A biomass-based hard carbon preparation system and a preparation method

Abstract

The application discloses a biomass-based hard carbon preparation system and a preparation method. The biomass-based hard carbon preparation system comprises sequentially connected material crushing devices, pre-carbonization devices, high-temperature carbonization devices and cooling devices, wherein the material crushing devices can be used for primary crushing of biomass materials and secondary crushing of pre-carbonized materials; the pre-carbonization devices can be used for pre-carbonization of biomass materials and gas-phase modification of pre-carbonized materials, and thus the device procurement cost and the occupied space are effectively reduced. The biomass-based hard carbon preparation method comprises the following steps: crushing raw materials, primary carbonization, secondary crushing and gas modification, so that the pre-carbonized materials contain a large number of uniformly distributed pores, and after high-temperature carbonization, biomass-based hard carbon with low specific surface area and rich in a large number of closed pores is obtained, and the reversible capacity and the initial efficiency of the biomass-based hard carbon product are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, and particularly relates to a preparation system for preparing biomass-based hard carbon for battery negative electrode materials and a method for preparing biomass-based hard carbon by using the preparation system. BACKGROUND

[0002] The development of lithium batteries is affected by the distribution of lithium resources, and developing new energy storage forms is conducive to solving the potential energy crisis in China. Among them, sodium ion batteries as the next generation of clean energy storage forms still face great challenges in industrialization.

[0003] The positive electrode material of sodium batteries has been initially mass-produced, and the electrolyte and separator materials have also been successfully developed. However, the negative electrode material has not been mass-produced due to various technical routes. The three mature hard carbon technical routes for negative electrode materials currently include biomass-based hard carbon, coal-based hard carbon, and polymer-based hard carbon. The cost of polymer-based hard carbon is relatively high, which reduces the cost advantage of sodium ion batteries assembled by it; and the coal-based hard carbon has many impurities, which makes it difficult to ensure the stability of the hard carbon product, and most manufacturers still develop hard carbon products from biomass precursors.

[0004] Biomass-based hard carbon precursors have a wide range of sources and low prices. The precursors reported in patent documents mainly include fruit shells, coconut shells, peanut shells, corn cobs, walnut shells, bamboo, eucalyptus wood, etc. The conventional biomass-based hard carbon technical route often adopts the methods of pre-carbonization, acid washing, alkali catalytic pore forming, re-washing, coating or gas deposition. The route of multiple acid washing and alkali catalytic pore forming has high energy consumption, large equipment / environmental protection investment, and limited product performance improvement. However, the types of biomass precursors are diverse, and it is difficult to collect them. The inconsistent post-processing schemes lead to inconsistent performance of biomass-based hard carbon, and the carbon source capacity cannot meet the mass production demand. SUMMARY

[0005] The present application aims to overcome the problems of inconsistent performance of biomass-based hard carbon in the prior art and difficulty in meeting the mass production demand, and provides a preparation system based on biomass-based hard carbon. The preparation system has a simple device structure, low investment, and is convenient for realizing the mass production demand of biomass-based hard carbon. In addition, the present application also provides a biomass-based hard carbon preparation method in combination with the preparation system. The method has a simple process route, low energy consumption, and effectively improves the reversible capacity, initial efficiency and stability of the prepared hard carbon, and has excellent performance.

[0006] To achieve the above object, in one aspect, the present application provides a biomass-based hard carbon preparation system, which comprises a material crushing device, a pre-carbonization device, a high-temperature carbonization device and a cooling device connected in sequence through a material conveying system; the material conveying system is connected to the material inlet and the material outlet of the material crushing device, the pre-carbonization device, the high-temperature carbonization device and the cooling device in sequence; the pre-carbonization device and the high-temperature carbonization device are each provided with a gas inlet and a gas outlet, and the gas inlets of the pre-carbonization device and the high-temperature carbonization device are connected to a gas source device, and the gas outlets of the pre-carbonization device and the high-temperature carbonization device are connected to a spraying device.

[0007] In the biomass-based hard carbon preparation system, the material crushing device is used for preliminary crushing of biomass materials and re-crushing of pre-carbonized materials; the pre-carbonization device is used for pre-carbonization treatment of biomass raw materials and gas phase modification treatment of pre-carbonized materials; the high-temperature carbonization device is used for high-temperature carbonization treatment of modified pre-carbonized materials obtained after gas phase modification, so that the modified pre-carbonized materials are further reacted to obtain hard carbon products; and the cooling device is used for rapid cooling of the materials after high-temperature carbonization, so as to reduce the exposure time of the products in the air. The pre-carbonization device and the high-temperature carbonization device are each provided with a gas inlet and a gas outlet, and the gas inlets of the two devices are connected to the gas source device, so as to facilitate the gas source device to convey various required gases to the pre-carbonization device and the high-temperature carbonization device. The gas outlets of the two devices are connected to the spraying device, and the spraying device is used for spray incineration treatment of tail gas generated by the pre-carbonization device and the high-temperature carbonization device.

