A pitch-based microcrystalline hard carbon material, a preparation method and application thereof

Abstract

The present application relates to the technical field of hard carbon material, and specifically discloses a pitch-based microcrystalline hard carbon material, a preparation method and application thereof. In an inert atmosphere, low-temperature pitch is subjected to a thermal polycondensation reaction at 300 DEG C to 550 DEG C and 0.01 MPa to 10 MPa to obtain mesophase pitch; the softening point of the low-temperature pitch is 18 DEG C to 48 DEG C; the mesophase pitch is subjected to oxidative crosslinking in an oxygen-containing atmosphere to obtain a hard carbon precursor; and the hard carbon precursor is subjected to carbonization treatment in an inert atmosphere to obtain the pitch-based microcrystalline hard carbon material. The present application creatively uses low-temperature pitch as raw material, is convenient to control the size of carbon microcrystals, and has low cost. The mesophase pitch with certain carbon microcrystal structure is formed through thermal polycondensation, and the mesophase pitch is subjected to oxidative crosslinking to expand the interlayer spacing of the carbon layer, so that the pitch-based microcrystalline hard carbon material with high capacity, large rate and long cycle is finally prepared, and has high market application value.

Description

Technical Field

[0001] This invention relates to the field of hard carbon materials technology, and in particular to a pitch-based microcrystalline hard carbon material, its preparation method, and its application. Background Technology

[0002] With the rapid development of lithium-ion batteries and the scarcity of lithium resources, sodium-ion batteries, which have similar electrochemical properties and are abundant, are gradually showing good commercial potential. + The ionic radius of Li + The ionic radius of Na is about 55% larger, and its diffusion kinetics are slow, therefore Na + Insertion and extraction into battery materials are more difficult. Sodium storage behavior typically exhibits a ramp potential region (0.1V~2.8V) and a plateau region (0.01V~0.10V), with the region below 1.0V generally being the area that contributes to energy density, and its actual proportion is usually less than 50%. To improve the reversible capacity and rate performance of sodium-ion batteries and increase the utilization rate of reversible capacity (below 1.0V), designing and synthesizing hard carbon structures has become a major breakthrough.

[0003] Currently, research on hard carbon materials focuses more on high capacity and high first-efficiency (FAE), with insufficient attention paid to long cycling performance. Methods to obtain high-performance hard carbon anode materials include structural engineering, defect engineering, surface engineering, and pre-sodiumization. Among these, structural engineering mainly involves morphology control and pore design. Pore control is largely constrained by the intrinsic composition, structure, and properties of the precursor. Furthermore, the process of controlling pore size requires balancing factors such as the first-efficiency coulombic efficiency and cycling performance of hard carbon, resulting in limited overall improvement potential. For example, controlling the size of the hard carbon microcrystalline structure, which affects cycling performance, is primarily achieved by controlling the carbonization process. However, the carbonization process has limited impact on materials with a fixed structure. Therefore, the carbonization process can only address some technical requirements (such as high capacity and FAE) and cannot meet the long cycling requirements of hard carbon materials. Therefore, there is an urgent need to develop a hard carbon material that simultaneously achieves high capacity, high rate capability, and long cycling performance to meet market demands. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an asphalt-based microcrystalline hard carbon material, its preparation method, and its application. Using low-temperature asphalt as raw material, an intermediate phase asphalt with a certain carbon microcrystalline structure (ordered structure) is formed through thermal polycondensation. The intermediate phase asphalt is then subjected to oxidative crosslinking to expand the interlayer spacing of the carbon layers, ultimately resulting in a high-capacity, high-rate, and long-cycle asphalt-based microcrystalline hard carbon material.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing pitch-based microcrystalline hard carbon material, comprising the following steps:

[0007] S1, under an inert atmosphere, low-temperature asphalt is subjected to thermal condensation reaction at 300℃~550℃ and 0.01MPa~10MPa to obtain mesophase asphalt;

[0008] The softening point of the low-temperature asphalt is 18℃~48℃;

[0009] S2, under an oxygen-containing atmosphere, the mesophase pitch is oxidized and crosslinked to obtain a hard carbon precursor;

[0010] S3. Under an inert atmosphere, the hard carbon precursor is carbonized to obtain pitch-based microcrystalline hard carbon material.

