Hard carbon material with thin carbon coating as well as preparation method and application of hard carbon material

Abstract

The invention belongs to the technical field of sodium ion battery negative electrode materials, and particularly discloses a hard carbon material with a thin carbon coating as well as a preparation method and application of the hard carbon material. The preparation method realizes accurate regulation and control of a material structure through a multi-stage carbonization process, and comprises the following steps: firstly, carrying out pre-oxidation treatment on a coal-based precursor, and then carbonizing in an inert atmosphere to obtain a hard carbon matrix; then uniformly loading saccharides on the surface of the hard carbon by adopting a liquid phase coating technology, and realizing controllable deposition of a carbon precursor through an esterification reaction catalyzed by hydrochloric acid; and finally, carrying out secondary carbonization treatment to form the continuous compact carbon coating with the nano-scale thickness. The interface engineering strategy provided by the invention provides a new thought for the design of the high-performance sodium-ion battery negative electrode material, can be widely used as the negative electrode material in the sodium-ion battery with high-performance requirements, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials for sodium-ion batteries, and particularly to a hard carbon material with a thin carbon coating, its preparation method and application. Background Art

[0002] The statements in this section only provide background information related to the disclosure of this application and may not constitute prior art.

[0003] Since the first commercialization, lithium-ion batteries have been dominant in major energy storage systems. However, the scarcity of lithium resources has hindered further technological progress. Sodium-ion batteries are becoming a promising alternative due to their excellent safety performance and low cost. Among them, finding low-cost and high-performance electrode materials is very important for the commercial success of sodium-ion batteries. Conventionally, graphite, which is used as the anode of lithium-ion batteries, is restricted in its application in sodium-ion batteries because it is difficult to form a stable intercalation compound with Na + Therefore, there is an urgent need to deeply study the anode materials of sodium-ion batteries. Among them, hard carbon is particularly prominent due to its rich availability, simple synthesis method and low cost. However, hard carbon also faces some challenges, including low initial Coulomb efficiency and unsatisfactory rate performance, which seriously hinder its commercialization.

[0004] The types of precursor materials for preparing hard carbon have a significant impact on the performance of the prepared hard carbon. Finding a precursor that is both cost-effective and has a high carbon yield, and can also provide excellent electrochemical performance is of great significance for improving the performance of hard carbon and promoting its application. Currently, the precursors for synthesizing hard carbon include biomass, resin, coal and pitch. Although the hard carbon synthesized using biomass and resin materials as precursors has relatively high capacity, they respectively have defects such as low carbon yield, unstable raw material sources, high prices, and difficulty in expanding production scale, and are not suitable for promotion and application.

[0005] Coal-based materials have the characteristics of rich sources and low cost, and at the same time have a unique pore structure, which is an ideal raw material for preparing hard carbon. However, due to its large molecular size and highly cross-linked skeleton, it is still necessary to design and construct its structure to obtain an ideal hard carbon material. The prior art has given some methods for modifying its structure: for example, Chinese Patent CN118666266A uses bituminous coal as a precursor, and by using a molten salt eutectic with good chemical stability and abundant availability as a pore-forming agent and an activator, more pores are formed, and supplemented with high-temperature carbonization treatment, an amorphous carbon with an increased interlayer spacing and rich defects is successfully prepared. However, the hard carbon prepared by this method has a high pore density, and a large amount of solid electrolyte interphase will form on the surface, reducing the initial Coulomb efficiency; secondly, due to the complexity of the mixed molten salt system, it is easy to have uneven reactions during the reaction process, especially in large-scale preparation processes, and it is not suitable for large-scale industrial applications.

