Low cost neutral aqueous organic iron-cerium flow battery

Abstract

A low-cost, neutral aqueous organic iron-cerium flow battery belongs to the field of electrochemical energy storage. Both the positive and negative electrolytes utilize aqueous organophosphorus ligands chelated with metals. The organophosphorus ligands are selected from one or more of the following: 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, hexamethylenediaminetetramethylidene phosphonic acid, polyaminopolyethermethyleneidene phosphonic acid, bis(1,6-hexylenetriaminepentamethylidene phosphonic acid), and their lithium, sodium, potassium, and ammonium salt derivatives. A supporting electrolyte is also included to adjust and stabilize the pH environment of the electrolyte. This invention achieves high conductivity and stable performance without the need for additional auxiliary electrolytes, opening up new possibilities for the development and application of flow battery technology. It features stable performance, low cost, widely available raw materials, and environmental friendliness, making it suitable for automotive power supplies, residential energy storage, backup power supplies, and large-scale energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically a low-cost, neutral aqueous organic iron-cerium flow battery that can be widely used in automotive power supplies, residential energy storage, backup power supplies, and large-scale energy storage devices such as wind and solar power. Background Technology

[0002] Currently, in the field of large-scale energy storage, flow batteries have received widespread attention due to their intrinsic safety. However, all-vanadium redox flow batteries face challenges such as high vanadium raw material costs and severe self-discharge, which significantly hinder their further development. In this context, developing low-cost, fully soluble flow batteries holds promise as a highly attractive alternative. Existing low-cost routes typically rely on iron-based flow batteries. However, the traditional technical route involves the deposition and stripping of Fe on the electrode at the negative electrode. The coordination structure of Fe ions with water easily triggers hydrogen evolution reactions, accelerating battery failure and capacity loss, and reducing the lifespan of the flow battery. Furthermore, some positive electrode ferrocyanide electrolytes also suffer from the problem of ferric hydroxide precipitation. To address the issues of iron precipitation at the negative electrode and precipitation at the positive electrode, this invention utilizes a novel organophosphorus ligand chelation method to prepare a low-cost, neutral aqueous organic iron-cerium flow battery. It is worth noting that the organophosphorus ligands innovatively used in this invention are all currently commercially available water additive products, commonly used in wastewater treatment and pipeline water scale and corrosion inhibition. They are characterized by low cost and wide availability, and do not require the addition of additional auxiliary electrolytes, opening up new possibilities for the development and application of flow battery technology. Summary of the Invention

[0003] The purpose of this invention is to provide a low-cost, neutral aqueous organic iron-cerium flow battery that is stable in performance and environmentally friendly, overcoming the problems of metal dendrite formation, hydrogen evolution reaction, severe self-discharge, and high cost in existing flow battery technologies, and expanding the market for China's abundant cerium resources.

[0004] This invention discloses a low-cost, neutral aqueous organic iron-cerium flow battery, which is mainly an improvement on existing flow batteries. The key to this invention lies in the electrolyte, specifically the negative electrode electrolyte, whose active component is a chelate of iron salt chemicals and organophosphorus ligands, and the positive electrode electrolyte, whose active component is a chelate of cerium salt chemicals and organophosphorus ligands, further enhanced by a supporting electrolyte to adjust the pH to a neutral environment.

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

[0006] 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 organophosphorus ligands, and the active component of the positive electrode electrolyte is a stable chelate formed by cerium salt chemicals and organophosphorus ligands. The reactions occurring on the electrode surfaces of the active materials in the electrolytes during charging are as follows:

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

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

[0009] The overall cell reaction is: Fe 3+ +Ce 3+ →Fe 2+ +Ce 4+

[0010] The discharge is the reverse reaction of the above reaction.

[0011] The organophosphine ligands are selected from one or a mixture of several of the following: 2-hydroxyphosphonoacetic acid (HPAA), hydroxyethylidene diphosphonic acid (HEDP), diethylenetriaminepentanephosphonic acid (DTPMPA), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), polyol phosphate (PAPE), hexamethylenediaminetetramethylenephosphonic acid (HDTMPA), polyaminopolyethermethylenephosphonic acid (PAPEMP), bis(1,6-hexylenetriaminepentanephosphonic acid) (BHMTPMPA), and their lithium, sodium, potassium, and ammonium salt derivatives.

