A hard carbon, a preparation method thereof and application of the hard carbon in a sodium ion battery

Abstract

The application relates to hard carbon and a preparation method and application thereof in sodium ion batteries, and belongs to the technical field of sodium ion batteries. The hard carbon comprises oxygen-containing functional groups, nitrogen doping and ultramicropore tunnel structures, the content of C=O accounts for 60%-80% of the total oxygen content, the content of graphitic nitrogen accounts for 85%-95% of the total content, and the pore volume of the ultramicropore tunnel structure is 0.48cm 3 / g-0.93cm 3 / g. By regulating the C=O bond, the content of graphitic nitrogen and the pore volume of the ultramicropore tunnel structure in the hard carbon, the hard carbon has excellent electrochemical performance and is suitable for application in high-initial-efficiency and high-rate sodium ion battery negative materials. The hard carbon prepared by the above method comprises C=O functional groups, graphitic nitrogen functional groups and ultramicropore tunnel structures. The reversible sodium ion adsorption and desorption capacity of the hard carbon, the conductivity of the material and the diffusion of sodium ions can be improved, and the sodium storage performance of the sodium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of hard carbon and its preparation method and application in sodium ion battery, belong to sodium ion battery technical field, especially a kind of high initial efficiency, high rate hard carbon negative electrode material. BACKGROUND

[0002] To build clean, safe and efficient energy system, which promotes the development of secondary battery to a great extent.As an effective supplement to lithium ion battery, sodium ion battery is widely used in large-scale energy storage and low-speed power vehicles, etc., due to its advantages of easy availability of raw materials, low cost, low working potential, wide working temperature range and long service life.

[0003] Low-cost, structurally diverse, environmentally friendly hard carbon is the most widely used sodium battery negative material. Research has found that high specific surface area carbon materials combined with rich supermicro porous channel structure can improve the initial efficiency, capacity and rate performance of sodium battery. At the same time, heteroatom doping also provides additional active sites to further improve the capacity of carbon materials. However, high specific surface area carbon materials usually require pore-forming activators and templates in the preparation method, and subsequent treatment will use hydrochloric acid, hydrofluoric acid and other corrosive reagents, so the preparation process has the defects of complex process, cumbersome operation, environmental pollution, high cost and harsh equipment requirements. SUMMARY

[0004] The technical problem of the present application is to overcome the shortcomings of the prior art and provide a kind of hard carbon and its preparation method and application in sodium ion battery. By adjusting the content of C=O bond in oxygen-containing functional group, the content of graphite nitrogen configuration in nitrogen doping and supermicro porous tunnel structure, the hard carbon has higher initial coulombic efficiency and rate performance.

[0005] The technical solution of the present application is:

[0006] A kind of hard carbon, which includes oxygen-containing functional group, nitrogen element and pore structure in the hard carbon;

[0007] The oxygen-containing functional group contains C=O;

[0008] The mass percentage of oxygen element in the hard carbon is 0.5%-8%, calculated based on the total mass of the hard carbon being 100%;

[0009] The mass percentage content of C=O is 60%-80% in the hard carbon, calculated based on the mass of all oxygen elements in the hard carbon; the C=O functional group has reversible adsorption and desorption of sodium ions, so that the material has a higher reversible sodium storage capacity; by controlling the content of the C=O bond, the reversible adsorption and desorption of sodium ions is realized, on the basis of ensuring the adsorption and desorption capacity of the hard carbon, the high capacity and high initial efficiency of the hard carbon are realized, and the energy density of the sodium ion battery is effectively improved; the oxygen element can inhibit the transition graphitization of the carbon material and promote the hard carbon to form a stable carbon layer structure;

[0010] The mass percentage content of nitrogen elements in the hard carbon is 0.5%-3%, calculated based on the total mass of the hard carbon;

[0011] The nitrogen element contains graphite nitrogen, and the mass percentage content of the graphite nitrogen is 85%-95% in the hard carbon, calculated based on the mass of all nitrogen elements in the hard carbon; the graphite nitrogen can make the material have higher conductivity, thereby improving the rate performance of the material; the graphite nitrogen can balance the defects and conductivity, thereby ensuring the rate performance of the sodium ion battery; the graphite nitrogen can effectively improve the conductivity of the hard carbon;