[0006] Chinese Patent CN118324120 A adopts another method. After pre-oxidizing anthracite powder, it is carbonized, and then heteroatom doping treatment is carried out to obtain the high-performance sodium-ion battery anode material based on anthracite, improving its sodium storage performance and initial Coulomb efficiency. However, in this method, to achieve heteroatom doping, additional dopants and complex preparation processes are required to ensure uniform doping of heteroatoms; this not only increases the preparation cost of the material but also improves the complexity and difficulty of the process, which is not conducive to large-scale production. Summary of the Invention

[0007] The purpose of the present invention is to provide a hard carbon material with a thin carbon coating, its preparation method and application, aiming at the problems existing in the current prior art. The coal-based material is pre-oxidized by gas phase and then carbonized to obtain a hard carbon material. Then, hydrochloric acid is added as a catalyst, and esterification reaction occurs through heating to graft chemically active sugar molecules onto the surface defects of the hard carbon, which can achieve a low-cost nano-scale carbon coating. The heating process not only facilitates the removal of water but also promotes the reaction kinetics. This novel design is the key to enabling the continuous progress of the esterification reaction. A large number of hydroxyl functional groups are contained in the sugar, which can not only effectively carry out the esterification reaction but also polymerize itself, thus easily forming a uniform carbon coating structure. And the prepared anode of the sodium-ion battery has excellent electrochemical performance, with its initial Coulomb efficiency reaching about 92.2%, and the initial charging capacity being 325.4 mAh g -1 。

[0008] The technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides a hard carbon material with a thin carbon coating, having a nano-scale carbon coating on the surface, and the nano-scale carbon coating is prepared by the esterification reaction and secondary carbonization of hard carbon and sugar molecules.

[0010] Preferably, the thickness of the nano-scale carbon coating is determined by the mass ratio of hard carbon and sugar molecules.

[0011] Preferably, the mass ratio of the sugar molecules to the hard carbon is 1 - 20:100.

[0012] Preferably, the thickness of the nano-scale carbon coating is 5 nm.

[0013] On the other hand, the present invention provides a hard carbon material with a thin carbon coating, including the following steps:

[0014] Step S1: The coal-based material is pre-oxidized and then carbonized under an inert atmosphere to obtain a hard carbon material;

[0015] Step S2: Dissolve the saccharides in deionized water, add hydrochloric acid and stir. Then add the hard carbon material in Step S1, stir vigorously, and heat to carry out an esterification reaction until completely dry;

[0016] Step S3: Carbonize the dried material under a protective atmosphere to obtain a hard carbon material with a nanoscale carbon coating.

[0017] According to a preferred embodiment, the coal-based material in Step S1 is one or more of coal tar pitch, anthracite, sub-bituminous coal, bituminous coal, and lignite.

[0018] According to a preferred embodiment, in Step S2, the saccharides are one or more of glucose, fructose, sucrose, lactose, and maltose. The mass ratio of the saccharides to the hard carbon material is 1-20:100, the concentration of hydrochloric acid is 1-5 mol / L, and the temperature of the esterification reaction is 60-120 °C.

[0019] According to a preferred embodiment, the protective atmosphere in Step S3 is one of nitrogen or argon. The carbonization temperature is 800-1300 °C, the heat preservation time is 1-4 h, the heating rate is 1-5 °C / min, and the cooling method is natural cooling.

[0020] According to a preferred embodiment, Step S1 further includes the following sub-steps:

[0021] Step S1.1: Crush and screen the coal-based material, and then remove impurities through pickling with hydrochloric acid and hydrofluoric acid to obtain a coal-based material powder;

[0022] Step S1.2: Place the coal-based material powder in Step S1.1 under flowing air for pre-oxidation treatment to obtain oxidized coal;

[0023] Step S1.3: Carry out high-temperature carbonization of the oxidized coal pre-oxidized in Step S1.2 under a protective atmosphere to obtain a hard carbon material.

[0024] According to a preferred embodiment, in Step S1.1: the screening particle size is 300 mesh; the concentration of hydrochloric acid is 1-10 mol / L, and the pickling time is 12 h; the concentration of hydrofluoric acid is 1-10 wt%, and the pickling time is 12 h.

[0025] According to a preferred embodiment, in Step S1.2: in an air atmosphere, the air flow rate is 200 ml / min, the pre-oxidation temperature is 260-330 °C, and the heat preservation time is 3-12 h.

[0026] According to a preferred embodiment, the inert atmosphere in Step S1.3 is one of nitrogen or argon. The carbonization temperature is 1000-1500 °C, the carbonization time is 2-5 h, and the heating rate is 1-5 °C / min.

