AU2020102517A4

AU2020102517A4 - A mixture of asphalt and sulfur powder as amorphous carbon anode material and preparation thereof

Info

Publication number: AU2020102517A4
Application number: AU2020102517A
Authority: AU
Inventors: Shuyi Chen; Yucheng Lian; Haicheng WANG; Zuobin Wang; Chenglong Wu
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2020-11-19
Anticipated expiration: 2028-09-30

Abstract

The invention discloses an amorphous carbon negative electrode material made of a sufficient mixture of asphalt and sulfur powder. The preparation method is as follows: the sufficient mixture of asphalt and sulfur powder is put into a tube furnace, and the temperature is pretreated under the protection of argon, and then the temperature is gradually lowered and the room temperature is leveled. Take the pretreated sample out of the tubular furnace and grind it in a mortar. After that, the sample is placed in a tubular furnace, the temperature is raised by more than 1000 °C and kept by 1.5-2 hours under the argon protection environment, and then the temperature is lowered by about 800 °C under the control of the cooling rate, and the amorphous carbon negative electrode material is obtained after cooling to room temperature. 1 Figure 1 20S-1200°C C: C: 10 20 30 40 50 60 70 20(°) Figure 2 1

Description

Figure 1

20S-1200°C

C: C:

10 20 30 40 50 60 70 20(°)

Figure 2

TITLE A mixture of asphalt and sulfur powder as amorphous carbon anode material and preparation thereof

FIELD OF THE INVENTION The invention discloses an amorphous carbon negative electrode material made of a sufficient mixture of asphalt and sulfur powder.

BACKGROUND OF THE INVENTION In recent years, since the lithium-ion battery is confronting the problem of short-coming lithium resources and rising costs, the demand for the sodium-ion battery is increasing. As a substitute, sodium has abundant resources beneath the earth, occupying 2.6% of crustal content. Also, its refining price is relativity low, could be produced to an economic-friendly battery. In the meantime, the modem electric car, and the large-grid-energy storage-industry desire more powerful and economical batteries. As a result, studying well-electrochemical-properties sodium-ion batteries has become a research hot pot. In recent years' study, many scientists found that SIBs still need more improvement, especially its relativity low electric capacity. However, Finding an appropriate sodium electrode material can improve it efficiently.

The use of amorphous carbon materials as anode material for batteries has many advantages. These materials are rich in raw material reserves and relatively inexpensive. And compared to other materials, it has better cycle stability. As an example of another common anode material - an alloy -, there is an Sn-SnS-C nano-composite [1], which gives a good electric capacity (664 mAh g Iat 20 mA gI and 350 mAh gl at 20 mAh g1). 1 at 800 mA gl), but it lacks good cycling stability and produces harmful volume expansion during the formation of the tin-sodium alloy

[2], which can have the consequence of disintegrating the electrode. In contrast, another battery using an amorphous carbon material - coal tar pitch - as the anode material [3] has good cycling stability with a loss of only 0.012 % of cycling capacity per 1000 cycles. However, its battery capacity is relatively small (272 mAh g-1 at 0.1 A g-1) and would not be commercially available to meet the capacity needs of electric vehicles and energy storage devices.

Currently, there are mainly two processes that could be used to improve the electrochemical properties, i.z pre-oxidized, and heat treatment,. According to the research done by Nour Daher's team[4], a pitch-based material which used pre-oxidized treatment delivers a remarkable 312 mAh.g- lof reversible capacity at C/20 for only 10 % of irreversibility at the first cycle. Lei and his team experimented with heat-treated asphalt-based materials[5], and also had very significant improvements, its reversible capacity was 482.8 mAh/g at 0.1 A/g for the first cycle and had values of 245.9 and 103.7 mAh/g at 0.5 and 5 A/g, respectively after 500 cycles. Given the good results of both processes, our team combined those two processes for making our samples.

pitch and sulfur are first combined in a certain proportion to synthesize the precursors. Then the sample is heated up to 300°C in an argon-protected furnace for the pre-treatment. After cooling it to the room temperature, it would be ground in the mortar until it is crushed completely. Then the sample will be heated up to 1200°C in a bigger furnace and mixed with sodium alginate powder in a ratio of 1 to 9. Finally, a certain amount of water is added into the sample and ground to the paste for coating on the fluid collecting aluminum foil. Using the SEM Microscope, the XRD, and the Raman spectrum and by gradually increasing the temperature, the electrochemical behavior of materials is observed and recorded, and the charge/discharge curve is applied to test the multiple cycle efficiency.