[0012] The pore structure is a super-micropore tunnel structure, and the pore diameter is 0.4nm-0.6nm; the structure can make the hard carbon have a higher ion diffusion rate, can improve the rate performance of the material, in addition, the dense structure of the super-micropore tunnel can also effectively improve the compaction density of the hard carbon, and the volume of the pore structure is 0.48cm 3 / g-0.93cm 3 / g, which can provide more storage sites for the storage of sodium ions and improve the storage capacity of sodium ions;

[0013] The specific surface area of the hard carbon is 600m 2 / g-900m 2 / g, which can provide more storage sites for the storage of sodium ions and improve the storage capacity of sodium ions;

[0014] A preparation method of a hard carbon, the steps of the method comprising:

[0015] In the first step, the amine is uniformly mixed with the halogenated olefin, and a dehalogenation polymerization reaction is carried out to obtain a precursor material;

[0016] In the second step, the precursor material obtained in the first step is subjected to a pre-oxidation treatment;

[0017] In the third step, carbonization treatment and grinding treatment are carried out to obtain the hard carbon.

[0018] The first step, the amine is at least one of diethylamine, triethylamine, triallylamine, tri-n-butylamine, dibutylamine, triisopropylamine, triisobutylamine; the halogenated olefin is at least one of hexabromobenzene, hexachlorobenzene, hexachlorobutadiene, tetrachloroethylene; the molar ratio of amine to halogenated olefin is 0.1-8:1; the dehalogenation polymerization temperature is 100-200 DEG C, and the time is 2-6h;

[0019] The second step, the pre-oxidation treatment is carried out in an air atmosphere, the temperature is 200 DEG C-400 DEG C, the heating rate is 0.5 DEG C / min-5 DEG C / min, and the time is 0.5h-2h;

[0020] The third step, the carbonization treatment temperature is 1000 DEG C-1600 DEG C, the heating rate during carbonization treatment is 0.5 DEG C / min-5 DEG C / min, and the carbonization treatment time is 1h-3h;

[0021] The third step, the grinding treatment mode is airflow grinding, mechanical grinding, roller grinding or ball grinding.

[0022] The application of the hard carbon in a sodium ion battery, the obtained hard carbon is coated on a metal substrate such as an aluminum foil and dried to obtain an electrode sheet, and the obtained electrode sheet is used as a negative electrode of a sodium ion battery,

[0023] When the hard carbon is coated on a metal substrate such as an aluminum foil, the hard carbon needs to be made into a coating agent and then coated on the metal substrate such as an aluminum foil, the coating agent is obtained by mixing the hard carbon, conductive carbon black (super P) and a carboxymethyl cellulose sodium (CMC) aqueous solution according to a mass ratio of 8:1:1, and the concentration of the carboxymethyl cellulose sodium (CMC) aqueous solution is 1%.

[0024] Advantages

[0025] The application provides a high-initial-efficiency and high-rate hard carbon and application thereof, and relates to the field of battery technology negative electrodes. 3 3 ​ / g. By regulating the C=O bond in hard carbon, the content of graphite nitrogen and the pore volume of the super-micropore tunnel structure, the hard carbon has excellent electrochemical performance and is suitable for application in high initial efficiency and high rate sodium ion battery negative electrode materials. The hard carbon prepared by the above method includes C=O functional groups, graphite nitrogen functional groups and super-micropore tunnel structures. Thus, the reversible sodium ion adsorption and desorption capacity of the hard carbon, the material conductivity and the diffusion of sodium ions can be improved, and the sodium storage performance of the sodium ion battery can be improved. By controlling the ratio of dehalogenation polymerization, the reaction temperature and the reaction time, the dehalogenation polymerization effect can be better, and the controllability in the preparation process is higher, so that the hard carbon with high conductivity and sodium ion diffusion rate can be prepared. By using carbonization and grinding treatment on the precursor material, the carbonization process effect can be better, and the hard carbon can be obtained. The hard carbon has C=O functional groups, graphite nitrogen functional groups and super-micropore tunnel structures. Thus, the reversible sodium ion adsorption and desorption capacity of the hard carbon, the material conductivity and the diffusion of sodium ions can be improved, and the sodium storage performance of the sodium ion battery can be improved. The electrode material prepared according to the present application is hard carbon with C=O functional groups, graphite nitrogen functional groups and super-micropore tunnel structures, and has excellent electrochemical performance and is suitable for application in sodium ion batteries. The electrode sheet made of the hard carbon of the present application can obtain a sodium ion battery with high initial efficiency and good rate performance, and can realize high specific capacity reversible charge and discharge. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Nitrogen adsorption-desorption curve of hard carbon Y1 prepared in Example 1;

