A preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres

Abstract

The application relates to a preparation method of crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres. It belongs to the field of battery negative electrode materials. First, microcrystalline cellulose and carbon nanotubes are mechanically stirred in an alkali-urea system and crosslinked by using epoxy chloropropane, and then emulsified into balls to obtain crosslinked cellulose / carbon nanotube composite microspheres. Then, the crosslinked cellulose / carbon nanotube microspheres are swelled with an ammonium molybdate solution, and a carbonized precursor is obtained through high-temperature hydrothermal treatment. Finally, the precursor is subjected to low-temperature dehydration and high-temperature carbonization in a tube furnace to obtain crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres. The negative electrode material has a wrinkled outer surface and a microporous structure, can improve the permeability of electrolyte and promote mass transfer. Compared with the prior art, the crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microsphere negative electrode material prepared by the application has high specific capacity and high coulombic efficiency, and is suitable for the field of high-capacity sodium ion battery negative electrode materials.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a battery negative electrode material, in particular to a preparation method of crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres. BACKGROUND

[0002] The development of new energy industry puts forward higher requirements for secondary energy storage batteries. In recent years, sodium ion batteries (SIBs) as a new type of secondary energy storage battery have attracted great attention. Sodium ion batteries are safe and low in cost, and especially in the environment of rapid rise of cobalt, copper and lithium resource cost, sodium ion batteries highlight their cost advantage. However, compared with lithium ion batteries (LIBs), sodium ions have larger ionic radius and solvation radius, so that it is difficult for solvated sodium ions to be freely deintercalated in commercial graphite, and therefore graphite and other commonly used electrodes cannot be used as the negative electrode of sodium ion batteries. Therefore, it is of great significance to develop a negative electrode material more suitable for sodium ion batteries. Similarly, metal alloy negative electrode materials also have the characteristics of high specific capacity and high initial efficiency, for example: Abel et al. found that the capacity retention rate of dense Ge film electrode dropped sharply after a few cycles under the condition of high initial capacity. Komaba et al. found that Sn also has the problem that the actual capacity retention rate is much lower than the theoretical value after a few cycles under the condition of high theoretical capacity. The high-capacity negative electrode materials of the fifth main group B, P, As and Bi are difficult to achieve engineering conditions due to their low abundance. The conversion type materials represented by sulfides and phosphides have insertion or alloying reactions while undergoing conversion reactions, but these materials have the disadvantage of structural damage due to large volume change while enjoying high specific capacity. At the same time, like some organic materials, the conversion type materials also have the problem of environmental pollution. Therefore, it is the key to the development of sodium ion batteries to find a battery negative electrode material with high capacity and low cost.

[0003] Hard carbon material is a kind of graphite-like material with short-range order, long-range disorder and rich pseudo-graphitization domains. Its irregular ion channels and large interlayer spacing facilitate the rapid insertion and extraction of sodium ions. At the same time, hard carbon material has the advantages of high specific capacity, low sodium storage voltage, stable cycle and environmental friendliness, which makes it a promising negative electrode material. However, hard carbon material also has the characteristics of low coulombic efficiency and poor cycle life, which seriously limits the further development of hard carbon material. Molybdenum disulfide is a two-dimensional layered metal alloy compound. The sodium storage behavior of molybdenum disulfide has been widely studied. It mainly relies on alloy transformation to store sodium. The highest experimental sodium storage capacity is up to 640 mAh / g, which is much higher than that of hard carbon. However, due to the large volume expansion of molybdenum disulfide during charging and discharging, the volume expansion rate is usually as high as 130%, so the pulverization of molybdenum disulfide electrode is serious, which is not conducive to the formation of stable SEI film. Based on the above characteristics, the strategy of molybdenum disulfide / carbon composite can effectively inhibit the expansion of molybdenum disulfide electrode and increase the cycle life of the electrode. SUMMARY

[0004] In view of the deficiencies in the background art, the present application provides a preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres which is suitable for both industrial application and laboratory, and has high sodium storage capacity, low volume expansion rate and good cycle life. The specific scheme is as follows:

[0005] A preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres, characterized in that:

[0006] (1) Preparation of cross-linked cellulose / carbon nanotube microspheres: 5.0 g of microcrystalline cellulose, 8.0 g of NaOH, 6.0 g of thiourea are added to 85 mL of deionized water, and mechanical stirring is carried out at 500 r / min in an ice water bath for 10 min, then 0 ~ 2.0 mg of carbon nanotubes are added, and mechanical stirring is carried out until a black suspension is formed, then 0 ~ 2.0 mL of epoxy chloropropane is added to form an aqueous phase; 80 mL of white oil, 160 mL of isooctane, 2.5 g of Tween-80, 8.0 g of Span-80 are prepared to form an oil phase; under mechanical stirring at 500 r / min, 20 mL of the aqueous phase is dispersed into 240 mL of the oil phase for 20 min, then 240 mL of 75% ethanol is added to form a ball, centrifuged at 7500 r / min, washed with 100 mL of ethanol for 3 times, then freeze-dried under reduced pressure to obtain the finished product of cross-linked cellulose / carbon nanotube microspheres;

