Device and method for inoculating artificial graphite negative electrode material by using high and low temperature molten iron

Abstract

The invention provides a device and a method for manufacturing an artificial graphite negative electrode material inoculated by high-temperature and low-temperature molten iron. The method comprises the following steps of: controllably and efficiently feeding preheated raw material powder in a controllable compaction state into molten iron by a variable compression ratio spiral conveyor in a vacuum atmosphere; the near-finished-product powder in the discharging blind area on the upper portion of the graphite crucible controllably forms a micro-compression-state near-finished-product powder aggregate through the pressure caused by buoyancy of the carbon powder in the liquid-solid two-phase area below the graphite crucible, the aggregate dynamically presses the carbon powder in the liquid-solid two-phase area, and after high-low-temperature inoculation treatment of molten iron, the carbon powder in the liquid-solid two-phase area is subjected to high-temperature inoculation treatment and high-temperature inoculation treatment of the molten iron. Liquid sealing is achieved through molten iron with the liquid level height larger than or equal to 1400 mm, a high-temperature gas-solid two-phase mixture in a blind area can be smoothly discharged and cooled during discharging, no carbon powder leaks to the outer space of a graphite crucible, the obtained artificial graphite powder is good in quality consistency and high in production efficiency, the gram volume of products produced in batches is higher than 355mAh / g, and the product quality is improved. And the first efficiency is greater than 93.5%.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion secondary batteries, in particular to artificial graphite negative electrode materials used therein. Background Art

[0002] Graphite powder, as the negative electrode active material of lithium-ion batteries, has high specific capacity, low reduction potential, good electrochemical reversibility, low volume expansion rate, high electronic conductivity, and a wide range of raw material sources. It is currently the mainstream negative electrode material for lithium-ion secondary batteries.

[0003] Commercial graphite powder negative electrode materials mainly include artificial graphite and natural graphite. The advantages of natural graphite are low cost and high compaction density. The main disadvantages are: (1) The surface of natural graphite powder is rough, with many active sites and large specific surface area. During the first charge and discharge, the process of forming the SEI film on the surface of the negative electrode active material consumes a lot of lithium resources, resulting in low first charge and discharge efficiency, which is referred to as low first efficiency in the industry. (2) The polycrystalline anisotropy of natural graphite is obvious, and the thickness of the SEI after the reaction and growth on the powder surface is uneven. The thicker SEI film will be more likely to be lost during the battery charge and discharge cycle. (3) The obvious anisotropy of natural graphite powder will also make it difficult for the volume expansion of the negative electrode material to offset each other during charge and discharge. The battery is prone to swell, resulting in large fluctuations in the distance between the electrode groups and a rapid decrease in the battery cycle life. (4) The anisotropy of natural graphite powder polycrystals also means that lithium ions can only be inserted or removed from certain end faces of natural graphite powder polycrystals, resulting in a small effective area for insertion or removal, poor charge and discharge rate characteristics of the battery, and easy lithium precipitation during fast charging, resulting in poor battery safety.

[0004] At present, the mainstream of power battery and energy storage battery industry is to use artificial graphite powder as negative electrode active material, such as all mesophase carbon microspheres or calcined needle coke as raw materials, high temperature graphitization treatment in the high temperature range of 2900-3100℃, and crushing and shaping after cooling to obtain artificial graphite powder. Compared with the anisotropic crystal orientation of the crystal structure of flaky natural graphite powder, the crystal orientation of the polycrystalline structure of artificial graphite powder is isotropic. The surface of the powder is relatively smooth, the active sites on the surface of the powder are relatively few, the specific surface area is small, and the initial efficiency is higher than that of natural graphite. The main disadvantage of artificial graphite powder as negative electrode material is that artificial graphite must be graphitized at high temperature, which has a long processing cycle and high energy consumption. The high-temperature graphitization temperature of traditional artificial graphite is as high as 2900-3100℃. The main technical principle of traditional artificial graphite to improve the graphitization degree is to use the thermal diffusion of carbon atoms at high temperature to re-participate in crystallization to increase the graphitization degree of graphite precursor. The high-temperature graphitization device usually adopts the classic Acheson graphitization furnace. The raw material powder of graphite precursor is loosely packed in the graphite crucible, and the tap density is generally less than 1.10g / cm 3 ; Carbon-based resistor particles are filled between graphite crucibles, and 70-80% of the heating heat is used for these crucibles, resistor materials, insulation materials and other process auxiliary materials. In order to produce uniform products, the heating and insulation time takes nearly 15 days, the cooling time is nearly 10 days, and the processing cycle of one furnace is nearly one month. The overall energy consumption is high, the energy utilization rate is low, the processing cycle is long, and the capital occupation cycle is long, which has become a bottleneck link in reducing the cost of artificial graphite.

