Manufacturing process for fluorine-doped material for positive electrodes of Prussian blue sodium-ion batteries

Abstract

Manufacturing process of a fluorine-doped Prussian blue cathode material for sodium-ion batteries, comprising the following steps: S1: Preparation of a mixed solution of sodium ferrocyanide and sodium fluoride and addition of an antioxidant to the mixed solution, wherein the sodium ferrocyanide has a concentration of 0.01 mol / L to 1 mol / L and the sodium fluoride has a concentration of 0.01 mol / L to 1 mol / L; S2: Adding a transition metal salt solution to the mixed solution at a specified flow rate, after the addition is complete, adding a sodium chloride solution to the mixed solution and performing an aging process; wherein the transition metal salt solution has a concentration of 0.01 mol / L to 1 mol / L and the volume ratio of the transition metal salt solution to the mixed solution is 0.9 : 1 to 1.1 : 1; and S3: Performing a solid-liquid separation on the aged material in step S2 to obtain a precipitation, and washing and drying the precipitation to obtain the Prussian blue material for sodium-ion batteries.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of sodium-ion batteries and, in particular, relates to a manufacturing method for a fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries. BACKGROUND

[0002] Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their long cycle life and high specific energy. However, potential safety risks and limited lithium resources prevent the use of lithium-ion batteries in large-scale energy storage systems. In this case, low-cost, long-cycle sodium-ion batteries represent a more attractive alternative to lithium-ion batteries for energy storage systems. Therefore, it is essential to develop sustainable electrode materials for sodium-ion batteries.

[0003] Sodium-ion batteries have the characteristics of low raw material costs, abundant resources, and high electrochemical performance potential, making them expected to be used in large-scale energy storage and represent an important research direction for the next generation of battery technologies. Currently, positive electrode materials for sodium-ion batteries mainly include transition metal oxides, phosphates, Prussian blue materials, and the like. Prussian blue materials have the advantages of a high-voltage platform (>3 V), a large ion channel, large specific capacity, low price, non-toxicity, and easy fabrication, becoming a research focus for positive electrode materials for sodium-ion batteries.However, when the material is used in a non-aqueous sodium-ion battery, cycle performance is poor.

[0004] The Prussian blue material for positive electrodes for sodium-ion batteries can be synthesized by a thermal decomposition method, a hydrothermal method, and a co-precipitation method. CN 1 09 824 060 A relates to an ammonia-rich concave Prussian blue material using a hydrothermal method. CN 1 07 611 404 A discloses a Prussian white composite material, as well as a production method and application thereof. The production method includes a hydrothermal reaction. The thermal decomposition method and the hydrothermal method both utilize a principle of decomposing a single iron source from sodium ferrocyanide. The resulting product has few crystal lattice defects and a low water content.However, both methods have low production efficiency and yield, and produce a toxic NaCN byproduct during the synthesis process, which pollutes the environment and is not suitable for large-scale production. The co-precipitation process is green and environmentally friendly and can achieve larger production.However, at present, patent literature relating to a method for preparing a Prussian blue cathode material by co-precipitation is mainly reported as follows: a method for preparing Prussian blue cathode material and a sodium ion battery (CN 1 07 364 875 A), a method for preparing nano-Prussian blue with low defects and use thereof (CN 1 06 745 068 A), doped Prussian blue material, production method and application thereof (CN 1 11 600 011 A), doped modified Prussian blue-based material for sodium ion batteries and production method (CN 1 09 761 246 A), Prussian blue material and production method thereof (CN 1 10 078 096 A) and surface-modified Ferrocyanide-based material and manufacturing process thereof (CN 1 10 165 167 A).However, in the above synthesis method, transition metal salts and a sodium ferrocyanide solution are simply mixed, a reaction rate is difficult to control, so the material has poor crystallinity, low sodium content, high water content and relatively poor electrochemical performance, and practical use is affected.

[0005] To further control the crystallization behavior of the material, complexing agents are used in the prior art to improve the crystallinity of the material. However, general complexing agents are expensive, and crystal surface residues caused by conventional complexing agents cannot be avoided. OVERVIEW

[0006] The present invention aims to solve at least one of the above technical problems in the prior art. Therefore, the present disclosure provides a manufacturing method for a fluorine-doped Prussian blue positive electrode material for sodium-ion batteries, and can solve the problems of poor crystallinity, poor cycle performance, and crystal surface residue of the Prussian blue positive electrode material for sodium-ion batteries.

