A long-flame coal-based hard carbon anode material, preparation method and sodium-ion battery

Abstract

The present invention provides a long-flame coal-based hard carbon anode material, a preparation method and a sodium-ion battery, belonging to the technical field of battery materials. After mixing long-flame coal and a biomass precursor, low-temperature pretreatment, low-temperature carbonization treatment and high-temperature carbonization treatment are carried out in sequence. The biomass precursor contains rich oxygen and hydrogen elements, and a large amount of oxygen and hydrogen free radicals will be generated in the low-temperature pretreatment stage. The oxygen and hydrogen free radicals will attack the aromatic structure of the coal itself, which is beneficial to promoting the transformation of the molecular structure of the coal from ordered to disordered. During the carbonization process, the long-flame coal and the biomass precursor interact and interpenetrate with each other to form a richer and more stable pore structure and a larger specific surface area, providing more channels and active sites for the insertion and extraction of sodium ions. Moreover, the raw material costs of long-flame coal and the biomass precursor are low and the reserves are abundant. The preparation method has a simple process, realizing the low-cost preparation of the long-flame coal-based hard carbon anode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a long-flame coal-based hard carbon anode material, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] With the continuous growth of energy demand and the pursuit of sustainable development, sodium-ion batteries have received extensive attention as a potential energy storage technology. Sodium-ion batteries have the advantages of low cost, safety, environmental protection, excellent low-temperature performance, etc., and their working principle is similar to that of lithium-ion batteries, which can adapt to the lithium-ion battery production process route and have the conditions for rapid industrialization. The anode material is a key component of sodium-ion batteries, and its performance directly affects the overall performance of sodium-ion batteries. However, since sodium ions cannot achieve large-capacity insertion and extraction in graphite anodes, the key to the commercialization of sodium-ion batteries lies in the development of high-capacity anode materials.

[0003] In sodium-ion batteries, hard carbon materials can achieve high-capacity insertion and extraction of sodium ions due to their long-range disordered and short-range ordered structure, and are currently the most promising anode materials for commercial sodium-ion batteries. Nowadays, the preparation process of hard carbon anode materials mostly relies on processes such as oxidation and activation to create pores to prepare coal-based hard carbon, which has problems such as high preparation cost and complex process.

[0004] In view of the above problems, there is an urgent need to design a preparation method for hard carbon anode materials with simple process and low cost. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention aims to provide a long-flame coal-based hard carbon anode material, a preparation method thereof, and a sodium-ion battery with a simple preparation process, high specific capacity, and high first Coulomb efficiency.

[0006] One of the purposes of the present invention is to provide a preparation method for a long-flame coal-based hard carbon anode material, and the preparation method includes:

[0007] First, mix long-flame coal and a biomass precursor to obtain a mixed material;

[0008] Then, perform low-temperature pretreatment and low-temperature carbonization treatment on the mixed material in sequence to obtain a low-carbon material;

[0009] Then, perform high-temperature carbonization treatment on the low-carbon material to obtain the long-flame coal-based hard carbon anode material;

[0010] Wherein, both the long-flame coal and the biomass precursor are in powder form.

[0011] Preferably, the biomass precursor includes one or more of bamboo, coconut shell, fruit wood, rice, lignin, cellulose, distillers' grains, or straw.

[0012] Preferably, the mass ratio of the long-flame coal to the biomass precursor is (5 - 10):(1 - 5).

[0013] Preferably, the long-flame coal and the biomass precursor are stirred and mixed at a rotation speed of 60 - 200 rpm, and the mixing time is 0.5 - 3 h.

[0014] Preferably, the long-flame coal and the biomass precursor are pre-crushed respectively first, and then mixed.

[0015] Preferably, the particle size D50 of the long-flame coal and the biomass precursor after pre-crushing treatment is independently 10 - 50 μm.

[0016] Preferably, the temperature of the low-temperature pretreatment is 250 - 400 °C, and the heat preservation time of the low-temperature pretreatment is 0.5 - 3 h.

