Zinc-iron flow battery electrolyte, preparation method and flow battery

Abstract

The invention relates to the technical field of alkaline zinc-iron flow batteries, discloses a zinc-iron flow battery electrolyte, a preparation method and a flow battery, and aims to improve the solubility of a zinc precursor and further improve the power density by improving a negative electrode electrolyte preparation method. The additive does not participate in the oxidation-reduction reaction in the charge-discharge process, and almost has no influence on the battery performance. The small-molecule additive is low in price and beneficial to control of battery cost. The excessive zinc precursor is added into the negative electrode electrolyte, and the small molecule additive is introduced, so that the total ion concentration and the ion strength of the negative electrode electrolyte are improved, and the inhibition effect on water migration is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow batteries, and in particular to a zinc-iron liquid flow battery electrolyte, a preparation method and a liquid flow battery. Background Art

[0002] In order to establish a safe and efficient energy system, enterprises need to seek cleaner and lower-carbon energy solutions to reduce carbon emissions and meet the requirements of emission quota trading. The development of flow batteries can be regarded as an important sustainable development initiative. As an energy storage device, flow batteries have the advantages of strong scalability, long cycle life, and rapid response. Compared with traditional batteries, flow batteries can adjust the energy storage capacity more flexibly, and there will be no safety hazards during the energy storage and release process. Therefore, they have broad application prospects in the fields of grid energy storage, renewable energy storage, and industrial applications. Zinc-iron flow battery, as a variant of flow battery technology, has attracted much attention in recent years. It uses the reversible electrochemical reaction between zinc and iron to store and release energy. Specifically, in zinc-iron flow batteries, zinc on the negative electrode undergoes an oxidation reaction during charging to generate zinc ions and release electrons; while during discharge, zinc ions are reduced to metallic zinc and absorb electrons at the same time. The iron on the positive electrode undergoes a similar reaction during charging and discharging, realizing energy storage and release.

[0003] However, zinc-iron flow batteries face some challenges in practical applications, one of which is the migration of water in the electrolyte. The migration of water molecules in the electrolyte will cause the concentration of the positive and negative electrolytes to change, which in turn affects the positive and negative electrode reactions and ultimately reduces the cycle life and energy efficiency of the battery. Therefore, solving the migration problem of water in the negative electrode electrolyte is crucial to improving the performance of zinc-iron flow batteries.

[0004] Patent CN114551934A provides a reverse osmosis device that can transfer water molecules in the positive electrode electrolyte back to the negative electrode through an external diaphragm under the action of a concentration gradient, thereby reducing the impact of water migration on battery performance. However, the device described in the patent has a complex structure and high maintenance costs.

[0005] Although patent CN115763878A limits water migration by adjusting the concentration and osmotic pressure of the electrolyte itself, the formula it provides has a large amount of redundant positive electrode active materials, resulting in capacity waste and a low energy density. Summary of the invention

[0006] In view of the shortcomings and defects of the prior art, the present invention provides a zinc-iron liquid flow battery electrolyte, a preparation method and a liquid flow battery. By adding a small molecule additive to the negative electrode electrolyte, the problems of high cost, complex technology or poor effect of the current commonly used technology are solved, and the requirements of long-term energy storage batteries for high reliability, long life and high capacity retention rate are achieved.

[0007] The purpose of the present invention can be achieved through the following technical solutions.

[0008] A zinc-iron liquid flow battery electrolyte comprises a positive electrode electrolyte and a negative electrode electrolyte.

[0009] The positive electrode electrolyte includes an iron precursor and a first strong base; the negative electrode electrolyte includes a zinc precursor, a second strong base, and a small molecule additive, wherein the small molecule additive includes at least one of potassium chloride, potassium sulfate, sodium sulfate, zinc acetate, sodium gluconate, and potassium ferrocyanide, and the concentration is 0.1 mol / L to 0.5 mol / L.

[0010] Preferably, the first strong base is one or more of potassium hydroxide, sodium hydroxide, and barium hydroxide. After the first strong base is dissolved in water, the concentration of hydroxide is 1 to 3 mol / L.

[0011] Preferably, the iron precursor is sodium ferrocyanide with a purity greater than 99.5%, and the concentration of ferrocyanide in the alkaline solution is 0.2-1 mol / L.

