Long flame coal-based hard carbon negative electrode material, preparation method and sodium ion battery

Abstract

The present invention provides a long flame coal-based hard carbon negative electrode material, a preparation method and a sodium ion battery, and belongs to the technical field of battery materials. The present invention mixes long flame coal and a biomass precursor, and then performs 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 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 conducive to promoting the molecular structure of the coal from order to disorder. During the carbonization process, the long flame coal and the biomass precursor interact and interweave to form a richer and more stable pore structure and a larger specific surface area, providing more channels and active sites for the embedding and extraction of sodium ions. In addition, the raw materials of long flame coal and biomass precursors are low in cost and abundant in reserves. The preparation method is simple in process, and the low-cost preparation of long flame coal-based hard carbon negative electrode materials is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials, and in particular relates to a long flame coal-based hard carbon negative electrode material, a preparation method 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 attracted widespread attention as a potential energy storage technology. Sodium-ion batteries have the advantages of low cost, safety, environmental protection, and excellent low-temperature performance. Their working principle is similar to that of lithium-ion batteries, and they can adapt to the production process of lithium-ion batteries and have the conditions for rapid industrialization. The negative electrode 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 be deintercalated and deintercalated at a large capacity in the graphite negative electrode, the key to the commercialization of sodium-ion batteries lies in the development of high-capacity negative electrode materials.

[0003] In sodium-ion batteries, hard carbon materials can achieve high-capacity sodium ion deintercalation due to their long-range disordered and short-range ordered structures, and are currently the most promising negative electrode materials for sodium-ion batteries. Nowadays, the preparation process of hard carbon negative electrode materials mostly relies on oxidation, activation and pore-forming processes to achieve coal-based hard carbon preparation, which has problems such as high preparation cost and complex process.

[0004] In view of the above problems, it is urgent to design a method for preparing hard carbon negative electrode materials with simple process and low cost. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention aims to provide a long flame coal-based hard carbon negative electrode material, a preparation method and a sodium ion battery with a simple preparation process, high specific capacity and high first coulombic efficiency.

[0006] One of the purposes of the present invention is to provide a method for preparing a long flame coal-based hard carbon negative electrode material, the preparation method comprising: 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 high-temperature carbonization treatment to obtain the long flame coal-based hard carbon negative electrode material; Wherein, the long flame coal and the biomass precursor are both in powder form.

[0007] Preferably, the biomass precursor includes one or more of bamboo, coconut shell, fruit wood, rice, lignin, cellulose, distiller's grains or straw.

[0008] Preferably, the mass ratio of the long flame coal to the biomass precursor is (5-10):(1-5).

[0009] 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.

[0010] Preferably, the long flame coal and the biomass precursor are pre-crushed separately and then mixed.

[0011] Preferably, the particle size D50 of the long flame coal and the biomass precursor after pre-crushing is independently 10-50 μm.

[0012] Preferably, the temperature of the low-temperature pretreatment is 250-400° C., and the insulation time of the low-temperature pretreatment is 0.5-3 h.

[0013] Preferably, 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.

[0014] Preferably, 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.

[0015] The second object of the present invention is to provide a long flame coal-based hard carbon negative electrode material, wherein the long flame coal-based hard carbon negative electrode material is prepared by the preparation method as described above.

[0016] A third object of the present invention is to provide a sodium ion battery, wherein the negative electrode of the sodium ion battery comprises the long flame coal-based hard carbon negative electrode material as described above.

[0017] The beneficial effects of the present invention include: The present invention mixes long flame coal and biomass precursor, and then sequentially performs low temperature pretreatment, low temperature carbonization treatment and high temperature carbonization treatment. 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 conducive to promoting the molecular structure of the coal from order to disorder. In 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 embedding and extraction of sodium ions. In addition, the raw materials of long flame coal and biomass precursors are low in cost and abundant in reserves. The preparation method is simple in process, and the low-cost preparation of long flame coal-based hard carbon negative electrode materials is realized. The battery prepared based on this has a high specific capacity (up to 290mAh / g) and a high first coulomb efficiency (up to 92%). BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of the preparation process of the long flame coal-based hard carbon negative electrode material provided in Example 1; Figure 2 This is an SEM image of the long flame coal-based hard carbon negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0019] In the following description, certain specific details are included to provide a comprehensive understanding of each disclosed embodiment. However, one skilled in the relevant art will recognize that the embodiments can be implemented without one or more of these specific details and with other methods, components, materials, etc.

[0020] Unless otherwise required herein, the words "include" and "comprising" should be interpreted as having an open and inclusive meaning, ie, "including but not limited to".

