Highly stable secondary water-based iron-polymer battery and its positive electrode and preparation method

Abstract

This invention discloses a highly stable secondary aqueous iron-polymer battery, its positive electrode, and a preparation method thereof. The positive electrode preparation method includes the following steps: using carbon cloth, graphite paper, or stainless steel as the positive electrode current collector, and using a polymer containing secondary / tertiary amine groups and conjugated groups as the positive electrode material, which is then coated onto the positive electrode current collector to obtain the positive electrode. Because Fe... 2+ It is a high-valence ion with a relatively high charge density, and polyaniline contains active nitrogen atoms, which is beneficial for reacting with Fe. 2+ Coordination occurs, and the process is highly reversible; using this cathode to fabricate a secondary aqueous iron polymer battery, it achieved over 39,000 cycles in an aqueous iron battery with 100% capacity retention, at current densities ranging from 5 to 25 A g. −1 The capacity released under these conditions is 209-133 mAh g. −1 Its cycle life exceeds that of all current aqueous iron batteries, and even surpasses that of most aqueous batteries.

Description

Technical Field

[0001] This invention belongs to the field of aqueous metal battery technology, specifically relating to a highly stable secondary aqueous iron-polymer battery, its positive electrode, and its preparation method. Background Technology

[0002] In the field of aqueous metal batteries, aqueous Fe metal batteries are very promising energy storage batteries due to their low cost and high global distribution.

[0003] Current research on secondary aqueous iron batteries, whether the earliest alkaline batteries (Fe-Ni and iron-based flow batteries) or the more recent batteries using neutral or weakly acidic electrolytes, all suffer from very low cycle life, severely limiting the widespread application of iron batteries. In general, the main reasons are as follows: 1. Fe 2+ It is unstable under alkaline conditions and easily forms precipitates of ferrous (Fe2+) or ferric (Fe3+) iron. Even in neutral or weakly acidic electrolytes, ferrous iron readily hydrolyzes to form Fe(OH)2; 2. Due to Fe... 2+ ionic radius and Li + The radii are very close, and the Fe in the positive divalent state is... 2+ The high surface charge density of ions makes it difficult to find matching cathode materials, and in addition, Fe... 2+ The slow kinetics and the tendency of iron, as an electrocatalyst, to produce hydrogen evolution are the main reasons for the slow development of aqueous iron batteries. To address these issues, many researchers have focused on improving the performance of aqueous iron batteries; however, limited battery life remains a major technical bottleneck restricting their development.

[0004] For example, the team led by Xiu-Lei Ji at Oregon State University developed a series of aqueous iron batteries. The Fe / Prussian blue and Fe / lithium iron phosphate batteries have cycle lives of 1000 and 100 cycles, respectively. The battery with a cycle life of 1000 cycles has a capacity of only 60 mAh g at a 2C rate. -1 The capacity (Adv. Funct. Mater. 2019, 29, 1900911). The initial capacity of the modified Fe / VOPO4∙2H2O battery is approximately 60 mAh g. -1 However, its cycle life is only about 800 cycles (Adv. Mater. 2021, 33, 2105234), and its capacity decay is significant; at 0.2 Ag -1 The Fe / S battery discharged to 950 mA g. -1 However, its cycle life is only about 30 cycles (Adv. Energy Mater. 2019, 1902422), which is far from meeting the requirements of applications.

[0005] For example, the Fe / I2 battery developed by Tianjin University achieved 550 cycles and a capacity of approximately 200 mAh g. -1 However, the iodine shuttle leads to severe self-discharge of the battery, and the participation of the electrolyte in the reaction is not suitable for large-scale promotion.

[0006] For example, the University of California, San Diego has developed a long-cycle alkaline Fe / Ni battery, achieving a cycle life of 1 A g. -1 Discharged at a current density of 98 mAg -1 The cycle count reached 2000 revolutions. However, the anode fabrication process is very complex (Nano Lett. 2020, 20, 1700−1706), which limits its practical application and promotion.

[0007] Although the above research can achieve Fe 2+ It is rechargeable, but there are still technical limitations that restrict Fe. 2+ The development and practical applications of batteries. For example, when Fe metal is used as the negative electrode material, it is easily hydrolyzed under weakly acidic conditions, making the electrolyte unstable. This is even more pronounced under neutral or alkaline electrolyte conditions. Furthermore, due to the nature of Fe... 2+ The high charge density of ions makes it difficult to find suitable cathode materials; even layered vanadium-based materials are merely H... + The insertion and extraction of Fe 2+ No capacity was contributed. To improve the lifespan of Fe batteries, ascorbic acid, NH4Cl (Nano Res. 2022, 15(4): 3187–3194), or composite electrolytes (FeCl2 / MgCl2 or FeCl2 / CaCl2) were added to the electrolyte. However, this only improved the electrochemical performance to a certain extent, without an order-of-magnitude improvement (ACS Cent.Sci. doi: 10.1021 / acscentsci.2c00293). Summary of the Invention

[0008] To address the aforementioned shortcomings, the present invention aims to provide a highly stable secondary aqueous iron-polymer battery, its positive electrode, and a preparation method thereof.