[0027] Figure 2 Pore size distribution diagram of hard carbon Y1 prepared in Example 1;

[0028] Figure 3 Nitrogen element high-resolution XPS diagram of hard carbon Y1 prepared in Example 1;

[0029] Figure 4 Oxygen element high-resolution XPS diagram of hard carbon Y1 prepared in Example 1;

[0030] Figure 5 Flowchart of the method of the present application. DETAILED DESCRIPTION

[0031] The present application will be described in detail below in combination with examples, comparative examples and drawings. It should be understood that these contents are only for illustration and explanation but not for limiting the present application.

[0032] In the following examples / comparative examples, a LAND CT2001A tester (Wuhan Blue Electric Co., Ltd.) was used to test the charge-discharge and cycle performance of the sodium ion battery.

[0033] The microstructure and composition of the hard carbon material are characterized in the embodiments of the present application, Figure 1 and Figure 2 A nitrogen adsorption / desorption curve pore size distribution diagram of hard carbon Y1 prepared according to Embodiment 1 of the present application.

[0034] In an embodiment of the present application, the microstructure of the hard carbon can include ultramicropore tunnel structure, the pore size of the ultramicropore tunnel structure in the material is 0.4 nm-0.6 nm, and the volume of the ultramicropore tunnel is 0.48 cm 3 / g-0.93 cm 3 / g. The embodiments of the present application are not limited thereto.

[0035] As an exemplary illustration, the volume of the pores in the above-mentioned material is 0.48 cm 3 / g-0.93 cm 3 / g. The value of the ratio of the values can be typically but not limited to, for example, 0.48 cm 3 / g, 0.58 cm 3 / g, 0.68 cm 3 / g, 0.78 cm 3 / g, 0.88 cm 3 / g, 0.93 cm 3 / g, and a number between any two of the above-mentioned numbers, all of which are desirable range values.

[0036] The microstructure and composition of the hard carbon material are characterized in the embodiments of the present application, Figure 3 and Figure 4 A high-resolution XPS diagram of nitrogen and oxygen elements of hard carbon Y1 prepared according to Embodiment 1 of the present application.

[0037] In an embodiment of the present application, the microstructure of the hard carbon can include oxygen-containing functional group structure, and the content of C=O bond in the oxygen-containing functional group in the material is 60%-80%. The embodiments of the present application are not limited thereto.

[0038] As an exemplary illustration, the content of C=O bond in the oxygen-containing functional group in the above-mentioned material is 60%-80%. The value of the ratio of the values can be typically but not limited to, for example, 60%, 65%, 70%, 75%, 80%, and a number between any two of the above-mentioned numbers, all of which are desirable range values.

[0039] In an embodiment of the present application, the microstructure of the hard carbon can include graphite nitrogen structure, and the content of the graphite nitrogen component in the material accounts for 85%-95% of the total nitrogen content. The embodiments of the present application are not limited thereto.

[0040] As an example, the nitrogen content of the graphite in the above-mentioned material is 85%-95%. The ratio of the values is typically but not limitatively, for example, 85%, 88%, 90%, 92%, 95%, and any number between any two of the above-mentioned values, all of which are acceptable range values.

[0041] In some embodiments of the present application, the oxygen content of the hard carbon is 0.5at%-8.0at%, and the nitrogen content of the hard carbon is 0.5at%-3.0at%.

[0042] In this way, the oxygen content and the nitrogen content are kept within the above-mentioned range, and the oxygen element can inhibit the transition graphitization of the carbon material and promote the hard carbon to form a stable carbon layer structure. The graphite nitrogen can effectively improve the conductivity of the hard carbon.

[0043] As an example, the oxygen content of the hard carbon can be measured by X-ray photoelectron spectroscopy in the embodiments of the present application, and the oxygen content of the hard carbon is 0.5at%-8at%. The ratio of the values is typically but not limitatively, for example, 0.5%, 2%, 3.5%, 6%, 8%, and any number between any two of the above-mentioned values, all of which are acceptable range values.