[0021] References to "one embodiment" or "an embodiment" or "a preferred embodiment" or "certain embodiments" throughout this specification mean that the specific referenced elements, structures or features described in connection with the embodiment are included in at least one embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" or "in a preferred embodiment" or "in certain embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. In addition, the specific elements, structures or features may be combined in any appropriate manner in one or more embodiments.

[0022] According to a first aspect of the present invention, a method for preparing a long flame coal-based hard carbon negative electrode material is provided, the preparation method comprising: 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 high-temperature carbonization treatment to obtain the long flame coal-based hard carbon negative electrode material; Wherein, the long flame coal and the biomass precursor are both in powder form.

[0023] 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 promote 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 embedding and extraction of sodium ions.

[0024] In addition, the long flame coal and biomass precursor raw materials are low in cost and abundant in reserves, and the preparation method is simple in process, thus achieving low-cost preparation of long flame coal-based hard carbon negative electrode materials.

[0025] 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.

[0026] 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.

[0027] In the present invention, these biomass precursors are widely available and renewable, and have low costs.

[0028] Bamboo has a high cellulose content and can form a relatively regular pore structure after carbonization, which is conducive to the storage and transmission of sodium ions. The trace elements it contains can have a positive effect on the electrochemical properties of the negative electrode material.

[0029] Coconut shells, after carbonization, usually have a rich microporous structure and a large specific surface area, which can provide more active sites and improve the capacity and cycle stability of negative electrode materials.

[0030] Fruit wood can form a unique microstructure during the carbonization process, which can improve the performance of the negative electrode material. The higher lignin content can also help improve the mechanical strength of the material.

[0031] Rice, after carbonization, is conducive to the formation of carbon materials with certain porosity and conductivity.

[0032] Lignin has a complex three-dimensional network structure, which can form a stable carbon skeleton after carbonization, thereby improving the structural stability of the negative electrode material.

[0033] Cellulose can provide a rich carbon source, and its long-chain structure can form an ordered carbon layer during the carbonization process, which is conducive to the embedding and extraction of sodium ions.

[0034] Wine lees are rich in organic matter and trace elements, which can provide additional active sites and conductive channels for negative electrode materials after carbonization.

[0035] Straw, mainly composed of cellulose, hemicellulose and lignin, can form a carbon material with a certain pore structure and mechanical strength after carbonization.

[0036] 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).

[0037] In the present invention, the selection range of long flame coal "5-10" may be, for example, 5, 6, 7, 8, 9 or 10, and the selection range of biomass precursor "1-5" may be, for example, 1, 2, 3, 4 or 5.

[0038] 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 be reduced, which will affect the conductivity and specific capacity of the negative electrode material and affect the rate performance. In addition, the biomass precursor may produce 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.

[0039] If the mass ratio of long flame coal and biomass precursor is too large, the structure formed after carbonization may be relatively dense, and the rich pore structure cannot be fully introduced, making it difficult to fully improve the storage and transport of sodium ions. This may reduce the electrochemical activity of the material, affect the battery's charge and discharge performance and cycle stability, and reduce the reversible capacity.

[0040] In a preferred embodiment of the present invention, the long flame coal and the biomass precursor are stirred and mixed.

[0041] Preferably, the stirring speed is 60-200 rpm, for example, 60 rpm, 100 rpm, 150 rpm or 200 rpm, and any value between the above two.

[0042] Preferably, the mixing time is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, and any value between any two of the above.

[0043] In a preferred embodiment of the present invention, the long flame coal and the biomass precursor are pre-crushed separately and then mixed.

[0044] In the present invention, the long flame coal and the biomass precursor are pre-crushed respectively, which helps to mix the two more fully, reduces the particle size, improves the reaction activity of the powder, and is more conducive to the formation of the "house of cards" structure.

[0045] Preferably, the pre-crushing treatment method of the long flame coal is one or more of hammer crushing, impact mill crushing, universal crushing, air flow crushing or ball milling.

[0046] 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 a ball mill.

[0047] 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 is 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.

[0048] In the present invention, the particle size is in the range of 20-30 μm, and the particle surface area of ​​the two materials is relatively large, which increases the chance of interaction and is beneficial for synergistic reaction in subsequent processing steps.

[0049] During the carbonization process, particles with a size of 20-30μm can conduct heat and material transfer faster, making the reaction more rapid and uniform, avoiding local overheating or uneven reaction. This helps to form a more uniform pore structure and carbon layer arrangement, which can maximize the porosity while ensuring the stability of the material structure.

