Lithium ion battery negative electrode material graphitization furnace and graphitization method and system

Abstract

According to the graphitization furnace for the negative electrode material of the lithium ion battery, cracks or cracks of the box plate can be reduced while the sealing performance of the box type furnace is guaranteed, the service life of the box plate is prolonged, and the thermal field uniformity and the thermal insulation performance of the box body are improved. The invention further provides a graphitization method of the lithium ion battery negative electrode material, the influence of exhaust and thermal expansion and cold contraction on the box body can be reduced, and meanwhile the graphitization quality of the negative electrode material can be guaranteed. The invention further provides a system for graphitizing the negative electrode material of the lithium ion battery, which is used for preheating the negative electrode material by using the waste gas generated by the method for graphitizing the negative electrode material of the lithium ion battery, so that the graphitizing energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery negative electrode materials, and particularly relates to a graphitization furnace for lithium ion battery negative electrode materials and a graphitization method and system. BACKGROUND

[0002] The negative electrode material is one of the four core materials of a lithium ion battery. The negative electrode of the lithium battery is mainly made of carbon material or non-carbon material, an adhesive and an additive mixed together, and is coated on both sides of a copper foil, and is then processed through drying, rolling and other processes. In the charging and discharging process of the lithium battery, under the action of the electrode voltage, lithium ions in the positive electrode undergo an "insertion" and "de-insertion" electrochemical reaction, and the negative electrode serves as a carrier to store and release lithium ions and make the electric current pass through the external circuit.

[0003] Artificial graphite and natural graphite are currently the two most popular graphite carbon material negative electrodes, and the composite graphite and the mesocarbon microbead are processed through doping modification and compound treatment; the amorphous carbon and the carbon nanomaterial graphene also belong to the carbon material negative electrode.

[0004] The upstream raw materials of the artificial graphite include coke (coal-based needle coke, petroleum-based needle coke and petroleum coke) and pitch. The upstream raw material of the natural graphite is natural flake graphite. The natural flake graphite is a single crystal, the crystal is in the form of a flake, and is obtained after the graphite ore is subjected to flotation. Compared with the natural graphite, the artificial graphite has good comprehensive performance and outstanding advantages, and will be more widely used in power batteries and energy storage batteries.

[0005] Graphitization is a core link of the production of the artificial graphite negative electrode, accounts for about 50% of the total cost of the production of the negative electrode material, and is a high-energy-consumption process, and the electricity cost accounts for 60% of the graphitization cost. There are three types of graphitization furnaces, namely, the Acheson graphitization furnace, the internal string graphitization furnace and the box-type graphitization furnace. The Acheson graphitization furnace relies on resistance material to heat the carbon material, and the impurities in the resistance material will diffuse into the material through high temperature, resulting in high ash content of the material. The box-type furnace is composed of a box plate structure of a material box to form a heating body, and the current is sent into the furnace core heating body through the furnace head electrode to generate high temperature to directly heat the material in the box to achieve the purpose of graphitization. The box-type furnace does not need resistance material, and therefore has low ash content. The ash content is required to be high for the battery negative electrode material, and therefore the box-type furnace is generally used to prepare the battery negative electrode material.

[0006] The box-type furnace has good sealing performance, but the exhaust of the box body is blocked, and in addition, the factors such as high-temperature thermal expansion and low-temperature cooling affect the box plate to easily generate cracks or cracks, thereby reducing the service life of the box plate and affecting the sealing performance of the subsequent box plate. In the subsequent use process, heat and gas are easily dissipated at the position of the cracks of the box plate, which can aggravate the crack diffusion, and can also cause uneven distribution of the heat field of the box body, resulting in problems such as increased energy consumption and reduced product quality. SUMMARY

[0007] In view of the problem that the exhaust and thermal expansion and contraction factors affect the box-type graphitization furnace, causing the box plate to easily produce cracks or cracks, the application provides a lithium ion battery negative electrode material graphitization furnace, which can reduce the production of cracks or cracks of the box plate while ensuring the sealing of the box-type furnace, prolong the service life of the box plate, and improve the thermal field uniformity and heat preservation performance of the box.

[0008] The application also provides a lithium ion battery negative electrode material graphitization method, which can reduce the influence of exhaust and thermal expansion and contraction on the box, while ensuring the quality of the negative electrode material graphitization.

[0009] The application also provides a lithium ion battery negative electrode material graphitization system using waste gas generated by the lithium ion battery negative electrode material graphitization method to preheat the negative electrode material, so as to reduce the graphitization energy consumption.

[0010] A lithium ion battery negative electrode material graphitization furnace comprises: A furnace body surrounded by a refractory brick wall; A lower heat preservation layer laid on the bottom of the furnace body; A surrounding box arranged in the interior of the furnace body and located above the lower heat preservation layer, which is formed by a box plate to accommodate materials and heat the materials; A side heat preservation layer filled between each side vertical surface of the surrounding box and the inner wall of the furnace body; An upper flow guide heat preservation layer located above the surrounding box; A sealing cover arranged above the furnace body; The surrounding box comprises a bottom plate assembly, a stand column, and a side plate assembly; The bottom plate assembly is formed by splicing a plurality of bottom plates, adjacent two bottom plates are provided with complementary bosses and the gap between the bottom plates is filled with graphite; the stand column is provided with a slot, and the two ends of the side plate assembly are connected with the slot of the stand column, and the space between the side plate assembly and the slot is filled with graphite; The side plate assembly is formed by splicing a plurality of side plates, adjacent two side plates are provided with semicircular grooves and form a circular hole, and a graphite rod is arranged in the circular hole.

