Preparation method and application of water-based iron ion battery positive electrode material

Abstract

The invention discloses a preparation method and application of an aqueous iron ion battery positive electrode material. The preparation method comprises the following steps: (1) respectively mixing a single type of ferric salt and potassium ferricyanide with water to obtain a solution A and a solution B; (2) mixing the solution A and the solution B, stirring in a water bath kettle, and carrying out a co-precipitation reaction to obtain a solid precipitate; and (3) centrifuging, washing and drying the solid precipitate to obtain the nano-particles with the particle size of 150-200nm. The obtained nanoparticles can be used as an aqueous iron ion battery positive electrode material, the positive electrode can realize Fe < 2 + > and NH4 < + > ion co-de-intercalation electrochemical reaction in the charging and discharging process, and the reversible specific capacity of the battery is remarkably improved; the embedded NH < 4 + > and N in the positive electrode material can form a stable hydrogen bond structure, so that the cycling stability of the battery is effectively improved. The preparation process is easy to operate, the product yield is high, the consistency is excellent, and the method is suitable for large-scale preparation and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and relates to a preparation method and application of a cathode material for an aqueous iron ion battery. Background Art

[0002] Aqueous batteries have many advantages such as low cost, high safety, and high energy conversion efficiency, and have great application prospects in the field of large-scale energy storage. In recent years, aqueous iron ion batteries using Fe 2+ as a carrier have received more and more research and attention, and their specific advantages are as follows: (1) Iron has a high abundance in the earth's crust and low raw material cost; (2) Iron-based materials can undergo multi-electron transfer reactions, and its metallic iron negative electrode has an ultra-high theoretical specific capacity (960 mAh / g, 7557 mAh / cm 3 ); (3) The aqueous electrolyte prepared with inexpensive inorganic iron salts has application advantages such as high ionic conductivity and environmental friendliness. It should be emphasized that the iron-based cathode material has an important impact on the performance of aqueous iron ion batteries. So far, the research on the cathode of iron ion batteries is still relatively scarce, and the developed cathode materials include conversion type (such as: S8, I2, etc.) and insertion / extraction type (such as: LiFeO4, Prussian blue analogs, etc.).

[0003] Iron-based Prussian blue analogs (Fe x [Fe(CN)6] y ·nH2O) are a kind of cathode materials with great application potential. It has a stable framework structure and three-dimensional open channels, providing rich reaction sites and fast ion transport channels for the reversible insertion / extraction of Fe 2+ ions. However, when assembling an aqueous iron ion battery with a Fe[Fe(CN)6] 0.75 ·3.5H2O cathode and a metallic iron negative electrode, its specific capacity is only 60 mAh / g; this low specific capacity is mainly attributed to the non-uniform mixing of Fe 0.75 and Fe 2+ and a large number of Fe(CN)6 vacancy defects in the prepared Fe[Fe(CN)6] 3+ ·3.5H2O structure. These defects increase the content of crystal water in the lattice gap and reduce the crystallinity of the material; the defects and disordered grain boundaries in the Fe[Fe(CN)6] 0.75 ·3.5H2O structure also hinder the Fe 3+ / Fe 2+ redox reaction, resulting in some active sites being unable to participate in the electrochemical reaction, causing capacity loss of the iron ion battery. Based on this, preparing a new type of Prussian blue analog cathode material and obtaining a preparation method for a high-crystallinity and low-defect material are crucial for developing aqueous iron ion batteries with high specific capacity and long cycle life. Summary of the Invention

[0004] In view of this, one of the objectives of the present invention is to provide a preparation method for the positive electrode material of an aqueous iron ion battery. This preparation method uses a single type of ferric salt as the iron source, and pure water as the reaction solvent. Uniform nanoparticles can be batch-produced without adding organic solvents and chelating agents. This preparation process has the advantages of low raw material cost, environmental friendliness, and simple operation, which is conducive to realizing large-scale production. Another objective of the present invention is to provide the positive electrode material of an aqueous iron ion battery prepared by the above method. This material is called Berlin green, and its chemical general formula is Fe[Fe(CN)6]·nH2O, abbreviated as FeHCF. This material has the characteristics of high crystallinity, high specific capacity, and stable structure. The third objective of the present invention is to provide the application of the above positive electrode material in the preparation of aqueous iron ion secondary batteries. When this material is used as the positive electrode of an iron ion battery, the specific capacity and cycling performance of the battery are both greatly improved.