[0011] Compared to existing technologies, the method for preparing pitch-based microcrystalline hard carbon materials provided by this invention uses low-temperature pitch as the main active material to store alkali metal ions. The low-temperature pitch has a very low content of aromatic components, which facilitates the control of carbon microcrystal size and reduces costs. Compared to medium- and high-temperature pitch raw materials, the low-temperature pitch has a very low content of aromatic components, making polymerization and cross-linking more difficult. This invention obtains anisotropic mesophase pitch with a certain carbon microcrystalline structure by controlling the temperature and pressure of the thermal polycondensation reaction. Compared to hard carbon materials with disordered structures, the irreversible capacity loss during cycling in mesophase pitch is reduced, and the cycling performance is greatly improved. Then, the surface and edges of the mesophase pitch are oxidized and cross-linked to expand the interlayer spacing of the carbon layers, further obtaining a carbon microcrystalline material with a disordered outer structure and an ordered internal structure as a hard carbon precursor. Combined with the relatively disordered combination of carbon microcrystals, the ramp and plateau regions of the battery material can store more alkali metal ions and respond more quickly to high-rate alkali metal ion diffusion, thereby improving the capacity and rate performance of the microcrystalline hard carbon material. Finally, through carbonization treatment, a high-capacity, high-rate, and long-cycle pitch-based microcrystalline hard carbon material is obtained.

[0012] The method for preparing pitch-based microcrystalline hard carbon materials provided by this invention creatively uses low-temperature pitch as raw material, which is readily available, low in cost, and simple and easy to operate. It is suitable for large-scale production and has high market application value.

[0013] Preferably, in step S3, the process further includes the following steps before the carbonization treatment:

[0014] High softening point asphalt is added to the hard carbon precursor, and granulation and spheroidization treatment is carried out to obtain coated hard carbon particle precursor.

[0015] The softening point of the high softening point asphalt is 180℃~320℃.

[0016] This invention coats the surface of a hard carbon precursor with high softening-point asphalt. High softening-point asphalt has a large molecular weight and is well-ordered, resulting in fewer defects in the hard carbon precursor. This reduces the specific surface area of ​​the microcrystalline hard carbon material, thereby reducing its irreversible capacity and improving its initial coulombic efficiency. It also increases the compaction density of the microcrystalline hard carbon material, allowing the anode to store more charge in the same volume, further optimizing its energy storage performance and thus improving the battery's energy density and range.

[0017] Preferably, in S1, the softening point of the low-temperature asphalt is 20℃~45℃.

[0018] Preferably, in S1, the coking value of the low-temperature asphalt is 15wt%~50wt%, more preferably 18wt%~48wt%, and even more preferably 25wt%~40wt%.

[0019] For example, in S1, the low-temperature bitumen is selected from petroleum bitumen or coal tar pitch.

[0020] Preferably, in S1, the low-temperature asphalt needs to be dried before the thermal polycondensation reaction.

[0021] For example, in S1, the drying temperature is 150℃~300℃ and the drying time is 1h~1.5h.

[0022] The present invention first dries the low-temperature asphalt, which can remove the moisture in the low-temperature asphalt and facilitate the subsequent thermal polycondensation reaction.

[0023] Preferably, in S1, the temperature is raised to 300℃~550℃ using a programmed temperature rise method, and the heating rate is 1℃ / min~20℃ / min (more preferably 1℃ / min~18℃ / min, more preferably 1℃ / min~10℃ / min).

[0024] Preferably, in S1, the temperature of the thermal polycondensation reaction is 350°C to 500°C, and the pressure is 0.01 MPa to 8 MPa (more preferably 0.5 MPa to 3 MPa).

[0025] Preferably, in S1, the thermal polycondensation reaction takes 0.5h to 30h, more preferably 1h to 30h, and even more preferably 2h to 20h.

[0026] Preferably, in S1, the inert atmosphere is selected from an argon atmosphere or a nitrogen atmosphere, and the gas flow rate is 10 mL / min to 200 mL / min, more preferably 10 mL / min to 180 mL / min, more preferably 15 mL / min to 120 mL / min, and even more preferably 20 mL / min to 80 mL / min.

