Heteroatom modified hard carbon material as well as preparation method and application thereof

Abstract

The invention provides a heteroatom modified hard carbon material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The hetero atom modified hard carbon material provided by the invention comprises hard carbon and a hetero atom layer wrapping the surface of the hard carbon, wherein hetero atoms of the hetero atom layer sequentially comprise a sulfur source, a phosphorus-sulfur mixture and a phosphorus source from inside to outside; the phosphorus source is elemental phosphorus, and the sulfur source is elemental sulfur. The surface of the hard carbon is coated with the heteroatom layer, the heteroatom layer is modified at the interface bonding position of the hard carbon, sulfur can improve the bonding capacity of phosphorus and the hard carbon, phosphorus can modify the hard carbon and reduce the energy storage barrier of the hard carbon, and therefore when the heteroatom modified hard carbon material serves as the negative electrode material of the lithium ion battery, the energy storage efficiency of the lithium ion battery is improved. And the assembled lithium ion battery still has excellent electrochemical performance at-40 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a heteroatom modified hard carbon material and a preparation method and application thereof. Background Art

[0002] Electrochemical energy storage devices have a wide range of application needs in extreme low temperature environments. As the most widely used electrochemical energy storage device, lithium-ion batteries experience adverse phenomena such as rapid performance decay and even failure as the ambient temperature decreases, making it impossible to provide the required high energy density and high power density for electrical devices. At present, commercial lithium-ion batteries can only be charged and discharged in a low temperature environment of 0°C, and the stored and released energy decays significantly compared to room temperature. At the same time, they fail at lower ambient temperatures, which seriously hinders their application in the low temperature field. Therefore, it is imperative to develop low-temperature electrode materials and improve the low-temperature performance of lithium-ion batteries.

[0003] Hard carbon materials have faster charge transfer behavior than other commercial negative electrode materials for lithium-ion batteries, making them potentially capable of operating at lower temperatures. Heteroatom modification is an effective way to improve the electrical conductivity of carbon materials, allowing them to maintain high capacity in low-temperature environments, broadening the scope of application of lithium-ion batteries in extreme low-temperature environments. For example, the relevant prior art provides a sulfur-phosphorus co-doped hard carbon composite material and a preparation method thereof. The composite material is a core-shell structure, with an outer shell of nitrogen-containing amorphous carbon, an inner core of sulfur and phosphorus atoms, and the rest of hard carbon. Although this method can improve the electrochemical properties of electrode materials, the preparation method requires high-temperature and high-pressure reaction conditions and a freeze-drying post-processing process. The preparation conditions are relatively harsh, and the assembled lithium-ion battery does not have good electrochemical properties at low temperatures.

[0004] Therefore, there is an urgent need to provide a heteroatom-modified hard carbon material that can enable lithium-ion batteries to have excellent electrochemical properties at low temperatures. Summary of the invention

[0005] The object of the present invention is to provide a heteroatom-modified hard carbon material capable of making a lithium-ion battery have excellent electrochemical performance at low temperature, and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a heteroatom modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are, from inside to outside, a sulfur source, a phosphorus-sulfur mixture and a phosphorus source;

[0008] The phosphorus source is phosphorus alone, and the sulfur source is sulfur alone.

[0009] Preferably, the mass ratio of the hard carbon to the heteroatom is 100:0-10, and the mass of the heteroatom is not zero.

[0010] Preferably, the mass ratio of the sulfur source to the heteroatom is 1-15:100.

[0011] Preferably, the phosphorus source includes one or more of red phosphorus, yellow phosphorus, white phosphorus and black phosphorus.

[0012] Preferably, the sulfur source includes one or more of orthorhombic sulfur, monoclinic sulfur and elastic sulfur.

[0013] The present invention also provides a method for preparing the heteroatom-modified hard carbon material described in the above technical solution, comprising the following steps:

[0014] (1) mixing hard carbon, a phosphorus source and a sulfur source to obtain a heteroatom-modified hard carbon precursor;

[0015] (2) The heteroatom-modified hard carbon precursor obtained in step (1) is subjected to high-temperature calcination, low-temperature calcination and furnace cooling in sequence to obtain a heteroatom-modified hard carbon material.

