A graphitization furnace for lithium ion battery negative electrode material and a graphitization method and system

Abstract

The application provides a graphitization furnace for lithium ion battery negative electrode materials, which can ensure the sealing of the box furnace, reduce the generation of cracks or cracks of the box plate, prolong the service life of the box plate, and improve the thermal field uniformity and heat preservation performance of the box. The application also provides a graphitization method for lithium ion battery negative electrode materials, which can reduce the influence of exhaust and thermal expansion and cold contraction on the box, and ensure the quality of the graphitization of the negative electrode materials. The application also provides a lithium ion battery negative electrode material graphitization system using waste gas generated by the graphitization method for lithium ion battery negative electrode materials to preheat the negative electrode materials, so as to reduce the graphitization energy consumption.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery anode material technology, and in particular to a graphitization furnace, graphitization method and system for lithium-ion battery anode materials. Background Technology

[0002] The negative electrode material is one of the four core materials of lithium-ion batteries. The negative electrode of a lithium battery is mainly made of a mixture of carbon or non-carbon active materials, binders, and additives, coated on both sides of a copper foil, and then processed through drying, rolling, and other processes. During the charging and discharging process of a lithium battery, under the influence of electrode voltage, lithium ions in the positive electrode undergo electrochemical reactions of "intercalation" and "deintercalation," while the negative electrode, as a carrier, is responsible for storing and releasing lithium ions and allowing current to flow through the external circuit.

[0003] Artificial graphite and natural graphite are currently the two most mainstream graphite-based carbon material anodes. Composite graphite and mesophase carbon microspheres are produced through doping modification and compound treatment. Amorphous carbon and carbon nanomaterials such as graphene also belong to carbon material anodes.

[0004] The upstream raw materials for artificial graphite include coke (coal-based needle coke, petroleum-based needle coke, and petroleum coke) and pitch. The upstream raw material for natural graphite is natural flake graphite. Natural flake graphite is a single crystal, with flake-like crystals, obtained from graphite ore through flotation. Compared to natural graphite, artificial graphite has better overall performance and more prominent advantages, and will be more widely used in power batteries and energy storage batteries.

[0005] Graphitization is the core step in the production of artificial graphite anodes, accounting for approximately 50% of the total cost of anode material production. It is also a high-energy-consuming process, with electricity costs accounting for 60% of the graphitization cost. There are three types of graphitization furnaces: Atchison furnaces, internal series graphitization furnaces, and box furnaces. Atchison furnaces rely on resistance heating of the carbon material. Impurities in the resistance material can diffuse into the material at high temperatures, resulting in excessively high ash content. Box furnaces, on the other hand, use a box structure where the heating element is formed by the furnace tank. Current is fed through the furnace head electrodes to the furnace core heating element, and the resulting high temperature directly heats the material inside the tank, achieving graphitization. Box furnaces do not require resistance heating, thus resulting in low ash content. Since battery anode materials have high ash content requirements, box furnaces are generally used to prepare battery anode materials.

[0006] Box-type furnaces offer good sealing, but this can also obstruct venting. Combined with factors like high-temperature thermal expansion and low-temperature cooling, the furnace panels are prone to cracking or fissures, reducing their lifespan and affecting their sealing performance in subsequent use. During use, heat and gas can easily escape from the cracked areas, exacerbating crack propagation and causing uneven thermal distribution within the furnace, leading to increased energy consumption and decreased product quality. Summary of the Invention

[0007] To address the problem that current box-type graphitization furnaces are prone to cracks or fissures in the furnace panels due to factors such as exhaust and thermal expansion and contraction, this application proposes a graphitization furnace for lithium-ion battery anode materials. This furnace can reduce the generation of cracks or fissures in the furnace panels while ensuring the furnace's airtightness, extending the service life of the furnace panels, and improving the uniformity of the thermal field and the insulation performance of the furnace body.

[0008] This application also proposes a graphitization method for lithium-ion battery anode materials, which can reduce the impact of exhaust and thermal expansion and contraction on the casing, while ensuring the quality of graphitization of the anode materials.

[0009] This application also proposes a graphitization system for lithium-ion battery anode materials that uses the waste gas generated by the graphitization method of lithium-ion battery anode materials to preheat the anode materials, so as to reduce the energy consumption of graphitization.

[0010] A method for graphitizing a lithium-ion battery anode material includes the following steps: Step 1: Sequentially fill the lower insulation layer, box body, side insulation layer, conductive components, negative electrode material, and upper current-guiding insulation layer of the graphitization furnace; Step 2: Gradient heating of the graphitized anode material; wherein, From room temperature to (200℃~250℃), the heating rate is 60℃~90℃ / h; (200℃~250℃) to 800℃, heating rate 30℃~50℃ / h; hold for 30 minutes for every 100℃ increase; Heating rate: 15℃~30℃ / h from 800℃ to 1000℃; hold at 850℃ for 2 hours; hold at 950℃ for 1.5 hours. 1000℃~2500℃, heating rate 80℃~120℃ / h; at 1500℃, hold for 1h; at 2000℃, hold for 2h, then close the vent. 2500℃~3000℃, heating rate 200~300℃ / h, hold at 3000℃ for 2h~3h.