[0017] Preferably, the temperature of the low-temperature carbonization treatment is 550 - 700 °C, and the heat preservation time of the low-temperature carbonization treatment is 1 - 3 h.

[0018] Preferably, the temperature of the high-temperature carbonization treatment is 1000 - 1400 °C, and the heat preservation time of the high-temperature carbonization treatment is 2 - 5 h.

[0019] The second object of the present invention is to provide a long-flame coal-based hard carbon negative electrode material, and the long-flame coal-based hard carbon negative electrode material is prepared by using the preparation method as described above.

[0020] The third object of the present invention is to provide a sodium ion battery, and the negative electrode of the sodium ion battery includes the long-flame coal-based hard carbon negative electrode material as described above.

[0021] The beneficial effects of the present invention include:

[0022] In the present invention, the long-flame coal and the biomass precursor are mixed and then subjected to low-temperature pretreatment, low-temperature carbonization treatment and high-temperature carbonization treatment in sequence. The biomass precursor contains rich oxygen and hydrogen elements, and a large number of oxygen and hydrogen free radicals will be generated in the low-temperature pretreatment stage. The oxygen and hydrogen free radicals will attack the aromatic structure of the coal itself, which is beneficial to promoting the transformation of the molecular structure of the coal from order to disorder. During the carbonization process, the long-flame coal and the biomass precursor interact and interpenetrate with each other to form a richer and more stable pore structure and a larger specific surface area, providing more channels and active sites for the insertion and extraction of sodium ions. Moreover, the raw material costs of the long-flame coal and the biomass precursor are low and the reserves are abundant, and the preparation method has a simple process, realizing the low-cost preparation of the long-flame coal-based hard carbon negative electrode material. The battery prepared based on this has a high specific capacity (up to 290 mAh / g at most) and a high first Coulomb efficiency (up to 92% at most). Description of the Drawings

[0023] Figure 1 Process flow chart for preparing the long-flame coal-based hard carbon anode material provided for Example 1;

[0024] Figure 2 SEM image of the long-flame coal-based hard carbon anode material provided for Example 1. Detailed implementation manners

[0025] In the following description, certain specific details are included to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments can be implemented without one or more of these specific details, and other methods, components, materials, etc. can be used.

[0026] Unless otherwise required in the present invention, the words "comprising" and "including" should be interpreted in an open, inclusive sense, i.e., "including but not limited to".

[0027] The phrase "in one embodiment" or "in an embodiment" or "in a preferred embodiment" or "in certain embodiments" mentioned throughout this specification means that in at least one embodiment, it includes the relevant specific reference elements, structures or features described in that embodiment. Therefore, the phrases "in one embodiment", "in an embodiment", "in a preferred embodiment" or "in certain embodiments" that appear at different positions throughout the specification do not necessarily all refer to the same embodiment. In addition, the specific elements, structures or features can be combined in one or more embodiments in any appropriate manner.

[0028] According to a first aspect of the present invention, a method for preparing a long-flame coal-based hard carbon anode material is provided, and the preparation method includes:

[0029] First, mix long-flame coal and a biomass precursor to obtain a mixed material;

[0030] Then, perform low-temperature pretreatment and low-temperature carbonization treatment on the mixed material in sequence to obtain a low-carbon material;

[0031] Then, perform high-temperature carbonization treatment on the low-carbon material to obtain the long-flame coal-based hard carbon anode material;

[0032] Wherein, both the long-flame coal and the biomass precursor are in powder form.

[0033] In the present invention, the biomass precursor contains abundant functional groups such as hydroxyl, carboxyl, carbonyl, and ether bonds. These functional groups rich in oxygen and hydrogen elements will generate a large number of oxygen and hydrogen free radicals during the low-temperature pretreatment stage. The oxygen and hydrogen free radicals will attack the aromatic structure of the coal itself, which is beneficial to promoting the transformation of the molecular structure of the coal from order to disorder. The biomass precursor will form a specific carbon layer arrangement during the carbonization process. During the carbonization process, the long-flame coal and the biomass precursor interact and interpenetrate with each other to form a richer and more stable pore structure and a larger specific surface area, providing more channels and active sites for the insertion and extraction of sodium ions.