[0044] In addition, the nitrogen content of the hard carbon is measured to be 0.5%-3%. The ratio of the values is typically but not limitatively, for example, 0.5%, 1%, 1.5%, 2%, 3%, and any number between any two of the above-mentioned values.

[0045] The embodiments of the present application also provide a preparation method of the hard carbon, as shown in the following formula: Figure 5 The preparation method comprises the following steps:

[0046] S301, uniformly mixing the amine and the halogenated olefin, and performing a dehalogenation polymerization reaction to obtain a precursor material.

[0047] In some embodiments of the present application, the precursor can be prepared first. Specifically, the halogenated olefin is added to a 50mL reaction kettle, and amines with different substituent groups are added respectively, and ultrasonic is performed at room temperature to ensure that the amine and the halogenated olefin molecules are uniformly mixed. Then, the mixed liquid is subjected to a dehalogenation polymerization reaction, and after being cooled to room temperature, a precursor material is obtained. The reaction temperature of the dehalogenation polymerization reaction is 100°C-200°C, and the reaction time is 2h-6h.

[0048] As an example, the reaction temperature of the dehalogenation polymerization reaction is 100°C-200°C. Specifically, it can be 100°C, 200°C, and any value between 100°C and 200°C, such as 110°C, 120°C, 150°C, 180°C, etc. Here, they are not listed one by one.

[0049] The carbonization treatment time is 2h-6h. Specifically, it can be 2h, 6h, and any value between 2h-6h, such as 2.5h, 3h, 4h, 5h, etc. Not listed here.

[0050] In some embodiments of the present application, the amine can include primary, secondary, tertiary amine, which can have different branched chains. For example, the amine can include at least one of the group consisting of diethylamine, triethylamine, triallylamine, tri-n-butylamine, dibutylamine, triisopropylamine and triisobutylamine.

[0051] In some embodiments of the present application, the halogenated olefin can be a halogenated reaction monomer with a carbon-carbon double bond. For example, the reaction monomer can include at least one of the group consisting of hexabromobenzene, hexachlorobenzene, hexachlorobutadiene and tetrachloroethylene.

[0052] It should be noted that the above-mentioned amine and halogenated olefin are only exemplary. The embodiments of the present application do not limit the specific implementation of the amine and halogenated olefin.

[0053] In some embodiments of the present application, the molar ratio of amine and halogenated olefin is (0.1-8):1.

[0054] As an example, the molar ratio of the above-mentioned amine and halogenated olefin is (0.1-8):1. The value of this numerical ratio is typical but not limited, for example, it can be 0.1:1, 8:1 and any two values between the above-mentioned values, such as 0.5:1, 2:1, 5:1, 7:1, etc. Not listed here.

[0055] As can be seen from the above, the embodiments of the present application can control the molar ratio of amine and halogenated olefin, so that the content of amine and halogenated olefin is more appropriate, so that they can fully carry out dehalogenation polymerization reaction. Further, it can subsequently form a hard carbon negative electrode material with C=O functional group, graphite nitrogen functional group and super-microporous tunnel structure.

[0056] S302, in some embodiments of the present application, the preparation of the precursor can be pre-oxidized. Specifically, the precursor material can be pre-oxidized in air atmosphere, and its temperature is naturally cooled to room temperature. The pre-oxidation treatment temperature is 200-400℃, the pre-oxidation treatment temperature is 0.5-5℃ / min, and the pre-oxidation treatment time is 0.5-2h. Then, the pre-oxidized and cooled to room temperature of the precursor material is ground after the next step of heat treatment, to obtain a hard carbon negative electrode material. The precursor material is the above-mentioned oxidation treatment material, which is not described here.

[0057] As an example, the pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0058] The pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0059] The pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0060] S302, in some embodiments of the present application, the preparation of the precursor can be pre-oxidized. Specifically, the precursor material can be pre-oxidized in an air atmosphere, and its temperature is naturally cooled to room temperature. Among them, the pre-oxidation temperature is 200-400°C, the pre-oxidation temperature is 0.5-5°C / min, and the pre-oxidation time is 0.5-2h. Then, the pre-oxidized and cooled to room temperature of the precursor material can be grinded after the next heat treatment to obtain a hard carbon negative electrode material. Among them, the precursor material is the oxidation treatment material described above, which is not repeated here.