[0008] As a preferred embodiment of the biomass-based hard carbon preparation system, the material inlet of the material crushing device comprises a biomass raw material inlet and a pre-carbonized material inlet. The material inlet of the material crushing device is provided with the biomass raw material inlet and the pre-carbonized material inlet, respectively, the biomass raw material enters the material crushing device through the biomass raw material inlet for preliminary crushing, and the pre-carbonized material obtained after pre-carbonization enters the material crushing device through the pre-carbonized material inlet for re-crushing.

[0009] As a preferred embodiment of the biomass-based hard carbon preparation system, a gas flow meter and a gas control valve are arranged between the gas inlet of the pre-carbonization device and the gas source device. More preferably, the gas source device comprises an inert gas source device, a modification gas source device and a coating gas source device. The gas flow meter and the gas control valve are arranged between the gas inlet of the pre-carbonization device and the gas source device, respectively, the gas flow meter is used for regulating the flow rate of the gas, and the gas control valve can be connected to the inert gas source device, the modification gas source device and the coating gas source device through pipelines, so that the gas source device can provide the required types of gases to the pre-carbonization device as needed.

[0010] As a preferred embodiment of the biomass-based hard carbon preparation system, a gas flow meter is arranged between the gas inlet of the high-temperature carbonization device and the gas source device. A gas flow meter is also arranged between the gas inlet of the high-temperature carbonization device and the gas source device to regulate the gas flow.

[0011] As a preferred embodiment of the biomass-based hard carbon preparation system, the cooling device is further connected with a finishing and packaging device. The finishing and packaging device is used for screening, demagnetizing and packaging the final hard carbon, and finally obtaining the hard carbon product.

[0012] As a preferred embodiment of the biomass-based hard carbon preparation system, the material crushing device is an air flow crushing device or a mechanical crushing device. The material crushing device includes but is not limited to an air flow crushing device and a mechanical crushing device. Regardless of the choice of crushing device, it includes a biomass raw material inlet and a pre-carbonized material inlet, and a common material outlet.

[0013] As a preferred embodiment of the biomass-based hard carbon preparation system, the pre-carbonization device is a rotary furnace. The pre-carbonization device can be selected to include but is not limited to a rotary furnace, which is provided with a material inlet and an outlet, and a gas inlet and an outlet.

[0014] As a preferred embodiment of the biomass-based hard carbon preparation system, the high-temperature carbonization device is a track kiln or a push plate kiln. The high-temperature carbonization device can be selected to include but is not limited to a track kiln and a push plate kiln. Regardless of the choice, it needs to be provided with a material inlet and an outlet, and a gas inlet and an outlet.

[0015] As a preferred embodiment of the biomass-based hard carbon preparation system, the cooling device is a rotary kiln. The cooling device is preferably but not limited to a rotary kiln. The cooling device is connected with the high-temperature carbonization device through a pipeline. After cooling, the material is transported into the finishing and packaging device through a material conveying system for packaging of the hard carbon product.

[0016] In another aspect, the present application aims to provide a hard carbon preparation method with simple process and excellent and stable performance. To achieve this purpose, the technical solution adopted by the present application is as follows:

[0017] S1, the biomass material is once crushed, then preliminarily carbonized to obtain pre-carbonized material;

[0018] S2, the pre-carbonized material is twice crushed, and then gas phase modification is carried out to obtain modified pre-carbonized material; the gas phase modification is sequentially carried out by gas phase pore forming modification and gas phase coating modification;

[0019] S3, carbonizing the modified pre-carbonized material obtained in step S2 to obtain hard carbon.

[0020] The biomass-based hard carbon preparation method in the present application can be carried out by using the biomass-based hard carbon preparation system as described above. The primary crushing and preliminary carbonization in step S1 are carried out in a material crushing device and a pre-carbonization device respectively. The pre-carbonized material obtained after the preliminary carbonization is again fed into the material crushing device for secondary crushing in step S2, and then is subjected to gas-phase modification in the pre-carbonization device. The gas-phase modification includes sequentially carried out gas-phase pore-forming modification and gas-phase coating modification. Different gases are used for the modification in sequence to obtain modified pre-carbonized material. The modified pre-carbonized material is crushed and then fed into a high-temperature carbonization device for high-temperature carbonization. The material after high-temperature carbonization is fed into a cooling device for cooling to obtain hard carbon.

