Preparation method of MnF2 / carbon composite material for sodium battery

Abstract

The invention discloses a preparation method of a MnF2 / carbon composite material for a sodium battery and belongs to the field of sodium ion batteries. The MnF2 / carbon composite material is prepared by adopting a room-temperature liquid phase method and annealing treatment, taking manganese acetylacetonate as a manganese source, polyvinylidene fluoride as a fluorine source and a carbon source and dicyanodiamine as a pore-forming agent, stirring at room temperature, drying, directly annealing at 600 DEG C, and sintering for 1 hour. The material is composed of a carbon skeleton and particles which grow on the carbon skeleton and have different particle sizes. 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 313.06 mAh / g (0.1 A / g), the specific capacity is still 362.72 mAh / g after 130 times of circulation, and the specific capacity of 224.98 mAh / g can still be provided even when the specific capacity is 5.0 A / g. The MnF2 / carbon composite 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 composite material for sodium batteries belongs to the field of sodium-ion batteries. Technical Background

[0002] With the wide popularization and application of new energy electric vehicles and wearable electronic devices, the rapid development of secondary batteries has been promoted. Due to the uneven distribution and high price of lithium resources, it is difficult for lithium batteries to meet the requirements of large-scale energy storage applications. Sodium and lithium belong to the same main group elements, and they have similar physical and chemical properties. However, sodium resources have the advantages of relatively high reserves and low price in China, so they are more conducive to the large-scale energy storage application requirements of sodium-ion batteries.

[0003] The research and development of high-performance anode materials is one of the key factors to promote the wide application of sodium-ion batteries. Currently, commercial graphite cannot meet the requirements of sodium batteries. Transition metal compounds, especially transition metal manganese fluoride, have been widely studied and applied in the field of lithium batteries due to their high specific capacity and good cycle stability. The synthesis methods in existing literature mostly use F2, NF3, HF gases or hydrofluoric acid and trifluoroacetic acid as fluorine sources. Since these gases or liquids are usually toxic or corrosive, and the requirements for equipment are relatively high, 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 such as ball milling to compound with it, and it 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); in addition, for the manganese fluoride / carbon-based composite material prepared by the high-temperature treatment method based on ammonium fluoride, most of them are used for lithium battery research, and there is less research in sodium-ion batteries, and the electrochemical performance needs to be improved. 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 room-temperature stirring and annealing treatment, the MnF2 / carbon composite material is successfully prepared, and when it is used as the anode of a sodium-ion battery, it has good electrochemical performance.

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

[0006] a) In a 50 ml beaker, add appropriate amounts of dimethylformamide, polyvinylidene fluoride, dicyandiamide and manganese acetylacetonate in sequence, then wrap the beaker mouth with plastic wrap, stir at a speed of 600 revolutions per minute at room temperature for 2 h, pour all the solution in the beaker into a ceramic ark with a length * width of 60 * 30 mm, and then transfer it to an oven at 75 °C for drying treatment;

[0007] b) Place the ceramic boat with solid substances after drying in a quartz tube furnace, continuously introduce argon, heat from 30 °C to a predetermined temperature at a heating rate of 3 °C / min, after heat preservation for a period of time, when cooling down to 350 °C with the furnace, adjust the gas flow rate, and then keep this gas flow rate and continue to cool down to room temperature with the furnace to obtain the MnF₂ / carbon composite material.

[0008] c) Apply the above MnF₂ / carbon composite material as an electrode material to a sodium-ion battery.

[0009] In the step a), the addition amounts of dimethylformamide, polyvinylidene fluoride (molecular weight of 5 million), dicyandiamide, and manganese acetylacetonate are 5.5 g, 1.2 g, 0.6 g, and 1.2 g respectively;

[0010] In the step b), under the condition that the gas flow rate of argon is 18 sccm, heat up to 600 °C at a heating rate of 3 °C / min, after heat preservation for 1 h, when cooling down to 350 °C with the furnace, adjust the gas flow rate of argon to 28 sccm;

[0011] In the step c) during the cycle performance test of the sodium-ion battery, its initial specific capacity is 313.06 mAh / g at 0.1 A / g, and the specific capacity is still 362.72 mAh / g after 130 cycles; even at 5.0 A / g, it can still provide a specific capacity of 224.98 mAh / g.

