Preparation method of electrolyte of high-voltage, high-current-density and high-stability aqueous alkaline zinc-iron flow battery

Abstract

The invention discloses a preparation method of an electrolyte of a high-voltage, high-current-density and high-stability aqueous alkaline zinc-iron flow battery in the field of flow batteries. The electrolyte is prepared by blending potassium diethyltriamine pentaacetate, zinc ions and potassium salt. According to the invention, the charge / discharge voltage of the zinc-iron flow battery in the cycle process and the cycle stability of the zinc-based flow battery under high current density are greatly improved, and the phenomena of hydrogen evolution and zinc dendrite of the zinc negative electrode in the existing alkaline aqueous zinc-iron flow battery are inhibited.

Description

Technical Field

[0001] This invention relates to the field of flow batteries, and particularly to a method for preparing an electrolyte for a high-voltage, high-current-density, and high-stability aqueous alkaline zinc-iron flow battery. This invention greatly improves the charge / discharge voltage and cycle stability of zinc-based flow batteries under high current density during cycling, and suppresses hydrogen evolution and zinc dendrite phenomena present at the zinc anode in existing alkaline aqueous zinc-iron flow batteries. Background Technology

[0002] In the process of transforming the energy structure towards cleaner and lower-carbon energy sources, large-scale energy storage technology has become a core support for balancing the output fluctuations of intermittent renewable energy sources such as solar and wind power with the stable operation of the power grid. Flow batteries, with their outstanding advantages such as independent regulation of power and energy, long cycle life, high operational safety, and good environmental compatibility, occupy an important position in the field of large-scale energy storage and demonstrate broad prospects for industrial application.

[0003] Among them, alkaline flow batteries, as a key branch of flow batteries, have become a research hotspot due to their low electrolyte cost ($100 / kWh) and high open-circuit voltage (1.74V). For example, patents CN201611133465.X and WOCN17111224 disclose typical alkaline zinc-iron flow battery technologies, whose positive electrode uses Fe(CN)6. 3- / Fe(CN)6 4- Redox couple, with Zn(OH)4 as the negative electrode. 2- The Zn redox couple. However, existing alkaline zinc-iron flow batteries still have two major technological limitations: on the one hand, while the 1.74V open-circuit voltage has certain advantages, it still restricts further improvements in battery energy density and power density. If we want to increase [Zn(OH)4]... 2- The redox potential requires a large amount of strongly alkaline electrolyte (usually ≥3 mol / L NaOH or KOH solution), which easily corrodes components such as the battery casing, pipelines, and separator, increasing the difficulty of system maintenance and safety risks; on the other hand, the negative electrode Zn(OH)4 2- During charge-discharge cycles, zinc dendrites are easily generated in the / Zn couple. These dendrites gradually pierce the battery separator, leading to cross-contamination of the positive and negative electrolytes and even causing internal short circuits in the battery. This severely shortens the battery's cycle life and operational safety, becoming a key bottleneck restricting its industrialization. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing an electrolyte for a high-voltage, high-current-density, and high-stability aqueous alkaline zinc-iron flow battery. This method significantly improves the charge / discharge voltage and cycle stability of zinc-based flow batteries under high current density during cycling, and suppresses hydrogen evolution and zinc dendrite formation at the zinc anode in existing alkaline aqueous zinc-iron flow batteries.

[0005] The objective of this invention is achieved as follows: a method for preparing an electrolyte for a high-voltage, high-current-density, and high-stability aqueous alkaline zinc-iron flow battery, comprising zinc chelate, deionized water, and potassium salt, with the specific steps as follows:

[0006] Step 1) Dissolve potassium diethyltriaminepentaacetate (DTPA-K) in water to obtain the basic electrolyte;

[0007] Step 2) Add zinc bromide (ZnBr2) to the basic electrolyte to obtain the electrolyte;

[0008] Step 3) Add potassium salt to the electrolyte obtained in Step 2), stir at the set speed for the set time until completely dissolved, and let stand to obtain the electrolyte of a high-voltage, high-current-density and high-stability aqueous alkaline zinc-iron flow battery.

[0009] Furthermore, the zinc chelate is a product of potassium diethyltriaminepentaacetate (DTPA-K) coordinating with zinc ions.

[0010] Furthermore, in step 2), the molar ratio of ZnBr2 to DTPA-K in step 1) is 1:4 to 1:2, the concentration of ZnBr2 is 0.45±0.05mol / L, and the concentration of DTPA-K is 0.4 to 1.5mol / L.

