Alkaline zinc-iron flow battery and preparation method thereof

Abstract

The invention discloses an alkaline zinc-iron flow battery and a preparation method thereof, and belongs to the technical field of flow batteries. The alkaline zinc-iron flow battery provided by the invention comprises a positive electrode electrolyte, a composite diaphragm and a negative electrode electrolyte, the positive electrode electrolyte and the negative electrode electrolyte are symmetrically positioned on the two sides of the composite diaphragm respectively; the composite diaphragm comprises a sulfonated polyether ether ketone diaphragm and a polybenzimidazole diaphragm; the sulfonated polyether ether ketone diaphragm is attached to the polybenzimidazole diaphragm; the sulfonated polyetheretherketone diaphragm faces the positive electrode side; the polybenzimidazole diaphragm faces the negative electrode side; the positive electrode electrolyte comprises Fe (CN) 6 < 4-> and OH <->; the negative electrode electrolyte is prepared from a zinc source, a complexing agent and an alkali source. The SPEEK diaphragm and the PBI diaphragm are compounded, and a complexing agent is effectively separated by the PBI diaphragm, so that the coulombic efficiency of the galvanic pile is improved, and the overall performance of the galvanic pile is improved; the problem of cathode zinc accumulation is solved and the cycling stability of the stack is improved.

Description

Technical Field

[0001] This application belongs to the technical field of flow batteries, and particularly relates to an alkaline zinc-iron flow battery and a preparation method thereof. Background Art

[0002] With the increasing depletion of fossil energy, the development and utilization of renewable energy sources such as wind energy and solar energy have become the focus of attention of various countries. Due to the discontinuous and unstable nature of wind energy and solar energy affected by factors such as weather, it will cause an impact on the power grid during the grid connection process of renewable energy power generation, affecting the power supply quality and grid stability. Energy storage technology can solve this problem and ensure the efficient and stable operation of renewable energy power generation grid connection. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among them, chemical energy storage represented by flow batteries has the most advantages in large-scale energy storage due to its many advantages such as independent power and capacity, rapid response, simple structure, easy design, long cycle life, and environmental friendliness. The alkaline zinc-iron flow battery uses zinc and iron with rich resources as active substances, and has the characteristics of low cost (~$100 / kWh) and high open-circuit voltage (1.74V), and has good application prospects in the field of energy storage, especially in the field of distributed energy storage.

[0003] In the invention patent CN116111142A, different from the traditional alkaline zinc-iron flow battery in which zinc exists in the form of alkaline zincate, by adopting a complexed zinc ion form at the negative electrode of the alkaline zinc-iron flow battery, the electrolyte migration problem in the alkaline zinc-iron flow battery is solved, and the battery cycle stability is improved; at the same time, the low-temperature performance of the battery is improved, and the working temperature range of the alkaline zinc-iron flow battery is broadened. However, in this system, when assembling the stack, there are obvious problems such as a significant decrease in the Coulomb efficiency of the battery and an increase in battery polarization, resulting in poor battery cycle stability. Summary of the Invention

[0004] To solve the main technical problems existing in the above-mentioned prior art, this application provides an alkaline zinc-iron flow battery and a preparation method thereof. By compounding the SPEEK separator with the polybenzimidazole (PBI) separator and utilizing the effective separation of the PBI membrane from the complexing agent, the Coulomb efficiency of the stack is improved, and the overall performance of the stack is enhanced; the problem of zinc accumulation at the negative electrode is solved, and the cycle stability of the stack is improved. At the same time, by optimizing the electrolyte formula and increasing the molar ratio of the complexing agent to zinc ions in the electrolyte, the problem that zinc hydroxide precipitates in the electrolyte due to insufficient complexing during the operation of the stack, resulting in a decline in battery performance or even battery failure, is solved.

[0005] To achieve the above-mentioned invention purpose, this application provides the following technical solutions:

[0006] On the one hand, this application provides an alkaline zinc-iron flow battery, including a positive electrolyte, a composite separator, and a negative electrolyte;

[0007] The positive electrode electrolyte and the negative electrode electrolyte are symmetrically located on both sides of the composite separator respectively;

[0008] The composite separator includes a sulfonated polyether ether ketone separator and a polybenzimidazole separator;

[0009] The sulfonated polyether ether ketone separator is adhered to the polybenzimidazole separator;

[0010] The sulfonated polyether ether ketone separator faces the positive electrode side;

[0011] The polybenzimidazole separator faces the negative electrode side;

[0012] The positive electrode electrolyte contains Fe(CN)6 4- and OH - ;

[0013] The negative electrode electrolyte is prepared from a zinc source, a complexing agent, and an alkali source.