[0061] As an example, the pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0062] The pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0063] The pre-oxidation temperature is 200-400°C. Specifically, it can be 200°C, 400°C, and any value between 200-400°C, such as 250°C, 280°C, 300°C, 350°C, etc. Not all are listed here.

[0064] S303、In some embodiments of the present application, the precursor prepared by the pre-oxidation treatment can be carbonized at a high temperature first. Specifically, the pre-oxidation treated precursor material can be subjected to a carbonization treatment in an inert atmosphere, and then naturally cooled to room temperature. The carbonization treatment temperature is 1000-1600°C, the pre-oxidation treatment heating rate is 0.5-5°C / min, and the pre-oxidation treatment time is 1-3h. Then, the carbon material subjected to the carbonization treatment and cooled to room temperature can be ground after a subsequent heat treatment to obtain a hard carbon negative electrode material. The hard carbon negative electrode material is the hard carbon negative electrode material described above, which will not be repeated here.

[0065] As an example, the carbonization treatment temperature described above is 1000-1600°C. Specifically, it can be 1000°C, 1600°C, and any value between 1000°C and 1600°C, such as 1100°C, 1300°C, 1500°C, etc. Here, they are not listed one by one.

[0066] The pre-oxidation heating rate described above is 0.5-5°C / min. Specifically, it can be 0.5°C / min, 5°C / min, and any value between 0.5°C / min and 5°C / min, such as 0.8°C / min, 1.5°C / min, 3.0°C / min, 4.5°C / min, etc. Here, they are not listed one by one.

[0067] The pre-oxidation treatment time described above is 1-3h. Specifically, it can be 1h, 3h, and any value between 1h and 3h, such as 1.2h, 1.5h, 1.8h, 2.2h, 2.5h, 2.8h, etc. Here, they are not listed one by one.

[0068] It can be understood that the calculated value of the above numerical ratio can have a certain measurement and test system error in actual test operation, and the values within the system error range can be understood as the range defined by the embodiments of the present application.

[0069] In some embodiments of the present application, during the grinding process of the carbonized material, the grinding method can include air flow grinding, mechanical grinding, roller grinding, ball grinding, etc. The embodiments of the present application do not specifically limit the grinding method.

[0070] The hard carbon negative electrode material described above is introduced below through specific embodiments.

[0071] Embodiment 1

[0072] S1: Triethylamine and hexachlorobutadiene were added to a 50mL polytetrafluoroethylene reaction kettle and mixed, ultrasonically for 2h at 25°C to form a uniform and stable solution, and then the reaction kettle was placed in a stainless steel outer shell in a forced air drying oven at 160°C for 6h;

[0073] wherein triethylamine 24 ml, hexachlorobutadiene 4 ml (molar ratio 1.25:1);

[0074] S2: After the reaction is completed, the crude product is cooled to room temperature, and is stored in a vacuum seal;

[0075] S3: The crude product is heat-treated at 300℃ for 1.5h in a tube furnace under air atmosphere;

[0076] S4: The crude product is heat-treated at 1500℃ for 2h in a vacuum tube furnace under argon atmosphere at a heating rate of 0.5℃ / min, to obtain hard carbon Y1 having C=O functional group, graphitic nitrogen functional group and ultramicroporous tunnel structure.

[0077] Examples 2-6

[0078] Except that the heat treatment in step S4 is replaced by 1000℃, 1100℃, 1300℃, 1400℃ and 1600℃ respectively, other same as Example 1, Examples 2-6 are sequentially carried out; the obtained hard carbons are named as Y2, Y3, Y4, Y5 and Y6 in turn.

[0079] Comparative Examples 1-6

[0080] Except that the triethylamine in step S1 is replaced by diethylamine, triallylamine, tri-n-butylamine, dibutylamine, triisopropylamine and triisobutylamine respectively, other same as Example 1, Comparative Examples 1-6 are sequentially carried out; the obtained hard carbons are named as D1, D2, D3, D4, D5 and D6 in turn.

[0081] Comparative Examples 7-9

[0082] Except that the heating rate in step S4 is replaced by 1℃ / min, 3℃ / min and 5℃ / min respectively, other same as Example 1, Comparative Examples 7-9 are sequentially carried out; the obtained hard carbons are named as D7, D8 and D9 in turn.

