CN116409775A - Coal pitch-based amorphous carbon and preparation method thereof - Google Patents
Coal pitch-based amorphous carbon and preparation method thereof Download PDFInfo
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- 229910003481 amorphous carbon Inorganic materials 0.000 title claims abstract description 65
- 239000011300 coal pitch Substances 0.000 title claims abstract description 26
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Chemical compound BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 claims abstract description 51
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 37
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 claims abstract description 36
- 229910052794 bromium Inorganic materials 0.000 claims abstract description 36
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- 239000007789 gas Substances 0.000 description 10
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- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 description 1
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- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention discloses a preparation method of a coal-based amorphous carbon material, which comprises the steps of firstly heating low-temperature coal tar pitch to 120-150 ℃ in a nitrogen atmosphere, carrying liquid bromine into a reaction system by adopting a nitrogen purging method after the coal tar pitch is fully softened to be in a flowing state, and obtaining brominated coal tar pitch; then, carrying out debromination polymerization reaction in a reaction container at the temperature of 350-420 ℃, ball-milling a debromination product, sieving to obtain powder solid, pre-carbonizing in the reaction container, and ball-milling and sieving to obtain finer powder solid; carbonizing the powder solid at 1000-1200 deg.c for 2-6 hr to obtain coal tar pitch base amorphous carbon. And to bromine versus coal pitch based amorphous carbon structure and electrochemical performance. The introduction of bromine also improves the quantity of mesoporous structures, is favorable for the increase of the size of the amorphous carbon layer and the improvement of the arrangement order, and remarkably improves the reversible capacity under high-current charge and discharge.
Description
Technical Field
The invention relates to the field of amorphous carbon preparation, in particular to a coal-based amorphous carbon material and a preparation method thereof.
Background
Unlike graphite having a perfect hexagonal system, amorphous carbon refers to a carbon material having a low degree of graphitization, like an amorphous state. Amorphous carbon can be classified into soft carbon (graphitizable) and hard carbon (non-graphitizable) depending on whether the precursor is converted via liquid phase carbonization or solid phase carbonization. The soft carbon is composed of a textured area with a graphite-like structure and a non-textured area with high twist crosslinking, and is typically composed of mesocarbon microbeads, petroleum coke and needle coke; hard carbon belongs to non-graphitizable carbon, the carbon network is generally of a three-dimensional cross-linked structure, and common hard carbon materials include carbon black, resin-based carbon and high polymer pyrolytic carbon. Compared with graphite materials, the amorphous carbon has higher theoretical capacity (500-700 mAh/g), better compatibility with electrolyte, and higher diffusion coefficient of lithium ions in the electrolyte, thereby being beneficial to rapid intercalation and deintercalation of lithium ions. Furthermore, amorphous carbon is prepared without graphitization treatment, which has a significant advantage in terms of cost. Therefore, amorphous carbon has been widely studied and developed as an important class of negative electrode materials.
Mochida uses naphthalene and methylnaphthalene mesophase pitch as a precursor, pre-carbonizes for 30min at 600 ℃, then carries out grinding treatment, screens with 325 meshes, screens powder and calcines at 700-1200 ℃ for 1h to obtain soft carbon. The authors found through analysis of the amorphous carbon lithium storage mechanism that intercalation of lithium ions was mainly achieved when the heat treatment temperature was higher than 800 ℃; when the heat treatment temperature is lower than 800 ℃, the storage of lithium ions is mainly realized through the charge transfer of the hexagonal plane network layer.
Fujimoto researches the influence of oxygen introduction on the structure and electrochemical performance of coal tar pitch-based hard carbon, air or ammonium peroxodisulfate initiates mild oxidation of the surface, the formed pores are favorable for intercalation/deintercalation of lithium ions, and phosphorus pentoxide and materials undergo strong oxidation, so that the pore structure is damaged, and the lithium intercalation amount is obviously reduced.