[0027] This invention improves the thermal conversion efficiency of low-temperature asphalt and enhances the quality of mesophase asphalt by controlling the conditions of the thermal polycondensation reaction. This invention can regulate the orderliness of the mesophase asphalt structure by adjusting the conditions of the thermal polycondensation reaction. Generally, the lower the softening point of the low-temperature asphalt and the lower its molecular activity, the lower the temperature and the longer the time of the thermal polycondensation reaction; the higher the temperature of the thermal polycondensation reaction and the faster the reaction rate, the more ordered the microcrystalline structure of the mesophase asphalt; the higher the heating rate, the more disordered the microcrystalline structure of the mesophase asphalt.

[0028] Preferably, in S2, the oxygen content of the gas in the oxygen-containing atmosphere is ≥60% v / v, and the gas flow rate is 10mL / min~200mL / min.

[0029] More preferably, in S2, the oxygen content of the gas in the oxygen-containing atmosphere is ≥65% v / v, and the gas flow rate is 20mL / min~200mL / min (more preferably 50mL / min~100mL / min).

[0030] Preferably, in S2, the temperature of the oxidative crosslinking is 150℃~380℃, and the time of the oxidative crosslinking is 0.5h~20h.

[0031] More preferably, in S2, the temperature of the oxidative crosslinking is 180℃~350℃, and the time of the oxidative crosslinking is 1h~18h (more preferably 1.5h~10h).

[0032] This invention, by defining the conditions for oxidative crosslinking, enables mild oxidative crosslinking of the surface and edges of the mesophase pitch, effectively controlling the interlayer spacing of the carbon layers, and thus controlling the adsorption capacity and filling capacity in alkali metal ion batteries. To save energy, the oxidative crosslinking process in S2 does not require heating; the residual heat from the thermal polycondensation reaction can be used for mild oxidative crosslinking.

[0033] For example, in S2, after the oxidative crosslinking is completed, the process also includes: cooling to room temperature, filtering, crushing, and obtaining a hard carbon precursor.

[0034] More preferably, in S3, the mass ratio of the hard carbon precursor to the high softening point asphalt is (3~40):1, more preferably (3~30):1, and even more preferably (3~10):1.

[0035] More preferably, in S3, the softening point of the high softening point asphalt is 190℃~310℃, more preferably 220℃~280℃.

[0036] More preferably, in S3, the coking value of the high softening point asphalt is 45wt%~88wt%, more preferably 50wt%~85wt%, and even more preferably 60wt%~80wt%.

[0037] For example, in S3, the high softening point bitumen is selected from petroleum bitumen, coal tar pitch, or natural bitumen.

[0038] More preferably, in S3, the conditions for the granulation and coating spheroidization treatment include: a temperature of 250℃~350℃, a vacuum degree of 0.01bar~1bar, and a time of 2h~4h.

[0039] More preferably, in S3, the conditions for the granulation and coating spheroidization treatment include: a temperature of 270℃~320℃, a vacuum degree of 0.1bar~1bar, and a time of 2.5h~3.5h.

[0040] For example, in S3, the granulation and spheroidization process is carried out under stirring conditions at a speed of 450 rpm to 550 rpm.

[0041] This invention, by limiting the softening point, coking value, dosage, and granulation coating spheroidization treatment conditions of high softening point asphalt, can better compensate for the surface defects of microcrystalline hard carbon materials, reduce their specific surface area, and thus further reduce the irreversible capacity of microcrystalline hard carbon materials and improve the first coulombic efficiency.

[0042] Preferably, in S3, the inert atmosphere is selected from argon atmosphere or nitrogen atmosphere, and the gas flow rate is 0.01L / min to 5L / min, more preferably 0.1L / min to 3L / min, and even more preferably 0.1L / min to 1L / min.

[0043] Preferably, in S3, the carbonization treatment conditions include: first, heating to 350℃~550℃ at a rate of 0.1℃ / min~50℃ / min and holding at that temperature for 0.5h~10h; then heating to 750℃~1600℃ at a rate of 0.5℃ / min~20℃ / min and holding at that temperature for 0.5h~10h.

[0044] Microcrystalline hard carbon materials treated with only one high-temperature carbonization process have relatively small pore volumes and large pore sizes. The carbonization process of this invention is carried out in two steps. First, a first carbonization treatment is performed at a specific temperature, causing the unstable structures in the precursor material to break down and generate gas, resulting in finer pores and increased pore volume. Then, a second carbonization treatment is performed at a specific temperature; the high-temperature gas generation significantly damages the material's pore size, further carbonizing the material. Compared to a single high-temperature carbonization treatment, this invention, through a two-step carbonization process under specific conditions, increases the pore volume of the pitch-based microcrystalline hard carbon material, facilitating the shuttle movement of alkali metal ions within the pitch-based microcrystalline hard carbon material, thereby improving the pore volume and rate capability of the battery material.