[0011] Furthermore, in step 3), the potassium salt is potassium chloride with a concentration of 2 ± 0.5 mol / L.

[0012] Furthermore, in step 3), the stirring speed is 800 rpm and the stirring time is 30 min.

[0013] A method for preparing an alkaline aqueous zinc-iron flow battery, wherein the positive electrode is a potassium ferrocyanide solution, the negative electrode is the electrolyte prepared above, the single cells are assembled in a certain order, and two sets of single cells are combined to finally prepare a full cell.

[0014] Furthermore, the assembly sequence of a single cell is as follows: positive electrode plate, bipolar current collector, positive electrode carbon felt, SPEEK membrane, negative electrode carbon felt, bipolar current collector, and negative electrode plate.

[0015] Furthermore, the fabricated battery requires 100 mA / cm². 2 Charge-discharge cycles are performed at current density.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The present invention uses DTPA-K as an organic ligand, which binds to Zn through coordinate bonds in the molecule. 2+ The combination forms a metal chelate, and the ligand forms a ring structure with zinc ions, reducing the presence of coordination water, enhancing the deposition / stripping potential and reversibility of zinc, and further suppressing the hydrogen evolution reaction present at the zinc anode under high current density.

[0018] (2) The present invention uses organic ligands to change the solvation structure of zinc ions, promote the uniform deposition of zinc ions, and further suppress the formation of dendrites during zinc ion deposition. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 This is a cyclic voltammetry scan curve of a three-electrode battery (glassy carbon electrode as working electrode, Ag / Agcl as reference electrode, and stone rod as counter electrode) assembled with the electrolytes obtained in Comparative Example 1 and Examples 1, 2 and 3 of this invention.

[0021] Figure 2 The Zn(OH)4 assembled from the electrolytes obtained in Comparative Example 2 and Example 4 of this invention 2- DTPA-Zn / Fe(CN)6 4- Zinc-iron flow batteries at 100 mA / cm 2 Charge-discharge curves for a charging capacity of 0.15Ah at current density.

[0022] Figure 3 This is a SEM image of zinc deposition on a carbon felt after 10 full-cell cycles of the zinc-iron flow battery assembled with the electrolytes obtained in Comparative Example 2 and Example 4 of this invention.

[0023] Figure 4 The full cell of the zinc-iron flow battery assembled with the electrolytes obtained in Comparative Example 2 and Example 4 of this invention achieves a voltage of 100 mA / cm². 2 Cyclic performance curves at current density.

[0024] Figure 5 This is a Fourier transform infrared (FTIR) test of the electrolytes obtained in Comparative Example 3 and Example 3 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] A method for preparing the negative electrode electrolyte of an aqueous alkaline zinc-iron flow battery includes the following steps:

[0028] Step 1) Dissolve 4 mmol DTPA-K in deionized water to obtain the basic electrolyte;

[0029] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 30 min, and let stand for 2 h to obtain the electrolyte, in which the concentration of DTPA-Zn is 0.4 mol / L.

[0030] Example 2

[0031] A method for preparing the negative electrode electrolyte of an aqueous alkaline zinc-iron flow battery includes the following steps:

[0032] Step 1) Dissolve 8 mmol DTPA-K in deionized water to obtain the basic electrolyte;

[0033] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 30 min, and let stand for 2 h to obtain the electrolyte, in which the concentration of DTPA-Zn is 0.4 mol / L.

[0034] Example 3

[0035] A method for preparing the negative electrode electrolyte of an aqueous alkaline zinc-iron flow battery includes the following steps:

[0036] Step 1) Dissolve 12 mmol DTPA-K in deionized water to obtain the basic electrolyte;

[0037] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 30 min, and let stand for 2 h to obtain the electrolyte, in which the concentration of DTPA-Zn is 0.4 mol / L.