CN201711326231.1 proposes a preparation method of hard carbon negative electrode material, asphalt or resin is firstly mixed with oxidant, then low-temperature oxidation treatment (50-100 ℃), high-temperature oxidation treatment (110-250 ℃), pre-carbonization and carbonization are sequentially carried out, and finally the hard carbon material with high capacity and high first coulombic efficiency is prepared, and the first reversible capacity of the material can reach 420mAh/g at 0.1 ℃, and the first coulombic efficiency is more than 81%.
CN201910384698.4 discloses a preparation method of amorphous carbon material, the amorphous carbon material is prepared by pretreating, sintering, activating and hydrogenation-reduction of carbon-rich precursor, the lithium intercalation site is effectively increased by hydrogenation-deoxidation, the occurrence of side reaction and the occurrence of battery flatulence are inhibited, the stability of SEI film is improved, and the material shows excellent high temperature performance (the 50 times of cycle capacity retention rate at 60 ℃ reaches 96%).
CN201711320084.7 reports a preparation method of a high temperature resistant negative electrode material, the method takes soft carbon or hard carbon powder particles as an inner core, a carbon coating and a nano coating are sequentially coated from inside to outside, nitrogen-containing or sulfur-containing multifunctional groups of the carbon coating effectively improve the wettability of an electrolyte on the surface of amorphous carbon, the nano coating can react with HF generated in the charge and discharge process to protect a stabilized SEI film, and the nano coating and the functionalized carbon coating have synergistic effects on the formation and stabilization of the SEI film at high temperature.
However, the effect of bromine on the amorphous carbon structure and the electrochemical performance is less reported, more is the effect of oxygen, nitrogen and sulfur introduced on the amorphous carbon structure and the electrochemical performance, and if the effect of bromine can be studied and explained in detail, the method has important reference significance for expanding the preparation method of abundant amorphous carbon and improving the electrochemical performance of amorphous carbon.
Disclosure of Invention
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method for preparing amorphous carbon with excellent properties using bromine.
The technical scheme of the invention is that the preparation method of coal tar pitch-based amorphous carbon comprises the following steps:
a. the low-temperature coal tar pitch is firstly heated to 120-150 ℃ under the nitrogen atmosphere, nitrogen is introduced to purge before heating, stirring is started when the coal tar pitch is fully softened and is in a flowing state, liquid bromine is carried into a reaction system by adopting a nitrogen purging method, and the nitrogen purging rate is 25-35mL min -1 The addition amount of bromine is 5-30wt% of the low-temperature asphalt, and the liquid bromine is continuously stirred and kept at the temperature for 0.1-1h after purging, so as to obtain brominated coal asphalt;
b. the brominated coal pitch is subjected to debromination polymerization reaction in a reaction vessel at the temperature of 350-420 ℃ for 6-12h, wherein the temperature rising rate is 3-10 ℃/min at the stage from the early stage of the reaction to the stage of 200 ℃; at the temperature of more than 200 ℃, the heating rate is not higher than 2.5 ℃/min; ball milling the debrominated product, and sieving to obtain powder solid 1; carrying out pre-carbonization treatment on the powder solid 1 in a reaction container, wherein the temperature is 550-700 ℃;
c. the pre-carbonized sample is subjected to ball milling and then is screened to obtain finer powder solid 2; carbonizing the powder solid 2 in a reaction vessel at 1000-1200 ℃ for 2-6h under the argon atmosphere to obtain the coal tar pitch-based amorphous carbon.
