Alkaline zinc-iron single flow battery

Abstract

The application relates to a kind of basic zinc iron single liquid flow batteries, battery module is formed by one section single battery or two or more single batteries in series or / and parallel, an electrolyte storage tank, a set of electrolyte circulating pump and pipeline composition;Negative electrolyte does not flow, only positive electrolyte flows.Carbon felt as electrode;Graphite plate as current collector.Positive electrolyte is ferrocyanide and strong alkali aqueous solution, and negative active material is zinc salt or zinc oxide and strong alkali reaction generated slurry.The zinc iron single liquid flow battery of the application only needs a set of electrolyte circulating device, the structure is simplified, the failure rate of system operation is reduced, the system maintenance and control cost are saved;The concentration of negative active material is greatly improved, the loss of system is reduced, and the energy efficiency of system is improved.

Description

Technical Field

[0001] This invention relates to the field of flow batteries, and particularly to the field of alkaline zinc-iron flow battery technology. Background Technology

[0002] With the depletion of fossil fuels and the intensification of the global greenhouse effect, renewable energy is playing an increasingly important role in the energy structure. However, the intermittent and unstable nature of renewable energy sources such as wind and solar power makes their direct utilization difficult. Therefore, utilizing energy storage technology to achieve a continuous supply of renewable energy has become key to solving these problems. Zinc-based flow batteries have advantages such as low cost, high theoretical energy density, and high safety, making them one of the promising technologies in the large-scale energy storage market. Compared with other zinc-based flow batteries, zinc-iron flow batteries are more suitable for distributed energy storage due to their low cost and relatively high energy density.

[0003] Traditional alkaline zinc-iron flow batteries employ a dual-pump, dual-pipeline design, where the electrolyte circulates within the battery and in a storage tank during charging and discharging. On one hand, the need for two electrolyte circulation systems results in significant energy loss during operation; on the other hand, auxiliary equipment such as pumps and storage tanks complicate the battery structure, reduce energy density, and increase the risk of system failure. Therefore, optimizing traditional alkaline zinc-iron dual-flow batteries is both necessary and urgent. Summary of the Invention

[0004] To address the above technical problems, this invention proposes an alkaline zinc-iron single-flow battery, the specific technical solution of which is as follows:

[0005] A zinc-iron single-flow battery includes a single cell and a battery module consisting of multiple single cells connected in series / parallel, and is equipped with a positive electrolyte storage tank, a circulation pump and circulation pipeline; the single cell includes positive and negative current collectors, electrodes and ion conduction membranes.

[0006] The electrode is a carbon felt electrode.

[0007] The positive electrode electrolyte is an aqueous solution formed by dissolving ferrocyanide in a strong alkaline solution, and the negative electrode active material is a slurry prepared by dissolving zinc salt in a strong alkaline solution.

[0008] The ferrocyanide in the positive electrode electrolyte includes one or more of potassium ferrocyanide, sodium ferrocyanide, magnesium ferrocyanide, lithium ferrocyanide, or calcium ferrocyanide; sodium ferrocyanide is preferred. The strong alkali includes one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide; potassium hydroxide is preferred.

[0009] The zinc salt in the negative electrode active material slurry includes one or more of zinc hydroxide, zinc chloride, zinc bromide, zinc iodide, zinc oxide, zinc carbonate, zinc nitrate, and zinc sulfate, preferably zinc bromide. The strong alkali includes one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide, preferably potassium hydroxide.

[0010] The beneficial effects of this invention are:

[0011] 1. Zinc-iron single-flow battery only requires one electrolyte circulation device. Compared with the two electrolyte circulation systems of traditional zinc-iron dual-flow battery, the structure is simplified, the failure rate of system operation is reduced, and the system maintenance and control costs are saved.

[0012] 2. Not only is the concentration of active material in the negative electrode significantly increased, but the battery operation requires only one set of pipelines, resulting in a substantial increase in energy density compared to the traditional zinc-iron dual-flow system. Simultaneously, system losses are reduced, and system energy efficiency is improved.

[0013] 3. Compared with existing technologies, an alkaline paste containing negative electrode active material is directly coated onto the electrode substrate. The high concentration of strong alkali can act as a binder. Compared with the paste of existing technologies, no other components (binder, conductive agent) are introduced, which comprehensively improves the battery voltage efficiency and power density.

[0014] 4. The zinc-iron single-flow battery of the present invention effectively avoids the flow channel blockage problem caused by zinc shedding during the charging and discharging process of traditional zinc-iron flow batteries, thus improving the reliability of the battery.

[0015] 5. The zinc-iron single-flow battery of the present invention has a certain amount of alkali added to the negative electrode, which can effectively increase the working current density of the battery, thereby increasing the power of the battery.