[0007] (2) Preparation of cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres: 0 ~ 8.0 g of ammonium molybdate tetrahydrate, 8.0 g of thiourea were dissolved in 100 mL of deionized water, and then 0 ~ 6.0 g of cross-linked cellulose / carbon nanotube microspheres obtained in the above step were added, and mechanical stirring was carried out at 30°C for 48 h, and then transferred to a polytetrafluoroethylene lined high-pressure reaction kettle, and incubated at 200°C for 18 h, and then centrifuged at 7500 r / min, to obtain cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres, and the microspheres were repeatedly washed with 250 mL of deionized water for 3 ~ 5 times, and dried at 65°C for 24 h;

[0008] (3) Carbonization process: warming up: 50 ~ 180°C warming up for 60 min, 180°C incubation for 60 min, 180 ~ 230°C warming up for 1800 min, 230°C incubation for 60 min, 230 ~ 1350°C warming up for 375 min, 1350°C incubation for 120 min; cooling down: 3°C / min cooling down to 200°C, stop heating.

[0009] As a preferred option:

[0010] (1) The preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein in the preparation process of cross-linked cellulose / carbon nanotube microspheres in step (1), the amount of carbon nanotubes added is 0 ~ 2.0 mg, and the amount of epoxy chloropropane added is 0 ~ 2.0 mL;

[0011] (2) The preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein in the preparation process of cross-linked cellulose / carbon nanotube microspheres in step (1), the alcohol water mass ratio of 240 mL of 75% ethanol regenerated into a ball is ethanol: water = 1:9 to 9:1;

[0012] (3) The preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein in the preparation process of cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres in step (2), the amount of ammonium molybdate tetrahydrate is 0 ~ 8.0 g;

[0013] (4) The preparation method of cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein in the preparation process of cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres in step (2), the mass of cross-linked cellulose / carbon nanotube microspheres added is 0 ~ 6.0 g;

[0014] (5) The preparation method of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein the carbonization process in step (3) is a first dehydration temperature of 50-180 DEG C, a temperature rising for 60 min, a 180 DEG C temperature keeping for 60 min, and a second dehydration temperature of 900-1600 DEG C, a temperature rising for 60 min, a 1350 DEG C temperature keeping for 120 min.

[0015] The preparation method of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres according to claim 1, wherein the carbonization process in step (3) is a first dehydration temperature of 50-180 DEG C, a temperature rising for 60 min, a 180 DEG C temperature keeping for 60 min, and a second dehydration temperature of 900-1600 DEG C, a temperature rising for 60 min, a 1350 DEG C temperature keeping for 120 min.

[0016] The beneficial effects of the present application are embodied as follows:

[0017] 1) The present application uses cross-linked cellulose / carbon nanotube microspheres as a carrier, and grows molybdenum disulfide nanosheets in situ on the surface of the microspheres in a space-limited manner to obtain cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres.

[0018] Through low-temperature dehydration and high-temperature carbonization, cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres are obtained.

[0019] The cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres prepared by the present application have interconnected macroporous structures and abundant microporous structures, which are beneficial to the rapid penetration of electrolyte.

[0020] The sodium storage capacity of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres prepared by the present application for NaPF6 electrolyte is as high as 627 mAh / g, and the coulombic efficiency is more than 88%. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The schematic diagram of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres prepared by the method of the present application, the SEM scanning electron microscope image, the particle size distribution, the thermogravimetry, and the pore size distribution diagram.

[0022] Figure 2 The TEM transmission electron microscope image of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres prepared by the method of the present application, and the XRD, Raman spectrum, and XPS characterization diagrams.

[0023] Figure 3 The half-cell cyclic voltammetry curve, the EIS impedance curve, the constant current charge and discharge curve, the rate performance, and the cycle performance curve of the cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres prepared by the method of the present application. DETAILED DESCRIPTION

[0024] The following examples further illustrate the present application but should not be construed as limiting the application. Modifications or variations of the method, steps or conditions of the application can be made by those skilled in the art without departing from the spirit and scope of the application.

[0025] Example 1 Crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres

[0026] 1. Preparation of crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres

[0027] This example uses the microemulsion method to prepare crosslinked cellulose / carbon nanotube as the starting step. First, nanometer molybdenum disulfide is grown in situ on the surface of crosslinked cellulose / carbon nanotube microspheres by space confinement method, and then high-temperature carbonization is performed to obtain crosslinked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres.