[0034] Moreover, the raw material costs of the long-flame coal and the biomass precursor are low and the reserves are abundant. The preparation method has a simple process, realizing the low-cost preparation of the hard carbon anode material based on long-flame coal.

[0035] Specifically, in the present invention, the temperature of the low-temperature pretreatment is 200 - 500 °C, the temperature of the low-temperature carbonization treatment is 500 - 800 °C, and the temperature of the high-temperature carbonization treatment is 950 - 1500 °C.

[0036] In a preferred embodiment of the present invention, the biomass precursor includes one or more of bamboo, coconut shell, fruit wood, rice, lignin, cellulose, distiller's grains, or straw.

[0037] In the present invention, these biomass precursors have a wide source, are renewable, and have a low cost.

[0038] Bamboo has a high cellulose content. After carbonization, it can form a relatively regular pore structure, which is beneficial to the storage and transmission of sodium ions. The trace elements contained can have a positive impact on the electrochemical performance of the anode material.

[0039] The coconut shell usually has a rich microporous structure and a large specific surface area after carbonization, which can provide more active sites and improve the capacity and cycle stability of the anode material.

[0040] Fruit wood can form a unique microstructure during the carbonization process, improving the performance of the anode material. The relatively high lignin content also helps to improve the mechanical strength of the material.

[0041] Rice is beneficial to forming a carbon material with a certain porosity and conductivity after carbonization.

[0042] Lignin has a complex three-dimensional network structure. After carbonization, it can form a stable carbon skeleton, improving the structural stability of the anode material.

[0043] Cellulose can provide a rich carbon source, and its long-chain structure can form an ordered carbon layer during the carbonization process, which is beneficial to the insertion and extraction of sodium ions.

[0044] Distillers' grains, which are rich in organic matter and trace elements, can provide additional active sites and conductive channels for the anode material after carbonization.

[0045] Straw, mainly composed of cellulose, hemicellulose and lignin, can form a carbon material with a certain pore structure and mechanical strength after carbonization.

[0046] In a preferred embodiment of the present invention, the mass ratio of the long-flame coal to the biomass precursor is (5 - 10):(1 - 5).

[0047] In the present invention, the selection range of "5 - 10" for the long-flame coal can be, for example, 5, 6, 7, 8, 9 or 10, etc., and the selection range of "1 - 5" for the biomass precursor can be, for example, 1, 2, 3, 4 or 5, etc.

[0048] In the present invention, if the mass ratio of the long-flame coal to the biomass precursor is too small, the overall carbon content of the material may decrease, which will affect the conductivity and specific capacity of the anode material and the rate performance. In addition, the biomass precursor may generate more pores during the carbonization process, but due to the small proportion of the long-flame coal, it is difficult to provide sufficient structural support, resulting in a decrease in the mechanical strength of the material, which may affect the cycle life and stability of the battery.

[0049] If the mass ratio of the long-flame coal to the biomass precursor is too large, it may lead to a relatively dense structure formed after carbonization, unable to fully introduce a rich pore structure, difficult to fully improve the storage and transmission of sodium ions, and may reduce the electrochemical activity of the material, affecting the charge-discharge performance and cycle stability of the battery, and reducing the reversible capacity.

[0050] In a preferred embodiment of the present invention, the long-flame coal and the biomass precursor are stirred and mixed.

[0051] Preferably, the rotation speed of the stirring is 60 - 200 rpm, for example, it can be 60 rpm, 100 rpm, 150 rpm or 200 rpm, and the point values between any two of the above.

[0052] Preferably, the mixing time is 0.5 - 3 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, and the point values between any two of the above.

[0053] In a preferred embodiment of the present invention, the long-flame coal and the biomass precursor are first pre-crushed respectively and then mixed.

[0054] In the present invention, pre-crushing the long-flame coal and the biomass precursor respectively helps them to be mixed more fully. The reduction of the particle size improves the powder reaction activity and is more conducive to the formation of the "card house" structure.

