Anti-oxidation low specific surface area carbonization crucible for air atmosphere tunnel kiln and application

Abstract

The present application belongs to the technical field of lithium ion battery negative electrode material preparation, especially to an anti-oxidation low specific surface area carbonization crucible for air atmosphere tunnel kiln and application. The crucible comprises a crucible body and a cover connected by a labyrinth joint, the labyrinth joint comprises a plurality of clamping grooves and a plurality of bosses matched with the shape of the clamping grooves, and the inside of the clamping groove is provided with a carbon source sealing medium which can generate in-situ curing reaction at a temperature above 250 DEG C. The present application provides a crucible assembly and a continuous carbonization process thereof, which is suitable for high-temperature carbonization treatment of carbon-containing powders in an oxidative atmosphere such as air.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material preparation technology, and particularly relates to an anti-oxidation low specific surface area carbonization crucible for use in an air atmosphere tunnel kiln and its application. Background Technology

[0002] In the preparation of lithium-ion battery anode materials, it is often necessary to mix and granulate a graphite substrate with a binder (such as 5%-15% asphalt, resin, etc.) and then perform carbonization treatment at high temperatures (such as around 1150℃). Currently, the mainstream process in the industry uses a roller kiln (RHK) with high-purity nitrogen protection and a graphite sagger. This process requires a huge investment in equipment, and the consumption of high-purity nitrogen leads to persistently high long-term operating costs (Opex).

[0003] The industry has been trying to replace roller kilns with continuous tunnel kilns (typically air or weakly oxidizing atmospheres), which have extremely low construction costs and operating energy consumption. However, this attempt faces a formidable technological bias and bottleneck: 1. The contradiction between venting and oxidation prevention: Asphalt releases a large amount of volatiles during carbonization (the residual carbon rate is usually around 50%). If the crucible is sealed too tightly, the drastically increased internal pressure will cause the crucible to crack; if a vent is provided or the seal is not tight, high-temperature air from the tunnel kiln will enter the crucible.

[0004] 2. Deterioration of specific surface area (BET): Invading oxygen burns the asphalt coating and erodes the graphite substrate, resulting in a large number of micropores on the material surface, which drastically increases the specific surface area and severely deteriorates the battery's first efficiency (ICE) and cycle performance.

[0005] 3. Fixture wear: Traditional graphite crucibles are easily oxidized and worn in air tunnel kilns, and cannot be recycled for a long time.

[0006] Therefore, there is an urgent need for an anti-oxidation, low specific surface area carbonization crucible for use in air-atmosphere tunnel kilns and its application to solve the above problems. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the crucible of this invention features a minimalist "self-breathing" anti-oxidation design. It does not require mechanical exhaust valves or top openings. It relies solely on the phase change characteristics of the sealing medium as it changes with temperature to create a micro-reduction environment in an air-atmosphere tunnel kiln, smoothly expelling asphalt volatiles while completely blocking oxygen and preventing the product's specific surface area from exceeding the standard.

[0008] To achieve one of the above objectives, the present invention adopts the following technical solution: An anti-oxidation low specific surface area carbonization crucible for use in an air atmosphere tunnel kiln, the crucible includes a crucible body and a cover body connected by a labyrinth joint. The labyrinth joint includes a number of slots and a number of protrusions adapted to the shape of the slots. The interior of the slots is provided with a carbon source sealing medium that can undergo in-situ curing reaction at a temperature above 250 degrees Celsius.

[0009] Preferably, the material of the crucible body is one of silicon carbide composites (such as clay-bonded silicon carbide, silicon nitride-bonded silicon carbide), mullite, cordierite, and corundum composite materials.

[0010] Preferably, the cover is a blind cover structure without any air holes, and the pressure per unit area generated by the weight of the cover on the contact surface of the slot is 500 Pa - 5000 Pa, so that the pressure of the cover is always greater than the exhaust pressure of the gas inside the crucible body.

[0011] Preferably, the carbon source sealing medium is one or a combination of sugar aqueous solution, phenolic resin solution, furan resin solution, liquid coal tar pitch, petroleum pitch, coal tar, heavy oil, lignin solution, and hydrocarbon polymer solution with high carbon residue.

[0012] Preferably, the interior of the crucible body is provided with a sacrificial oxygen-consuming isolation layer.