[0012] Preferably, the second strong base is one or more of potassium hydroxide, sodium hydroxide, and barium hydroxide. After the second strong base is dissolved in water, the concentration of hydroxide is 15 to 20 mol / L.

[0013] Preferably, the zinc precursor is one or more of zinc oxide, zinc chloride, zinc bromide and zinc acetate, which is dissolved in a second strong alkaline solution to obtain a negative electrode concentrated solution, and the concentration of zincate in the negative electrode concentrated solution is 0.1 to 7 mol / L.

[0014] A method for preparing a zinc-iron liquid flow battery electrolyte includes a method for preparing a positive electrode electrolyte and a method for preparing a negative electrode electrolyte.

[0015] a. The method for preparing the positive electrode electrolyte comprises the following steps.

[0016] The iron precursor and the first strong base are mixed in a beaker and then deionized water is added.

[0017] The mixture was stirred with a magnetic stirrer for 30 to 60 minutes to obtain a positive electrode electrolyte.

[0018] b. The method for preparing the negative electrode electrolyte comprises the following steps.

[0019] The zinc precursor and the second strong base are mixed in a beaker and a small amount of deionized water is added.

[0020] The mixture was stirred with a magnetic stirrer for 20 to 30 minutes to obtain a negative electrode concentrated solution.

[0021] Pour the negative electrode concentrate into a beaker filled with deionized water 3 to 7 times the volume of the negative electrode concentrate.

[0022] After stirring with a magnetic stirrer for 5 to 10 minutes, a small molecule additive is added thereto.

[0023] The mixture was stirred with a magnetic stirrer for 30 to 60 minutes to obtain a negative electrode electrolyte.

[0024] Preferably, when pouring the negative electrode concentrate into the beaker containing deionized water, the negative electrode concentrate needs to be slowly added in 2 to 4 times.

[0025] Preferably, when the iron precursor and the first strong base are mixed in a beaker, the iron precursor needs to be slowly poured into the beaker in 2 to 4 times.

[0026] Preferably, the length of the stirring bar of the magnetic stirrer is 5 cm, and the rotation speed is 600 rpm.

[0027] A liquid flow battery comprises a positive electrode, a negative electrode, an electrolyte and a separator.

[0028] The electrolyte adopts the zinc-iron liquid flow battery electrolyte or the zinc-iron liquid flow battery electrolyte prepared by the preparation method.

[0029] Beneficial effects of the present invention: The present invention improves the solubility of the zinc precursor and thus improves the power density by improving the negative electrode electrolyte configuration method. The additive does not participate in the redox reaction during the charge and discharge process and has almost no effect on the battery performance. The small molecule additive is inexpensive and is conducive to controlling the battery cost. By adding an excess of zinc precursor to the negative electrode electrolyte and introducing a small molecule additive, the total ion concentration and ionic strength of the negative electrode electrolyte are increased, thereby achieving an inhibitory effect on water migration. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a test result diagram of the change in volume of the positive electrode of the electrolyte in the comparative example of the present invention and Examples 1-5 as the battery runs over time.

[0031] Figure 2 The figure is a test result diagram of the battery capacity changing with the number of battery cycles in the comparative example and embodiments 1-5 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention.

[0033] The positive electrode reacts during charging and discharging: When charged, 2-valent iron becomes 3-valent iron and loses electrons.

[0034] The negative electrode reacts during charging and discharging: When charging, zincate gains electrons and turns into zinc element.

[0035] The overall reaction is: During the charging and discharging process, the redox reaction between iron and zinc causes charge movement, thereby generating current.

[0036] The total ion concentration is the sum of the concentrations of each ion in the electrolyte. The ion concentration calculation formula is as follows: , where I is the ionic strength, is the molar concentration of each ion in the solution, is the valence of the ion, and ∑ represents the sum of all ion types.

[0037] The iron precursor in the positive electrode electrolyte is the active substance of the positive electrode. It loses electrons during the charging process and gains electrons during the discharging process, playing the role of energy storage and release. The first strong alkali releases cation ions and hydroxide ions after dissolving, and is an important carrier of internal conductivity in the battery; the zinc precursor in the negative electrode electrolyte is the active substance of the negative electrode. It gains electrons during the charging process and loses electrons during the discharging process, playing the role of energy storage and release. Excess zinc precursor has the same role as the additive, increasing the ion concentration and ion strength of the negative electrode electrolyte, thereby inhibiting water migration.

