CN117819531A

CN117819531A - An activated cross-linked semi-coke-based hard carbon material and its preparation method and application

Info

Publication number: CN117819531A
Application number: CN202410014583.7A
Authority: CN
Inventors: 张月; 马慧珍; 唐亚昆; 刘浪
Original assignee: Xinjiang University
Current assignee: Xinjiang University
Priority date: 2024-01-05
Filing date: 2024-01-05
Publication date: 2024-04-05
Anticipated expiration: 2044-01-05
Also published as: CN117819531B

Abstract

The invention belongs to the technical field of hard carbon materials and sodium ion electrode materials, and particularly relates to an activated cross-linked semicoke-based hard carbon material, and a preparation method and application thereof. According to the invention, activated carbocoal is subjected to activation modification by inorganic alkali, the obtained activated carbocoal and a crosslinking agent are subjected to chemical crosslinking reaction, and the obtained activated crosslinked carbocoal is calcined to obtain the activated crosslinked carbocoal-based hard carbon material. The invention adopts a modified alkali oxidation synergistic chemical crosslinking strategy, and regulates and controls the microcrystalline structure of the semicoke hard carbon by constructing the C-O-C. The kind of oxygen-containing functional groups is accurately increased by an alkaline oxidation method, and then chemical crosslinking reaction is carried out with a crosslinking agent to successfully construct a C-O-C structure. The hard carbon material obtained by carbonizing the precursor contains abundant pseudo-graphite phase and closed pores, is favorable for improving the sodium storage capacity and the initial coulombic efficiency, and can also increase the carbon yield of the material by a chemical crosslinking strategy.

Description

Activated crosslinked semicoke-based hard carbon material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of hard carbon materials and sodium ion electrode materials, and particularly relates to an activated cross-linked semicoke-based hard carbon material, and a preparation method and application thereof.

Background

At present, the energy storage technology is in the stage of diversified development, the main energy storage types are physical energy storage and electrochemical energy storage, and the electrochemical energy storage is a main development trend. Currently, secondary batteries play an important role as a principal angle in electrochemical energy storage.

With the continuous increase of new energy automobiles, the lithium ion battery industry presents explosive development. Worldwide new energy automobiles increased from 12.5 to 675 thousands of vehicles in 2012-2021. However, the increasing demand for lithium ion batteries has led to a continual increase in the price of lithium carbonate, a lithium ion battery material, and the disadvantages of relatively scarce resources, uneven global distribution, and the like in lithium storage, which directly lead to a great resistance in the use of lithium ion batteries in large-scale energy storage devices. In contrast, sodium reserves are abundant and widely distributed, have similar chemical properties to lithium, and are expected to compensate lithium ion batteries in large energy storage devices. However, the radius of sodium ionGreater than lithium ion radius->The large ionic radius makes it difficult for sodium ion batteries to find a suitable electrode material. For example, the interlayer spacing of the graphite anode materials commercialized for lithium ion batteries does not match the radius of sodium ions, and the binding energy of the sodium ion-graphite intercalation reaction is greater than 0, so graphite is not suitable for sodium ion batteries. Sodium ion battery anode materials are involved in a very large variety, wherein carbonaceous materials are relatively promising due to the abundance of resources, low cost, and good quality. Carbonaceous materials are classified into graphite-based materials, nano-carbon materials, and amorphous carbon materials according to their microstructure, wherein the amorphous carbon materials are mainstream due to low price and high sodium storage capacity. Amorphous carbon is further divided into soft carbon and hard carbon according to the ease of graphitization at high temperature carbonization. The soft carbon material has strong conductivity but sodium storage compared with hard carbonEnergy difference. According to the sodium storage performance and the comprehensive cost performance, the hard carbon becomes a main research object of the negative electrode material of the sodium ion battery.

Hard carbon refers to a carbon material that is difficult to achieve complete graphitization at extremely high temperatures. The structure is called as a 'card house' structure, and consists of a large number of disordered graphite crystals and amorphous areas, the graphitization degree is low, the layered structure is undeveloped, and the interlayer spacing is larger than that of graphite. The hard carbon has larger interlayer spacing, is favorable for the diffusion of sodium ions and the structural stability, and the unordered amorphous structure ensures that the material has abundant defects and micropores, and provides more active sodium storage sites. However, defect concentration directly affects initial coulombic efficiency. During cycling, some sodium ions remain irreversibly at the defect, significantly reducing the initial coulombic efficiency. In summary, the poor rate performance, low initial coulombic efficiency and platform capacity of hard carbon have hampered further industrial development. In addition, the precursors play a critical role in the physicochemical properties of hard carbon. Biomass hard carbon is widely studied because of its abundant resources, simple processing, and eco-friendliness, but biomass hard carbon has poor initial coulombic efficiency and low carbon yield. Currently available polymers such as epoxy, phenolic and polyacrylonitrile have been used to synthesize hard carbon, but are less cost effective. Therefore, finding a suitable carbon source to produce hard carbon with low cost, high initial coulombic efficiency, and high platform capacity is a key to achieving commercial development.

