Preparation method of cross-linked cellulose hard carbon microsphere negative electrode material

Abstract

The application relates to a preparation method of a crosslinked cellulose hard carbon microsphere negative material. The method is used in the field of battery negative materials. First, microcrystalline cellulose is dissolved in an alkali urea system to obtain a microcrystalline cellulose solution. Then, the microcrystalline cellulose solution is crosslinked into balls by adopting a certain equivalent of epichlorohydrin through an emulsification method. Finally, low-temperature dehydration and high-temperature carbonization are adopted to obtain the crosslinked cellulose hard carbon microsphere negative material. The crosslinked cellulose hard carbon microsphere negative material has a mutual crosslinking macroporous and microporous structure dual-pore structure, can promote the penetration and mass transfer of electrolyte, meanwhile, the negative material also has a highly disordered curled carbon layer structure, and realizes the rapid deintercalation of sodium ions. The cellulose hard carbon microsphere negative material prepared by the application has high specific capacity, high coulombic efficiency and low charging and discharging platform, and is suitable for the field of super-fast-charging sodium ion battery negative 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 a crosslinked cellulose hard carbon microsphere negative electrode material. BACKGROUND

[0002] In recent years, sodium ion batteries have been widely concerned by the academic and industrial circles at home and abroad due to their advantages such as low cost, high safety and excellent electrochemical performance. Sodium ion batteries have similar energy storage mechanism as lithium ion batteries, and compared with lithium ions, sodium ions have the advantages of abundant reserves, low extraction cost, high energy density, safety and environmental protection. From the development history of lithium ion batteries, the research on negative electrode materials plays an important role in the commercialization of lithium ion batteries. In particular, the emergence of graphite as a representative negative electrode material directly promotes the commercial application of lithium ion batteries. However, the small spacing of graphite makes it difficult for sodium ions with large size to be embedded in the graphite interstices. In order to realize the industrialization of sodium ion batteries, a negative electrode material with low cost and excellent performance like the graphite negative electrode of lithium ion batteries needs to be found.

[0003] Hard carbon is a kind of amorphous carbon material which is difficult to graphitize, and its sources are wide, usually divided into resin-based carbon, organic polymer pyrolysis carbon, carbon black and biomass carbon. Hard carbon material has the characteristics of high reversible specific capacity, wide electrochemical window, low sodium intercalation voltage, high charge and discharge rate, stable properties at high and low temperatures, good compatibility with electrolyte, not easy to self-ignite, etc. More importantly, the amorphous structure of hard carbon makes its interstices larger, which can embed sodium ions with large size, so it is considered as an ideal negative electrode material for sodium ion batteries. In 2000, Stevens used glucose as a precursor to prepare a hard carbon material with a sodium storage capacity of 300 mAh / g for the first time, and successfully matched it with a positive electrode material. Based on this, the application uses renewable microcrystalline cellulose as a precursor, adopts molecular crosslinking and regeneration strategies to adjust the crystallinity and crosslinking degree of microcrystalline cellulose microspheres, and then carbonizes them. The prepared crosslinked cellulose hard carbon microspheres have through macroporous structure and rich microporous structure on the macro level, which is helpful for efficient wetting of electrolyte. SUMMARY

[0004] A preparation method of a crosslinked cellulose hard carbon microsphere negative electrode material, characterized in that:

[0005] (1) Preparation of cross-linked cellulose microspheres: 100 mL three-necked flask was added 5.0 g NaOH, 4.0 g thiourea, 50 mL deionized water, ice water bath mechanical stirring, then 3.0 g microcrystalline cellulose was added, and mechanical stirring was carried out for 15 ~ 20 min, then 0 ~ 2.0 mL epoxy chloropropane was added to obtain a microcrystalline cellulose solution, at the same time, 40 mL white oil, 80 mL isooctane, 1.0 g Tween 80, 4.0 g Span 80 were mechanically stirred to prepare an oil phase, 10 mL microcrystalline cellulose solution was slowly injected into the oil phase to emulsify into balls, the temperature was 35℃, the time was 30 ~ 60 min, centrifugation, the prepared cross-linked cellulose microspheres were replaced with 15 mL isopropyl alcohol and 10 mL water solution for three times, then washed with deionized water until neutral, freeze-dried to obtain cross-linked cellulose microspheres;