[0011] The upper flow guide heat preservation layer comprises, from bottom to top, carbon felt, a cover plate layer, a gas permeable layer, and an upper heat preservation layer, the upper heat preservation layer is provided with a through hole at intervals, and the through hole is filled with gas permeable filler; the cover plate layer comprises a plurality of cover plates, and gaps for gas to pass through are left between the cover plates.

[0012] Preferably, the conductive assembly comprises a plurality of conductive pads, flexible graphite gaskets, and conductive columns, the conductive pads are arranged from bottom to top, the conductive pads at the bottom are located on the bottom plate assembly, the conductive pads are filled with flexible graphite gaskets, and the two ends of the conductive columns are connected with the conductive pads at the top.

[0013] Preferably, the lower heat preservation layer comprises, from bottom to top, a recarburizer layer, a refractory brick layer, and a carbon black layer.

[0014] Preferably, the material of the air-permeable layer and the air-permeable filler is calcined coke with a size of 8-25 mm.

[0015] A graphitization method of a lithium ion battery negative electrode material comprises the following steps: Step 1: sequentially filling the lower heat preservation layer, the box body, the side heat preservation layer, the conductive assembly, the negative electrode material, and the upper flow guide heat preservation layer of a graphitization furnace; Step 2: gradient heating of the graphitized negative electrode material; wherein, from room temperature to (200-250℃) at a heating rate of 60-90℃ / h; from (200-250℃) to 800℃ at a heating rate of 30-50℃ / h; for each 100℃ of temperature rise, heat preservation is performed for 30 min; from 800℃ to 1000℃ at a heating rate of 15-30℃ / h; heat preservation is performed for 2 h at 850℃ and for 1.5 h at 950℃; from 1000℃ to 2500℃ at a heating rate of 80-120℃ / h; heat preservation is performed for 1 h at 1500℃ and for 2 h at 2000℃, and then the exhaust hole is closed; from 2500℃ to 3000℃ at a heating rate of 200-300℃ / h; heat preservation is performed for 2-3 h when reaching 3000℃.

[0016] Step 3: cooling.

[0017] A graphitization system of a lithium ion battery negative electrode material comprises a graphitization furnace, a steam generator, a negative pressure fan, a heat exchanger, a waste heat boiler, and a preheating chamber; one end of a sealing cover of the graphitization furnace is connected to the steam generator through a pipeline, the other end of the sealing cover is connected to the air inlet of the negative pressure fan through a pipeline, the air outlet of the negative pressure fan is connected to one end of the heat pipe of the heat exchanger, and the other end of the heat pipe of the heat exchanger is connected to the waste heat boiler; the sidewall of the preheating chamber is provided with a heating coil, and the coolant pipe of the heat exchanger is connected to the heating coil of the preheating chamber; meanwhile, the waste heat boiler is provided with a circulating water pipe, and the coolant pipe is also connected to the circulating water pipe.

[0018] The technical effect of the present application is that the graphitization furnace of the lithium ion battery negative electrode material of the present application can significantly improve the deformation or even cracking of the box body by disassembling the enclosing box body into a plurality of bottom plate assemblies, side plate assemblies and columns, and the natural gap between the components can play a buffering role during thermal expansion and contraction, thereby significantly improving the deformation or even cracking of the box body and prolonging the service life of the box plate. The interlocking relationship between the components and the sealing effect of the graphite can also ensure the sealing of the box body, so that the heat dissipation in the enclosing box body is less and the thermal field is more uniform, thereby reducing the energy consumption of graphitization. At the same time, the design of carbon felt, cover plate, air permeable layer and air permeable filler, combined with the well-sealed enclosing box body, can guide the gas generated during thermal decomposition to flow upwards, prevent the pressure in the box body from being too large, and prevent the box body from deforming or cracking.

[0019] The graphitization method of the lithium ion battery negative electrode material of the present application can guide the slow release of the gas generated by the negative electrode material through a unique gradient heating method, and can also use these gases to continuously form a micro-positive pressure environment in the furnace, prevent air from entering the carbon oxide material, reduce the consumption of heat preservation materials, and ensure the quality of the negative electrode material after graphitization. At the same time, since the waste gas itself can form a micro-positive pressure environment, it is not necessary to introduce argon or nitrogen gas or other protective gas into the furnace, thereby reducing the production cost.

[0020] The graphitization system of the lithium ion battery negative electrode material of the present application uses the waste gas generated during the graphitization cooling process to preheat the negative electrode material, thereby significantly reducing the energy consumption during the graphitization process. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the graphitization furnace of the lithium ion battery negative electrode material of the present application.

[0022] Figure 2 It is a partial structural schematic diagram of the box body of the present application.