[0011] Step 3: Cooling down; wherein, at 3000℃~800℃, cooling is carried out by steam extraction, with a cooling rate of 13℃~15℃ / h.

[0012] The graphitization furnace includes: The furnace body is enclosed by refractory brick walls; The lower insulation layer is laid at the bottom of the furnace body; An enclosed box is set inside the furnace body, above the lower insulation layer, and is formed by enclosing the box panels to contain and heat the materials. Side insulation layer, filled between the side facades of the enclosed box and the inner wall of the furnace; The upper heat-insulating layer is located above the enclosed box. A sealing cover is installed above the furnace body; The enclosed box includes a base plate assembly, columns, and side plate assemblies; The base plate assembly is formed by splicing together several base plates. Adjacent base plates have complementary protrusions and the gaps between the base plates are filled with graphite. The column has a slot, and the two ends of the side plate assembly are engaged with the slots of the column. The gap between the side plate assembly and the slot is filled with graphite. The side plate assembly is formed by splicing together several side plates. Two adjacent side plates are provided with semi-circular grooves to form a circular hole, and a graphite rod is provided in the circular hole.

[0013] The upper heat-insulating layer comprises, from bottom to top, carbon felt, cover plate layer, breathable layer and upper heat-insulating layer. The upper heat-insulating layer is provided with venting holes at intervals, and the venting holes are filled with breathable filler. The cover plate layer includes several cover plates, with gaps between the cover plates for gas passage.

[0014] Preferably, the conductive component includes a plurality of conductive pads, flexible graphite pads, and conductive pillars. The conductive pads are arranged from bottom to top, with the bottom conductive pads located on the base plate assembly. The conductive pads are spaced together by flexible graphite pads, and the two ends of the conductive pillars are connected to the top conductive pads.

[0015] Preferably, the lower insulation layer comprises, from bottom to top, a carbonizer layer, a refractory brick layer, and a carbon black layer.

[0016] Preferably, the material of the air-permeable layer and the air-permeable filler is 8-25 mm thick calcined coke.

[0017] A graphitization system for lithium-ion battery anode materials includes a graphitization furnace, a steam generator, a negative pressure fan, a heat exchanger, a waste heat boiler, and a preheating chamber. One end of the sealing cover of the graphitization furnace is connected to the steam generator via a pipe, and the other end of the sealing cover is connected to the air inlet of the negative pressure fan via a pipe. The air outlet of the negative pressure fan is connected to one end of the heat exchanger, and the other end of the heat exchanger is connected to the waste heat boiler. The side wall of the preheating chamber is equipped with a heating coil, and the refrigerant pipe of the heat exchanger is connected to the heating coil of the preheating chamber. At the same time, the waste heat boiler is equipped with a circulating water pipe, and the refrigerant pipe is also connected to the circulating water pipe. The water heated by the waste heat boiler is further heated by the heat exchanger for heating the materials in the preheating chamber.

[0018] The technical advantages of this application are as follows: The graphitization furnace for lithium-ion battery anode materials of this application, by disassembling the enclosed box into several bottom plate components, side plate components, and columns, allows the natural gaps between the components to act as a buffer during thermal expansion and contraction, thereby significantly improving the deformation and even cracking of the box and extending the service life of the box. The interlocking connection between the components, combined with the sealing effect of graphite, ensures the sealing of the box, resulting in less heat dissipation and a more uniform thermal field within the enclosed box, thus reducing the energy consumption of graphitization. Simultaneously, the design of the carbon felt, cover plate, breathable layer, and breathable filler, combined with the well-sealed enclosed box, guides the gas generated during thermal decomposition to flow upwards, preventing excessive pressure inside the box, which could lead to deformation or cracking of the box.

[0019] The graphitization method for lithium-ion battery anode materials disclosed in this application utilizes a unique gradient heating approach. This method guides the slow release of gases generated by the anode material and leverages these gases to continuously create a slightly positive pressure environment within the furnace. This prevents air from entering the carbon oxide material, reduces the consumption of insulation material, and ensures the quality of the graphitized anode material. Furthermore, since the exhaust gas itself creates a slightly positive pressure environment, there is no need to introduce protective gases such as argon or nitrogen into the furnace, thereby reducing production costs.

[0020] The graphitization system for lithium-ion battery anode materials in this application utilizes the waste gas generated during the graphitization cooling process to preheat the anode material, significantly reducing energy consumption during the graphitization process. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the graphitization furnace for the lithium-ion battery anode material of this application.

[0022] Figure 2 This is a partial structural diagram of the box body of this application.

[0023] Figure 3 This is a schematic diagram of the installation structure of the base plate assembly and side plate assembly of this application.

[0024] Figure 4 This is a schematic diagram of the installation structure of the side panel assembly of this application.

[0025] Figure 5 This is a cross-sectional view of the graphitization furnace for the lithium-ion battery anode material of this application.

[0026] Figure 6 This is a schematic diagram of the graphitization system of the lithium-ion battery anode material of this application.