[0050] In a preferred embodiment of the present invention, the temperature of the low-temperature pretreatment is 250-400°C, for example, 250°C, 300°C, 350°C or 400°C, and any value between the above two.

[0051] In the present invention, if the temperature of the low-temperature pretreatment is too low, the 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 long flame coal after carbonization may agglomerate, affecting the uniformity and stability of the material.

[0052] Preferably, the holding 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 any value between any two of the above.

[0053] In the present invention, within the range of 0.5-3h of holding time, the mixture of long flame coal and biomass precursor can have enough time to react during the low temperature pretreatment process. In this process, oxygen free radicals and hydrogen free radicals are gradually formed, and the structure of the material will also undergo preliminary adjustments. If the holding time is too short, the reaction may be insufficient; if the holding time is too long, the material may be over-pyrolyzed, and the structure may become too loose or unstable.

[0054] Preferably, the low temperature pretreatment is performed in an inert atmosphere, such as nitrogen and / or argon.

[0055] 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, and any point value between any two of the above.

[0056] 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, and any point value between the above two.

[0057] 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 carbonization degree is too high, which affects the formation of the internal structure of the hard carbon.

[0058] Preferably, the holding time of the low-temperature carbonization treatment is 1-3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, and any value between any two of the above.

[0059] Preferably, the low-temperature carbonization treatment is performed in an inert atmosphere, such as nitrogen and / or argon.

[0060] 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, and any point value between any two of the above.

[0061] 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, and any point value between the above two.

[0062] Preferably, the holding time of the high temperature carbonization treatment is 2-5 h, for example, 2 h, 3 h, 4 h or 5 h, and any value in between.

[0063] Preferably, the high-temperature carbonization treatment is carried out in an inert atmosphere, such as nitrogen and / or argon.

[0064] 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, and any point value between any two of the above.

[0065] Preferably, the low-carbon material is firstly subjected to a pulverization treatment, and after obtaining the pulverized material, a high-temperature carbonization treatment is then performed.

[0066] Preferably, the particle size D50 of the crushed material is 2-10 μm, preferably 4-8 μm.

[0067] In a preferred embodiment of the present invention, the preparation method comprises the following steps: (1) The long flame coal and the biomass precursor are pulverized separately to 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 hours to obtain a mixture; Wherein, the mass ratio of long flame coal and biomass precursor is (5-10):(1-5); (2) in an inert atmosphere, heating the mixture to 250-400°C at a heating rate of 2-10°C / min, performing a low-temperature pretreatment on the mixture for 0.5-3h, and then heating the mixture to 550-700°C at a heating rate of 2-10°C / min in an inert atmosphere, performing a low-temperature carbonization treatment for 1-3h to obtain a low-carbon material; (3) The low-carbon material is pulverized to obtain a pulverized 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 pulverized material is subjected to a high-temperature carbonization treatment for 2-5 hours to obtain the long flame coal-based hard carbon negative electrode material.

[0068] According to a second aspect of the present invention, a long flame coal-based hard carbon negative electrode material is provided. The long flame coal-based hard carbon negative electrode material is prepared by the preparation method described in the first aspect.

[0069] According to a third aspect of the present invention, a sodium ion battery is provided, wherein the negative electrode of the sodium ion battery comprises the long flame coal-based hard carbon negative electrode material as described above.

[0070] Example The present invention is further described in detail below in conjunction with the embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0071] In the following examples, unless otherwise specified, all raw materials are commercially available products.

[0072] Example 1 This embodiment provides a method for preparing a long flame coal-based hard carbon negative electrode material, and its preparation process flow chart is as follows: Figure 1 As shown, the preparation method comprises the following steps: (1) The long flame coal and the biomass precursor were pulverized separately to 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 speed of 100 rpm for 1.5 hours to obtain a mixture; The biomass precursor is bamboo, and the mass ratio of long flame coal to biomass precursor is 8:3; (2) in a nitrogen atmosphere, the temperature is raised to 300° C. at a heating rate of 7° C. / min, 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, and a low-temperature carbonization treatment is performed for 2 h to obtain a low-carbon material; (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 increased to 1200° C. at a heating rate of 3° C. / min in a nitrogen atmosphere, and the pulverized material is subjected to high-temperature carbonization treatment for 3 h to obtain the long flame coal-based hard carbon negative electrode material.