[0005] To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0006] The present invention provides a preparation method for the positive electrode material of an aqueous iron ion battery, specifically including the following steps:

[0007] (1) Mix a single type of ferric salt and potassium ferrocyanide with deionized water respectively to obtain solutions A and B;

[0008] (2) Mix solution A and solution B, and carry out a coprecipitation reaction in a water bath at a certain stirring speed, temperature, and time to obtain a solid precipitate;

[0009] (3) Centrifuge, wash, and dry the above solid precipitate to obtain the positive electrode material of the aqueous iron ion battery;

[0010] Among them, the positive electrode material of the aqueous iron ion battery contains a Fe[Fe(CN)6]·nH2O crystal structure, and the water of crystallization content n ≤ 3.

[0011] In some embodiments of the present invention, in the step (1), the ferric metal salt includes one of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, and ferric acetate.

[0012] In some embodiments of the present invention, in the step (1), the concentration of the ferric salt is 0.05 - 2 mol / L; the concentration of potassium ferrocyanide is 0.05 - 3 mol / L.

[0013] In some embodiments of the present invention, in the step (2), the molar ratio of solution A to solution B is 3:2.

[0014] In some embodiments of the present invention, in the step (2), the mixing method is to drop solution A into solution B, and the dropping speed is 0.5 - 100 mL / min;

[0015] In some embodiments of the present invention, in step (2), the reaction conditions involved in the coprecipitation reaction are as follows: stirring speed: 200 - 800 revolutions per minute, temperature: 30 - 100 °C, reaction duration: 0.5 - 10 hours.

[0016] In some embodiments of the present invention, in step (3), the washing solvent is absolute ethanol, the drying method is vacuum drying, the drying temperature is 40 - 100 °C, and the drying time is 6 - 24 hours.

[0017] The present invention also provides a positive electrode material for an aqueous iron ion battery. The positive electrode material is prepared according to the above preparation method. The material is in the form of nanoparticles, has a face-centered cubic structure, has good crystallinity, and the particle size is distributed between 150 - 200 nm.

[0018] The present invention also provides the application of the Prussian blue analogue positive electrode material obtained according to the above preparation method in an aqueous iron ion secondary battery, which includes the following steps:

[0019] (1) Grind and mix the above positive electrode material, conductive agent acetylene black, and binder PVDF according to a mass ratio of 8:1:1, then add an appropriate amount of N-methylpyrrolidone, and stir at room temperature for 8 - 12 hours to obtain a black viscous slurry; coat the slurry evenly on a carbon cloth current collector with a certain thickness, perform a drying treatment, and cut to obtain an electrode sheet;

[0020] (2) Use the electrode sheet prepared in step (1) as the positive electrode, activated carbon as the negative electrode, and an aqueous solution of FeSO4 and NH4Cl mixed as the electrolyte to assemble an aqueous iron ion battery.

[0021] Among them, the battery uses Fe 2+ and NH4 + as co-insertion / extraction carriers: Fe 2+ can activate the low-spin active iron sites in the positive electrode sheet to participate in the electrochemical reaction and improve the specific capacity of the battery; NH4 + On the one hand, it can undergo an insertion / extraction reaction at the remaining active sites to improve the specific capacity of the battery. On the other hand, it can form hydrogen bonds with the N atoms in the FeHCF lattice, effectively alleviating the volume strain during the Fe 2+ / NH4 + insertion / extraction process and significantly improving the cycle stability of the battery.

[0022] In some embodiments of the present invention, in the electrolyte described in step (2), the concentration of FeSO4 is 0.5 - 2 mol / L, the concentration of NH4Cl is 0.5 - 2 mol / L, and the molar ratio of FeSO4 to NH4Cl is 3:1 - 1:2.