Disclosure of Invention

The invention aims to provide an activated cross-linked semicoke-based hard carbon material, a preparation method and application thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of an activated cross-linked semicoke-based hard carbon material, which comprises the following steps:

activating and modifying the semicoke by using inorganic strong alkali to obtain activated semicoke;

carrying out chemical crosslinking reaction on the activated semicoke and a crosslinking agent to obtain the activated crosslinked semicoke; the cross-linking agent comprises one or more of polyalcohol, polyhydroxy saccharide compound, polybasic acid and hydroxycarboxylic acid compound;

and calcining the activated crosslinked semicoke in the atmosphere of protective gas to obtain the activated crosslinked semicoke-based hard carbon material.

Preferably, the activation modification comprises the steps of: and mixing and heating the semicoke, inorganic strong alkali and water, and performing activation modification.

Preferably, the inorganic strong base comprises sodium hydroxide; the mass ratio of the inorganic strong base to the semicoke is 1 (1-3).

Preferably, the activation and modification temperature is 130-200 ℃ and the time is 5-12 h.

Preferably, the chemical crosslinking reaction comprises the steps of: and mixing and heating the activated semicoke and the crosslinking agent, and carrying out chemical crosslinking reaction.

Preferably, the cross-linking agent comprises citric acid or sucrose; the mass ratio of the cross-linking agent to the activated semicoke is (1-5): 5.

Preferably, the calcining temperature is 1000-1400 ℃, and the heat preservation time is 1-4 hours; the temperature rising rate from room temperature to the calcining temperature is 1-5 ℃/min.

The invention provides the activated cross-linked semicoke-based hard carbon material obtained by the preparation method.

The invention provides application of the activated cross-linked semicoke-based hard carbon material as an electrode material of an ion battery.

Preferably, the ion battery is a sodium ion battery.

The invention provides a preparation method of an activated cross-linked semicoke-based hard carbon material, which comprises the following steps: activating and modifying the semicoke by using inorganic strong alkali to obtain activated semicoke; carrying out chemical crosslinking reaction on the activated semicoke and a crosslinking agent to obtain the activated crosslinked semicoke; the cross-linking agent comprises one or more of polyalcohol, polyhydroxy saccharide compound, polybasic acid and hydroxycarboxylic acid compound; and calcining the activated crosslinked semicoke in the atmosphere of protective gas to obtain the activated crosslinked semicoke-based hard carbon material. The invention adopts a modified alkali-oxygen oxidation synergistic chemical crosslinking strategy to construct a microcrystalline structure of the semicoke hard carbon with a C-O-C structure (representing a carbon layer structure connected by oxygen). Firstly, the semicoke is subjected to modified alkali oxidation treatment by inorganic alkali, so that oxygen-containing functional groups (carboxyl groups) are introduced into the semicoke, the ash content of the semicoke is effectively reduced, and active sites and spaces are provided for subsequent chemical crosslinking reactions. Under the condition, the invention takes the polyalcohol, the polyhydroxy saccharide compound, the polybasic acid and the hydroxycarboxylic acid compound as the crosslinking agent to carry out chemical crosslinking reaction (comprising esterification reaction, decarboxylation reaction and hydrolysis reaction) with the oxygen-containing functional group in the activated semicoke, so that the obtained activated crosslinked semicoke contains rich C-O-C structures. The C-O-C structure can prevent the graphite layer from sliding in the carbonization process, and further inhibit the graphitization degree of the material. In addition, the crosslinking reaction of the crosslinking agent with the activated semicoke has two effects during carbonization. On one hand, the foaming behavior of the cross-linking agent is inhibited, and on the other hand, the cross-linking agent can effectively wrap and fill open pores and large pores left by a modified alkaline oxidation method and convert the open pores and the large pores into closed pores or micro pores, so that the initial coulomb efficiency and the sodium storage capacity of the semicoke-based hard carbon are improved. In conclusion, the preparation method provided by the invention adopts the modified alkali-oxygen oxidation synergistic chemical crosslinking strategy to regulate the microcrystalline structure of the semicoke hard carbon in a multi-scale manner, accurately increases the variety of oxygen-containing functional groups, effectively constructs the semicoke hard carbon obtained by carbonizing the C-O-C structure, contains abundant pseudo-graphite phases and closed pores, and is beneficial to improving the sodium storage performance. In addition, chemical crosslinking reactions increase the carbon yield of the material.

The invention provides the activated cross-linked semicoke-based hard carbon material obtained by the preparation method. The activated cross-linked semicoke-based hard carbon material structure provided by the invention contains closed pores or micropores, and the carbon layer arrangement is mainly based on pseudo-graphite phase. The activated cross-linked semicoke-based hard carbon material provided by the invention is applied to sodium ion batteries, has excellent initial coulombic efficiency and sodium storage capacity, is low in cost, and is suitable for industrial application.

Drawings

FIG. 1 is XRD and Raman patterns of R-HC, AHC-2, ASHC-2 and SAHC in examples and comparative examples of the present invention;

FIG. 2 is a scanning electron microscope image of R-HC, AHC-2 and ASHC-2 in examples and comparative examples of the present invention;

FIG. 3 is a graph showing the rate performance of R-HC, AHC-2, ASHC-2 and SAHC in examples and comparative examples of the present invention;

FIG. 4 shows the first-cycle charge-discharge curves of R-HC, AHC-2, ASHC-2 and SAHC in examples and comparative examples of the present invention;

FIG. 5 is a plot of the capacity contribution ratio for the second cycle discharge for R-HC, AHC-2, ASHC-2 and SAHC in examples and comparative examples of the present invention;