[0009] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0010] A method for preparing a positive electrode for a highly stable secondary aqueous iron-polymer battery includes the following steps:

[0011] (1) Preparation of positive electrode current collector: Prepare carbon cloth, graphite paper or stainless steel as positive electrode current collector;

[0012] (2) Preparation of cathode materials: Prepare polymers containing secondary / tertiary amine groups and conjugated groups as cathode materials; because Fe 2+ These are high-valence ions with a high charge density, making them difficult to integrate with common cathode materials or to embed into cathode materials due to high electrostatic effects. We use polyaniline-based polymers as the cathode, as polyaniline contains active nitrogen atoms, which facilitates interaction with Fe. 2+ Coordination occurs, and the process is highly reversible. Specifically, it includes the following steps: (2.1) Preparing a liquid comprising a strong acid solution and a substance containing an active N atom dissolved in the strong acid solution; the strong acid solution is hydrochloric acid or sulfuric acid, and the substance containing the active N atom is one or more of aniline, diphenylamine, melamine, tris(4-aminophenyl)amine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, and quinone organic compounds containing an aniline group; such mixing methods may be used. 1. Add 0.1-1M aniline to a container containing 1-10M hydrochloric acid or sulfuric acid; 2. Add 0.1-1M aniline and a quinone organic compound containing an aniline group to a container containing 1-10M hydrochloric acid or sulfuric acid; 3. Add 0.1-1M aniline and 0.001-1M diphenylamine to a container containing 1-10M hydrochloric acid or sulfuric acid; 4. Add 0.1-1M aniline, 0.001-1M diphenylamine, and 0.001-1M diphenylamine to a container containing 1-10M hydrochloric acid or sulfuric acid. 5. Add 0.1-1M aniline, 0.001-1M diphenylamine, and 0.001-1M tris(4-aminophenyl)amine to a container containing 1-10M hydrochloric acid or sulfuric acid; 6. Add 0.1-1M aniline, 0.001-1M diphenylamine, and 0.001-1M 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to a container containing 1-10M hydrochloric acid or sulfuric acid. This can improve electron transport by acting on cross-linking points. (2.2) A solution of ammonium persulfate with a hydrochloric acid concentration of 0.1 to 1.25 times is slowly added to the liquid at a temperature of -5 to 10 degrees Celsius to carry out the reaction, preferably for 10 to 48 hours; (2.3) After the reaction is complete, the mixture is washed with water, ethanol or acetone and then dried to obtain polyaniline; (2.4) The polyaniline, conductive carbon black and binder are mixed in a mass ratio of 4 to 7: 2 to 4: 1 to 2 to obtain the positive electrode material.

[0013] (3) Preparation of the positive electrode: The positive electrode material is coated onto the positive electrode current collector, and after drying, the positive electrode is obtained. For porous positive electrode current collectors that are stable in acid solutions, the positive electrode current collector is immersed in the reaction solution during the preparation process; for flexible positive electrode current collectors, the same coating process is used to fabricate the electrode. This positive electrode material is a polymer containing abundant nitrogen elements (or secondary / tertiary amine groups) and conjugated groups, and has the characteristics of high stability, easy preparation, and non-toxicity and environmental friendliness.

[0014] A high-stability aqueous secondary iron-polymer battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is prepared using the aforementioned method for preparing the positive electrode of a high-stability aqueous secondary iron-polymer battery, and the negative electrode is metallic Fe with a purity ≥98%. If the Fe electrode is treated in an air-isolated environment, this part of the Fe electrode needs to be polished. The polishing sandpaper used ranges from 400 grit to 3000 grit to ensure a smooth Fe surface. Isolation from air is to prevent contact between metallic Fe and oxygen and water molecules in the air, which could cause oxidation on the Fe surface and the formation of an iron oxide film that would affect battery performance. If the battery is assembled in an atmospheric environment, it can be soaked in 0.01M–3M hydrochloric acid or 0.01M–3M sulfuric acid solution for 1–60 minutes, followed by rinsing with water, and finally treating the metallic iron surface with acetone to remove surface residues, drying, and then isolating it from air for later use. The electrolyte is slightly acidic, with a pH value of pH 2–5. The electrolyte is preferably ferrous trifluoromethanesulfonate, ferrous dichloride, or ferrous sulfate. If using slightly acidic ferrous trifluoromethanesulfonate, the concentration can range from 0.01 M to 5 M. If FeCl2 or FeSO4 is used as the electrolyte, an acid with the corresponding anion must be added during solution preparation to adjust the pH to 2-5. The acidity is intended to provide protons, which not only contribute to capacity but also provide faster kinetics, thus improving battery performance. The deionized water used to prepare the electrolyte must be heated to boiling to remove any oxygen present.