[0023] As can be seen from the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention prepares the cathode material of the aqueous iron ion battery by a simple liquid-phase coprecipitation method. Trivalent iron salts with oxidizing properties and potassium ferricyanide are selected as raw materials. Through the tight Fe 3+ -CN-Fe bridging between Fe and the ferricyanide ligand [Fe(CN)6] 3- , a highly complete structural framework is constructed, thereby reducing the lattice vacancy defects and the content of crystal water in the material and improving its crystallinity. The present invention also optimizes the temperature and reaction time of the coprecipitation reaction, strengthens the coordination reaction kinetics of Fe 3+ , promotes the dense growth of the lattice, and effectively balances the coordination integrity, particle uniformity and lattice stability of the material. 3+ 3+ 3- 3+

[0025] (2) The preparation process involved in the present invention uses a single type of trivalent iron salt as the iron source and pure water as the solvent. Through the strong coordination ability of [Fe(CN)6] in potassium ferricyanide, the free migration of Fe 3- is restricted. Without adding organic solvents and chelating agents, the anisotropic growth of the material is effectively inhibited, and finally nanoparticles with uniform particle size can be batch-produced. This preparation process has the advantages of low raw material cost, environmental friendliness, simple operation, etc., which is conducive to realizing large-scale production. 3+ 2+

[0026] (3) The present invention applies the prepared FeHCF as the cathode of the aqueous iron ion secondary battery, and uses a mixed solution of FeSO4 and NH4Cl as the electrolyte; by means of the co-insertion / extraction storage mechanism of Fe 2+ and NH4 + , the low-spin active iron sites in FeHCF are activated to participate in the electrochemical reaction, significantly improving the specific capacity of the battery. In addition, NH4 + can form a hydrogen bond with N in the ferricyanide, effectively buffering the volume strain of FeHCF caused by the insertion / extraction of Fe 2+ and NH4 + , stabilizing the lattice structure and improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0028] Figure 1 They are (a) Scanning Electron Microscope (SEM) of FeHCF material; (b) X-ray Diffraction (XRD); (c) Raman Spectrum (Raman) diagram; (d) Thermogravimetric (TG) curve.

[0029] Figure 2 Electrochemical performance diagrams of the FeHCF positive electrode in an iron-based aqueous electrolyte, specifically including: (a) linear cyclic voltammetry (CV) curves, (b) galvanostatic charge-discharge (GCD) curves, and (c) long-cycle test curves.

[0030] Figure 3 Electrochemical performance diagrams of an aqueous iron-ion secondary battery assembled with the FeHCF positive electrode, specifically including: (a) GCD curves and (b) long-cycle curves. Detailed implementation manners

[0031] Next, the preferred embodiments of the present invention will be described in detail in conjunction with the embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The scope of the present invention should not be construed as being limited to the embodiments described below. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0032] Embodiment 1

[0033] 1. Preparation of a positive electrode material for an aqueous iron-ion battery:

[0034] (1) Dissolve 0.135 mol of anhydrous ferric chloride in 40 mL of deionized water to prepare solution A; dissolve 0.09 mol of potassium ferricyanide in 40 mL of deionized water to prepare solution B.

[0035] (2) Drop solution A into solution B at a dropping rate of 1 mL / min, stir to mix them evenly, place the obtained mixed solution in a 60 °C constant temperature water bath, stir at a speed of 600 revolutions / min, and obtain a dark green precipitate after reacting for 3 hours.

[0036] (3) Filter the above reaction product and wash it 3 times with absolute ethanol; dry the washed product in a 60 °C constant temperature drying oven to obtain FeHCF powder particles with uniform size and high crystallinity.

[0037] The morphology of the FeHCF material is as shown in SEM( Figure 1 a), the powder is in the form of nanoparticles, with a face-centered cubic structure, good crystallinity, uniform particle size, and the size distribution is between 150 and 200 nm. The XRD test results( Figure 1 b) show that the diffraction peaks that appear are highly matched with Berlin green (JCPDS card number: 01-0239), and the strong and sharp diffraction peaks prove that the material has the characteristics of high crystallinity. The Raman spectroscopy test results are as shown in Figure 1 c, 2073 cm -1 and 2141 cm -1The vibration peaks that appear correspond to the stretching vibrations of C≡N and A respectively. g and A 1g vibration modes, which indicates that the valence state of Fe remains unchanged during the liquid-phase reaction. The TG test results ( 3+ (d) show that the powder undergoes different degrees of mass loss between 100 - 200 °C and 200 - 300 °C. The mass loss below 200 °C is caused by the loss of water in the lattice interstitial of the powder, while the loss above 200 °C is caused by its coordinated water and self-decomposition. In summary, the chemical formula of the Prussian blue cathode material prepared in this example is: Fe[Fe(CN)6]·2.8H2O. Figure 1 d) show that the powder undergoes different degrees of mass loss between 100 - 200 °C and 200 - 300 °C. The mass loss below 200 °C is caused by the loss of water in the lattice interstitial of the powder, while the loss above 200 °C is caused by its coordinated water and self-decomposition. In summary, the chemical formula of the Prussian blue cathode material prepared in this example is: Fe[Fe(CN)6]·2.8H2O.