[0028] (1) Preparation of crosslinked cellulose / carbon nanotube microspheres

[0029] 5.0 g of microcrystalline cellulose, 8.0 g of NaOH, 6.0 g of thiourea, 85 mL of deionized water, 500 r / min mechanical stirring in ice water bath for 10 min, then 0.5 mg of carbon nanotubes, forced mechanical stirring to form a black suspension, then 1.5 mL of epoxy chloropropane, form the water phase; 80 mL of white oil, 160 mL of isooctane, 2.5 g of Tween-80, 8.0 g of Span-80, prepare to form the oil phase; 500 r / min mechanical stirring, 20 mL of water phase dispersed into 240 mL of oil phase for 20 min, then 240 mL of 75% ethanol to re-form the ball, 7500 r / min centrifugation, 100 mL of ethanol washing for 3 times, then freeze-drying under reduced pressure to form the product crosslinked cellulose / carbon nanotube microspheres;

[0030] (2) Preparation of crosslinked cellulose / carbon nanotube / molybdenum disulfide microspheres

[0031] 4.0 g of ammonium molybdate tetrahydrate, 8.0 g of thiourea, 100 mL of deionized water, then 2.0 g of crosslinked cellulose / carbon nanotube microspheres obtained in the previous step, 30℃ mechanical stirring for 48 h, transfer to a polytetrafluoroethylene lined high-pressure reaction kettle, 200℃ for 18 h, then 7500 r / min centrifugation to obtain crosslinked cellulose / carbon nanotube / molybdenum disulfide microspheres, the microspheres are repeatedly washed with 250 mL of deionized water for 3-5 times, and dried at 65℃ for 24 h;

[0032] (3) Carbonization process

[0033] Temperature rising: 50 ~ 180℃, rising for 60 min, 180℃, holding for 60 min, 180 ~ 230℃, rising for 1800 min, 230℃, holding for 60 min, 230 ~ 1350℃, rising for 375 min, 1350℃, holding for 120 min; Temperature falling: 3℃ / min to 200℃, stop heating.

[0034] 2. Half-cell assembly

[0035] Half-cell assembly and test, negative electrode preparation: 0.92 g crosslinked cellulose / carbon nanotube / molybdenum disulfide microspheres, 0.03 g Super P, 0.10 g 1.5 wt% sodium carboxymethyl cellulose solution, 0.07 g 40 wt% butadiene-styrene rubber solution, 0.60 g deionized water, homogenized for 20 min, using a four-side preparation device, evenly spread the slurry on the surface of a single-side polished copper foil with a thickness of 100 μm, dried at 105℃ for 8 h, and cut into a piece with a diameter of 12 mm using a piece cutting machine; positive electrode preparation: metal sodium was pressed into a piece with a thickness of 0.8 mm using a roller press, and punched into a piece with a diameter of 12 mm; button cell assembly sequence (from bottom to top): positive electrode shell, spring, gasket, sodium piece, glass fiber separator, sodium hexafluorophosphate electrolyte (1 mol / L NaPF6 dissolved in ethylene carbonate: ethylene carbonate, volume ratio 1:1), negative electrode piece, negative electrode shell. All assembly processes were carried out in an anaerobic box (O2 concentration ≤0.5 ppm, water concentration ≤0.1 ppm).

Claims

1. A method for preparing cross-linked cellulose / carbon nanotube / molybdenum disulfide hard carbon microspheres, characterized by Comprising the following steps: (1) Preparation of cross-linked cellulose / carbon nanotube microspheres: 5.0 g of microcrystalline cellulose, 8.0 g of NaOH, 6.0 g of thiourea were added to 85 mL of deionized water, and mechanical stirring was carried out at 500 r / min in an ice water bath for 10 min, then 0.5 mg of carbon nanotubes was added, and after forced mechanical stirring to form a black suspension, 1.5 mL of epichlorohydrin was added to form an aqueous phase; 80 mL of white oil, 160 mL of isooctane, 2.5 g of Tween-80, and 8.0 g of Span-80 were prepared to form an oil phase; under mechanical stirring at 500 r / min, 20 mL of the aqueous phase was dispersed into 240 mL of the oil phase for 20 min, and then 240 mL of 75% ethanol was used to re-form the microspheres, which were centrifuged at 7500 r / min, washed with 100 mL of ethanol for 3 times, and then freeze-dried under reduced pressure to obtain the finished cross-linked cellulose / carbon nanotube microspheres; (2) Preparation of cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres: 4.0 g of ammonium molybdate tetrahydrate and 8.0 g of thiourea were dissolved in 100 mL of deionized water, and then 2.0 g of the cross-linked cellulose / carbon nanotube microspheres obtained in the previous step were added, and mechanical stirring was carried out at 30℃ for 48 h, then the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle, and heated at 200℃ for 18 h, and then centrifuged at 7500 r / min to obtain cross-linked cellulose / carbon nanotube / molybdenum disulfide microspheres, which were repeatedly washed with 250 mL of deionized water for 3-5 times, and dried at 65℃ for 24 h; (3) Carbonization process: temperature rising: 50-180℃ for 60 min, 180℃ for 60 min, 180-230℃ for 1800 min, 230℃ for 60 min, 230-1350℃ for 375 min, and 1350℃ for 120 min; temperature falling: 3℃ / min to 200℃, and stop heating.

Images