[0023] Figure 3 It is a schematic diagram of the installation structure of the bottom plate assembly and the side plate assembly of the present application.

[0024] Figure 4 It is a schematic diagram of the installation structure of the side plate assembly of the present application.

[0025] Figure 5 It is a sectional view of the graphitization furnace of the lithium ion battery negative electrode material of the present application.

[0026] Figure 6 It is a schematic diagram of the graphitization system of the lithium ion battery negative electrode material of the present application.

[0027] In the figure: graphitization furnace 1, furnace body 11, lower heat preservation layer 12, carbonizer 121 layer, 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 clamp 134, side heat preservation layer 14, upper flow guide heat preservation layer 15, carbon felt 151, cover plate layer 152, air permeable layer 153, upper heat preservation layer 154, dredging hole 1541, sealing cover 16, conductive assembly 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 DESCRIPTION

[0028] The technical scheme of the present application will be described in detail below. The following examples are only used to more clearly illustrate the technical scheme of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0029] Please refer to Figures 1 to 5 A graphitization furnace 1 for lithium ion battery negative electrode material includes: a furnace body 11 surrounded by a refractory brick wall; A lower heat preservation layer 12 is laid on the bottom of the furnace body 11; A surrounding box body 13 is arranged inside the furnace body 11 and above the lower heat preservation layer 12, and is formed by surrounding box plates to accommodate materials and heat the materials; A side heat preservation layer 14 is filled between each side of the surrounding box body 13 and the inner wall of the furnace body; An upper flow guide heat preservation layer 15 is located above the surrounding box body 13; A sealing cover 16 is arranged above the furnace body; The surrounding box body 13 includes a bottom plate assembly 131, a column 132, and a side plate assembly 133; The bottom plate assembly 131 is formed by splicing a plurality of bottom plates, and adjacent two bottom plates are provided with complementary bosses 1311 and the gap between the bottom plates is filled with graphite; The column 132 is provided with a slot, and the two ends of the side plate assembly 133 are connected with the slot of the column 132, and the gap between the side plate assembly 133 and the slot is filled with graphite; The side plate assembly 133 is formed by splicing a plurality of side plates, and adjacent two side plates are provided with semicircular grooves and form a circular hole, and a graphite rod 1331 is arranged in the circular hole.

[0030] Further, the upper flow guide heat preservation layer 15 includes, from bottom to top, carbon felt 151, cover plate layer 152, air permeable layer 153, and upper heat preservation layer 154 in sequence, the upper heat preservation layer 154 is provided with a dredging hole 1541, and the dredging hole 1541 is filled with air permeable filler; the cover plate layer 152 includes a plurality of cover plates, and gaps for gas to pass through are left between the cover plates.

[0031] In a preferred embodiment, the box 13 is provided with an electrically conductive assembly 17 for the supplementary heating of the negative material in the box 13. The electrically conductive assembly 17 comprises a plurality of electrically conductive pads 171, flexible graphite pads 172 and electrically conductive columns 173. The electrically conductive pads 171 are arranged from bottom to top, with the bottom electrically conductive pads 171 being arranged on the bottom plate assembly 131. The electrically conductive pads 171 are filled with the flexible graphite pads 172. The two ends of the electrically conductive columns 173 are connected to the top electrically conductive pads 171.

[0032] In a preferred embodiment, the material of the gas-permeable layer 153 and the gas-permeable filler is calcined coke with a size of 8-25 mm.

[0033] In a preferred embodiment, the lower heat insulation layer 12 is composed of carbon black. The carbon black is arranged in two layers. The first layer has a thickness of 45-55 cm. After being compacted, the second layer is arranged, also with a thickness of 45-55 cm and being compacted.

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

[0035] The bottom plate assembly 131 of the present application is used to isolate the lower heat insulation layer 12 and the negative material, and to heat the negative material at the bottom. The negative material of the present application is in powder form. For the sake of convenience, the negative material is referred to as negative powder hereinafter. The bottom plate assembly 131 is composed of a plurality of bottom plates.

[0036] In a preferred embodiment, please refer to Figure 3 The bottom plate assembly 131 is composed of three types of bottom plates, i.e. type A bottom plate, type B bottom plate and type C bottom plate. The type A bottom plate is provided with a square reserved opening at two corners. The type B bottom plate is not provided with a reserved opening. The type C bottom plate is provided with a reserved opening at the middle position of the short side. When being spliced, the type A bottom plate is arranged at the two sides of the box 13, and the type B bottom plate is arranged between the type A bottom plate and the type C bottom plate. The distance between the two vertical columns 132 is different, and the number of the type B bottom plates between the type A bottom plate and the type C bottom plate is also different. One long side of the type A bottom plate is neat, and the other long side is provided with a boss. Correspondingly, the long side of the type B bottom plate adjacent to the type A bottom plate is provided with a complementary boss, so that the type A bottom plate and the type B bottom plate are engaged with each other. The gap between the type A bottom plate and the type B bottom plate is filled with graphite. The same is true between two adjacent type B bottom plates, and the same is true between the adjacent type B bottom plate and the type C bottom plate.