[0006] (2) Preparation of cross-linked cellulose hard carbon microspheres: 10 g of cross-linked cellulose microspheres obtained in the above step was placed in a corundum crucible, high-purity argon gas (99.999% purity) was set as the protective gas, the temperature rising rate curve was set as 50℃ ~ 180℃ rising for 60 min, 180℃ ~ 230℃ rising for 1800 min, 3℃ / min rising to 900 ~ 1200℃, and the temperature was kept for 1 ~ 2 h; the temperature decreasing rate curve was set as: -3℃ / min decreasing to 200℃, then natural cooling, finally the obtained cross-linked cellulose hard carbon microspheres were washed with 20% KOH at 70℃ for 2 h, 2 mol / L HCl solution at 60℃ for 15 h, and deionized water until neutral, and dried at 110℃ for 12 h to obtain cross-linked cellulose hard carbon microspheres.

[0007] As preferred options:

[0008] (1) The preparation method of the cross-linked cellulose hard carbon microsphere negative material according to claim 1, wherein in the preparation process of the cross-linked cellulose microspheres mentioned in step (2), the equivalent of epoxy chloropropane is 1.2 mL;

[0009] (2) The preparation method of the cross-linked cellulose hard carbon microsphere negative material according to claim 1, wherein in the preparation process of the cross-linked cellulose microspheres mentioned in step (1), the volume ratio of white oil to isooctane in the oil phase preparation is 2:1;

[0010] (3) The preparation method of the cross-linked cellulose hard carbon microsphere negative material according to claim 1, wherein in the preparation process of the cross-linked cellulose hard carbon microspheres mentioned in step (2), the temperature rising rate curve is 50℃ ~ 180℃ rising for 60 min, 180℃ ~ 230℃ rising for 1800 min, 230℃ ~ 1200℃ rising for 320 min, and 1200℃ keeping for 60 min;

[0011] (4) The preparation method of the cross-linked cellulose hard carbon microsphere negative material according to claim 1, wherein the cooling rate curve is set as 1200℃ ~ 50℃ cooling for 380 min in the process of preparing the cross-linked cellulose hard carbon microspheres.

[0012] (5) The preparation method of the cross-linked cellulose hard carbon microsphere negative material according to claim 1, wherein the post-processing process in the process of preparing the cross-linked cellulose hard carbon microspheres is 20% KOH washing at 70℃ for 2h, 2mol / L HCl solution washing at 60℃ for 15h, then washing with deionized water until neutral, and drying at 110℃ for 12h.

[0013] The beneficial effects of the present application are embodied as follows:

[0014] (1) The present application uses renewable microcrystalline cellulose as a precursor, and the original crystal structure of the microcrystalline cellulose is destroyed by molecular cross-linking, thereby reducing the crystallinity of the raw material and promoting the formation of hard carbon pseudo-graphitization domains.

[0015] (2) The cross-linked cellulose hard carbon microsphere negative material prepared by the present application has high specific capacity, high coulombic efficiency and low charge-discharge platform for sodium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 : The scanning electron microscope picture of the cross-linked cellulose hard carbon microsphere negative material prepared by the method of the present application;

[0017] Figure 2 : The constant current charge-discharge curve of the cross-linked cellulose hard carbon microsphere prepared by the method of the present application. DETAILED DESCRIPTION

[0018] The following examples further illustrate the present application, but should not be construed as limiting the present application. Modifications or replacements of the method, steps or conditions of the present application, without departing from the spirit and essence of the present application, all belong to the scope of the present application.

