Preparation method of FeF3 / FeF3. 0.33 H2O mixture for sodium electricity

Abstract

The invention discloses a preparation method of a FeF3 / FeF3. 0.33 H2O mixture for a sodium battery, and belongs to the field of sodium ion batteries. A FeF3 / FeF3. 0.33 H2O mixture is subjected to room-temperature co-precipitation and low-temperature annealing treatment, ferric chloride hexahydrate is taken as an iron source, ammonium fluoride is taken as a fluorine source, absolute ethyl alcohol and deionized water are taken as solvents, room-temperature precipitates are subjected to centrifugal cleaning for four times, then 240-DEG C low-temperature treatment is directly carried out, sintering is carried out for 1 hour, and the mixed material is synthesized. The material is composed of irregular sheets composed of nano-particles and particles with different particle sizes. When the material is used as a positive electrode material of a sodium battery for an electrochemical performance test, the initial specific capacity of the material can reach 482.78 mAh / g (0.1 A / g), and the specific capacity of the material is still 160.83 mAh / g after 110 cycles. The FeF3 / FeF3. 0.33 H2O mixture electrode material prepared by the invention has the characteristics of high specific capacity, good cycle performance, short period of the preparation method, safety and the like.

Description

Technical Field

[0001] The invention discloses a method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium electricity, belonging 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 increased the consumption of lithium resources, causing its price to be further increased, making it difficult for lithium batteries to meet the requirements of large-scale energy storage applications. Traditional lead-acid batteries are large in size and low in energy density, making it difficult to meet people's application needs for high-energy-density and lightweight energy storage devices; on the contrary, sodium resources have the advantages of high reserves and low prices. At the same time, sodium and lithium belong to the same group of elements and have similar properties, so sodium-ion batteries can meet the requirements of large-scale energy storage applications.

[0003] The development of high specific capacity cathode materials is one of the key factors to promote the widespread application of sodium ion batteries. Compared with traditional intercalation cathode materials, conversion cathode materials can provide higher theoretical specific capacity and are more likely to improve the energy density of sodium ion batteries. In particular, iron fluoride-based materials, such as iron trifluoride (FeF3), have higher theoretical specific capacity (712mAh / g), and have attracted widespread attention due to their advantages such as high working voltage, abundant iron resources and relatively low price. The synthesis methods in existing literature include gas phase synthesis, solid phase synthesis and liquid phase method. 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℃) process, which is characterized by high energy consumption, which is contrary to the original intention of low-cost sodium ion batteries; liquid phase synthesis has the advantages of better control of reaction parameters and morphology regulation. In order to improve the yield of iron fluoride preparation, organic solvents or ionic liquids are usually used as solvents. However, ionic liquids are expensive and not conducive to industrial preparation. In addition, most existing methods use high-pressure reactors or are combined with annealing treatment. High-pressure reactors are not conducive to large-scale preparation due to safety and other reasons. Annealing treatment is often greater than 300°C (CN202311545112, CN202311530234). In addition, most of them use corrosive hydrofluoric acid as a fluorine source (CN202311578607, CN202410196611), which are not conducive to the industrial preparation of iron fluoride. Summary of the invention

[0004] The invention provides a method with short preparation period, simple operation and safety. A FeF3 / FeF3·0.33H2O mixture is successfully prepared by a synthesis method of room temperature coprecipitation and low temperature annealing. When the mixture is used as a positive electrode of a sodium ion battery, the mixture has good electrochemical performance.

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

[0006] a) In a 50 ml beaker, add appropriate amount of deionized water and ammonium fluoride powder, stir for 10 minutes, and then transfer all of them into a 20 ml syringe for later use;

[0007] b) In a 100 ml beaker, add an appropriate amount of anhydrous ethanol and ferric chloride hexahydrate powder, stir for 15 minutes, then drop the ammonium fluoride solution in the syringe into the ferric chloride solution at a certain injection speed, stirring at a certain speed while dropping, and continue to stir at room temperature at the same speed for 40 minutes after the dropwise addition, then use deionized water for centrifugal washing, and transfer the bottom precipitate in the centrifuge tube to the ceramic ark;

[0008] c) placing the ceramic ark containing the precipitate in a quartz tube furnace, continuously introducing nitrogen, heating from 20°C to a predetermined temperature at a heating rate of 8°C / min, and after a period of heat preservation, cooling down to room temperature with the furnace to obtain a FeF3 / FeF3·0.33H2O mixture.