FIG. 6 is XRD and Raman patterns of R-HC, AHC-2, ACHC-2 and CAHC in examples and comparative examples of the present invention;

FIG. 7 is a scanning electron microscope image of R-HC, AHC-2 and ACHC-2 in examples and comparative examples of the present invention;

FIG. 8 is a transmission electron microscope image of R-HC prepared in comparative example of the present invention;

FIG. 9 is a transmission electron microscope image of AHC-2 prepared according to the comparative example of the present invention;

FIG. 10 is a transmission electron microscope image of ACHC-2 prepared in accordance with an embodiment of the present invention;

FIG. 11 is a SAED pattern of R-HC, AHC-2 and ACHC-2 in examples and comparative examples of the present invention;

FIG. 12 is a BET plot and pore size distribution plot of R-HC prepared in comparative example of the present invention;

FIG. 13 is a BET plot and pore size distribution plot of AHC-2 prepared in accordance with comparative example of the present invention;

FIG. 14 is a BET plot and pore size distribution plot of ACHC-2 prepared in accordance with an embodiment of the present invention;

FIG. 15 is a BET plot and pore size distribution plot of CAHC prepared according to comparative example of the present invention;

FIG. 16 is a graph showing the rate performance of R-HC, AHC-2, ACHC-2 and CAHC in examples and comparative examples of the present invention;

FIG. 17 is a plot of the first-cycle charge and discharge of R-HC, AHC-2, ACHC-2 and CAHC for examples and comparative examples of the present invention;

FIG. 18 is a plot of the capacity contribution ratio for the second cycle discharge for R-HC, AHC-2, ACHC-2 and CAHC for examples and comparative examples of the present invention;

FIG. 19 is a long cycle chart of R-HC, AHC-2 and ACHC-2 in examples and comparative examples of the present invention;

FIG. 20 is a CV curve of R-HC prepared in comparative example of the present invention;

FIG. 21 is a CV curve of AHC-2 prepared in accordance with the comparative example of the present invention;

FIG. 22 is a CV curve of ACHC-2 prepared in accordance with an embodiment of the present invention;

FIG. 23 is a CV curve of CAHC prepared in comparative example of the present invention.

Detailed Description

In the present invention, all preparation materials/components are commercially available products well known to those skilled in the art unless specified otherwise.

According to the invention, activated semicoke is obtained by activating and modifying semicoke by using inorganic strong alkali. In the invention, the semicoke is preferably high-ash semicoke, and the production area with the ash content of more than or equal to 13% is Xinjiang Hami. Semicoke belongs to coal-series heavy carbon, and is a solid product obtained by carbonizing coal at medium and low temperatures, crushing and screening. The semicoke has the advantages of high fixed carbon, low volatile, low sulfur and the like, and the structure of the semicoke is controllable. At present, semicoke is mainly applied to preparing porous carbon and graphite in an electrode, but the semicoke is almost not used for preparing hard carbon and being applied to sodium ion batteries. Because semicoke belongs to coal-based heavy carbon, ordered growth of carbon microcrystals is difficult to inhibit in the high-temperature carbonization process, interlayer spacing is too narrow, and intercalation/deintercalation of sodium ions is prevented. The key to realizing high-performance sodium storage coal hard carbon is to effectively inhibit the growth of graphite microcrystals in the carbonization process.

In the present invention, the inorganic strong base preferably includes sodium hydroxide. The water is preferably deionized water. The mass ratio of the inorganic strong base to the semicoke is preferably 1 (1-3), and more preferably 1:2. The activation modification preferably comprises the steps of: and mixing and heating the semicoke, inorganic strong alkali and water, and performing activation modification. The activation and modification temperature is preferably 130-200 ℃, and the time is preferably 5-12 h.

In the invention, semicoke contains limited oxygen-containing functional groups, and a C-O-C structure is difficult to directly construct. Therefore, the invention adopts inorganic strong alkali to activate the semicoke in advance, and increases the quantity of oxygen-containing functional groups in the semicoke material. Studies have shown that the nature and number of oxy functional groups severely affect sodium storage performance. Combining experiments and density functional theory, it was found that the adsorption energy of oxygen groups is too negative, which may cause problems in the desalination process, thereby increasing irreversible adsorption. In this regard, carboxylated carbon has proper adsorption interaction with the surface of sodium ions, and the repulsive force between adjacent carbon layers is increased, so that the reversible capacity of the surface adsorption and interlayer insertion for facilitating sodium ions can be enhanced. Thus, the activation process of semicoke can be strategically utilized to increase the number of carboxyl groups, which is advantageous not only for modulating the C-O-C structure in the precursor, but also for additional carboxyl groups to improve electrochemical performance.

In the invention, the consumption of the inorganic strong alkali cannot be too small or too large, the oxidation strength is reduced due to too small inorganic strong alkali, the number of carboxyl groups cannot be effectively increased, ash is removed, the semicoke structure is collapsed due to too large inorganic strong alkali, and the sodium storage performance of the inorganic strong alkali is seriously affected.

In the invention, the activation and modification temperature cannot be too high or too low, and the too high oxidation strength can cause the collapse of the structure, so that the sodium storage performance of the carbocoal is seriously affected, the too low oxidation strength can cause the reduction of the oxidation strength, and the number of oxygen functional groups in the carbocoal cannot be effectively increased.