[0073] Example 2 This embodiment provides a method for preparing a long flame coal-based hard carbon negative electrode material, the preparation method comprising the following steps: (1) The long flame coal and the biomass precursor were pulverized separately to 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 speed of 60 rpm for 3 hours to obtain a mixture; Among them, the biomass precursor is fruit wood, and the mass ratio of long flame coal to biomass precursor is 5:5; (2) in an argon atmosphere, the temperature is raised to 250° C. at a heating rate of 5° C. / min, the mixed material 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, and a low-temperature carbonization treatment is performed for 3 h to obtain a low-carbon material; (3) The low-carbon material is subjected to air flow pulverization treatment to obtain a pulverized material with a particle size D50 of 4 μm, and then the pulverized material is heated to 1000° C. at a heating rate of 2° C. / min in an argon atmosphere, and the pulverized material is subjected to high-temperature carbonization treatment for 5 hours to obtain the long flame coal-based hard carbon negative electrode material.

[0074] Example 3 This embodiment provides a method for preparing a long flame coal-based hard carbon negative electrode material, the preparation method comprising the following steps: (1) The long flame coal and the biomass precursor were pulverized separately to obtain fine powder particles with a particle size D50 of 10 μm, and then mixed and put into a high-efficiency mixer, and stirred and mixed at a speed of 200 rpm for 0.5 h to obtain a mixture; Among them, the biomass precursor is rice, and the mass ratio of long flame coal to biomass precursor is 10:1; (2) in an inert atmosphere, heating the mixture to 400° C. at a heating rate of 5° C. / min, performing a low-temperature pretreatment on the mixture for 0.5 h, and then heating the mixture to 700° C. at a heating rate of 5° C. / min in an inert atmosphere, performing a low-temperature carbonization treatment for 1 h, to obtain a low-carbon material; (3) The low-carbon material is subjected to air flow pulverization treatment to obtain a pulverized material with a particle size D50 of 6 μm, and then the temperature is increased to 1400° C. at a heating rate of 5° C. / min in an inert atmosphere, and the pulverized material is subjected to high-temperature carbonization treatment for 2 h to obtain the long flame coal-based hard carbon negative electrode material.

[0075] Example 4 The difference between this embodiment and embodiment 1 is that the mass ratio of long flame coal to biomass precursor is 5:10; The rest of the preparation methods and parameters were the same as those in Example 1.

[0076] Example 5 The difference between this embodiment and embodiment 1 is that the mass ratio of long flame coal to biomass precursor is 5:5; The rest of the preparation methods and parameters were the same as those in Example 1.

[0077] Example 6 The difference between this embodiment and embodiment 1 is that the mass ratio of long flame coal to biomass precursor is 10:1; The rest of the preparation methods and parameters were the same as those in Example 1.

[0078] Example 7 The difference between this embodiment and embodiment 1 is that the mass ratio of long flame coal to biomass precursor is 15:1; The rest of the preparation methods and parameters were the same as those in Example 1.

[0079] Example 8 The difference between this embodiment and embodiment 1 is that the mixture is subjected to low temperature pretreatment for 1.5 h in a nitrogen atmosphere by heating the mixture to 200° C. at a heating rate of 5° C. / min; The rest of the preparation methods and parameters were the same as those in Example 1.

[0080] Example 9 The difference between this embodiment and embodiment 1 is that the mixture is subjected to low temperature pretreatment for 1.5 h in a nitrogen atmosphere by heating the mixture to 250° C. at a heating rate of 6° C. / min; The rest of the preparation methods and parameters were the same as those in Example 1.

[0081] Example 10 The difference between this embodiment and embodiment 1 is that the mixture is subjected to low temperature pretreatment for 1.5 h in a nitrogen atmosphere by heating the mixture to 400° C. at a heating rate of 9° C. / min; The rest of the preparation methods and parameters were the same as those in Example 1.

[0082] Embodiment 11 The difference between this embodiment and embodiment 1 is that the mixture is subjected to low temperature pretreatment for 1.5 h in a nitrogen atmosphere by heating the mixture to 500° C. at a heating rate of 10° C. / min; The rest of the preparation methods and parameters were the same as those in Example 1.

[0083] Example 12 The difference between this embodiment and embodiment 1 is that the temperature is raised to 500°C at a heating rate of 6°C / min in an argon atmosphere and a low-temperature carbonization treatment is performed for 2h; The rest of the preparation methods and parameters were the same as those in Example 1.

[0084] Embodiment 13 The difference between this embodiment and embodiment 1 is that the temperature is raised to 550°C at a heating rate of 6.5°C / min in an argon atmosphere and a low-temperature carbonization treatment is performed for 2h; The rest of the preparation methods and parameters were the same as those in Example 1.

[0085] Embodiment 14 The difference between this embodiment and embodiment 1 is that the low-temperature carbonization treatment is carried out by heating the mixture to 700°C at a heating rate of 8°C / min for 2 hours. The rest of the preparation methods and parameters were the same as those in Example 1.