[0013] Preferably, the sacrificial oxygen-consuming isolation layer is one or more of the following: carbon paper, carbon cloth, porous carbon felt, foamed carbon, graphite foil, graphite plate, activated carbon layer, carbon black layer, graphite powder layer, and organic polymers (such as phenolic resin board or polyacrylonitrile (PAN) nonwoven fabric) with a carbon residue rate of more than 20% in an inert atmosphere at 1000°C.

[0014] Preferably, the number of slots is the same as the number of bosses, and the number of slots is one or two arranged sequentially along the radial direction of the crucible body; the vertical cross-section of the slot is U-shaped.

[0015] Preferably, the slot is embedded on the outer edge of the top of the crucible body, and the boss is set on the outer edge of the bottom of the cover. Both the slot and the boss are annular and their sizes are compatible.

[0016] Preferably, the slot is embedded on the outer edge of the bottom of the cover, and the boss is set on the outer edge of the top of the crucible body. Both the slot and the boss are annular and their sizes are compatible.

[0017] To achieve the second objective mentioned above, this invention provides an application of an anti-oxidation, low specific surface area carbonization crucible for use in an air-atmosphere tunnel kiln, the specific steps of which are as follows: S1. Assembly Preparation: Fill the crucible body with the powder to be carbonized, and lay a sacrificial oxygen-consuming isolation layer on top of the powder; inject the carbon source sealing medium into the slot of the labyrinth joint and press the cover closed. The slot and the boss engage. After the crucible completes the initial assembly, it is pushed into the air atmosphere tunnel kiln with the kiln car; gradually raise the temperature from room temperature to about 300°C in the preheating zone; at this time, the powder has not yet undergone violent pyrolysis, while the carbon source sealing medium in the slot softens and melts when heated, and the viscosity decreases, forming a complete closed-loop "liquid sealing pool" in the slot, achieving initial isolation from the external air; S2. Dynamic exhaust and gas seal: As the kiln car moves to the medium temperature zone, the powder inside the crucible produces volatile gas, which causes the internal pressure to rise sharply. The volatile gas overcomes the resistance of the flowing or molten carbon source sealing medium and overflows outward to release pressure, forming a dynamic positive pressure air curtain at the gap of the labyrinth joint to prevent the backflow of external oxygen. S3, In-situ coking seal: As the kiln car continues to move to the 600℃-850℃ temperature zone, the release of volatile gas generated by the powder decreases sharply, the internal pressure of the crucible drops, and the carbon source sealing medium (5) undergoes an in-situ solidification reaction at high temperature, transforming into a dense amorphous solid carbon skeleton, which physically seals the gaps of the labyrinth joint. S4. Constant temperature carbonization and heat preservation: The kiln car enters the high temperature constant temperature zone for deep carbonization. The completely sealed solid carbon skeleton is used to isolate the strong oxidizing atmosphere outside, and the internal sacrificial oxygen-consuming isolation layer (6) is used to deplete the residual oxygen first. After carbonization, the kiln is cooled and the outer edge of the brittle solid carbon layer is broken to open the lid and demold.

[0018] Preferably, the temperature in the temperate zone is 300℃-600℃; the temperature in the high-temperature constant temperature zone is ≥1000℃.

[0019] Preferably, in step S4, after the kiln car is removed from the tunnel kiln, the sacrificial oxygen-consuming isolation layer with a solid carbon skeleton is removed, and a new sacrificial oxygen-consuming isolation layer is installed for the next use.

[0020] The advantages of this invention are: (1) The present invention proposes a crucible assembly and its continuous carbonization process, which is suitable for high-temperature carbonization treatment of carbon-containing powder (e.g., graphite-coated granules) in an oxidizing atmosphere such as air.

[0021] (2) The crucible of the present invention has a very simple structure and a “self-breathing” anti-oxidation design. It does not require a mechanical exhaust valve or a top opening. It can create a micro-reduction environment in the air atmosphere tunnel kiln by relying solely on the phase change characteristics of the sealing medium as the temperature changes, smoothly discharge the volatile asphalt, and completely block oxygen to avoid the product’s specific surface area from exceeding the standard.