[0012] In addition to the active substances and ligands, the positive and negative electrode electrolytes also contain pH-supporting electrolytes for stabilizing the chelate structure of the active substances and for adjusting the pH. These electrolytes are 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, ferric ammonium sulfate, and ferric sulfate; the cerium salt chemical used in the positive electrode is 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 consisting of a stable chelate formed by iron salt chemicals and organophosphorus ligands, and a pH-supporting electrolyte.

[0015] The negative electrode electrolyte is an aqueous solution consisting of a stable chelate formed by cerium salt chemicals and organophosphorus ligands, and a pH-supporting electrolyte.

[0016] The concentration of cerium active material in the positive electrode of the electrolyte is 0–2 mol / L and not zero, preferably 0.5–1.5 mol / L; the concentration of iron active material in the negative electrode of the electrolyte is 0–2 mol / L and not zero, preferably 0.5–1.5 mol / L; the ratio of cerium to iron active material is 1.2:1 to 1:1, preferably 1.05:1. The concentration ratio of organophosphorus ligand to 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 5–9, preferably pH = 7.

[0017] The low-cost, neutral aqueous organic iron-cerium flow battery includes positive and negative electrodes, a battery separator, and a current collector.

[0018] The positive and negative electrode materials are selected from one of the following inert materials: 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 10-90℃. 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 electrode electrolytes of this invention form stable compounds with iron salts, cerium salts and organophosphorus ligands through chelation coordination, which avoids the problems of iron forming metal dendrites and hydrogen evolution reaction in traditional processes, improves the life of flow batteries and reduces the operating cost of flow battery systems.

[0021] 2. Organophosphine ligands contain multiple P, N, and O groups. The introduction of these ligands can disrupt the original solvation structure of iron and cerium in H₂O, allowing iron and cerium to form new coordination groups with the O and N groups in the ligands. Simultaneously, the presence of P further enhances the electron-donating ability of O, thereby increasing the coordination stability with the active substance.

[0022] 3. The larger molecular volume of chelates enhances steric hindrance, eliminates capacity and energy losses caused by ligand transmembrane transport, improves battery stability, and reduces the loss of active materials caused by side reactions.

[0023] 4. The active substances, chelating agents, and supporting electrolytes used in this invention are all industrial chemicals that are widely used in the market. The production process is simple, the cost is low, it is easy to scale up, and there are no environmental or safety hazards.

[0024] 5. The rare earth metal elements used in this invention are domestically advantageous resources, providing a new option for comprehensive, circular, and green utilization, and have broad application prospects and potential.

[0025] 6. Thanks to the properties of organophosphorus ligands, the electrolyte of this invention can operate normally in a higher temperature range, with the operating temperature range extended to 90°C (the limit temperature of existing flow batteries is 60-70°C, while the temperature of this invention exceeds the above limit temperature, and can even operate at a temperature of (60-70)-90°C). Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an iron-cerium redox flow battery.

[0027] Figure 2 This is a schematic diagram of the molecular structure of organophosphine ligands.

[0028] Figure 3 The charge-discharge curves of the iron-cerium redox flow battery in Example 1 are shown.

[0029] Figure 4 The results show the cycle efficiency of the iron-cerium flow battery in Example 1.

[0030] Figure 5 The results show the cycle efficiency of the iron-cerium flow battery in Example 2.

[0031] Figure 6 The results show the cycle efficiency of the iron-cerium flow battery in Example 3.

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

[0033] Table 1 shows the average CE, VE, and EE of different electrolytes in battery testing. Detailed Implementation

[0034] The present invention will be described in detail below through specific embodiments. However, the purpose and use of these illustrative embodiments are only for illustrating the present invention and do not constitute any limitation on the actual protection scope of the present invention, nor are they intended to limit the protection scope of the present invention to these embodiments.

[0035] Example 1:

[0036] like Figure 1 The schematic diagram of the iron-cerium redox flow battery shown mainly includes a single cell, positive and negative electrode storage tanks, a peristaltic pump, and corrosion-resistant circulation piping. The single cell assembly includes: an aluminum end plate, a polytetrafluoroethylene (PTFE) gasket, a current collector, a graphite bipolar plate, a fluororubber gasket, a proton exchange membrane, and a graphite felt electrode. During testing, the positive and negative electrolytes flow into the single cell via the pump, undergo a redox reaction, and then return to the electrolyte tank. The active component of the negative electrode electrolyte is a chelate of iron salt chemicals and organophosphorus ligands, and the active component of the positive electrode electrolyte is a chelate of cerium salt chemicals and organophosphorus ligands. A supporting electrolyte is then added to adjust the pH to a neutral environment.