[0021] In the biomass-based hard carbon preparation method in the present application, biomass materials are used as raw materials. The biomass materials refer to hard materials such as wood powder, bamboo, and nut shells. Preferably, the biomass materials are selected from materials that are stable in supply and abundant, such as bamboo and commercial wood powder.

[0022] As a preferred embodiment of the biomass-based hard carbon preparation method in the present application, the modification gas used in the gas-phase pore-forming modification in step S2 is an oxygen-containing molecular gas with a diameter of less than or equal to 0.33 nm or a high-temperature pyrolysis product containing an oxygen-containing molecular gas with a diameter of less than or equal to 0.33 nm. In the gas-phase pore-forming modification, the oxygen-containing molecular gas with a diameter of less than 0.33 nm is used for gas-phase pore-forming. The modification gas can enter the inside of the pre-carbonized material for activation and pore-forming to obtain a large amount of uniformly distributed porous pre-carbonized material. After coating by a coating gas and surface gas-phase deposition, biomass-based hard carbon with low specific surface area and rich in a large amount of closed pores is obtained, which greatly improves the reversible capacity and initial efficiency of the product.

[0023] The gas-phase modification in step S2 needs to sequentially carry out gas-phase pore-forming modification and gas-phase coating modification. The modification gas used in the gas-phase pore-forming modification is an oxygen-containing molecule with a diameter of less than or equal to 0.33 nm, such as water vapor, carbon dioxide, etc., or a high-temperature pyrolysis product containing an oxygen-containing molecule with a diameter of less than or equal to 0.33 nm, such as formic acid, acetic acid, etc. More preferably, the modification gas used in step S2 includes at least one of water vapor, carbon dioxide, sulfur dioxide, formaldehyde, glyoxal, formic acid, and acetic acid.

[0024] As a preferred embodiment of the biomass-based hard carbon preparation method in the present application, the coating gas used in the gas-phase coating modification in step S2 is an unsaturated hydrocarbon or a gas that can polymerize to form an oligomer at high temperature.

[0025] The coating gas used in the gas phase coating modification in the step S2 is an unsaturated hydrocarbon, a gas that is easy to polymerize to form an oligomer at high temperature, such as ethylene, propylene, etc. More preferably, the coating gas used in the step S2 includes at least one of ethylene, propylene, butadiene, acetylene, and propyne.

[0026] As a preferred embodiment of the biomass-based hard carbon preparation method of the present application, in the gas phase pore-forming modification, the modification gas is used alone to perform pore-forming modification on the pre-carbonized material; or the modification gas is mixed with an inert gas to perform pore-forming modification on the pre-carbonized material. In the gas phase pore-forming modification, the modification gas can be used alone to perform pore-forming modification on the pre-carbonized material, or can be mixed with an inert gas to perform pore-forming modification on the pre-carbonized material. For example, when the modification gas is a water-containing small molecule, the modification gas is used alone to perform pore-forming modification on the pre-carbonized material. When the modification gas is a carbon dioxide-containing small molecule, the modification gas is mixed with an inert gas to perform pore-forming modification on the pre-carbonized material, and the volume ratio of the modification gas to the inert gas is 0.05-0.2:1.

[0027] As a preferred embodiment of the biomass-based hard carbon preparation method of the present application, in the gas phase coating modification, the coating gas is mixed with an inert gas to perform coating modification on the pre-carbonized material. In the gas phase coating modification, the coating gas needs to be mixed with an inert gas to perform coating modification on the pre-carbonized material. Preferably, the volume ratio of the coating gas to the inert gas is 0.01-0.2:1.

[0028] In the gas phase modification in the step S2, the pre-carbonized material is first subjected to gas phase pore-forming modification by the modification gas, and then is subjected to gas phase coating modification by the coating gas, and the modification sequence cannot be changed.

[0029] As a preferred embodiment of the biomass-based hard carbon preparation method of the present application, the particle size of the once-crushed biomass material in the step S1 is 1-10 cm. The particle size of the once-crushed biomass material is generally controlled to be 1-10 cm, which is appropriate for subsequent preliminary carbonization treatment.

[0030] As a preferred embodiment of the biomass-based hard carbon preparation method of the present application, the temperature of the preliminary carbonization in the step S1 is 400-600°C, and the time is at least 1 h. The heating rate of the preliminary carbonization in the step S1 is 5-10°C / min. More preferably, in the preliminary carbonization in the step S1, the temperature is raised to 500°C at a heating rate of 10°C / min, and then the temperature is maintained for carbonization for 1 h.

[0031] As a preferred embodiment of the biomass-based hard carbon preparation method, the particle size D50 of the secondary crushing in step S2 is between 9 and 12 μm. The particle size D50 of the secondary crushing needs to be controlled between 9 and 12 μm, so as to facilitate the subsequent gas phase modification treatment.