[0045] More preferably, in S3, the carbonization treatment conditions include: first, heating to 350℃~550℃ at a rate of 1℃ / min~40℃ / min and holding at that temperature for 0.5h~8h; then heating to 750℃~1600℃ at a rate of 2℃ / min~15℃ / min and holding at that temperature for 0.5h~8h.

[0046] More preferably, in S3, the carbonization treatment conditions include: first, heating to 400℃~500℃ at a rate of 2℃ / min~20℃ / min and holding at that temperature for 0.6h~5h; then heating to 800℃~1500℃ at a rate of 4℃ / min~10℃ / min and holding at that temperature for 1h~6h.

[0047] For example, in S3, after the carbonization process is completed, the process also includes: cooling to room temperature, crushing, and obtaining pitch-based microcrystalline hard carbon material.

[0048] Preferably, the particle size of the pitch-based microcrystalline hard carbon material is D. 50 =4μm~18μm.

[0049] Secondly, the present invention provides an asphalt-based microcrystalline hard carbon material, which is prepared by the method for preparing the asphalt-based microcrystalline hard carbon material.

[0050] The pitch-based microcrystalline hard carbon material provided by this invention has an ordered structure of larger internal carbon microcrystals with low irreversible lithium or sodium intercalation capacity, and the disordered stacking structure between carbon microcrystals expands the filling capacity; the external oxygen-containing disordered structure has the function of adsorption and filling capacity, so that the pitch-based microcrystalline hard carbon material has both high capacity and long cycle characteristics; the large interlayer spacing of oxygen-containing materials improves the diffusion rate of alkali metal ions, and can withstand a higher current density.

[0051] In addition, when using high softening point asphalt for coating, the surface defects of microcrystalline hard carbon materials can be reduced, the irreversible capacity of microcrystalline hard carbon materials can be reduced, and the asphalt-based microcrystalline hard carbon materials can have high first-efficiency characteristics.

[0052] Thirdly, the present invention also provides an application of the asphalt-based microcrystalline hard carbon material in an alkali metal ion battery, wherein the alkali metal ion battery is selected from at least one of sodium ion batteries or lithium ion batteries.

[0053] Preferably, the pitch-based microcrystalline hard carbon material is the positive electrode material of the alkali metal ion battery.

[0054] The results of the examples show that when the pitch-based microcrystalline hard carbon material provided by the present invention is applied to sodium-ion batteries, the specific capacity can reach more than 220 mA·h / g, the initial coulombic efficiency can reach more than 60%, the 6C / 1C capacity retention rate can reach more than 60%, the capacity retention rate after 50 cycles at 1C can reach more than 60%, and the carbonization yield can reach more than 40%. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] This invention provides a method for preparing pitch-based microcrystalline hard carbon material, comprising the following steps:

[0057] S1, In an inert gas atmosphere, low-temperature asphalt is subjected to thermal condensation reaction at 300℃~550℃ and 0.01MPa~10MPa to obtain mesophase asphalt;

[0058] The softening point of the low-temperature asphalt is 18℃~48℃;

[0059] S2, under an oxygen-containing gas atmosphere, the mesophase pitch is oxidized and crosslinked to obtain a hard carbon precursor;

[0060] S3, add high softening point asphalt to the hard carbon precursor and perform granulation and spheroidization treatment to obtain coated hard carbon particle precursor.

[0061] The softening point of the high softening point asphalt is 180℃~320℃;

[0062] S4. Under an inert gas atmosphere, the coated hard carbon particle precursor is carbonized to obtain asphalt-based microcrystalline hard carbon material.

[0063] SP represents the coking value, and CV represents the coking value.

[0064] To better illustrate the present invention, further examples are provided below.