[0005] As a long-life negative electrode material for power batteries and energy storage batteries, some artificial graphite powders adopt a core-shell structured coated product structure, such as using carbon precursors such as asphalt or furfural resin to coat and modify natural graphite powder or needle coke powder, and then subjecting it to medium-temperature carbonization and medium-temperature graphitization treatment to manufacture coated artificial graphite, in the hope of obtaining a carbon material surface layer with low crystallinity and low graphitization degree, in the hope of reducing the thickness of the SEI film formed by the reaction when the powder surface initially contacts the electrolyte, and in the hope of improving the uniformity of the SEI film growth, thereby improving the initial efficiency and cycle life of the battery; the traditional artificial graphite coating process has the following disadvantages: (1) The process is complex and the product manufacturing is complex. The cycle is long and the overall energy consumption is still relatively high; (2) The interface strength between the shell and the core of the traditional coated artificial graphite powder material is limited. When the negative electrode is manufactured during strong rolling, the coated shell layer is easily crushed, resulting in the battery's initial efficiency being still unsatisfactory, the cycle life has quality fluctuations, and the battery consistency needs to be improved; (3) The third disadvantage of the traditional coating method for manufacturing artificial graphite powder is that the uniformity of the coated carbon layer is difficult to control. After coating and high-temperature carbonization, a crushing process is required. The broken surface of the powder formed after crushing has a high reaction activity. The coating layer formed after crushing is microscopically uneven, which affects the specific surface area and initial efficiency of the powder, and the film formation uniformity of the SEI film is not good.

[0006] The traditional method of manufacturing artificial graphite negative electrode materials by high-temperature graphitization and carbonization after coating has the above-mentioned disadvantages of high energy consumption, long production cycle, and uneven surface coating layer, and needs to be improved.

[0007] The inventor proposed a technical method and a manufacturing device for manufacturing artificial graphite negative electrode materials by using a high-low temperature molten iron inoculation method in Chinese invention patent applications CN202210708922.2, CN202210702022.7, CN202210889452.4, and CN202310603657.6. The basic idea of ​​using a high-low temperature molten iron inoculation method to manufacture artificial graphite negative electrode materials is that: 1. High-temperature molten iron in the high temperature range of 1650-2150°C has good lubricity for graphite precursor powder (i.e., refined carbon powder, hereinafter referred to as carbon powder). 1. Wetting, the contact angle between carbon powder and high-temperature molten iron is less than 90 degrees; 2. Compared with low-temperature molten iron, high-temperature molten iron has a relatively higher saturated solubility for carbon; 3. As a polycrystalline carbon powder, it includes most crystalline carbon elements and a small amount of amorphous carbon elements. When the carbon powder comes into contact with high-temperature molten iron and presents a wet state, compared with the crystalline carbon elements, the high-temperature molten iron has a preferred dissolution characteristic for the amorphous carbon elements in the carbon powder and the carbon elements with higher activity on the surface of the powder; 4. In the low temperature range between 1350-1650℃ Sometimes in the relatively low temperature range of 1300-1550°C, compared with the above-mentioned high-temperature molten iron, the low-temperature molten iron has a relatively low saturated solubility and non-wetting property for carbon, that is, the contact angle between the carbon powder and the low-temperature molten iron is greater than 90 degrees (about 110 degrees); 5. During the high-temperature inoculation treatment, there are also concentration fluctuations and temperature fluctuations in the liquid-solid two-phase mixture of molten iron and carbon powder. After dissolving in the high-temperature molten iron, some amorphous carbon may dynamically re-precipitate and re-participate in crystallization at certain positions of the grain boundary or surface of the carbon powder polycrystal; Therefore, based on the above 5 technical characteristics, through the temperature-variable process of high-temperature inoculation and low-temperature inoculation of carbon powder by molten iron (referred to as the high-low temperature inoculation process of carbon powder), part of the carbon element in the carbon powder can be dissolved in the molten iron at high temperature and precipitated at low temperature, and the precipitated carbon element can participate in the recrystallization of the carbon powder to increase the graphitization degree of the carbon powder, or deposit on the surface of the carbon powder to form an artificial graphite powder structure with a natural coating core-shell structure; using the density difference between molten iron and carbon powder and the characteristics of poor wettability at low temperature, the carbon powder can be naturally floated from the low-temperature molten iron due to buoyancy. The technical solutions adopted by the above four invention patent applications are to use a main piston made of graphite to cooperate with the inner circle of the graphite crucible, press the carbon powder and immerse it in high-temperature molten iron to achieve precipitation, coating and recrystallization during high-temperature inoculation and cooling, that is, low-temperature inoculation.