[0086] Embodiment 15 The difference between this embodiment and embodiment 1 is that the low-temperature carbonization treatment is carried out by heating the mixture to 800°C at a heating rate of 10°C / min for 2 hours. The rest of the preparation methods and parameters were the same as those in Example 1.

[0087] Comparative Example 1 The difference between this comparative example and Example 1 is that no low-temperature pretreatment process is performed.

[0088] The rest of the preparation methods and parameters were the same as those in Example 1.

[0089] Comparative Example 2 The difference between this comparative example and Example 1 is that the low-temperature carbonization process is not performed.

[0090] The rest of the preparation methods and parameters were the same as those in Example 1.

[0091] Comparative Example 3 The difference between this comparative example and Example 1 is that step (2) is not performed.

[0092] The rest of the preparation methods and parameters were the same as those in Example 1.

[0093] Performance Testing (1) The microstructure of the long flame coal-based hard carbon negative electrode material prepared in Example 1 was characterized, and its SEM image is shown in FIG. Figure 2 shown.

[0094] (2) The long flame coal-based hard carbon negative electrode material provided in the above embodiment and comparative example is made into a hard carbon electrode sheet, and the preparation method of the hard carbon electrode sheet comprises: mixing the prepared hard carbon, conductive carbon black (Super P), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) according to a formula ratio of 91:2:2:5 for slurry. The prepared slurry is scraped on the carbon-coated copper foil, and then transferred to a 65°C forced air drying oven until the electrode sheet is dry (about 1-2 h), and then transferred to a vacuum drying oven for drying for 12 h to obtain a hard carbon electrode sheet.

[0095] Then, the hard carbon electrode is assembled with the sodium metal electrode, the diaphragm (cellulose diaphragm) and the electrolyte (specific electrolyte for sodium ion batteries) to obtain a sodium ion half-cell.

[0096] The electrochemical performance tests of the above sodium-ion batteries were carried out, including capacity performance and initial efficiency.

[0097] The test conditions for capacity performance and first efficiency are: discharge to 0V at 0.1C constant current, let stand for 5 minutes, then charge to 2.0V at 0.1C constant current, and the test temperature is 25℃.

[0098] The test results are shown in Table 1.

[0099] Table 1 Test results of Examples 1-15 and Comparative Examples 1-3

[0100] analyze: As can be seen from Table 1, the present invention utilizes the advantages of long flame coal combined with high oxygen content and high hydrogen content of biomass precursors to generate a large number of oxygen free radicals and hydrogen free radicals in the low-temperature pretreatment stage, and attacks the aromatic structure of the coal itself, promoting the molecular structure of the coal from order to disorder, and realizing the low-cost preparation of long flame coal-based hard carbon negative electrode materials. In addition, the preparation method is simple, and the prepared long flame coal-based hard carbon negative electrode material has a "house of cards" structure. The battery prepared based on this has a high specific capacity (up to 290mAh / g) and a high first coulomb efficiency (up to 92%).

[0101] It can be seen from Example 1 and Examples 4-7 that if the mass ratio of long flame coal to biomass precursor is too small, it will increase the cost, reduce the electrical conductivity, and affect the rate performance; if the mass ratio of long flame coal to biomass precursor is too large, the modification effect on the long flame coal is not strong and the specific capacity is reduced.

[0102] It can be seen from Examples 1 and 8-11 that if the low-temperature pretreatment temperature is too low, it is difficult for oxygen and hydrogen radicals in the biomass to escape; if the low-temperature pretreatment temperature is too high, the biomass will be coal-like and difficult to modify.

[0103] It can be seen from Example 1 and Examples 12-15 that 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.

[0104] It can be seen from Example 1 and Comparative Example 1 that 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 first efficiency are low.

[0105] It can be seen from Example 1 and Comparative Example 2 that if the low-temperature carbonization process in step (2) is not performed, the carbon structure will be affected, and the specific capacity and initial efficiency will be low.

[0106] It can be seen from Example 1 and Comparative Example 3 that if step (2) is not performed, the sodium storage performance will be seriously affected, and the specific capacity and initial efficiency will be low.

[0107] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and 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 high-temperature carbonization treatment to obtain the long flame coal-based hard carbon negative electrode material; Wherein, the long flame coal and the biomass precursor are both in powder form.

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 pretreatment is 250-400° C., and the insulation time of the low temperature pretreatment is 0.5-3 hours.

7. 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.

8. The preparation method according to any one of claims 1 to 7, 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.

9. 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 8.

10. 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 claimed in claim 9.

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