[0027] In the diagram: Graphitization furnace 1, furnace body 11, lower insulation layer 12, carbon raiser layer 121, refractory brick layer 122, carbon black layer 123, box body 13, bottom plate assembly 131, boss 1311, column 132, side plate assembly 133, graphite rod 1331, fixing clip 134, side insulation layer 14, upper flow guiding insulation layer 15, carbon felt 151, cover plate layer 152, air permeable layer 153, upper insulation layer 154, unblocking hole 1541, sealing cover 16, conductive component 17, conductive pad 171, flexible graphite gasket 172, conductive column 173, steam generator 2, negative pressure fan 3, heat exchanger 4, refrigerant pipe 41, waste heat boiler 5, circulating water pipe 51, preheating chamber 6. Detailed Implementation

[0028] The technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0029] Please refer to Figures 1 to 5 A graphitization furnace 1 for a lithium-ion battery negative electrode material includes: a furnace body 11 surrounded by refractory brick walls; The lower insulation layer 12 is laid at the bottom of the furnace body 11; The enclosing box 13 is set inside the furnace body 11, above the lower insulation layer 12, and is formed by the box panels to contain materials and heat the materials; Side insulation layer 14 is filled between the side facades of the enclosed box 13 and the inner wall of the furnace. The upper heat-insulating layer 15 is located above the enclosed box 13; Sealing cover 16 is installed above the furnace body; The enclosed box 13 includes a bottom plate assembly 131, a column 132, and a side plate assembly 133; The base plate assembly 131 is formed by splicing together several base plates, with complementary protrusions 1311 on two adjacent base plates and the gaps between the base plates being filled with graphite. The column 132 is provided with a slot, and both ends of the side plate assembly 133 are engaged with the slot of the column 132. The space between the side plate assembly 133 and the slot is filled with graphite. The side plate assembly 133 is formed by splicing together several side plates. Two adjacent side plates are provided with semi-circular grooves to form a circular hole, and a graphite rod 1331 is provided in the circular hole.

[0030] Furthermore, the upper heat-insulating layer 15 includes, from bottom to top, a carbon felt 151, a cover plate layer 152, a breathable layer 153, and an upper heat-insulating layer 154. The upper heat-insulating layer 154 is provided with dredging holes 1541 at intervals, and the dredging holes 1541 are filled with breathable filler. The cover plate layer 152 includes a plurality of cover plates, and gaps are left between the cover plates for gas to pass through.

[0031] In a preferred embodiment, a conductive component 17 is provided inside the enclosure 13 for supplemental heating of the negative electrode material inside the enclosure 13; The conductive component 17 includes a plurality of conductive pads 171, flexible graphite pads 172, and conductive posts 173. The conductive pads 171 are arranged from bottom to top, with the bottom conductive pads 171 located on the base plate component 131. The conductive pads 171 are supported by flexible graphite pads 172. The two ends of the conductive posts 173 are connected to the top conductive pads 171.

[0032] In a preferred embodiment, the materials of the permeable layer 153 and the permeable filler are 8-25 mm thick calcined coke.

[0033] In a preferred embodiment, the lower insulation layer 12 is composed of carbon black. The carbon black is laid in two layers. The first layer is 45-55 cm thick, and after compaction, the second layer, also 45-55 cm thick, is laid and compacted.

[0034] In another preferred embodiment, the lower insulation layer 12 is composed of a carbon raiser, refractory bricks, and carbon black. The bottom layer is a carbon raiser with a thickness of 45–55 cm; the middle layer is refractory bricks with a thickness of 5–10 cm; and the top layer is carbon black with a thickness of 45–55 cm.

[0035] The base plate assembly 131 of this application is used to isolate the lower insulation layer 12 and the negative electrode material, and also to heat the negative electrode material at the bottom. The negative electrode material of this application is in powder form, and for ease of explanation, it will be referred to as negative electrode powder below. The base plate assembly 131 is formed by splicing together several base plates.

[0036] In a preferred embodiment, please refer to Figure 3 The base plate assembly 131 consists of three types of base plates: Type A, Type B, and Type C. Type A base plates have square pre-drilled openings at both corners, Type B base plates have no pre-drilled openings, and Type C base plates have a pre-drilled opening in the middle of their short sides. During assembly, Type A base plates are positioned on both sides of the enclosing box 13, with Type B base plates positioned between Type A and Type C base plates. The number of Type B base plates between Type A and Type C base plates varies depending on the distance between the two uprights 132. One long side of the Type A base plate is flush, while the other long side has a protrusion. Correspondingly, the long side of the adjacent Type B base plate has a complementary protrusion, allowing the Type A and Type B base plates to interlock. The gaps between Type A and Type B base plates are filled with graphite. The same applies between two adjacent Type B base plates, and also between adjacent Type B and Type C base plates.

[0037] In this way, it is difficult for the gas inside the furnace to escape through the bottom plate assembly 131, and it is also difficult for the outside gas to enter through the bottom plate assembly 131, thus ensuring the airtightness of the enclosed box 13 from the bottom.

[0038] When the base plate assembly 131 expands under high temperature, the stress is released at the joints of the base plates, which are assembled from multiple base plates. The deformation of the base plates is controllable under the pressure of the negative electrode powder, thus extending the lifespan of the base plate assembly 131. Simultaneously, due to the complementary protrusions between adjacent bottom sections and the graphite sealing, the overall sealing performance of the base plate assembly 131 is good, making it difficult for gas to pass through from the bottom of the housing 13.