[0055] Preferably, the pre-crushing treatment method of the long-flame coal is one or more of hammer crushing, impact mill crushing, universal crushing, jet milling or ball milling.

[0056] Preferably, the pre-crushing treatment method of the biomass precursor is one or more of a universal grinder, a biomass crusher, a biomass shredder or ball milling.

[0057] In a preferred embodiment of the present invention, the particle size D50 of the long-flame coal and the biomass precursor after pre-crushing treatment are each independently 10 - 50 μm, for example, it can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, and values between any two of the above, preferably 20 - 30 μm.

[0058] In the present invention, within the range of 20 - 30 μm in particle size, the particle surface areas of the two materials are relatively large, increasing the opportunity of interaction, which is beneficial to the synergistic reaction in subsequent treatment steps.

[0059] During the carbonization process, particles with a particle size of 20 - 30 μm can conduct heat and transfer substances more quickly, making the reaction more rapid and uniform, and can avoid local overheating or uneven reaction. This helps to form a more uniform pore structure and carbon layer arrangement, and can maximize the porosity while ensuring the structural stability of the material.

[0060] In a preferred embodiment of the present invention, the temperature of the low-temperature pretreatment is 250 - 400 °C, for example, it can be 250 °C, 300 °C, 350 °C or 400 °C, and point values between any two of the above.

[0061] In the present invention, if the temperature of the low-temperature pretreatment is too low, oxygen and hydrogen free radicals in the biomass cannot escape; if the temperature of the low-temperature pretreatment is too high, the long-flame coal will be carbonized, which is not conducive to modification. In addition, the carbonized long-flame coal may agglomerate, affecting the uniformity and stability of the material.

[0062] Preferably, the heat preservation time of the low-temperature pretreatment is 0.5 - 3 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, and point values between any two of the above.

[0063] In the present invention, within the range of heat preservation time from 0.5 to 3 hours, the mixture of long-flame coal and biomass precursor can have sufficient time to react during the low-temperature pretreatment process. During this process, oxygen free radicals and hydrogen free radicals are gradually formed, and the structure of the material will also be preliminarily adjusted. If the heat preservation time is too short, it may lead to insufficient reaction; if the heat preservation time is too long, it may cause excessive pyrolysis of the material, and the structure becomes too loose or unstable.

[0064] Preferably, the low-temperature pretreatment is carried out in an inert atmosphere, such as nitrogen and / or argon.

[0065] Preferably, the heating rate of the low-temperature pretreatment is 2-10 °C / min, for example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, as well as the point values between any two of the above.

[0066] In a preferred embodiment of the present invention, the temperature of the low-temperature carbonization treatment is 550-700 °C, for example, it can be 550 °C, 600 °C, 650 °C or 700 °C, as well as the point values between any two of the above.

[0067] In the present invention, if the temperature of the low-temperature carbonization treatment is too low, the volatile matter cannot be completely released; if the temperature of the low-temperature carbonization treatment is too high, the degree of carbonization is too high, which affects the formation of the internal structure of the hard carbon.

[0068] Preferably, the heat preservation time of the low-temperature carbonization treatment is 1-3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, as well as the point values between any two of the above.

[0069] Preferably, the low-temperature carbonization treatment is carried out in an inert atmosphere, such as nitrogen and / or argon.

[0070] Preferably, the heating rate of the low-temperature carbonization treatment is 2-10 °C / min, for example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, as well as the point values between any two of the above.

[0071] In a preferred embodiment of the present invention, the temperature of the high-temperature carbonization treatment is 1000-1400 °C, for example, it can be 1000 °C, 1100 °C, 1200 °C, 1300 °C or 1400 °C, as well as the point values between any two of the above.

[0072] Preferably, the heat preservation time of the high-temperature carbonization treatment is 2 - 5 h, for example, it can be 2 h, 3 h, 4 h, or 5 h, as well as the point values between any two of the above.

[0073] Preferably, the high-temperature carbonization treatment is carried out in an inert atmosphere, such as nitrogen and / or argon, etc.

[0074] Preferably, the heating rate of the high-temperature carbonization treatment is 2 - 10 °C / min, for example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min, as well as the point values between any two of the above.