[0007] According to one aspect of the present invention, a manufacturing method for a fluorine-doped Prussian blue cathode material for sodium-ion batteries comprises the following steps: S1: Preparing a mixed solution of sodium ferrocyanide and sodium fluoride and adding an antioxidant to the mixed solution, wherein in the mixed solution the sodium ferrocyanide has a concentration of 0.01 mol / L to 1 mol / L and the sodium fluoride has a concentration of 0.01 mol / L to 1 mol / L; S2: Adding a transition metal salt solution to the mixed solution at a certain flow rate after the feeding is completed, adding a sodium chloride solution to the mixed solution, and performing aging; wherein the transition metal salt solution has a concentration of 0.01 mol / L to 1 mol / L and the volume ratio of the transition metal salt solution to the mixed solution is 0.9:1 to 1.1:1; and S3: Performing solid-liquid separation on the aged material in step S2 to obtain a precipitate, and washing and drying the precipitate to obtain the Prussian blue cathode material for sodium ion batteries.

[0008] In some embodiments of the present invention, the antioxidant in step S1 is one or more of butylhydroxyanisole, dibutylhydroxytoluene, propyl gallate, tert-butylhydroquinone, and ascorbic acid.

[0009] In some embodiments of the present invention, the antioxidant in step S1 has a concentration of 0.001 mol / L -0.25 mol / L in the mixed solution.

[0010] In some embodiments of the present invention, in step S2, the transition metal salt solution is at least one of the solutions of nickel sulfate, cobalt sulfate, manganese sulfate, ferric sulfate, ferrous sulfate, nickel nitrate, cobalt nitrate, manganese nitrate, ferric nitrate, ferrous nitrate, nickel chloride, cobalt chloride, manganese chloride, ferric chloride, and ferrous chloride.

[0011] In some embodiments of the present invention, the transition metal salt solution is added in step S2 at a flow rate of 25 mL / h - 50 mL / h.

[0012] In some embodiments of the present invention, in step S2, the sodium chloride solution has a concentration of 1 mol / L to 4 mol / L and a volume ratio of the sodium chloride solution to the mixed solution is from 0.9:1 to 1.1:1.

[0013] In some embodiments of the present invention, in step S2, aging is performed for 2h to 48h.

[0014] In some embodiments of the present invention, in step S3, the precipitate is washed by using deionized water and absolute ethanol.

[0015] In some embodiments of the present invention, in step S3, the precipitate is dried in vacuum at 100°C to 120°C for 12h to 24h.

[0016] A preferred embodiment of the present invention has at least the following advantageous effects: 1. Ferrocyanide ions are easily converted into ferricyanide ions under the influence of light or dissociate into ferric ions and cyanide ions. An antioxidant is added to mitigate the occurrence of this reaction and also improves the purity of the target product. 2. A mixed solution contains a large amount of fluoride ions. When transition metal ions are added, the fluoride ions form a complex with the transition metal ions, thereby inhibiting the precipitation reaction rate, slowing crystallization, and yielding particles with better crystallinity. A metal sodium salt complexed with the fluoride precipitates during the reaction and coprecipitates with the ferrocyanide to form a co-crystal. The fluoride ions are used as complexing agents. Unlike general complexes, no residue is formed. The fluoride ions serve directly as part of a cathode material. During a subsequent charge and discharge process, the fluoride ions act as a support structure for the material; for example, Na4MeF6 is converted to Na2MeF6 during charging. The fluoride ions have a lower mass and can further increase the gram capacity of the material.Currently, the use of fluoride as a material for positive electrodes of sodium-ion batteries is extremely rarely reported. 3. A sodium chloride solution with a higher concentration is added to the mixed solution for long-term aging, so that metal ion complexes are further precipitated, the co-crystallization is more stable, and the production efficiency of the product is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is described in more detail below with reference to the accompanying drawings and embodiments. Fig. 1 is a scanning electron microscope (SEM) image of the fluorine-doped Prussian blue positive electrode material for sodium ion batteries prepared in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0018] The concepts and technical effects of the present invention are described clearly and completely below in conjunction with embodiments so that the objects, features, and effects of the present invention can be fully understood. Obviously, the described embodiments are only some and not all embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should be considered within the scope of the present invention. Embodiment 1