In the invention, the activated modified material is directly obtained after activation modification, and the activated semicoke is preferably obtained by washing the activated modified material with hydrochloric acid and water in sequence and then drying the washed material. The washing is preferably deionized water washing, and the washing is carried out after inorganic alkali is neutralized by hydrochloric acid, so that the washing is required to be slightly acidic. The drying temperature is preferably 60-100 ℃ and the drying time is preferably 15-24 h.

After activated semicoke is obtained, the activated semicoke and a crosslinking agent are subjected to chemical crosslinking reaction to obtain activated crosslinked semicoke; the crosslinking agent comprises one or more of polyhydric alcohols, polyhydric saccharides, polybasic acids and hydroxycarboxylic acids. In the present invention, the crosslinking agent preferably includes citric acid or sucrose. The mass ratio of the cross-linking agent to the activated semicoke is preferably (1-5): 5, more preferably 2:5 when sucrose is the cross-linking agent, and more preferably 3:5 when citric acid is the cross-linking agent. The chemical crosslinking reaction comprises the following steps: and mixing and heating the activated semicoke and the crosslinking agent, and carrying out chemical crosslinking reaction. In the present invention, the chemical crosslinking reaction is preferably performed under a heating reflux condition.

In the present invention, the non-graphitizing nature of the hard carbon is due to the inter-layer crosslinking and covalent bonding of the precursor. The invention adopts one or more of polyalcohol, polyhydroxy saccharide compound, polybasic acid and hydroxycarboxylic acid compound as cross-linking agent, and semicoke after chemical cross-linking reaction contains abundant C-O-C structure, which is beneficial to.

In the invention, the dosage of the cross-linking agent cannot be too small or too large, and the too small dosage can not realize effective cross-linking with the activated semicoke, so that the ordered arrangement of graphite domains is difficult to inhibit during high-temperature carbonization; too much can lead to dominant foaming behavior of the cross-linking agent, so that the surface of the material has too many open pores, and the initial coulombic efficiency is seriously reduced.

According to the invention, the chemical crosslinking reaction is carried out by adopting the crosslinking agent, so that the carbon material can be prevented from melting and rearranging in the high-temperature carbonization process, and the graphitization degree of the carbon material can be inhibited. If a small molecular cross-linking agent or a template agent is adopted to be mixed with semicoke, uniform fusion is difficult to realize, so that a pore structure formed after pore formation is nonuniform, macropores can be generated even, a hard carbon microstructure is damaged, and the behavior of the hard carbon sodium storage performance is seriously influenced. Compared with the prior art, the invention adopts one or more of polyalcohol, polyhydroxy saccharide compound, polybasic acid and hydroxycarboxylic acid compound as the cross-linking agent to realize uniform fusion with activated semicoke, and the semicoke after chemical cross-linking reaction contains enough C-O-C structure, thereby being beneficial to the retention or cross-linking of oxygen atoms in the structure and forming nano-void and disordered structure after carbonization.

According to the invention, the variety of oxygen-containing functional groups is accurately increased in activated semicoke by controlling the variety of the cross-linking agent, and the C-O-C structure is effectively constructed, so that the increase of pseudo-graphite phase and closed pores of the material is beneficial to the improvement of the platform capacity. Meanwhile, the invention increases the carbon yield of the material by a chemical crosslinking strategy.

The invention adopts inorganic strong alkali for activation (modified alkali oxidation). Although effective in reducing semicoke ash, it results in increased open cell and defects, severely affecting initial coulombic efficiency. When the crosslinking reaction is further carried out, the crosslinking agent can effectively cover the defects, and meanwhile, the open pores are wrapped or filled, so that the open pores are converted into closed pores or micropores.

After activated cross-linked semicoke is obtained, the activated cross-linked semicoke is calcined in a protective gas atmosphere to obtain the activated cross-linked semicoke-based hard carbon material. In the present invention, the activated crosslinked semicoke is carbonized during the calcination, preferably in a tube furnace, and the shielding gas is preferably an inert gas, more preferably argon. The calcination temperature is preferably 1000-1400 ℃, more preferably 1200 ℃, and the heat preservation time is preferably 1-4 h, more preferably 2h; the heating rate from room temperature to the calcination temperature is preferably 1 to 5℃per minute, more preferably 2℃per minute.

In the invention, the temperature rising rate from room temperature to the calcining temperature cannot be too high, defects and the specific surface area are excessively large due to the too high temperature rising rate, and the initial coulombic efficiency of the material is reduced due to the increase of the solid electrolyte interface film.

The activated cross-linked semicoke-based hard carbon material provided by the invention has a closed pore or micropore structure, and the carbon layer arrangement is mainly based on pseudo-graphite phase. The surface defect of the activated cross-linked semicoke-based hard carbon material provided by the invention is critical for avoiding large irreversible capacity and realizing high initial coulomb efficiency in the initial charge and discharge process, and the formation of a closed cell structure is beneficial to the filling of sodium ions.

In the present invention, the ion battery is preferably a sodium ion battery.

The technical solutions provided by the present invention are described in detail below in conjunction with examples for further illustrating the present invention, but they should not be construed as limiting the scope of the present invention.