[0038] 2. Preparation of FeHCF cathode and testing of its electrochemical performance:

[0039] (1) Take the above-mentioned Fe[Fe(CN)6]·2.8H2O powder, acetylene black conductive agent and PVDF binder, grind and mix them evenly according to a mass ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone solvent, and stir at room temperature for 12 hours to obtain a black viscous slurry; use a scraper to evenly coat the slurry onto a carbon cloth current collector, and after drying, the FeHCF cathode is obtained, where the active material loading in the cathode sheet is 8 mg / cm 2 .

[0040] (2) Using the above FeHCF cathode as the working electrode, an Ag / AgCl electrode as the reference electrode, a platinum wire as the counter electrode, and a mixed aqueous solution of 1 mol / L FeSO4 and 1 mol / L NH4Cl as the electrolyte, assemble a three-electrode test system. In this system, perform CV tests at a scan rate of 1 mV / s to verify the reversibility of the electrochemical reaction of the cathode. Change the concentration of FeSO4 in the test system to configure the mixed electrolyte. When the FeSO4 concentrations are 0 / 0.5 / 1 / 1.5 / 2 mol / L respectively, perform GCD tests at a current density of 5 A / g to verify the specific capacity of the cathode. In a three-electrode system composed of a mixed electrolyte of 1 mol / L FeSO4 and 1 mol / L NH4Cl, charge and discharge repeatedly at a current density of 5 A / g to test the cycle stability of the electrode.

[0041] The CV test results of this FeHCF cathode are as Figure 2 shown in a. In the FeSO4 / NH4Cl mixed electrolyte, the CV curve shows two pairs of redox peaks. The redox peaks located at 0.38 V and 0.17 V correspond to the reversible deintercalation and intercalation of NH4 + , and the redox peaks located at 0.75 V and 0.31 V correspond to the reversible deintercalation and intercalation of Fe 2+ ; this result confirms that this cathode material has abundant reactive sites and can achieve the reversible deintercalation and intercalation of NH4 +and Fe 2+ co - deintercalation. The GCD test curves ( Figure 2 b) show that, with the concentration of NH4Cl kept constant, as the concentration of Fe 2 + increases, the specific capacity of this positive electrode first increases and then tends to be stable. When the concentration of Fe 2+ is greater than or equal to 1 mol / L, the specific capacity of the positive electrode can be stabilized at about 150 mAh / g. Thus, it can be seen that the high specific capacity characteristic of the prepared FeCHF mainly benefits from the increase in the electrochemically reactive sites in the material. The cyclic stability test results of this positive electrode are as shown in Figure 2 c. When performing continuous GCD tests at a rate of 5 A / g for 1000 cycles, the retention rate of the electrode specific capacity is as high as 83.47%, proving that this positive electrode material has excellent cyclic stability.

[0042] 3. Assembly and electrochemical performance detection of aqueous iron - ion batteries:

[0043] Assemble a full cell with the above - mentioned FeHCF positive electrode sheet, activated carbon negative electrode sheet, and an electrolyte of a mixed aqueous solution of 1 mol / L FeSO4 and 1 mol / L NH4Cl; carry out electrochemical performance detection on the full cell at room temperature: perform GCD tests at a current density of 0.5 A / g to verify the specific capacity of the battery; repeatedly charge and discharge at a current density of 6 A / g to verify the cyclic stability of the battery.