[0032] As a preferred embodiment of the biomass-based hard carbon preparation method, the temperature of the gas phase pore-forming modification in step S2 is 800-1000°C, and the modification time is 1-4 h. More preferably, the temperature of the gas phase pore-forming modification in step S2 is 900-1000°C, and the modification time is 2-3 h.

[0033] As a preferred embodiment of the biomass-based hard carbon preparation method, the temperature of the gas phase pore-forming modification in step S2 is 800-1000°C, and the modification time is 1-4 h. More preferably, the temperature of the gas phase pore-forming modification in step S2 is 900-1000°C, and the modification time is 2-3 h.

[0034] As a preferred embodiment of the biomass-based hard carbon preparation method, the temperature of the high-temperature carbonization in step S3 is 1200-1800°C. More preferably, the temperature of the high-temperature carbonization in step S3 is 1300-1400°C. In step S3, the high-temperature carbonization needs to be carried out under the protection of an inert gas, which includes but is not limited to Ar inert gas.

[0035] In the biomass-based hard carbon preparation method, the inert gas used is a conventional inert gas known at present, which includes but is not limited to helium (He), neon (Ne), argon (Ar), etc.

[0036] Finally, the present application also provides a biomass-based hard carbon prepared by the above method. The biomass-based hard carbon prepared by the method has not only good reversible capacity and initial efficiency, but also good stability.

[0037] The biomass-based hard carbon preparation system provided by the application comprises a material crushing device, a pre-carbonization device, a high-temperature carbonization device and a cooling device which are sequentially connected, wherein the material crushing device can be used for primary crushing of biomass materials and secondary crushing of pre-carbonized materials; the pre-carbonization device can be used for pre-carbonization of biomass materials and gas-phase modification of pre-carbonized materials; and the gas source device and the spraying device are arranged, which is beneficial to recycling of the gas. The biomass-based hard carbon preparation system provided by the application can effectively reduce the device procurement cost and the occupied space, and realize recycling of resources.

[0038] The biomass-based hard carbon preparation method provided by the application comprises the following steps: crushing and primary carbonizing raw materials, secondarily crushing the pre-carbonized materials and adopting a gas modification process, and completing the specific gas-phase modification sequence of pore forming and coating in one process, which can not only reduce the process flow and energy consumption, has good repeatability and controllability, but also can make the pre-carbonized materials contain a large number of uniformly distributed pores by selecting specific modification gas and coating gas, so that the biomass-based hard carbon with low specific surface area and rich in a large number of closed pores can be obtained after high-temperature carbonization, and the reversible capacity and initial efficiency of the biomass-based hard carbon product are greatly improved, and the competitiveness of the biomass-based hard carbon product is improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a structure schematic view of an embodiment of the biomass-based hard carbon preparation system provided by the application;

[0040] Figure 2 It is a first charge-discharge curve of Example 2 at a current density of 0.1C (1C=300 mAh / g);

[0041] Figure 3 It is a first charge-discharge curve of Example 3 at a current density of 0.1C (1C=300 mAh / g);

[0042] Figure 4 It is a first charge-discharge curve of Example 4 at a current density of 0.1C (1C=300 mAh / g);

[0043] Figure 5 It is a first charge-discharge curve of Comparative Example 1 at a current density of 0.1C (1C=300 mAh / g);

[0044] Figure 6 It is a first charge-discharge curve of Comparative Example 2 at a current density of 0.1C (1C=300 mAh / g);

[0045] Figure 7 It is a stability curve of Examples 2-4 and Comparative Examples 1-2 after 100 cycles;

[0046] Figure 1 In the figure, 1 is a material pulverizing device, 101 is a material conveying system, 2 is a pre-carbonization device, 3 is a high-temperature carbonization device, 4 is a gas control valve, 5 is a spraying device, 501 is tail gas conveying to a incineration device, 6 is a cooling device, 601 is material conveying to a finishing and packaging device, 7-10 are all gas flow meters, and 11 is a gas source device (including an inert gas source device, a modified gas source device and a coating gas source device). DETAILED DESCRIPTION

[0047] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with the drawings and specific embodiments.

[0048] Embodiment 1

[0049] An embodiment of the biomass-based hard carbon preparation system described in the present application is shown in the figure, which comprises a material pulverizing device 1, a pre-carbonization device 2, a high-temperature carbonization device 3 and a cooling device 6 connected in sequence through a material conveying system 101. Figure 1 The material conveying system 101 is connected to the material inlet and the material outlet of the material pulverizing device 1, the pre-carbonization device 2, the high-temperature carbonization device 3 and the cooling device 6 in sequence. The pre-carbonization device 2 and the high-temperature carbonization device 3 are both provided with a gas inlet and a gas outlet, the gas inlets of the pre-carbonization device 2 and the high-temperature carbonization device 3 are connected to a gas source device 11, and the gas outlets of the pre-carbonization device 2 and the high-temperature carbonization device 3 are connected to a spraying device 5.

