Biomass-based hard carbon material and preparation method thereof, and sodium ion battery

Abstract

The application is suitable for the technical field of materials, and provides a biomass-based hard carbon material, a preparation method thereof and a sodium ion battery, and comprises the following steps: placing a biomass precursor subjected to acid washing and ash removal in an inert atmosphere, and performing low-temperature pre-carbonization treatment to obtain a pre-carbonized material; performing water vapor multi-step activation treatment on the carbonized material to obtain an activated material; performing ball milling treatment on the activated material, and then performing pitch coating treatment, and performing high-temperature carbonization treatment to obtain the biomass-based hard carbon material. Based on the synergistic effect between the steps, the ash is removed by using acid, preliminary carbonization is performed by pre-carbonization, the pore structure is further adjusted by water vapor multi-step activation, and finally, pitch coating and high-temperature sintering are performed to obtain the biomass-based hard carbon material with high specific capacity, high ICE and high kinetic performance, and the biomass-based hard carbon material has rich and suitable pore structures, and in particular, the ramp region capacity of the hard carbon material is improved, and the problems of low capacity and low ICE of the current hard carbon can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of materials, and particularly relates to a biomass-based hard carbon material and a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] With the rapid development of human society, people's demand for energy has increased dramatically, and energy storage technology has attracted much attention. Lithium batteries are considered the most valuable energy storage technology at present due to their high power density and energy density. The demand for lithium batteries in the consumer market and the power market is increasing. However, the domestic lithium resources are scarce and heavily dependent on imports, which poses a great risk to the healthy development of the domestic battery industry. Sodium and lithium have similar chemical properties, and sodium resources are abundant and inexpensive. Therefore, sodium ion batteries are considered to replace lithium batteries in some fields, and it is necessary to develop sodium ion batteries from a strategic point of view.

[0003] Unlike lithium batteries, in carbon-based negative electrode materials, due to the larger ionic radius of Na + than Li + , it is extremely difficult for Na + to diffuse in the interlayer spacing of graphite and to destroy the layered structure. In addition, theoretical studies have shown that Na + cannot form a stable first-order intercalation compound with graphite, and the fundamental reason is that the thermodynamic imbalance prevents Na + from effectively intercalating in graphite, resulting in a specific capacity of only 35 mAh / g when graphite is used as a sodium battery negative electrode material. Hard carbon has a large interlayer spacing, a complex microstructure, high defects, and high porosity, which supports sodium ion intercalation, adsorption, and other storage mechanisms in hard carbon. Its theoretical sodium storage capacity can be as high as 530 mAh / g, but it also has low initial coulombic efficiency (ICE), poor rate performance, and poor cycle stability. The sources of hard carbon mainly include resins, pitch, low-rank coal, and biomass. Biomass, as a renewable resource, has the advantages of wide availability, environmental friendliness, and low price, and is therefore attracting much attention as a source of hard carbon raw materials.

[0004] Biomass-based hard carbon as a negative electrode material for sodium ion batteries also has some shortcomings. Cellulose and lignin form short-range disordered graphite-like crystallites during carbonization, which cannot grow and extend like graphite, resulting in hard carbon with more defects, a large specific surface area, and a low tap density. When used as a negative electrode material for sodium ion batteries, it exhibits low capacity, low ICE, and low compaction. Currently, resin-coated biomass hard carbon precursors or carbon-hydrogen gas phase deposition to fill pores are commonly used to improve the capacity of hard carbon. The former has poor uniformity due to the poor compatibility between biomass and resin. The latter has a high cost, high process requirements, and certain safety hazards, which are not conducive to mass production. SUMMARY

[0005] The embodiment of the present application aims to provide a preparation method of biomass-based hard carbon material, and aims to solve the problems of low capacity, low ICE and low compaction, and high cost of existing biomass-based hard carbon material.

[0006] The embodiment of the present application is implemented in this way, a preparation method of biomass-based hard carbon material, comprising:

[0007] The biomass precursor treated by acid washing and ash removal is placed in an inert atmosphere for low-temperature pre-carbonization treatment to obtain pre-carbonized material;

[0008] The pre-carbonized material is subjected to water vapor multi-step activation treatment to obtain activated material; wherein the first step activation treatment parameters are: the volume ratio of water vapor and nitrogen is between 0.5-2, and the activation time is between 1-5h; the second step activation treatment parameters are: the volume ratio of water vapor and nitrogen is between 2-5, and the activation time is between 1-6h; the third step activation treatment parameters are: the volume ratio of water vapor and nitrogen is between 5-10, and the activation time is between 1-8h;

[0009] The activated material is subjected to ball milling treatment and then pitch coating treatment, and is subjected to high-temperature carbonization treatment to obtain biomass-based hard carbon material.