[0027] On the other hand, the present invention provides an application of a hard carbon material with a thin carbon coating in the preparation of a negative electrode for a sodium-ion battery, and the hard carbon material with a thin carbon coating is as described above or prepared by the preparation method as described above.

[0028] On the other hand, the present invention provides a sodium-ion battery, which has a positive electrode and a negative electrode, and the negative electrode is made of the hard carbon material with a thin carbon coating as described above or the hard carbon material with a thin carbon coating prepared by the preparation method as described above.

[0029] Preferably, the first Coulombic efficiency of the sodium-ion battery reaches 92.2%, and the first charging capacity is 325.4 mAh g -1 .

[0030] On the other hand, the present invention provides a negative electrode sheet for a sodium-ion battery, which includes a conductive agent, a binder, a flexible binder, and the hard carbon material with a thin carbon coating as described above or the hard carbon material prepared by the preparation method as described above.

[0031] On the other hand, the present invention provides a sodium-ion battery, which has a positive electrode and a negative electrode, and the negative electrode sheet is prepared from the hard carbon material with a thin carbon coating as described above or the hard carbon material with a thin carbon coating prepared by the preparation method as described above.

[0032] Compared with the existing technology, the beneficial effects of the present invention are as follows:

[0033] 1. A hard carbon material with a thin carbon coating forms chemical bonds through the reaction between sugars and surface functional groups of hard carbon to coat hard carbon in solution; after the sugar molecules are carbonized, a thin carbon layer with fewer defects is formed on the surface of hard carbon, reducing the specific surface area, adjusting the pore structure, and improving the sodium ion transport rate;

[0034] 2. A preparation method of a hard carbon material with a thin carbon coating. Compared with biomass and resin materials, the required raw material, coal-based material, has the characteristics of low raw material cost, high carbon yield, wide source, and stable raw material supply; compared with the method of heteroatom doping, the modified raw material cost is low and the source is wide; the preparation method and process requirements are simple; there is no need to consider the uniformity of atom doping, which is more conducive to wide promotion and application, saving raw material cost, equipment cost, and economic cost;

[0035] 2. An application of a hard carbon material with a thin carbon coating. The coal-based hard carbon material prepared by the present invention has excellent sodium storage performance, and when used as the negative electrode of a sodium-ion battery and assembled into a button-type half-cell, it has a first Coulombic efficiency of 92.2% and a reversible specific capacity of 325.4 mAh g -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 XRD pattern of the hard carbon anode material prepared in Example 1;

[0037] Figure 2 SEM image of the hard carbon anode material prepared in Example 1;

[0038] Figure 3 TEM image of the hard carbon anode material prepared in Example 1. Detailed implementation manners

[0039] The specific examples enumerated in the present invention are only used as examples of the present invention, and the present invention is not limited to the specific examples described below. For those skilled in the art, any equivalent modifications and substitutions made to the examples described below are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should all be covered within the scope of the present invention. For those conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. All reagents or instruments not indicated by the manufacturer can be obtained through commercially available conventional products. In order to better illustrate the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can be implemented without some specific details. In other embodiments, methods, means, equipment, and steps well-known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art. Without special instructions, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0041] The features and properties of the present invention will be further described in detail below in conjunction with the examples.

[0042] Example 1

[0043] The embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0044] S1.1: Take 30 g of lignite for ball milling and crushing, and pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0045] S1.2: Place the lignite powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it up to 300 °C at a heating rate of 5 °C / min, and after heat preservation treatment for 3 h, obtain oxidized coal;

[0046] S1.3: Carry out high-temperature carbonization on the oxidized coal in S1.2, heat it up to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0047] S2: Dissolve 0.5 g of glucose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until it is completely dried.

[0048] S3: Under an argon atmosphere, carbonize the material dried in S2, heat it up to 1000 °C at a heating rate of 2 °C / min, keep it warm for 2 h, and the cooling method is natural cooling to obtain a hard carbon material with a thin carbon coating.