[0016] Preferably, the calcination temperature in the step (2) is 450-600° C., and the holding time of the calcination is 3-5 hours.

[0017] Preferably, the calcination temperature of the low-temperature calcination in step (2) is 280-300° C., and the insulation time of the low-temperature calcination is 20-24 hours.

[0018] Preferably, the atmospheres for the mixing in step (1) and the high-temperature calcination, low-temperature calcination and furnace cooling in step (2) are independently inert atmospheres.

[0019] The present invention also provides the use of the heteroatom modified hard carbon material described in the above technical solution or the heteroatom modified hard carbon material prepared by the preparation method described in the above technical solution as a negative electrode material for a lithium ion battery.

[0020] The present invention provides a heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are, from the inside to the outside, a sulfur source, a phosphorus-sulfur mixture and a phosphorus source; the phosphorus source is a single phosphorus, and the sulfur source is a single sulfur. The present invention wraps a heteroatom layer on the surface of the hard carbon, and the heteroatom layer is modified at the interface of the hard carbon. Sulfur can improve the binding ability of phosphorus and hard carbon, and phosphorus can modify the hard carbon to reduce the storage energy barrier of the hard carbon, so that when the heteroatom-modified hard carbon material is used as the negative electrode material of the lithium ion battery, the assembled lithium ion battery can still have excellent electrochemical performance at a lower temperature. The results of the embodiment show that the lithium ion battery assembled with the heteroatom-modified hard carbon material provided by the present invention has a discharge specific capacity of 36.2% of the reversible specific capacity at room temperature at -40°C, while the lithium ion battery assembled with the hard carbon has a discharge specific capacity of only 5.8% of the reversible specific capacity at room temperature at -40°C. It can be seen that the heteroatom-modified hard carbon material provided by the present invention can significantly improve the electrochemical performance of lithium ion batteries at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the process of preparing heteroatom-modified hard carbon materials according to Examples 1 to 5 of the present invention;

[0022] Figure 2 The charge and discharge curve of a lithium-ion battery assembled with the heteroatom-modified hard carbon material prepared in Example 1 of the present invention at 25°C;

[0023] Figure 3 The charge and discharge curve of a lithium-ion battery assembled with the heteroatom-modified hard carbon material prepared in Example 1 of the present invention at -40°C;

[0024] Figure 4 The reversible specific capacity retention rate of the lithium ion batteries assembled in Examples 1 to 5 of the present invention and Comparative Example 1 at low temperature. DETAILED DESCRIPTION

[0025] The present invention provides a heteroatom modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are, from inside to outside, a sulfur source, a phosphorus-sulfur mixture and a phosphorus source;

[0026] The phosphorus source is phosphorus alone, and the sulfur source is sulfur alone.

[0027] The heteroatom-modified hard carbon material provided by the present invention includes hard carbon.

[0028] The present invention has no special limitation on the source of the hard carbon, and any commercial hard carbon available to those skilled in the art can be used. In an embodiment of the present invention, the particle size of the hard carbon is preferably 2 to 10 μm, and the source of the hard carbon can be Japan Kuraray Co., Ltd., China Bestec Co., Ltd., or China Zhongke Haina Co., Ltd.

[0029] The heteroatom modified hard carbon material provided by the present invention comprises a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms in the heteroatom layer are sulfur source, phosphorus-sulfur mixture and phosphorus source from inside to outside.

[0030] In the present invention, the mass ratio of the hard carbon to the heteroatom is preferably 100: 0 to 10, more preferably 100: 3 to 7. The present invention controls the mass of the hard carbon and the heteroatom within the above range, so that the heteroatom can fully wrap the hard carbon, and the formed heteroatom layer can reduce the storage energy barrier of the hard carbon after modifying the hard carbon.

[0031] The thickness of the heteroatom layer is not particularly limited in the present invention, as long as the mass ratio of hard carbon to heteroatoms is controlled within the above range.