[0010] Another purpose of the embodiment of the present application is a biomass-based hard carbon material, which is prepared by the above-mentioned preparation method of biomass-based hard carbon material.

[0011] Another purpose of the embodiment of the present application is a sodium ion battery, which comprises the above-mentioned biomass-based hard carbon material.

[0012] The preparation method of biomass-based hard carbon material provided by the embodiment of the present application is based on the synergistic effect between each step, uses acid to remove ash, pre-carbonization to preliminarily form carbon, water vapor multi-step activation to further adjust the pore structure, and finally pitch coating and high-temperature sintering to obtain biomass-based hard carbon material with high specific capacity, high ICE and high kinetic performance, and rich and suitable pore structure, especially the slope region capacity of the hard carbon material is improved, which can effectively improve the problems of low capacity and low ICE of the current hard carbon. In addition, the method is low in cost and low in pollution, and is conducive to realizing industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The first circle charge-discharge curve diagram of the biomass-based hard carbon material provided for the embodiment 1 of the present application corresponds to a sodium ion battery;

[0014] Figure 2 The SEM diagram of the biomass-based hard carbon material provided for the embodiment 1 of the present application corresponds to a sodium ion battery;

[0015] Figure 3 The first circle charge-discharge curve diagram of the biomass-based hard carbon material provided in Example 5 of the present application corresponds to a sodium ion battery;

[0016] Figure 4 The first circle charge-discharge curve diagram of the biomass-based hard carbon material provided in Example 9 of the present application corresponds to a sodium ion battery;

[0017] Figure 5 The first circle charge-discharge curve diagram of the biomass-based hard carbon material provided in Comparative Example 1 of the present application corresponds to a sodium ion battery;

[0018] Figure 6 The first circle charge-discharge curve diagram of the biomass-based hard carbon material provided in Comparative Example 2 of the present application corresponds to a sodium ion battery. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0020] The present application provides a preparation method of a biomass-based hard carbon material, comprising:

[0021] The biomass precursor treated by acid washing and ash removal is placed in an inert atmosphere for low-temperature pre-carbonization treatment to obtain a pre-carbonized material;

[0022] The pre-carbonized material is subjected to multi-step steam activation treatment to obtain an activated material;

[0023] The activated material is subjected to ball milling treatment and then pitch coating treatment, and is subjected to high-temperature carbonization treatment to obtain a biomass-based hard carbon material.

[0024] In the present application, the first step activation treatment parameters are: the volume ratio of steam and nitrogen is between 0.5 and 2, and the activation time is between 1 and 5h; the second step activation treatment parameters are: the volume ratio of steam and nitrogen is between 2 and 5, and the activation time is between 1 and 6h; the third step activation treatment parameters are: the volume ratio of steam and nitrogen is between 5 and 10, and the activation time is between 1 and 8h.

[0025] Preferably, the first step activation treatment parameters are: the volume ratio of steam and nitrogen is between 0.5 and 1.8, and the activation time is between 1 and 4h; the second step activation treatment parameters are: the volume ratio of steam and nitrogen is between 2 and 4.5, and the activation time is between 1 and 3h; the third step activation treatment parameters are: the volume ratio of steam and nitrogen is between 5 and 8, and the activation time is between 2 and 6h.

[0026] More preferably, when the low-temperature pre-carbonization treatment temperature is 700℃, the first-step activation treatment parameters are: the volume ratio of water vapor and nitrogen is 0.5, and the activation time is 2h; the second-step activation treatment parameters are: the volume ratio of water vapor and nitrogen is between 3 and 4, and the activation time is 1h; and the third-step activation treatment parameters are: the volume ratio of water vapor and nitrogen is 6, and the activation time is 4h. The present application selects a low-activity water vapor to perform multi-step activation on the pre-carbonized material, has the characteristics of low cost and environmental friendliness compared with phosphoric acid, zinc chloride and other alkali metal activators; in addition, the volume ratio of water vapor and nitrogen and the activation time are regulated to further regulate the pore structure inside the carbon material, especially to increase the slope area capacity to 35-36%, and improve the battery kinetics performance, the first circle discharge capacity reaches 367-370mAh / g, and the ICE reaches 92-93%.

[0027] In the embodiments of the present application, the biomass precursor is one or more of bamboo, wood and shell.

[0028] In the embodiments of the present application, the acid washing and ash removal treatment conditions are: the acid concentration is 1-5mol / L, the liquid-solid ratio is 1-5, the heating temperature is 20℃-80℃, and the time is 2-24h. In the present application, part of the lignin and cellulose is decomposed during the acid washing and ash removal process, and the carbonized material has more defects, which will further form closed pores to improve the capacity after high-temperature carbonization; at the same time, most of the metal impurities are removed, which will reduce the influence of metal impurities on carbonization.

