An activated cross-linked semi-coke-based hard carbon material, a preparation method and applications thereof

Abstract

The application belongs to the technical field of hard carbon materials and sodium ion electrode materials, and particularly relates to an activated cross-linked semi-coke-based hard carbon material and a preparation method and application thereof. In the application, semi-coke is modified by using inorganic strong alkali, and the obtained activated semi-coke is subjected to a chemical cross-linking reaction with a cross-linking agent, and the obtained activated cross-linked semi-coke is calcined to obtain the activated cross-linked semi-coke-based hard carbon material. In the application, a modified alkali-oxidation and chemical cross-linking strategy is adopted, and the microcrystalline structure of the semi-coke-based hard carbon is regulated by constructing C-O-C. The alkali-oxidation method is used to precisely increase the types of oxygen-containing functional groups, and then the chemical cross-linking reaction with the cross-linking agent is performed to successfully construct the C-O-C structure. The hard carbon material obtained by carbonizing the precursor contains rich pseudo-graphite phases and closed pores, which is beneficial to improving the sodium storage capacity and initial coulombic efficiency, and the chemical cross-linking strategy can also increase the carbon yield of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hard carbon materials and sodium ion electrode materials, and particularly relates to an activated cross-linked semi-coke-based hard carbon material and a preparation method and application thereof. BACKGROUND

[0002] At present, energy storage technology is in a stage of diversified development. The main energy storage types are physical energy storage and electrochemical energy storage, and electrochemical energy storage is the main development trend. At present, secondary batteries, as the main role in electrochemical energy storage, play an important role.

[0003] With the increasing demand for new energy vehicles, the lithium ion battery industry is developing explosively. From 2012 to 2021, the global new energy vehicles increased from 125,000 to 6.75 million. However, the increasing demand for lithium ion batteries has led to a continuous rise in the price of lithium carbonate, a lithium ion battery material, and the relative scarcity of lithium reserves, uneven global distribution and other shortcomings, which directly lead to great resistance to the use of lithium ion batteries in large-scale energy storage devices. In contrast, sodium is abundant and widely distributed, and has similar chemical properties to lithium, which is expected to make up for lithium ion batteries in large-scale energy storage devices. However, the radius of sodium ions is larger than the radius of lithium ions The larger ionic radius makes it difficult to find suitable electrode materials for sodium ion batteries. For example, the interlayer spacing of the commercial graphite negative electrode material of lithium ion batteries does not match the radius of sodium ions, and the binding energy of sodium ion-graphite intercalation reaction is greater than 0, so graphite is not suitable for sodium ion batteries. Sodium ion battery negative electrode materials involve a wide variety of types, among which carbonaceous materials are relatively promising due to their abundant resources, low cost and good quality. According to the microstructure, carbonaceous materials are divided into graphite materials, nanocarbon materials and amorphous carbon materials, among which amorphous carbon materials are the mainstream due to their low price and high sodium storage capacity. Amorphous carbon is further divided into soft carbon and hard carbon according to the difficulty of graphitization during high-temperature carbonization. Soft carbon materials have strong electrical conductivity, but their sodium storage performance is poorer than that of hard carbon. According to the sodium storage performance and comprehensive cost performance, hard carbon has become the main research object of sodium ion battery negative electrode materials.

[0004] Hard carbon refers to carbon materials that are difficult to achieve complete graphitization at extremely high temperatures. Its structure is called "card house" structure, which is composed of a large number of disordered graphite crystals and amorphous regions, and has a low degree of graphitization, a less developed layered structure, and a larger interlayer spacing than graphite. The large interlayer spacing of hard carbon is beneficial to the diffusion of sodium ions and the stability of the structure, and the disordered amorphous structure provides more active sodium storage sites. However, the defect concentration directly affects the initial coulomb efficiency. During the cycle process, some sodium ions are irreversibly retained in the defects, which significantly reduces the initial coulomb efficiency. In summary, the poor rate performance, low initial coulomb efficiency and platform capacity of hard carbon hinder its further industrial development. In addition, the precursor plays a key role in the physical and chemical properties of hard carbon. Biomass hard carbon has been widely studied due to its abundant resources, simple processing and ecological friendliness, but it has poor initial coulomb efficiency and low carbon yield. Currently available polymers, such as epoxy resin, phenolic resin and polyacrylonitrile, have been used to synthesize hard carbon, but the cost performance is low. Therefore, finding a suitable carbon source to prepare low-cost, high-initial coulomb efficiency and high-platform capacity hard carbon is the key to commercial development. SUMMARY

[0005] The purpose of the present application is to provide an activated cross-linked semi-coke-based hard carbon material and its preparation method and application. The activated cross-linked semi-coke-based hard carbon material provided by the present application has excellent initial coulomb efficiency and sodium storage performance, and is low in cost, suitable for industrial application.

[0006] In order to achieve the above purpose, the present application provides the following technical solutions:

[0007] The present application provides a preparation method of an activated cross-linked semi-coke-based hard carbon material, comprising the following steps:

[0008] The semi-coke is activated and modified with an inorganic strong base to obtain activated semi-coke.

[0009] The activated semi-coke is subjected to a chemical cross-linking reaction with a cross-linking agent to obtain activated cross-linked semi-coke. The cross-linking agent includes one or more of polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds.