[0050] The material pulverizing device 1 is used for the preliminary pulverization of biomass materials and the re-pulverization of pre-carbonized materials. The pre-carbonization device 2 is used for the pre-carbonization treatment of biomass raw materials and the gas phase modification treatment of pre-carbonized materials. The high-temperature carbonization device 3 is used for the high-temperature carbonization treatment of modified pre-carbonized materials obtained after the gas phase modification, so that the modified pre-carbonized materials are further reacted to obtain hard carbon products. The cooling device 6 is used for the rapid cooling of materials after high-temperature carbonization, so as to reduce the exposure time of the products in the air. The pre-carbonization device 2 and the high-temperature carbonization device 3 are both provided with a gas inlet and a gas outlet, and the gas inlets of the two are both connected to the gas source device 11, so as to facilitate the gas source device 11 to convey various required gases to the pre-carbonization device 2 and the high-temperature carbonization device 3. The gas outlets of the two are both connected to the spraying device 5, and the spraying device 5 is used for conveying the tail gas generated by the pre-carbonization device 2 and the high-temperature carbonization device 3 to the incineration device 501 for spraying incineration treatment.

[0051] The material inlet of the material crushing device 1 comprises a biomass raw material inlet and a pre-carbonized material inlet, the biomass raw material enters the material crushing device through the biomass raw material inlet for preliminary crushing, and the pre-carbonized material obtained after pre-carbonization enters the material crushing device through the pre-carbonized material inlet for re-crushing, both of which are discharged through a common outlet.

[0052] The gas inlet of the pre-carbonization device 2 is provided with a gas flow meter 7-9 and a gas control valve 4 between the gas inlet and a gas source device; the gas source device 11 comprises an inert gas source device, a modified gas source device and a coating gas source device. The gas flow meter 7-9 and the gas control valve 4 are respectively arranged between the gas inlet of the pre-carbonization device 2 and the gas source device 11, the gas flow meter is used to regulate the flow of gas, and the gas control valve 4 can be connected with the inert gas source device, the modified gas source device and the coating gas source device through a pipeline, and the gas source device can provide the required gas type to the pre-carbonization device according to the need

[0053] The gas inlet of the high-temperature carbonization device 3 is provided with a gas flow meter 10 between the gas inlet and the gas source device 11, and the gas flow meter 10 is used to regulate the flow of gas.

[0054] The cooling device 6 is also connected with a material conveying and finishing and packaging device 601, the finishing and packaging device is used for screening, removing magnetism and packaging of the finally obtained hard carbon, and finally obtains a biomass-based hard carbon product

[0055] In the embodiment, the material crushing device can be preferably but not limited to an airflow crushing device and a mechanical crushing device; the pre-carbonization device can be preferably but not limited to a rotary furnace; the high-temperature carbonization device can be preferably but not limited to a track kiln or a push plate kiln; and the cooling device can be preferably but not limited to a rotary kiln.

[0056] The biomass-based hard carbon preparation system described in the embodiment is used, biomass material is first fed into the biomass material inlet of the material crushing device from the material conveying system, preliminary crushing is performed in the material crushing device, and then the material is fed into the pre-carbonization device through the material conveying system, preliminary carbonization is performed under the protection of an inert atmosphere, and pre-carbonized material is obtained. The pre-carbonized material is again fed into the material crushing device through the pre-carbonized material inlet of the material crushing device through the material conveying system, and secondary crushing is performed in the material crushing device. The crushed pre-carbonized material is again fed into the pre-carbonization device through the material conveying system, heated to a certain temperature under the protection of nitrogen, and modified by gas-phase pore-forming. After modification, the modified gas is switched to a mixture of coating gas and inert gas, and the pre-carbonized material is further coated. After coating, modified pre-carbonized material is obtained. The modified pre-carbonized material is then fed into the high-temperature carbonization device through the material conveying system for high-temperature hard carbonization treatment. After high-temperature treatment, hard carbon material is obtained, which is then transported to the cooling device for further cooling, and hard carbon is obtained. Finally, the obtained hard carbon is screened, demagnetized, and packaged through the finishing and packaging device, and biomass-based hard carbon products are obtained.