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

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

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

[0012] The precipitate obtained by centrifugation in step c) is directly transferred to a quartz tube furnace for treatment without drying; at the same time, the temperature is raised to 240° C. at a heating rate of 8° C. / min under a nitrogen ventilation rate of 37 sccm, and the temperature is kept at this temperature for 1 hour;

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

[0014] Compared with other methods for preparing iron trifluoride-based materials, this method has a safe preparation process, a short cycle, and a lower sintering temperature, making it suitable for large-scale batch production; when the FeF3 / FeF3·0.33H2O mixture is used in sodium ion batteries, it has a higher specific capacity and cycle performance.

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

[0016] Depend on Figure 1 It can be seen that under the condition of annealing time of 1h, when the annealing temperature is 220℃(a), the stronger diffraction peak of the obtained product is attributed to the diffraction peak of FeF3·0.33H2O (JCPDS card No.76-1262); when the annealing temperature is 240℃(b), in addition to the diffraction peak of FeF3·0.33H2O, there is also an obvious diffraction peak of FeF3 (JCPDS card No.84-1101); when the annealing temperature is 270℃(c), in addition to the strong diffraction peak of FeF3, there is also a weaker diffraction peak of FeF3·0.33H2O; it shows that with the increase of annealing temperature, the FeF3·0.33H2O phase in the product is gradually transformed into a material dominated by the FeF3 phase. Figure 2 It can be seen that under the condition of annealing temperature of 240°C and annealing time of 1 hour, the product obtained in Embodiment 2 is composed of irregular flakes composed of nanoparticles and particles of different sizes. Figure 3 and Figure 4 b It can be seen that the FeF3 / FeF3·0.33H2O mixture prepared in Implementation Scheme 2 has an initial specific capacity of 482.78 mAh / g at 0.1 A / g as a sodium electrode material, and the charge and discharge curves are basically overlapped after 30 cycles, indicating that it has stable electrochemical performance. Even after 110 cycles, the specific capacity is still 160.83 mAh / g; At the same time, when the products prepared in Implementation Schemes 1 and 3 are used as sodium electrode materials, the initial capacities are 327.41 mAh / g ( Figure 4 a) and 383.72 mAh / g( Figure 4 c), after 110 cycles, the specific capacity of the two schemes is also lower than that of Implementation 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the X-ray diffraction pattern of the product obtained at different annealing temperatures;

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

[0019] Figure 3 is a charge and discharge curve diagram of the product obtained in Implementation Option 2;

[0020] Figure 4 It is a cycle curve diagram of the product obtained by the implementation scheme. DETAILED DESCRIPTION