[0083] The hard carbon negative electrode materials prepared in the above Examples 1-6 and Comparative Examples 1-9 and the corresponding surface area, pore size distribution and element composition are characterized and sodium ion batteries are tested for performance.

[0084] The characterization and test results are as follows:

[0085] The specific surface area, pore volume, pore size distribution and specific nitrogen / oxygen content of the samples Y1-Y6 obtained in Examples 1-6 and samples D1-D9 obtained in Comparative Examples 1-9 are characterized;

[0086] According to the method of Example 1, Figure 1The same test method, the nitrogen adsorption-desorption curves of Y1-Y6 were obtained, and the specific surface area and pore volume of each material were different, as shown in Table 1, and the relevant data of Y1 were also listed for comparison.

[0087] Table 1: Material structure and composition characterization data of each sample

[0088]

[0089]

[0090] In some embodiments of the present application, the technical characterization of specific surface area, pore volume and pore size distribution is shown in Table 1. It can be seen that the specific surface area of Y1 is as high as 896.4 m 2 / g, the material contains rich ultramicroporous structure, and the pore volume reaches 0.925 cm 3 / g. Through the data in Table 1, it can be found that the hard carbon prepared by changing the type of amine in Comparative Examples 1-6. It can be found that the reaction of primary amine and secondary amine with conjugated halogenated olefin can reduce the surface area and pore volume of the prepared hard carbon. Among different branched tertiary amines, triethylamine has the best ultramicropore pore size distribution, which can effectively improve the initial efficiency and rate of the material. By adjusting the heating rate, Comparative Examples 7-9 obtain hard carbon. It can be found that the heating rate has a serious effect on the surface area and pore size distribution, the surface area decreases and the pore size increases. More irreversible adsorption is produced, which reduces the initial efficiency and capacity of the material. By adjusting the heat treatment temperature, Examples 2-6 control the content of C=O bond in oxygen-containing functional groups, the content of graphite nitrogen configuration in nitrogen doping, and the ultramicroporous tunnel structure of hard carbon negative electrode material, so that the C=O bond content, the content of graphite nitrogen configuration in nitrogen doping, and the ultramicroporous tunnel structure parameters of the hard carbon negative electrode material are maintained within a certain range, which ensures that the hard carbon negative electrode material has higher electrical conductivity, faster sodium ion diffusion rate, and can promote the desolvation of sodium ions. Thus, the material has higher initial coulombic efficiency and rate performance.

[0091] Electrochemical performance test: In some embodiments of the present application, in order to characterize the effect of the material on improving the sodium electrochemical performance, the electrode prepared by using Y1 was subjected to charge-discharge test under different current densities in a sodium ion battery. When the discharge current density is 30 mA / g, the initial efficiency of Y1 can reach 90.9%. The calculated capacity of the sodium ion battery is 357.2 mAh / g, and the capacity of the battery still remains at 108.7 mAh / g under a current density of 2 A / g. This indicates that the material Y1 can be charged and discharged under large current density, showing excellent capacity and large rate charge-discharge performance.

[0092] Therefore, the hard carbon negative electrode with C=O functional groups, graphite nitrogen functional groups and ultramicropore tunnel structure obtained according to the application has excellent electrochemical performance, and can be used as a battery negative electrode material, especially an electrode material of a sodium ion battery, and has good application prospect and industrial production potential in the field of electrochemical energy storage.

[0093] Electrochemical performance characterization of samples Y1-Y6 obtained in Examples 1-6 and samples D1-D9 obtained in Comparative Examples 1-9: The battery electrodes obtained from Y1-Y6 and D1-D9 respectively were tested, and it was found through calculation that the first efficiency, reversible capacity and rate performance of each material in the sodium ion battery at a current density of 30 mA / g and 2 A / g were as shown in Table 2 below. For ease of comparison, Y1 in the sodium ion battery is also listed.