In the step a, bromine is introduced into the reaction vessel not in the form of droplets but in the form of nitrogen purging entrained liquid bromine. For example, a three-necked flask was additionally installed beside the main reactor, and bromine was weighed and placed in the three-necked flask. In this way, the concentration of bromine can be effectively dispersed and reduced; the introduction of bromine in this manner, mainly due to the too high reactivity of bromine, can easily lead to excessive local substitution reactions, to non-uniform overall quality, and even to the risk of excessive cross-linking scorch if added in the form of droplets via a separatory funnel. The liquid bromine introducing speed is controlled by the nitrogen blowing speed and can be properly slowed down. The nitrogen bubbling rate can be appropriately reduced in the latter stage of the reaction. If the nitrogen blowing rate is 5-15 mL.min in the later stage of the reaction -1 。
The later reaction stage not only comprises the completion of liquid bromine purging, but also comprises a reaction stage before the completion of liquid bromine purging, and the introduction of bromine causes polymerization reaction, so that the viscosity of a system is increased, and the diffusion of bromine is more difficult, so that the introduction amount of bromine in unit time is reduced, the disturbance condition of the liquid surface is mainly observed, sufficient disturbance is required to occur, and the later stirring rate is much slower. Throughout the reaction, the preferred stirring rate is about 10-300rpm. More preferably 20-200rpm. According to the viscosity degree of the liquid level in the reaction process, the stirring rate is reduced when the liquid level is viscous, and the reaction rate is increased when the liquid level is thin.
In the step b, the debromination reaction is directly heated to remove bromine; as for the heating rate, the heating rate can be properly increased in the early stage of the reaction (200 ℃) and can not be too fast when the temperature is between 200 and 350 ℃ or between 200 and 420 ℃, and is generally not higher than 2.5 ℃/min so as to ensure relatively soft debromination polycondensation reaction.
The atmosphere in step c is argon, which is more stable at high temperatures than nitrogen. Preferably, the argon gas has a gas velocity of 100-200 mL/min -1 。
According to the method for preparing coal tar pitch-based amorphous carbon of the present invention, it is preferable that the low temperature pitch in the step a is pitch having a softening point of 60-70 ℃.
Preferably, the toluene soluble component TS content in the low temperature asphalt is 85-95wt%; toluene insoluble-pyridine soluble fraction TI-PS content of 5-9wt%; the pyridine insoluble-quinoline soluble component PI-QS content is 0.3-0.7wt%; the quinoline insoluble component QI content is 0.5-3wt%.
Preferably, the heating mode in the step a is oil bath heating.
According to the method for preparing coal tar pitch-based amorphous carbon of the present invention, it is preferable that the reaction vessel in the step b is a tube furnace.
According to the preparation method of coal tar pitch-based amorphous carbon of the present invention, preferably, the sieving in the step b is 40-100 mesh; and c, sieving the mixture to 300-400 meshes.
According to the method for preparing coal tar pitch-based amorphous carbon of the present invention, it is preferable that the pre-carbonization time in the step b is 0.5 to 5 hours.
According to the preparation method of coal tar pitch-based amorphous carbon, the heating rate in the step c is preferably 120-170 ℃/h; the heat preservation time after temperature rising is 1-5 hours.
The invention also provides the coal pitch-based amorphous carbon prepared by the preparation method of the coal pitch-based amorphous carbon, wherein the coal pitch-based amorphous carbon has a mesoporous structure of 2.0-4.5nm; the discharge capacity of the coal tar pitch-based amorphous carbon after 100 times of circulation is more than 280mAh/g under the current density of 200mA g-1, and the capacity retention rate is more than 92%. The aperture distribution data can refer to the DFT aperture distribution of fig. 2; regarding ordered stacking and defect site reduction, reference may be made to a TEM image of an amorphous carbon sample, which may support an increase in ordered stacking degree, a reduction in defect site.
The invention discloses a preparation method of a coal-based amorphous carbon material, in particular to the influence of bromine on a coal pitch-based amorphous carbon structure and electrochemical performance, the introduction of bromine improves the quantity of mesoporous structures, is beneficial to the increase of the size of an amorphous carbon layer and the improvement of arrangement order, and remarkably improves reversible capacity under high-current charge and discharge.