[0029] In the embodiments of the present application, the low-temperature pre-carbonization treatment conditions are: the temperature is 300℃-800℃, and the holding time is 1h-5h. If the low-temperature pre-carbonization treatment temperature is too low or the time is too short, the carbonization will be incomplete; similarly, if the carbonization temperature is too high and the time is too long, over-carbonization will occur, which will affect the subsequent activation effect.

[0030] In the embodiments of the present application, the ball milling treatment parameters are: the rotation speed is 400-800r / min, and the ball milling time is 0.5-4h.

[0031] In the embodiments of the present application, the pitch coating treatment parameters are: the softening point of the pitch is 150℃-280℃, and the coating amount of the pitch is 2%-20%. In the present application, a low-cost pitch is selected as the coating agent, which can fill the defects on the surface of the carbon material and improve the ICE of the hard carbon; at the same time, the pitch has a high slope capacity ratio, and using the pitch as the coating agent of the hard carbon helps to improve the kinetics performance of the material. Compared with gas phase hole filling and resin coating, the pitch coating process is relatively simple and has a lower cost.

[0032] In the embodiments of the present application, the high-temperature carbonization treatment parameters are: the carbonization temperature is 1000℃-1400℃, the heating rate is 2-5℃ / min, and the carbonization time is 1-6h.

[0033] In the embodiments of the present application, before the step of placing the acid-washed and deashed biomass precursor in an inert atmosphere and performing low-temperature pre-carbonization treatment to obtain a pre-carbonized material, the following step is further included:

[0034] The biomass precursor is placed in a temperature condition of 60-80°C for drying treatment for 6-12h, and after crushing treatment, it is passed through a 60-mesh screen and subjected to acid washing and deashing treatment.

[0035] The biomass-based hard carbon material, the preparation method thereof, and the sodium ion battery are described in detail in the following specific embodiments, and the specific embodiments are as follows. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; and unless otherwise specified, the materials, reagents, etc. used can be obtained through commercial channels.

[0036] Example 1

[0037] S1. A certain amount of bamboo powder is placed in a forced air drying oven, the temperature is set to 60°C, and the bamboo powder is dried until the mass is constant;

[0038] S2. Acid washing and deashing treatment: 100g of dried bamboo powder is placed in an acid washing kettle, according to a liquid-solid ratio of 5:1 and an acid concentration of 1M, an appropriate amount of HCl is added, the constant temperature is 80°C, and the acid washing time is 12h. The bamboo powder is washed with water for no less than 3 times, and then is completely dried in an oven.

[0039] S3. Pre-carbonization treatment: the acid-washed bamboo powder is placed in a rotary furnace, the temperature is raised to 500°C at a rate of 3°C / min, and the temperature is maintained for 3h.

[0040] S4. Activation treatment: after the pre-carbonization maintaining time ends, the temperature is continuously raised to 800°C, water vapor (V 水蒸气 / V 氮气 =0.5) is introduced for activation for 2h, water vapor (V 水蒸气 / V 氮气 =2) is continuously introduced for activation for 1h, and water vapor (V 水蒸气 / V 氮气 =5) is continuously introduced for activation for 3h.

[0041] S5. Milling treatment: the pre-carbonized material is subjected to ball milling at a speed of 800r / min for 40min, and the milled material is passed through a 325-mesh screen.

[0042] S6. Coating treatment: according to 14% of the absolute dry weight of the material to be coated, the above asphalt is completely dissolved in a heated stirring tank with tetrahydrofuran (THF), and then the carbonized material to be coated is added and uniformly mixed. After the THF is completely evaporated, the pre-carbonized material with a uniform asphalt coating on the surface is obtained.

[0043] S7. High temperature carbonization treatment, the above material is placed in a high temperature furnace, heated to 1200℃ at 2℃ / min in nitrogen atmosphere, and kept for 4h to obtain a biomass-based hard carbon material.

[0044] Example 2

[0045] This embodiment provides a preparation method of a biomass-based hard carbon material with bamboo powder as a precursor, which has basically the same preparation process as that of Example 1, except that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 = 1) is continued to be introduced for 2h, and water vapor (V 水蒸气 / V 氮气 = 2) is continued to be introduced for 1h, and water vapor (V 水蒸气 / V 氮气 = 5) is continued to be introduced for 3h.

