A preparation method of a FeF3 / FeF3*0.33H2O mixture for sodium batteries

Abstract

The application discloses a preparation method of a FeF3 / FeF3*0.33H2O mixture for sodium electricity, and belongs to the field of sodium ion batteries. The FeF3 / FeF3*0.33H2O mixture is prepared by a room-temperature co-precipitation and low-temperature annealing method, with iron chloride hexahydrate as an iron source, ammonium fluoride as a fluorine source, and anhydrous ethanol and deionized water as solvents. After 4 centrifugal cleanings of the room-temperature precipitate, the mixture is directly subjected to low-temperature treatment at 240 DEG C, and after sintering for 1 h, the mixture is synthesized. The mixture is composed of irregular sheets and particles with different particle sizes. When the mixture is used as a positive electrode material of sodium electricity, the initial specific capacity of the mixture reaches 482.78 mAh / g (0.1 A / g), and after 110 cycles, the specific capacity of the mixture is still 160.83 mAh / g. The FeF3 / FeF3*0.33H2O mixture electrode material prepared by the method has the characteristics of high specific capacity, good cycle performance, short preparation period, safety and the like.

Description

Technical Field

[0001] A method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium batteries belongs to the field of sodium-ion batteries. Technical Background

[0002] The widespread use of new energy electric vehicles and portable electronic devices such as wearables has greatly exacerbated the consumption of lithium resources, leading to a further increase in their price and making it difficult for lithium batteries to meet the requirements of large-scale energy storage applications. Traditional lead-acid batteries, due to their large size and low energy density, struggle to meet the demand for energy storage devices with high energy density and lightweight design. Conversely, sodium resources have the advantages of high reserves and low price. Furthermore, sodium and lithium belong to the same element group and have similar properties, making sodium-ion batteries capable of meeting the requirements of large-scale energy storage applications.

[0003] The development of high-specific-capacity cathode materials is one of the key factors driving the widespread application of sodium-ion batteries. Compared with traditional intercalated cathode materials, conversion-type cathode materials can provide higher theoretical specific capacity and more easily improve the energy density of sodium-ion batteries. In particular, iron fluoride-based materials, such as iron trifluoride (FeF3), have a high theoretical specific capacity (712 mAh / g), and have attracted widespread attention due to their advantages such as high operating voltage, abundant iron resources, and relatively low price. Existing synthesis methods include gas-phase synthesis, solid-phase synthesis, and liquid-phase methods. Among them, gas-phase synthesis often uses F2, NF3, and HF gases as fluorine sources. Since these gases are usually toxic, they are not conducive to large-scale preparation. Solid-phase synthesis often requires high-temperature sintering (>400℃), which is energy-intensive and contradicts the original intention of low-cost sodium-ion batteries. Liquid-phase synthesis has advantages such as better control of reaction parameters and morphology adjustment. To improve the yield of ferrofluoride preparation, organic solvents or ionic liquids are usually used as solvents. However, ionic liquids are expensive and not conducive to industrial-scale preparation. In addition, most existing methods use high-pressure reactors or combine them with annealing treatment. High-pressure reactors are not conducive to large-scale preparation due to safety reasons, and annealing treatment is often above 300℃ (CN202311545112, CN202311530234). In addition, most of them use corrosive hydrofluoric acid as fluorine source (CN202311578607, CN202410196611), which is not conducive to the industrial-scale preparation of ferrofluoride. Summary of the Invention

[0004] This invention provides a method with a short preparation cycle, simple operation, and safety. By using room temperature coprecipitation and low temperature annealing, a FeF3 / FeF3·0.33H2O mixture was successfully prepared. When used as the positive electrode of a sodium-ion battery, it exhibits good electrochemical performance.

[0005] The present invention provides a method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium batteries, comprising the following steps:

[0006] a) In a 50ml beaker, add an appropriate amount of deionized water and ammonium fluoride powder, stir for 10 minutes, and then transfer the mixture to a 20ml syringe for later use.

[0007] b) In a 100ml beaker, add an appropriate amount of anhydrous ethanol and ferric chloride hexahydrate powder. After stirring for 15 minutes, add the ammonium fluoride solution from the syringe to the ferric chloride solution dropwise at a certain injection rate while stirring at a certain rate. After the addition is complete, continue stirring at the same rate at room temperature for 40 minutes. Then, wash the solution with deionized water by centrifugation and transfer the precipitate at the bottom of the centrifuge tube to a ceramic boat.

[0008] c) Place the ceramic boat containing the precipitate in a quartz tube furnace, continuously introduce nitrogen gas, and heat from 20°C to the predetermined temperature at a heating rate of 8°C / min. After holding at this temperature for a period of time, cool the furnace to room temperature to obtain a FeF3 / FeF3·0.33H2O mixture.