[0016] 6. Compared with the prior art, the negative electrode preparation process of the present invention does not contain binders, which will not reduce the active surface area of ​​the negative electrode; there is also no addition of high specific surface area conductive carbon in the preparation process, thereby avoiding rapid corrosion of metallic zinc due to carbon catalytic oxygen reduction. Attached Figure Description

[0017] Figure 1 Schematic diagram of an alkaline zinc-iron single-flow battery. 1. Negative electrode current collector, 2. Positive electrode current collector, 3. Separator, 4. Positive electrode electrolyte, 5. Pump, 6. Positive electrode carbon felt, 7. Negative electrode carbon felt, 8. End plate. Detailed Implementation

[0018] Example 1

[0019] The alkaline zinc-iron single-flow battery negative electrode active material electrode is prepared according to the following process:

[0020] A zinc bromide aqueous solution was added to a potassium hydroxide aqueous solution, with a final zinc bromide concentration of 0.8 mol / L and a final potassium hydroxide concentration of 2.4 mol / L. The mixture was stirred continuously for 2 hours, and water was evaporated to obtain a paste. This paste was then applied to one side of a carbon felt electrode, with a paste concentration of 1 g / cm³ on the electrode. 2 It is applied to the carbon felt electrode; the solid content of the paste is 70%; the standard electrode potential of the negative electrode is -1.25V (relative to the standard hydrogen electrode); the actual battery discharge voltage can be higher than 1.6V.

[0021] Assemble an alkaline zinc-iron single-flow battery in the following order: positive electrode plate, graphite current collector, and positive electrode carbon felt (3*3*0.6cm). 2 ), ion-conducting membrane, and carbon felt negative electrode with paste-like substance (3*3*0.6cm) 2 The battery consists of a graphite current collector and a negative electrode plate. It is only equipped with a positive electrolyte reservoir (containing 150ml of electrolyte), a circulation pump, and piping. The battery structure is as follows: Figure 1 As shown. The positive electrolyte in the positive electrode electrolyte storage tank flows through a circulation pump and pipeline into the chamber between the graphite current collector and the ion-conducting membrane where the positive electrode is located. The positive electrolyte is an aqueous solution of 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide. The negative electrode uses the carbon felt negative electrode prepared above and coated with a paste. 20 mA / cm 2 Constant current charging and discharging, charging time is 4 hours, charging surface capacity is 80mAh / cm². 2 The charging cutoff voltage is 2V, and the discharging cutoff voltage is 0.4V. The average coulombic efficiency of the battery for the first 40 cycles is 95.5%, and the average energy efficiency is 78.4%.

[0022] Comparative Example 1

[0023] Same as Example 1, except that the negative electrode is a carbon felt (3*3*0.6cm). 2 A 70% zinc bromide solution at a concentration of 20 mA / cm² is injected into the cavity between the graphite current collector (located at the negative electrode) and the ion-conducting membrane. 2 Constant current charge / discharge, charging time up to 4 hours. The battery is equipped only with a positive electrolyte reservoir (containing 150ml of electrolyte), a circulation pump, and piping. The battery structure is as follows. Figure 1As shown. The positive electrolyte in the positive electrode reservoir flows through a circulation pump and pipeline into the chamber between the graphite current collector and the ion-conducting membrane at the positive electrode. The positive electrolyte is an aqueous solution of 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide. The standard negative electrode potential is -0.76V (relative to the standard hydrogen electrode), mainly because the negative electrolyte is slightly acidic, and the actual battery discharge voltage does not exceed 1.2V. Furthermore, because the negative electrolyte is acidic and the positive electrolyte is alkaline, the positive and negative electrolytes are incompatible, and the battery cannot achieve more than 10 charge-discharge cycles with a coulombic efficiency greater than 80%. Therefore, it cannot achieve the performance of the zinc-iron single-fluid battery of Example 1.

[0024] Comparative Example 2

[0025] Same as Example 1, except that the negative electrode is a carbon felt (3*3*0.6cm). 2 The battery is equipped with a positive electrolyte reservoir (containing 150ml of electrolyte, a 0.5mol / L sodium ferrocyanide + 1.25mol / L potassium hydroxide aqueous solution), a positive electrode circulation pump, and tubing. It also has a negative electrolyte reservoir (containing 150ml of a paste-like substance with a solid content of 70%) and a negative electrode circulation pump. The positive electrolyte in the reservoir flows through the positive electrode circulation pump and tubing between the graphite current collector and the ion-conducting membrane at the positive electrode. The negative electrode paste in the reservoir attempts to flow through the negative electrode circulation pump and tubing between the graphite current collector and the ion-conducting membrane at the negative electrode. The standard negative electrode potential is -1.25V (relative to the standard hydrogen electrode). If the circulation pump cannot drive the paste-like substance through the battery, or if the negative electrode active material clogs the pump or / and tubing, the voltage will be 20mA / cm. 2 During constant current charging and discharging, the battery voltage rises to the cutoff voltage of 2V after 4 hours of charging, which cannot achieve the performance of the zinc-iron single-liquid flow battery in Example 1.

[0026] Comparative Example 3

[0027] Similar to Example 1, but differing in that the paste applied to the negative electrode consisted of zinc oxide added to a potassium hydroxide solution at a mass ratio of zinc to potassium hydroxide of 10:1. The solid content of the paste was 70%, and the standard electrode potential of the negative electrode was -1.25V (relative to the standard hydrogen electrode). Due to the excessively low concentration of potassium hydroxide, the zinc oxide in the negative electrode electrolyte could not be effectively utilized. 20mA / cm 2 During constant current charging and discharging, the battery cannot be charged for 4 hours before the voltage rises to the cutoff voltage of 2V, failing to achieve the performance of the zinc-iron single-liquid flow battery of Example 1.