[0065] Example 1

[0066] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0067] Sa, 100g of low-temperature asphalt (SP=25℃, CV=32wt%) was placed in a high-temperature reactor in a flask and dried from room temperature to 200℃ for 1h to remove moisture. Argon gas was introduced at a flow rate of 50mL / min, and the dried low-temperature asphalt was heated to 400℃ at a rate of 1℃ / min and subjected to thermal polycondensation reaction at 1MPa for 6h. After the reaction, the obtained mesophase asphalt was immediately transferred to a round-bottom flask, and the gas was switched to oxygen-containing gas with an oxygen content of 65% v / v through a glass tube at a flow rate of 80mL / min. Oxidative crosslinking was carried out for 2h, then cooled to room temperature, filtered, and crushed to obtain the hard carbon precursor.

[0068] Sb, the hard carbon precursor was transferred to a high-temperature fusion granulator, and high softening point asphalt (SP=260℃, CV=73wt%) was added. The mass ratio of hard carbon precursor to high softening point asphalt was 3:1. Granulation and coating spheroidization treatment was carried out at 290℃ and 0.99 bar. The mixture was stirred and kept at the temperature for 3 hours to obtain coated hard carbon particle precursor.

[0069] Sc, the coated hard carbon particle precursor was transferred to a reactor, and under an argon atmosphere at a flow rate of 0.15 L / min, it was first heated to 460℃ at a rate of 5℃ / min for a first carbonization treatment and held at that temperature for 1 h; then, it was heated to 1350℃ at a rate of 7℃ / min for a second pre-carbonization treatment and held at that temperature for 3 h; after cooling to room temperature, it was crushed to obtain particles with a size of D 50 Pitch-based microcrystalline hard carbon material with a diameter of 6 μm.

[0070] Example 2

[0071] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0072] Sa, 100g of low-temperature asphalt (SP=30℃, CV=40wt%) was placed in a high-temperature reactor in a flask and dried at 220℃ from room temperature for 1 hour to remove moisture. Argon gas was introduced at a flow rate of 100mL / min, and the dried low-temperature asphalt was heated to 450℃ at a rate of 5℃ / min and subjected to thermal polycondensation reaction at 2MPa for 5 hours. After the reaction, the obtained mesophase asphalt was immediately transferred to a round-bottom flask, and the gas was switched to oxygen-containing gas with an oxygen content of 60% v / v through a glass tube at a flow rate of 100mL / min. Oxidative crosslinking was carried out for 3 hours, then cooled to room temperature, filtered, and crushed to obtain the hard carbon precursor.

[0073] Sb, the hard carbon precursor is transferred to a high-temperature fusion granulator, and high softening point asphalt (SP=310℃, CV=85wt%) is added. The mass ratio of hard carbon precursor to high softening point asphalt is 10:1. Granulation and coating spheroidization treatment is carried out at 340℃ and 0.50 bar. The mixture is stirred and kept at the temperature for 2 hours to obtain coated hard carbon particle precursor.

[0074] Sc, the coated hard carbon particle precursor was transferred to a reactor, and under an argon atmosphere at a flow rate of 0.1 L / min, it was first heated to 530℃ at a rate of 45℃ / min for a first carbonization treatment and held at that temperature for 6 h; then, it was heated to 1600℃ at a rate of 18℃ / min for a second pre-carbonization treatment and held at that temperature for 0.8 h; after cooling to room temperature, it was crushed to obtain particles with a size of D 50 Pitch-based microcrystalline hard carbon material with a diameter of 8μm.

[0075] Example 3

[0076] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0077] Sa, 100g of low-temperature asphalt (SP=20℃, CV=20wt%) was placed in a high-temperature reactor in a flask and dried at 180℃ from room temperature for 1.5h to remove moisture. Nitrogen gas was introduced at a flow rate of 30mL / min, and the dried low-temperature asphalt was heated to 350℃ at a rate of 10℃ / min and subjected to thermal polycondensation reaction at 0.5MPa for 8h. After the reaction, the obtained mesophase asphalt was immediately transferred to a round-bottom flask, and the gas was switched to oxygen-containing gas with an oxygen content of 70% v / v through a glass tube at a flow rate of 50mL / min. Oxidative crosslinking was carried out for 1.5h, then cooled to room temperature, filtered, and crushed to obtain the hard carbon precursor.

[0078] Sb, the hard carbon precursor was transferred to a high-temperature fusion granulator, and high softening point asphalt (SP=190℃, CV=48wt%) was added. The mass ratio of hard carbon precursor to high softening point asphalt was 30:1. Granulation and coating spheroidization treatment was carried out at 260℃ and 0.1 bar. The mixture was stirred and kept at the temperature for 4 hours to obtain coated hard carbon particle precursor.