[0039] Similarly, the side panel assemblies 133 are connected by columns 132, which significantly shortens the manufacturing length of the side panels and makes them less prone to cracking due to deformation. The slots on the sides of the columns 132 ensure the vertical stability of the side panel assemblies 133 and prevent them from tipping over.

[0040] The gap between the slot and the side panel assembly 133 is filled with graphite.

[0041] In a preferred embodiment, the gap between the slot and the side plate is filled with graphite as follows: Wrap multiple layers of graphite paper around the edge of the side panel, and then insert the side panel into the slot from top to bottom.

[0042] In another preferred embodiment, the gap between the slot and the side plate is filled with graphite as follows: Mix graphite powder with binder to form a paste, then apply the paste mixture to the edges of the side panel, and finally insert the side panel into the slot from top to bottom.

[0043] Graphite fills the gap between the side plate and the slot, which firstly prevents poor contact between the slot and the side plate, thus increasing resistance; secondly, it provides a good seal, reducing the leakage of heat and gas from the gap.

[0044] In a preferred embodiment, the side plate assembly 133 is composed of two types of side plates. The lowermost and uppermost side plates are type A side plates, which have a semi-circular groove on only one side. Type B side plates have semi-circular grooves on both sides. Graphite rods 1331 fill the circular holes formed by the semi-circular grooves. When the side plates expand due to heat and release stress at their edges, the side plates and graphite rods 1331 can be evenly stressed. Simultaneously, the graphite rods 1331 have good lubrication properties. When the side plates deform, they can promptly change their angle to prevent excessive stress in the vertical direction and potential damage from compression.

[0045] In this way, the sealing of the bottom and sides of the enclosure 13 can be guaranteed.

[0046] To prevent the column 132 from tilting inward or outward during installation or filling, this application also provides a fixing clip 134 at the top of the column 132, which is engaged with the top of the column 132.

[0047] The base plate assembly 131, side plate assembly 133, column 132, and fixing clip 134 of this application are all made of the same material. This ensures that the overall expansion performance, electrical conductivity, and compressive strength are consistent.

[0048] The carbon felt 151, cover plate layer 152, breathable layer 153, and upper insulation layer 154 above the enclosure box 13 of this application can guide the gas in the enclosure box 13 to be discharged in time while keeping it warm, so as to prevent the pressure inside the box 13 from being abnormal due to accumulation.

[0049] The carbon felt 151 has good heat resistance and insulation properties. At the same time, the micropores in the carbon felt 151 facilitate the passage of gas within the enclosure 13.

[0050] The cover plate layer 152 can play a certain sealing role, guide gas through the gaps between the cover plates, and effectively reduce radiative heat release.

[0051] The permeable layer 153 can buffer gases to a certain extent, preventing abnormal pressure inside the housing 13 due to sudden temperature changes. It can also impede the flow of external gases. For example, during the cooling process, when outside air enters through the permeable packing of the vent 1541, the permeable layer 153 can both contain the air and consume the oxygen in the air through an oxidation reaction, preventing the negative electrode powder from being oxidized.

[0052] The upper insulation layer 154 is used for thermal insulation. Gas enters the sealing cover 16 through the carbon felt 151, the gaps in the cover plate, the breathable layer 153, and the vent holes of the upper insulation layer 154, and is then discharged.

[0053] In a preferred embodiment, the lower insulation layer 12 comprises, from bottom to top, a carbon raiser layer 121, a refractory brick layer 122, and a carbon black layer 123.

[0054] In a preferred embodiment, the materials of the permeable layer 153 and the permeable filler are 8-25 mm thick calcined coke.

[0055] A method for graphitizing a lithium-ion battery anode material includes the following steps: Step 1: Sequentially fill the lower insulation layer 12, the enclosing box 13, the side insulation layer 14, the conductive components, the negative electrode material, and the upper flow-guiding insulation layer 15 of the graphitization furnace 1. Step 2: Gradient heating of the graphitized anode material; wherein, From room temperature to (200℃~250℃), the heating rate is 60℃~90℃ / h. During this stage, the main purpose is to remove free water and low volatiles from the graphite. Simultaneously, the airflow also slowly expels air from the gaps between particles, reducing subsequent oxidation reactions. Regarding the thermal expansion of the enclosure 13, this prevents thermal shock caused by rapid heating of the cold enclosure 13.

[0056] The temperature is increased from 200℃ to 250℃ to 800℃ at a rate of 30℃ to 50℃ / h; for every 100℃ increase, the temperature is held for 30 minutes. During this stage, a large amount of volatile matter is generated, such as the release or decomposition of adsorbed water, bound water, low-molecular-weight hydrocarbons, and asphaltenes. The slower heating rate allows the volatile gases to be released slowly. During this stage, a small amount of oxygen also reacts with carbon to produce carbon monoxide. Reducing the heating rate helps stabilize the pressure inside the enclosure 13.

[0057] The heating rate is 15℃~30℃ / h from 800℃ to 1000℃; at 850℃, the temperature is held for 2 hours; at 950℃, the temperature is held for 1.5 hours. During this stage, the release rate of volatiles in the material reaches its peak. Slowing down the heating rate can avoid excessive pressure inside the enclosure 13, which could cause deformation of the enclosure 13.