[0022] (3) The core of this invention lies in the synergistic cooperation between structure and materials, always maintaining "P" seal< (P int – P ext ) <P lid The dynamic exhaust critical condition is met, and it has the following advantages: a. Significantly reduce operating costs: Successfully realize the application of air atmosphere tunnel kiln in high-temperature carbonization of high-end graphite anode, completely eliminating the consumption of high-purity nitrogen and RHK equipment investment. b. Perfect control of product BET: Through three-level protection of "liquid seal exhaust, solid seal oxygen barrier, and internal oxygen consumption", oxidation and etching are eliminated, ensuring the integrity of the coated carbon layer, the product specific surface area is stable, and the electrochemical performance is comparable to that of traditional nitrogen roller kiln. c. Extremely simple and highly reliable: No vents or moving mechanical parts, completely eliminating major engineering hazards such as mechanical valve jamming or explosion caused by tar coking at high temperatures; high jig turnover rate, long service life, and easy demolding and cleaning (the brittle solidified carbon layer can be broken by tapping after exiting the kiln, thus opening the lid). Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention. Figure 1 .

[0024] Figure 2 This is a schematic diagram of the structure of the present invention. Figure 2 .

[0025] Figure 3 This is a model diagram of the dynamic temperature-pressure response of the self-breathing crucible of the present invention in a tunnel kiln.

[0026] The meanings of the symbols in the diagram are as follows: 1-Cruxetine body, 2-Lid, 3-Slot, 4-Boss, 5-Carbon source sealing medium, 6-Sacrificial oxygen-consuming isolation layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] like Figure 1 As shown in Figure 2, an anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln includes the following structure: 1. Crucible base material: Both the crucible body 1 (i.e., the crucible body) and the lid 2 are made of non-metallic ceramic materials that are resistant to high temperature and have excellent oxidation resistance in air. Preferably, they are one of silicon carbide composites (such as clay-bonded silicon carbide, silicon nitride-bonded silicon carbide), mullite, cordierite and corundum composite materials.

[0029] 2. Minimalist, holeless blind cap and self-weight pressing structure: The top of the cap 2 is a "blind cap" structure without any vent holes. The cap 2 relies on its own weight to press and fit tightly against the crucible body 1.

[0030] 3. Phase Change Type Dynamic Labyrinth Seal: The upper edge of the crucible body 1 and the edge of the cover 2 are provided with a matching labyrinth-type joint. The labyrinth-type joint consists of several slots 3 and several protrusions 4 that are adapted to the shape of the slots 3. The slots 3 have a U-shaped structure (which may have an outward flaring slope or a bell mouth). In use, the slots 3 are filled with a carbon source sealing medium 5 that is easily coked by heat. This labyrinth-type joint constitutes a "phase change type one-way self-breathing valve", and its dynamic mechanism is as follows: Cryogenic liquid seal venting stage (approximately 300℃-700℃): The asphalt in the powder filling inside the crucible undergoes violent pyrolysis, generating a large amount of high-pressure volatile gas. At this time, the carbon source sealing medium 5 in slot 3 is heated and transformed into a viscous liquid / semi-fluid state. The high-pressure volatile gas is released outward in the form of bubbling, overcoming the liquid seal resistance. The high-speed outward airflow forms a positive pressure air curtain at the gaps of the labyrinthine joint, preventing the backflow of external oxygen.

[0031] High-temperature solidification and oxygen barrier stage (approximately 700℃-1150℃): The release of internal high-pressure volatile gases is basically complete. At this time, the carbon source sealing medium 5 in the slot 3 undergoes a complete coking and condensation reaction at high temperature, transforming in situ into a dense amorphous solid carbon skeleton. This solid carbon skeleton perfectly fills the assembly gap between the crucible body 1 and the cover 2, forming an irreversible physical seal, completely blocking the intrusion of high-temperature oxygen in the tunnel kiln at 1000℃.

[0032] Engineering constraint parameters: The weight of the cover 2 itself is greater than the critical pressure resistance required for the internal high-pressure volatile gas to push open the liquid carbon source sealing medium 5, so as to prevent the cover 2 from being lifted and displaced as a whole during the exhaust process.

[0033] Furthermore, such as Figure 1 As shown, the slot 3 is embedded on the outer edge of the top of the crucible body 1, and the boss 4 is set on the outer edge of the bottom of the cover 2. Both the slot 3 and the boss 4 are annular, and their sizes are compatible.

[0034] Furthermore, such as Figure 2 As shown, the slot 3 is embedded in the outer edge of the bottom of the cover 2, and the boss 4 is set on the outer edge of the top of the crucible body 1. Both the slot 3 and the boss 4 are annular, and their sizes are compatible.