The invention takes low-temperature coal pitch (physical parameters are shown in table 1) with softening point of about 65 ℃ as raw material, and the coal pitch-based amorphous carbon is prepared by bromination, debromination polymerization, pre-carbonization and carbonization, thus explaining the influence of bromine introduction on the amorphous carbon structure and electrochemical performance thereof.
The existing technology generally comprises that asphalt is directly carbonized to prepare asphalt-based soft carbon, or asphalt is subjected to one-step oxidation/crosslinking reaction (air oxidation, oxidant and crosslinking agent) to form a carbon-rich precursor with a three-dimensional crosslinking structure, and then carbonized to prepare hard carbon with carbon layers stacked in disorder, so that no related report on amorphous carbon structure and performance by bromine exists at present.
The invention has the advantages that:
1. unlike conventional asphalt carbonization or oxidative carbonization, the process is to modify and structurally induce precursor asphalt through the introduction and removal of bromine, and is aided with fine control of the preparation process to directionally control the formation of carbon network, so as to prepare amorphous carbon material suitable for lithium ion intercalation and deintercalation;
2. the introduction of a proper amount of bromine is beneficial to the ordered stacking of the carbon layers and the reduction of defect sites, so that the reversible capacity is improved;
3. the introduction of bromine is beneficial to the formation of a mesoporous structure (2.0-4.5 nm), so that the transmission of lithium ions and the infiltration of electrolyte are facilitated, and the multiplying power performance is improved;
4. the amorphous carbon is densified by bromine, so that the rigidity of a carbon wall is improved, and the damage of an amorphous carbon structure under high-current charge and discharge is avoided;
drawings
Fig. 1 is a flow chart of the present invention.
Fig. 2 TEM image of amorphous carbon sample.
FIG. 3 DFT pore size distribution of amorphous carbon samples.
FIG. 4 illustrates a rate performance curve for amorphous carbon samples.
Fig. 5 is a Raman spectrum of an amorphous carbon sample.
Detailed Description
[ embodiment one ]
200g of low-temperature coal tar pitch is weighed and put into a 250mL three-neck flask, the oil bath is heated to 120 ℃, and mechanical stirring (rotating speed of 75 rpm) and nitrogen purging (gas speed of 30 mL.min) are started -1 ) After stirring for 0.5h, 30g of liquid bromine is weighed and added into a 100mL three-neck flask, two three-neck flasks are connected by a glass tube with rubber tubes nested at two ends, and the nitrogen gas speed is reduced to 10 mL/min -1 And the bromination reaction is started, the viscosity of the system is correspondingly improved along with the increase of the bromine introduction amount in the reaction process, the adequate stirring is ensured by moderately increasing the temperature, and the reaction is stopped after the liquid bromine is completely purged and then kept for 0.5 h.
The brominated coal pitch is placed in a tube furnace, the temperature is raised to 410 ℃ at the heating rate of 2 ℃/min and kept for 10 hours, the obtained debrominated pitch is subjected to grinding and pre-crushing under the protection of nitrogen atmosphere (air speed), and then the obtained debrominated pitch is placed in a planetary ball mill, and the obtained ball-milled sample is screened by a 60-mesh screen to obtain a powder solid sample.
Placing the powder solid sample in a horizontal tube furnace, heating to 600 ℃ at a heating rate of 5 ℃/min and keeping for 0.5h, placing the obtained pre-carbonized sample in a planetary ball mill, and sieving the obtained ball-milled sample by a 325-mesh screen to obtain the pre-carbonized powder sample.
Placing the pre-carbonized powder sample in a high-temperature box-type furnace, and introducing argon (gas velocity 150 mL. Min) -1 ) The amorphous carbon sample obtained was labeled AC15-1000, which was raised to 1000℃at a heating rate of 150℃per hour and maintained for two hours.