[0032] In the present invention, the sulfur source is sulfur, and the sulfur source preferably includes one or more of orthorhombic sulfur, monoclinic sulfur and elastic sulfur, and more preferably orthorhombic sulfur or monoclinic sulfur. The present invention adopts the above sulfur source, which has a higher purity and is more conducive to improving the electrochemical performance of lithium ions assembled by heteroatom-modified hard carbon materials at low temperatures.

[0033] In the present invention, the phosphorus source is a single phosphorus substance, and the phosphorus source preferably includes one or more of red phosphorus, yellow phosphorus, white phosphorus and black phosphorus, and more preferably red phosphorus, yellow phosphorus, white phosphorus or black phosphorus. The present invention adopts the above phosphorus source, which has a higher purity and is more conducive to improving the electrochemical performance of lithium ions assembled by heteroatom-modified hard carbon materials at low temperatures.

[0034] In the present invention, the mass ratio of the sulfur source to the heteroatom is preferably 1 to 15: 100, more preferably 9 to 11: 100. The present invention controls the mass ratio of the sulfur source to the heteroatom within the above range, which is more conducive to improving the binding ability of the phosphorus source and the hard carbon.

[0035] The present invention wraps a heteroatom layer on the surface of hard carbon, and the heteroatom layer is modified at the interface of the hard carbon. Sulfur can improve the binding ability of phosphorus and hard carbon, and phosphorus can modify the hard carbon to reduce the storage energy barrier of the hard carbon. Therefore, when the heteroatom-modified hard carbon material is used as the negative electrode material of a lithium ion battery, the assembled lithium ion battery can still have excellent electrochemical performance at a relatively low temperature.

[0036] The present invention also provides a method for preparing the heteroatom-modified hard carbon material described in the above technical solution, comprising the following steps:

[0037] (1) mixing hard carbon, a phosphorus source and a sulfur source to obtain a heteroatom-modified hard carbon precursor;

[0038] (2) The heteroatom-modified hard carbon precursor obtained in step (1) is subjected to high-temperature calcination, low-temperature calcination and furnace cooling in sequence to obtain a heteroatom-modified hard carbon material.

[0039] The invention mixes hard carbon, a phosphorus source and a sulfur source to obtain a heteroatom-modified hard carbon precursor.

[0040] The present invention has no particular limitation on the method of mixing the hard carbon, phosphorus source and sulfur source, as long as the components can be mixed uniformly. In an embodiment of the present invention, the mixing method can be grinding and mixing in a mortar.

[0041] After obtaining the heteroatom-modified hard carbon precursor, the present invention sequentially performs high-temperature calcination, low-temperature calcination and furnace cooling on the heteroatom-modified hard carbon precursor to obtain the heteroatom-modified hard carbon material.

[0042] In the present invention, the calcination temperature of the high temperature calcination is preferably 450-600°C, more preferably 450-500°C; the holding time of the high temperature calcination is preferably 3-5h, more preferably 3-4h. The present invention can sublime the sulfur source and the phosphorus source through high temperature calcination.

[0043] In the present invention, the calcination temperature of the low-temperature calcination is preferably 280-300°C, more preferably 280-290°C; the holding time of the low-temperature calcination is preferably 20-24h, more preferably 20-22h. The present invention can make the sulfur source in the sublimated sulfur source and phosphorus source deposit on the hard carbon first through low-temperature calcination, thereby wrapping the hard carbon.

[0044] The present invention can gradually deposit the phosphorus source on the sulfur source by cooling with the furnace, and in the process of deposition, a phosphorus-sulfur mixture is first formed at the place where it contacts the sulfur source. This combination of phosphorus and sulfur source has a buffering effect and improves the binding force between phosphorus and hard carbon.

[0045] In the present invention, the atmospheres of the mixing, high temperature calcination, low temperature calcination and furnace cooling are independently preferably inert atmospheres, the gas of the inert atmosphere is preferably an inert gas, and the inert gas is preferably helium, neon or argon, more preferably argon. The present invention performs the above operations under an inert gas, which can prevent and reduce impurities in the heteroatom-modified hard carbon material.