[0049] Example 2

[0050] The embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0051] S1.1: Take 30 g of lignite for ball milling and crushing treatment, and pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0052] S1.2: Place the lignite powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it up to 300 °C at a heating rate of 5 °C / min, and after heat preservation treatment for 3 h, obtain oxidized coal;

[0053] S1.3: Carry out high-temperature carbonization on the oxidized coal in S1.2, heat it up to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0054] S2: Dissolve 1 g of glucose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until it is completely dried.

[0055] S3: Under an argon atmosphere, carbonize the material dried in S2 at a heating rate of 2 °C / min up to 1000 °C, hold for 2 h, and cool it in a natural cooling manner to obtain a hard carbon material with a thin carbon coating.

[0056] Example 3

[0057] An embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0058] S1.1: Take 30 g of lignite and perform ball milling and crushing. Pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0059] S1.2: Place the lignite powder obtained in step S1.1 in a tubular furnace, introduce air at a flow rate of 200 ml / min, heat it at a heating rate of 5 °C / min up to 300 °C, hold for 3 h to obtain oxidized coal;

[0060] S1.3: Perform high-temperature carbonization on the oxidized coal in S1.2 at a heating rate of 5 °C / min up to 1200 °C, hold for 3 h, and cool it in a natural cooling manner to obtain a hard carbon material.

[0061] S2: Dissolve 2 g of glucose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until completely dry.

[0062] S3: Under an argon atmosphere, carbonize the material dried in S2 at a heating rate of 2 °C / min up to 1000 °C, hold for 2 h, and cool it in a natural cooling manner to obtain a hard carbon material with a thin carbon coating.

[0063] Example 4

[0064] An embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0065] S1.1: Take 30 g of lignite and perform ball milling and crushing. Pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0066] S1.2: Place the lignite powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it up to 300 °C at a heating rate of 5 °C / min, and after heat preservation treatment for 3 h, obtain oxidized coal;

[0067] S1.3: Perform high-temperature carbonization on the oxidized coal in S1.2, heat it up to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0068] S2: Dissolve 0.1 g of glucose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until it is completely dried.

[0069] S3: Under an argon atmosphere, carbonize the material dried in S2, heat it up to 1000 °C at a heating rate of 2 °C / min, keep it warm for 2 h, and the cooling method is natural cooling to obtain a hard carbon material with a thin carbon coating.

[0070] Example 5

[0071] The embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0072] S1.1: Take 30 g of coal tar pitch for ball milling and crushing treatment, and pass the crushed coal tar pitch powder through a 300-mesh sieve; perform pickling on the coal tar pitch powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to perform pickling on the coal tar pitch powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0073] S1.2: Place the coal tar pitch powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it up to 300 °C at a heating rate of 5 °C / min, and after heat preservation treatment for 3 h, obtain oxidized pitch;

[0074] S1.3: Perform high-temperature carbonization on the oxidized pitch in S1.2, heat it up to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0075] S2: Dissolve 0.5 g of glucose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until it is completely dried.

[0076] S3: Under an argon atmosphere, carbonize the material dried in S2 at a heating rate of 2 °C / min to 1000 °C, hold for 2 h, and cool naturally to obtain a hard carbon material with a thin carbon coating.

[0077] Example 6

[0078] An embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0079] S1.1: Take 30 g of lignite for ball milling and crushing, and pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0080] S1.2: Place the lignite powder obtained in step S1.1 in a tube furnace, introduce air at a flow rate of 200 ml / min, heat to 300 °C at a heating rate of 5 °C / min, hold for 3 h to obtain oxidized coal;

[0081] S1.3: Subject the oxidized coal in S1.2 to high-temperature carbonization, heat to 1200 °C at a heating rate of 5 °C / min, hold for 3 h, and cool naturally to obtain a hard carbon material.

[0082] S2: Dissolve 0.5 g of sucrose in deionized water, add 20 mL of 1 mol / L hydrochloric acid, stir for about 30 min, and then add 10 g of the hard carbon powder obtained in step S1.3 to the glucose aqueous solution. While stirring vigorously, esterify the suspension at 80 °C and continue heating until completely dry.