[0010] The activated cross-linked semi-coke is calcined in a protective gas atmosphere to obtain an activated cross-linked semi-coke-based hard carbon material.

[0011] Preferably, the activation and modification includes the following steps: mixing and heating the semi-coke, inorganic strong base and water to perform activation and modification.

[0012] Preferably, the inorganic strong base includes sodium hydroxide; and the mass ratio of the inorganic strong base to the semi-coke is 1:(1-3).

[0013] Preferably, the temperature of the activation modification is 130-200 DEG C, and the time is 5-12h.

[0014] Preferably, the chemical cross-linking reaction comprises the following steps: mixing and heating the activated semi-coke and a cross-linking agent to perform the chemical cross-linking reaction.

[0015] Preferably, the cross-linking agent comprises citric acid or sucrose; and the mass ratio of the cross-linking agent to the activated semi-coke is (1-5):5.

[0016] Preferably, the temperature of the calcination is 1000-1400 DEG C, the holding time is 1-4h, and the heating rate from room temperature to the calcination temperature is 1-5 DEG C / min.

[0017] The application provides an activated cross-linked semi-coke-based hard carbon material prepared by the preparation method.

[0018] The application provides an application of the activated cross-linked semi-coke-based hard carbon material as an electrode material of an ion battery.

[0019] Preferably, the ion battery is a sodium ion battery.

[0020] The application provides a preparation method of activated cross-linked semi-coke-based hard carbon material, comprising the following steps: modifying and activating semi-coke by using inorganic strong base to obtain activated semi-coke; performing chemical cross-linking reaction on the activated semi-coke by using a cross-linking agent to obtain activated cross-linked semi-coke; the cross-linking agent comprises one or more of polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds; and performing calcination on the activated cross-linked semi-coke in a protective gas atmosphere to obtain activated cross-linked semi-coke-based hard carbon material. The application adopts a modified alkali-oxygen oxidation and chemical cross-linking strategy to construct C-O-C structure (representing an oxygen-connected carbon layer structure) to regulate the crystalline structure of semi-coke-based hard carbon. First, the modified alkali-oxygen oxidation treatment of semi-coke by using inorganic strong base not only introduces oxygen-containing functional groups (carboxyl groups) on the semi-coke, but also effectively reduces the ash content of the semi-coke, thereby providing active sites and space for the subsequent chemical cross-linking reaction. In this case, the application uses polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds as the cross-linking agent to perform chemical cross-linking reaction (including esterification reaction, decarboxylation reaction and hydrolysis reaction) with the oxygen-containing functional groups in the activated semi-coke, so that the obtained activated cross-linked semi-coke contains rich C-O-C structure. The C-O-C structure can hinder the sliding of graphite layers during carbonization, and further inhibit the graphitization degree of the material. In addition, the cross-linking reaction between the cross-linking agent and the activated semi-coke during carbonization has two effects. On the one hand, it inhibits the foaming behavior of the cross-linking agent, and on the other hand, the cross-linking agent can effectively wrap and fill the open pores and large pores left by the modified alkali-oxygen oxidation method, and convert them into closed pores or micropores, thereby improving the initial coulombic efficiency and sodium storage capacity of the semi-coke-based hard carbon. In summary, the preparation method provided by the application adopts a modified alkali-oxygen oxidation and chemical cross-linking strategy to regulate the crystalline structure of semi-coke-based hard carbon at multiple scales, accurately increases the types of oxygen-containing functional groups, and effectively constructs C-O-C structure. The semi-coke-based hard carbon obtained by carbonization contains rich pseudo-graphite phase and closed pores, which is beneficial to the improvement of sodium storage performance. In addition, the chemical cross-linking reaction increases the carbon yield of the material.

[0021] The application provides an activated cross-linked semi-coke-based hard carbon material obtained by the preparation method. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 XRD and Raman patterns of R-HC, AHC-2, ASHC-2 and SAHC in the examples and comparative examples of the application;

[0023] Figure 2Scanning electron microscope images of R-HC, AHC-2 and ACHC-2 in the examples and comparative examples of the present application;

[0024] Figure 3 Rate capability plots of R-HC, AHC-2, ASHC-2 and SAHC in the examples and comparative examples of the present application;

[0025] Figure 4 First cycle charge-discharge curves of R-HC, AHC-2, ASHC-2 and SAHC in the examples and comparative examples of the present application;

[0026] Figure 5 Capacity contribution percentage of the second cycle discharge of R-HC, AHC-2, ASHC-2 and SAHC in the examples and comparative examples of the present application;

[0027] Figure 6 XRD and Raman plots of R-HC, AHC-2, ACHC-2 and CAHC in the examples and comparative examples of the present application;

[0028] Figure 7 Scanning electron microscope images of R-HC, AHC-2 and ACHC-2 in the examples and comparative examples of the present application;

[0029] Figure 8 Transmission electron microscope images of R-HC prepared in the comparative examples of the present application;

[0030] Figure 9 Transmission electron microscope images of AHC-2 prepared in the comparative examples of the present application;

[0031] Figure 10 Transmission electron microscope images of ACHC-2 prepared in the examples of the present application;