[0038] Example 4

[0039] A method for preparing an aqueous alkaline zinc-iron flow battery includes the following steps:

[0040] Step 1) Dissolve 12 mmol DTPA-K in deionized water to obtain the basic electrolyte;

[0041] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 30 min, and let stand for 2 h to obtain the electrolyte, in which the concentration of DTPA-Zn is 0.4 mol / L;

[0042] Step 3) Add 5 mmol of NaOH and 20 mmol of KCl to the electrolyte obtained in Step 2) as supporting electrolytes;

[0043] Step 4) Using the electrolyte prepared in Step 3) as the negative electrode electrolyte, 12 mmol of K4[Fe(CN)6] is dissolved in deionized water to prepare the positive electrode electrolyte; the single cell is configured with a positive terminal plate, a bipolar current collector, and a positive electrode of 2×2.5 cm. 2 Carbon felt, SPEEK membrane, negative electrode 2×2.5 cm 2 The carbon felt, bipolar current collector, and negative terminal plate are assembled in that order.

[0044] Comparative Example 1

[0045] A method for preparing the negative electrode electrolyte of an aqueous alkaline zinc-iron flow battery includes the following steps:

[0046] Step 1) Dissolve 60 mmol KOH in deionized water to obtain the basic electrolyte;

[0047] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 1 hour, and let stand for 2 hours to obtain the electrolyte, in which [Zn(OH)4] is added. 2- The concentration was 0.4 mol / L.

[0048] Comparative Example 2

[0049] A method for preparing an aqueous alkaline zinc-iron flow battery includes the following steps:

[0050] Step 1) Dissolve 60 mmol KOH in deionized water to obtain the basic electrolyte;

[0051] Step 2) Add 4 mmol ZnBr2 to the basic electrolyte, stir at 800 rpm for 1 h, and let stand for 2 h to obtain the electrolyte, in which [Zn(OH)4] is present. 2- The concentration was 0.4 mol / L;

[0052] Step 3) Use the electrolyte prepared in Step 2) as the negative electrode electrolyte, and then add 12 mmol of Fe(CN)6 4- The positive electrode electrolyte was prepared by dissolving it in deionized water; a single cell was constructed with a positive electrode plate, a bipolar current collector, and a positive electrode 2×2.5 cm... 2 Carbon felt, SPEEK membrane, negative electrode 2×2.5 cm 2 The carbon felt, bipolar current collector, and negative terminal plate are assembled in that order.

[0053] Comparative Example 3

[0054] A method for preparing a ligand electrolyte for an aqueous alkaline zinc-iron flow battery includes the following steps:

[0055] Step 1) Dissolve 12 mmol of DTPA-K in deionized water to obtain the basic electrolyte.

[0056] By analyzing Examples 1-5 and Comparative Examples 1-3, the following conclusions were drawn:

[0057] (1) Through analysis Figure 1 As can be seen, compared with the electrolyte of Comparative Example 1, the redox peaks of the chelate electrolyte in the examples exhibit better symmetry and a more negative deposition stripping potential with increasing molar ratio of ligand to zinc ions, reaching a minimum of -1.575. The stability constant of DTPA-Zn is known to be... The concentration of the chelate DTPA-Zn was 0.4 mol / L, and the excess DTPA concentration was 0.8 mol / L. The stability constant was determined using the following expression:

[0058] ,

[0059] Calculate free Zn 2+ concentration mol / L, known zinc ion potential According to the Nernst equation:

[0060] ,

[0061] in Substituting into the calculation, we can obtain In Ag / Agcl Under the reference electrode, the calculations yielded The result is -1.575. Highly consistent, according to the total electromotive force formula:

[0062] ,

[0063] The positive electrode K4[Fe(CN)6] potential is 0.28. Calculation 1.817 V.

[0064] (2) Through analysis Figure 2 As can be seen, compared with the electrolyte of Comparative Example 2, the electrolyte in Example 4 exhibits a higher charging and discharging plateau, with an equilibrium voltage as high as 1.8V, consistent with the analysis. Figure 1 The calculated results are in high agreement, further verifying the theoretical voltage platform of the zinc-iron flow battery composed of potassium ferrocyanide, which shows better battery voltage and energy density.

[0065] (3) Through analysis Figure 3 As can be seen in Example 4 (Figure a), the zinc deposition surface exhibits a denser and smoother structure; while in Comparative Example 2 (Figure b), irregular dendrites appear on the zinc deposition surface, indicating that the solvation structure formed with the ligand can better regulate the deposition / stripping of zinc, promote uniform deposition of zinc ions, and further suppress the generation of dendrites during zinc ion deposition, thereby reducing the probability of the battery separator being punctured and reducing the possibility of shortening the battery life.

