Preparation method of MnF2 / carbon fiber for sodium battery

Abstract

The invention relates to a preparation method of MnF2 / carbon fiber for a sodium battery and belongs to the field of sodium ion batteries. The MnF2 / carbon fiber is subjected to electrostatic spinning and one-step annealing treatment, manganese acetylacetonate is taken as a manganese source, polyvinylidene fluoride and polyacrylonitrile are taken as a fluorine source and a carbon source, after electrostatic spinning, annealing treatment at the temperature of 550 DEG C is directly carried out, sintering is carried out for 1 h, and the material can be prepared and is composed of nano-particles with different particle sizes embedded in the carbon fiber. When the material is used as a negative electrode material of a sodium battery for an electrochemical performance test, the initial specific capacity of the material is 386.06 mAh / g (0.1 A / g), and the specific capacity of the material is still 205.34 mAh / g even after 150 cycles. The MnF2 / carbon fiber material prepared by the invention has the characteristics of high specific capacity, good cycle performance, simple preparation method, safety and the like.

Description

Technical Field

[0001] A preparation method of MnF2 / carbon fiber for sodium batteries belongs to the field of sodium-ion batteries. Technical Background

[0002] With the wide application of new energy electric vehicles and wearable portable electronic devices, the development of energy storage devices has been greatly promoted. Among them, lithium-ion batteries have been widely used due to their relatively small volume and weight, as well as high energy density. However, limited by the uneven distribution and large consumption of lithium resources, the price of lithium sources is relatively high, making it difficult for lithium batteries to meet the requirements of large-scale energy storage applications. On the contrary, sodium resources have the advantages of relatively high reserves and low prices in China. In addition, sodium and lithium belong to the same group of elements and have similar physical and chemical properties, so it is more conducive to the large-scale energy storage application requirements of sodium-ion batteries.

[0003] The realization of high-performance anode materials is one of the key factors to promote the popularization and application of sodium batteries. Currently, commercial graphite cannot meet the requirements of sodium batteries. Transition metal fluorides, especially manganese fluoride, have been widely studied in the field of lithium batteries due to their high specific capacity and good electrochemical stability. Existing literature mostly uses gases such as fluorine gas, nitrogen trifluoride, hydrogen fluoride, or hydrofluoric acid and trifluoroacetic acid as fluorine sources. Since these gases or liquids are often toxic or corrosive, and have high requirements for equipment, it is not conducive to large-scale preparation; for the liquid-phase synthesis method based on organic solvents or ionic liquids, due to the high price of ionic liquids, and the poor conductivity of manganese fluoride synthesized by the liquid-phase method, it is also necessary to introduce substances with higher conductivity through methods such as ball milling to compound with it, which is difficult to ensure the uniformity of the composite, and the process is also relatively cumbersome, so it is not conducive to industrial preparation (CN102034965A); the manganese fluoride carbon-based composite materials synthesized by the high-temperature treatment method based on ammonium fluoride are mostly used in the research of lithium batteries, and there is less research in sodium-ion batteries, and their electrochemical performance needs to be improved; in addition, there are few reports on the synthesis of MnF2 / carbon fiber by electrospinning and one-step annealing methods. Summary of the Invention

[0004] The present invention provides a method with a short preparation period, simple and safe operation. By using the synthesis method of electrospinning and one-step annealing treatment, MnF2 / carbon fiber materials are successfully prepared. When used as the anode of sodium-ion batteries, they have good electrochemical performance.

[0005] A preparation method of MnF2 / carbon fiber for sodium batteries provided by the present invention includes the following steps:

[0006] a) An appropriate amount of dimethylformamide, polymethyl methacrylate, polyacrylonitrile, and polyvinylidene fluoride were successively added to a 10-ml sealed reagent bottle. After sealing, it was placed in an 85°C water bath and stirred at a speed of 820 revolutions per minute for 1 h. Then, manganese acetylacetonate was added. After sealing again, it was placed in a 30°C water bath and continuously stirred for 3 h. The sealed reagent bottle containing the spinning solution was taken out;