[0008] Compared with the traditional method of manufacturing artificial graphite negative electrode materials using high-temperature graphitization of an Acheson furnace, the artificial graphite powder manufactured by the high- and low-temperature molten iron inoculation method has a higher degree of graphitization and a lower specific surface area, and can achieve efficient conversion of amorphous carbon in carbon polycrystalline powder materials and highly active carbon on the surface of the powder to crystalline carbon, that is, the graphitization degree of the carbon powder is efficiently improved; when used as a negative electrode material in a lithium-ion battery, the SEI film grown by the reaction between the surface of the artificial graphite powder manufactured by the high- and low-temperature molten iron inoculation method and the electrolyte is relatively uniform, the battery has a high first efficiency, and the product has the advantages of large gram capacity and long battery cycle life.

[0009] The shortcoming of the above-mentioned high and low temperature molten iron inoculation method for making artificial graphite powder is that the high and low temperature molten iron inoculation method for making artificial graphite negative electrode material powder requires a process of dynamically feeding multiple batches of graphite precursor refined powder raw materials into the molten iron. The nearly finished carbon powder after high and low temperature inoculation treatment also needs to be dynamically negatively sucked into the storage tank outside the vacuum furnace. Negative pressure suction is essentially the use of pressure difference driven pneumatic conveying to discharge the treated nearly finished carbon powder out of the vacuum furnace. In the above four patent applications for high and low temperature molten iron inoculation methods for making artificial graphite negative electrode materials, the technical solutions for realizing the immersion of carbon powder in molten iron all use the up and down displacement control of the main piston to realize the forced compression of the carbon powder and immersion in the molten iron, or to float the carbon powder after the main piston moves up in the low temperature range. Since the main piston and the inner wall of the graphite crucible There is a fitting gap between the inner hole of the main piston and the outer circle of the auxiliary piston, and a special high-temperature sealing, breathable and dust-proof design must be adopted to prevent carbon powder from flying to the external space of the graphite crucible in the vacuum furnace; in the process of adding raw material powder into the molten iron, or in the process of discharging the finished powder material out of the vacuum furnace, there is an engineering problem that the carbon powder floats to the outside of the graphite crucible in the vacuum furnace with the gas; for example, in the process of negative pressure suction and discharging nearly finished powder materials, when inert gas is blown into the vacuum chamber and the material area inside the graphite crucible, part of the artificial graphite powder floating above the molten iron liquid surface will float to the outside of the graphite crucible through the fitting gap, affecting the power safety of the induction heating coil and its electrical connection components, and there are hidden dangers of equipment accidents such as short circuit and sparking.

[0010] Although the technical principle of the manufacturing method proposed in the above invention application for the high- and low-temperature molten iron inoculation method for manufacturing artificial graphite negative electrode materials is feasible, there is still room for improvement and enhancement in the production efficiency of mass production and reduction of production costs. CN202210708922.2 proposes a technical solution of using inert gas to blow and transport graphite precursor powder into molten iron. The gas blowing and transporting of powder raw materials consumes a large amount of inert gas, which affects the production cost; the gas blowing and transporting of powder raw materials requires a large gas flow rate, which has a cooling effect on the molten iron, and the production feeding speed is inhibited; in addition, there is a hidden danger of powder flying to the outside of the graphite crucible.