[0058] The heating temperature ranges from 1000℃ to 2500℃, with a heating rate of 80℃ to 120℃ / h. At 1500℃, the temperature is held for 1 hour; at 2000℃, it is held for 2 hours, after which the vent is closed. During this stage, the organic functional groups and amorphous carbon structures in the carbon material undergo thermal decomposition, generating gases such as H2, CH2, and C2H2. Simultaneously, after 2000℃, some ash reacts with carbon to generate volatile gases, and some metallic impurities, such as aluminum, sublimate after generation. However, the overall gas production is relatively low. The accelerated heating rate helps to expel the gas and maintains a slightly positive pressure in the enclosure 13, preventing air from entering from the top. It should be noted that the enclosure 13 of this application has good sealing on the sides and bottom. Air has difficulty entering the enclosure 13 from these two points, while the top, with its vent, allows gas to enter more easily. When heated to 2500℃, very little gas is generated inside the enclosure 13. To maintain a slightly positive pressure environment within the enclosure 13, the vent is closed. This ensures that the gas generated by the material will cause the pressure inside the enclosure 13 to be slightly higher than the external pressure. Simultaneously, the insulation of the enclosure 13 will be improved, which is beneficial for the subsequent graphitization of the negative electrode powder.

[0059] 2500℃~3000℃, heating rate 200~300℃ / h, hold at 3000℃ for 2h~3h.

[0060] Because the graphitization furnace 1 of this application has excellent sealing properties, and with the improved temperature control measures, a slightly positive pressure environment can be maintained inside the enclosed chamber 13. This eliminates the need for protective gases such as nitrogen or argon, thus effectively reducing this part of the production cost. Since there is no protective gas like nitrogen, the volatile substances produced in this application can also be used for combustion to preheat the enclosed chamber 13 of other furnaces.

[0061] Step 3: Cooling down; 3000℃~800℃, vacuum cooling, cooling rate 13℃~15℃ / h; The exhaust cooling method described in this application involves opening the exhaust ports at both ends of the sealing cover 16, with one end connected to a fan and the other end connected to a steam generator 2. The steam generator 2 then produces steam, which is drawn into the sealing cover 16 by the fan. The steam carries away the high temperature inside the sealing cover 16. The heat carried away by the steam can be used to preheat the negative electrode powder through heat exchange, thereby reducing energy consumption.

[0062] While carrying away heat, the water vapor also reacts with petroleum coke and other gases in the insulation layer to produce carbon monoxide and hydrogen. This reaction is endothermic, allowing for faster cooling of the insulation layer. Simultaneously, the gases produced can be used as fuel to preheat the negative electrode powder.

[0063] When the temperature inside the sealed enclosure 16 drops to 800℃, cooling via water vapor becomes inefficient, and the reaction between air and carbon is very slow. To save costs, ventilation cooling is implemented instead of extraction cooling.

[0064] That is, at temperatures between 800℃ and 600℃, the sealing cover 16 is removed, and ventilation is used for cooling at a rate of 3℃ to 4℃ / h. It should be noted that at 800℃, the sealing cover 16 is removed. During on-site operation, body temperature is not constantly measured; therefore, based on experience, removing the sealing cover 16 at 800℃ ± 20℃ is acceptable. Because the graphitization furnace 1 of this application has good insulation, the efficiency of ventilation cooling is relatively low, and correspondingly, the cooling cost is also relatively low. At the same time, after opening the sealing cover 16, hot air will enter the workshop. If the cooling is too rapid at this time, the heat will quickly transfer to other parts of the workshop, causing the workshop temperature to rise rapidly, which is detrimental to workers' work.

[0065] At 600℃~400℃, remove half of the upper insulation layer 154, and continue ventilation to cool down at a rate of 3~4℃ / h. After the enclosed box 13 is cooled to 600 degrees Celsius, the temperature difference between the inside and outside of the furnace body 11 is significantly reduced, and considering the workers' tolerance to the workshop temperature, half of the upper insulation layer 154 is removed at 600℃±20℃, making it easier for the negative electrode powder inside the enclosed box 13 to cool down.

[0066] At 400℃~200℃, remove the remaining half of the upper insulation layer 154, and continue ventilation to cool down at a rate of 3~4℃ / h; At 200℃~60℃, remove the breathable layer 153, remove the cover plate layer 152 and carbon felt 151, and continue to cool down at a rate of 2℃~3℃ / h. At 60℃, the material was allowed to cool naturally for 48 hours, after which the graphitized anode material was extracted.

[0067] At this time, the temperature is still relatively high, and the operation of the cover plate layer 152 and carbon felt 151 is best carried out mechanically. If manual operation is necessary, then proper heat insulation and protection measures must be taken.

[0068] Both the extraction of insulation material and the negative electrode powder are done mechanically. The powder is pumped into the collection silo through a negative pressure pipeline.

[0069] Based on the detailed graphitization process described above, this application also proposes a graphitization system for lithium-ion battery anode materials, which utilizes the waste gas generated during the graphitization process to preheat the anode powder, thereby reducing the energy consumption of graphitization.