[0066] (4) Through analysis Figure 4 As can be seen, in Comparative Example 2, after the 32nd cycle, the zinc dendrites pierced the separator, causing a short circuit in the battery. In contrast, the electrolyte in Example 4 allowed the battery to maintain a high discharge capacity of 149mAh, a coulombic efficiency of 99%, and a high energy efficiency of 82% after 400 cycles, significantly improving battery life.

[0067] (5) Through analysis Figure 5 It can be seen that the symmetric stretching vibration peak of the DTPA carboxyl group in Comparative Example 3 is located at 1407 cm⁻¹. -1 In Example 3, the peak redshifted to 1366 cm⁻¹. -1 (Displacement 41 cm) -1 This is the combination of carboxyl oxygen atom and Zn. 2+ This directly reflects the decrease in the CO bond force constant due to the formation of Zn-O coordination bonds and the reduction in carboxyl electron cloud density; simultaneously, both are at 1600 cm⁻¹. -1 The peak positions of the asymmetric stretching vibrations of the carboxyl groups in the vicinity are almost identical, ruling out interference from non-complexing factors such as impurities or solvents, further confirming the specificity of the red shift of the carboxyl symmetric stretching peak; in addition, the stretching vibration peak of the CN single bond in Comparative Example 3 is located at 1116 cm⁻¹. -1 In Example 3, the redshift was 1098 cm. -1 (Displacement 18 cm) -1 This is the interaction between amino nitrogen atoms and Zn. 2+ Formation of Zn-N coordination bonds, nitrogen atom electron cloud towards Zn 2+The transfer directly signals the decrease in the CN bond force constant. The two-site chelation between the carboxyl oxygen and amino nitrogen, as indicated by the significant redshift of the carboxyl symmetric stretching vibration peak and the CN bond stretching vibration peak, demonstrates the interaction between DTPA-K and Zn. 2+ A stable chelate was successfully formed.

[0068] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an electrolyte of a high-voltage, high-current density, and high-stability aqueous alkaline zinc-iron flow battery, characterized in that, The zinc chelate, deionized water and potassium salt are included, and the specific steps are as follows: Step 1) potassium diethylenetriamine pentaacetate (DTPA-K) is dissolved in water to obtain a basic electrolyte; Step 2) zinc bromide (ZnBr2) is added to the basic electrolyte to obtain an electrolyte; Step 3) potassium salt is added to the electrolyte obtained in step 2), stirred at a set speed for a set time until completely dissolved, and after standing, an electrolyte for a high-voltage, high-current density and high-stability water-based zinc-iron flow battery is obtained.

2. The method for preparing the electrolyte of a high-voltage, high-current-density, and high-stability aqueous alkaline zinc-iron flow battery according to claim 1, characterized in that, The zinc chelate is a product after coordination of potassium diethylenetriamine pentaacetate (DTPA-K) and zinc ions.

3. The method for preparing the electrolyte of a high-voltage, high-current-density, and high-stability aqueous alkaline zinc-iron flow battery according to claim 1, characterized in that, The molar ratio of ZnBr2 in step 2) to DTPA-K in step 1) is 1:4-1:2, the concentration of ZnBr2 is 0.45±0.05 mol / L, and the concentration of DTPA-K is 0.4-1.5 mol / L.

4. The process for the preparation of electrolyte for high voltage, high current density and high stability aqueous alkaline zinc-iron flow battery as claimed in claim 1 wherein, The potassium salt in step 3) is potassium chloride, and the concentration is 2±0.5 mol / L. ​ 5. The process for the preparation of electrolyte for high voltage, high current density and high stability aqueous alkaline zinc-iron flow battery as claimed in claim 1 wherein, The stirring speed in step 3) is 800 rpm, and the rotation time is 30 min. ​ 6. A method of making an alkaline aqueous zinc-iron flow battery, characterized in that, The positive electrode is selected as potassium ferrocyanide solution, the negative electrode is selected as the electrolyte prepared by claim 1, the single cell is assembled in a certain order, two groups of single cells are combined, and finally a full cell is prepared.

7. The method of making a zinc-iron flow battery with alkaline electrolytes of claim 6, wherein, The assembly sequence of the single cell is positive end plate, bipolar plate current collector, positive carbon felt, SPEEK film, negative carbon felt, bipolar plate current, and negative end plate.

8. The method of making a zinc-iron flow battery with alkaline electrolytes of claim 6, wherein, The prepared battery was subjected to charge-discharge cycles at 100 mA / cm 2 current density.

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