[0028] Example 2

[0029] Similar to Example 1, except that zinc chloride was added to a sodium hydroxide solution, with a final concentration of 0.8 mol / L for zinc chloride and 5 mol / L for sodium hydroxide. The mixture was stirred continuously for 2 hours, and water was evaporated to obtain a paste. The solid content of the paste was 65%. This paste was then applied to one side of a carbon felt electrode, with a paste concentration of 1 g / cm³ on the electrode. 2 The negative electrode standard potential is -1.25V (relative to the standard hydrogen electrode). 20mA / cm 2 Constant current charging and discharging, charging time is 4 hours, charging surface capacity is 80mAh / cm². 2 The charging cutoff voltage is 2V, and the discharging cutoff voltage is 0.4V. The average coulombic efficiency of the battery in the first 40 cycles is 94.9%, and the average energy efficiency is 77.8%, which is at the same level as in Example 1.

[0030] Example 3

[0031] Similar to Example 1, except that zinc chloride was added to a sodium hydroxide solution, with a final concentration of 0.8 mol / L for zinc chloride and 5 mol / L for sodium hydroxide. The mixture was stirred continuously for 2 hours, and water was evaporated to obtain a paste. The solid content of the paste was 85%. This paste was then applied to one side of a carbon felt electrode, with a paste concentration of 1 g / cm³ on the electrode. 2 The negative electrode standard potential is -1.25V (relative to the standard hydrogen electrode). 20mA / cm 2 Constant current charging and discharging, charging time is 4 hours, charging surface capacity is 80mAh / cm². 2 The charging cutoff voltage is 2V, and the discharging cutoff voltage is 0.4V. The average coulombic efficiency of the battery in the first 40 cycles is 95.3%, and the average energy efficiency is 78.1%, which is at the same level as in Example 1.

[0032] Example 4

[0033] Similar to Example 1, except that in Example 1, an aqueous solution of zinc bromide was added to an aqueous solution of potassium hydroxide, with a final concentration of zinc bromide of 0.8 mol / L and a final concentration of potassium hydroxide of 5 mol / L. The mixture was stirred continuously for 2 hours, and water was evaporated to obtain a paste. The solid content of the paste was 76%. This paste was then applied to one side of a carbon felt electrode, with a concentration of 0.7 g / cm³ on the electrode. 2 The average coulombic efficiency of the battery in the first 40 cycles was 94.7%, and the average energy efficiency was 77.5%, which is at the same level as in Example 1.

Claims

1. A zinc-iron alkaline single flow battery, comprising a battery module composed of one or two single batteries in series and / or parallel, characterized in that: the single battery comprises a positive current collector, a carbon felt positive electrode, an ion-conducting membrane, a carbon felt negative electrode with paste, and a negative current collector arranged in sequence; further comprising a positive electrolyte storage tank, a circulating pump, and a circulating pipeline; the positive electrolyte in the positive electrolyte storage tank flows through the circulating pump and the pipeline to the chamber between the graphite current collector and the ion-conducting membrane where the positive electrode is located; the carbon felt negative electrode with paste is prepared according to the following process: A zinc source is added to a strong aqueous alkali solution to obtain a mixed solution, the stirring is continued for more than 10 minutes, water is evaporated to obtain a paste, and the paste is applied to a carbon felt electrode; the solid content of the paste is 60-90%, and the amount of the paste on the carbon felt electrode is 0.2-1.5 g / cm 2 .

2. The battery according to claim 1, characterized in that: the zinc source comprises one or more of zinc hydroxide, zinc chloride, zinc bromide, zinc iodide, zinc oxide, zinc carbonate, zinc nitrate, and zinc sulfate; and the strong base comprises one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

3. The battery according to claim 1 or 2, characterized in that: the concentration of the strong base is 1-10 mol / L; the molar ratio of the strong base to zinc in the zinc source added during the preparation of the paste is 0.2-5:

1.

4. The battery according to claim 1, characterized in that: the positive electrolyte is an aqueous solution formed by dissolving ferrocyanide in a strong base solution; the ferrocyanide in the positive electrolyte comprises one or more of potassium ferrocyanide, sodium ferrocyanide, magnesium ferrocyanide, lithium ferrocyanide, and calcium ferrocyanide; the strong base comprises one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide; the concentration of the ferrocyanide in the positive electrolyte is 0.3-0.8 mol / L, and the concentration of the strong base is 0.5-4 mol / L.

5. The battery according to claim 1, characterized in that: A zinc source is added to a strong aqueous alkali solution to obtain a mixed solution, the stirring is continued for 2-10 hours, water is evaporated to obtain a paste, which is applied to a carbon felt electrode; the solid content of the paste is 65-80%, and the amount of the paste on the carbon felt electrode is 1 g / cm 2 .

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