[0035] 4. Sacrificial Oxygen-Depleting Isolation Layer 6 (Double Insurance): Inside the crucible, above the carbon-containing powder to be processed, at least one highly active sacrificial oxygen-depleting isolation layer 6 (which can be carbon paper, carbon cloth, porous carbon felt, carbon foam, graphite foil, activated carbon layer, carbon black layer, and graphite powder layer, etc.) is laid flat. This sacrificial oxygen-depleting isolation layer 6 has a dual function: (1) As a physical barrier, it prevents carbon slag that may be generated at the top or labyrinthine junction from falling and contaminating the powder; (2) As a preferred oxidant, it preferentially and rapidly consumes the oxygen remaining in the crucible or the trace amount that has seeped in during the initial heating or pressure difference conversion, ensuring that the graphite substrate and coating at the bottom of the crucible are in an absolutely oxygen-deficient and safe state.

[0036] In addition to the non-perforated blind cap, the cap body 2 can also adopt a semi-blind cap structure with a microporous ceramic plug. The carbon source sealing medium 5 is one or a combination of sugar aqueous solution, phenolic resin solution, furan resin solution, liquid coal tar pitch, petroleum pitch, coal tar, heavy oil, lignin solution, and hydrocarbon polymer solution with high carbon residue.

[0037] like Figure 3 As shown, the application of an anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln includes the following specific steps: Step 1: Loading and Component Assembly (Ambient Temperature Operation) 1. Filling with powder: The carbon-containing powder to be carbonized (such as asphalt-coated graphite precursor after mixing and granulation) is filled into the crucible body 1 and compacted appropriately.

[0038] 2. Laying the sacrificial layer: In the remaining space on top of the powder, lay at least one layer of highly active sacrificial oxygen-consuming isolation layer 6 to completely cover the powder below.

[0039] 3. Injection of liquid sealant: Inject an appropriate amount of phase change carbon source sealing medium 5 evenly into the slot 3.

[0040] 4. Blind cap pressing: Place the cap 2 above the crucible body 1, insert the boss 4 into the U-shaped groove 3 and immerse it in the carbon source sealing medium 5. The initial assembly of the crucible is completed by the weight of the cap 2 itself.

[0041] Step 2: Kiln entry and liquid seal establishment (room temperature - 300℃ range)

[0042] The assembled crucible is placed on the tunnel kiln car and pushed directly into the tunnel kiln, which is under atmospheric pressure. As the kiln car moves through the preheating zone, the temperature gradually rises from room temperature to approximately 300°C. At this point, the powder has not yet undergone severe pyrolysis, while the carbon source sealing medium 5 in the slot 3 softens and melts upon heating, reducing its viscosity and forming a complete closed-loop "liquid sealing pool" at the labyrinthine junction, thus achieving initial isolation from the external air.

[0043] Step 3: Controlled pressure relief and positive pressure sealing (300℃ - 600℃ range)

[0044] As the kiln car enters the mid-temperature zone (approximately 300℃-600℃), the binders such as asphalt / resin in the powder undergo violent pyrolysis, generating a massive amount of high-pressure volatile gases, causing the pressure inside the crucible to rise sharply.

[0045] High-pressure volatile gases flow through the assembly gap between the cover 2 and the crucible body 1, overcoming the viscous resistance of the carbon source sealing medium 5, and are discharged outward in a controlled manner as a bubble jet. The high-speed exhaust gas forms a powerful "dynamic positive pressure air curtain" at the gap, preventing the high-temperature air inside the tunnel kiln from flowing back in. At the same time, thanks to its strictly designed self-weight, the cover 2 always maintains a downward pressure greater than the exhaust jet force, ensuring that the cover 2 does not slip or shift.

[0046] Step 4: Liquid-solid phase change and physical sealing (600℃ - 850℃ range)

[0047] As the kiln car continued to move to temperatures above 600°C, the release of volatile matter from the pyrolysis of the powder decreased sharply, and the internal air pressure began to drop rapidly.

[0048] At the critical point where the internal and external pressure difference disappears, the carbon source sealing medium 5 in the slot 3 reaches its own coking temperature and rapidly undergoes dehydration, condensation, and aromatization reactions (in-situ solidification reaction). The carbon source sealing medium 5 transforms from a viscous liquid in situ into a dense, hard amorphous "solid carbon skeleton." This phase change process irreversibly welds the original "one-way liquid seal valve" shut, transforming it into a robust physical isolation wall, completely blocking the negative pressure oxygen absorption channel that may be generated by internal cooling later.