[0079] Sc, the coated hard carbon particle precursor was transferred to a reactor. Under a nitrogen atmosphere at a flow rate of 5 L / min, the temperature was first increased to 360℃ at a rate of 0.3℃ / min for a first carbonization treatment, and held at this temperature for 0.6 h. Then, the temperature was increased to 780℃ at a rate of 0.7℃ / min for a second pre-carbonization treatment, and held at this temperature for 8 h. After cooling to room temperature, the particles were crushed to obtain particles with a diameter of D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 10 μm.

[0080] Example 4

[0081] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0082] Sa, 100g of low-temperature asphalt (SP=18℃, CV=20wt%) was placed in a high-temperature reactor in a flask and dried at 200℃ from room temperature for 1 hour to remove moisture. Argon gas was introduced at a flow rate of 200mL / min, and the dried low-temperature asphalt was heated to 300℃ at a rate of 18℃ / min. Thermal polycondensation reaction was carried out at 0.01MPa for 20 hours. After the reaction, the resulting mesophase asphalt was immediately transferred to a round-bottom flask. The gas was switched to oxygen-containing gas with an oxygen content of 90% v / v through a glass tube at a flow rate of 10mL / min. Oxidative crosslinking was carried out for 10 hours, then cooled to room temperature, filtered, and crushed to obtain the hard carbon precursor.

[0083] Sb~Sc, same as in Example 1, will not be described again. The final particle size is D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 16 μm.

[0084] Example 5

[0085] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0086] Sa, 100g of low-temperature asphalt (SP=45℃, CV=48wt%) was placed in a high-temperature reactor in a flask and dried from room temperature to 200℃ for 1h to remove moisture. Argon gas was introduced at a flow rate of 15mL / min, and the dried low-temperature asphalt was heated to 530℃ at a rate of 1.5℃ / min and subjected to thermal polycondensation reaction at 10MPa for 0.8h. After the reaction, the obtained mesophase asphalt was immediately transferred to a round-bottom flask, and the gas was switched to oxygen-containing gas with an oxygen content of 60% v / v through a glass tube at a flow rate of 200mL / min. Oxidative crosslinking was carried out for 10h, then cooled to room temperature, filtered, and crushed to obtain the hard carbon precursor.

[0087] Sb~Sc, same as in Example 1, will not be described again. The final particle size is D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 4μm.

[0088] Example 6

[0089] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, similar to Example 1, except that the oxygen content of the oxygen-containing gas in Sa is replaced with 40% v / v, the flow rate is replaced with 150 mL / min, and the oxidative crosslinking time is replaced with 5 h. The remaining operations are the same as in Example 1 and will not be repeated. The final particle size is D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 8μm.

[0090] Example 7

[0091] This embodiment provides a method for preparing an asphalt-based microcrystalline hard carbon material (without high softening point asphalt coating), including the following steps:

[0092] Sa, the same as in Example 1, will not be described again.

[0093] Sb: The hard carbon precursor was transferred to a reactor and subjected to a first carbonization treatment at 460℃ with a flow rate of 5℃ / min under an argon atmosphere at a flow rate of 0.15 L / min, and held for 1 h. Then, a second pre-carbonization treatment was performed at 1350℃ with a flow rate of 7℃ / min, and held for 3 h. After cooling to room temperature, the mixture was crushed to obtain particles with a size of D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 6 μm.

[0094] Example 8

[0095] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0096] Sa~Sb are the same as in Example 1, and will not be described again.

[0097] Sc, the coated hard carbon particle precursor was transferred to a reactor and carbonized at 600℃ at a rate of 5℃ / min under an argon atmosphere at a flow rate of 0.15L / min, and held at that temperature for 2h; after cooling to room temperature, it was crushed to obtain particles with a size of D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 10 μm.

[0098] Example 9

[0099] This embodiment provides a method for preparing pitch-based microcrystalline hard carbon material, including the following steps:

[0100] Sa~Sb are the same as in Example 1, and will not be described again.