[0007] b) A 3.5-ml spinning solution was aspirated with a spinning syringe, equipped with a spinning needle head with a certain inner diameter. After adjusting the distance from the receiving roller, setting the injection speed of the spinning solution, the rotation speed of the receiving roller, and the spinning voltage, spinning could be carried out until the spinning was completed;

[0008] c) The spun film was taken off the surface of the roller, folded into a state with a length and width of 7 * 3 cm, and placed in a porcelain ark with a length and width of 8 * 4 cm. Then, it was transferred to a tubular furnace, and argon was continuously introduced. At a heating rate of 2°C / min, it was heated from 30°C to a predetermined temperature. After heat preservation for a period of time, when it was cooled with the furnace to 380°C, the ventilation rate was adjusted, and then the MnF2 / carbon fiber could be obtained by maintaining this ventilation rate and further cooling with the furnace to room temperature;

[0009] d) The above-mentioned MnF2 / carbon fiber was used as an electrode material in a sodium-ion battery.

[0010] In step a), the addition amounts of dimethylformamide, polymethyl methacrylate (molecular weight 15,000), polyacrylonitrile (molecular weight 150,000), polyvinylidene fluoride (molecular weight 500,000), and manganese acetylacetonate were 5.0 g, 0.25 g, 0.2 g, 0.3 g, and 1.0 g, respectively.

[0011] In step b), the inner diameter of the spinning needle head was 0.41 mm (22G model), the distance from the receiving roller was 11 cm, the injection speed of the spinning solution was 0.8 mL / h, the rotation speed of the receiving roller was 310 revolutions per minute, and the spinning voltage was 19 KV.

[0012] In step c), under the condition that the ventilation rate of argon was 16 sccm, it was heated to 550°C at a heating rate of 2°C / min. After heat preservation for 1 h, when it was cooled with the furnace to 380°C, the ventilation rate of argon was adjusted to 35 sccm.

[0013] In step d), in the cycle performance test of the sodium-ion battery, its initial specific capacity was 386.06 mAh / g at 0.1 A / g, and even after 150 cycles, the specific capacity was still 205.34 mAh / g.

[0014] Compared with other methods for preparing manganese fluoride-based materials, this method has a safe preparation process, a short cycle, and simple operation, making it suitable for large-scale batch production. When the MnF2 / carbon composite material is used in sodium-ion batteries, it has a high specific capacity and cycling performance.

[0015] The structure of the prepared material was determined using a Bruker Advance D8 X-ray powder diffractometer (Cu Kα radiation, 2θ = 10 - 80°). The surface morphology of the prepared material was observed using a Hitachi S-4800 scanning electron microscope. The battery performance was tested using an electrochemical workstation (CHI 660E) and a Neware battery test system.

[0016] It can be Figure 1 seen that under the condition of an annealing time of 1 h, when the annealing temperature is 550 °C, the strong diffraction peaks of the obtained product are attributed to the diffraction peaks of the tetragonal phase (JCPDS card No. 80-0927) and orthorhombic phase (JCPDS card No. 17-0864) of MnF2, indicating that the MnF2 in the product has a mixed-phase structure. When the annealing temperature is 650 °C, in addition to the diffraction peaks of the tetragonal phase and orthorhombic phase of MnF2, there are also obvious diffraction peaks of the cubic phase of MnO (JCPDS card No. 78-0424). It can be Figure 2 seen that under the condition of an annealing temperature of 550 °C, when the annealing time is 1 h, the product obtained in Example 1 is composed of carbon fibers and nanoparticles embedded on them, where the particle sizes of the nanoparticles are different, and the size is about 15 - 40 nm. It can be Figure 3 seen that when the MnF2 / carbon fiber obtained in Example 1 is used as the electrode material of a sodium-ion battery and cyclic voltammetry tests are carried out at a scan rate of 0.2 mV / s, the cyclic curves from the second cycle to the fourth cycle basically coincide, indicating stable electrochemical performance. It can be Figure 4 seen that when the MnF2 / carbon fiber prepared in Example 1 is used as the sodium battery electrode material at 0.1 A / g, the initial specific capacity is 386.06 mAh / g, and the charge-discharge curves of the second and third cycles basically coincide, indicating stable electrochemical performance. Even after 150 cycles, the specific capacity is still 205.34 mAh / g ( Figure 5 at 550 °C in Figure 5 ); meanwhile, when the carbon fiber prepared in Example 3 is used as the sodium battery electrode material, the initial specific capacity is 203.22 mAh / g ( Figure 5 carbon fiber in Description of the Drawings