[0012] Compared with other methods for preparing manganese fluoride-based materials, this method has a safe preparation process, a short cycle, simple operation, and is suitable for large-scale batch production; when the MnF₂ / carbon composite material is used in a sodium-ion battery, it has a high specific capacity and rate performance.

[0013] Use a Bruker Advance D8 X-ray powder diffractometer (Cu Kα radiation, 2θ = 10 - 80°) to determine the structure of the prepared material. Use a Hitachi S4800 scanning electron microscope to observe the surface morphology of the prepared material. Use a Neware battery test system to test the battery performance.

[0014] By Figure 1It can be seen that under the condition of an annealing time of 1 h, when the annealing temperature is 500 °C and 600 °C, the strong diffraction peaks of the obtained products are attributed to the diffraction peaks of the orthorhombic phase (JCPDS card No. 17-0864) and the tetragonal phase (JCPDS card No. 80-0927) of MnF2, indicating that the MnF2 in the product has a mixed-phase structure; when the annealing temperature is 700 °C, in addition to the diffraction peaks of the orthorhombic phase and the tetragonal phase of MnF2, there are also obvious diffraction peaks of the cubic phase of MnO (JCPDS card No. 78-0424). From Figure 2 It can be seen that under the condition of an annealing temperature of 600 °C, when the annealing time is 1 h, the product obtained in Embodiment 1 is composed of a carbon skeleton and particles of different particle sizes growing on it. From Figure 3 It can be seen that when the MnF2 / carbon composite material obtained in Embodiment 1 is used as the electrode material for 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 third cycle basically coincide, indicating stable electrochemical performance. From Figure 4 It can be seen that when the MnF2 / carbon composite material prepared in Embodiment 1 is used as the sodium battery electrode material at 0.1 A / g, the initial specific capacity is 313.06 mAh / g. After 20 cycles, the specific capacity basically does not fluctuate greatly, indicating stable electrochemical performance. Even after 130 cycles, the specific capacity is still 362.72 mAh / g ( Figure 4 at 600 °C in ); at the same time, when the product prepared in Embodiment 2 is used as the sodium battery electrode material, the initial specific capacity is 238.89 mAh / g ( Figure 4 at 500 °C in ), and after 130 cycles, its specific capacity is also lower than that of Embodiment 1. From Figure 5 It can be seen that when the MnF2 / carbon composite material prepared in Embodiment 1 is used as the sodium battery electrode material at 5.0 A / g, it can still provide a specific capacity of 224.98 mAh / g ( Figure 5 at 600 °C in ), indicating good rate performance; at the same time, when the product prepared in Embodiment 2 is used as the sodium battery electrode material at 5.0 A / g, it can only provide a specific capacity of 151.09 mAh / g ( Figure 5 at 500 °C in ), and at the remaining current densities, the specific capacity of Embodiment 2 is also lower than that of Embodiment 1. From this, it can be shown that when the annealing temperature is 600 °C and the annealing time is 1 h, the prepared MnF2 / carbon composite material provides better electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the X-ray diffraction pattern of the products obtained at different annealing temperatures;

[0016] Figure 2It is the SEM image of the product obtained in Embodiment 1;

[0017] Figure 3 It is the CV curve of the product obtained in Embodiment 1;

[0018] Figure 4 It is the cycling curve of the product obtained in the embodiment;

[0019] Figure 5 It is the rate performance diagram of the product obtained in the embodiment. Detailed implementation manners

[0020] 1. In a 50 ml beaker, successively add 5.5 g of dimethylformamide, 1.2 g of polyvinylidene fluoride (molecular weight of 5 million), 0.6 g of dicyandiamide and 1.2 g of manganese acetylacetonate. Then wrap the mouth of the beaker with plastic wrap and stir at a speed of 600 revolutions per minute at room temperature for 2 h. After that, pour all the solution in the beaker into a ceramic boat with a length * width of 60 * 30 mm, and then transfer it to a 75 °C oven for drying; place the ceramic boat with the solid substance after drying in a quartz tube tube furnace. Under the condition that the argon gas flow rate is 18 sccm, heat from 30 °C to 600 °C at a heating rate of 3 °C / min, hold for 1 h, and then cool down to 350 °C with the furnace. When the temperature reaches 350 °C, adjust the argon gas flow rate to 28 sccm, and then keep this flow rate and cool down to room temperature with the furnace to obtain the MnF2 / carbon composite material (see Figure 1 at 600 °C in Figure 2 , Figure 3 , Figure 4 at 600 °C in Figure 5 and at 600 °C in