[0101] Sc, the coated hard carbon particle precursor was transferred to a reactor and pre-carbonized at 1300℃ at a rate of 7℃ / min under an argon atmosphere at a flow rate of 0.15L / min, and held at this temperature for 7h; after cooling to room temperature, it was crushed to obtain particles with a size of D. 50 Pitch-based microcrystalline hard carbon material with a diameter of 10 μm.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing an asphalt-based microcrystalline hard carbon material, similar to Example 1, except that in Sa, the low-temperature asphalt is replaced with medium-temperature asphalt (SP=60℃, CV=32wt%). All other conditions are the same as in Example 1 and will not be repeated here.

[0104] Comparative Example 2

[0105] This comparative example provides a method for preparing pitch-based microcrystalline hard carbon material, similar to Example 1, except that in Sa, the temperature of the thermal polycondensation reaction is replaced with 200°C and the pressure is replaced with 0.01 MPa. All other conditions are the same as in Example 1 and will not be repeated here.

[0106] Comparative Example 3

[0107] This comparative example provides a method for preparing pitch-based microcrystalline hard carbon material, similar to Example 1, except that in Sa, the temperature of the thermal polycondensation reaction is replaced with 700°C and the pressure is replaced with 10 MPa. All other conditions are the same as in Example 1 and will not be repeated here.

[0108] Comparative Example 4

[0109] This comparative example provides a method for preparing pitch-based microcrystalline hard carbon material (omitting oxidative crosslinking), including the following steps:

[0110] Sa, 100g of low-temperature asphalt (SP=25℃, CV=32wt%) was placed in a high-temperature reactor in a flask and dried at 200℃ from room temperature for 1 hour to remove moisture. Argon gas was introduced at a flow rate of 50mL / min, and the dried low-temperature asphalt was heated to 400℃ at a rate of 1℃ / min. Thermal polycondensation reaction was carried out at 1MPa for 6 hours to obtain mesophase asphalt.

[0111] Sb, the mesophase asphalt was transferred to a high-temperature fusion granulator, and high softening point asphalt (SP=260℃, CV=73wt%) was added. The mass ratio of hard carbon precursor to high softening point asphalt was 3:1. Granulation and coating spheroidization treatment was carried out at 290℃ and 0.99 bar. The mixture was stirred and kept at the temperature for 3 hours to obtain coated hard carbon particle precursor.

[0112] Sc, the same as in Example 1, will not be described again.

[0113] Application Example 1

[0114] This application example provides a 2032 coin cell battery, which uses the pitch-based microcrystalline hard carbon material provided in Example 1 as the positive electrode material.

[0115] The preparation method of 2032 coin cell includes the following steps:

[0116] The positive electrode material, conductive agent SP, binder SBR, and binder CMC were mixed in a mass ratio of 95.5:1.5:1.5:1.5. The positive electrode material, conductive agent SP, binder SBR, and binder CMC were homogenized into a slurry, coated, and then dried to obtain the positive electrode sheet with a compacted density of 1.05 g / cm³. 3The negative electrode uses a 600μm thick sodium sheet, with added electrolyte, and is assembled into a 2032 coin cell.

[0117] Application Examples 2-9

[0118] Application Examples 2-9 provide a 2032 coin cell, and respectively use the asphalt-based microcrystalline hard carbon material provided in Examples 2-9 as the positive electrode material.

[0119] The preparation method of the 2032 button cell is the same as that in Application Example 1, and will not be repeated here.

[0120] Compare and contrast examples 1-4

[0121] Comparative Application Examples 1-4 provide a 2032 coin cell, using the pitch-based microcrystalline hard carbon material provided in Comparative Examples 1-4 as the positive electrode material.

[0122] The preparation method of the 2032 button cell is the same as that in Application Example 1, and will not be repeated here.

[0123] Charge and discharge test

[0124] The following procedures were followed to perform charge / discharge tests on the 2032 coin cells corresponding to test cases 1-9 and comparative application examples 1-4: In the 0-2.5V range, a constant current of 0.1C was first applied to 2.5V, followed by a constant voltage of 2.5V until the current was less than 0.02C. After two cycles, a constant current of 1C was applied for charging and discharging. This cycle was repeated for 50 cycles before removing the 2032 coin cells. The rate test involved constant 1C charging and discharging at 0.5C, 1C, 2C, 3C, 4C, 5C, or 6C, with each discharge rate cycled for 5 cycles. Specific test results are shown in Table 1.

[0125] Table 1. Charge and discharge test results of 2032 button cells in application examples and comparative application examples.