[ example two ]
200g of low-temperature coal tar pitch is weighed and put into a 250mL three-neck flask, the oil bath is heated to 120 ℃, and mechanical stirring (rotating speed of 75 rpm) and nitrogen purging (gas speed of 30 mL.min) are started -1 ) After stirring for 0.5h, 60g of liquid bromine is weighed and added into a 100mL three-neck flask, two three-neck flasks are connected by a glass tube with rubber tubes nested at two ends, and the nitrogen gas speed is reduced to 10 mL/min -1 And start bromination reaction, and the viscosity of the system is corresponding with the increase of bromine introduction amount in the reaction processAnd (3) raising the temperature moderately, ensuring sufficient stirring, and keeping the temperature for 0.5h after the liquid bromine is completely purged to stop the reaction.
The brominated coal pitch is placed in a tube furnace, the temperature is raised to 410 ℃ at the heating rate of 2 ℃/min and kept for 10 hours, the obtained debrominated pitch is subjected to grinding and pre-crushing under the protection of nitrogen atmosphere (air speed), and then the obtained debrominated pitch is placed in a planetary ball mill, and the obtained ball-milled sample is screened by a 60-mesh screen to obtain a powder solid sample.
Placing the powder solid sample in a horizontal tube furnace, heating to 600 ℃ at a heating rate of 5 ℃/min and keeping for 0.5h, placing the obtained pre-carbonized sample in a planetary ball mill, and sieving the obtained ball-milled sample by a 325-mesh screen to obtain the pre-carbonized powder sample.
Placing the pre-carbonized powder sample in a high-temperature box-type furnace, and introducing argon (gas velocity 150 mL. Min) -1 ) The amorphous carbon sample obtained was labeled AC30-1000, which was raised to 1000℃at a heating rate of 150℃per hour and maintained for two hours.
[ example III ]
200g of low-temperature coal tar pitch is weighed and put into a 250mL three-neck flask, the oil bath is heated to 120 ℃, and mechanical stirring (rotating speed of 75 rpm) and nitrogen purging (gas speed of 30 mL.min) are started -1 ) After stirring for 0.5h, 30g of liquid bromine is weighed and added into a 100mL three-neck flask, two three-neck flasks are connected by a glass tube with rubber tubes nested at two ends, and the nitrogen gas speed is reduced to 10 mL/min -1 And the bromination reaction is started, the viscosity of the system is correspondingly improved along with the increase of the bromine introduction amount in the reaction process, the adequate stirring is ensured by moderately increasing the temperature, and the reaction is stopped after the liquid bromine is completely purged and then kept for 0.5 h.
The brominated coal pitch is placed in a tube furnace, the temperature is raised to 410 ℃ at the heating rate of 2 ℃/min and kept for 10 hours, the obtained debrominated pitch is subjected to grinding and pre-crushing under the protection of nitrogen atmosphere (air speed), and then the obtained debrominated pitch is placed in a planetary ball mill, and the obtained ball-milled sample is screened by a 60-mesh screen to obtain a powder solid sample.
Placing the powder solid sample in a horizontal tube furnace, heating to 600 ℃ at a heating rate of 5 ℃/min and keeping for 0.5h, placing the obtained pre-carbonized sample in a planetary ball mill, and sieving the obtained ball-milled sample by a 325-mesh screen to obtain the pre-carbonized powder sample.
Pre-charcoalPlacing the powder sample in a high temperature box furnace, and introducing argon (gas velocity 150 mL. Min) -1 ) The amorphous carbon sample was labeled AC15-1200 by heating to 1200deg.C at a rate of 150deg.C/h and holding for 2 h.
[ comparative example one ]
200g of low-temperature coal tar pitch is weighed and put into a 250mL three-neck flask, the oil bath is heated to 120 ℃, and mechanical stirring (rotating speed of 75 rpm) and nitrogen purging (gas speed of 30 mL.min) are started -1 ) After 2h incubation, the reaction was stopped.