[0046] The flow chart of the preparation method of the heteroatom modified hard carbon material provided by the present invention is preferably as follows Figure 1 As shown. Figure 1 It can be seen that the present invention mixes hard carbon, a phosphorus source and a sulfur source to obtain a heteroatom-modified hard carbon precursor, then first performs high-temperature calcination at 450°C, and then performs low-temperature calcination at 280°C, and then obtains a heteroatom-modified hard carbon material after cooling. The operation method provided by the present invention is simple and easy to control, and the storage energy barrier of hard carbon is reduced by modifying the heteroatom layer at the interface of hard carbon.

[0047] The present invention also provides the use of the heteroatom modified hard carbon material described in the above technical solution as a negative electrode material for a lithium ion battery.

[0048] The present invention does not specifically limit the method for using the heteroatom-modified hard carbon material as a negative electrode material for lithium-ion batteries. The lithium-ion battery can be assembled using a conventional method for using carbon materials as negative electrode materials for lithium-ion batteries.

[0049] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example 1

[0051] A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are sulfur, phosphorus, a mixture of sulfur, and phosphorus from the inside to the outside, respectively; wherein the mass ratio of hard carbon to heteroatoms is 100:7, and the mass ratio of sulfur to heteroatoms is 11:100;

[0052] The preparation method of the heteroatom modified hard carbon material is:

[0053] (1) In a glove box filled with argon, hard carbon, red phosphorus and orthorhombic sulfur are placed in a mortar and uniformly mixed to obtain a heteroatom-modified hard carbon precursor;

[0054] (2) In a glove box filled with argon, the heteroatom-modified hard carbon precursor obtained in step (1) is placed in a ceramic crucible, and the temperature is raised to 450° C. and kept for 3 h for high-temperature calcination, and then the temperature is lowered to 280° C. and kept for 20 h for low-temperature calcination, and then cooled in the furnace to obtain a heteroatom-modified hard carbon material.

[0055] Example 2

[0056] A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are sulfur, phosphorus, a mixture of sulfur, and phosphorus from the inside to the outside, respectively; wherein the mass ratio of hard carbon to heteroatoms is 100:6, and the mass ratio of sulfur to heteroatoms is 9:100;

[0057] The preparation method of the heteroatom modified hard carbon material is:

[0058] (1) In a glove box filled with argon, hard carbon, red phosphorus and orthorhombic sulfur are placed in a mortar and uniformly mixed to obtain a heteroatom-modified hard carbon precursor;

[0059] (2) In a glove box filled with argon, the heteroatom-modified hard carbon precursor obtained in step (1) is placed in a ceramic crucible, and the temperature is raised to 450° C. and kept for 3 h for high-temperature calcination, and then the temperature is lowered to 280° C. and kept for 20 h for low-temperature calcination, and then cooled in the furnace to obtain a heteroatom-modified hard carbon material.

[0060] Example 3

[0061] A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are, from inside to outside, sulfur, phosphorus, a mixture of sulfur, and phosphorus; wherein the mass ratio of hard carbon to heteroatoms is 100:3, and the mass ratio of sulfur to heteroatoms is 1:100;

[0062] The preparation method of the heteroatom modified hard carbon material is:

[0063] (1) In a glove box filled with argon, hard carbon, red phosphorus and orthorhombic sulfur are placed in a mortar and uniformly mixed to obtain a heteroatom-modified hard carbon precursor;

[0064] (2) In a glove box filled with argon, the heteroatom-modified hard carbon precursor obtained in step (1) is placed in a ceramic crucible, and the temperature is raised to 450° C. and kept for 3 h for high-temperature calcination, and then the temperature is lowered to 280° C. and kept for 20 h for low-temperature calcination, and then cooled in the furnace to obtain a heteroatom-modified hard carbon material.

[0065] Example 4

[0066] A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are sulfur, phosphorus, a mixture of sulfur, and phosphorus from the inside to the outside, respectively; wherein the mass ratio of hard carbon to heteroatoms is 100:7, and the mass ratio of sulfur to heteroatoms is 11:100;

[0067] The preparation method of the heteroatom modified hard carbon material is:

[0068] (1) In a glove box filled with argon, hard carbon, white phosphorus and orthorhombic sulfur are placed in a mortar and uniformly mixed to obtain a heteroatom-modified hard carbon precursor;

[0069] (2) In a glove box filled with argon, the heteroatom-modified hard carbon precursor obtained in step (1) is placed in a ceramic crucible, and the temperature is raised to 450° C. and kept for 3 h for high-temperature calcination, and then the temperature is lowered to 280° C. and kept for 20 h for low-temperature calcination, and then cooled in the furnace to obtain a heteroatom-modified hard carbon material.