[0070] Please refer to Figure 6 A graphitization system for lithium-ion battery anode materials includes a graphitization furnace 1, a steam generator 2, a negative pressure fan 3, a heat exchanger 4, a waste heat boiler 5, and a preheating chamber 6. One end of the sealing cover 16 of the graphitization furnace 1 is connected to the steam generator 2 via a pipe, and the other end of the sealing cover 16 is connected to the air inlet of the negative pressure fan 3 via a pipe. The air outlet of the negative pressure fan 3 is connected to one end of the heat exchanger 4, and the other end of the heat exchanger 4 is connected to the waste heat boiler 5. The high-temperature gas in the graphitization furnace 1 is cooled down by heat exchange with the heat exchanger 4 and then enters the waste heat boiler for combustion. The side wall of the preheating chamber 6 is equipped with a heating coil, and the refrigerant pipe of the heat exchanger 4 is connected to the heating coil of the preheating chamber 6. At the same time, the waste heat boiler 5 is equipped with a circulating water pipe 51, and the refrigerant pipe is also connected to the circulating water pipe 51. The water heated by the waste heat boiler 5 is further heated by the heat exchanger 4 for heating the materials in the preheating chamber 6.

[0071] Steam generated by steam generator 2 is carried into graphitization furnace 1 by negative pressure fan 3. Through convective heat transfer and endothermic chemical reactions, heat is carried away from the furnace. The generated high-temperature flue gas is carried into heat exchanger 4 to heat the circulating water. The flue gas then enters waste heat boiler 5 as fuel to heat the circulating water. The circulating water, heated by waste heat boiler 5, is further heated by the flue gas and then enters preheating chamber 6 for preheating the negative electrode material. In a preferred embodiment, the refrigerant pipe 41 of heat exchanger 4 is also connected to steam generator 2, and some of the heated water enters steam generator 2 to be converted into steam for cooling graphitization furnace 1.

[0072] The following are examples of the graphitization method for lithium-ion battery anode materials of this application.

[0073] Example 1 A method for graphitizing a lithium-ion battery anode material includes the following steps: Step 1: Sequentially fill the lower insulation layer 12, enclosing box 13, side insulation layer 14, conductive component 17, negative electrode material, and upper current-guiding insulation layer 15 of graphitization furnace 1. Step 2: Gradient heating of the graphitized anode material; wherein, From room temperature to 200℃, the heating rate is 60℃ / h; From 200℃ to 800℃, the heating rate is 30℃ / h; for every 100℃ increase, hold for 30 minutes. Heating rate: 15℃ / h from 800℃ to 1000℃; hold at 850℃ for 2 hours; hold at 950℃ for 1.5 hours. 1000℃~2500℃, heating rate 80℃ / h; at 1500℃, hold for 1h; at 2000℃, hold for 2h, then close the vent. Temperature range: 2500℃~3000℃, heating rate: 200℃ / h, hold at 3000℃ for 2 hours.

[0074] Step 3: Cooling down; 3000℃~800℃, air extraction for cooling, cooling rate 13℃ / h; At 800℃~600℃, remove the sealing cover 16, ventilate and cool down at a rate of 3℃ / h. At 600℃~400℃, remove half of the upper insulation layer 154, continue ventilation to cool down, with a cooling rate of 3℃ / h; At 400℃~200℃, remove the remaining half of the insulation layer and continue cooling at a rate of 3℃ / h. 200℃~60℃; remove the breathable layer 153, remove the cover plate layer 152 and carbon felt 151, and continue to cool down at a rate of 2℃ / h. At 60℃, the material was allowed to cool naturally for 48 hours, after which the graphitized anode material was extracted.

[0075] Example 2 A method for graphitizing a lithium-ion battery anode material includes the following steps: Step 1: Sequentially fill the lower insulation layer 12, the enclosing box 13, the side insulation layer 14, the conductive components, the negative electrode material, and the upper flow-guiding insulation layer 15 of the graphitization furnace 1. Step 2: Gradient heating of the graphitized anode material; wherein, From room temperature to 250℃, the heating rate is 90℃ / h; From 250℃ to 800℃, the heating rate is 50℃ / h; for every 100℃ increase, hold for 30 minutes. Heating rate: 30℃ / h from 800℃ to 1000℃; hold at 850℃ for 2 hours; hold at 950℃ for 1.5 hours. 1000℃~2500℃, heating rate 120℃ / h; at 1500℃, hold for 1h; at 2000℃, hold for 2h, then close the vent. Temperature range: 2500℃~3000℃, heating rate: 300℃ / h, hold at 3000℃ for 3 hours.

[0076] Step 3: Cooling down; 3000℃~800℃, exhaust cooling, cooling rate 15℃ / h; At 800℃~600℃, remove the sealing cover 16, ventilate and cool down at a rate of 4℃ / h. At 600℃~400℃, remove half of the upper insulation layer 154 and continue ventilation to cool down at a rate of 4℃ / h. At 400℃~200℃, remove the remaining half of the insulation layer and continue cooling at a rate of 4℃ / h. 200℃~60℃; remove the breathable layer 153, remove the cover plate layer 152 and carbon felt 151, and continue to cool down at a rate of 3℃ / h. At 60℃, the material was allowed to cool naturally for 48 hours, after which the graphitized anode material was extracted.