[0046] Example 3

[0047] S1. A certain amount of bamboo powder is weighed and placed in a forced air drying oven, and the temperature is set to 60℃, and the bamboo powder is dried until the mass is constant;

[0048] S2. Acid washing and deashing treatment, 100g of dried bamboo powder is placed in an acid washing kettle, according to the liquid-solid ratio of 5:1, and the acid concentration is 1M, and an appropriate amount of HCl is added, and the constant temperature is 80℃, and the acid washing time is 12h. The bamboo powder is washed with water for not less than 3 times, and then dried in an oven.

[0049] S3. Pre-carbonization treatment, the above acid-washed bamboo powder is placed in a rotary furnace, and heated to 600℃ at a heating rate of 3℃ / min, and kept for 3h.

[0050] S4. Activation treatment, after the pre-carbonization keeping time ends, continue to heat to 800℃, and introduce water vapor (V 水蒸气 / V 氮气 = 1) for 2h, and continue to introduce water vapor (V 水蒸气 / V 氮气 = 2) for 2h, and continue to introduce water vapor (V 水蒸气 / V 氮气 = 5) for 3h.

[0051] S5. Grinding treatment, the above pre-carbonized material is ball milled, the ball milling speed is set to 800r / min, and the ball milling time is set to 40min, and the ball milled material is passed through a 325 mesh screen.

[0052] S6. Coating treatment, according to the dry weight of 14% of the material to be coated, the above-mentioned asphalt is weighed and dissolved in a heated stirring tank with tetrahydrofuran (THF), then the carbide to be coated is added and mixed uniformly. After the THF is completely evaporated, the pre-carbide with uniform asphalt coating on the surface is obtained.

[0053] S7. High-temperature carbonization treatment, the above-mentioned material is placed in a high-temperature furnace, heated to 1200℃ at 2℃ / min in a nitrogen atmosphere, and kept for 4h to obtain a biomass-based hard carbon material.

[0054] Example 4

[0055] This embodiment provides a preparation method of a biomass-based hard carbon material with bamboo powder as a precursor. The preparation process is basically the same as that of Example 3, except that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 =1) is continuously introduced for 1h, water vapor (V 水蒸气 / V 氮气 =2) is continuously introduced for 2h, water vapor (V 水蒸气 / V 氮气 =5) is continuously introduced for 3h.

[0056] Example 5

[0057] S1. A certain amount of bamboo powder is weighed and placed in a forced air drying oven, and the temperature is set to 60℃. The bamboo powder is dried until the mass is constant.

[0058] S2. Acid pickling and deashing treatment, 100g of dried bamboo powder is placed in an acid pickling kettle, according to the liquid-solid ratio of 5:1, the acid concentration is 1M, and an appropriate amount of HCl is added. The constant temperature is 80℃, and the acid pickling time is 12h. The bamboo powder is washed with water for not less than 3 times, and then dried in an oven.

[0059] S3. Pre-carbonization treatment, the above-mentioned acid-washed bamboo powder is placed in a rotary furnace, heated to 700℃ at a rate of 2℃ / min, and kept for 3h.

[0060] S4. Activation treatment, after the pre-carbonization holding time ends, continue to heat to 800℃, introduce water vapor (V 水蒸气 / V 氮气 =0.5) for 2h, continue to introduce water vapor (V 水蒸气 / V 氮气 =3) for 1h, continue to introduce water vapor (V 水蒸气 / V 氮气 =6) for 4h.

[0061] S5. Milling treatment, the above pre-carbonization is ball milled, the ball milling speed is set to 800 r / min, the ball milling time is set to 40 min, and the milled material is sieved through a 325 mesh screen.

[0062] S6. Coating treatment, according to 14% of the absolute dry weight of the material to be coated, the above asphalt is weighed, completely dissolved in a heated stirring tank with tetrahydrofuran (THF), and then the carbonide to be coated is added and uniformly mixed. After the THF is completely evaporated, the pre-carbonization with a uniform asphalt coating on the surface is obtained.

[0063] S7. High-temperature carbonization treatment, the above material is placed in a high-temperature furnace, heated to 1200℃ at 2℃ / min in a nitrogen atmosphere, and kept for 4h to obtain a biomass-based hard carbon material.

[0064] Example 6

[0065] This example provides a preparation method of a biomass-based hard carbon material with bamboo powder as a precursor, and the preparation process is basically the same as that of Example 5, except that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 =0.5) is introduced for 2h, water vapor (V 水蒸气 / V 氮气 =4) is continuously introduced for 1h, and water vapor (V 水蒸气 / V 氮气 =6) is continuously introduced for 4h.

[0066] Example 7

[0067] This example provides a preparation method of a biomass-based hard carbon material with bamboo powder as a precursor, and the preparation process is basically the same as that of Example 6, except that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 =0.5) is introduced for 5h, water vapor (V 水蒸气 / V 氮气 =4) is continuously introduced for 1h, and water vapor (V 水蒸气 / V 氮气 =6) is continuously introduced for 4h.