[0070] Example 5

[0071] A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are sulfur, phosphorus, a mixture of sulfur, and phosphorus from the inside to the outside, respectively; wherein the mass ratio of hard carbon to heteroatoms is 100:7, and the mass ratio of sulfur to heteroatoms is 11:100;

[0072] The preparation method of the heteroatom modified hard carbon material is:

[0073] (1) In a glove box filled with argon, hard carbon, red phosphorus and monoclinic sulfur are placed in a mortar and uniformly mixed to obtain a heteroatom-modified hard carbon precursor;

[0074] (2) In a glove box filled with argon, the heteroatom-modified hard carbon precursor obtained in step (1) is placed in a ceramic crucible, and the temperature is raised to 450° C. and kept for 3 h for high-temperature calcination, and then the temperature is lowered to 280° C. and kept for 20 h for low-temperature calcination, and then cooled in the furnace to obtain a heteroatom-modified hard carbon material.

[0075] Comparative Example 1

[0076] Examples 1 to 4 used hard carbon.

[0077] Application Example 1

[0078] The heteroatom-modified hard carbon material prepared in Example 1 was used as an electrode, and a lithium-ion low-temperature electrolyte (ethyl difluoroacetate-based electrolyte, with an electrolyte addition amount of 100 μL) and a lithium metal electrode were assembled into a lithium-ion battery in an argon-filled glove box.

[0079] The electrochemical performance of the obtained lithium-ion battery was tested using a blue-electric test device at room temperature and -40°C; Figure 2 The charge and discharge curve of the battery assembled in Example 1 at 25°C; Figure 3 The charge and discharge curves of the battery assembled in Example 1 at -40°C.

[0080] In this application example 1, the discharge capacity of the lithium-ion battery assembled with the hard carbon electrode material of Example 1 at 25°C is 233 mAh g -1 The discharge capacity at -40°C is 100.87 mAh g -1 , reaching 43.0% of the reversible specific capacity at room temperature.

[0081] Application Example 2

[0082] The difference from Application Example 1 is that the heteroatom-modified hard carbon material prepared in Example 2 is used to assemble a lithium-ion battery, and the method of Application Example 1 is used to perform testing to obtain a charge and discharge curve.

[0083] In this application example 2, the discharge capacity of the lithium-ion battery assembled with the hard carbon electrode material of Example 2 at 25°C is 230.6 mAh g -1 The discharge capacity at -40°C is 71.4 mAh g -1 , reaching 31% of the reversible specific capacity at room temperature.

[0084] Application Example 3

[0085] The difference from Application Example 1 is that the heteroatom-modified hard carbon material prepared in Example 3 is used to assemble a lithium-ion battery, and the method of Application Example 1 is used to perform testing to obtain a charge and discharge curve.

[0086] In this application example 3, the discharge capacity of the lithium-ion battery assembled with the hard carbon electrode material of Example 3 at 25°C is 219.7 mAh g -1 The discharge capacity at -40°C is 39.8 mAh g -1 , reaching 18.12% of the reversible specific capacity at room temperature.

[0087] Application Example 4

[0088] The difference from Application Example 1 is that the heteroatom-modified hard carbon material prepared in Example 4 is used to assemble a lithium-ion battery, and the method of Application Example 1 is used to perform testing to obtain a charge and discharge curve.

[0089] In this application example 4, the discharge capacity of the lithium-ion battery assembled with the hard carbon electrode material of Example 4 at 25°C is 231.4 mAh g -1 The discharge capacity at -40°C is 80.9 mAh g -1 , reaching 35.0% of the reversible specific capacity at room temperature.

