic iron cerium flow battery, comprising a positive electrode electrolyte and a negative electrode electrolyte, characterized in that: The active component of the negative electrode electrolyte is a stable chelate formed by iron salt chemicals and organic phosphine ligands, and the active component of the positive electrode electrolyte is a stable chelate formed by cerium salt chemicals and organic phosphine ligands. The reaction of the active substance of the electrolyte on the electrode surface during charging is as follows: Negative electrode reaction: Fe 3+ +e→Fe 2+ Positive electrode reaction: Ce 3+ -e→Ce 4+ The total battery reaction is: Fe 3+ +Ce 3+ →Fe 2+ +Ce 4+ Discharging is the reverse reaction of the above reaction; The organic phosphine ligand is selected from 2-hydroxyphosphonoacetic acid (HPAA), hydroxyethylidene diphosphonic acid (HEDP), diethylene triamine penta (methylene phosphonic acid) (DTPMPA), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), polyol phosphate (PAPE), hexamethylene diamine tetra (methylene phosphonic acid) (HDTMPA), polyamino polyether methylene phosphonic acid (PAPEMP), bis (1,6-hexamethylene triamine penta (methylene phosphonic acid) (BHMTPMPA) and lithium, sodium, potassium, ammonium salt derivative chemicals thereof or a mixture of several thereof.

2. A low-cost neutral aqueous organic iron cerium flow battery according to claim 1, characterized in that: In addition to active substances and ligands, the positive and negative electrolytes also contain a pH supporting electrolyte for stabilizing the chelating structure of the active substances for adjusting the pH, which is selected from one or more of potassium carbonate, sodium carbonate, lithium carbonate, potassium tetraborate, sodium tetraborate, potassium hydroxide, and sodium hydroxide.

3. A low-cost neutral aqueous organic iron cerium flow battery according to claim 1, characterized in that: The iron salt active material used in the negative electrode electrolyte is selected from one or more of ferric chloride, ferric nitrate, ferric acetate, ammonium ferric sulfate, and ferric sulfate; the cerium salt chemicals used in the positive electrode are selected from one or more of cerium trichloride, cerium oxalate, cerium sulfate, cerium acetate, and cerium nitrate.

4. A low-cost neutral aqueous organic iron cerium flow battery according to claim 1, characterized in that: The positive electrode electrolyte is an aqueous solution composed of a stable chelate formed by iron salt chemicals and organic phosphine ligands and a pH supporting electrolyte; The negative electrode electrolyte is an aqueous solution composed of a stable chelate formed by cerium salt chemicals and organic phosphine ligands and a pH supporting electrolyte.

5. A low-cost neutral aqueous organic iron cerium flow battery according to claim 1, characterized in that: The concentration of the positive electrode cerium active material in the electrolyte is 0 to 2 mol / L and not 0, preferably in the range of 0.5 to 1.5 mol / L; the concentration of the negative electrode iron active material in the electrolyte is 0 to 2 mol / L and not 0, preferably in the range of 0.5 to 1.5 mol / L; the ratio of cerium to iron active material is 1.2:1 to 1:1, preferably 1.05:

1. The ratio of the concentration of the organic phosphine ligand to the active material is 2:1 to 1:1; an appropriate pH adjuster is added to adjust the pH of the electrolyte to a neutral range of 5 to 9, preferably pH=7.

6. A low-cost neutral aqueous organic iron cerium flow battery according to claim 1, characterized in that: It includes positive and negative electrodes, battery separators, and current collectors; the positive and negative electrode materials are selected from one of the inert materials of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth, one of Nafion117, Nafion115, Nafion212, and Nafion211 is the battery separator, and the current collector is a metal plate or a carbon bipolar plate.

7. A low-cost neutral aqueous organic iron cerium flow battery according to any one of claims 1 to 6, characterized in that: The operating temperature is 10-90°C, and the electrolyte is circulated by a pump.

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