[0011] CN202210702022.7 and CN202210889452.4 propose a technical solution of using the bottom negative pressure of the auxiliary piston to adsorb the barrel filled with graphite precursor powder into the molten iron; the negative pressure adsorption barrel method of delivering powdered raw materials also has the disadvantage of insufficient delivery efficiency. The use of iron barrels to deliver powdered raw materials also has the disadvantage of accumulation of molten iron weight, and some of the high-temperature molten iron needs to be removed regularly.

[0012] The above high and low temperature molten iron inoculation method for manufacturing artificial graphite negative electrode materials also has room for improvement in the discharging link. When the powder material is discharged to the outside of the vacuum furnace by negative pressure suction pneumatic conveying, the high-temperature artificial graphite powder is prone to local bridging when flowing in the spiral cooling flow channel used for discharging. The discharging has the disadvantage of poor flow and the production efficiency is not satisfactory. CN202310603657.6 proposes a technical solution of using a spiral quantitative conveyor made of graphite material to directly convey raw material powder into molten iron and a two-stage gas-solid separation barrier of carbon fiber woven cloth and carbon brushes as high-temperature sealing measures to prevent carbon powder from floating to the outside of the crucible, which can improve the above problems to a certain extent. Due to the pore size of the carbon fiber woven cloth and the fatigue life of the carbon brush made of carbon fiber, the air permeability and dustproof sealing reliability of the high-temperature sealing material, and how to meet the long service life, are still engineering issues to be improved.

[0013] In the above-mentioned patent application technical solution for the high and low temperature molten iron inoculation method for manufacturing artificial graphite negative electrode materials, no special treatment measures were adopted between the graphite crucible and the refractory brick support. When high-temperature inoculation was carried out at a high temperature above 1650°C, a carbon thermal reduction reaction was easily caused at the interface between the graphite crucible and the porous oxide refractory brick, resulting in melting corrosion of the graphite crucible and the refractory brick support base, thereby affecting the high stability of the graphite crucible and the normal function of the equipment.

[0014] The present invention is proposed in view of the above-mentioned shortcomings of the traditional artificial graphite manufacturing method and the above-mentioned shortcomings and deficiencies of the method and device for inoculating artificial graphite with high and low temperature molten iron. Summary of the invention

[0015] The present invention proposes a manufacturing device and a corresponding manufacturing method for artificial graphite negative electrode materials inoculated with high and low temperature molten iron for mass production, which is economical, environmentally friendly, has high energy utilization efficiency, fast production speed, high raw material utilization rate, high production efficiency and low manufacturing cost, large product capacity per gram, high initial efficiency, and long cycle life. The specific technical and economic advantages are described as follows.