[0019] A fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries was prepared by the embodiment and specifically included the following steps: (1) 100 mL of a mixed solution of sodium ferrocyanide and sodium fluoride was prepared and ascorbic acid was added as an antioxidant, wherein in the mixed solution, the sodium ferrocyanide had a concentration of 0.1 mol / L, the sodium fluoride had a concentration of 0.6 mol / L, and the antioxidant had a concentration of 0.01 mol / L; (2) 100 mL of a manganese sulfate solution with a concentration of 0.1 mol / L and 100 mL of a sodium chloride solution with a concentration of 2 mol / L were prepared separately; (3) the manganese sulfate solution was added into the mixed solution of sodium ferrocyanide and sodium fluoride at a certain flow rate of 25 mL / h; (4) after the feeding was completed, the sodium chloride solution was added to the mixed solution and aging was carried out for 12 h; (5) a solid-liquid separation was carried out to obtain a precipitate; and (6) The precipitate was washed with deionized water and absolute ethanol, and the precipitate was dried in vacuum at 100-120 °C for 12-24 h to obtain a fluorine-doped Prussian blue positive electrode material for sodium-ion batteries with a chemical formula Na6Mn2[Fe(CN)6]F6. Embodiment 2

[0020] A fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries was prepared by the embodiment and specifically included the following steps: (1) 100 mL of a mixed solution of sodium ferrocyanide and sodium fluoride was prepared and ascorbic acid was added as an antioxidant, wherein in the mixed solution, the sodium ferrocyanide had a concentration of 0.1 mol / L, the sodium fluoride had a concentration of 0.6 mol / L, and the antioxidant had a concentration of 0.01 mol / L; (2) 100 mL of a mixed solution of ferrous chloride with a concentration of 0.25 mol / L and ferric chloride with a concentration of 0.05 mol / L and 100 mL of a sodium chloride solution with a concentration of 2 mol / L were prepared; (3) a mixed ferric salt solution was added into the mixed solution of sodium ferrocyanide and sodium fluoride at a certain flow rate of 25 mL / h; (4) after the feeding was completed, the sodium chloride solution was added to the mixed solution and aging was carried out for 48 h; (5) a solid-liquid separation was carried out to obtain a precipitate; and (6) The precipitate was washed with deionized water and absolute ethanol, and the precipitate was dried in vacuum at 100-120 °C for 12-24 h to obtain a fluorine-doped Prussian blue positive electrode material for sodium-ion batteries.

[0021] In the embodiment, the fluoride ions did not complex with iron(II) ions, a ferrous fluoride precipitate was prepared, the sodium ferrocyanide and the iron(II) ions were complexed in a ratio of 1:1, the fluoride ions and the iron(III) ions were complexed in a ratio of 3:1 for complexation, and after sodium chloride was added and after a long period of aging and recrystallization, a crystal with a chemical formula Na7Fe6[Fe(CN)6]2F was obtained. 12 receive. Embodiment 3

[0022] A fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries was prepared by the embodiment and specifically included the following steps: (1) 100 mL of a mixed solution of sodium ferrocyanide and sodium fluoride was prepared and butylhydroxyanisole was added as an antioxidant, wherein in the mixed solution, the sodium ferrocyanide had a concentration of 0.01 mol / L, the sodium fluoride had a concentration of 0.06 mol / L, and the antioxidant had a concentration of 0.001 mol / L; (2) 100 mL of a cobalt sulfate solution with a concentration of 0.01 mol / L and 100 mL of a sodium chloride solution with a concentration of 4 mol / L were prepared separately; (3) the cobalt sulfate solution was added into the mixed solution of sodium ferrocyanide and sodium fluoride at a certain flow rate of 50 mL / h; (4) after the feeding was completed, the sodium chloride solution was added to the mixed solution and aging was carried out for 24 h; (5) a solid-liquid separation was carried out to obtain a precipitate; and (6) The precipitate was washed with deionized water and absolute ethanol, and the precipitate was dried in vacuum at 100-120 °C for 12-24 h to obtain a fluorine-doped Prussian blue positive electrode material for sodium-ion batteries with a chemical formula Na6Co2[Fe(CN)6]F6. Comparative embodiment