[0075] Preferably, first, the low-carbon material is crushed to obtain a crushed material, and then the high-temperature carbonization treatment is carried out.

[0076] Preferably, the particle size D50 of the crushed material is particles of 2 - 10 μm, preferably 4 - 8 μm.

[0077] In a preferred embodiment of the present invention, the preparation method includes the following steps:

[0078] (1) The long-flame coal and the biomass precursor are respectively crushed to independently obtain fine powder particles with a particle size D50 of 10 - 50 μm, and then mixed at a rotation speed of 60 - 200 rpm for 0.5 - 3 h to obtain a mixed material;

[0079] Among them, the mass ratio of the long-flame coal to the biomass precursor is (5 - 10):(1 - 5);

[0080] (2) In an inert atmosphere, the temperature is raised to 250 - 400 °C at a heating rate of 2 - 10 °C / min, and the mixed material is subjected to a low-temperature pretreatment for 0.5 - 3 h, and then the temperature is raised to 550 - 700 °C at a heating rate of 2 - 10 °C / min in an inert atmosphere for 1 - 3 h of low-temperature carbonization treatment to obtain a low-carbon material;

[0081] (3) The low-carbon material is crushed to obtain a crushed material with a particle size D50 of 2 - 10 μm, and then the temperature is raised to 1000 - 1400 °C at a heating rate of 2 - 5 °C / min in an inert atmosphere, and the crushed material is subjected to a high-temperature carbonization treatment for 2 - 5 h to obtain the long-flame coal-based hard carbon negative electrode material.

[0082] According to the second aspect of the present invention, a long-flame coal-based hard carbon negative electrode material is provided, and the long-flame coal-based hard carbon negative electrode material is prepared by using the preparation method described in the first aspect.

[0083] According to the third aspect of the present invention, a sodium-ion battery is provided, and the negative electrode of the sodium-ion battery includes the long-flame coal-based hard carbon negative electrode material as described above.

[0084] Examples

[0085] The present invention will be further described in detail below with reference to examples. It can be understood that the specific examples described herein are only used to explain the related invention, rather than limiting the invention. It should be noted that, without conflict, the examples in the present invention and the features in the examples can be combined with each other.

[0086] In the following examples, unless otherwise specified, each raw material component is a commercially available product.

[0087] Example 1

[0088] This example provides a preparation method of a long-flame coal-based hard carbon negative electrode material, and its preparation process flow chart is as Figure 1 shown, and the preparation method includes the following steps:

[0089] (1) The long-flame coal and the biomass precursor are respectively pulverized to independently obtain fine powder particles with a particle size D50 of 20 μm, and then mixed and put into a high-efficiency mixer, and stirred and mixed at a rotation speed of 100 rpm for 1.5 h to obtain a mixed material;

[0090] Among them, the biomass precursor is bamboo, and the mass ratio of the long-flame coal to the biomass precursor is 8:3;

[0091] (2) In a nitrogen atmosphere, the temperature is raised to 300 °C at a heating rate of 7 °C / min, and the mixed material is subjected to a low-temperature pretreatment for 1.5 h, and then the temperature is raised to 600 °C at a heating rate of 7 °C / min in a nitrogen atmosphere for a low-temperature carbonization treatment for 2 h to obtain a low-carbon material;

[0092] (3) The low-carbon material is subjected to air-flow pulverization treatment to obtain a pulverized material with a particle size D50 of 5 μm, and then the temperature is raised to 1200 °C at a heating rate of 3 °C / min in a nitrogen atmosphere, and the pulverized material is subjected to a high-temperature carbonization treatment for 3 h to obtain the long-flame coal-based hard carbon negative electrode material.