[0032] Figure 11 SAED plots of R-HC, AHC-2 and ACHC-2 in the examples and comparative examples of the present application;

[0033] Figure 12 BET and pore size distribution plots of R-HC prepared in the comparative examples of the present application;

[0034] Figure 13 BET and pore size distribution plots of AHC-2 prepared in the comparative examples of the present application;

[0035] Figure 14 BET and pore size distribution plots of ACHC-2 prepared in the examples of the present application;

[0036] Figure 15 BET and pore size distribution plots of CAHC prepared in the comparative examples of the present application;

[0037] Figure 16Rate capability plots for R-HC, AHC-2, ACHC-2 and CAHC in inventive examples and comparative examples of the present application;

[0038] Figure 17 First cycle charge-discharge plots for R-HC, AHC-2, ACHC-2 and CAHC in inventive examples and comparative examples of the present application;

[0039] Figure 18 Capacity contribution percentage for the second cycle discharge for R-HC, AHC-2, ACHC-2 and CAHC in inventive examples and comparative examples of the present application;

[0040] Figure 19 Long cycle plots for R-HC, AHC-2 and ACHC-2 in inventive examples and comparative examples of the present application;

[0041] Figure 20 CV plots for R-HC prepared in comparative examples of the present application;

[0042] Figure 21 CV plots for AHC-2 prepared in comparative examples of the present application;

[0043] Figure 22 CV plots for ACHC-2 prepared in inventive examples of the present application;

[0044] Figure 23 CV plots for CAHC prepared in comparative examples of the present application. DETAILED DESCRIPTION

[0045] The present application provides a method for preparing an activated cross-linked semi-coke based hard carbon material, comprising the following steps:

[0046] Activating and modifying the semi-coke with an inorganic strong base to obtain an activated semi-coke;

[0047] Carrying out a chemical cross-linking reaction of the activated semi-coke with a cross-linking agent to obtain an activated cross-linked semi-coke; the cross-linking agent comprises one or more of a polyol, a polyhydroxy sugar compound, a polyacid and a hydroxyl carboxylic acid compound;

[0048] Carrying out calcination of the activated cross-linked semi-coke in a protective gas atmosphere to obtain an activated cross-linked semi-coke based hard carbon material.

[0049] In the present application, all the raw materials / components are commercially available products well known to those skilled in the art, unless otherwise specified.

[0050] The present application activates and modifies semi-coke with inorganic strong base to obtain activated semi-coke. In the present application, the semi-coke is preferably high-ash semi-coke with ash content ≥13% from Xinjiang Hami. Semi-coke is heavy carbon from coal, which is obtained by medium-low temperature carbonization, crushing and screening. Semi-coke has the advantages of high fixed carbon, low volatile matter and low sulfur, which makes the structure of semi-coke controllable. At present, the application of semi-coke in electrodes is mainly to prepare porous carbon and graphite, and there is almost no application of semi-coke in preparing hard carbon for sodium ion batteries. Since semi-coke is heavy carbon from coal, it is difficult to inhibit the ordered growth of carbon microcrystals during high-temperature carbonization, resulting in too narrow interlayer spacing, which hinders the intercalation / deintercalation of sodium ions. The key to realizing high-performance sodium storage coal-based hard carbon is to effectively inhibit the growth of graphite microcrystals during carbonization.

[0051] In the present application, the inorganic strong base preferably includes sodium hydroxide. The water is preferably deionized water. The mass ratio of the inorganic strong base to the semi-coke is preferably 1:(1-3), more preferably 1:2. The activation modification preferably includes the following steps: mixing and heating the semi-coke, inorganic strong base and water to activate and modify. The temperature of the activation modification is preferably 130-200°C, and the time is preferably 5-12h.

[0052] In the present application, semi-coke contains limited oxygen-containing functional groups, which is difficult to directly build C-O-C structure. Therefore, the present application uses inorganic strong base to pre-activate semi-coke to increase the number of oxygen-containing functional groups in semi-coke material. Studies have shown that the type and number of oxygen-containing functional groups seriously affect the sodium storage performance. Combined with experiments and density functional theory, it is found that the adsorption energy of oxygen groups is too negative, which may cause problems in the desalination process, thereby increasing the irreversible adsorption. In this regard, carboxylated carbon has appropriate adsorption interaction with sodium ions on the surface, the repulsive force between adjacent carbon layers increases, which can enhance the surface adsorption and interlayer insertion to help the reversible ability of sodium ions. Therefore, the activation process of semi-coke can be used strategically to increase the number of carboxyl groups, which not only helps to adjust the C-O-C structure in the precursor, but also helps to improve the electrochemical performance.

[0053] In the present application, the amount of inorganic strong base cannot be too little or too much. Too little will cause the oxidation intensity to decrease, which cannot effectively increase the number of carboxyl groups and remove ash. Too much will cause the structure of semi-coke to collapse, which seriously affects its sodium storage performance.

[0054] In the present application, the temperature of the activation modification cannot be too high or too low. Too high will cause the structure to collapse due to excessive oxidation intensity, which seriously affects the sodium storage performance of semi-coke-based hard carbon. Too low will cause the oxidation intensity to decrease, which cannot effectively increase the number of oxygen functional groups in semi-coke.