[0037] Figure 2 This is a schematic diagram of the molecular structure of organophosphorus ligands. Organophosphorus ligands contain multiple N, P, and O groups. The introduction of these ligands disrupts the original solvation structure of iron and cerium in H₂O, allowing iron and cerium to form new coordination groups with the O and N groups in the ligands. Simultaneously, the presence of P further enhances the electron-donating ability of O, thereby increasing the coordination stability with the active substance.

[0038] In this embodiment, the negative electrode electrolyte uses ferric sulfate as the iron salt, organophosphorus ligand HPAA as the chelating agent, potassium tetraborate as the supporting electrolyte, and deionized water as the solvent. The iron ion concentration is 0.5 mol / L, the HPAA concentration is 1 mol / L, and potassium tetraborate is added to adjust the final pH of the solution to approximately 7.

[0039] In this embodiment, the cerium salt used in the positive electrode electrolyte is cerium sulfate, the chelating agent is the organophosphorus ligand HPAA, potassium tetraborate is the supporting electrolyte, and deionized water is the solvent. The concentration of cerium ions is 0.5 mol / L, the concentration of the organophosphorus ligand HPAA is 1 mol / L, and potassium tetraborate is added to adjust the final pH of the solution to approximately 7.

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

[0041] The aforementioned iron-cerium flow battery was subjected to 1000 charge-discharge cycles, with the charge-discharge current set to 80 mA / cm². 2 The upper and lower limits for charging and discharging are 1.2V and 0.01V, respectively, and the results of their charge-discharge curves are as follows: Figure 3 As shown, Fe / Ce HPAA exhibits excellent performance. Figure 4 The efficiency results of the flow battery in the embodiment are shown over 1000 cycles at 100% state of charge (SOC). At the beginning of the cycle, the coulombic efficiency (CE) is ~93%, which gradually increases as the cycle progresses and eventually stabilizes at around ~99%. Its energy efficiency (EE) stabilizes at ~77% after a certain number of cycles, which fully demonstrates the cycle stability of the battery.

[0042] Example 2:

[0043] In this embodiment, the negative electrode electrolyte uses ferric chloride as the iron salt, the chelating agent is the organophosphorus ligand HEDP, potassium carbonate is the supporting electrolyte, and deionized water is the solvent. The iron ion concentration is 0.5 mol / L, the HEDP concentration is 1 mol / L, and potassium carbonate is added to adjust the final pH of the solution to approximately 7.

[0044] In this embodiment, the cerium salt used in the positive electrode electrolyte is cerium chloride, the chelating agent is the organophosphorus ligand HEDP, the supporting electrolyte is potassium carbonate, and the solvent is deionized water. The concentration of cerium ions is 0.5 mol / L, the concentration of the organophosphorus ligand HEDP is 1 mol / L, and potassium carbonate is added to adjust the final pH of the solution to approximately 7.

[0045] The remaining steps are the same as in Example 1. Figure 5 The results show the battery cycle efficiency (200 cycles) of the electrolyte in Example 2 above. The results indicate that its coulombic efficiency remained close to 100%, and the battery performance increased slightly with each cycle. This is because the membrane material and electrolyte were incompatible in the early stages of cycling; as cycling progressed and the electrolyte and membrane material were activated and wetted, the battery performance gradually improved.

[0046] Example 3:

[0047] In this embodiment, the negative electrode electrolyte uses ferric chloride as the iron salt, the chelating agent is the organophosphorus ligand DTPMPA, lithium carbonate is the supporting electrolyte, and deionized water is the solvent. The iron ion concentration is 0.5 mol / L, the DTPMPA concentration is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to approximately 7.

[0048] In this embodiment, the cerium salt used in the positive electrode electrolyte is cerium chloride, the chelating agent is the organophosphorus ligand DTPMPA, potassium carbonate is the supporting electrolyte, and deionized water is the solvent. The concentration of cerium ions is 0.5 mol / L, the concentration of the organophosphorus ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to approximately 7.

[0049] The remaining steps are the same as in Example 1. Figure 6 The results show the battery cycle efficiency of the electrolyte in Example 3 above. The results indicate that, compared to Examples 1 and 2, the stability was further improved by introducing nitrogen into the organophosphorus ligand backbone and adding more phosphonic acid, while reducing the amount of organophosphorus ligand used. It exhibited superior stability compared to the electrolyte described above within 500 cycles, with CE and EE consistently greater than 97% and 78% respectively (EE remained approximately around 80%).