[0014] Optionally, the molar concentration of the Fe(CN)6 4- is 0.4 - 2 M;

[0015] The molar concentration of the OH - is 0.4 - 2 M.

[0016] Preferably, the molar concentration of the Fe(CN)6 4- is 0.6 - 1 M;

[0017] The molar concentration of the OH - is 0.6 - 1 M.

[0018] Optionally, the molar concentration of the Fe(CN)6 4- is independently selected from any value of 0.4 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, 2 M or a range value between any two of them.

[0019] Optionally, the molar concentration of the OH - is independently selected from any value of 0.4 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, 2 M or a range value between any two of them.

[0020] Optionally, the zinc source includes at least one of zinc sulfate, zinc bromide, zinc chloride, zinc nitrate, zinc acetate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, zinc bis(oxalato)borate.

[0021] Optionally, the complexing agent includes at least one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid, cyclohexanetetraacetic acid, ethylenediaminetetrapropionic acid.

[0022] Optionally, the base source includes NaOH and / or KOH.

[0023] Optionally, the molar ratio of the zinc source to the complexing agent is 1:1.1 to 1.5.

[0024] Optionally, the molar ratio of the zinc source to the complexing agent is independently selected from any value among 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or the range value between any two of them.

[0025] Optionally, the molar ratio of the complexing agent to the base source is 1:1.1 to 1.3.

[0026] Optionally, the molar ratio of the complexing agent to the base source is independently selected from any value among 1:1, 1:2, 1:3 or the range value between any two of them.

[0027] In a second aspect, the present application also provides a method for preparing the above alkaline zinc-iron flow battery, including the following steps:

[0028] (1) Obtain the positive electrolyte;

[0029] (2) Obtain the negative electrolyte;

[0030] (3) Bond the sulfonated polyether ether ketone membrane and the polybenzimidazole membrane to obtain a composite membrane;

[0031] (4) Symmetrically place the positive electrolyte and the negative electrolyte on both sides of the composite membrane, wherein the sulfonated polyether ether ketone membrane in the composite membrane faces the positive electrode side and the polybenzimidazole membrane faces the negative electrode side, and assemble to obtain the alkaline zinc-iron flow battery.

[0032] Optionally, in step (1), the positive electrolyte contains Fe(CN)6 4- and OH - .

[0033] Optionally, the molar concentration of Fe(CN)6 4- is 0.4 to 2 M;

[0034] The molar concentration of OH - is 0.4 to 2 M.

[0035] Preferably, the molar concentration of Fe(CN)6 4- is 0.6 to 1 M;

[0036] The molar concentration of OH - is 0.6 to 1 M.

[0037] Optionally, the Fe(CN)6 4-The molar concentration of is independently selected from any value among 0.4M, 0.6M, 0.8M, 1M, 1.2M, 1.4M, 1.6M, 1.8M, 2M or a range value between any two of them.

[0038] Optionally, the OH - The molar concentration of is independently selected from any value among 0.4M, 0.6M, 0.8M, 1M, 1.2M, 1.4M, 1.6M, 1.8M, 2M or a range value between any two of them.

[0039] Optionally, step (2) includes: mixing a complexing agent with an alkali source, then adding a zinc source, and adjusting the pH value of the system to 9 - 13 to obtain a negative electrode electrolyte.

[0040] Optionally, the zinc source includes at least one of zinc sulfate, zinc bromide, zinc chloride, zinc nitrate, zinc acetate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, zinc bis(oxalato)borate.

[0041] Optionally, the complexing agent includes at least one of ethylenediaminetetraacetic acid, ethylene glycol bis(2 - aminoethyl ether) - N,N,N',N'-tetraacetic acid, cyclohexanetetraacetic acid, ethylenediaminetetrapropionic acid.

[0042] Optionally, the alkali source includes NaOH and / or KOH.

[0043] Optionally, the molar ratio of the zinc source to the complexing agent is 1:1.1 - 1.5.

[0044] Optionally, the molar ratio of the zinc source to the complexing agent is independently selected from any value among 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or a range value between any two of them.