[0077] In Example 1, the lower limit of the temperature rate is used, and in Example 2, the upper limit of the temperature rate is used. Table 1 shows a comparison between the graphitization energy consumption of Example 1 and Example 2 and the existing graphitization energy consumption and the loss of the enclosing box 13.

[0078] Meanwhile, there are also existing graphitization furnaces with similar structures to this application, such as the one with patent number 202223574721.2, entitled "A Box-type Furnace for Graphitization of Battery Anode Materials".

[0079] The graphitization furnace 1 in this application differs from that in the following ways: The base plate assembly 131 is formed by splicing together several base plates, with complementary protrusions on two adjacent base plates and the gaps between the base plates being filled with graphite. The column 132 is provided with a slot, and both ends of the side plate assembly 133 are engaged with the slot of the column 132. The space between the side plate assembly 133 and the slot is filled with graphite. The side plate assembly 133 is formed by splicing together several side plates. Two adjacent side plates are provided with semi-circular grooves to form a circular hole, and a graphite rod 1331 is provided in the circular hole. The fixing clip 134 is engaged with the top of the column 132; The upper heat-insulating layer 15 includes, from bottom to top, a carbon felt 151, a cover plate layer 152, a breathable layer 153, and an upper heat-insulating layer 154. The upper heat-insulating layer 154 is provided with dredging holes 1541 at intervals, and the dredging holes 1541 are filled with breathable filler. The cover plate layer 152 includes a number of cover plates, and gaps are left between the cover plates for gas to pass through.

[0080] The sealing measures of the graphitization furnace 1 in this application, such as the addition of graphite rods 1331 between the side plates and the filling of graphite between the slot of the column 132 and the side plates, also have a significant effect on reducing graphitization energy consumption and extending the service life of the enclosure 13. At the same time, the enclosure 13 of this application, together with the flow-guiding and heat-insulating layer 15, has a significant effect on reducing graphitization energy consumption, extending the service life of the enclosure 13, and improving the quality of the negative electrode material.

[0081] This application also sets up the following comparative examples for verification.

[0082] Comparative Example 1 The process is the same as steps 2 and 3 in Embodiment 1, except that the side panel assembly 133 in step 1 is made by splicing several side panels, without setting graphite rods 1331, and without filling the gaps with graphite.

[0083] Comparative Example 2 The steps 2 and 3 of the embodiment are the same, except that the upper insulation layer 154 in step 1 adopts a common structure in the prior art, namely carbon felt 151, cover plate layer 152, upper insulation layer 154, and the upper insulation layer 154 has a chimney. See patent number 202122978100.X, a box furnace with good top ventilation.

[0084] Comparative Example 3 The steps 2 and 3 are the same as in Example 1, except that an air inlet is opened below the side wall of the enclosing box 13 of the graphitization furnace 1 in Comparative Example 1 to simulate the conventional method of introducing nitrogen gas to prevent the negative electrode powder from being oxidized.

[0085] Table 1: Unit energy consumption, panel life, and degree of graphitization under different implementation conditions As can be seen from Table 1, the unit energy consumption of graphitization of the negative electrode material in Examples 1 and 2 is similar, the service life of the enclosed box 13 is 8 cycles, and the degree of graphitization is also very similar.

[0086] Compared to Comparative Example 1, Example 1 shows a significant reduction in energy consumption, with a unit energy consumption decrease of 388 kWh / ton due to the better sealing of the enclosure 13. Simultaneously, the uneven thermal expansion and contraction caused by the poor sealing of the enclosure 13 in Comparative Example 1 increases the service life of the enclosure plate by two cycles. The graphitization degree of the negative electrode material prepared in Example 1 reaches 97.2%, an increase of nearly 2% compared to the 95.3% graphitization rate of Comparative Example 1. Because of the better sealing of the enclosure 13, the thermal field inside the enclosure 13 is more uniform, which improves the graphitization degree of the negative electrode material while reducing energy consumption.

[0087] Compared to Comparative Example 2, Example 1 shows a significant reduction in energy consumption, with a unit energy consumption decrease of 479 kW·h / ton due to the better sealing of the upper heat-insulating layer 15. Because outside air can more easily enter through the chimney in Comparative Example 2, resulting in uneven thermal expansion and contraction within the enclosed box 13, the service life of the box panels in Example 1 is increased by two cycles compared to Comparative Example 2. Furthermore, Example 1 exhibits better sealing and a higher degree of graphitization.