[0068] Example 8

[0069] This example provides a preparation method of a biomass-based hard carbon material with bamboo powder as a precursor, and the preparation process is basically the same as that of Example 6, except that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 =0.5) is introduced for 2h, water vapor (V 水蒸气 / V 氮气 =4) is continuously introduced for 4h, and water vapor (V水蒸气 / V 氮气 = 6) for 4h.

[0070] Example 9

[0071] S1. A certain amount of bamboo powder was weighed and placed in a forced air drying oven, the temperature was set to 60℃, and the bamboo powder was dried until the mass was constant;

[0072] S2. Acid pickling and deliming treatment, 100g of dried bamboo powder was placed in an acid pickling kettle, according to the liquid-solid ratio 5:1, the acid concentration was 1M, and an appropriate amount of HCl was added, the constant temperature was 80℃, and the acid pickling time was 12h. The bamboo powder was washed with water for not less than 3 times, and then dried in an oven.

[0073] S3. Pre-carbonization treatment, the above acid-pickled bamboo powder was placed in a rotary furnace, the temperature was raised to 800℃ at a rate of 2℃ / min, and the temperature was maintained for 3h.

[0074] S4. Activation treatment, after the pre-carbonization holding time ended, water vapor (V 水蒸气 / V 氮气 = 1.5) was introduced for 2h, and the water vapor (V 水蒸气 / V 氮气 = 3) was introduced for 1.5h, and the water vapor (V 水蒸气 / V 氮气 = 6) for 4h.

[0075] S5. Grinding treatment, the above pre-carbonized material was ball milled, the ball milling speed was set to 800r / min, and the ball milling time was set to 40min. The ground material was passed through a 325 mesh screen.

[0076] S6. Coating treatment, according to the absolute dry weight of the material to be coated 14%, the above asphalt was weighed and completely dissolved in a heated stirring tank with tetrahydrofuran (THF), then the carbonized material to be coated was added and mixed uniformly, and after the THF was completely evaporated, the pre-carbonized material with uniform asphalt coating on the surface was obtained.

[0077] S7. High temperature carbonization treatment, the above material was placed in a high temperature furnace, and the temperature was raised to 1200℃ at a rate of 2℃ / min in a nitrogen atmosphere, and the temperature was maintained for 4h, to obtain a biomass-based hard carbon material.

[0078] Example 10

[0079] The difference between the two is that: S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 = 1.5) was introduced for 2h, and the water vapor (V 水蒸气 / V氮气 = 3) activation for 2.5h, continue to pass water vapor (V 水蒸气 / 氮气 = 6) activation for 4h.

[0080] Example 11

[0081] S1. A certain amount of bamboo powder is weighed and placed in a forced air drying oven, the temperature is set to 60℃, and the bamboo powder is dried until the mass is constant;

[0082] S2. Acid pickling and deliming treatment, 100g of dried bamboo powder is placed in an acid pickling kettle, according to the liquid-solid ratio of 5:1, the acid concentration is 1M, and an appropriate amount of HCl is added, the constant temperature is 80℃, and the acid pickling time is 12h. The bamboo powder is washed with water for not less than 3 times, and then dried in an oven.

[0083] S3. Pre-carbonization treatment, the above acid-washed bamboo powder is placed in a rotary furnace, the temperature is raised to 600℃ at a rate of 3℃ / min, and the temperature is maintained for 3h.

[0084] S4. Activation treatment, after the pre-carbonization holding time ends, the temperature is raised to 800℃, and water vapor (V 水蒸气 / 氮气 = 3) activation for 3h, continue to pass water vapor (V 水蒸气 / 氮气 = 5) activation for 4h.

[0085] S5. Grinding treatment, the above pre-carbonized material is ball milled, the ball milling speed is set to 800r / min, and the ball milling time is set to 40min. The milled material is passed through a 325 mesh screen.

[0086] S6. Coating treatment, according to the absolute dry weight of the material to be coated 14%, the above asphalt is weighed and completely dissolved in a heated stirring tank with tetrahydrofuran (THF), then the carbonized material to be coated is added and mixed uniformly, and after the THF is completely evaporated, the pre-carbonized material with uniform asphalt coating on the surface is obtained.

[0087] S7. High temperature carbonization treatment, the above material is placed in a high temperature furnace, the temperature is raised to 900℃ at a rate of 2℃ / min in a nitrogen atmosphere, and the temperature is maintained for 4h to obtain a biomass-based hard carbon material.