[0083] S3: Under an argon atmosphere, carbonize the material dried in S2 at a heating rate of 2 °C / min to 1000 °C, hold for 2 h, and cool naturally to obtain a hard carbon material with a thin carbon coating.

[0084] Example 7

[0085] An embodiment of the present invention provides a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0086] S1.1: Take 30 g of lignite for ball milling and crushing, and pass the crushed lignite powder through a 300-mesh sieve; pickle the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the lignite powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0087] S1.2: Place the lignite powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it to 300 °C at a heating rate of 5 °C / min, and obtain oxidized coal after heat preservation treatment for 3 h;

[0088] S1.3: Perform high-temperature carbonization on the oxidized coal in S1.2, heat it to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0089] Example 8

[0090] The embodiments of the present invention provide a hard carbon material with a thin carbon coating and a preparation method thereof, including the following steps:

[0091] S1.1: Take 30 g of coal tar pitch for ball milling and crushing treatment, and pass the crushed coal tar pitch powder through a 300-mesh sieve; pickling the lignite powder with a 5 mol / L hydrochloric acid solution at 60 °C for 12 h to remove metal impurities; after suction filtration and washing, continue to pickle the coal tar pitch powder with 10 wt% hydrofluoric acid at room temperature for 12 h to remove silicon-containing impurities.

[0092] S1.2: Place the coal tar pitch powder obtained in step S1.1 into a tubular furnace, introduce air with a flow rate of 200 ml / min, heat it to 300 °C at a heating rate of 5 °C / min, and obtain oxidized pitch after heat preservation treatment for 3 h;

[0093] S1.3: Perform high-temperature carbonization on the oxidized pitch in S1.2, heat it to 1200 °C at a heating rate of 5 °C / min, keep it warm for 3 h, and the cooling method is natural cooling to obtain a hard carbon material.

[0094] Electrochemical performance test:

[0095] Preparation of the negative electrode plate of the sodium-ion battery: According to the mass ratio of 93.5%: 2%: 1.5%: 3%, weigh the hard carbon material, conductive carbon black, carboxymethyl cellulose, and styrene-butadiene rubber in all the above embodiments, add an appropriate amount of deionized water, stir until it becomes a uniform paste, and use a 100-μm scraper to uniformly coat it on the surface of the aluminum foil. Dry it in a blast drying oven at 70 °C for 12 h, cut the aluminum foil with the active material into round negative electrode plates, and immediately transfer them to a glove box for standby.

[0096] Assembly of the sodium-ion battery: The assembly of the battery is carried out in a glove box filled with an argon atmosphere. Use the prepared hard carbon material electrode plate as the negative electrode, 1.0 mol / L NaPF6 / EC:DMC (1:1) (V:V) commercial electrolyte as the electrolyte, Na metal sheet as the counter electrode, and glass fiber GF / D as the separator to assemble a CR2032 button battery.

[0097] Electrochemical performance tests were carried out. Specifically, in the voltage range of 0.001 - 2.5 V and at a current density of 0.1 C (30 mA g -1 ), the specific discharge capacity (mAh g -1 ) and the specific charge capacity (mAh g -1 ) of the first discharge were measured, and the first Coulombic efficiency was calculated.

[0098] The parameter comparisons of the above different embodiments are summarized as follows (Table 1):

[0099] Table 1. Parameter comparisons of different embodiments

[0100]

[0101] Examples 1, 2, 3, and 4 explored the effects of different ratios of hard carbon to glucose on the performance of lignite-based hard carbon with a thin carbon coating. An appropriate coating thickness is also crucial. An overly thick glucose coating will reduce the structural stability of the coating, resulting in a decrease in material performance; the hard carbon material provided in Example 1 has the best performance. In Example 5, lignite was replaced with coal tar pitch to explore the electrochemical performance of coal tar pitch-based hard carbon under this method. In Example 6, glucose was replaced with sucrose to explore the performance of sucrose as a coating carbon source. After replacement, its first Coulombic efficiency is higher than that without a carbon coating. In Example 7, the electrochemical performance of lignite-based hard carbon without a thin carbon coating was prepared. Compared with Examples 1 - 4 and 6, its electrochemical performance is significantly lower. In Example 8, the electrochemical performance of bituminous coal-based hard carbon without a thin carbon coating was prepared. Compared with Example 5, the electrochemical performance is significantly lower.