[0045] Optionally, the molar ratio of the complexing agent to the alkali source is 1:3 - 5.

[0046] Optionally, the molar ratio of the complexing agent to the alkali source is independently selected from any value among 1:3, 1:4, 1:5 or a range value between any two of them.

[0047] Compared with the prior art, the present application has the following beneficial effects:

[0048] (1) For the alkaline zinc - iron flow battery provided by the present application, by using a composite of SPEEK diaphragm and PBI diaphragm, and taking advantage of the effective separation of the complexing agent by the PBI membrane, the coulombic efficiency of the stack is improved, and the overall performance of the stack is enhanced; the problem of zinc accumulation at the negative electrode is solved, and the cycle stability of the stack is improved.

[0049] (2) By optimizing the electrolyte formula and increasing the molar ratio of the complexing agent to zinc ions in the electrolyte, this application solves the problem of zinc hydroxide precipitation in the electrolyte due to insufficient complexation during the operation of the stack, and improves the cycling stability of the stack. Description of the Drawings

[0050] Figure 1 This is the stack operation efficiency diagram when the molar ratio of ZnBr2 to EDTA in the electrolyte of the experimental example of this application is 1:1. Detailed Embodiments

[0051] The following further elaborates this application in conjunction with specific embodiments. The following descriptions are only several embodiments of this application and do not impose any form of limitation on this application. Although this application is disclosed as preferred embodiments, it is not intended to limit this application. Any person skilled in the relevant art, without departing from the scope of the technical solution of this application, can make some changes or modifications using the disclosed technical content, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

[0052] Unless otherwise specified, the raw materials in the embodiments of this application are purchased through commercial channels and used directly without any special treatment.

[0053] Unless otherwise specified, the analysis methods in the embodiments adopt the conventional settings and conventional analysis methods of the instruments or equipment.

[0054] The charge-discharge performance in this application is tested using an Arbin charge-discharge instrument.

[0055] Example 1

[0056] An alkaline zinc-iron flow battery stack with 10 cells is assembled using a SPEEK and PBI composite membrane. In the composite membrane, the SPEEK membrane faces the positive electrode side and the PBI membrane faces the negative electrode side. The positive electrolyte composition is 0.4 mol / L Na4Fe(CN)6 + 0.4 mol / L K4Fe(CN)6 + 0.4 mol / L NaOH + 0.4 mol / L KOH; the negative electrolyte is prepared by first reacting 0.66 mol / L EDTA with 2.64 mol / L NaOH, then adding 0.6 mol / L ZnBr2, and adjusting the pH of the electrolyte to 12 with 2 mol / L NaOH. The volume of the positive electrolyte is 60 L; the volume of the negative electrolyte is 60 L; charge for 2 h under a current density condition of 40 mA / cm 2 and discharge to 8 V under a current density condition of 40 mA / cm 2 .

[0057] The test results show that the charge-discharge performance of the stack is stable, the stack CE is 98%, the VE is 85%, and the EE is 84%; the battery operates for 500 cycles without obvious attenuation.

[0058] Example 2

[0059] A 10-cell stack of an alkaline zinc-iron flow battery was assembled with a composite diaphragm of SPEEK and PBI. In the composite membrane, the SPEEK diaphragm faces the positive electrode side and the PBI membrane faces the negative electrode side. The positive electrolyte composition is 0.4 mol / L Na4Fe(CN)6 + 0.4 mol / L K4Fe(CN)6 + 0.4 mol / L NaOH + 0.4 mol / L KOH; the concentration of ZnBr2 in the negative electrolyte is 0.6 mol / L, and the molar ratios of ZnBr2 to EDTA in the negative electrolyte are 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 respectively. The molar ratio of EDTA to NaOH is 1:4. And 2 mol / L NaOH was used to adjust the pH of the electrolyte to 12. The volume of the positive electrolyte is 60 L; the volume of the negative electrolyte is 60 L; at a current density of 40 mA / cm 2 it was charged for 2 h under the condition of a current density of, and 40 mA / cm 2 it was discharged to 8 V under the condition of a current density of.