[0090] Application Example 5

[0091] The difference from Application Example 1 is that the heteroatom-modified hard carbon material prepared in Example 5 is used to assemble a lithium-ion battery, and the method of Application Example 1 is used to perform testing to obtain a charge and discharge curve.

[0092] In this application example 5, the discharge capacity of the lithium-ion battery assembled with the hard carbon electrode material of Example 5 at 25°C is 236.7 mAh g -1 The discharge capacity at -40°C is 85.7 mAh g -1, reaching 36.2% of the reversible specific capacity at room temperature.

[0093] Comparative application example 1

[0094] The difference from Application Example 1 is that the heteroatom-modified hard carbon material prepared in Comparative Example 1 is used to assemble a lithium-ion battery, and the method of Application Example 1 is used to perform testing to obtain a charge and discharge curve.

[0095] In this application example 5, the discharge capacity of the lithium-ion battery assembled with hard carbon in comparative example 1 at 25°C is 226.8 mAh g -1 The discharge capacity at -40°C is 13.3 mAh g -1 , reaching 5.8% of the reversible specific capacity at room temperature.

[0096] The reversible specific capacity retention rate of the lithium ion batteries assembled in Examples 1 to 5 of the present invention and Comparative Example 1 at low temperature is as follows: Figure 4 As shown. Figure 4 It can be seen that the lithium-ion battery assembled with the heteroatom-modified hard carbon material provided by the present invention still has excellent electrochemical performance at a temperature as low as -40°C. This is because the present invention modifies the hard carbon by using a heteroatom layer. This modification does not change the structure of the hard carbon, but reduces the storage energy barrier of the hard carbon by modifying the interface of the hard carbon, thereby being able to have excellent electrochemical performance at low temperatures. The method provided by the present invention is simple to operate and easy to control, which solves the problems of complex preparation methods and harsh conditions of conventional heteroatom-modified hard carbon materials.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A heteroatom-modified hard carbon material, comprising hard carbon and a heteroatom layer wrapped on the surface of the hard carbon, wherein the heteroatoms of the heteroatom layer are, from inside to outside, a sulfur source, a phosphorus-sulfur mixture, and a phosphorus source; The phosphorus source is phosphorus alone, and the sulfur source is sulfur alone.

2. The heteroatom-modified hard carbon material according to claim 1, characterized in that: The mass ratio of the hard carbon to the heteroatom is 100:0-10, and the mass of the heteroatom is not zero.

3. The heteroatom-modified hard carbon material according to claim 1, characterized in that: The mass ratio of the sulfur source to the heteroatom is 1 to 15:

100.

4. The heteroatom-modified hard carbon material according to claim 1, characterized in that: The phosphorus source includes one or more of red phosphorus, yellow phosphorus, white phosphorus and black phosphorus.

5. The heteroatom-modified hard carbon material according to claim 1, characterized in that: The sulfur source includes one or more of orthorhombic sulfur, monoclinic sulfur and elastic sulfur.

6. The method for preparing the heteroatom-modified hard carbon material according to any one of claims 1 to 5, comprising the following steps: (1) mixing hard carbon, a phosphorus source and a sulfur source to obtain a heteroatom-modified hard carbon precursor; (2) The heteroatom-modified hard carbon precursor obtained in step (1) is subjected to high-temperature calcination, low-temperature calcination and furnace cooling in sequence to obtain a heteroatom-modified hard carbon material.

7. The preparation method according to claim 6, characterized in that: The calcination temperature of the high temperature calcination in the step (2) is 450-600° C., and the heat preservation time of the high temperature calcination is 3-5 hours.

8. The preparation method according to claim 6, characterized in that: The calcination temperature of the low-temperature calcination in the step (2) is 280-300° C., and the insulation time of the low-temperature calcination is 20-24 hours.

9. The preparation method according to claim 6, characterized in that: The atmospheres for the mixing in step (1) and the high-temperature calcination, low-temperature calcination and furnace cooling in step (2) are independently inert atmospheres.

10. Use of the heteroatom-modified hard carbon material according to any one of claims 1 to 5 or the heteroatom-modified hard carbon material prepared by the preparation method according to any one of claims 6 to 9 as a negative electrode material for lithium-ion batteries.

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