[0019] Example 1:

[0020] Preparation of crosslinked cellulose microspheres: 100 mL three-necked flask was added 5.0 g NaOH, 4.0 g thiourea, 50 mL deionized water, ice water bath mechanical stirring, then 3.0 g microcrystalline cellulose was added, and mechanical stirring was carried out for 15 ~ 20 min, then 1.2 mL epoxy chloropropane was added to obtain a microcrystalline cellulose solution, at the same time, 40 mL white oil, 80 mL isooctane, 1.0 g Tween 80, 4.0 g Span 80 were mechanically stirred to prepare an oil phase, 10 mL microcrystalline cellulose solution was slowly injected into the oil phase to emulsify into balls, the temperature was 35℃, the time was 30 ~ 60 min, centrifugation, the prepared crosslinked cellulose microspheres were replaced with 15 mL isopropyl alcohol and 10 mL water solution for three times, then washed with deionized water until neutral, freeze-dried to obtain crosslinked cellulose microspheres;

[0021] (2) Preparation of crosslinked cellulose hard carbon microspheres: 10 g of crosslinked cellulose microspheres obtained in the above step were placed in a corundum crucible, high-purity argon gas (99.999% purity) was used as the protective gas, the temperature rising rate curve was set as 50℃ ~ 180℃ rising for 60 min, 180℃ ~ 230℃ rising for 1800 min, 230℃ ~ 1200℃ rising for 323 min, and 1200℃ was kept for 2 h; the temperature decreasing rate curve was set as 1200 ~ 300℃ decreasing for 300 min, and natural cooling was started, finally the obtained crosslinked cellulose hard carbon microspheres were washed with 20% KOH at 70℃ for 2 h, 2 mol / L HCl solution at 60℃ for 15 h, and deionized water until neutral, and then dried at 110℃ for 12 h to obtain crosslinked cellulose hard carbon microspheres.

[0022] Case 2:

[0023] Half-cell assembly and test, negative electrode sheet preparation: 0.92 g crosslinked cellulose hard carbon microspheres, 0.03 g SuperP, 0.10 g 1.5 wt% carboxymethyl cellulose sodium solution, 0.07 g 40 wt% butadiene-styrene rubber solution, 0.60 g deionized water, homogenate for 20 min, use four sides to prepare the device, evenly spread 100 μm of the slurry on the surface of the single-side polished copper foil, dry at 105℃ for 8 h, and cut the sheet with a sheet cutting machine to a diameter of 12 mm; positive electrode sheet preparation: metal sodium was pressed into a sheet with a thickness of 0.8 mm by a roller press, and punched into a diameter of 12 mm; the assembly sequence of the button cell (from bottom to top) was as follows: positive electrode shell, spring, gasket, sodium sheet, glass fiber separator, sodium hexafluorophosphate electrolyte (1 mol / L NaPF6 dissolved in ethylene carbonate: ethylene carbonate, volume ratio 1:1), negative electrode sheet, and 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 a cross-linked cellulose hard carbon microsphere negative material, characterized in that Comprising the following steps: (1) Preparation of crosslinked cellulose microspheres: 100 mL three-necked flask was added 5.0 g NaOH, 4.0 g thiourea, 50 mL deionized water, ice water bath mechanical stirring, then 3.0 g microcrystalline cellulose, strong mechanical stirring 15 ~ 20 min, then 1.2 mL epichlorohydrin, obtained microcrystalline cellulose solution, at the same time, 40 mL white oil, 80 mL isooctane, 1.0 g Tween 80, 4.0 g Span 80 mechanical stirring to prepare oil phase, 10 mL microcrystalline cellulose solution was slowly injected into the oil phase to emulsify into ball, temperature 35℃, time 30 ~ 60 min, centrifugation, the prepared crosslinked cellulose microspheres were replaced with 16 mL isopropyl alcohol and 4 mL water mixed solvent for three times, then washed with deionized water until neutral, freeze-drying, crosslinked cellulose microspheres were obtained; (2) Preparation of crosslinked cellulose hard carbon microspheres: 10 g crosslinked cellulose microspheres obtained in the above step were placed in a corundum crucible, the protective gas was set to 99.999% pure high-purity argon, the temperature rising rate curve was set to 50℃~ 180℃, rising for 60 min, 180℃~ 230℃, rising for 1800 min, 230℃~ 1200℃, rising for 320 min, 1200℃, holding for 60 min, the cooling rate curve was set to 1200℃~ 50℃, cooling for 380 min, finally the obtained crosslinked cellulose hard carbon microspheres were washed with 20% KOH at 70℃ for 2h, 2mol / L HCl solution at 60℃ for 15h, then washed with deionized water until neutral, dried at 110℃ for 12h, crosslinked cellulose hard carbon microspheres were obtained.

Images