[0060] Comparative Example 1

[0061] A 10-cell stack of an alkaline zinc-iron flow battery was assembled with a SPEEK diaphragm. The positive electrolyte composition is 0.4 mol / L Na4Fe(CN)6 + 0.4 mol / L K4Fe(CN)6 + 0.4 mol / L NaOH + 0.4 mol / L KOH; the negative electrolyte is prepared by first reacting 0.66 mol / L EDTA with 2.64 mol / L NaOH, then adding 0.6 mol / L of ZnBr2, and using 2 mol / L NaOH to adjust the pH of the electrolyte to 12. The volume of the positive electrolyte is 60 L; the volume of the negative electrolyte is 60 L; at a current density of 40 mA / cm 2 it was charged for 2 h under the condition of a current density of, and 40 mA / cm 2 it was discharged to 8 V under the condition of a current density of.

[0062] The test results show that the stack has a CE of 94%, a VE of 91%, and an EE of 86%. Compared with the stack of the alkaline zinc-iron flow battery assembled with the composite diaphragm of SPEEK and PBI, the CE of the stack decreases by 4%, which is mainly due to the complexing agent penetrating through the diaphragm and reacting with ferrocyanide. Due to the consumption of ferrocyanide in the positive electrolyte, zinc accumulates at the negative electrode, and zinc dendrites pierce the diaphragm after 200 cycles of the stack operation, resulting in the failure of the stack.

[0063] Through analysis, it is considered that since a sulfonated polyether ether ketone (SPEEK) ion-conducting membrane is used as the separator, there is a problem of low Coulomb efficiency of the battery during the operation of the stack due to the complexing agent permeating through the separator and reacting with ferrocyanide. At the same time, zinc accumulation occurs at the negative electrode, which in turn affects the cycle performance of the battery. In addition, in the electrolyte formulation of this system, the molar ratio of the complexing agent to zinc ions is 1:1. During the operation of the stack, zinc hydroxide will precipitate in the electrolyte due to insufficient complexation, resulting in a decline in battery performance and even failure.

[0064] Comparative Example 2

[0065] An alkaline zinc-iron flow battery stack with 10 cells was assembled using a SPEEK and PBI composite membrane. In the composite membrane, the SPEEK membrane faces the negative electrode side and the PBI membrane faces the positive electrode side. The composition of the positive electrolyte is 0.4 mol / L Na4Fe(CN)6 + 0.4 mol / L K4Fe(CN)6 + 0.4 mol / L NaOH + 0.4 mol / L KOH; the negative electrolyte is prepared by first reacting 0.66 mol / L EDTA with 2.64 mol / L NaOH, then adding 0.6 mol / L ZnBr2, and adjusting the pH of the electrolyte to 12 with 2 mol / L NaOH. The volume of the positive electrolyte is 60 L; the volume of the negative electrolyte is 60 L; at a current density of 40 mA / cm 2 the stack was charged for 2 h, and discharged to 8 V at a current density of 40 mA / cm 2

[0066] The test results show that the stack has a CE of 98%, a VE of 85%, and an EE of 84%. The CE of the battery gradually decreases during 200 cycles, which is mainly due to the poor alkali resistance of the PBI membrane and the high alkali concentration in the positive electrolyte side, resulting in membrane damage during the cycle.

[0067] Comparative Example 3

[0068] An alkaline zinc-iron flow battery stack with 10 cells was assembled using a SPEEK and PBI composite membrane. In the composite membrane, the SPEEK membrane faces the positive electrode side and the PBI membrane faces the negative electrode side. The composition of the positive electrolyte is 0.4 mol / L Na4Fe(CN)6 + 0.4 mol / L K4Fe(CN)6 + 0.4 mol / L NaOH + 0.4 mol / L KOH; the concentration of ZnBr2 in the negative electrolyte is 0.6 mol / L, and the molar ratio of ZnBr2 to EDTA in the negative electrolyte is 1:1. The molar ratio of EDTA to NaOH is 1:4. And the pH of the electrolyte was adjusted to 12 with 2 mol / L NaOH. The volume of the positive electrolyte is 60 L; the volume of the negative electrolyte is 60 L; at a current density of 40 mA / cm 2 the stack was charged for 2 h, and 40 mA / cm 2Discharge to 8V under the current density condition.

[0069] Experimental Example 1

[0070] Taking Example 2 and Comparative Example 3 as examples, the performance of the stack was studied when the molar ratio of ZnBr2 to EDTA in the negative electrolyte was different. The results are shown in Table 1.