[0037] In this way, it is difficult for the gas in the furnace to go out through the bottom plate assembly 131, and it is also difficult for the gas from the outside to come in through the bottom plate assembly 131, thereby ensuring the sealing of the box 13 from the bottom.

[0038] When the bottom plate assembly 131 is expanded by high temperature, stress is released at the joint of the bottom plate because the bottom plate assembly 131 is assembled by multiple bottom plates. The deformation of the bottom plate is controllable due to the extrusion of the negative electrode powder, thus prolonging the service life of the bottom plate assembly 131. Meanwhile, the sealing of the bottom plate assembly 131 is good as a whole because the bosses between two adjacent bottom plates are complementary and sealed by graphite, and gas is difficult to pass through the bottom of the box 13.

[0039] Similarly, the side plate assembly 133 is connected by the column 132, which significantly shortens the length of the side plate and makes the side plate less likely to crack due to deformation. The slot on the side of the column 132 can ensure the stability of the side plate assembly 133 in the vertical direction and prevent the side plate assembly 133 from falling over.

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

[0041] In a preferred embodiment, the gap between the slot and the side plate is filled with graphite in the following way: The side plate is wrapped with multiple layers of graphite paper at the edge, and then the side plate is inserted 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 in the following way: The graphite powder is mixed with a binder to form a paste, which is then applied to the edge of the side plate, and then the side plate is inserted into the slot from top to bottom.

[0043] Filling the gap between the slot and the side plate with graphite can prevent the slot from not contacting the side plate well and increase the resistance, and can also play a good sealing role to reduce the outflow 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 only one edge with a semicircular groove. Type B side plates have two edges with semicircular grooves. The graphite rod 1331 is filled in the circular hole formed by the semicircular grooves. When the side plate expands due to heat and releases stress at the edge of the side plate, the side plate and the graphite rod 1331 can bear stress uniformly. At the same time, the graphite rod 1331 has good lubricating properties. When the side plate deforms, it can change the angle in time to prevent excessive stress in the vertical direction and extrusion damage.

[0045] In this way, the sealing of the bottom and the side of the box 13 can be ensured.

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

[0047] The bottom plate assembly 131, the side plate assembly 133, the column 132 and the fixing clip 134 of the application are made of the same material. In this way, the expansion performance, the electrical conductivity and the compression resistance of the whole can be ensured to be consistent.

[0048] The carbon felt 151, the cover plate layer 152, the air-permeable layer 153 and the upper thermal insulation layer 154 on the box 13 of the application can guide the gas in the box 13 to be discharged in time while keeping warm, so as to prevent the pressure in the box 13 from being abnormal due to accumulation.

[0049] The carbon felt 151 has good heat resistance and thermal insulation performance. At the same time, the micropores in the carbon felt 151 can facilitate the passage of the gas in the box 13.

[0050] The cover plate layer 152 can play a certain sealing role, and can guide the gas to pass through the gap between the cover plates and effectively reduce the radiation heat dissipation.

[0051] The air-permeable layer 153 can play a certain role in buffering the gas, preventing the pressure in the box 13 from being abnormal due to temperature mutation, and can also play a certain role in hindering the external gas. For example, in the cooling process, when the external air enters along the air-permeable filler of the through hole 1541, the air-permeable layer 153 can accommodate the air on one hand, and consume the oxygen in the air through oxidation reaction on the other hand, preventing the negative electrode powder from being oxidized.

[0052] The upper thermal insulation layer 154 is used for thermal insulation. The gas enters the sealed cover 16 along the carbon felt 151, the cover plate gap, the air-permeable layer 153 and the air-permeable hole of the upper thermal insulation layer 154, and is then discharged.

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

[0054] In a preferred embodiment, the material of the air-permeable layer 153 and the air-permeable filler is calcined coke with a size of 8-25 mm.

[0055] A graphitization method of a lithium ion battery negative electrode material includes the following steps: Step 1: sequentially filling the lower thermal insulation layer 12, the box 13, the side thermal insulation layer 14, the conductive assembly, the negative electrode material and the upper flow guide thermal insulation layer 15 of the graphitization furnace 1; Step 2: gradient heating of the graphitized negative electrode material; wherein, Normal temperature to (200℃-250℃), the heating rate is 60℃-90℃ / h; in this stage, mainly to exclude the free water and low volatile in graphite, and the airflow will also drive the air in the gap between the particles slowly out, reduce the occurrence of subsequent oxidation reaction. For the thermal expansion of the box 13, the cold box 13 can avoid the thermal shock caused by rapid heating.

[0056] (200℃-250℃) to 800℃, the heating rate is 30℃-50℃ / h; every 100℃, the temperature is kept for 30min; in this stage, the volatile is more, such as the release or decomposition of adsorbed water, bound water, low molecular hydrocarbons, asphaltene, etc., the slow heating rate can let the volatile gas slowly out. In this stage, a small amount of oxygen will also react with carbon to generate carbon monoxide. Reducing the heating rate helps to stabilize the pressure in the box 13.