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

[0018] Figure 2 is the scanning electron microscopy image of the product prepared in Example 1;

[0019] Figure 3 is the CV curve of the product prepared in Example 1;

[0020] Figure 4 is the charge-discharge curve of the product prepared in Example 1;

[0021] Figure 5 is the cycle curve of the product prepared in the Example. Detailed implementation manners

[0022] 1. First, add 5.0 g of dimethylformamide, 0.25 g of polymethyl methacrylate (molecular weight of 15,000), 0.2 g of polyacrylonitrile (molecular weight of 150,000), and 0.3 g of polyvinylidene fluoride (molecular weight of 500,000) into a 10 ml sealed reagent bottle in sequence. After sealing, place it in an 85°C water bath and stir at a speed of 820 revolutions per minute for 1 h. Then add 1.0 g of manganese acetylacetonate, seal it again, and place it in a 30°C water bath. Continue to stir for 3 h, and then take out the sealed reagent bottle with the spinning solution. Use a spinning syringe to suck 3.5 ml of the spinning solution, install a spinning needle with an inner diameter of 0.41 mm (22G model), and the distance between the needle and the receiving roller is 11 cm. Set the solution injection speed to 0.8 mL / h and the rotation speed of the receiving roller to 310 revolutions per minute. At the same time, the spinning voltage is 19 KV, and then spinning can be carried out. After spinning is completed, take the spinning film from the surface of the roller, fold it into a state with a length and width of 7*3 cm, and put it into a porcelain ark with a length and width of 8*4 cm. Then transfer it to a tubular furnace. Under the condition that the argon gas flow rate is 16 sccm, heat it to 550°C at a heating rate of 2°C / min, keep it for 1 h, and then cool it down to 380°C with the furnace. When the temperature drops to 380°C, adjust the argon gas flow rate to 35 sccm, and then keep this gas flow rate and continue to cool down to room temperature with the furnace to obtain MnF2 / carbon fiber (see Figure 1 at 550°C, Figure 2 , Figure 3 , Figure 4 and Figure 5 at 550°C).

[0023] 2. 5.0 g of dimethylformamide, 0.25 g of polymethyl methacrylate (molecular weight of 15,000), 0.2 g of polyacrylonitrile (molecular weight of 150,000), and 0.3 g of polyvinylidene fluoride (molecular weight of 500,000) were successively added into a 10 ml sealed reagent bottle. After sealing, it was placed in an 85 °C water bath and stirred at a speed of 820 revolutions per minute for 1 h. Then, 1.0 g of manganese acetylacetonate was added. After sealing again, it was placed in a 30 °C water bath and continuously stirred for 3 h. Then, the sealed reagent bottle containing the spinning solution was taken out. 3.5 ml of the spinning solution was aspirated with a spinning syringe, and a spinning needle with an inner diameter of 0.41 mm (22G model) was installed. The distance between the needle and the receiving drum was 11 cm. The solution injection speed was set at 0.8 mL / h, the rotation speed of the receiving drum was 310 revolutions per minute, and the spinning voltage was 19 KV. Then, spinning could be carried out. After spinning was completed, the spun film was taken off from the surface of the drum, folded into a state with a length and width of 7 * 3 cm, and placed in a porcelain ark with a length and width of 8 * 4 cm. Then, it was transferred to a tube furnace. Under the condition that the argon gas flow rate was 16 sccm, it was heated to 650 °C at a heating rate of 2 °C / min. After heat preservation treatment for 1 h, it was cooled down to 380 °C with the furnace. When the temperature reached 380 °C, the argon gas flow rate was adjusted to 35 sccm, and then it was cooled down to room temperature with the furnace while maintaining this gas flow rate. The product could be obtained (see Figure 1 in 650 °C).