SUMMARY OF THE INVENTION Step 1: preparation Pitch and sulfur are used to synthesize the precursors in different proportions (X=5%, %, 20%, 30%, 40%, and 50%; X is the percentage of sulfur doping). What's more, the total mass of each precursor with doping of S in different proportions is constantly 6g. Step 2: Morphological Studies We add sulfur powder and coal tar pitch at different mass ratio and carry out SEM tests at different carbonization temperatures. After a series of experiments, we can conclude that the samples with doping of 2 0 % S have better electrochemical performance. Step 3: Raman Studies The amorphous structure of the material and the defect properties of the structure can be characterized by Raman spectroscopy. The two peaks of Raman spectrum at 1320 cm- and 1590 cm- represent D and G peaks, respectively. Step 4: Electrochemical Studies We can see that after the first charge and discharge cycle, the slope capacity and platform capacity of the battery are relatively large, indicating that the material with doping of sulfur can form nano pores, which is conducive to the storage of sodium ions. DESCRIPTION OF THE DRAWINGS Figure 1: the amorphous carbon material with doping of 20% S at carbonization temperature of 1200°C(20S-1200C) has a porous particle structure. Figure 2: XRD Studies Figure 3: Raman spectroscopy of 20S-1200°C Figure 4 shows the charge-discharge curve of 20S-1200 after one and two cycles. Figure after circulating for 50 times at the discharge current density of 1 A/g, the capacity retention rate of 20S-1200 is 87.22%.

DESCRIPTION OF PREFERRED EMBODIMENT 4.2. Procedure Embodiments of the present disclosure are described below.

Embodiment 1: The present disclosure according to embodiment 1 relates to a method for producing a pitch with doping of S.

Step 1: preparation Pitch and sulfur are used to synthesize the precursors in different proportions (X= 5 %

, %, 20%, 30%, 40%, and 50%; X is the percentage of sulfur doping). What's more, the total mass of each precursor with doping of S in different proportions is constantly 6g. We put the samples into small type tube furnace in an argon protected environment, heating up to 300°C at a rate of3C/min. We keep the samples at this temperature for 3 hours and then gradually cooling to the room temperature. The samples have a certain degree of expansion after pretreatment. We take the samples s after pretreatment out of the small type tube furnace and grind them in the mortar for 30 min ensuring the particles crushed completely. The samples are put into large type tube furnace in an argon protected environment. Then the samples are calcined respectively at various temperatures (1000°C, 1200°C, and 1400C) at a heating rate of3C/min. We keep the samples at this temperature for 2 hours and then cooling to 800°C at a cooling rate of3C/min. Finally, the samples gradually cooling to the room temperature. We get porous amorphous carbon material with doping of S(S-CTP) with good electrochemical performance. The samples are used as the active material of anode material for the preparation of sodium ion battery. The sodium alginate powder was mixed with the samples in a ratio of 1 to 9. Then the samples are added by an appropriate amount of water and ground to the paste that is coated on the fluid collecting aluminum foil. We cut the aluminum foil into (8x8) mm2 sheets after drying. The sheets are dried for 10 hours at 120°C at vacuum condition, and then transfer to the glove box as a backup. The simulated battery is assembled in the glove box in an argon protected environment, with metallic sodium as the counter electrode and 1 mole of NaPF dissolves in 1L of EC and DMC with a volume ratio of 1:1 as the electrolyte.

Step 2: Morphological Studies We add sulfur powder and coal tar pitch at different mass ratio and carry out SEM tests at different carbonization temperatures. After a series of experiments, we can conclude that the samples with doping of 2 0 % S have better electrochemical performance. In Fig.1, the amorphous carbon material with doping of 20% S at carbonization temperature of 1200°C(20S-1200C) has a porous particle structure. The average particle size is 1-70m. Compared with other samples at carbonization temperature of 1000°C the sample at carbonization temperature of 1200°C has smaller particle size. The particles become smaller as the temperature rises. The structure will have more pores, which facilitate transportation of sodium ion and improve electrochemical performance.