[0088] Example 12

[0089] The difference between this embodiment and Example 11 is that S4. Activation treatment, water vapor (V 水蒸气 / 氮气 = 3) activation for 3h, continue to pass water vapor (V 水蒸气 / 氮气= 7) for 4h.

[0090] Example 13

[0091] S1. A certain amount of bamboo powder was weighed and placed in a forced air drying oven, the temperature was set to 60℃, and the bamboo powder was dried until the mass was constant;

[0092] S2. Acid pickling and deliming treatment, 100g of dried bamboo powder was placed in an acid pickling kettle, according to the liquid-solid ratio 5:1, the acid concentration was 1M, and an appropriate amount of HCl was added, the constant temperature was 80℃, and the acid pickling time was 12h. The bamboo powder was washed with water for not less than 3 times, and then dried in an oven.

[0093] S3. Pre-carbonization treatment, the above acid-pickled bamboo powder was placed in a rotary furnace, the temperature was raised to 800℃ at a rate of 2℃ / min, and the temperature was maintained for 3h.

[0094] S4. Activation treatment, after the pre-carbonization holding time ended, water vapor (V 水蒸气 / V 氮气 = 1.5) was introduced for 2h, and water vapor (V 水蒸气 / V 氮气 = 7) was introduced for 6h.

[0095] S5. Grinding treatment, the above pre-carbonized material was ball milled, the ball milling speed was set to 800r / min, and the ball milling time was set to 40min. The ground material was passed through a 325 mesh screen.

[0096] S6. Coating treatment, according to the absolute dry weight of the material to be coated 6%, the above asphalt was weighed and completely dissolved in a heated stirring tank with tetrahydrofuran (THF), then the carbonized material to be coated was added and mixed uniformly, and after the THF was completely evaporated, the pre-carbonized material with uniform asphalt coating on the surface was obtained.

[0097] S7. High temperature carbonization treatment, the above material was placed in a high temperature furnace, and the temperature was raised to 1200℃ at a rate of 2℃ / min in a nitrogen atmosphere, and the temperature was maintained for 4h, to obtain a biomass-based hard carbon material.

[0098] Example 14

[0099] The preparation method of the biomass-based hard carbon material with bamboo powder as the precursor provided in this embodiment is the same as that of Example 13, except that in S4. Activation treatment, water vapor (V 水蒸气 / V 氮气 = 1.5) was introduced for 2h, and water vapor (V 水蒸气 / V 氮气 = 6) was introduced for 6h.

[0100] Comparative Example 1

[0101] S1. A certain amount of bamboo powder was placed in a forced air drying oven, the temperature was set to 60°C, and the bamboo powder was dried until the mass remained unchanged;

[0102] S2. Acid pickling and ash removal treatment, 100g of dried bamboo powder was placed in an acid pickling kettle, according to the liquid-solid ratio 1:5, the acid concentration was 1M, and appropriate amount of HCl was added, the constant temperature was 80°C, and the acid pickling time was 12h. The bamboo powder was washed with water for not less than 3 times, and then dried again.

[0103] S3. Pre-carbonization treatment, the ash-removed and dried bamboo powder was placed in a rotary furnace, the temperature was raised to 700°C at a rate of 3°C / min, and the temperature was maintained for 3h.

[0104] S4. Grinding treatment, the pre-carbonized material was ball milled, the ball milling speed was set to 800r / min, and the ball milling time was set to 40min. The milled material was sieved through a 325 mesh screen.

[0105] S5. High temperature carbonization treatment, the sample was placed in a high temperature furnace, the temperature was raised to 1200°C at a rate of 2°C / min in a nitrogen atmosphere, and the temperature was maintained for 4h to obtain a high temperature carbonized biomass-based hard carbon material.

[0106] Comparative Example 2

[0107] S1. A certain amount of bamboo powder was placed in a forced air drying oven, the temperature was set to 60°C, and the bamboo powder was dried until the mass remained unchanged;

[0108] S2. Acid pickling and ash removal treatment, 100g of dried bamboo powder was placed in an acid pickling kettle, according to the liquid-solid ratio 1:5, the acid concentration was 1M, and appropriate amount of HCl was added, the constant temperature was 80°C, and the acid pickling time was 12h. The bamboo powder was washed with water for not less than 3 times, and then dried again.

[0109] S3. Pre-carbonization treatment, the ash-removed and dried bamboo powder was placed in a rotary furnace, the temperature was raised to 700°C at a rate of 3°C / min, and the temperature was maintained for 3h.

[0110] S4. S5. Activation treatment, after the pre-carbonization temperature maintaining time ended, the temperature was continued to be raised to 800°C, water vapor (V 水蒸气 / V 氮气 =3) was introduced for 8h of activation.