[0016] The manufacturing device of the present invention does not use the main piston to press the carbon powder into the molten iron for high and low temperature inoculation treatment, but uses a part of the carbon powder in a nearly finished state that floats up from the molten iron to be confined to the discharge blind area on the upper part of the graphite crucible (see the attached figure of the specification for details). Figure 1 The circled part I and the accompanying drawings of the specification Figure 2), the upper part of the graphite crucible adopts a fixed upper cover plate and corresponding graphite packing to form a static sealing and dustproof measure, and a discharge blind area (I) functional area of ​​the upper part of the graphite crucible is artificially set above the molten iron liquid level and between the upper cover plate of the graphite crucible to construct, and the upward buoyancy formed by the remaining carbon powders that are still immersed in the molten iron at the bottom and have not yet floated up is used to apply upward pressure to the part of the carbon powders in the near-finished state in the discharge blind area of ​​the upper part of the graphite crucible, so that the part of the carbon powders in the near-finished state in the discharge blind area of ​​the upper part of the graphite crucible forms a "slightly compressed near-finished powder aggregate", which is used to replace the pressing function of the main piston in the above four high-temperature molten iron incubation artificial graphite patent applications, that is, stone The "slightly compressed near-finished powder aggregates" in the blind discharge zone at the top of the graphite crucible dynamically suppress the remaining carbon powder immersed in the molten iron and not yet floated up in the molten iron; inside the graphite crucible, the carbon powder immersed in the molten iron and not yet floated up to the surface of the molten iron forms an iron / carbon liquid-solid two-phase region with the molten iron; the present invention adopts a combination of negative pressure suction / pneumatic conveying and screw conveying during discharge, and dynamically negatively suctions the "slightly compressed near-finished powder aggregates" in the blind discharge zone at the top of the graphite crucible into the interior of the graphite discharge pipe and the connected powder discharge water-cooled screw conveyor, so that the carbon powder in the iron / carbon liquid-solid two-phase region at the bottom of the blind discharge zone of the graphite crucible naturally floats to the blind discharge zone in stages. The present invention adopts molten iron or a liquid-solid two-phase mixture of molten iron and carbon powder with a liquid level greater than or equal to 1400 mm to achieve liquid sealing for the inert gas introduced into the vacuum furnace for the discharge process, thereby preventing the inert gas with a pressure close to one atmosphere used during discharge from carrying the powder to the external space of the graphite crucible in the furnace chamber; the present invention does not need to adopt an unreliable high-temperature dynamic sealing breathable dustproof design, and fundamentally solves the engineering problem of carbon powder flying and leaking to the outside of the graphite crucible along with the flow of inert gas; in the link of conveying carbon powder raw materials for feeding, the present invention adopts a spiral quantitative conveyor with a variable compression ratio of 1.0 to a maximum of 1.6 to directly feed the preheated carbon powder raw materials into the molten iron, and the spiral quantitative conveyor A graphite blade with stirring and dispersing function is arranged at the lower discharge port of the device, and the carbon powder aggregates in a controllable compacted state conveyed by the spiral quantitative conveyor at the lower outlet are centrifuged and dispersed and distributed in the molten iron, and the subsequent high and low temperature inoculation treatment is carried out in the molten iron; when the high temperature inoculation treatment is carried out at a high temperature above 1650°C, a melting reaction is easily generated between the graphite crucible and the traditional mullite or alumina refractory brick support base. The present invention adopts a diffusion barrier material at the interface between the graphite crucible and the refractory brick support base, and the refractory brick support base adopts a high-strength and low-thermal conductivity refractory material sintered at high temperature by a zirconium oxide series material, wherein the content of zirconium oxide-hafnium oxide is greater than 91wt.%, and the volume density is between 4.5-5.6g / cm 3The diffusion barrier material adopts porous ceramic material mainly composed of ZrC. The present invention can comprehensively realize the following through the above technical scheme: the device has the reliability of high temperature sealing, the device has a long service life, the production process is not easily interrupted, and the system manufacturing of smooth and efficient carbon powder feeding-high and low temperature inoculation treatment in molten iron-stable discharge of nearly finished powder can be realized.