[0057] 800℃ to 1000℃, the heating rate is 15℃-30℃ / h; 850℃, keep for 2h; 950℃, keep for 1.5h; in this stage, the release speed of volatile in the material reaches the peak. Slow down the heating rate can avoid the problem of too large pressure in the box 13, causing the deformation of the box 13.

[0058] 1000℃-2500℃, the heating rate is 80℃-120℃ / h; 1500℃, keep for 1h; 2000℃, keep for 2h, then close the exhaust hole; in this stage, the organic functional groups and amorphous carbon structure in the carbon material are thermally decomposed to generate gas, such as H2, CH2, C2H2, etc. At the same time, after 2000℃, part of the ash will react with carbon to generate volatile gas, and part of the metal impurities will sublimate, such as aluminum. But the total gas production is less, and the heating rate is faster, which helps to exhaust the gas and keep the box 13 in a slightly positive pressure state to prevent air from entering from the top. It should be noted that the box 13 of the present application has good sealing performance on the side and bottom. Air is difficult to enter the box 13 from these two places, and gas is more likely to enter from the top because of the exhaust hole. When heated to 2500℃, little gas is generated in the box 13. In order to ensure the slightly positive pressure environment in the box 13, the exhaust hole is closed. In this way, the gas generated by the material will make the pressure in the box 13 slightly higher than the outside. At the same time, the heat preservation of the box 13 will be better, which helps the subsequent graphitization of the negative electrode powder.

[0059] 2500℃-3000℃, the heating rate is 200-300℃ / h, and when reaching 3000℃, keep for 2h-3h.

[0060] Due to the very good sealing of the graphitization furnace 1 of the present application, and through the improved temperature control measures, the box 13 can maintain a micro-positive pressure environment. There is no need to fill nitrogen or argon protective gas, thus effectively reducing the production cost of this part. Due to the absence of nitrogen and other protective gases, the volatile substances generated by the present application can also be used for combustion to preheat the box 13 of other furnaces.

[0061] Step 3: cooling; 3000℃-800℃, air cooling, cooling rate 13℃-15℃ / h; The air cooling of the present application is to open the exhaust port at both ends of the sealing cover 16, one end is connected with the fan, and the other end is connected with the steam generator 2. Then the steam generator 2 generates water vapor which is sucked into the sealing cover 16 by the fan. The high temperature in the sealing cover 16 is taken away by the water vapor. The heat taken away by the water vapor can be used to preheat the negative electrode powder through heat exchange, thereby reducing energy consumption.

[0062] The water vapor takes away the heat at the same time, and also reacts with the petroleum coke of the heat preservation layer to generate carbon monoxide and hydrogen. This reaction is an endothermic reaction, which can quickly cool the heat preservation layer. At the same time, the gas produced by the reaction can be used as fuel to preheat the negative electrode powder.

[0063] When the temperature in the sealing cover 16 is reduced to 800℃, the efficiency of cooling by water vapor is relatively low, and at the same time, the reaction of air and carbon is very slow. In order to save cost, air cooling is no longer used, but ventilation cooling is used.

[0064] That is, 800℃-600℃, remove the sealing cover 16, ventilation cooling, cooling rate 3℃-4℃ / h. It should be noted that when the temperature is 800℃, the sealing cover 16 is removed, and the body temperature is not measured at all times during the on-site operation. Therefore, according to experience, the sealing cover 16 can be removed when the temperature is 800℃±20℃. Due to the good heat preservation effect of the graphitization furnace 1 of the present application, the efficiency of ventilation cooling is relatively low, and accordingly, 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 fast at this time, the heat will quickly transfer to other places in the workshop, and the temperature in the workshop will rise quickly, which is not conducive to the work of workers.

[0065] 600℃-400℃, remove one-half of the upper heat preservation layer 154, continue ventilation cooling, cooling rate 3-4℃ / h; After the box 13 is cooled to 600℃, due to the significant reduction of the temperature difference between the inside and outside of the furnace body 11, and considering the acceptance of the workers to the temperature in the workshop, when the temperature is 600℃±20℃, one-half of the upper heat preservation layer 154 is removed, so that the negative electrode powder in the box 13 can be cooled more easily.

[0066] 400℃~200℃, remove the upper half of the remaining insulation layer 154, continue to ventilate and cool, the cooling rate is 3-4℃ / h; 200℃~60℃, remove the gas permeable layer 153, remove the cover layer 152 and the carbon felt 151, continue to cool, the cooling rate is 2-3℃ / h; At 60℃, naturally cool for 48h, and then remove the graphitized negative electrode material.

[0067] At this time, the temperature is still relatively high, and the cover layer 152 and the carbon felt 151 are preferably operated by a machine. If manual operation is necessary, heat protection should be done.

[0068] Both the removal of the insulation layer material and the negative electrode powder are performed by a machine. The powder is sucked into a collection bin through a negative pressure pipeline.

[0069] Through the above detailed graphitization process of the present application, a graphitization system for lithium ion battery negative electrode material is also provided, which uses the waste gas generated during graphitization to preheat the negative electrode powder, thereby reducing the energy consumption of graphitization.