[0094] Table 2: Capacity values and first efficiency of each sample material in the sodium ion battery at different current densities

[0095] Sample Initial efficiency (%) Reversible capacity (mAh / g) Rate performance (mAh / g @ 2 A / g) Y1 90.9 357.2 108.7 Y2 80.1 314.9 101.8 Y3 87.1 321.1 94.3 Y4 87.9 312.8 101.2 Y5 85.8 324.4 95.3 D1 79.0 286.1 29.4 D2 76.3 298.4 45.7 D3 73.2 302.3 47.2 D4 71.9 301.6 46.4 D5 76.6 283.7 38.7 D6 67.8 189.3 54.2 D7 88.7 203.6 74.4 D8 47.2 291.7 64.7 D9 78.9 223.1 58.4

[0096] The application provides a method for preparing a hard carbon negative electrode material, which takes amine and halogenated olefin as raw materials, and controls the polymer structure based on dehalogenation polymerization reaction. By exploring the proportion of C=O bond and graphite nitrogen configuration in oxygen and nitrogen elements in the hard carbon, and the structure-activity relationship between specific surface area and pore volume and sodium storage performance, the optimal parameter range with excellent sodium storage performance is determined, the high electron transmission characteristics and fast ion diffusion rate of the hard carbon are ensured, and the overall sodium storage performance of the hard carbon is improved.

[0097] To sum up, the above is only a preferred embodiment of the application, and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A hard carbon, characterized by: The hard carbon comprises oxygen-containing functional groups, nitrogen elements and pore structures; The oxygen-containing functional groups comprise C=O; The mass percentage of oxygen elements in the hard carbon is 0.5%-8%, calculated based on the total mass of the hard carbon as 100%; The mass percentage of C=O is 60%-80%, calculated based on the mass of all oxygen elements in the hard carbon as 100%; The mass percentage of nitrogen elements in the hard carbon is 0.5%-3%, calculated based on the total mass of the hard carbon as 100%; The nitrogen elements comprise graphite nitrogen, and the mass percentage of graphite nitrogen is 85%-95%, calculated based on the mass of all nitrogen elements in the hard carbon as 100%; The pore structure is a super-micropore tunnel structure, the pore size is 0.4 nm-0.6 nm, the volume is 0.48 cm 3 / g -0.93 cm 3 / g. 2.The hard carbon according to claim 1, characterized in that: The specific surface area of the hard carbon is 600 m 2 / g-900 m 2 / g.

3. The method of claim 1, wherein the hard carbon is prepared by The steps of the method comprise: In the first step, triethylamine is mixed with a halogenated olefin to undergo a dehalogenation polymerization reaction to obtain a precursor material; In the second step, the precursor material obtained in the first step is subjected to pre-oxidation treatment; In the third step, the product after the pre-oxidation treatment in the second step is first subjected to carbonization treatment and then subjected to grinding treatment, the heating rate during the carbonization treatment is 0.5 ℃ / min, and the hard carbon is obtained. 4.The method for preparing the hard carbon according to claim 3, characterized in that: In the first step, the halogenated olefin is at least one of hexabromobenzene, hexachlorobenzene, hexachlorobutadiene and tetrachloroethylene; the molar ratio of the amine to the halogenated olefin is 0.1-8:1; the dehalogenation polymerization reaction temperature is 100-200 ℃, and the time is 2-6 h. 5.The method for preparing the hard carbon according to claim 3 or 4, characterized in that: In the second step, the pre-oxidation treatment is carried out in an air atmosphere, the temperature is 200 ℃-400 ℃, the heating rate is 0.5 ℃ / min-5 ℃ / min, and the time is 0.5 h-2 h. 6.The method for preparing the hard carbon according to claim 5, characterized in that: In the third step, the carbonization treatment temperature is 1000 ℃-1600 ℃, and the carbonization treatment time is 1 h-3 h. 7.The method for preparing the hard carbon according to claim 3, characterized in that: In the third step, the grinding treatment mode is airflow grinding, mechanical grinding, roller grinding or ball grinding. 8.Use of the hard carbon in a sodium ion battery, characterized in that: The hard carbon prepared by the method of claim 3 is made into a coating agent, which is coated on a metal substrate and dried to obtain an electrode sheet, and the electrode sheet is used as a negative electrode of a sodium ion battery. 9.Use of the hard carbon in a sodium ion battery according to claim 8, characterized in that: The coating agent is obtained by mixing the hard carbon, conductive carbon black (super P) and a carboxymethyl cellulose sodium (CMC) aqueous solution in a mass ratio of 8:1:1, and the concentration of the carboxymethyl cellulose sodium (CMC) aqueous solution is 1%. 10.Use of the hard carbon in a sodium ion battery according to claim 8 or 9, characterized in that: The metal substrate is an aluminum foil.

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