The raw material types and raw material sources used in the following examples and comparative examples are shown in table 1:

table 1 types and sources of raw materials used in examples and comparative examples

Example 1

1g of semicoke was mixed with 0.5g of NaOH (NaOH to semicoke mass ratio 2:1), thoroughly mixed in 50mL of deionized water, and then subjected to hydrothermal reaction at 180℃for 10 hours. The obtained material is washed by HCl and deionized water for multiple times, and dried for 24 hours at 80 ℃ to obtain active semicoke (ASC-2).

0.2g of sucrose and 0.5g of activated carbocoal (the mass ratio of citric acid to activated carbocoal is 3:5) are thoroughly mixed in 50mL of ethanol solution and then solvothermal reacted at 80 ℃ for 2 hours. And finally, placing the obtained sample in a tube furnace, calcining for 2 hours at 1200 ℃ in an argon atmosphere, and obtaining the activated cross-linked semicoke-based hard carbon material ASHC-2 at a heating rate of 2 ℃/min.

Comparative example 1

And (3) placing 1g of semicoke into a tubular furnace, calcining for 2 hours at 1200 ℃ under the argon atmosphere, and obtaining the semicoke-based hard carbon material, which is named as R-HC, wherein the heating rate is 2 ℃/min.

Comparative example 2

1g of semicoke was mixed with 0.5g of NaOH (NaOH to semicoke mass ratio 5:1), thoroughly mixed in 50mL of deionized water, and then subjected to hydrothermal reaction at 180℃for 10 hours. The obtained material is washed by HCl and deionized water for multiple times, and dried for 24 hours at 80 ℃ to obtain active semicoke (ASC-2).

And (3) placing the activated semicoke into a tubular furnace, calcining for 2 hours at 1200 ℃ under argon atmosphere, wherein the heating rate is 2 ℃/min, and the obtained hard carbon material is named AHC-2.

Comparative example 3

1g of citric acid was placed in a tube furnace, calcined at 1200℃for 2 hours under an argon atmosphere at a heating rate of 2℃per minute, and the obtained carbon material was named CAHC.

Comparative example 4

1g of sucrose was placed in a tube furnace, calcined at 1200℃for 2 hours under an argon atmosphere at a heating rate of 2℃per minute, and the obtained carbon material was designated SAHC.

Comparative example 5

0.5g of citric acid was mixed with 0.3g of semicoke (mass ratio of citric acid to semicoke 3:5) and heated to reflux at 110 ℃. And finally, placing the obtained sample in a tube furnace, calcining for 2 hours at 1200 ℃ in an argon atmosphere, and obtaining the activated cross-linked semicoke-based hard carbon material at a heating rate of 2 ℃/min. However, the C-O-C structure cannot be regulated due to the limited oxygen content in the semicoke, and the sodium storage performance is very poor.

In example 1, the number of oxygen-containing functional groups is greatly increased after the carbocoal is subjected to alkali oxidation, and the regulation and control of the carbocoal microcrystalline structure (a large number of closed cell structures are arranged, and the carbon layer arrangement is mainly based on pseudo-graphite phase) is further realized through chemical crosslinking.

Comparative example 6

The semicoke is subjected to pre-oxidation (activation) treatment by adopting air, the increase of inter-chain oxygen or oxygen-containing functional groups in the semicoke is small, and meanwhile, the types involved in introducing the oxygen-containing groups are more, and precise regulation is lacking.

Comparative example 7

Using an oxidizing agent (KMnO) ₄ Or H ₂ O ₂ ) And oxidizing the semicoke, and then continuing carbonization. This approach introduces a large number of oxy functional groups to provide a large number of attachment sites for sodium ions while providing better assistance for the increase in interlayer spacing. However, the use of a strong oxidizer is dangerous, and a large amount of deionized water is needed for post-treatment, so that the environment is seriously polluted, and the commercialization development is difficult to realize.

Example 2

1g of semicoke was mixed with 0.5g of NaOH (NaOH to semicoke mass ratio 2:1), thoroughly mixed in 50mL of deionized water, and then subjected to hydrothermal reaction at 180℃for 10 hours. The obtained material is washed by HCl and deionized water for multiple times, and dried for 24 hours at 80 ℃ to obtain Active Semicoke (ASC).

0.3g of citric acid was mixed with 0.5g of activated semicoke (mass ratio of citric acid to activated semicoke 3:5) and heated to reflux at 110 ℃. And finally, placing the obtained sample in a tube furnace, calcining for 2 hours at 1200 ℃ in an argon atmosphere, and obtaining the activated cross-linked semicoke-based hard carbon material named ACHC-2, wherein the heating rate is 2 ℃/min.

Test case

The morphology of the samples prepared in the examples and comparative examples was characterized using a field emission scanning electron microscope (SEM, hitachi SU8010 cube) and a transmission electron microscope (TEM, FEI Tecnai F30) and an energy spectrometer (EDS). Selective Area Electron Diffraction (SAED) patterns were recorded on a high resolution transmission electron microscope (HRTEM, hitachi JEM-2100F). Using Cu-K radiation sourcesThe crystalline phases of the examples and comparative examples were characterized by X-ray diffraction (XRD, bruker D8) and Raman spectroscopy (Bruker Senterra R-L). The specific surface area and pore structure were determined by the Brunauer-Emmet-Teller (BET, ASAP 2460) method.The thermal loss behavior of the carbocoal precursor was studied using a thermal analyzer (NETZSCH STA449F3, germany).