[0055] In the present application, the activated modified material is directly obtained after the activation modification, and the activated modified material is sequentially washed by hydrochloric acid and water, and then dried to obtain the activated semi-coke. The water washing is preferably deionized water washing, and the water washing after neutralization of the hydrochloric acid with the inorganic base is required to be to weakly acidic. The drying temperature is preferably 60-100 DEG C, and the time is preferably 15-24h.

[0056] After obtaining the activated semi-coke, the activated semi-coke is chemically cross-linked with a cross-linking agent to obtain activated cross-linked semi-coke, and the cross-linking agent includes one or more of polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds. In the present application, the cross-linking agent preferably includes citric acid or sucrose. The mass ratio of the cross-linking agent to the activated semi-coke 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 cross-linking reaction includes the following steps: mixing and heating the activated semi-coke and the cross-linking agent to perform chemical cross-linking reaction. In the present application, the chemical cross-linking reaction is preferably performed under heating reflux conditions.

[0057] In the present application, the non-graphitization property of the hard carbon is attributed to the interlayer cross-linking and covalent bond of the precursor. The present application uses one or more of polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds as the cross-linking agent, and the semi-coke after chemical cross-linking reaction contains rich C-O-C structure, which is beneficial to.

[0058] In the present application, the amount of the cross-linking agent cannot be too little or too much. Too little will cause that the activated semi-coke cannot be effectively cross-linked, so that it is difficult to inhibit the ordered arrangement of the graphite domain during high-temperature carbonization. Too much will cause that the foaming behavior of the cross-linking agent dominates, so that the opening on the surface of the material is too much, which seriously reduces the initial coulomb efficiency.

[0059] By using the above cross-linking agent for chemical cross-linking reaction, the present application can prevent the carbon material from melting and rearranging during high-temperature carbonization, and inhibit the graphitization degree. If a small molecule cross-linking agent or a template agent is mixed with the semi-coke, it will be difficult to realize uniform fusion, resulting in non-uniform pore structure after pore forming, and even large pores, which destroys the microstructure of the hard carbon and seriously affects the sodium storage performance of the hard carbon. Compared with the prior art, the present application uses one or more of polyols, polyhydroxy sugar compounds, polybasic acids and hydroxyl carboxylic acid compounds as the cross-linking agent to realize uniform fusion with the activated semi-coke, and the semi-coke after chemical cross-linking reaction contains sufficient C-O-C structure, which is beneficial to the retention or cross-linking of the oxygen atoms in the structure, and forms nanovoids and disordered structure after carbonization.

[0060] The application effectively constructs C-O-C structure by controlling the type of cross-linking agent, precisely increasing the type of oxygen-containing functional groups in activated semi-coke, so that the pseudo-graphite phase and closed pores of the material increase, which is beneficial to the improvement of platform capacity. Meanwhile, the chemical cross-linking strategy is used to increase the carbon yield of the material.

[0061] In the application, inorganic strong alkali is used for activation (modified alkali oxygen oxidation). Although it effectively reduces the ash content of semi-coke, it causes the increase of open pores and defects, which seriously affects the initial coulomb efficiency. When the cross-linking reaction is further carried out, the cross-linking agent can effectively cover the defects, and at the same time, it can wrap or fill the open pores, so that the open pores are converted into closed pores or micropores.

[0062] After obtaining the activated cross-linked semi-coke, the application calcines the activated cross-linked semi-coke in a protective gas atmosphere to obtain an activated cross-linked semi-coke-based hard carbon material. In the application, carbonization of the activated cross-linked semi-coke occurs during the calcination, and the calcination is preferably carried out in a tube furnace, and the protective gas is preferably an inert gas, more preferably argon. The temperature of the calcination is preferably 1000-1400℃, more preferably 1200℃, and the holding time is preferably 1-4h, more preferably 2h; the heating rate from room temperature to the calcination temperature is preferably 1-5℃ / min, more preferably 2℃ / min.

[0063] In the application, the heating rate from room temperature to the calcination temperature cannot be too high, and a too high heating rate will cause defects and a too large specific surface area, increase the solid electrolyte interface film, and reduce the initial coulomb efficiency of the material.

[0064] The application provides an activated cross-linked semi-coke-based hard carbon material prepared by the preparation method.

[0065] The activated cross-linked semi-coke-based hard carbon material provided by the application has a closed pore or micropore structure, and the carbon layer arrangement is mainly in the form of pseudo-graphite phase. The surface defects of the activated cross-linked semi-coke-based hard carbon material provided by the application are crucial for avoiding large irreversible capacity and achieving high initial coulomb efficiency during the initial charge and discharge process, and the formation of closed pore structure is beneficial to the filling of sodium ions.

[0066] The application provides an application of the activated cross-linked semi-coke-based hard carbon material as an electrode material of an ion battery.

[0067] In the application, the ion battery is preferably a sodium ion battery.

[0068] In order to further illustrate the application, the technical solutions provided by the application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the application.

[0069] The types and sources of raw materials used in the following examples and comparative examples are shown in Table 1.