[0070] Please refer to Figure 6 A graphitization system for lithium ion battery negative electrode material 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 a sealed cover 16 of the graphitization furnace 1 is in communication with the steam generator 2 through a pipeline, the other end of the sealed cover 16 is in communication with the air inlet of the negative pressure fan 3 through a pipeline, the air outlet of the negative pressure fan 3 is connected with one end of the heat pipe of the heat exchanger 4, and the other end of the heat pipe of the heat exchanger 4 is connected with the waste heat boiler 5. The high-temperature gas in the graphitization furnace 1 is combusted in the waste heat boiler after being cooled by the heat exchanger 4. The side wall of the preheating chamber 6 is provided with a heating coil, and the coolant pipe of the heat exchanger 4 is connected with the heating coil of the preheating chamber 6. At the same time, the waste heat boiler 5 is provided with a circulating water pipe 51, and the coolant pipe is also connected with the circulating water pipe 51. The water heated by the waste heat boiler 5 is further heated by the heat exchanger 4, and is used for heating the materials in the preheating chamber 6.

[0071] The water vapor generated by the steam generator 2 is brought into the graphitization furnace 1 by the negative pressure fan 3. Through convection heat transfer and endothermic chemical reaction, the heat in the furnace is taken away. The generated high-temperature flue gas is brought into the heat exchanger 4 to heat the circulating water. Then the flue gas enters the waste heat boiler 5 as fuel to heat the circulating water. The circulating water heated by the waste heat boiler 5 is further heated by the flue gas, and then enters the preheating chamber 6 for preheating of the negative electrode material. At the same time, in a preferred embodiment, the coolant pipe 41 of the heat exchanger 4 is also connected with the steam generator 2, and part of the heated water enters the steam generator 2 to be prepared into steam for cooling of the graphitization furnace 1.

[0072] The following is an embodiment of the present application for a graphitization method of a lithium ion battery negative electrode material.

[0073] Embodiment 1 A graphitization method of a lithium ion battery negative electrode material includes the following steps: Step 1: sequentially loading the lower heat preservation layer 12, the box 13, the side heat preservation layer 14, the conductive assembly 17, the negative electrode material, and the upper conductive heat preservation layer 15 of the graphitization furnace 1; Step 2: gradient heating of the graphitized negative electrode 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℃ of temperature rise, heat preservation for 30min; from 800℃ to 1000℃, the heating rate is 15℃ / h; heat preservation for 2h at 850℃; heat preservation for 1.5h at 950℃; from 1000℃ to 2500℃, the heating rate is 80℃ / h; heat preservation for 1h at 1500℃; heat preservation for 2h at 2000℃, and then the exhaust hole is closed; from 2500℃ to 3000℃, the heating rate is 200℃ / h, and heat preservation for 2h when reaching 3000℃.

[0074] Step 3: cooling; from 3000℃ to 800℃, air extraction cooling, the cooling rate is 13℃ / h; from 800℃ to 600℃, removing the sealing cover 16, ventilation cooling, the cooling rate is 3℃ / h; from 600℃ to 400℃, removing one half of the upper heat preservation layer 154, continuing ventilation cooling, the cooling rate is 3℃ / h; from 400℃ to 200℃, removing the remaining half of the heat preservation layer, continuing cooling, the cooling rate is 3℃ / h; from 200℃ to 60℃, removing the air permeable layer 153, removing the cover layer 152 and the carbon felt 151, continuing cooling, the cooling rate is 2℃ / h; at 60℃, natural cooling for 48h, and then extracting the graphitized negative electrode material.

[0075] Embodiment 2 A graphitization method of a lithium ion battery negative electrode material includes the following steps: Step 1: sequentially loading the lower heat preservation layer 12, the box 13, the side heat preservation layer 14, the conductive assembly, the negative electrode material, and the upper conductive heat preservation layer 15 of the graphitization furnace 1; Step 2: gradient heating of the graphitized negative electrode material; wherein, from room temperature to (250℃, the heating rate is 90℃ / h; 250-800℃, 50℃ / h; 30min for each 100℃; 800-1000℃, 30℃ / h; 2h at 850℃; 1.5h at 950℃; 1000-2500℃, 120℃ / h; 1h at 1500℃; 2h at 2000℃, then close the exhaust hole; 2500-3000℃, 300℃ / h, 3h at 3000℃.

[0076] Step 3: cooling; 3000-800℃, air cooling, 15℃ / h; 800-600℃, remove the sealing cover 16, air cooling, 4℃ / h; 600-400℃, remove half of the upper insulation layer 154, continue air cooling, 4℃ / h; 400-200℃, remove the remaining half of the insulation layer, continue cooling, 4℃ / h; 200-60℃, remove the air-permeable layer 153, remove the cover layer 152 and carbon felt 151, continue cooling, 3℃ / h; 60℃, natural cooling for 48h, then extract the graphitized negative electrode material.

[0077] In the above table, the lower limit of the temperature rate is taken in Example 1, and the upper limit of the temperature rate is taken in Example 2. The graphitization energy consumption of Example 1 and Example 2 is compared with the existing graphitization energy consumption and the loss of the box 13 as shown in Table 1.

[0078] At the same time, the prior art also has a graphitization furnace 1 similar in structure to the present application, for example, patent number 202223574721.2, named "Battery negative electrode material graphitization box furnace".