[0038] Take 80ml of positive and negative electrolytes, and the effective area of ​​the battery is 25cm 2 , using constant current charge and discharge mode, set the current density to 60mA / cm 2 , the charge cut-off voltage is 2V, the discharge cut-off voltage is 0.1V, and the test results of the comparative example and embodiments 1-5 are shown in Table 1.

[0039] Comparative example.

[0040] No excessive zinc oxide or small molecule additives were added: polybenzimidazole ion diaphragm was used as the diaphragm, and the positive electrolyte was 0.6 mol / L + 2mol / L Solution, total ion concentration is 7mol / L, ionic strength is 8; negative electrode electrolyte is 0.3mol / L + 2mol / L The total ion concentration of the solution is 6.9 and the ionic strength is 3.9. Its water migration data is as follows Figure 1 , the volume of the positive electrode electrolyte continued to increase, increasing by 25 ml in the 240th hour.

[0041] Example 1.

[0042] Add excess zinc oxide on the basis of the comparative example: use polybenzimidazole ion diaphragm as diaphragm, positive electrode electrolyte is 0.6 mol / L + 2mol / L solution, the total ion concentration is 7 mol / L, the ionic strength is 8; the negative electrode electrolyte is 0.6 mol / L and 2mol / L Solution composition: zinc oxide dissolves into zincate ions in the second strong base, half of which is used for the storage and release of electricity, and the other half is used as an additive to significantly increase the ion concentration and ion strength of the negative electrode electrolyte. The equivalent additive concentration is 0.5 mol / min, the total ion concentration of the negative electrode electrolyte is 7.8, and the ion strength is 4.8. Its water migration data is as follows: Figure 1 , the volume of the positive electrode electrolyte first decreased and then increased, increasing by 17 ml at 240h.

[0043] Example 2.

[0044] Potassium sulfate was added as an additive on the basis of Example 1: a polybenzimidazole ion diaphragm was used as a diaphragm, and the positive electrode electrolyte was 0.6 mol / L + 2mol / L Solution, total ion concentration is 7mol / L, ionic strength is 8; negative electrode electrolyte is 0.6mol / L + 2mol / L + 0.2mol / L The total ion concentration of the solution is 8.4 and the ionic strength is 5.4. Its water migration data is as follows Figure 1 , the volume of the positive electrode electrolyte first decreased and then increased, increasing by 9 ml at 240h.

[0045] Example 3.

[0046] Sodium gluconate was added as an additive on the basis of Example 1: a polybenzimidazole ion diaphragm was used as a diaphragm, and the positive electrode electrolyte was 0.6 mol / L + 2mol / L Solution, total ion concentration is 7mol / L, ionic strength is 8; negative electrode electrolyte is 0.6mol / L + 2mol / L + 0.2mol / L The total ion concentration of the solution is 8.2 and the ionic strength is 5. Its water migration data is as follows Figure 1 , the volume of the positive electrode electrolyte first decreased and then increased, increasing by 10 ml in the 240th hour.

[0047] Example 4.

[0048] Zinc acetate was added as an additive on the basis of Example 1: a polybenzimidazole ion diaphragm was used as a diaphragm, and the positive electrode electrolyte was 0.6 mol / L + 2mol / L Solution, total ion concentration is 7mol / L, ionic strength is 8; negative electrode electrolyte is 0.6mol / L + 2mol / L + 0.2mol / L The total ion concentration of the solution is 8.4 and the ionic strength is 5.4. Its water migration data is as follows Figure 1 , the volume of the positive electrode electrolyte first decreased and then increased, increasing by 7 ml at 240 h.

[0049] Example 5.

[0050] Potassium ferrocyanide was added as an additive on the basis of Example 1: a polybenzimidazole ion membrane was used as a separator, and the positive electrode electrolyte was 0.6 mol / L + 2mol / L Solution, total ion concentration is 7mol / L, ionic strength is 8; negative electrode electrolyte is 0.6mol / L + 2mol / L + 0.2mol / L Solution, using potassium ion additives can avoid the risk of electrolyte precipitation due to the common ion effect. Ferrocyanide is a tetravalent ion. Adding 0.2 mol / L potassium ferrocyanide greatly increases the ionic strength. The total ion concentration of the negative electrode electrolyte is 8.8 and the ionic strength is 6.8. Its water migration data is as follows Figure 1 , the volume of the positive electrode electrolyte first decreased and then increased, increasing by 2 ml at 240h.