[0093] Example 2

[0094] This example provides a preparation method of a long-flame coal-based hard carbon negative electrode material, and the preparation method includes the following steps:

[0095] (1) The long-flame coal and the biomass precursor are respectively pulverized to independently obtain fine powder particles with a particle size D50 of 50 μm, and then mixed and put into a high-efficiency mixer, and stirred and mixed at a rotation speed of 60 rpm for 3 h to obtain a mixed material;

[0096] Among them, the biomass precursor is fruit wood, and the mass ratio of long-flame coal to the biomass precursor is 5:5;

[0097] (2) In an argon atmosphere, the temperature is raised to 250 °C at a heating rate of 5 °C / min, and the mixture is subjected to a low-temperature pretreatment for 3 h, and then the temperature is raised to 550 °C at a heating rate of 5 °C / min in an argon atmosphere for a low-temperature carbonization treatment for 3 h to obtain a low-carbon material;

[0098] (3) The low-carbon material is subjected to airflow pulverization treatment to obtain a pulverized material with a D50 particle size of 4 μm, and then the temperature is raised to 1000 °C at a heating rate of 2 °C / min in an argon atmosphere, and the pulverized material is subjected to a high-temperature carbonization treatment for 5 h to obtain the long-flame coal-based hard carbon negative electrode material.

[0099] Example 3

[0100] This example provides a method for preparing a long-flame coal-based hard carbon negative electrode material, and the preparation method includes the following steps:

[0101] (1) The long-flame coal and the biomass precursor are respectively pulverized to independently obtain fine powder particles with a D50 particle size of 10 μm, and then mixed and put into a high-efficiency mixer and stirred and mixed at a rotation speed of 200 rpm for 0.5 h to obtain a mixture;

[0102] Among them, the biomass precursor is paddy rice, and the mass ratio of long-flame coal to the biomass precursor is 10:1;

[0103] (2) In an inert atmosphere, the temperature is raised to 400 °C at a heating rate of 5 °C / min, and the mixture is subjected to a low-temperature pretreatment for 0.5 h, and then the temperature is raised to 700 °C at a heating rate of 5 °C / min in an inert atmosphere for a low-temperature carbonization treatment for 1 h to obtain a low-carbon material;

[0104] (3) The low-carbon material is subjected to airflow pulverization treatment to obtain a pulverized material with a D50 particle size of 6 μm, and then the temperature is raised to 1400 °C at a heating rate of 5 °C / min in an inert atmosphere, and the pulverized material is subjected to a high-temperature carbonization treatment for 2 h to obtain the long-flame coal-based hard carbon negative electrode material.

[0105] Example 4

[0106] The difference between this example and Example 1 is that the mass ratio of long-flame coal to the biomass precursor is 5:10;

[0107] The remaining preparation methods and parameters are the same as those in Example 1.

[0108] Example 5

[0109] The difference between this example and Example 1 is that the mass ratio of long-flame coal to biomass precursor is 5:5;

[0110] The remaining preparation methods and parameters are the same as those in Example 1.

[0111] Example 6

[0112] The difference between this example and Example 1 is that the mass ratio of long-flame coal to biomass precursor is 10:1;

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Example 7

[0115] The difference between this example and Example 1 is that the mass ratio of long-flame coal to biomass precursor is 15:1;

[0116] The remaining preparation methods and parameters are the same as those in Example 1.

[0117] Example 8

[0118] The difference between this example and Example 1 is that in a nitrogen atmosphere, the temperature is raised to 200 °C at a heating rate of 5 °C / min, and the mixture is subjected to a low-temperature pretreatment for 1.5 h;

[0119] The remaining preparation methods and parameters are the same as those in Example 1.

[0120] Example 9

[0121] The difference between this example and Example 1 is that in a nitrogen atmosphere, the temperature is raised to 250 °C at a heating rate of 6 °C / min, and the mixture is subjected to a low-temperature pretreatment for 1.5 h;

[0122] The remaining preparation methods and parameters are the same as those in Example 1.

[0123] Example 10

[0124] The difference between this example and Example 1 is that in a nitrogen atmosphere, the temperature is raised to 400 °C at a heating rate of 9 °C / min, and the mixture is subjected to a low-temperature pretreatment for 1.5 h;

[0125] The remaining preparation methods and parameters are the same as those in Example 1.