The sample green is placed in a tube furnace, the temperature is raised to 410 ℃ at the heating rate of 2 ℃/min and kept for 10 hours, the obtained debrominated asphalt is subjected to grinding and pre-crushing under the protection of nitrogen atmosphere (air speed), and then the obtained ball-milled sample is placed in a planetary ball mill, and the obtained ball-milled sample is screened by a 60-mesh screen to obtain a powder solid sample.
Placing the powder solid sample in a horizontal tube furnace, heating to 600 ℃ at a heating rate of 5 ℃/min and keeping for 0.5h, placing the obtained pre-carbonized sample in a planetary ball mill, and sieving the obtained ball-milled sample by a 325-mesh screen to obtain the pre-carbonized powder sample.
Placing the pre-carbonized powder sample in a high-temperature box-type furnace, and introducing argon (gas velocity 150 mL. Min) -1 ) The amorphous carbon sample obtained was labeled AC0-1000, which was raised to 1000℃at a heating rate of 150℃per hour and maintained for 2 hours.
The half-cell assembly and test method comprises the following steps:
uniformly dispersing an amorphous carbon material, super C and polyvinylidene fluoride in N-methyl-2-pyrrolidone according to a mass ratio of 8:1:1, uniformly coating the slurry on a copper foil current collector, and vacuum drying at 110 ℃; then, a CR2016 button half-cell was assembled in a glove box, a lithium sheet as a counter electrode, celgard 2400 as a separator, and electrolyte solution of 1mol/LLiPF6/EC+DMC+EMC (volume ratio 1:1:1). Constant current charge and discharge tests are carried out on a LAND CT2001A instrument, and the charge and discharge voltage range is 0-2V.
Table 1 general physical Properties parameters of coal Pitch raw Material
a ΔDiff.＝100-C-H-N.
Compared with AC0-1000, the introduction of bromine improves the orientation degree of the carbon layer arrangement of the amorphous carbon sample on one hand, and the regular carbon layer orientation is beneficial to the transmission of lithium ions and the improvement of reversible capacity; on the other hand, bromine contributes to the improvement of the molecular weight and the polymerization degree of coal pitch, the amorphous carbon crystallite size is increased, and the number of lithium storage sites between graphite sheets is increased.
TABLE 2 pore Structure parameters of amorphous carbon
Compared with AC0-1000, the introduction of bromine significantly increases the number of mesoporous structures (2.0-4.5 nm), and the existence of the mesoporous structures is beneficial to the full infiltration of electrolyte and amorphous carbon material and the transmission of lithium ions therein, so that the rate performance is improved.
Compared with AC0-1000, the introduction of bromine remarkably improves the discharge capacity of the amorphous carbon sample under each current density, and the capacity difference under large current density is more obvious when the current density is higher than 2000mA g -1 Fall back to 50mA g -1 When both AC15-1000 and AC30-1000 were able to recover the initial capacity level, whereas AC0-1000 was recovered to only 86% of the initial capacity, indicating that the introduction of bromine helped the maintenance of the amorphous carbon structure. The results of the tests of the examples and comparative examples are shown in FIGS. 2 to 5.
To illustrate the reduction of defect sites, raman spectroscopic analysis was performed on the samples herein, and the results indicated that the ID/IG values for the three AC0-1000, AC15-1000 and AC30-1000 were 1.05, 0.99, 1.01, respectively, indicating that the introduction of bromine contributed to the reduction of defect sites and ordered stacking of graphite platelets, consistent with TEM results.
With respect to reversible capacity, the cycling performance of samples AC0-1000, AC15-1000 at 200mA g-1 current density is as follows: the discharge capacity of the AC15-1000 after 100 times of circulation is 286mAh/g, and the capacity retention rate is 92.9%; the discharge capacity of the AC0-1000 after 100 times of circulation is 274mAh/g, and the capacity retention rate is 90.1%, so that the circulation performance of the AC15-1000 is superior to that of the AC0-1000, the introduction of bromine is beneficial to the improvement of the circulation performance of the material, the electrolyte is fully infiltrated with the material due to a certain amount of mesoporous structures of the AC15-1000.