[0057] Embodiment 2

[0058] In one embodiment of the biomass-based hard carbon preparation method described in the present application, the biomass-based hard carbon preparation method described in the embodiment can be carried out using the preparation system described in Embodiment 1, and specifically includes the following steps:

[0059] S1, bamboo is fed into the material crushing device for primary crushing, the particle size after crushing is controlled to be within 10 cm, and then the crushed bamboo is transported to the pre-carbonization device. The temperature in the pre-carbonization device is raised to 500℃ at a rate of 10℃ / min under the protection of nitrogen, and then the pre-carbonization is completed by maintaining the temperature for 1h, and pre-carbonized material is obtained;

[0060] S2, the pre-carbonized material obtained in step S1 is again fed into the crushing device for secondary crushing, and the crushing is performed to D50 = 9-12μm. Then the pre-carbonized material is again fed into the pre-carbonization device, and the temperature in the pre-carbonization device is raised to 900℃ at a rate of 10℃ / min under the protection of nitrogen. The nitrogen is switched to water vapor, and the water vapor is introduced for 3h to complete the gas-phase pore-forming modification. The water vapor is switched to a mixture of acetylene and nitrogen gas with a volume ratio of 0.04:1, the temperature of the pre-carbonization device is adjusted to 850℃, and the gas-phase coating modification is completed by maintaining the temperature for 1h, and modified pre-carbonized material is obtained;

[0061] S3, the modified pre-carbonized material obtained in step S2 is transported to the high-temperature carbonization device, and the temperature is raised to 1400℃ at a rate of 3℃ / min under an argon atmosphere. The high-temperature carbonization is completed by maintaining the temperature for 1h, and then the hard carbon after high-temperature carbonization is transported to the cooling device for cooling. The temperature is lowered to below 50℃ under a nitrogen atmosphere, and then the hard carbon product is packaged in the finishing and packaging device, and a biomass-based hard carbon product is obtained.

[0062] Example 3

[0063] In an embodiment of the biomass-based hard carbon preparation method, the biomass-based hard carbon preparation method can be carried out by using the preparation system in Example 1, and specifically includes the following steps:

[0064] S1, wood is sent into a material crushing device for primary crushing, the particle size after crushing is controlled to be within 10 cm, and then the crushed wood is transported to a pre-carbonization device, the temperature in the pre-carbonization device is raised to 500 DEG C at a rate of 10 DEG C / min under nitrogen protection, and then pre-carbonization is completed by keeping the temperature for 1 h to obtain pre-carbonized material;

[0065] S2, the pre-carbonized material obtained in step S1 is again sent into a crushing device for secondary crushing, and the crushing is performed to D50 = 9-12 μm, and then the pre-carbonized material is again sent into a pre-carbonization device, the temperature in the pre-carbonization device is raised to 1000 DEG C at a rate of 10 DEG C / min under nitrogen protection, the nitrogen gas is switched to a mixed gas of carbon dioxide and nitrogen with a volume ratio of 0.1:1, and the gas is passed for 2 h to complete the gas phase pore-forming modification; the temperature of the pre-carbonization device is adjusted to 550 DEG C, the mixed gas is switched to a mixed gas of ethylene and nitrogen with a volume ratio of 0.2:1, and the modification is completed by keeping the temperature for 1 h to obtain modified pre-carbonized material;

[0066] S3, the modified pre-carbonized material obtained in step S2 is transported to a high-temperature carbonization device, the temperature is raised to 1400 DEG C at a rate of 3 DEG C / min under argon atmosphere, and high-temperature carbonization is completed by keeping the temperature for 1 h, and then the hard carbon after high-temperature carbonization is transported to a cooling device for cooling, the temperature is lowered to below 50 DEG C under nitrogen atmosphere, and then the hard carbon product is packaged in a finishing and packaging device to complete the packaging of the hard carbon product, thereby obtaining a biomass-based hard carbon product.

[0067] Example 4

[0068] In an embodiment of the biomass-based hard carbon preparation method, the biomass-based hard carbon preparation method can be carried out by using the preparation system in Example 1, and specifically includes the following steps:

[0069] S1, wood is sent into a material crushing device for primary crushing, the particle size after crushing is controlled to be within 10 cm, and then the crushed wood is transported to a pre-carbonization device, the temperature in the pre-carbonization device is raised to 500 DEG C at a rate of 10 DEG C / min under nitrogen protection, and then pre-carbonization is completed by keeping the temperature for 1 h to obtain pre-carbonized material;

[0070] S2, the pre-carbonization material obtained in step S1 is again introduced into a crushing device, crushed to D50 = 9-12 μm, and then again sent into a pre-carbonization device, the temperature in the pre-carbonization device is increased to 900℃ at 10℃ / min under nitrogen protection, the nitrogen is switched to water vapor, and the gas phase pore forming modification is completed by passing the water vapor for 4h; the water vapor is switched to a mixed gas of carbon dioxide and nitrogen with a volume ratio of 0.2:1, and the gas phase coating modification is completed by keeping warm for 1h, to obtain modified pre-carbonization material;