[0126] Example 11

[0127] The difference between this example and Example 1 is that in a nitrogen atmosphere, the temperature is raised to 500 °C at a heating rate of 10 °C / min, and the mixture is subjected to a low-temperature pretreatment for 1.5 h;

[0128] The remaining preparation methods and parameters are the same as those in Example 1.

[0129] Example 12

[0130] The difference between this example and Example 1 is that the temperature is raised to 500 °C at a heating rate of 6 °C / min in an argon atmosphere for 2 h of low-temperature carbonization treatment;

[0131] The remaining preparation methods and parameters are the same as those in Example 1.

[0132] Example 13

[0133] The difference between this example and Example 1 is that the temperature is raised to 550 °C at a heating rate of 6.5 °C / min in an argon atmosphere for 2 h of low-temperature carbonization treatment;

[0134] The remaining preparation methods and parameters are the same as those in Example 1.

[0135] Example 14

[0136] The difference between this example and Example 1 is that for the low-temperature carbonization treatment, the temperature is raised to 700 °C at a heating rate of 8 °C / min, and the mixture is subjected to 2 h of low-temperature carbonization treatment;

[0137] The remaining preparation methods and parameters are the same as those in Example 1.

[0138] Example 15

[0139] The difference between this example and Example 1 is that for the low-temperature carbonization treatment, the temperature is raised to 800 °C at a heating rate of 10 °C / min, and the mixture is subjected to 2 h of low-temperature carbonization treatment;

[0140] The remaining preparation methods and parameters are the same as those in Example 1.

[0141] Comparative Example 1

[0142] The difference between this comparative example and Example 1 is that the process of low-temperature pretreatment is not carried out.

[0143] The remaining preparation methods and parameters are the same as those in Example 1.

[0144] Comparative Example 2

[0145] The difference between this comparative example and Example 1 is that the process of low-temperature carbonization treatment is not carried out.

[0146] The remaining preparation methods and parameters are the same as those in Example 1.

[0147] Comparative Example 3

[0148] The difference between this comparative example and Example 1 is that step (2) is not carried out.

[0149] The remaining preparation methods and parameters are the same as those in Example 1.

[0150] Performance test

[0151] (1) The microstructure of the long-flame coal-based hard carbon anode material prepared in Example 1 was characterized, and its SEM image is as Figure 2 shown.

[0152] (2) The long-flame coal-based hard carbon anode materials provided in the above examples and comparative examples were made into hard carbon electrode sheets. The preparation method of the hard carbon electrode sheets includes: mixing the prepared hard carbon, conductive carbon black (Super P), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) according to the formulation ratio of 91:2:2:5 to make a slurry. The prepared slurry was scraped onto a carbon-coated copper foil, and then transferred to a forced-air drying oven at 65 °C until the electrode sheet was dry (about 1-2 h), and then transferred to a vacuum drying oven for drying for 12 h to obtain the hard carbon electrode sheet.

[0153] Then, the hard carbon electrode sheet was assembled with a sodium metal electrode sheet, a separator (cellulose separator), and an electrolyte (special electrolyte for sodium-ion batteries) to obtain a sodium-ion half-cell.

[0154] The above sodium-ion batteries were subjected to electrochemical performance tests, including capacity performance and initial efficiency.

[0155] The test conditions for capacity performance and initial efficiency were: constant current discharge at 0.1C to 0V, standing for 5 min, and then constant current charging at 0.1C to 2.0V. The test temperature was 25 °C.

[0156] The test results are shown in Table 1.

[0157] Table 1 Test results of Examples 1-15 and Comparative Examples 1-3

[0158]

[0159] Analysis:

[0160] As can be seen from Table 1, the present invention utilizes the advantages of high oxygen content and high hydrogen content of long-flame coal combined with biomass precursors to generate a large number of oxygen free radicals and hydrogen free radicals during the low-temperature pretreatment stage, which attack the aromatic structure of the coal itself, promote the transformation of the molecular structure of the coal from ordered to disordered, and realize the low-cost preparation of the long-flame coal-based hard carbon anode material. Moreover, the preparation method has a simple process, and the prepared long-flame coal-based hard carbon anode material has a "card house" structure. Based on this, the prepared battery has a high specific capacity (up to 290 mAh / g at most) and a high initial Coulomb efficiency (up to 92% at most).