The blue-ray testing system (CT 2001A, wuhan Land) performs constant-current charge and discharge test, rate performance test and long-cycle test on the sodium half cell, and the test voltage range is 0.01-3V (vs Na/Na) ⁺ ). Cyclic voltammetry was performed at an electrochemical workstation (CHI 660E, shanghai Chen Hua) at a scan rate of 0.2mV s ^-1 ～2mV s ^-1 The voltage range is 0.01-3V (vs Na/Na ⁺ )。

Preparation of hard carbon negative electrode: active substances, acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, binder) are weighed according to the mass ratio of 85:5:10, are placed in an agate mortar for uniform mixing, are added dropwise with N-methyl pyrrolidone (NMP, solvent) for size mixing, the size mixed size is uniformly coated on copper foil (current collector), and after natural drying, the copper foil is dried in vacuum for 15 hours at 120 ℃, and then cut into small discs for standby.

Assembling a battery: the test assembly is CR2025 button cell, the metal sodium is used as the counter electrode, the diaphragm is glass fiber GF/F, and the electrolyte is 1M NaClO ₄ Dissolved in solvent (EC/PC, 1:1vol%). The assembly process was performed in an argon filled glove box with less than 1ppm of both water and oxygen. And assembling the battery according to the sequence of the positive electrode shell, the electrode plate, the diaphragm, the sodium metal plate, the gasket, the elastic sheet and the negative electrode shell, pressing and sealing the battery by a tablet press, taking the battery out of a glove box, standing the battery for 12-24 hours, and testing the electrochemical performance of the battery.

The test results are characterized as follows:

in the embodiment 1 of the invention, the quantity of carboxyl is accurately increased by an alkaline oxidation method, and then sucrose is used as a cross-linking agent to generate chemical cross-linking reaction with oxygen-containing functional groups in activated semicoke to construct a hard carbon precursor rich in a C-O-C structure. The C-O-C structure can effectively inhibit the graphitization degree of the carbonization early-stage material.

(1) FIG. 1 shows the XRD patterns of samples R-HC, AHC-2, ASHC-2 and SAHC, and FIG. 1 shows the Raman patterns of samples R-HC, AHC-2, ASHC-2 and SAHC. The R-HC obtained without pretreatment in graph a in FIG. 1 shows characteristic peaks of silica and alumina. AHC-2 and ASHC-2The impurity peak in the catalyst is obviously weakened, which indicates that the alkali oxidation method can effectively reduce impurities. Two broad diffraction peaks at-24 deg. and-43 deg. correspond to the (002) and (100) planes of the carbon material, respectively. Calculated according to the Bragg equation, the R-HC layer spacing was found to be 0.354nm and the SAHC layer spacing was found to be 0.400nm. The interlayer spacing of samples AHC-2 and ASHC-2 was between 0.354 and 0.400. Raman test in panel b of fig. 1, D band represents sp caused by disordered and defective structure ³ Hybridization was at-1355 cm ^-1 And G band represents sp generated by graphite crystal ² The hybridized peak is at-1595 cm ^-1 . A of R-HC _D /A _G 1.306.CAHC A _D /A _G 1.791. ASHC-2A _D /A _G The value is 1.533, between R-HC and CAHC, which is fully consistent with XRD testing.

(2) FIG. 2 is a scanning electron microscope image of samples R-HC, AHC-2 and ASHC-2. Semicoke is obtained by pyrolysis of coal to release tar molecules and other light volatile substances, so that a small amount of open pores exist on the surface of R-HC. As the modified alkaline oxidation method reduces the ash content in the precursor and causes the material to have a swelling effect, the number of open pores on the surface of the AHC-2 sample is increased. The preparation of the precursor rich in C-O-C structure can obtain ASHC-2 sample surface with a large amount of cross-linked structure, and the cross-linked molecules fill or wrap open pores to finally form closed pores.

(3) Fig. 3, 4 and 5 are graphs of the rate performance of samples R-HC, AHC-2, ashc-2 and SAHC (fig. 3), the first-cycle charge-discharge curve (fig. 4) and the capacity contribution ratio of the second-cycle discharge (fig. 5). As shown in FIG. 3, the current density is 30-1000mA g ^-1 The following rate capability. At current densities of 30, 50, 100, 200, 500 and 1000mAg ^-1 The reversible capacity of ASHC-2 was 280.8mAh g ^-1 ，278.3mAh g ^-1 ，255.6mAh g ^-1 ，194.9mAh g ^-1 ，76mAh g ^-1 And 52mAh g ^-1 . When the current density returns to 30mAg ^-1 In the process, ACHC-2 can still obtain 271.50mAh g ^-1 Higher than R-HC, AHC-2 and CAHC. As shown in FIG. 4, the ICE of R-HC, AHC-2, ASHC-2 and SAHC are 59.54%, 67.37%, 73.65% and 65.58%, respectively, saidThe precursor can be effectively stabilized by constructing the C-O-C structure, the overflow of gas micromolecules during high-temperature carbonization is inhibited, and the formation of surface defects is inhibited. In addition, this strategy also affects the sodium storage behavior of semicoke-based hard carbons. From the capacity contribution graph of fig. 5 for the second-round discharge plateau and ramp regions, it can be seen that the plateau capacity contribution of ASHC-2 increases from 38.71% to 59.92% compared to R-HC. This promotion results from the increase in pseudo-graphite phase and closed cells, thereby promoting intercalation/deintercalation of sodium ions.