[0024] 3. 5.0 g of dimethylformamide, 0.25 g of polymethyl methacrylate (molecular weight of 15,000), 0.2 g of polyacrylonitrile (molecular weight of 150,000), and 0.3 g of polyvinylidene fluoride (molecular weight of 500,000) were successively added into a 10 ml sealed reagent bottle. After sealing, it was placed in an 85 °C water bath and stirred at a speed of 820 revolutions per minute for 3 h. Then, the sealed reagent bottle containing the spinning solution was taken out. 3.5 ml of the spinning solution was aspirated with a spinning syringe, and a spinning needle with an inner diameter of 0.41 mm (22G model) was installed. The distance between the needle and the receiving drum was 11 cm. The solution injection speed was set at 0.8 mL / h, the rotation speed of the receiving drum was 310 revolutions per minute, and the spinning voltage was 17.5 KV. Then, spinning could be carried out. After spinning was completed, the spun film was taken off from the surface of the drum, folded into a state with a length and width of 7 * 3 cm, and placed in a porcelain ark with a length and width of 8 * 4 cm. Then, it was transferred to a tube furnace. Under the condition that the argon gas flow rate was 30 sccm, it was heated to 550 °C at a heating rate of 2 °C / min. After heat preservation treatment for 1 h, it was cooled down to room temperature with the furnace. The carbon fiber could be obtained (see Figure 5 in carbon fiber).

Claims

1. A preparation method of MnF2 / carbon fiber for sodium batteries, comprising the following steps: a) Add appropriate amounts of dimethylformamide, polymethyl methacrylate, polyacrylonitrile, and polyvinylidene fluoride into a 10 ml sealed reagent bottle successively. After sealing, place it in an 85°C water bath and stir at a speed of 820 revolutions per minute for 1 h. Then add manganese acetylacetonate, seal it again, place it in a 30°C water bath, continue to stir for 3 h, and take out the sealed reagent bottle with the spinning solution; b) Draw 3.5 ml of the spinning solution with a spinning syringe, install a spinning needle head with a certain inner diameter, adjust the distance from the receiving roller, set the injection speed of the spinning solution, the rotation speed of the receiving roller, and the spinning voltage, and then spinning can be carried out until the spinning is completed; c) Take down the spun film from the surface of the roller, fold it into a state with a length and width of 7*3 cm, and put it into a porcelain boat with a length and width of 8*4 cm. Then transfer it to a tube furnace, continuously introduce argon, heat from 30°C to a predetermined temperature at a heating rate of 2°C / min, keep it for a period of time, and then cool it down to 380°C with the furnace. Adjust the gas flow rate, and then keep this gas flow rate and continue to cool it down to room temperature with the furnace to obtain MnF2 / carbon fiber.

2. The preparation method of MnF2 / carbon fiber for sodium battery according to claim 1, characterized in that In the step a), the addition amounts of dimethylformamide, polymethyl methacrylate (molecular weight of 15000), polyacrylonitrile (molecular weight of 150000), polyvinylidene fluoride (molecular weight of 500,000), and manganese acetylacetonate are 5.0 g, 0.25 g, 0.2 g, 0.3 g, and 1.0 g respectively.

3. The preparation method of MnF2 / carbon fiber for sodium battery according to claim 1, characterized in that, In the step b), the inner diameter of the spinning needle head is 0.41 mm (22G model), the distance from the receiving roller is 11 cm, the injection speed of the spinning solution is 0.8 mL / h, the rotation speed of the receiving roller is 310 revolutions per minute, and the spinning voltage is 19 KV at the same time.

4. The preparation method of MnF2 / carbon fiber for sodium battery according to claim 1, characterized in that, In the step c), under the condition that the gas flow rate of argon is 16 sccm, heat it to 550°C at a heating rate of 2°C / min, keep it for 1 h, and then cool it down to 380°C with the furnace. Adjust the gas flow rate of argon to 35 sccm.

Images