[0161] As can be seen from Example 1 and Examples 4-7, if the mass ratio of long-flame coal to biomass precursor is too small, the cost will increase, the conductivity will decrease, and the rate performance will be affected; if the mass ratio of long-flame coal to biomass precursor is too large, the modification effect on long-flame coal is not strong and the specific capacity decreases.

[0162] As can be seen from Example 1 and Examples 8-11, if the low-temperature pretreatment temperature is too low, it is difficult for oxygen and hydrogen free radicals in the biomass to escape; if the low-temperature pretreatment temperature is too high, the long-flame coal will be carbonized and it is not easy to carry out modification.

[0163] As can be seen from Example 1 and Examples 12-15, if the temperature of the low-temperature carbonization treatment is too low, it is difficult to completely release the volatile matter; if the temperature of the low-temperature carbonization treatment is too high, the degree of carbonization is too high, affecting the internal structure of the hard carbon.

[0164] As can be seen from Example 1 and Comparative Example 1, if the low-temperature pretreatment process in step (2) is not carried out, the long-flame coal cannot form a good hard carbon structure, and the specific capacity and initial efficiency are low.

[0165] As can be seen from Example 1 and Comparative Example 2, if the low-temperature carbonization treatment process in step (2) is not carried out, the carbon structure will be affected, and the specific capacity and initial efficiency are low.

[0166] As can be seen from Example 1 and Comparative Example 3, if step (2) is not carried out, the sodium storage performance will be seriously affected, and the specific capacity and initial efficiency are low.

[0167] The applicant declares that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a long flame coal-based hard carbon negative electrode material, characterized in that: The preparation method comprises: First, long flame coal and biomass precursor are mixed to obtain a mixed material; Then, the mixed material is subjected to low-temperature pretreatment and low-temperature carbonization treatment in sequence to obtain a low-carbon material; Then, the low-carbon material is subjected to air flow pulverization treatment to obtain a pulverized material with a particle size D50 of 2 to 10 μm; Then, the crushed material is subjected to high temperature carbonization treatment to obtain the long flame coal-based hard carbon negative electrode material; The temperature of the low temperature pretreatment is 250-400°C, and the insulation time of the low temperature pretreatment is 0.5-3h; The long flame coal and biomass precursor are both in powder form. In the subsequent low-temperature pretreatment stage, the biomass precursor generates oxygen and hydrogen free radicals, which attack the aromatic structure of the long flame coal and promote the transformation of the molecular structure from order to disorder.

2. The preparation method according to claim 1, characterized in that The biomass precursor includes one or more of bamboo, coconut shell, fruit wood, rice, lignin, cellulose, wine lees or straw.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the long flame coal to the biomass precursor is (5-10):(1-5).

4. The preparation method according to claim 1, characterized in that: The long flame coal and the biomass precursor are stirred and mixed at a rotation speed of 60-200 rpm, and the mixing time is 0.5-3 hours.

5. The preparation method according to claim 1, characterized in that: Firstly, the long flame coal and the biomass precursor are pre-crushed respectively, and then the two are mixed; The particle size D50 of the long flame coal and the biomass precursor after pre-crushing is independently 10-50 μm.

6. The preparation method according to claim 1, characterized in that: The temperature of the low-temperature carbonization treatment is 550-700° C., and the insulation time of the low-temperature carbonization treatment is 1-3 hours.

7. The preparation method according to claim 1, characterized in that: The temperature of the high-temperature carbonization treatment is 1000-1400° C., and the insulation time of the high-temperature carbonization treatment is 2-5 hours.

8. A long flame coal-based hard carbon negative electrode material, characterized in that: The long flame coal-based hard carbon negative electrode material is prepared by the preparation method according to any one of claims 1 to 7.

9. A sodium ion battery, characterized in that: The negative electrode of the sodium ion battery includes the long flame coal-based hard carbon negative electrode material as described in claim 8.

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