[0079] The graphitization furnace 1 of the present application is different from the application in that: The bottom plate assembly 131 is formed by splicing a plurality of bottom plates, and adjacent two bottom plates are provided with complementary bosses and the gap between the bottom plates is filled with graphite; The stand column 132 is provided with a slot, and the two ends of the side plate assembly 133 are clamped and connected with the slot of the stand column 132, and the side plate assembly 133 and the slot are filled with graphite; The side plate assembly 133 is formed by splicing a plurality of side plates, and adjacent two side plates are provided with semicircular grooves and form a circular hole, and a graphite rod 1331 is arranged in the circular hole; The fixed clasp 134 is in snap connection with the top of the column 132. The upper flow guide heat preservation layer 15 includes, from bottom to top, carbon felt 151, cover plate layer 152, air permeable layer 153, and upper heat preservation layer 154. The upper heat preservation layer 154 is provided with a through hole 1541, and the through hole 1541 is filled with air permeable 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.

[0080] Due to the sealing measures of the graphitization furnace 1 of the present application, such as the installation of graphite rods 1331 between the side plates, and the filling of graphite between the column 132 slot and the side plates, the energy consumption of graphitization is reduced, and the service life of the box 13 is also significantly improved. At the same time, the box 13 of the present application cooperates with the upper flow guide heat preservation layer 15 to significantly reduce the energy consumption of graphitization, prolong the service life of the box 13, and improve the quality of the negative electrode material.

[0081] The present application also sets the following comparative examples for verification.

[0082] Comparative Example 1 The same as steps 2 and 3 of Example 1, the difference is that the side plate assembly 133 of step 1 is spliced with a plurality of side plates, without graphite rods 1331, and without filling graphite in the gap.

[0083] Comparative Example 2 The same as steps 2 and 3 of Example 1, the difference is that the upper heat preservation layer 154 of step 1 adopts the structure commonly used in the prior art, i.e. carbon felt 151, cover plate layer 152, and upper heat preservation layer 154, and the upper heat preservation layer 154 is provided with a chimney. Referring to Patent No. 202122978100.X, a box furnace with good top sealing and air permeability.

[0084] Comparative Example 3 The same as steps 2 and 3 of Example 1, the difference is that the graphitization furnace 1 of Comparative Example 1 is provided with an air inlet hole below the side wall of the box 13, simulating the conventional way of preventing the negative electrode powder from being oxidized by introducing nitrogen.

[0085] Table 1: Unit energy consumption, box plate service life, and graphitization degree under different implementation conditions As can be seen from Table 1, the unit energy consumption of the negative electrode material graphitization of Example 1 and Example 2 is close, the service life of the box 13 is 8 times, and the graphitization degree is also close.

[0086] Compared with the comparative example 1, the unit energy consumption of the example 1 is reduced by 388KW.h / ton due to the better sealing of the box 13, and the energy consumption is significantly reduced. At the same time, due to the uneven thermal expansion and contraction caused by the poor sealing of the box 13 of the comparative example 1, the service life of the box plate of the application is increased by 2 times. The graphitization degree of the negative electrode material prepared in the example 1 reaches 97.2%, which is nearly 2% higher than the graphitization rate of 95.3% of the comparative example 1. Due to the better sealing of the box 13, the thermal field inside the box 13 is more uniform, which can reduce the energy consumption and improve the graphitization degree of the negative electrode material.

[0087] Compared with the comparative example 2, the unit energy consumption of the example 1 is reduced by 479KW.h / ton due to the good sealing of the upper flow guide heat preservation layer 15, and the energy consumption is significantly reduced. Due to the fact that the outside air is more likely to enter from the chimney, the thermal expansion and contraction inside the box 13 is uneven, and the service life of the box plate of the example 1 is 2 times longer than that of the comparative example 2. At the same time, the sealing of the example 1 is better, and the graphitization degree is higher.

[0088] The comparative example 3 is to prevent the oxidation of the negative electrode material, and nitrogen is introduced. Correspondingly, due to the faster gas flow, the heat loss is also higher. At the same time, the temperature and flowability of the gas itself are inconsistent with the thermal field, which affects the uniformity of the thermal field of the box 13, resulting in uneven thermal expansion and contraction, affecting the service life of the box plate, and also affecting the graphitization degree.

[0089] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the application examples.

Claims

1. A graphitization furnace (1) for lithium ion battery negative electrode material, comprising: a furnace body (11) surrounded by a wall of refractory bricks; a lower heat preservation layer (12) laid on the bottom of the furnace body (11) ; a surrounding box (13) arranged inside the furnace body (11) above the lower heat preservation layer (12), formed by a box plate to contain materials and heat the materials; a side heat preservation layer (14) filled between each side vertical surface of the surrounding box (13) and the inner wall of the furnace body; an upper flow guide heat preservation layer (15) above the surrounding box (13) ; a sealing cover (16) arranged above the furnace body (11) ; characterized in that the surrounding box (4) comprises a bottom plate assembly (131), a stand column (132), and a side plate assembly (133) ; the bottom plate assembly (131) is spliced by a plurality of bottom plates, and adjacent two bottom plates are provided with complementary bosses (1311) and the gap between the bottom plates is filled with graphite; the stand column (132) is provided with a slot, and the two ends of the side plate assembly (133) are connected with the slot of the stand column (132), and the side plate assembly (133) and the slot are filled with graphite; the side plate assembly (133) is spliced by a plurality of side plates, and adjacent two side plates are provided with semicircular grooves to form a circular hole, and a graphite rod (1331) is arranged in the circular hole.