[0015] The beneficial effects of this invention are as follows: The high-stability secondary aqueous iron-polymer battery provided by this invention uses metallic Fe with a purity ≥98% as the negative electrode. Because Fe... 2+ These are high-valence ions with a relatively high charge density, making them suitable for insertion into the cathode material. Polyaniline-based polymers are rationally chosen as the cathode material because polyaniline contains active nitrogen atoms, which facilitates interaction with Fe. 2+ Coordination occurs, and the process is highly reversible, enabling reversible long-cycle batteries in aqueous electrolytes. It features high stability, ease of preparation, and non-toxicity and environmental friendliness.

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the proton transport mechanism.

[0018] Figure 2 This is a schematic diagram illustrating the rate performance of the battery of the present invention.

[0019] Figure 3 This is a schematic diagram of the cycle life of the battery of the present invention. Detailed Implementation

[0020] Example: This example provides a highly stable secondary aqueous iron-polymer battery, which includes the following steps:

[0021] (I) Preparation of positive electrode current collector:

[0022] Carbon cloth, graphite paper, or stainless steel can be used as the positive electrode current collector;

[0023] (II) Preparation of cathode materials:

[0024] Due to Fe 2+ These are high-valence ions with a high charge density, making them difficult to integrate with common cathode materials or to embed into cathode materials due to high electrostatic effects. We use polyaniline-based polymers as the cathode, as polyaniline contains nitrogen atoms as active sites, which facilitates interaction with Fe. 2+ The process involves a complexation process that is highly reversible. The cathode material is prepared using a chemical oxidation method. The liquid can be prepared using one of the following A and B methods.

[0025] A: Add 0.1-1M aniline to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0026] B: Add 0.1-1M aniline and quinone organic compounds containing aniline groups to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0027] C: Add 0.1-1M aniline and 0.001-1M diphenylamine to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0028] D: Add 0.1-1M aniline, 0.001-1M diphenylamine and 0.001-1M melamine to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0029] E: Add 0.1-1M aniline, 0.001-1M diphenylamine and 0.001-1M tris(4-aminophenyl)amine to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0030] F: Add 0.1-1M aniline, 0.001-1M diphenylamine and 0.001-1M 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to a container containing 1-10M hydrochloric acid or sulfuric acid;

[0031] A solution of ammonium persulfate with a hydrochloric acid concentration of 0.1–1.25 times is slowly added to the liquid in any one of steps S1–S6 at a temperature of -5–10°C to carry out the reaction. After the reaction is complete for 10–48 hours, the mixture is washed repeatedly with water, ethanol, or acetone and then dried to obtain polyaniline. For a smooth positive electrode current collector, polyaniline, conductive carbon black, and binder can be mixed in a mass ratio of 4:4:2, 6:3:1, 7:2:1, or 8:1:1 to prepare the positive electrode material. For a porous positive electrode current collector that is stable in acidic solutions, the current collector can be immersed in the reaction solution during the preparation process. For a flexible positive electrode current collector, a coating process can also be used to fabricate the electrode. The resulting positive electrode material is a polymer containing abundant nitrogen (or secondary / tertiary amine groups) and conjugated groups, exhibiting high stability, ease of preparation, and non-toxicity and environmental friendliness.

[0032] (III) Battery assembly:

[0033] The above-prepared positive electrode, separator, and negative electrode are assembled and sealed after electrolyte injection. The negative electrode is made of Fe metal with a purity ≥98%. The Fe metal is treated using the following method:

[0034] Method 1: If the Fe battery is assembled in a glove box, the Fe metal sheet should be polished with sandpaper of different grits, ranging from 600 grit to 3000 grit. At the same time, the processed Fe metal sheet should be prevented from contacting oxygen and water molecules in the air to prevent it from being oxidized into an oxide film. The oxide film has poor conductivity and can easily affect the performance of the battery.