The rate performance curve of fig. 4 illustrates that the introduction of appropriate bromine can significantly improve the rate performance.
TABLE 3 percentage of capacities at different current densities of coal-based amorphous carbon at different bromine incorporation levels of 50mA g-1
100mA g -1 The capacity retention rate of each sample is not much different when the current density is higher than 200mA g -1 At the time, the rate capacity retention of each sample showed a significant difference, with the rate capacity retention of AC15-1000 being the highest, AC30-1000 times, and the rate capacity retention of AC0-1000 being the lowest, mainly because the debrominated asphaltic-based amorphous carbon contains a considerable amount of mesoporous structure, contributing to Li under high current charge and discharge + Is a rapid migration of (c). When the current density drops back to 50mA g -1 When the capacity of AC0-1000 is only 86% of the initial capacity, lower than AC15-1000 (97.7%) and AC30-1000 (96.0%), this is probably due to the change in material structure under high-current charge and discharge, resulting in a reduction in the amount of lithium intercalation.
Claims (9)
1. A preparation method of coal tar pitch-based amorphous carbon is characterized by comprising the following steps: the method comprises the following steps:
a. the low-temperature coal tar pitch is firstly heated to 120-150 ℃ under the nitrogen atmosphere, nitrogen is introduced to purge before heating, stirring is started when the coal tar pitch is fully softened and is in a flowing state, liquid bromine is carried into a reaction system by adopting a nitrogen purging method, and the nitrogen purging rate is 25-35mL min -1 The addition amount of bromine is 5-30wt% of the low-temperature asphalt, and stirring is continued after the liquid bromine is purgedMixing and preserving heat for 0.1-1h to obtain brominated coal pitch;
b. the brominated coal pitch is subjected to debromination polymerization reaction in a reaction vessel at the temperature of 350-420 ℃ for 6-12h, wherein the temperature rising rate is 3-10 ℃/min at the stage from the early stage of the reaction to the stage of 200 ℃; at the temperature of more than 200 ℃, the heating rate is not higher than 2.5 ℃/min; ball milling the debrominated product, and sieving to obtain powder solid 1; carrying out pre-carbonization treatment on the powder solid 1 in a reaction container, wherein the temperature is 550-700 ℃;
c. the pre-carbonized sample is subjected to ball milling and then is screened to obtain finer powder solid 2; carbonizing the powder solid 2 in a reaction vessel at 1000-1200 ℃ for 2-6h under the argon atmosphere to obtain the coal tar pitch-based amorphous carbon.
2. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: the low-temperature asphalt in the step a is asphalt with a softening point of 60-70 ℃.
3. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: the toluene soluble component TS content in the low-temperature asphalt is 85-95wt%; toluene insoluble-pyridine soluble fraction TI-PS content of 5-9wt%; the pyridine insoluble-quinoline soluble component PI-QS content is 0.3-0.7wt%; the quinoline insoluble component QI content is 0.5-3wt%.
4. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: and b, the reaction vessel is a tube furnace.
5. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: and b, sieving the mixture to 40-100 meshes.
6. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: and c, sieving the mixture to 300-400 meshes.
7. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: and b, the pre-carbonization time is 0.5-5h.
8. The method for preparing coal pitch based amorphous carbon according to claim 1, wherein: the temperature rising speed in the step c is 120-170 ℃/h; the heat preservation time after temperature rising is 1-5 hours.
9. The coal pitch based amorphous carbon prepared by the method for preparing coal pitch based amorphous carbon as claimed in claim 1, characterized in that: the coal tar pitch-based amorphous carbon has a mesoporous structure of 2.0-4.5nm; the discharge capacity of the coal tar pitch-based amorphous carbon after 100 times of circulation is more than 280mAh/g under the current density of 200mA g-1, and the capacity retention rate is more than 92%.
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