[0126]

[0127] In the table, "specific capacity" represents the ratio of the electrical capacity that the active material inside the battery can release to the mass of the active material; "6C / 1C capacity retention rate" represents the ratio of the battery charging capacity at 6C rate to the battery charging capacity at 1C rate; "carbonization yield" is the ratio of the products before and after carbonization, which is the mass ratio of asphalt-based microcrystalline hard carbon material to coated hard carbon particle precursor (or hard carbon precursor).

[0128] As can be seen from the test results in Table 1, in the preparation method of the asphalt-based microcrystalline hard carbon material provided by the present invention, the introduction of oxygen-containing gas for oxidative crosslinking can increase the disorder of the surface and edges of the mesophase asphalt, increase the interlayer spacing, and improve the hard carbon ratio; through the disordered layer structure, the adsorption and filling capacity of sodium ions are increased, thereby improving the specific capacity; controlling the time of the thermal polycondensation reaction of low-temperature asphalt can regulate the size of carbon microcrystals; using high softening point asphalt for coating can reduce the specific surface area and surface defects of the microcrystalline hard carbon material and improve the first coulombic efficiency.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a pitch-based microcrystalline hard carbon material, characterized in that, Includes the following steps: S1, under an inert atmosphere, low-temperature asphalt is subjected to thermal condensation reaction at 300℃~550℃ and 0.01MPa~10MPa to obtain mesophase asphalt; The softening point of the low-temperature asphalt is 18℃~48℃; S2, under an oxygen-containing atmosphere, the mesophase pitch is oxidized and crosslinked to obtain a hard carbon precursor; the oxygen content of the gas in the oxygen-containing atmosphere is ≥60% v / v; S3, add high softening point asphalt to the hard carbon precursor and perform granulation and coating spheroidization treatment to obtain coated hard carbon particle precursor; the softening point of the high softening point asphalt is 180℃~320℃. The coated hard carbon particle precursor is carbonized in an inert atmosphere to obtain asphalt-based microcrystalline hard carbon material.

2. The method for preparing pitch-based microcrystalline hard carbon material as described in claim 1, characterized in that, In S3, the carbonization treatment conditions include: first, heating to 350℃~550℃ at a rate of 0.1℃ / min~50℃ / min and holding at that temperature for 0.5h~10h; then heating to 750℃~1600℃ at a rate of 0.5℃ / min~20℃ / min and holding at that temperature for 0.5h~10h.

3. The method for preparing pitch-based microcrystalline hard carbon material as described in claim 1, characterized in that, In S1, the coking value of the low-temperature asphalt is 15wt%~50wt%; In S3, the coking value of the high softening point asphalt is 45wt%~88wt%.

4. The method for preparing pitch-based microcrystalline hard carbon material according to any one of claims 1 to 3, characterized in that, In S1, the temperature is raised to 300℃~550℃ using a programmed temperature rise method, with a heating rate of 1℃ / min~20℃ / min; In S1, the thermal polycondensation reaction takes 0.5 h to 30 h.

5. The method for preparing pitch-based microcrystalline hard carbon material according to any one of claims 1 to 3, characterized in that, In S2, the flow rate of the gas in the oxygen-containing atmosphere is 10 mL / min to 200 mL / min; In S2, the temperature of the oxidative crosslinking is 150℃~380℃, and the time of the oxidative crosslinking is 0.5h~20h.

6. The method for preparing pitch-based microcrystalline hard carbon material as described in claim 1, characterized in that, In S3, the mass ratio of the hard carbon precursor to the high softening point asphalt is (3~40):1; In S3, the conditions for the granulation and spheroidization treatment include: a temperature of 250℃~350℃, a vacuum degree of 0.01bar~1bar, and a time of 2h~4h.

7. A pitch-based microcrystalline hard carbon material, characterized in that, It is prepared by the method for preparing pitch-based microcrystalline hard carbon material according to any one of claims 1 to 6.

8. The application of the pitch-based microcrystalline hard carbon material according to claim 7 in alkali metal ion batteries, characterized in that, The alkali metal ion battery is selected from at least one of sodium ion batteries or lithium ion batteries.

9. The application of the pitch-based microcrystalline hard carbon material as described in claim 8 in alkali metal ion batteries, characterized in that, The pitch-based microcrystalline hard carbon material is the positive electrode material of the alkali metal ion battery.

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