[0021] 2. In a 50 ml beaker, successively add 5.5 g of dimethylformamide, 1.2 g of polyvinylidene fluoride (molecular weight of 5 million), 0.6 g of dicyandiamide and 1.2 g of manganese acetylacetonate. Then wrap the mouth of the beaker with plastic wrap and stir at a speed of 600 revolutions per minute at room temperature for 2 h. After that, pour all the solution in the beaker into a ceramic boat with a length * width of 60 * 30 mm, and then transfer it to a 75 °C oven for drying; place the ceramic boat with the solid substance after drying in a quartz tube tube furnace. Under the condition that the argon gas flow rate is 18 sccm, heat from 30 °C to 500 °C at a heating rate of 3 °C / mi n n, hold for 1 h, and then cool down to 350 °C with the furnace. When the temperature reaches 350 °C, adjust the argon gas flow rate to 28 sccm, and then keep this flow rate and cool down to room temperature with the furnace to obtain the MnF2 / carbon composite material (see Figure 1 at 500 °C in Figure 4 at 500 °C in Figure 5 and at 500 °C in

[0022] 3. In a 50 ml beaker, successively add 5.5 g of dimethylformamide, 1.2 g of polyvinylidene fluoride (molecular weight of 5 million), 0.6 g of dicyandiamide, and 1.2 g of manganese acetylacetonate. Then wrap the mouth of the beaker with plastic wrap and stir at a speed of 600 revolutions per minute at room temperature for 2 h. Pour all the solution in the beaker into a ceramic boat with a length * width of 60 * 30 mm, and then transfer it to an oven at 75 °C for drying: Place the dried ceramic boat with solid matter in a quartz tube furnace. Under the condition that the argon gas flow rate is 18 sccm, heat it from 30 °C to 700 °C at a heating rate of 3 °C / min, hold for 1 h, and then cool it down to 350 °C with the furnace. When the temperature reaches 350 °C, adjust the argon gas flow rate to 28 sccm, and then keep this flow rate and cool it down to room temperature with the furnace to obtain the product (see Figure 1 Figure 700 °C).

Claims

1. A preparation method of MnF2 / carbon composite material for sodium battery, comprising the following steps: a) In a 50-ml beaker, add appropriate amounts of dimethylformamide, polyvinylidene fluoride, dicyandiamide and manganese acetylacetonate successively. Then wrap the mouth of the beaker with plastic wrap and stir at a speed of 600 revolutions per minute at room temperature for 2 h. Pour all the solution in the beaker into a ceramic ark with a length * width of 60 * 30 mm, and then transfer it to an oven at 75 °C for drying treatment; b) Place the dried ceramic ark with solid substances in a quartz tube tube furnace, continuously introduce argon, and heat from 30 °C to a predetermined temperature at a heating rate of 3 °C / min. After heat preservation for a period of time, when it is cooled to 350 °C with the furnace, adjust the ventilation rate, and then keep this ventilation rate and continue to cool to room temperature with the furnace to obtain the MnF2 / carbon composite material.

2. The preparation method of the MnF2 / carbon composite material for sodium batteries according to claim 1, characterized in that, In step a), the addition amounts of dimethylformamide, polyvinylidene fluoride (molecular weight of 5 million), dicyandiamide and manganese acetylacetonate are 5.5 g, 1.2 g, 0.6 g and 1.2 g respectively.

3. The preparation method of the MnF2 / carbon composite material for sodium batteries according to claim 1, characterized in that, In step b), under the condition that the ventilation rate of argon is 18 sccm, heat to 600 °C at a heating rate of 3 °C / min, after heat preservation for 1 h, when it is cooled to 350 °C with the furnace, adjust the ventilation rate of argon to 28 sccm.

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