[0070] Table 1 Types and sources of raw materials used in examples and comparative examples

[0071]

[0072]

[0073] Example 1

[0074] 1 g of semi-coke was mixed with 0.5 g of NaOH (mass ratio of NaOH to semi-coke was 2:1), mixed well in 50 mL of deionized water, and then subjected to hydrothermal reaction at 180 °C for 10 h. The obtained material was washed with HCl and deionized water for several times, and dried at 80 °C for 24 h to obtain an activated semi-coke (ASC-2).

[0075] 0.2 g of sucrose was mixed with 0.5 g of activated semi-coke (mass ratio of citric acid to activated semi-coke was 3:5), mixed well in 50 mL of ethanol solution, and then subjected to solvothermal reaction at 80 °C for 2 h. Finally, the obtained sample was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere, with a heating rate of 2 °C / min, to obtain an activated cross-linked semi-coke-based hard carbon material ASHC-2.

[0076] Comparative Example 1

[0077] 1 g of semi-coke was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere, with a heating rate of 2 °C / min, to obtain a semi-coke-based hard carbon material, named R-HC.

[0078] Comparative Example 2

[0079] 1 g of semi-coke was mixed with 0.5 g of NaOH (mass ratio of NaOH to semi-coke was 5:1), mixed well in 50 mL of deionized water, and then subjected to hydrothermal reaction at 180 °C for 10 h. The obtained material was washed with HCl and deionized water for several times, and dried at 80 °C for 24 h to obtain an activated semi-coke (ASC-2).

[0080] The activated semi-coke was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere, with a heating rate of 2 °C / min, to obtain a hard carbon material, named AHC-2.

[0081] Comparative Example 3

[0082] 1 g of citric acid was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere, with a heating rate of 2 °C / min, to obtain a carbon material, named CAHC.

[0083] Comparative Example 4

[0084] 1 g sucrose was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere with a heating rate of 2 °C / min. The obtained carbon material was named as SAHC.

[0085] Comparative Example 5

[0086] 0.5 g of citric acid was mixed with 0.3 g of semi-coke (mass ratio of citric acid to semi-coke was 3:5) and heated to reflux at 110 °C. Finally, the obtained sample was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere with a heating rate of 2 °C / min to obtain an activated cross-linked semi-coke-based hard carbon material. However, due to the limited oxygen content in the semi-coke, the C-O-C structure could not be controlled, and the sodium storage performance was very poor.

[0087] Example 1 greatly increased the number of oxygen-containing functional groups after alkali-oxygen oxidation of the semi-coke, and further realized the regulation of the semi-coke microcrystalline structure (with a large number of closed pore structures, and the carbon layer arrangement was mainly in pseudo-graphite phase) through chemical cross-linking.

[0088] Comparative Example 6

[0089] Air was used to pre-oxidize (activate) the semi-coke. The increase of inter-chain oxygen or oxygen-containing functional groups in the semi-coke was small, and the types of oxygen-containing groups involved were more, lacking precise regulation.

[0090] Comparative Example 7

[0091] Oxidizing agents (KMnO4 or H2O2) were used to oxidize the semi-coke, and then carbonization was continued. This method introduced a large number of oxygen-containing functional groups to provide a large number of attachment sites for sodium ions, and at the same time provided better help for the increase of interlayer spacing. However, the use of strong oxidizing agents is dangerous, and a large amount of deionized water is needed for post-treatment, which seriously pollutes the environment and is difficult to realize commercial development.

[0092] Example 2

[0093] 1 g of semi-coke was mixed with 0.5 g of NaOH (mass ratio of NaOH to semi-coke was 2:1), and then mixed in 50 mL of deionized water. Then, hydrothermal reaction was carried out at 180 °C for 10 h. The obtained material was washed with HCl and deionized water for several times, and then dried at 80 °C for 24 h to obtain active semi-coke (ASC).

[0094] 0.3 g of citric acid was mixed with 0.5 g of activated semi-coke (mass ratio of citric acid to activated semi-coke was 3:5) and heated to reflux at 110 °C. Finally, the obtained sample was placed in a tube furnace, calcined at 1200 °C for 2 h under argon atmosphere with a heating rate of 2 °C / min to obtain an activated cross-linked semi-coke-based hard carbon material, which was named as ACHC-2.

[0095] Test Examples

[0096] The morphology of the samples prepared in the examples and comparative examples was characterized by field emission scanning electron microscopy (SEM, Hitachi SU8010 cube) and transmission electron microscopy (TEM, FEI Tecnai F30) and energy dispersive spectroscopy (EDS). Selected area electron diffraction (SAED) patterns were recorded on a high-resolution transmission electron microscope (HRTEM, Hitachi JEM-2100F) using a Cu-K radiation source The crystalline phase of the samples in the examples and comparative examples was characterized by X-ray diffraction (XRD, Bruker D8) and Raman spectrometer (Bruker Senterra R200-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 semi-coke-based hard carbon precursor was studied by a thermal analyzer (NETZSCH STA449F3, Germany).

[0097] The sodium half-batteries were tested by constant current charge-discharge, rate performance and long cycle test using a blue electronic test system (CT2001A, Wuhan Land) with a voltage range of 0.01-3 V (vs Na / Na + ). Cyclic voltammetry was performed on an electrochemical workstation (CHI660E, Shanghai Chen Hua) with a scan rate of 0.2 mV s -1 -2 mV s -1 and a voltage range of 0.01-3 V (vs Na / Na + ).