[0111] S5. Grinding treatment, the pre-carbonized material was ball milled, the ball milling speed was set to 800r / min, and the ball milling time was set to 40min. The milled material was sieved through a 325 mesh screen.

[0112] S6. Coating treatment, 14% of the mass of the carbon to be coated was asphalt, which was completely dissolved in tetrahydrofuran (THF) in a heated stirring tank, and the carbon to be coated was added and mixed uniformly. After the THF was completely evaporated, the pre-carbonized material with uniform asphalt coating on the surface was obtained.

[0113] S7. High temperature carbonization treatment, the above sample was placed in a high temperature furnace, heated to 1200℃ at 2℃ / min in nitrogen atmosphere, and kept for 4h to obtain the biomass-based hard carbon material.

[0114] Comparative Example 3

[0115] S1. A certain amount of bamboo powder was weighed and placed in a forced air drying oven, and the temperature was set to 60℃. The bamboo powder was dried until the mass was constant.

[0116] S2. Acid washing and deashing treatment, 100g of dried bamboo powder was placed in an acid washing kettle, the liquid-solid ratio was 1:5, the acid concentration was 1M, and an appropriate amount of HCl was added, the constant temperature was 80℃, and the acid washing time was 12h. The bamboo powder was washed with water for not less than 3 times, and then dried again.

[0117] S3. Pre-carbonization treatment, the deashed and dried bamboo powder was placed in a rotary furnace, and heated to 700℃ at a heating rate of 2℃ / min, and kept for 3h.

[0118] S4. Activation treatment, after the pre-carbonization holding time ended, the temperature was continued to be raised to 800℃, and water vapor (V 水蒸气 / V 氮气 = 6) was introduced for 5h of activation.

[0119] S5. Grinding treatment, the above pre-carbonized material was ball milled, the ball milling speed was set to 800r / min, and the ball milling time was set to 40min. The milled material was passed through a 325 mesh screen.

[0120] S6. Coating treatment, 14% of the above to-be-coated carbon mass of pitch was weighed, dissolved completely in a heated stirring tank with tetrahydrofuran (THF), and mixed uniformly with the to-be-coated carbon. After the THF was completely evaporated, the pre-carbonized material with uniform pitch coating on the surface was obtained.

[0121] S7. High temperature carbonization treatment, the above sample was placed in a high temperature furnace, heated to 1200℃ at 2℃ / min in nitrogen atmosphere, and kept for 4h to obtain the biomass-based hard carbon material.

[0122] The biomass-based hard carbon materials prepared in the above Examples 1-14 and Comparative Examples 1-3 were assembled into sodium-ion button cells, and the cell performance was tested, and the test results are shown in Table 1. Specifically, according to a mass ratio of 92%:3%:1.5%:3.5%, 184 mg of hard carbon, 6 mg of conductive carbon black, 6 mg of a carboxymethyl cellulose solution with a concentration of 2% (w / w), 17.5 mg of butadiene-styrene rubber with a concentration of 40% (w / w), and an appropriate amount of deionized water were weighed, stirred for 20 min until the slurry was uniform, and then uniformly coated on the surface of a copper foil using a 100-um doctor blade. The copper foil with the active material was dried in a 105°C air-drying oven for 2 h, cut into a circular negative electrode sheet, and then transferred into a glove box for standby use. The assembly of the simulated battery was carried out in an Ar-filled MIKROUNA glove box, using the prepared carbon material sheet as the negative electrode, a commercial electrolyte 1.0 mol / L NaPF6 / EC:DMC (1:1) (v:v) as the electrolyte, and metallic sodium as the counter electrode to assemble a 2016 button cell.

[0123] The first cycle charge-discharge curve of the sodium-ion battery assembled with the biomass-based hard carbon material prepared in Example 1 is shown in Figure 1 The SEM image of the biomass-based hard carbon material prepared in Example 1 is shown in Figure 2 The first cycle charge-discharge curve of the sodium-ion battery assembled with the biomass-based hard carbon material prepared in Example 5 is shown in Figure 3 The first cycle charge-discharge curve of the sodium-ion battery assembled with the biomass-based hard carbon material prepared in Example 9 is shown in Figure 4 The first cycle charge-discharge curve of the sodium-ion battery assembled with the biomass-based hard carbon material prepared in Comparative Example 1 is shown in Figure 5 The first cycle charge-discharge curve of the sodium-ion battery assembled with the biomass-based hard carbon material prepared in Comparative Example 2 is shown in Figure 6

[0124] Table 1

[0125]

[0126]