[0102] The XRD pattern of the hard carbon negative electrode material prepared in the optimal Example 1 is as Figure 1 shown. Figure 2 This is the SEM image of the hard carbon negative electrode material prepared in Example 1. Figure 3 This is the TEM image of the hard carbon negative electrode material prepared in Example 1. It can be seen from the figure that there is a nanoscale carbon coating, and the thickness of the nanoscale carbon coating is about 5 nm.

[0103] The above-described embodiments only represent the specific implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application.

Claims

1. A hard carbon material with a thin carbon coating, characterized in that, The surface has a nanoscale carbon coating, and the nanoscale carbon coating is prepared by esterification reaction and secondary carbonization of hard carbon and sugar molecules.

2. A method for preparing a hard carbon material with a thin carbon coating, characterized in that, It includes the following steps: Step S1: The coal-based material is pre-oxidized and then carbonized in an inert atmosphere to obtain a hard carbon material; Step S2: Dissolve the sugar in deionized water, add hydrochloric acid and stir, then add the hard carbon material in Step S1, stir vigorously, and heat to carry out the esterification reaction until completely dry; Step S3: Carbonize the dried material in a protective atmosphere to obtain a hard carbon material with a nanoscale carbon coating.

3. The preparation method of a hard carbon material with a thin carbon coating according to claim 2, characterized in that, The coal-based material in Step S1 is one or more of coal tar pitch, anthracite, sub-bituminous coal, bituminous coal, and lignite.

4. The preparation method of a hard carbon material with a thin carbon coating according to claim 2, characterized in that, In Step S2, the sugar is one or more of glucose, fructose, sucrose, lactose, and maltose. The mass ratio of the sugar to the hard carbon material is 1-20:100, and the temperature of the esterification reaction is 60-120 °C.

5. The preparation method of a hard carbon material with a thin carbon coating according to claim 2, characterized in that, In Step S3, the carbonization temperature is 800-1300 °C, the heat preservation time is 1-4 h, the heating rate is 1-5 °C / min, and the cooling method is natural cooling.

6. The preparation method of a hard carbon material with a thin carbon coating according to claim 2, characterized in that, Step S1 further includes the following sub-steps: Step S1.1: Crush and screen the coal-based material, and then remove impurities by pickling with hydrochloric acid and hydrofluoric acid to obtain a coal-based material powder; Step S1.2: Place the coal-based material powder in Step S1.1 under flowing air for pre-oxidation treatment to obtain oxidized coal; Step S1.3: Carry out high-temperature carbonization of the oxidized coal pre-oxidized in Step S1.2 in a protective atmosphere to obtain a hard carbon material.

7. The preparation method of a hard carbon material with a thin carbon coating according to claim 6, characterized in that, In Step S1.1: The screening particle size is 300 mesh; the concentration of the hydrochloric acid is 1-10 mol / L, and the pickling time is 12 h; the concentration of the hydrofluoric acid is 1-10 wt%, and the pickling time is 12 h; in Step S1.3: the inert atmosphere is one of nitrogen or argon, the carbonization temperature is 1000-1500 °C, the carbonization time is 2-5 h, and the heating rate is 1-5 °C / min.

8. Application of a hard carbon material with a thin carbon coating in preparing an anode of a sodium-ion battery, characterized in that, The hard carbon material with a thin carbon coating is as described in Claim 1 or is prepared by the preparation method described in any one of Claims 2-7.

9. A negative electrode sheet of a sodium ion battery, characterized in that, It includes a conductive agent, a binder, a flexible binder, and the hard carbon material with a thin carbon coating as described in Claim 1 or a hard carbon material prepared by the preparation method described in any one of Claims 2-7.

10. A sodium-ion battery, characterized in that, It has a positive electrode and a negative electrode, and the electrode sheet of the negative electrode is prepared from the hard carbon material with a thin carbon coating as described in Claim 1 or a hard carbon material with a thin carbon coating prepared by the preparation method described in any one of Claims 2-7.

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