[0050] Example 4:

[0051] In this embodiment, the negative electrode electrolyte uses ferric chloride as the iron salt, the chelating agent is the organophosphorus ligand DTPMPA, lithium carbonate is the supporting electrolyte, and deionized water is the solvent. The iron ion concentration is 0.5 mol / L, the DTPMPA concentration is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to approximately 7.

[0052] In this embodiment, the cerium salt used in the positive electrode electrolyte is cerium chloride, the chelating agent is the organophosphorus ligand DTPMPA, potassium carbonate is the supporting electrolyte, and deionized water is the solvent. The concentration of cerium ions is 0.5 mol / L, the concentration of the organophosphorus ligand DTPMPA is 0.5 mol / L, and lithium carbonate is added to adjust the final pH of the solution to approximately 7.

[0053] The test conditions were set to raise the room temperature to 90°C, and the remaining steps were the same as in Example 3. Figure 7 The results show the cycle efficiency of the iron-cerium flow battery in Example 4 at 90°C. Within 80 cycles, CE and EE decreased slightly compared to room temperature. This is because the increased molecular thermal motion at high temperatures leads to enhanced membrane permeability, exacerbating self-discharge and side reactions, but overall, a stable EE > 70% was maintained.

[0054] The remaining ligands were configured according to the proportions of the methods in Examples 1 and 2. The battery test results are the average efficiency over 100 cycles, which are summarized in Table 1.

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

[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 organophosphorus ligands, while the active component of the positive electrode electrolyte is a stable chelate formed by cerium salt chemicals and organophosphorus ligands. The reactions that occur on the electrode surface of the active materials of the electrolyte during charging are as follows: Negative electrode reaction: Fe 3+ + e → Fe 2+ Positive electrode reaction: Ce 3+ - e → Ce 4+ The overall cell reaction is: Fe 3+ + Ce 3+ → Fe 2+ + Ce 4+ The discharge is the reverse reaction of the above reaction; The organophosphine ligand is selected from one or a mixture of several of the following: 2-hydroxyphosphonoacetic acid (HPAA), hydroxyethylidene diphosphonic acid (HEDP), diethylenetriaminepentamethylenephosphonic acid (DTPMPA), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), polyol phosphate (PAPE), hexamethylenediaminetetramethylenephosphonic acid (HDTMPA), polyaminopolyethermethylenephosphonic acid (PAPEMP), bis(1,6-hexylenetriaminepentamethylenephosphonic acid) (BHMTPMPA), and their lithium, sodium, potassium, and ammonium salt derivatives; the supporting electrolyte adjusts the pH to neutral. The iron-cerium redox flow battery can operate at a temperature of 90°C, and the electrolyte is circulated by a pump.

2. A low-cost, neutral aqueous organic iron-cerium flow battery according to claim 1, characterized in that, In addition to the active substances and ligands, the positive and negative electrode electrolytes also contain pH-supporting electrolytes for stabilizing the chelate structure of the active substances and for adjusting the pH. These electrolytes are 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, ferric ammonium sulfate, and ferric sulfate; the cerium salt chemical used in the positive electrode is 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 negative electrode electrolyte is an aqueous solution consisting of a stable chelate formed by iron salt chemicals and organophosphorus ligands, and a pH-supporting electrolyte. The positive electrode electrolyte is an aqueous solution consisting of a stable chelate formed by cerium salt chemicals and organophosphorus 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 cerium active material in the positive electrode in the electrolyte is 0 ~ 2 mol / L and not 0; the concentration of iron active material in the negative electrode in the electrolyte is 0 ~ 2 mol / L and not 0; the ratio of cerium to iron active material is 1.2:1 ~ 1:1; the ratio of organophosphorus ligand concentration to active material concentration is 2:1 ~ 1:1; an appropriate pH adjuster is added to adjust the pH of the electrolyte to a neutral range of 5 ~ 9.

6. A low-cost, neutral aqueous organic iron-cerium flow battery according to claim 5, characterized in that, The concentration of cerium active material in the positive electrode in the electrolyte is 0.5 ~ 1.5 mol / L; the concentration of iron active material in the negative electrode in the electrolyte is 0.5 ~ 1.5 mol / L; the ratio of cerium to iron active material is 1.05:1; and the pH of the electrolyte is adjusted to 7.

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

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