In the embodiment 2 of the invention, the quantity of carboxyl groups is accurately increased by an alkaline oxidation method, and then, citric acid is used as a cross-linking agent to perform esterification reaction and decarboxylation reaction with oxygen-containing functional groups in activated semicoke to construct a hard carbon precursor rich in C- (O) -O (carboxyl or ester groups), wherein the C-O-C structure comprises a C- (O) -O structure, and the structure is a three-dimensional structure, so that the graphitization degree of a carbonization early material can be effectively inhibited. The precursor is carbonized to obtain hard carbon rich in pseudo-graphite phase and closed pores.

(1) Panel a in FIG. 6 shows XRD patterns of samples R-HC, AHC-2, ACHC-2 and CAHC, and panel b in FIG. 6 shows Raman patterns of samples R-HC, AHC-2, ACHC-2 and CAHC. The R-HC obtained by directly carbonizing semicoke in graph a in fig. 1 shows characteristic peaks of silica and alumina. Impurity peaks in AHC-2 and ACHC-2 are significantly reduced, indicating that the alkaline oxidation process is effective in reducing impurities. Two broad diffraction peaks at-24 deg. and-43 deg. correspond to the (002) and (100) planes of the carbon material, respectively. Calculated according to the Bragg equation, the R-HC layer spacing was found to be 0.354nm and the CAHC layer spacing was found to be 0.400nm. The interlayer spacing between samples AHC-2 and ACHC-2 was between 0.36 and 0.40. This is because the addition of citric acid effectively builds up a C- (O) -O structure, further inhibiting the formation and growth of graphite crystallites. Panel b in FIG. 6 is a Raman analysis of R-HC, AHC-2, ACHC-2 and CAHC. Of which are 1355 and 1595cm ^-1 The two broadband at which directly give the D-band (sp caused by disorder and defect structure ³ Hybridization) and G-bands (sp generated by graphite crystals ² Hybrid). A of R-HC _D /A _G 1.306.CAHC A _D /A _G 1.821.AHC-2 and ACHC-2A _D /A _G The value is 1.306-1.821.

(2) FIG. 7 is a scanning electron microscope image of samples R-HC, AHC-2 and ACHC-2. Semicoke is obtained by pyrolysis of coal to release tar molecules and other light volatile substances, so that a small amount of open pores exist on the surface of R-HC. As the alkali-oxygen oxidation method reduces the ash content in the precursor and causes the material to have a swelling effect, the number of open pores on the surface of the AHC-2 sample is increased. Preparation of precursors rich in C- (O) -O structures gives rise to a large number of crosslinked structures on the surface of the ACHC-2 sample, which fill or encapsulate open pores to eventually form closed pores. See also, FIGS. 8, 9 and 10 for transmission electron microscopy images of R-HC, AHC-2 and ACHC-2, respectively. As can be seen from fig. 3, 4 and 5, the carbon layers of R-HC are arranged in order, with the graphite phase being the dominant. The surface of AHC-2 is capable of observing a small number of closed cells, since the random arrangement of curved fringes may lead to the appearance of closed cells. Compared with AHC-2, the open pores on the surface of ACHC-2 disappear, a large number of closed pore structures appear, and the carbon layer arrangement is mainly based on pseudo-graphite phase. The sharpness of the dispersed diffraction rings in the SAED patterns (FIG. 11) was progressively reduced for samples R-HC, AHC-2 and ACHC-2, further confirming the increased disorder of the local carbon structure.

(3) FIG. 12 shows the adsorption and desorption curve (BET) and pore size distribution of an R-HC sample, FIG. 13 shows the BET and pore size distribution of an AHC-2 sample, FIG. 14 shows the BET and pore size distribution of an ACHC-2 sample, and FIG. 15 shows the BET and pore size distribution of a CAHC sample. As can be seen from fig. 12 to 15: specific surface areas of R-HC, AHC-2, ACHC-2 and CAHC were 24.15m, respectively ² g ^-1 、27.88m ² g ^-1 、3.24m ² g ^-1 And 45.97m ² g ^-1 . The specific surface area of ACHC-2 is the smallest because citric acid and activated semicoke undergo chemical crosslinking reaction and successfully construct a C- (O) -O structure. The structure effectively inhibits the overflow of gas micromolecules of the precursor of ACHC-2 during high-temperature carbonization, and simultaneously, the citric acid effectively wraps the activated semicoke so that the open pores are converted into closed pores. Small surface defects are critical to avoid large irreversible capacity and to achieve high initial coulombic efficiency during initial charge and discharge, while closed cell formation facilitates sodium ion packing.