[0009] d) The above FeF3 / FeF3·0.33H2O mixture is used as an electrode material in sodium-ion batteries.

[0010] In step a), the amounts of deionized water and ammonium fluoride added are 12 ml and 2.25 g, respectively.

[0011] In step b), the amounts of anhydrous ethanol and ferric chloride hexahydrate added are 40 ml and 2.57 g, respectively; the injection rate is 39 ml / h, and the stirring speed and the stirring speed at room temperature for 40 min are both 790 rpm; then the centrifuge is performed at 8200 rpm for 7 min for a total of 4 centrifugation washes, each time using 40 ml of deionized water, and the centrifuge tubes are 50 ml in size.

[0012] The precipitate obtained by centrifugation in step c) does not need to be dried and is directly transferred to a quartz tube furnace for treatment; at the same time, under the condition of nitrogen gas flow rate of 37 sccm, the temperature is raised to 240℃ at a heating rate of 8℃ / min and held for 1 hour.

[0013] In step d), during the sodium-ion battery cycle performance test, the initial specific capacity reached 482.78 mAh / g at 0.1 A / g, and even after 110 cycles, the specific capacity was still 160.83 mAh / g.

[0014] Compared with other methods for preparing iron trifluoride-based materials, this method is safer, has a shorter cycle time, and lowers the sintering temperature, making it suitable for large-scale mass production. When the FeF3 / FeF3·0.33H2O mixture is used in sodium-ion batteries, it exhibits high specific capacity and cycle performance.

[0015] A Bruker Advance D8 X-ray powder diffractometer (Cu Kα radiation) was used. The structure of the prepared material was determined using a 2θ = 10⁻⁷⁵° microscope. The surface morphology of the prepared material was observed using a Hitachi S-4800 scanning electron microscope. Battery performance was tested using a Neware battery testing system.

[0016] Depend on Figure 1 It can be seen that, under the condition of annealing time of 1 hour, when the annealing temperature is 220℃ (a), the stronger diffraction peaks of the obtained product are attributed to the diffraction peaks of FeF3·0.33H2O (JCPDS card No. 76-1262); when the annealing temperature is 240℃ (b), in addition to the diffraction peaks of FeF3·0.33H2O, there are also obvious diffraction peaks of FeF3 (JCPDS card No. 84-1101); when the annealing temperature is 270℃ (c), in addition to the strong diffraction peaks of FeF3, there are also weaker diffraction peaks of FeF3·0.33H2O; indicating that as the annealing temperature increases, the FeF3·0.33H2O phase in the product gradually transforms into a material dominated by the FeF3 phase. Figure 2 It can be seen that, under the condition of an annealing temperature of 240℃ and an annealing time of 1 hour, the product obtained in Scheme 2 consists of irregular flakes composed of nanoparticles and particles of varying sizes. Figure 3 and Figure 4 As shown in b, the FeF3 / FeF3·0.33H2O mixture prepared in Scheme 2, when used as a sodium electrode material, has an initial specific capacity of 482.78 mAh / g at 0.1 A / g. After 30 cycles, the charge-discharge curves are basically identical, indicating stable electrochemical performance. Even after 110 cycles, the specific capacity is still 160.83 mAh / g. Meanwhile, the products prepared in Schemes 1 and 3, when used as sodium electrode materials, have initial capacities of 327.41 mAh / g, respectively. Figure 4 a) and 383.72mAh / g ( Figure 4 c) After 110 cycles, the specific capacity of both schemes was lower than that of scheme 2. Attached Figure Description

[0017] Figure 1 These are X-ray diffraction patterns of the products obtained at different annealing temperatures;

[0018] Figure 2 This is a scanning electron microscope image of the product obtained in Implementation Scheme 2;

[0019] Figure 3 This is a charge-discharge curve of the product obtained in Implementation Scheme 2;

[0020] Figure 4 It is a cycle curve of the product obtained by implementing the scheme. Detailed Implementation

[0021] 1. In a 50ml beaker, add 12ml of deionized water and 2.25g of ammonium fluoride powder, stir for 10 minutes, then transfer the entire solution to a 20ml syringe for later use. In a 100ml beaker, add 40ml of anhydrous ethanol and 2.57g of ferric chloride hexahydrate powder, stir for 15 minutes, then add the ammonium fluoride solution from the syringe dropwise to the ferric chloride solution at an injection rate of 39ml / h, stirring at 790 rpm while adding. After the addition is complete, continue stirring at this rate at room temperature for 40 minutes. The precipitate was washed by centrifugation using 40 ml of deionized water at 8200 rpm for 7 min, repeated four times. The precipitate at the bottom of the centrifuge tube was then transferred to a ceramic boat. The ceramic boat containing the precipitate was then transferred directly to a quartz tube furnace without drying. Nitrogen gas was introduced at a purge rate of 37 sccm, and the temperature was increased from 20°C to 220°C at a rate of 8°C / min and held for 1 h. The furnace was then cooled to room temperature to obtain a product mainly composed of FeF3·0.33H2O (see...). Figure 1 a and Figure 4 a).