[0098] Preparation of hard carbon anode: The active material, acetylene black (conductive agent), and polyvinylidene fluoride (PVDF, binder) were weighed according to a mass ratio of 85:5:10, then placed in a marquetry mortar for uniform mixing, followed by dropwise addition of N-methyl pyrrolidone (NMP, solvent) for slurry preparation. The prepared slurry was uniformly coated on a copper foil (current collector), naturally air-dried, vacuum dried at 120°C for 15 h, and then the copper foil was cut into small round pieces for use.

[0099] Battery assembly: The batteries tested in this paper were all CR2025 type button batteries, with metallic sodium as the counter electrode, glass fiber GF / F as the separator, and 1M NaClO4 dissolved in solvent (EC / PC, 1:1 vol%) as the electrolyte. The assembly process was carried out in an argon-filled glove box with water and oxygen content less than 1 ppm. According to the order of positive electrode shell-electrode sheet-separator-sodium metal sheet-gasket-spring sheet-negative electrode shell, the battery was assembled and sealed by pressing with a tablet press, then taken out of the glove box, and left to stand for 12-24 h before testing its electrochemical performance.

[0100] The test results are characterized as follows:

[0101] In Example 1 of this invention, the number of carboxyl groups is precisely increased using an alkaline-oxygen oxidation method. Then, sucrose is used as a crosslinking agent to chemically crosslink with oxygen-containing functional groups in activated semi-coke to construct a hard carbon precursor rich in COC structure. The COC structure can effectively suppress the graphitization degree of materials in the early stages of carbonization.

[0102] (1) Figure 1 Figure a in the diagram shows the XRD patterns of samples R-HC, AHC-2, ASHC-2, and SAHC. Figure 1 Figure b in the figure shows the Raman spectra of samples R-HC, AHC-2, ASHC-2, and SAHC. Figure 1 In Figure a, the untreated R-HC exhibits characteristic peaks of silica and alumina. The impurity peaks in AHC-2 and ASHC-2 are significantly reduced, indicating that the alkaline-oxygen oxidation method effectively reduces impurities. Two broad diffraction peaks are observed at ~24° and ~43°, corresponding to the (002) and (100) planes of the carbon material, respectively. Based on the Bragg equation, the interlayer spacing of R-HC is calculated to be 0.354 nm, and that of SAHC is 0.400 nm. The interlayer spacing of samples AHC-2 and ASHC-2 is between 0.354 and 0.400 nm. Figure 1 In Figure b, the Raman test shows that band D represents the sp band caused by disordered and defective structures. 3 Hybridization is located at ~1355 cm⁻¹ -1 The G-band represents sp generated by graphite crystals. 2 The hybridization peak is located at ~1595 cm⁻¹ -1 R-HC's A D / A G It is 1.306. CAHC's A D / A G It is 1.791. ASHC-2's A D / A G The value is 1.533, which is between R-HC and CAHC, and this is in perfect agreement with the XRD test.

[0103] (2) Figure 2 The images show scanning electron microscope (SEM) images of samples R-HC, AHC-2, and ASHC-2. Semi-coke is obtained by thermally decomposing coal to release tar molecules and other light volatile substances; therefore, R-HC has a small number of open pores on its surface. Due to the reduction of ash content in the precursor and the swelling effect caused by the modified alkaline oxy-oxidation method, the number of open pores on the surface of the AHC-2 sample increases. The ASHC-2 sample, prepared from a precursor rich in COC structures, exhibits numerous cross-linked structures on its surface. These cross-linked molecules fill or encapsulate the open pores, ultimately forming closed pores.

[0104] (3) Figure 3 、 Figure 4 and Figure 5 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. Figure 3 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. Figure 4 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. Figure 5 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. Figure 3 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. -1 The reversible capacities of ASHC-2 were 280.8 mAh g-1, 278.3 mAh g-1, 255.6 mAh g-1, 194.9 mAh g-1, 76 mAh g-1and 52 mAh g-1at current densities of 30, 50, 100, 200, 500 and 1000 mAg-1, respectively. Figure 4 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC. Figure 5 Rate performance plots (Fig. 1), the first cycle charge-discharge curves (Fig. 2) and the capacity contribution ratio of the second cycle discharge plateau and slope region (Fig. 3) of samples R-HC, AHC-2, ASHC-2 and SAHC.

[0105] The present embodiment 2 precisely increases the number of carboxyl groups by alkali-oxygen oxidation method, and then constructs a hard carbon precursor rich in C-(O)-O (carboxyl or ester group, C-O-C structure contains C-(O)-O) structure by esterification reaction and decarboxylation reaction between the activated semi-coke and the crosslinking agent of citric acid. The structure is a three-dimensional structure, which can effectively inhibit the graphitization degree of the material in the early carbonization stage. The precursor is carbonized to obtain a hard carbon rich in pseudo-graphite phase and closed pores.