[0049] Step 5: Deep isothermal carbonization and internal oxygen consumption as a safety net (above 1000℃)

[0050] The kiln car enters the high-temperature constant temperature zone of the tunnel kiln, where the material undergoes deep aromatization and densification within a completely sealed crucible. If a trace amount of oxygen infiltrates during this stage and before the phase transition, the sacrificial oxygen-consuming isolation layer 6 (carbon paper) covering the powder will preferentially undergo an oxidation combustion reaction, consuming all the infiltrated free oxygen and ensuring that the negative electrode powder at the bottom is not subject to any oxidation or etching.

[0051] Step Six: Cooling and unloading from the kiln and demolding (cooling down to room temperature)

[0052] After carbonization, the kiln car is cooled by the cooling zone and removed from the tunnel kiln. Once the crucible has cooled to a safe temperature, the solid carbon skeleton inside the slot 3 exhibits a certain degree of brittleness. The operator can easily break the solid carbon seal by gently tapping the edge of the labyrinthine joint with a tool, allowing the cover 2 to be easily removed and the well-carbonized negative electrode material to be poured out. After cleaning the residual carbon slag in the slot, the crucible can be reused in the next cycle.

[0053] Example 1

[0054] This embodiment uses the processing of pitch-coated graphite powder with an addition amount of 10% and a residual carbon content of 50% as an example. After the crucible is pushed into the air-atmosphere tunnel kiln, it undergoes a continuous heating process from room temperature to 1150°C. The internal air pressure of the crucible is set to P. int The ambient pressure in the tunnel kiln is P ext The downward pressure generated by the weight of the blind cover is P. lid The liquid seal resistance pressure of the carbon source sealing medium (high-concentration syrup) in the card slot is P. seal The specific steps are as follows: Phase 1: Preheating and medium melting zone (room temperature - 300℃) 1. Material and Pressure State: The asphalt begins to soften and melt, but has not yet undergone violent pyrolysis, and the total amount of gas inside the crucible changes very little. At this time, the internal pressure Pint ≈ Pext.

[0055] 2. Sealing state: The carbon source sealing medium in the slot is heated and dehydrated, reducing its viscosity and forming a closed-loop "liquid seal pool". As the internal and external pressure difference approaches zero, the liquid seal layer remains stationary, providing excellent initial oxygen barrier function.

[0056] Second stage: Violent pyrolysis and high-pressure exhaust zone (300℃ -600℃)

[0057] 1. Material and Pressure State: This temperature range is the core area of ​​asphalt pyrolysis, where large molecular hydrocarbons undergo violent chain breakage, instantly releasing a massive amount of volatiles (such as CH4, H2, tar vapor, etc.). The internal pressure P of the crucible... int A sharp rise led to (P) int -P ext )>P seal .

[0058] 2. Dynamic Response Mechanism: 1. Directional Pressure Relief: High-pressure volatile gas flows along the assembly gap between the crucible body and the lid, overcoming the resistance of the liquid carbon source sealing medium (i.e., greater than P). seal ), continuously discharged outwards in the form of bubble jets. 2. Anti-top cover shape preservation: The weight of the cover is strictly designed to ensure its downward pressure P. lid Always greater than the maximum exhaust force of the internal gas (i.e., P) lid >P int -P ext Therefore, the exhaust process only manifests as the "boiling" of gas from the liquid seal layer, while the cover itself remains stable and will not experience mechanical displacement or slippage. 3. Positive pressure gas seal for oxygen prevention: The continuously injected high-pressure pyrolysis gas forms a high-intensity dynamic positive pressure gas curtain at the slot, ensuring that oxygen from the external tunnel kiln cannot flow backward into the crucible from a hydrodynamic perspective.

[0059] Phase 3: Pressure drop and phase change solidification zone (600℃-850℃)

[0060] 1. Material and Pressure State: The pyrolysis of asphalt is basically complete, and the release of volatile gases under high pressure drops sharply. Internal pressure P int It began to fall rapidly, gradually approaching the ambient pressure P. ext Approaching. In traditional processes, this stage is prone to drawing in external oxygen due to the "slight negative pressure" generated by the cooling and contraction of internal gases.