[0071] S3, the modified pre-carbonization material obtained in step S2 is transported to a high-temperature carbonization device, and the temperature is increased to 1300℃ at 3℃ / min under an argon atmosphere, and kept warm for 2h to complete high-temperature carbonization, and then the hard carbon after high-temperature carbonization is transported to a cooling device for cooling, and the temperature is reduced to below 50℃ under a nitrogen atmosphere, and then transported to a finishing and packaging device to complete the packaging of the hard carbon product, to obtain a biomass-based hard carbon product.

[0072] Comparative Example 1

[0073] The biomass-based hard carbon preparation method of the present application is a comparative example, and the preparation method of the biomass-based hard carbon in the comparative example can be carried out using the preparation system described in Example 1, and specifically includes the following steps:

[0074] S1, the bamboo is sent into a material crushing device for primary crushing, and the particle size after crushing is controlled to be within 10cm, and then the crushed bamboo is transported to a pre-carbonization device, and the temperature in the pre-carbonization device is increased to 500℃ at 10℃ / min under nitrogen protection, and then kept warm for 1h to complete pre-carbonization, to obtain pre-carbonization material;

[0075] S2, the pre-carbonization material obtained in step S1 is again introduced into a crushing device for secondary crushing, and crushed to D50 = 9-12 μm;

[0076] S3, the pre-carbonization material after secondary crushing in step S2 is transported to a high-temperature carbonization device, and the temperature is increased to 1400℃ at 3℃ / min under an argon atmosphere, and kept warm for 1h to complete high-temperature carbonization, and then the hard carbon after high-temperature carbonization is transported to a cooling device for cooling, and the temperature is reduced to below 50℃ under a nitrogen atmosphere, and then transported to a finishing and packaging device to complete the packaging of the hard carbon product, to obtain a biomass-based hard carbon product.

[0077] The comparative example is compared with Example 2, and the only difference is that the pre-carbonization material after secondary crushing in step S2 is not subjected to gas phase modification.

[0078] Comparative Example 2

[0079] The biomass-based hard carbon preparation method of the present application is a comparative example, and the preparation method of the biomass-based hard carbon in the comparative example can be carried out using the preparation system described in Example 1, and specifically includes the following steps:

[0080] S1, the commodity wood powder is transported to a pre-carbonization device, the temperature in the pre-carbonization device is increased to 600 DEG C at 10 DEG C / min under the protection of nitrogen, and pre-carbonization is completed by keeping the temperature for 1h, and pre-carbonized material is obtained;

[0081] S2, the pre-carbonized material obtained in step S1 is again introduced into a crushing device, and is crushed to D50 = 9-12 μm;

[0082] S3, the pre-carbonized material after secondary crushing in step S2 is transported to a high-temperature carbonization device, and is increased to 1300 DEG C at 3 DEG C / min under an argon atmosphere, and high-temperature carbonization is completed by keeping the temperature for 2h, and then the hard carbon after high-temperature carbonization is transported to a cooling device for cooling, and is decreased to below 50 DEG C under a nitrogen atmosphere, and is transported to a finishing and packaging device, and the packaging of the hard carbon product is completed, and a biomass-based hard carbon product is obtained.

[0083] The present comparative example is compared with example 4, and the only difference is that the pre-carbonized material after secondary crushing in step S2 is not subjected to gas phase modification.

[0084] Effect example 1

[0085] Material characterization and electrochemical performance test experiment of the biomass-based hard carbon described in the present application

[0086] The biomass-based hard carbon materials prepared in examples 2-4 and comparative examples 1-2 described above are respectively used to prepare negative electrode sheets, and the sodium storage performance is tested.

[0087] The negative electrode sheet preparation method of each group is as follows: the prepared hard carbon material powder, SP and CMC are uniformly mixed according to a mass ratio of 93:5:5, water is added and stirred to prepare a slurry, the slurry is coated on an aluminum foil, and after drying, the aluminum foil is cut into a negative electrode sheet with a diameter of 12mm.

[0088] The sodium storage performance test method is as follows: the prepared negative electrode sheet is placed in a vacuum oven, vacuum dried at 90 DEG C for 12 hours, and after cooling, the negative electrode sheet is weighed. Sodium sheet is used as a counter electrode, 1mol / L NaPF6 solution in Diglyme solution is used as an electrolyte, and a CR2016 button cell is prepared in an argon glove box with a water oxygen content of less than 0.5ppm, and the button cell is tested by using a Shenzhen Xinwei battery test system, the half-cell test voltage range is 0-2V, and the charge and discharge current is 0.1C (1C = 300mAh / g). The test results are shown in Table 1 and Table 2. Figures 2-7 and Table 1.