[0023] A fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries was prepared by the comparative embodiment and specifically included the following steps: (1) 100 mL of a sodium ferrocyanide solution was prepared and ascorbic acid was added as an antioxidant, wherein the sodium ferrocyanide in the solution had a concentration of 0.1 mol / L and the antioxidant had a concentration of 0.01 mol / L; (2) 100 mL of a manganese sulfate solution with a concentration of 0.1 mol / L was prepared; (3) the manganese sulfate solution was added into the sodium ferrocyanide solution at a certain flow rate of 25 mL / h; (4) after feeding was completed, aging was carried out for 12 hours; (5) a solid-liquid separation was carried out to obtain a precipitate; and (6) The precipitate was washed with deionized water and absolute ethanol, and the precipitate was dried in vacuum at 100-120 °C for 12-24 h to obtain a Prussian blue positive electrode material for sodium-ion batteries with the chemical formula Na2Mn[Fe(CN)6]. Test execution form

[0024] The Prussian blue materials for positive electrodes for sodium-ion batteries prepared in the embodiments and the comparative embodiment were assembled into a sodium-ion half-battery with an organic electrolyte system, and an electrochemical performance test was conducted. The test results were as shown in Table 1. Table 1 0.1 C initial specific discharge capacity (mAh / g) Specific discharge capacity after 200 cycles (mAh / g) Embodiment 1 157,6 130,8 Embodiment 2 162,7 137,6 Embodiment 3 152,1 123,1 Comparative embodiment 138,1 93,2

[0025] From Table 1, it can be seen that, compared to the embodiments, the non-fluorine-doped Prussian blue material for positive electrodes for sodium-ion batteries in the comparative embodiment exhibits significantly lower specific capacity and cycle performance. This is because, in the comparative embodiment, a transition metal salt was simply mixed with the sodium ferrocyanide solution, the reaction rate was difficult to control, the material had low crystallinity and low sodium content, and thus, its electrochemical performance was poor.

[0026] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above-mentioned embodiments. Various modifications can be made within the scope of knowledge possessed by a person skilled in the art without departing from the purpose of the present disclosure. Furthermore, the embodiments in the present invention and the features in the embodiments can be combined with each other in a non-competitive situation.

Claims

[1] Manufacturing process of a fluorine-doped Prussian blue cathode material for sodium-ion batteries, comprising the following steps: S1: Preparing a mixed solution of sodium ferrocyanide and sodium fluoride and adding an antioxidant to the mixed solution, wherein in the mixed solution the sodium ferrocyanide has a concentration of 0.01 mol / L to 1 mol / L and the sodium fluoride has a concentration of 0.01 mol / L to 1 mol / L; S2: Adding a transition metal salt solution to the mixed solution at a certain flow rate after the feeding is completed, adding a sodium chloride solution to the mixed solution, and performing aging; wherein the transition metal salt solution has a concentration of 0.01 mol / L to 1 mol / L and the volume ratio of the transition metal salt solution to the mixed solution is 0.9:1 to 1.1:1; and S3: Performing solid-liquid separation on the aged material in step S2 to obtain a precipitate, and washing and drying the precipitate to obtain the Prussian blue material for sodium ion batteries. [2] The manufacturing method according to claim 1, wherein in step S1, the antioxidant is one or more of butylhydroxyanisole, dibutylhydroxytoluene, propyl gallate, tert-butylhydroquinone and ascorbic acid. [3] The manufacturing method according to claim 1, wherein in step S1, the antioxidant has a concentration of 0.001 mol / L to 0.25 mol / L in the mixed solution. [4] The manufacturing method according to claim 1, wherein in step S2, the transition metal salt solution is at least one of the solutions of nickel sulfate, cobalt sulfate, manganese sulfate, ferric sulfate, ferrous sulfate, nickel nitrate, cobalt nitrate, manganese nitrate, ferric nitrate, ferrous nitrate, nickel chloride, cobalt chloride, manganese chloride, ferric chloride, and ferrous chloride. [5] The manufacturing method according to claim 1, wherein in step S2, the transition metal salt solution is added at a flow rate of 25 mL / h to 50 mL / h. [6] The manufacturing method according to claim 1, wherein in step S2, the sodium chloride solution has a concentration of 1 mol / L to 4 mol / L and a volume ratio of the sodium chloride solution to the mixed solution is 0.9:1 to 1.1:

1. [7] The manufacturing method according to claim 1, wherein in step S2, the aging is carried out for 2 h to 48 h. [8] The manufacturing method according to claim 1, wherein in step S3, the precipitate is washed by using deionized water and absolute ethanol. [9] The manufacturing method according to claim 1, wherein in step S3 the precipitate is dried in vacuum at 100 °C to 120 °C for 12 h to 24 h.

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