[0044] The GCD test results of this full cell are as shown in Figure 3 a. The working voltage of the full cell is increased to 1.1 V, and its specific capacity can reach 160 mAh / g; the long - cycle charge - discharge test results of the battery are as shown in Figure 3 b. After 500 cycles, the capacity retention rate of the battery is 94%. This result proves that the FeHCF positive electrode material prepared by the present invention is completely applicable to the aqueous iron - ion battery system and can significantly improve the specific capacity and cyclic stability of the battery.

[0045] The above - mentioned embodiments are only used to illustrate the preferred embodiments of the present invention, rather than to limit the concept and protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the concept and principles of this application shall be included within the protection scope of this application.

Claims

1. A preparation method of a positive electrode material for an aqueous iron ion battery, characterized in that: Specifically, it includes the following steps: (1) Mix a single type of ferric salt and potassium ferrocyanide with deionized water respectively to obtain solutions A and B; (2) Mix solution A and solution B, and carry out a coprecipitation reaction in a water bath at a certain stirring speed, temperature and time to obtain a solid precipitate; (3) Centrifuge, wash and dry the above solid precipitate to obtain a positive electrode material for an aqueous iron ion battery; Among them, the positive electrode material for the aqueous iron ion battery contains a Fe[Fe(CN)6]·nH2O crystal structure, and the water of crystallization content n ≤ 3.

2. The preparation method according to claim 1, characterized in that: In the step (1), the ferric salt includes one of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate and ferric acetate.

3. The preparation method according to claim 1, characterized in that: In the step (1), the concentration of the ferric salt is 0.05 - 2 mol / L; the concentration of potassium ferrocyanide is 0.05 - 3 mol / L.

4. The preparation method according to claim 1, characterized in that: In the step (2), the molar ratio of solution A to solution B is 3:

2.

5. The preparation method according to claim 1, characterized in that: In the step (2), the mixing method is to drop solution A into solution B, and the dropping speed is 0.5 - 100 mL / min.

6. The preparation method according to claim 1, characterized in that: In the step (2), the reaction conditions involved in the coprecipitation reaction are: stirring speed: 200 - 800 revolutions / min; Temperature: 30 - 100 °C; reaction duration: 0.5 - 10 hours.

7. The preparation method according to claim 1, wherein: In the step (3), the washing solvent is absolute ethanol, the drying method is vacuum drying, the drying temperature is 40 - 100 °C, and the drying time is 6 - 24 hours.

8. The cathode material prepared by any of the methods according to claims 1 to 7, characterized in that: The positive electrode material is in the form of nanoparticles, has a face-centered cubic structure, has good crystallinity, and the particle size distribution is between 150 - 200 nm.

9. Use of the cathode material according to claim 8 in the preparation of an aqueous iron ion secondary battery, characterized in that, It includes the following steps: (1) Grind and mix the positive electrode material, conductive agent acetylene black and binder PVDF according to a mass ratio of 8:1:1, then add an appropriate amount of N-methylpyrrolidone, and stir at room temperature for 8 - 12 hours to obtain a black viscous slurry; uniformly coat the slurry on a carbon cloth current collector with a certain thickness, carry out a drying treatment, and cut to obtain an electrode sheet. (2) The electrode sheet prepared in step (1) is used as the positive electrode, activated carbon is used as the negative electrode, and an aqueous solution of FeSO4 and NH4Cl is used as the electrolyte to assemble an aqueous iron ion full battery; Among them, in the aqueous iron-ion secondary battery, Fe 2+ and NH4 + are co-inserted / extracted carriers: Fe 2+ can activate the low-spin active iron sites in the positive electrode plate to participate in the electrochemical reaction and improve the specific capacity of the battery; NH4 + On the one hand, it can undergo insertion / extraction reactions at the remaining active sites to improve the specific capacity of the battery. On the other hand, it can also form hydrogen bonds with the N atoms in the FeHCF lattice, effectively alleviating the volume strain during the Fe 2+ / NH4 + insertion / extraction process and significantly improving the cycle stability of the battery.

10. The application according to claim 9, characterized in that In the electrolyte described in step (2), the concentration of FeSO4 is 0.5 - 2 mol / L, the concentration of NH4Cl is 0.5 - 2 mol / L, and the molar ratio of FeSO4 to NH4Cl is 3:1 - 1:2.

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