[0061] 2. Dynamic Response Mechanism: As the temperature surpasses 600℃, the carbon source sealing medium within the slot reaches its own coking temperature. During this stage, the medium rapidly undergoes a dehydration and condensation reaction, transforming from a viscous liquid in situ into a dense, hard amorphous solid carbon skeleton. This "liquid-solid phase transition" is completed instantaneously before the pressure difference disappears, completely sealing off the original "one-way liquid seal valve" and transforming it into a "solid physical wall," perfectly blocking the negative pressure oxygen absorption channel.

[0062] Fourth stage: High-temperature deep carbonization zone (above 1000℃)

[0063] 1. Material and Pressure State: During the isothermal deep processing stage, the asphalt residual skeleton undergoes aromatization, and the graphite coating layer becomes denser. At this point, the interior is completely sealed, and the pressure P... int The solid carbon skeleton is fully capable of withstanding the minute expansion caused by the ideal gas law.

[0064] 2. Internal sacrificial layer at the bottom: Even if a trace amount (PPM level) of oxygen seeps in during the extremely short instant of the phase transition in the third stage, the porous carbon paper (or carbon felt) covering the powder will act as a highly active oxygen-consuming material, instantly consuming the free oxygen at high temperature, ensuring that the specific surface area (BET) of the powder at the bottom is not affected by oxidation or etching in the slightest.

[0065] Experimental Design

[0066] 1. Preparation of experimental materials: Select artificial graphite substrate materials of the same batch and specifications, and uniformly mix 10% medium-temperature coal tar pitch (theoretical residual carbon rate of about 50%) as a coating agent to prepare the powder to be carbonized.

[0067] 2. Experimental group setup: The above-mentioned powder to be carbonized was divided into three portions, and each portion was subjected to high-temperature carbonization treatment using the following three different processes and fixtures. The maximum carbonization temperature was set to 1150℃, and the holding time was 4 hours.

[0068] 3. Comparative Example 1 (existing mainstream process): A roller kiln (RHK) was used, and high-purity nitrogen (O2 concentration <50ppm) was introduced for protection. The fixture used was a traditional graphite sagger and ordinary cover plate.

[0069] 4. Comparative Example 2 (Traditional Failed Attempt): A continuous tunnel kiln was used, with an air atmosphere (atmospheric pressure). The fixture used was a common silicon carbide crucible and a common silicon carbide cover plate (rigid cover pressing, without dynamic sealing and oxygen-consuming layer).

[0070] 5. Embodiment 1 of the present invention: A continuous tunnel kiln is used, with an air atmosphere (atmospheric pressure), and the fixture is the self-breathing anti-oxidation crucible of the present invention (made of silicon carbide, with a non-porous blind cover, syrup phase change liquid seal, and internal carbon paper sacrificial layer).

[0071] 6. Test Indicators: After carbonization, allow the material to cool to room temperature before removing it from the furnace. Test the residual carbon rate of the coating layer, specific surface area (BET), and first coulombic efficiency (ICE) of the half-cell for the three groups of materials, and calculate the overall operating costs of the fixture and gas.

[0072] Table 1 Comparison of Experimental Data

[0073] As shown in Table 1: (1) Comparison of Comparative Example 1 and Comparative Example 2: This demonstrates the existing technical bias in the industry, namely, the use of ordinary crucibles in air tunnel kilns, which allows for a large influx of oxygen, resulting in extremely low pitch carbon content (only 12.3%) and severe etching of the graphite substrate, with the BET soaring to 6.85 m. 2 / g, electrochemical performance (ICE) deteriorates directly and the product becomes unusable.

[0074] (2) Comparative Example 1 and Comparative Example 2: Under the same harsh air tunnel kiln environment, only the special crucible of Example 1 was replaced, and the product's BET (1.22 m) was significantly improved. 2 The improvement in the percentage of carbon residue (47.8%) and carbon residue ( / g) is orders of magnitude, which fully demonstrates the excellent exhaust and oxygen-free effect of the "phase change dynamic seal + sacrificial layer".

[0075] (3) Comparative Example 1 and Comparative Example 1: Example 1 prepared high-end materials with core physical and electrochemical indicators (BET, ICE) that were almost equivalent to those produced by the extremely expensive "nitrogen roller kiln + graphite sagger" in an air tunnel kiln with extremely low cost, perfectly achieving the ultimate invention goal of cost reduction and efficiency improvement.