(4) FIGS. 16 to 23 show the R-HC samplesAHC-2, ACHC-2 and CAHC rate capability graphs (FIG. 11), first cycle charge-discharge curves (FIG. 17), second cycle discharge capacity contribution ratios (FIG. 18); CV curves for R-HC, AHC-2 and ACHC-2 (FIG. 19) and R-HC, AHC-2, ACHC-2 and CAHC (FIGS. 20, 21, 22 and 23, respectively). As shown in FIG. 16, the current density is 30-1000mAg ^-1 The following rate capability. When the current density is 30, 50, 100, 200, 500 and 1000mA g ^-1 At the time, the reversible capacity of ACHC-2 is 302.59mAh g respectively ^-1 ，294.75mAh g ^-1 ，269.06mAh g ^-1 ，194.77mAh g ^-1 ，87.81mAh g ^-1 And 68.71mAh g ^-1 When the current density returns to 30mAg ^-1 In the process, ACHC-2 can still obtain 289.89mAh g ^-1 Higher than R-HC, AHC-2 and CAHC. Fig. 17 is a constant current discharge-charge curve. ICE of R-HC, AHC-2, ACHC-2 and CAHC are 59.54%, 67.37%, 80.65% and 61.45%, respectively, which shows that the precursor can be effectively stabilized by constructing the structure of C- (O) -O, the overflow of gas small molecules at high temperature carbonization is suppressed, and the formation of surface defects is suppressed. In addition, this strategy also affects the sodium storage behavior of semicoke-based hard carbons. From the capacity contribution graph of the second-round discharge plateau and ramp regions of fig. 18, it can be seen that the plateau capacity contribution of ACHC-2 increases from 38.71% to 59.72% compared to R-HC. This promotion results from the increase in pseudo-graphite phase and closed cells, thereby promoting intercalation/deintercalation of sodium ions. At 30mAg ^-1 A long cycle test was performed (as in FIG. 19), and the ACHC-2 electrode showed a reversible capacity of 294.0mAh g after 100 cycles ^-1 Exceeds R-HC (120.8 mAh g) ^-1 ) And AHC-2 (236.7 mAh g) ^-1 ). Unexpectedly, the ACHC-2 can reach high capacity retention rate of 96.20% after 100 cycles, and the hard carbon ACHC-2 prepared from the precursor rich in the C- (O) -O structure is proved to have excellent cycle stability. FIGS. 20-23 are CV curves for samples R-HC, AHC-2, ACHC-2 and CAHC, respectively, at a scan rate of 0.2 mV/s. The curves of fig. 20 to 23 show typical characteristics of the carbon material, and since the SEI film is formed, irreversible peaks appear near 0.5V and 1.2V in the first-turn CV curves of all electrodes. Clearly, the irreversible peak of AHC-2 is more prominent than R-HC, which may be associated with increased porosity and irreversible adsorption enhancement. Does not takeHowever, ACHC-2 has a smaller irreversible peak than R-HC because further chemical crosslinking encapsulates the open pores into closed pores. From the second scan, the CV curves were similar in shape and high in overlap, indicating good reversibility of the electrode. In addition, the CV curve shows a peak around 0.1V and a wide hump between 0.2 and 2.0V, which are respectively Na ⁺ Is inserted/removed, surface defects or adsorbed storage. The peak area of the ACHC-2 electrode is greatest around 0.1V, indicating that closed pores and proper inter-layer spacing are favorable for plateau capacity formation.

From the above examples, the invention uses Hami high ash semicoke as a precursor and adopts an alkaline oxidation synergistic chemical crosslinking strategy to construct a C-O-C regulated semicoke-based hard carbon microcrystalline structure. The alkali-oxygen oxidation treatment not only introduces oxygen-containing functional groups, but also effectively reduces ash content, and provides necessary space for subsequent chemical crosslinking reaction. In this case, the polyol, the polyhydroxy saccharide compound, the polybasic acid and the hydroxycarboxylic acid compound are used as crosslinking agents, and a chemical crosslinking reaction is carried out with the oxygen-containing functional groups in the activated semicoke, so that the precursor contains rich C-O-C structures. The C-O-C structure can prevent the graphite layer from sliding in early carbonization, and further inhibit the graphitization degree of the material. Meanwhile, the cross-linking agent can effectively wrap and fill open pores and large pores left by ash removal, so that the cross-linking agent is converted into closed pores or micropores, and the initial coulomb efficiency and the sodium storage capacity of semicoke are improved.

Although the foregoing embodiments have been described in some, but not all embodiments of the invention, other embodiments may be obtained according to the present embodiments without departing from the scope of the invention.

Claims

1. The preparation method of the activated cross-linked semicoke-based hard carbon material is characterized by comprising the following steps of:

2. The method of preparation according to claim 1, wherein the activation modification comprises the steps of: and mixing and heating the semicoke, inorganic strong alkali and water, and performing activation modification.

3. The method of preparation according to claim 1 or 2, wherein the inorganic strong base comprises sodium hydroxide; the mass ratio of the inorganic strong base to the semicoke is 1 (1-3).

4. The preparation method according to claim 1 or 2, wherein the activation modification is carried out at a temperature of 130 to 200 ℃ for a time of 5 to 12 hours.

5. The method of claim 1, wherein the chemical crosslinking reaction comprises the steps of: and mixing and heating the activated semicoke and the crosslinking agent, and carrying out chemical crosslinking reaction.

6. The method of claim 1 or 5, wherein the cross-linking agent comprises citric acid or sucrose; the mass ratio of the cross-linking agent to the activated semicoke is (1-5): 5.

7. The preparation method according to claim 1, wherein the calcination temperature is 1000-1400 ℃ and the heat preservation time is 1-4 hours; the temperature rising rate from room temperature to the calcining temperature is 1-5 ℃/min.

8. The activated crosslinked semicoke-based hard carbon material obtained by the preparation method of any one of claims 1 to 7.

9. The use of the activated cross-linked semicoke-based hard carbon material as claimed in claim 8 as an electrode material of an ion battery.

10. The use according to claim 9, wherein the ion battery is a sodium ion battery.