Step 2: XRD Studies In order to study the effect of carbonization temperature on material structure, the X-ray diffraction techniques have been used to show a limited change of structure of S-1200°C compared with 20S-1000°C We can see that the XRD pattern has two relatively wide diffraction peak at 230 and 430, corresponding to the crystal surface of d(oo 2) and dool) of amorphous carbon, respectively, which indicates that the sample has a low degree of crystallinity and graphitization. As the carbonization temperature rises, the diffraction peak shifts to a lower angle and the spacing among grains is increased, which can facilitate the sodium-ion transportation and improve the electrochemical performance.

Step 3: Raman Studies The amorphous structure of the material and the defect properties of the structure can be characterized by Raman spectroscopy. In Fig.3, we can see Raman spectroscopy of 20S-1200°C The two peaks of Raman spectrum at 1320 cm- and 1590 cm- represent D and G peaks, respectively. The intensity of D peak indicates a low degree of graphitization and defects in material structure. The two ratios of the intensity of D peak to the intensity of G peak (ID/IG) at carbonization temperature of 1000°Cand 1200°Care 1.217 and 1.130, respectively. As the carbonization temperature rises, ID/IG has a downward trend. The higher the ratio, the greater the defect degree. In a sodium-ion battery, the greater the intrinsic defect, the easier the electrons are to transmit and the more efficient the electrode's circulation. However, ID/IG at carbonization temperature of 1000°C is greater than ID/IG at carbonization temperature of 1200°C, which indicates intrinsic defects increase moderately and there is another factor on electrochemical performance. We speculate that impurity defects have a significant increase and most of them are irreversible. With the increase of temperature, the balance between dissolution and deposition in the SEI membrane tends to dissolve, resulting in the reduction of electrolyte in the weak part of the SEI membrane due to the acquisition of electrons, which will lead to the continuous irreversible loss of active sodium and is not conducive to transportation of sodium ion.

Step 4: Electrochemical Studies The Fig.4 shows the charge-discharge curve of 20S-1200 after one and two cycles. We can see that after the first charge and discharge cycle, the slope capacity and platform capacity of the battery are relatively large, indicating that the material with doping of sulfur can form nano pores, which is conducive to the storage of sodium ions. With the rise of temperature, sulfur combines with carbon in the form of stacking and interlacing. The process can increase the platform capacity and expand the layer spacing, which contributes to the transportation of sodium ions. After the second charge and discharge cycle, both the slope capacity and platform capacity of the battery have declined. Compared with 110 mAh/g of 20S-1000 and 181 mAh/g of 20S-1400, the platform capacity of 20S-1200 still remains at 250 mAh/g, indicating that the sulfur significantly improves the electrochemical performance of the battery at carbonization temperature of 1200°G In Fig.5, after circulating for 50 times at the discharge current density of 1 A/g, the capacity retention rate of 20S-1200 is 87.22%. The capacity retention rates of 20S-1000 and 20S-1400 are 73.78% and 77.42%, respectively. It shows that the morphology and structure of 20S-1200 compared with 20S-1000 and S-1400 is relatively good during the discharging cycle, and deformation or destruction occurs moderately. The analysis results in Figure 5 are consistent with the results above.

Claims

1. A process for preparing an amorphous carbon cathode material from a sufficient mixture of pitch and sulfur powder, characterized in that the process comprises: Asphalt and sulfur powder were mixed and crushed, and sample groups with different sulfur contents were set up respectively to explore the influence of sulfur-containing examples on the properties of negative electrode materials, pretreatment is carried out in a tube furnace; after pretreatment, the sample is placed in a tubular furnace, and the temperature is increased by 1000 °C-1400 °C at a heating rate of 3 °C/min; and the temperature is kept at 1.5-2 hours at this temperature, then the cooling rate is controlled, the cooling rate is reduced to 800 °C at a cooling rate of 3 °C/min, and then the temperature is gradually reduced to room temperature to obtain the amorphous carbon negative electrode material.

2. The preparation method according to claim 1, further comprising: introducing argon gas during the heat treatment for surface coating; At the rate of 3 0 C/min, the temperature increases by about 300 ° C; At this temperature, it is kept at 2.5-3.5 hours, and then gradually reduces the temperature and makes the room temperature flat.

3. The preparation method according to claim 1, wherein the pulverizing and mixing specifically comprises: mechanical pulverizing, spherical pulverizing, pulverizing, pulverizing, pulverizing, pulverizing, pulverizing Grinding.

Figure 2 Figure 1

Figure 4 Figure 3

Figure 5