[0076] It should be noted that the continuous carbonization process applicable to this invention is not limited to the specific parameters mentioned above. Typically, the binder / coating agent added can account for 2%-20% by mass, and the maximum carbonization temperature range can be set between 800℃ and 1300℃. Within this parameter range, the self-breathing crucible of this invention can effectively achieve the functions of anti-oxidation and explosion-proof exhaust.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and 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 low-specific-surface-area carbonization crucible for use in an air-atmosphere tunnel kiln, characterized in that: The crucible includes a crucible body (1) and a lid (2) connected by a labyrinth joint. The labyrinth joint includes several slots (3) and several bosses (4) that are adapted to the shape of the slots (3). The interior of the slots (3) is provided with a carbon source sealing medium (5) that can undergo in-situ curing reaction at a temperature above 250 degrees.

2. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 1, characterized in that: The pressure per unit area generated by the weight of the cover (2) on the contact surface of the slot (3) is 500 Pa - 5000 Pa.

3. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 1, characterized in that: The carbon source sealing medium (5) is one or more of the following: sugar aqueous solution, phenolic resin liquid, furan resin liquid, liquid coal tar pitch, petroleum pitch, coal tar, heavy oil, lignin liquid, and organic polymer fluid with a carbon residue rate of more than 20% under an inert atmosphere at 1000℃.

4. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 1, characterized in that: The crucible body (1) is provided with a sacrificial oxygen-consuming isolation layer (6) inside.

5. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 4, characterized in that: The sacrificial oxygen-consuming isolation layer (6) is one or more of the following: carbon paper, carbon cloth, porous carbon felt, foamed carbon, graphite foil, graphite plate, activated carbon layer, carbon black layer, graphite powder layer, and organic polymers with a carbon residue rate of more than 20% under an inert atmosphere at 1000°C.

6. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 1, characterized in that: The slot (3) is embedded on the outer edge of the top of the crucible body (1), and the boss (4) is set on the outer edge of the bottom of the cover (2). The slot (3) and the boss (4) are both annular and their sizes are compatible.

7. The anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 1, characterized in that: The slot (3) is embedded in the outer edge of the bottom of the cover (2), and the boss (4) is set on the outer edge of the top of the crucible body (1). The slot (3) and the boss (4) are both annular and their sizes are compatible.

8. The application of the anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln as described in any one of claims 1-7, characterized in that, The specific steps include: S1. Assembly preparation: Fill the crucible body (1) with the powder to be carbonized, and lay a sacrificial oxygen-consuming isolation layer (6) on top of the powder; inject the carbon source sealing medium (5) into the groove (3) of the labyrinth joint and press the cover (2) together. After the crucible completes the initial assembly, push it into the air atmosphere tunnel kiln with the kiln car; gradually raise the temperature from room temperature to about 300°C in the preheating zone, and use the carbon source sealing medium (5) to melt and soften to establish the initial liquid seal; S2. Dynamic exhaust and gas seal: As the kiln car moves to the medium temperature zone, the powder inside the crucible produces volatile gas, which causes the internal pressure to rise. The volatile gas is discharged outward to release pressure and forms a dynamic positive pressure air curtain at the gap of the labyrinth joint to prevent the backflow of external oxygen. S3, In-situ coking seal: As the kiln car continues to move to the 600℃-850℃ temperature zone, the release of volatile gas generated by the powder decreases sharply, the internal pressure of the crucible drops, and the carbon source sealing medium (5) undergoes an in-situ solidification reaction, transforming into a dense amorphous solid carbon skeleton, which physically seals the gaps of the labyrinth joint. S4. Constant Temperature Carbonization and Heat Preservation: The kiln car enters the high temperature constant temperature zone for deep carbonization. After carbonization, it is cooled and removed from the kiln. The brittle solidified carbon layer on the outer edge is broken to open the lid and demold.

9. The application of the anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 8, characterized in that: The temperature of the intermediate temperature zone is 300℃-600℃; the temperature of the high temperature constant temperature zone is ≥1000℃.

10. The application of the anti-oxidation low specific surface area carbonization crucible for an air atmosphere tunnel kiln according to claim 8, characterized in that: In step S4, after the kiln car is removed from the tunnel kiln, the sacrificial oxygen-consuming isolation layer (6), which is a solid carbon skeleton, is removed. The sacrificial oxygen-consuming isolation layer (6) is reinstalled the next time it is used.

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