[0051] Table 1

[0052]

[0053] The results show that small molecule additives have little effect on the coulombic efficiency and energy efficiency of the battery, but have a significant inhibitory effect on the water migration of the electrolyte. Within a certain concentration range, the inhibitory effect increases with the increase of the ionic strength of the negative electrode electrolyte. In the comparative example, the amount of water migration reached 25ml, and there was no trend of stopping migration. Although its coulombic efficiency and energy efficiency were still at normal levels, its capacity showed attenuation (reference Figure 2), while the electrolyte of Example 5 only migrated 2 ml and was basically stable, with no obvious capacity decay, ensuring the reliability of the long-term operation of the battery.

[0054] The above embodiments are descriptions of specific implementation methods of the present invention rather than limitations of the present invention. Technical personnel in the relevant technical field may make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A zinc-iron flow battery electrolyte, characterized in that: Including positive electrode electrolyte and negative electrode electrolyte; The positive electrode electrolyte includes an iron precursor and a first strong base; the negative electrode electrolyte includes a zinc precursor, a second strong base, and a small molecule additive, wherein the small molecule additive includes at least one of potassium chloride, potassium sulfate, sodium sulfate, zinc acetate, sodium gluconate, and potassium ferrocyanide, and the concentration is 0.1 mol / L to 0.5 mol / L.

2. A zinc-iron flow battery electrolyte according to claim 1, characterized in that: The first strong base is one or more of potassium hydroxide, sodium hydroxide, and barium hydroxide. After the first strong base is dissolved in water, the concentration of hydroxide is 1 to 3 mol / L.

3. The zinc-iron flow battery electrolyte according to claim 1, characterized in that: The iron precursor is sodium ferrocyanide with a purity greater than 99.5%, and the concentration of ferrocyanide in the alkaline solution is 0.2-1 mol / L.

4. The zinc-iron flow battery electrolyte according to claim 1, characterized in that: The second strong base is one or more of potassium hydroxide, sodium hydroxide, and barium hydroxide. After the second strong base is dissolved in water, the concentration of hydroxide is 15 to 20 mol / L.

5. The zinc-iron liquid flow battery electrolyte according to claim 1, characterized in that: The zinc precursor is one or more of zinc oxide, zinc chloride, zinc bromide and zinc acetate, which is dissolved in a second strong alkaline solution to obtain a negative electrode concentrated solution, and the concentration of zincate in the negative electrode concentrated solution is 0.1-7 mol / L.

6. A method for preparing a zinc-iron flow battery electrolyte, characterized in that: include: a. Preparation method of positive electrode electrolyte: Mix the iron precursor and the first strong base in a beaker and add deionized water; Stirring with a magnetic stirrer for 30 to 60 minutes to obtain a positive electrode electrolyte; b. Preparation method of negative electrode electrolyte: Mix the zinc precursor and the second strong base in a beaker and add a small amount of deionized water; Stirring with a magnetic stirrer for 20 to 30 minutes to obtain a negative electrode concentrated solution; Pour the negative electrode concentrate into a beaker containing 3 to 7 times the volume of deionized water of the negative electrode concentrate; After stirring with a magnetic stirrer for 5 to 10 minutes, a small molecule additive is added thereto; The mixture was stirred with a magnetic stirrer for 30 to 60 minutes to obtain a negative electrode electrolyte.

7. The method for preparing a zinc-iron flow battery electrolyte according to claim 6, characterized in that: When pouring the negative electrode concentrate into a beaker filled with deionized water, the negative electrode concentrate needs to be added slowly in 2 to 4 times.

8. The method for preparing a zinc-iron flow battery electrolyte according to claim 6, characterized in that: When the iron precursor and the first strong base are mixed in a beaker, the iron precursor needs to be slowly poured into the beaker in 2 to 4 times.

9. The method for preparing a zinc-iron flow battery electrolyte according to claim 6, characterized in that: The length of the stirring bar of the magnetic stirrer is 5 cm, and the rotation speed is 600 rpm.

10. A liquid flow battery, characterized in that: Including positive electrode, negative electrode, electrolyte and separator; The electrolyte is the zinc-iron liquid flow battery electrolyte described in any one of claims 1-5 or the zinc-iron liquid flow battery electrolyte prepared by the preparation method described in any one of claims 6-9.

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