[0035] Method 2: If assembling the battery in an atmospheric environment, it can be soaked in 0.01M~3M hydrochloric acid or 0.01M~3M sulfuric acid solution for 1~60 minutes, then rinsed with water several times, and finally treated with acetone to remove the surface residue, dried, and isolated from air for later use.

[0036] The preferred acidity of the electrolyte is ferrous trifluoromethanesulfonate, ferrous dichloride, or ferrous sulfate. If ferrous trifluoromethanesulfonate is used, the concentration ranges from 0.01 to 5 M. If FeCl2 or FeSO4 is used as the electrolyte, an acid with the corresponding anion must be added during solution preparation to adjust the pH to 2-5. The purpose of acidity is to provide protons, which not only contributes to capacity but also provides faster kinetics, thus improving battery performance. See details... Figure 1 This is the proton transport mechanism, where the large sphere represents an oxygen atom and the small sphere represents a hydrogen atom. The deionized water used to prepare the electrolyte must be heated to boiling to remove any oxygen present in the water.

[0037] After testing, see Figure 2 and Figure 3The high-stability secondary aqueous iron-polymer battery prepared by this invention achieves over 39,000 cycles in an aqueous iron battery system with 100% capacity retention, at current densities ranging from 5 to 25 A g. −1 The capacity released is 209-133 mAh g. −1 Its cycle life exceeds that of all current aqueous iron batteries, and even surpasses that of most aqueous batteries.

[0038] Based on the disclosure and teachings of the above specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention. As described in the above embodiments of the present invention, other batteries, cathode materials, and preparation methods obtained using the same or similar methods and components are all within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode for a highly stable secondary aqueous iron-polymer battery, characterized in that, It includes the following steps: (1) Preparation of positive electrode current collector: Prepare carbon cloth, graphite paper or stainless steel as positive electrode current collector; (2) Preparation of cathode material: Prepare polymers containing secondary / tertiary amine groups and conjugated groups as cathode materials; (3) Preparation of positive electrode: The positive electrode material is coated on the positive electrode current collector and dried to obtain the positive electrode.

2. The method for preparing the positive electrode of a high-stability secondary aqueous iron-polymer battery according to claim 1, characterized in that, The polymer in step (2) is a polyaniline-based polymer.

3. The method for preparing the positive electrode of a high-stability secondary aqueous iron-polymer battery according to claim 2, characterized in that, Step (2) specifically includes the following steps: (2.1) Preparing a liquid, the liquid comprising a strong acid solution and a substance containing an active site N atom dissolved in the strong acid solution; the strong acid solution is hydrochloric acid, and the substance containing an active site N atom is one or a mixture of aniline, diphenylamine, melamine, tris(4-aminophenyl)amine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and quinone organic compounds containing an aniline group; (2.2) A solution of ammonium persulfate with a concentration of 0.1 to 1.25 times that of hydrochloric acid is slowly added to the liquid at a temperature of -5 to 10 degrees Celsius to carry out the reaction; (2.3) After the reaction is complete, wash with water, ethanol or acetone and then dry to obtain polyaniline; (2.4) The polyaniline, conductive carbon black and binder are mixed to obtain the positive electrode material.

4. The method for preparing the positive electrode of a high-stability secondary aqueous iron-polymer battery according to claim 3, characterized in that, The reaction time for step (2.2) is 10 to 48 hours.

5. The method for preparing the positive electrode of a high-stability secondary aqueous iron-polymer battery according to claim 4, characterized in that, In step (2.2), the mass ratio of polyaniline, conductive carbon black and binder is 4-7:2-4:1-2.

6. A positive electrode prepared by the method for preparing a high-stability secondary aqueous iron-polymer battery according to any one of claims 1-5.

7. A highly stable secondary aqueous iron-polymer battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode is prepared by the positive electrode preparation method of the high-stability secondary aqueous iron-polymer battery according to any one of claims 1-5 or the positive electrode according to claim 6, the electrolyte is slightly acidic, and the negative electrode is metallic Fe with a purity of ≥98%.

8. The high-stability secondary aqueous iron-polymer battery according to claim 7, characterized in that, The Fe metal is placed in a sealed space isolated from air and polished until the surface is smooth.

9. The high-stability secondary aqueous iron-polymer battery according to claim 7, characterized in that, The electrolyte has a pH value of pH 2 to 5.

10. The high-stability secondary aqueous iron-polymer battery according to claim 7, characterized in that, The electrolyte is ferrous trifluoromethanesulfonate, ferrous dichloride, or ferrous sulfate.

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