[0089] Table 1 performance test results of the negative electrode sheets prepared from the hard carbons described in examples 2-4 and comparative examples 1-2

[0090]

[0091]

[0092] From the appendix Figures 2-7 As shown in Table 1, the reversible capacity and initial efficiency of the negative electrode sheets prepared from biomass-based hard carbon in Examples 2-4 are significantly higher than those in the comparative examples. This indicates that the biomass-based hard carbon prepared in Comparative Examples 1-2 without gas-phase modification has poor capacity and initial efficiency due to the lack of gas-phase pore-forming and gas-phase coating modifications. In contrast, the reversible capacity and initial efficiency of the biomass-based hard carbon materials prepared in Examples 2-4 after gas-phase modification are significantly improved, meeting the performance requirements of commercial hard carbon.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing biomass-based hard carbon, characterized in that, Includes the following steps: S1. The biomass material is crushed once and then pre-carbonized to obtain pre-carbonized material; S2. The pre-carbonized material is pulverized twice and then subjected to gas phase modification to obtain modified pre-carbonized material; the gas phase modification is performed by sequentially performing gas phase pore-forming modification and gas phase coating modification. S3. The modified pre-carbonized material obtained in step S2 is subjected to high-temperature carbonization to obtain hard carbon. In step S2, the modified gas used for gas-phase pore-forming modification is an oxygen-containing molecular gas with a diameter of less than or equal to 0.33 nm or a high-temperature pyrolysis product containing an oxygen-containing molecular gas with a molecular diameter of less than or equal to 0.33 nm; the modified gas enters the interior of the pre-carbonized material to activate and form pores, resulting in a uniformly distributed porous pre-carbonized material. In step S2, the gas used for vapor-phase coating modification is an unsaturated hydrocarbon or a gas that can polymerize at high temperatures to form oligomers; through coating with the gas and surface vapor deposition, a modified pre-carbonized material with low specific surface area and rich closed pores is obtained. In step S2, the temperature for vapor phase pore-forming modification is 800~1000℃, and the modification time is 1~4h; the temperature for vapor phase coating modification is 500~900℃, and the time is 1~4h.

2. The method for preparing biomass-based hard carbon as described in claim 1, characterized in that, The modified gas used in step S2 includes at least one of water vapor, carbon dioxide, sulfur dioxide, formaldehyde, glyoxal, formic acid, and acetic acid. And / or, the coating gas used in step S2 includes at least one of ethylene, propylene, butadiene, acetylene, and propyne; And / or, in the gas phase pore-forming modification, the modifying gas alone performs pore-forming modification on the pre-carbonized material; or the modifying gas and the inert gas are mixed together to perform pore-forming modification on the pre-carbonized material. And / or, in the gas-phase coating modification, the coating gas and the inert gas are mixed to jointly coat and modify the pre-carbonized material.

3. The method for preparing biomass-based hard carbon as described in claim 2, characterized in that, The modified gas is a water-containing small molecule, and the modified gas alone modifies the pre-carbonized material to create pores. And / or, the modified gas is a small molecule containing carbon dioxide, the modified gas is mixed with an inert gas to jointly modify the pre-carbonized material to form pores, and the volume ratio of the modified gas to the inert gas is 0.05~0.2:1; And / or, the volume ratio of the coating gas to the inert gas is 0.01~0.2:

1.

4. The method for preparing biomass-based hard carbon as described in claim 1, characterized in that, The particle size after one crushing in step S1 is 1~10cm; And / or, the initial carbonization temperature in step S1 is 400~600℃, and the time is at least 1 hour; And / or, the particle size D50 of the secondary crushing in step S2 is between 9 and 12 μm; And / or, in step S3, the high-temperature carbonization temperature is 1200~1800℃.

5. The method for preparing biomass-based hard carbon as described in claim 4, characterized in that, The heating rate for the initial carbonization in step S1 is 5~10℃ / min; And / or, the temperature of the vapor phase pore-forming modification in step S2 is 900~1000℃, and the modification time is 2~3h; And / or, in step S2, the coating gas in the gas-phase coating modification is ethylene, the coating modification temperature is 500~600℃, and the time is 1~2h; or, the coating gas in the gas-phase coating modification is acetylene, the coating modification temperature is 800~900℃, and the time is 1~2h. And / or, in step S3, the high-temperature carbonization temperature is 1300~1400℃.

6. A biomass-based hard carbon prepared by the method described in any one of claims 1 to 5.

Images