[0106] (1) Figure 6Figure a in the diagram shows the XRD patterns of R-HC, AHC-2, ACHC-2, and CAHC in the sample. Figure 6 Figure b in the figure shows the Raman spectra of samples R-HC, AHC-2, ACHC-2, and CAHC. Figure 1 In Figure a, R-HC obtained by direct carbonization of semi-coke exhibits characteristic peaks of silica and alumina. The impurity peaks in AHC-2 and ACHC-2 are significantly reduced, indicating that the alkaline-oxygen oxidation method effectively reduces impurities. Two broad diffraction peaks are observed at ~24° and ~43°, corresponding to the (002) and (100) planes of the carbon material, respectively. Based on the Bragg equation, the interlayer spacing of R-HC is calculated to be 0.354 nm, and that of CAHC is 0.400 nm. The interlayer spacing of samples AHC-2 and ACHC-2 is between 0.36 and 0.40 nm. This is because the addition of citric acid effectively constructs the C-(O)-O structure, further inhibiting the formation and growth of graphite crystallites. Figure 6 Figure b shows the Raman chromatograms of R-HC, AHC-2, ACHC-2, and CAHC. The values ​​at ~1355 and ~1595 cm⁻¹ are also shown. -1 The two widebands at that point directly give the D-band (sp caused by disorder and defect structure). 3 Hybridization) and G-band (sp generated by graphite crystals) 2 Information about hybridization. A in R-HC D / A G It is 1.306. CAHC's A D / A G It is 1.821. The A values ​​of AHC-2 and ACHC-2 are... D / A G The value is between 1.306 and 1.821.

[0107] (2) Figure 7 The images show scanning electron microscope (SEM) images of samples R-HC, AHC-2, and ACHC-2. Semi-coke is obtained by thermally decomposing coal to release tar molecules and other light volatile substances; therefore, R-HC has a small number of open pores on its surface. Due to the reduction of ash content in the precursor and the swelling effect caused by the alkaline-oxygen oxidation method, the number of open pores on the surface of the AHC-2 sample increases. The ACHC-2 sample, prepared using a precursor rich in C-(O)-O structures, exhibits numerous cross-linked structures on its surface. These cross-linked molecules fill or encapsulate the open pores, ultimately forming closed pores. Figure 8 , Figure 9 and Figure 10 The images are transmission electron microscope (TEM) images of R-HC, AHC-2, and ACHC-2, respectively. Figure 3 , Figure 4 and Figure 5It can be found that the carbon layer arrangement of R-HC is ordered, mainly in graphite phase. A small amount of closed pores can be observed on the surface of AHC-2, which is due to the random arrangement of curved stripes that may lead to the appearance of closed pores. Compared with AHC-2, the open pores on the surface of AHC-2 disappear, a large number of closed pore structures appear, and the carbon layer arrangement is mainly in pseudo-graphite phase. For samples R-HC, AHC-2 and AHC-2, the clarity of the dispersed diffraction ring in the SAED pattern Figure 11 ) gradually weakens, further confirming the increase in the disorder degree of the local carbon structure.

[0108] (3) Figure 12 is the adsorption-desorption curve (BET) and pore size distribution of the R-HC sample, Figure 13 is the BET and pore size distribution of the AHC-2 sample, Figure 14 is the BET and pore size distribution of the AHC-2 sample, Figure 15 is the BET and pore size distribution of the CAHC sample. It can be seen that: Figure 12 to Figure 15 the specific surface areas of R-HC, AHC-2, AHC-2 and CAHC are 24.15 m 2 g -1 , 27.88 m 2 g -1 , 3.24 m 2 g -1 and 45.97 m 2 g -1 , respectively. The specific surface area of AHC-2 is the smallest, which is due to the chemical cross-linking reaction between citric acid and activated semi-coke and the successful construction of C-(O)-O structure. This structure effectively inhibits the overflow of small gas molecules during the carbonization of the precursor of AHC-2 at high temperature, and at the same time, citric acid effectively wraps the activated semi-coke, making the open pores change into closed pores. Small surface defects are crucial for avoiding large irreversible capacity and achieving high initial coulombic efficiency during the initial charge and discharge process, and the formation of closed pores is beneficial for the filling of sodium ions.