[0022] 2. In a 50ml beaker, add 12ml of deionized water and 2.25g of ammonium fluoride powder, stir for 10 minutes, and then transfer the entire solution to a 20ml syringe for later use. In a 100ml beaker, add 40ml of anhydrous ethanol and 2.57g of ferric chloride hexahydrate powder, stir for 15 minutes, and then add the ammonium fluoride solution from the syringe dropwise to the ferric chloride solution at an injection rate of 39ml / h, stirring at 790 rpm while adding. After the addition is complete, continue stirring at this rate at room temperature for 40 minutes, and then let... The precipitate was washed by centrifugation with 40 ml of deionized water at 8200 rpm for 7 min, and the centrifugation was repeated 4 times. The precipitate at the bottom of the centrifuge tube was then transferred to a ceramic boat. The ceramic boat containing the precipitate was then transferred directly to a quartz tube furnace without drying. Nitrogen gas was introduced at a purge rate of 37 sccm, and the temperature was increased from 20°C to 240°C at a rate of 8°C / min and held for 1 h. The furnace was then cooled to room temperature to obtain a FeF3 / FeF3·0.33H2O mixture (see...). Figure 1 b、 Figure 2 , Figure 3 and Figure 4 b).

[0023] 3. In a 50ml beaker, add 12ml of deionized water and 2.25g of ammonium fluoride powder, stir for 10 minutes, and then transfer the entire solution to a 20ml syringe for later use. In a 100ml beaker, add 40ml of anhydrous ethanol and 2.57g of ferric chloride hexahydrate powder, stir for 15 minutes, and then add the ammonium fluoride solution from the syringe dropwise to the ferric chloride solution at an injection rate of 39ml / h, stirring at 790 rpm while adding. After the addition is complete, continue stirring at this rate at room temperature for 40 minutes, and then let... The precipitate was washed by centrifugation with 40 ml of deionized water at 8200 rpm for 7 min, and the centrifugation was repeated 4 times. The precipitate at the bottom of the centrifuge tube was then transferred to a ceramic boat. The ceramic boat containing the precipitate was then transferred directly to a quartz tube furnace without drying. Nitrogen gas was introduced at a purge rate of 37 sccm, and the temperature was increased from 20°C to 270°C at a rate of 8°C / min and held for 1 h. The furnace was then cooled to room temperature to obtain a FeF3 / FeF3·0.33H2O mixture (see...). Figure 1 c and Figure 4 c).

Claims

1. A method for preparing a FeF3 / FeF3*0.33H2O mixture for sodium-ion batteries, comprising the following steps: a) adding an appropriate amount of deionized water and ammonium fluoride powder into a beaker of 50 ml size, stirring for 10 min, and then transferring all into a syringe of 20 ml size for standby; b) adding an appropriate amount of anhydrous ethanol and iron trichloride hexahydrate powder into a beaker of 100 ml size, stirring for 15 min, and then adding the ammonium fluoride solution in the syringe into the iron trichloride solution at a certain injection rate, stirring at a certain speed during the dropping, continuing to stir at the speed for 40 min at room temperature after the dropping, and then washing by centrifugation with deionized water, and transferring the precipitate at the bottom of the centrifuge tube to a ceramic canister; c) placing the ceramic canister containing the precipitate in a quartz tube furnace, continuously passing nitrogen, heating from 20℃ to a predetermined temperature at a heating rate of 8℃ / min, cooling to room temperature after holding for a period of time, and obtaining the FeF3 / FeF3*0.33H2O mixture; the amount of deionized water and ammonium fluoride added in step a) is 12 ml and 2.25 g, respectively; the amount of anhydrous ethanol and iron trichloride hexahydrate added in step b) is 40 ml and 2.57 g, respectively; the injection rate in step b) is 39 ml / h, and the stirring speed during the dropping and the stirring speed for 40 min at room temperature are both 790 rpm; the precipitate obtained by centrifugation in step c) does not need to be dried before being transferred to the quartz tube furnace for treatment; and under the condition of a nitrogen flow rate of 37 sccm, the temperature is increased to 240℃ at a heating rate of 8℃ / min, and the temperature is held for 1 h. In step b), the centrifugation is performed at a speed of 8200 rpm for 7 min, and the centrifugation is repeated 4 times, each time using 40 ml of deionized water, and the centrifuge tube is of 50 ml size. ​ ​ ​ ​ ​ ​ ​ 2. The method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium electrolysis according to claim 1, characterized in that, ​

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