[0021] 1. In a 50ml beaker, add 12ml of deionized water and 2.25g of ammonium fluoride powder, stir for 10min, and then transfer all of them to a 20ml syringe for standby use; in a 100ml beaker, add 40ml of anhydrous ethanol and 2.57g of ferric chloride hexahydrate powder, stir for 15min, and then drop the ammonium fluoride solution in the syringe into the ferric chloride solution at an injection rate of 39ml / h, stirring at a speed of 790 rpm while dropping. After the addition is complete, continue to stir at this speed at room temperature for 40min, and then The precipitate was washed by centrifugation with 40 ml of deionized water, at a speed of 8200 rpm for 7 min. After 4 centrifugal washings, the bottom precipitate in the centrifuge tube was transferred to a ceramic ark. The ceramic ark containing the precipitate was directly transferred to a quartz tube furnace without drying, and nitrogen was introduced at a ventilation rate of 37 sccm. Then, the temperature was increased from 20°C to 220°C at a rate of 8°C / min, and kept at this temperature for 1 h. Then, the temperature was cooled to room temperature with the furnace, and a product mainly composed of FeF3·0.33H2O was obtained (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 10min, and then transfer all of them 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 15min, and then drop the ammonium fluoride solution in the syringe into the ferric chloride solution at an injection rate of 39ml / h, stirring at a speed of 790 rpm while dropping. After the addition is complete, continue stirring at this speed at room temperature for 40min, and then The precipitate was washed by centrifugation with 40 ml of deionized water, at a speed of 8200 rpm for 7 min. After 4 times of centrifugal washing, the precipitate at the bottom of the centrifuge tube was transferred to a ceramic ark. The ceramic ark containing the precipitate was directly transferred to a quartz tube furnace without drying, and nitrogen was introduced at a ventilation rate of 37 sccm. Then, the temperature was increased from 20°C to 240°C at a rate of 8°C / min, and the temperature was kept for 1 h. Then, the mixture was cooled to room temperature with the furnace 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 10min, and then transfer all of them 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 15min, and then drop the ammonium fluoride solution in the syringe into the ferric chloride solution at an injection rate of 39ml / h, stirring at a speed of 790 rpm while dropping. After the addition is complete, continue stirring at this speed at room temperature for 40min, and then The precipitate was washed by centrifugation with 40 ml of deionized water at a speed of 8200 rpm for 7 min. After 4 times of centrifugal washing, the precipitate at the bottom of the centrifuge tube was transferred to a ceramic ark. The ceramic ark containing the precipitate was directly transferred to a quartz tube furnace without drying, and nitrogen was introduced at a ventilation rate of 37 sccm. Then, the temperature was increased from 20°C to 270°C at a rate of 8°C / min, and the temperature was kept for 1 h. Then, the mixture was cooled to room temperature with the furnace 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 electricity, comprising the following steps: a) In a 50 ml beaker, add appropriate amount of deionized water and ammonium fluoride powder, stir for 10 minutes, and then transfer all of them into a 20 ml syringe for later use; b) In a 100 ml beaker, add an appropriate amount of anhydrous ethanol and ferric chloride hexahydrate powder, stir for 15 minutes, then drop the ammonium fluoride solution in the syringe into the ferric chloride solution at a certain injection speed, stirring at a certain speed while dropping, and continue to stir at room temperature at the same speed for 40 minutes after the dropwise addition, then use deionized water for centrifugal washing, and transfer the bottom precipitate in the centrifuge tube to the ceramic ark; c) placing the ceramic ark containing the precipitate in a quartz tube furnace, continuously introducing nitrogen, heating from 20°C to a predetermined temperature at a heating rate of 8°C / min, and after a period of heat preservation, cooling down to room temperature with the furnace to obtain a FeF3 / FeF3·0.33H2O mixture. In the step a), the added amounts of deionized water and ammonium fluoride are 12 ml and 2.25 g respectively. In the step b), the added amounts of anhydrous ethanol and ferric chloride hexahydrate are 40 ml and 2.57 g respectively.

2. The method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium electricity according to claim 1, characterized in that: In the step b), the injection speed is 39 ml / h, and the stirring speed while dropping and the stirring speed for 40 min at room temperature are both 790 rpm.

3. The method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium electricity according to claim 1, characterized in that: In the step b), the mixture is centrifuged at 8200 rpm for 7 min for a total of 4 times, each time using 40 ml of deionized water, wherein the centrifuge tube is of 50 ml specification.

4. The method for preparing a FeF3 / FeF3·0.33H2O mixture for sodium electricity according to claim 1, characterized in that: The precipitate obtained by centrifugation in step c) is directly transferred to a quartz tube furnace for treatment without drying; at the same time, the temperature is raised to 240° C. at a heating rate of 8° C. / min under a nitrogen ventilation rate of 37 sccm and kept warm for 1 hour.

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