[0109] (4) Figure 16 to Figure 23 are the rate performance graphs ( Figure 11 ), the first cycle charge-discharge curves ( Figure 17 ), the proportion of capacity contribution of the second cycle discharge ( Figure 18 ) of samples R-HC, AHC-2, AHC-2 and CAHC; the long cycle ( Figure 19 ) of R-HC, AHC-2 and AHC-2; and the CV curves of R-HC, AHC-2, AHC-2 and CAHC (respectively Figure 20 , Figure 21 , Figure 22 and Figure 23 ). As Figure 16is the rate performance of current density under 30-1000 mA g -1 When the current density is 30, 50, 100, 200, 500 and 1000 mA g -1 , the reversible capacity of ACHC-2 is 302.59 mAh g -1 , 294.75 mAh g -1 , 269.06 mAh g -1 , 194.77 mAh g -1 , 87.81 mAh g -1 and 68.71 mAh g -1 , when the current density returns to 30 mA g -1 , ACHC-2 can still obtain a high capacity of 289.89 mAh g -1 , which is higher than R-HC, AHC-2 and CAHC. As Figure 17 is the galvanostatic discharge-charge curve. The ICE of R-HC, AHC-2, ACHC-2 and CAHC is 59.54%, 67.37%, 80.65% and 61.45%, respectively, indicating that the construction of C-(O)-O structure can effectively stabilize the precursor, inhibit the overflow of gas molecules and inhibit the formation of surface defects during high-temperature carbonization. In addition, this strategy also affects the sodium storage behavior of semicoke-based hard carbon. From Figure 18 the capacity contribution graph of the second circle discharge platform area and the slope area, it can be found that the platform capacity contribution of ACHC-2 increases from 38.71% to 59.72% compared with R-HC. This improvement is due to the increase of pseudo-graphite phase and closed pores, thereby promoting the insertion / extraction of sodium ions. Long cycle test (as Figure 19 ) was carried out at 30 mA g -1 , ACHC-2 electrode showed a reversible capacity of 294.0 mAh g -1 after 100 cycles, which is higher than R-HC (120.8 mAh g -1 ) and AHC-2 (236.7 mAh g -1 ). Surprisingly, ACHC-2 can reach a high capacity retention rate of 96.20% after 100 cycles, which verifies that the hard carbon ACHC-2 prepared by the precursor rich in C-(O)-O structure has excellent cycle stability. Figure 20 to Figure 23 are the CV curves of samples R-HC, AHC-2, ACHC-2 and CAHC at a scan rate of 0.2 mV / s, respectively. Figure 20 to Figure 23The curves exhibit typical characteristics of carbon materials. Due to the formation of the SEI film, irreversible peaks appeared near 0.5 V and 1.2 V in the first round of CV curves for all electrodes. Clearly, the irreversible peak of AHC-2 was more prominent than that of R-HC, which may be related to increased porosity and enhanced irreversible adsorption. However, the irreversible peak of AHC-2 was smaller than that of R-HC because further chemical cross-linking encapsulated the open pores into closed pores. From the second round of scanning, the CV curves showed similar shapes and high overlap, indicating good reversibility of the electrodes. Furthermore, a sharp peak appeared at around 0.1 V in the CV curves, and a broad hump appeared between 0.2 and 2.0 V, which correspond to Na, respectively. + Storage can be achieved through insertion / extraction, surface defects, or adsorption. The ACHC-2 electrode exhibits the largest peak area around 0.1V, indicating that closed pores and appropriate interlayer spacing are conducive to plateau capacity formation.

[0110] As can be seen from the above embodiments, this invention uses Hami high-ash semi-coke as a precursor and employs an alkali-oxygen oxidation synergistic chemical crosslinking strategy to construct a COC-regulated microcrystalline structure of semi-coke-based hard carbon. The alkali-oxygen oxidation treatment not only introduces oxygen-containing functional groups but also effectively reduces the ash content, providing the necessary space for subsequent chemical crosslinking reactions. In this case, polyols, polyhydroxy sugars, polyacids, and hydroxycarboxylic acids are used as crosslinking agents to react chemically with the oxygen-containing functional groups in the activated semi-coke, resulting in a precursor rich in COC structures. The COC structure can prevent the slippage of the graphite layer in the early stages of carbonization, further inhibiting the degree of graphitization of the material. Simultaneously, the crosslinking agents can effectively encapsulate and fill the open and large pores left by ash removal, transforming them into closed or micropores, thereby improving the initial coulombic efficiency and sodium storage capacity of the semi-coke.

[0111] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for producing an activated cross-linked semi-coke-based hard carbon material, characterized by, The method comprises the following steps: The semi-coke, inorganic strong base and water are mixed and heated to activate and modify the semi-coke, to obtain activated semi-coke, wherein the mass ratio of the inorganic strong base to the semi-coke is 1:(1-3), and the temperature of the activation and modification is 130-200℃; The activated semi-coke is subjected to chemical cross-linking reaction with a cross-linking agent to obtain activated cross-linked semi-coke, wherein the cross-linking agent comprises one or more of polyol, polyhydroxy sugar compound, polyacid and hydroxyl carboxylic acid compound; The activated cross-linked semi-coke is calcined in a protective gas atmosphere to obtain activated cross-linked semi-coke-based hard carbon material.

2. The production method according to claim 1, characterized by, The inorganic strong base comprises sodium hydroxide.

3. The production method according to claim 1, characterized by, The time of the activation and modification is 5-12h.

4. The method of claim 1, wherein, The chemical cross-linking reaction comprises the following steps: the activated semi-coke and the cross-linking agent are mixed and heated to perform chemical cross-linking reaction.

5. The production method according to claim 1 or 4, characterized by, The cross-linking agent comprises citric acid or sucrose, and the mass ratio of the cross-linking agent to the activated semi-coke is (1-5):

5.

6. The method of claim 1, wherein, The temperature of the calcination is 1000-1400℃, the holding time is 1-4h, and the temperature rising rate from room temperature to the calcination temperature is 1-5℃ / min.

7. Activated cross-linked semi-coke-based hard carbon material obtained by the preparation method in any one of claims 1-6.

8. Application of the activated cross-linked semi-coke-based hard carbon material in claim 7 as electrode material of ion battery.

9. Use according to claim 8, characterized in that, The ion battery is sodium ion battery.

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