[0088] Comparative Example 3 introduced nitrogen gas to prevent oxidation of the negative electrode material. Consequently, due to the faster gas flow, heat loss was also higher. At the same time, the inconsistency between the gas temperature and the thermal field, as well as its fluidity, affected the uniformity of the thermal field in the enclosure 13, leading to uneven thermal expansion and contraction, which affected the lifespan of the enclosure and, similarly, the degree of graphitization.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for graphitizing a lithium-ion battery anode material, characterized in that: Includes the following steps: Step 1: Sequentially fill the lower insulation layer (12), enclosing box (13), side insulation layer (14), negative electrode material, and upper flow guiding insulation layer (15) of the graphitization furnace (1). Step 2: Gradient heating of the graphitized anode material; wherein, From room temperature to (200℃~250℃), the heating rate is 60℃~90℃ / h; (200℃~250℃) to 800℃, heating rate 30℃~50℃ / h; hold for 30 minutes for every 100℃ increase; Heating rate: 15℃~30℃ / h from 800℃ to 1000℃; hold at 850℃ for 2 hours; hold at 950℃ for 1.5 hours. 1000℃~2500℃, heating rate 80℃~120℃ / h; at 1500℃, hold for 1h; at 2000℃, hold for 2h, then close the vent. 2500℃~3000℃, heating rate 200~300℃ / h, hold at 3000℃ for 2~3h; Step 3: Cooling down; wherein, at 3000℃~800℃, cooling is carried out by steam extraction, with a cooling rate of 13℃~15℃ / h; The graphitization furnace (1) includes a furnace body (11) surrounded by refractory brick walls. The lower insulation layer (12) is laid at the bottom of the furnace body (11); The enclosed box (13) is set inside the furnace body (11) and above the lower insulation layer (12). It is formed by the enclosure of the box panels to accommodate materials and heat the materials. Side insulation layer (14) is filled between the side facades of the enclosed box (13) and the inner wall of the furnace. The upper heat-insulating layer (15) is located above the enclosed box (13); A sealing cover (16) is installed above the furnace body (11); The enclosed box (13) includes a bottom plate assembly (131), a column (132), and a side plate assembly (133). The base plate assembly (131) is formed by splicing together several base plates, with complementary bosses (1311) on two adjacent base plates and the gaps between the base plates being filled with graphite. The column (132) is provided with a slot, and the two ends of the side plate assembly (133) are engaged with the slot of the column (132), and the space between the side plate assembly (133) and the slot is filled with graphite. The side plate assembly (133) is formed by splicing together several side plates. Two adjacent side plates are provided with semi-circular grooves and form a circular hole, and a graphite rod (1331) is provided in the circular hole. The upper heat-insulating layer (15) includes, from bottom to top, a carbon felt (151), a cover plate layer (152), a breathable layer (153), and an upper heat-insulating layer (154). The upper heat-insulating layer (154) is provided with dredging holes (1541) at intervals, and the dredging holes (1541) are filled with breathable filler. The cover plate layer (152) includes several cover plates, and there are gaps between the cover plates for gas to pass through.

2. The method for graphitizing lithium-ion battery anode materials as described in claim 1, characterized in that: Step 3, the cooling process, also includes: At 800℃~600℃, remove the sealing cover and ventilate to cool down at a rate of 3℃~4℃ / h. At 600℃~400℃, remove half of the upper insulation layer (154) and continue ventilation to cool down at a rate of 3~4℃ / h. At 400℃~200℃, continue to remove half of the upper insulation layer (154) and continue to cool down at a rate of 3℃~4℃ / h. At 200℃~60℃, remove the breathable layer (153), the cover plate layer (152), and the carbon felt (151), and continue cooling at a rate of 2℃~3℃ / h. At 60℃, the material was allowed to cool naturally for 48 hours, after which the graphitized anode material was extracted.

3. The method for graphitizing lithium-ion battery anode materials as described in claim 1, characterized in that: The graphitization furnace (1) also includes a conductive component to supplement the heating of the negative electrode material. The conductive component includes several conductive pads (171), flexible graphite pads (172), and conductive pillars (173). The conductive pads (171) are arranged from bottom to top. The bottom conductive pads (171) are located on the bottom plate assembly (131). The conductive pads (171) are padded with flexible graphite pads (172). The two ends of the conductive pillars (173) are connected to the top conductive pads (171).

4. The method for graphitizing lithium-ion battery anode materials as described in claim 1, characterized in that: The lower insulation layer (12) includes, from bottom to top, a carbon raiser layer (121), a refractory brick layer (122), and a carbon black layer (123).

5. The method for graphitizing lithium-ion battery anode materials as described in claim 1, characterized in that: The material of the permeable layer (153) and the permeable filler is 8-25 mm calcined coke.

6. A graphitization system for a lithium-ion battery anode material, characterized in that: The structure includes: The graphitization furnace (1), steam generator (2), negative pressure fan (3), heat exchanger (4), waste heat boiler (5), and preheating chamber (6) as described in claim 1; one end of the sealing cover (16) of the graphitization furnace (1) is connected to the steam generator (2) through a pipe, and the other end of the sealing cover (16) is connected to the air inlet of the negative pressure fan (3) through a pipe, the air outlet of the negative pressure fan (3) is connected to one end of the heat exchanger (4), and the other end of the heat exchanger (4) is connected to the waste heat boiler (5); the side wall of the preheating chamber (6) is provided with a heating coil, and the refrigerant pipe (41) of the heat exchanger (4) is connected to the heating coil (61) of the preheating chamber (6); at the same time, the waste heat boiler (5) is provided with a circulating water pipe (51), and the refrigerant pipe (41) is also connected to the circulating water pipe (51). The water heated by the waste heat boiler (5) is further heated by the heat exchanger (4) for heating the materials in the preheating chamber (6).

7. The graphitization system for a lithium-ion battery anode material as described in claim 6, characterized in that: The refrigerant pipe of the heat exchanger (4) is also connected to the steam generator (2).

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