[0071] Table 1 Performance of the stack when the molar ratio of ZnBr2 to EDTA in the negative electrolyte is different

[0072]

[0073] As can be seen from Table 1, as the molar ratio of EDTA to ZnBr2 in the negative electrolyte increases, the voltage efficiency of the stack gradually decreases. This is mainly because the increase in the concentration of EDTA in the electrolyte leads to an increase in the viscosity of the electrolyte. When the molar ratio of ZnBr2 to EDTA in the electrolyte is 1:1, after the stack operates for more than 200 cycles, there is a sudden drop in voltage during discharge and it cannot work properly (as Figure 1 shown). This is mainly because when the molar ratio of ZnBr2 to EDTA is 1:1, during the operation of the stack, the complexing agent and zinc ions are not fully complexed, resulting in the precipitation of zinc hydroxide in the electrolyte and causing the battery to fail. After increasing the molar ratio of EDTA to ZnBr2, the performance of the stack remains stable after 500 cycles.

[0074] As mentioned above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. An alkaline zinc-iron flow battery, characterized in that, It includes a positive electrolyte, a composite separator, and a negative electrolyte; The positive electrolyte and the negative electrolyte are symmetrically located on both sides of the composite separator respectively; The composite separator includes a sulfonated polyether ether ketone separator and a polybenzimidazole separator; The sulfonated polyether ether ketone separator is adhered to the polybenzimidazole separator; The sulfonated polyether ether ketone separator faces the positive electrode side; The polybenzimidazole separator faces the negative electrode side; The positive electrode electrolyte contains Fe(CN)6 4- and OH - ; The negative electrolyte is prepared from a zinc source, a complexing agent, and an alkali source.

2. The alkaline zinc-iron flow battery according to claim 1, characterized in that, The Fe(CN)6 4- has a molar concentration of 0.4 to 2 M; The OH - has a molar concentration of 0.4 to 2 M.

3. The alkaline zinc-iron flow battery according to claim 1, characterized in that, The zinc source includes at least one of zinc sulfate, zinc bromide, zinc chloride, zinc nitrate, zinc acetate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, and zinc bis(oxalato)borate.

4. The alkaline zinc-iron flow battery according to claim 1, characterized in that, The complexing agent includes at least one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid, cyclohexanetetraacetic acid, and ethylenediaminetetrapropionic acid.

5. The alkaline zinc-iron flow battery according to claim 1, characterized in that, The alkali source includes NaOH and / or KOH.

6. The alkaline zinc-iron flow battery according to claim 1, characterized in that, The molar ratio of the zinc source to the complexing agent is 1:1.1 to 1.5; Preferably, the molar ratio of the complexing agent to the alkali source is 1:3 to 5.

7. A method for preparing the alkaline zinc-iron flow battery according to any one of claims 1 to 6, characterized in that, It includes the following steps: (1) Obtain the positive electrolyte; (2) Obtain the negative electrolyte; (3) Adhere the sulfonated polyether ether ketone separator and the polybenzimidazole separator to obtain a composite separator; (4) Symmetrically place the positive electrolyte and the negative electrolyte on both sides of the composite separator respectively, wherein the sulfonated polyether ether ketone separator in the composite separator faces the positive electrode side and the polybenzimidazole separator faces the negative electrode side, and assemble to obtain the alkaline zinc-iron flow battery.

8. The method for preparing the alkaline zinc-iron flow battery according to claim 7, characterized in that, In step (1), the positive electrode electrolyte contains Fe(CN)6 4- and OH - ; Preferably, the molar concentration of the Fe(CN)6 4- is 0.4 to 2 M; The OH - has a molar concentration of 0.4 to 2 M.

9. The method for preparing the alkaline zinc-iron flow battery according to claim 7, characterized in that, Step (2) includes: mixing the complexing agent and the alkali source, then adding the zinc source, and adjusting the pH value of the system to 9 to 13 to obtain the negative electrolyte.

10. The method for preparing the alkaline zinc-iron flow battery according to claim 9, characterized in that, The zinc source includes at least one of zinc sulfate, zinc bromide, zinc chloride, zinc nitrate, zinc acetate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, and zinc bis(oxalato)borate; Preferably, the complexing agent includes at least one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid, cyclohexanetetraacetic acid, and ethylenediaminetetrapropionic acid; Preferably, the alkali source includes NaOH and / or KOH; Preferably, the molar ratio of the zinc source to the complexing agent is 1:1.1 to 1.5; Preferably, the molar ratio of the complexing agent to the alkali source is 1:1.1 to 1.3.

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