2. Graphitization furnace (1) for lithium-ion battery anode materials according to claim 1, characterized in that: The upper flow guide heat preservation layer (15) comprises, from bottom to top, a carbon felt (151), a cover plate layer (152), an air permeable layer (153), and an upper heat preservation layer (154), the upper heat preservation layer (154) is provided with a through hole (1541), and the through hole (1541) is filled with air permeable filler; the cover plate layer (152) comprises a plurality of cover plates, and gaps are left between the cover plates for gas to pass through.

3. A graphitization furnace (1) for lithium-ion battery anode material as claimed in claim 1, characterized in that: It further comprises an electrically conductive assembly to supplement the heating of the negative electrode material, the electrically conductive assembly comprises a plurality of electrically conductive pads (171), flexible graphite gaskets (172), and electrically conductive columns (173), the electrically conductive pads (171) are arranged from bottom to top, the bottom electrically conductive pad (171) is arranged on the bottom plate assembly (131), the electrically conductive pads (171) are padded with the flexible graphite gaskets (172), and the two ends of the electrically conductive column (173) are connected with the top electrically conductive pad (171).

4. A graphitization furnace for lithium ion battery anode material as claimed in claim 1, wherein: The lower heat preservation layer (12) comprises, from bottom to top, a carbon additive layer (121), a refractory brick layer (122), and a carbon black layer (123).

5. A graphitization furnace for lithium-ion battery anode material as claimed in claim 1, wherein: The material of the air permeable layer (153) and the air permeable filler is calcined coke with a size of 8-25 mm.

6. A method of graphitizing a lithium-ion battery anode material, the method comprising: It comprises the following steps: ​ Step 1: sequentially filling the lower heat preservation layer (12), the surrounding box (13), the side heat preservation layer (14), the negative electrode material, and the upper flow guide heat preservation layer (15) of the graphitization furnace (1) according to any one of claims 1-4; Step 2: gradient heating of the graphitized negative electrode material; wherein, from room temperature to (200-250℃) at a heating rate of 60-90℃ / h; from (200-250℃) to 800℃ at a heating rate of 30-50℃ / h; 30 min of heat preservation for every 100℃ of temperature rise; from 800℃ to 1000℃ at a heating rate of 15-30℃ / h; 2h of heat preservation at 850℃; 1.5h of heat preservation at 950℃; and 1000℃~2500℃, heating rate 80℃~120℃ / h; 1500℃, holding for 1h; 2000℃, holding for 2h, then close the exhaust hole; 2500℃~3000℃, heating rate 200~300℃ / h, holding for 2~3h when reaching 3000℃; Step 3: cooling down.

7. The graphitization process for lithium-ion battery anode material as claimed in claim 6, wherein: Step 3: the process of cooling down is: 3000℃~800℃, air extraction cooling, cooling rate 13℃~15℃ / h; 800℃~600℃, remove the sealing cover, ventilation cooling, cooling rate 3℃~4℃ / h; 600℃~400℃, extract one half of the upper insulation layer (154), continue ventilation cooling, cooling rate 3~4℃ / h; 400℃~200℃, continue to extract one half of the upper insulation layer (154), continue cooling, cooling rate 3℃~4℃ / h; 200℃~60℃, extract the air-permeable layer (153), remove the cover layer (152) and the carbon felt (151), continue cooling, cooling rate 2℃~3℃ / h When 60℃, natural cooling for 48h, then extract the graphitized negative electrode material.

8. A method of graphitizing a lithium-ion battery anode material as claimed in claim 7, characterized by: In step 3, 3000℃~800℃, air extraction cooling is carried out by water vapor.

9. A graphitization system for lithium-ion battery anode material, characterized by: The structure comprises: The graphitization furnace (1) according to any one of claims 1~4; a steam generator (2), a negative pressure fan (3), a heat exchanger (4), a waste heat boiler (5), a preheating chamber (6); one end of the sealing cover (16) of the graphitization furnace (1) is in communication with the steam generator (2) through a pipeline, the other end of the sealing cover (16) is in communication with the air inlet of the negative pressure fan (3) through a pipeline, the air outlet of the negative pressure fan (3) is connected with one end of the heat pipe of the heat exchanger (4), the other end of the heat pipe of the heat exchanger (4) is connected with the waste heat boiler (5); the sidewall of the preheating chamber (6) is provided with a heating coil, the refrigerant pipe (41) of the heat exchanger (4) is connected with 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 with the circulating water pipe (51).

10. A graphitization system for lithium-ion battery anode material as claimed in claim 9, wherein: The refrigerant pipe of the heat exchanger (4) is also connected with the steam generator (2).

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