[0127] ​In summary, the embodiment of the present application selects low-cost water vapor to activate the pre-carbonized material to adjust the pore structure of the material. In the water vapor activation process, water molecules gradually diffuse from the surface layer of the material to the inside. Under high temperature conditions, water molecules react with the carbon atoms with strong activity that they contact to remove the carbon atoms. When the concentration of water vapor is high, the water molecules will quickly react with the carbon atoms on the surface layer of the material. Since it is difficult for water molecules to diffuse in the micropores in the material, the adjustment effect of water vapor on the pore structure of the surface layer of the material is obvious, but the adjustment effect on the pore structure in the inside is weak. The embodiment of the present application controls the concentration of water molecules by using multi-step activation to activate the material. In the first step, low-concentration water vapor is introduced to adjust the pore structure of the material to produce new defects to widen the pore distance. In the second step, the concentration of water vapor is slightly increased to further adjust the micropores in the material to increase the micropores and part of the pore size. In the third step, the concentration of water vapor is further increased to stably adjust the pore structure of the material. The pore structure of the biomass-based hard carbon material obtained by the method is more controllable and more uniform than that obtained by one-step water vapor activation.

[0128] According to the above Table 1, the main factors affecting the final performance of the material by water vapor activation are: gas flow and activation time; increasing the gas flow and prolonging the activation time during the activation process can improve the capacity and kinetic capacity ratio of the material; the capacity, initial efficiency and kinetic capacity ratio all decrease in Example 7 and Example 8, and in Example 11 and Example 14, respectively, because the average pore size increases by prolonging the activation time, water vapor is more easily passed through the pore channel, the pore size is further increased by high-temperature activation, and part of the pitch is melted during the coating process and enters the carbon inside to fill the pores and reduce the pore size, which is not conducive to the embedding and extraction of sodium ions.

[0129] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

[0130] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a biomass-based hard carbon material, characterized in that: include: The biomass precursor that has been subjected to acid washing and deashing treatment is placed in an inert atmosphere and subjected to low-temperature pre-carbonization treatment to obtain a pre-carbonized material; The pre-carbonized material is subjected to a multi-step activation treatment with water vapor to obtain an activated material; wherein the parameters for the first activation treatment are: a volume ratio of water vapor to nitrogen is between 0.5 and 2, and an activation time is between 1 and 5 hours; the parameters for the second activation treatment are: a volume ratio of water vapor to nitrogen is between 2 and 5, and an activation time is between 1 and 6 hours; and the parameters for the third activation treatment are: a volume ratio of water vapor to nitrogen is between 5 and 10, and an activation time is between 1 and 8 hours; The activated material is subjected to ball milling treatment, then subjected to asphalt coating treatment, and subjected to high-temperature carbonization treatment to obtain a biomass-based hard carbon material; The parameters of acid washing and deashing treatment are: acid concentration 1-5 mol / L, liquid-solid ratio 1-5, heating temperature 20℃-80℃, time 2-24h; The low-temperature pre-carbonization treatment parameters are: temperature 300℃~800℃, holding time 1h~5h; The high-temperature carbonization treatment parameters are: carbonization temperature 1000°C to 1400°C, and carbonization time 1 to 6 hours.

2. The method for preparing a biomass-based hard carbon material according to claim 1, wherein: The activation treatment parameters for the first step are: the volume ratio of water vapor and nitrogen is between 0.5 and 1.8, and the activation time is between 1 and 4 hours; the activation treatment parameters for the second step are: the volume ratio of water vapor and nitrogen is between 2 and 4.5, and the activation time is between 1 and 3 hours; the activation treatment parameters for the third step are: the volume ratio of water vapor and nitrogen is between 5 and 8, and the activation time is between 2 and 6 hours.

3. The method for preparing a biomass-based hard carbon material according to claim 1, wherein: The ball milling parameters are: rotation speed 400-800 r / min, ball milling time 0.5-4 h.

4. The method for preparing a biomass-based hard carbon material according to claim 1, wherein: The asphalt coating treatment parameters are: asphalt softening point 150°C to 280°C, asphalt coating amount 2% to 20%.

5. The method for preparing a biomass-based hard carbon material according to claim 1, wherein: During high temperature carbonization treatment: heating rate 2-5°C / min.

6. The method for preparing a biomass-based hard carbon material according to claim 1, wherein: Before the step of placing the biomass precursor that has undergone acid washing and deashing treatment in an inert atmosphere for low-temperature pre-carbonization treatment to obtain a pre-carbonized material, the method further includes: The biomass precursor is placed at a temperature of 60° C. to 80° C. for drying for 6 to 12 hours, and after being crushed, passed through a 60-mesh sieve and subjected to acid washing and deashing.

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

8. A sodium ion battery, characterized in that: The sodium ion battery comprises the biomass-based hard carbon material according to claim 7.

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