[0017] The schematic diagram of a typical device embodying the design concept of the present invention is shown in the attached figure of the specification. Figure 1 , Figure 2 ,and Figure 3The device for inoculating artificial graphite negative electrode materials with high and low temperature molten iron of the present invention mainly comprises: a storage bin arranged at the upper part of the device, which is equipped with a stirring paddle inside, a flap valve is arranged at the bottom of the storage bin and is connected to the upper vacuum chamber below, the upper cover of the storage bin is equipped with a vacuum valve and an air charging valve, and a driving motor is arranged in the middle of the upper cover of the storage bin, which is used to drive the stirring paddle to rotate, and is used to transport the raw material powder downward through the channel at the flap valve to the graphite bin with a preheating function in the upper vacuum chamber; the upper vacuum chamber is arranged in the middle of the device, and a conical bin for caching the raw material powder and having an induction preheating function is arranged inside the upper vacuum chamber, the conical bin is made of graphite material, and a stirring rod is arranged in the center, and a water-cooled driving rod connecting the inside and the outside is arranged at the upper position of the stirring rod, and the part of the water-cooled driving rod outside the upper vacuum chamber is provided with circulating cooling water through a rotating joint, and the part of the water-cooled driving rod outside the upper vacuum chamber is connected to a driving motor, and the water-cooled driving rod is fixedly installed on the cover plate of the upper vacuum chamber through a bearing and a water-cooled dynamic seal, and the water-cooled driving rod is fixed on the cover plate of the upper vacuum chamber through a bearing and a water-cooled dynamic seal. The interior of the empty chamber is connected and fixed to a stirring rod made of graphite material; the stirring rod is provided with a stirring blade with a stirring function at a height between the conical silo, and the stirring blade is made of a graphite rod or a graphite plate and fixed on the stirring rod; the lower part of the stirring rod is close to the bottom of the conical silo, and is provided with a variable compression ratio spiral quantitative conveyor and its corresponding graphite sleeve, the variable compression ratio spiral quantitative conveyor is made of graphite material, and the variable compression ratio spiral quantitative conveyor and the graphite sleeve are similar to a single screw extruder. The structure has the function of quantitatively conveying high-temperature carbon powder raw materials in the graphite crucible molten iron in the downward vacuum chamber. The spiral of the variable compression ratio spiral quantitative conveyor is from top to bottom, and the compression ratio transitions from 1.0 to a maximum of 1.6. For example, the compression ratio gradually increases from 1.0 to 1.6, that is, the compression ratio gradually adopts 1.1, 1.2, 1.3, 1.4, 1.5, 1.6; or the compression ratio gradually transitions from 1.0 to 1.5, that is, the compression ratio gradually adopts 1.1, 1.2, 1.3, 1.4, 1.5. Too small a compression ratio is not conducive to the raw material carbon powder to overcome the buoyancy of the molten iron and be transported downward. Too large a compression ratio will lead to strong compression and local micro-adhesion between the carbon powders, which are not easy to be broken up and dispersed by the dispersion paddle at the lower spiral outlet, resulting in the formation of carbon powder aggregates containing more iron inclusions after subsequent high and low temperature inoculation treatment and floating. A dispersion paddle is arranged at the lower outlet of the variable compression ratio spiral quantitative conveyor, and the tail end of the variable compression ratio spiral quantitative conveyor and its graphite sleeve and the stirring paddle at the bottom are directly immersed in the molten iron. The water-cooled induction coil A for preheating the raw material powder is located at the bottom of the conical graphite silo. and / or the outside of the graphite sleeve. Before or while conveying the raw material powder, the raw material powder is preheated to 1200-1700℃ by electromagnetic induction heating. The preheated raw material powder is directly conveyed into the molten iron inside the graphite crucible by a variable compression ratio spiral quantitative conveyor. The preheated raw material powder is easy to quickly wet and disperse with the molten iron, and can quickly carry out the high-temperature inoculation process. All untreated carbon raw material powders must first contact the molten iron inside the graphite sleeve and then contact the molten iron outside the graphite sleeve after being dispersed and floated from the bottom, achieving at least 2.The discharge blind area on the top of the graphite crucible can only be reached after a travel of 8 meters; the lower part of the device is arranged with a lower vacuum furnace body connected to the upper vacuum chamber, that is, the lower vacuum chamber furnace cavity, the atmosphere between the upper and lower vacuum chambers is connected, and a vacuum system is shared; the lower vacuum chamber furnace cavity is equipped with a graphite crucible and its insulation layer, and the outer ring of the insulation layer is equipped with a water-cooled induction coil B for induction heating the material inside the graphite crucible; the upper part of the graphite crucible is equipped with an upper cover, a graphite pressure plate and corresponding graphite packing for static sealing, and the graphite crucible The central hole of the crucible cover passes through the variable compression ratio screw conveyor and its graphite sleeve; the discharge blind area on the upper part of the graphite crucible is equipped with an air inlet pipe and an air inlet, and is equipped with an inclined upward graphite discharge pipe for discharge and a connected powder discharge water-cooling screw conveyor, which is used to discharge the floating artificial graphite powder to the outside of the furnace; the height and inclination of the inclined upward graphite discharge pipe can prevent molten iron from entering the inside of the powder discharge water-cooling screw conveyor; the discharge adopts negative pressure suction pneumatic conveying and a combination of powder discharge water-cooling screw conveyor The inert gas for discharge is introduced from the graphite air inlet pipe at the top of the graphite crucible, and is introduced into the discharge blind area at the top of the graphite crucible through the air inlet processed on the wall of the graphite crucible. In the discharge blind area, the high-temperature gas-solid two-phase mixture first enters the graphite discharge pipe through pneumatic conveying, and then enters the powder discharge water-cooled screw conveyor. After the strong heat exchange on the wall of the powder discharge water-cooled screw conveyor, the gas-solid two-phase mixture of artificial graphite powder and conveying gas is cooled to below 300°C inside the powder discharge water-cooled screw conveyor, and then enters the cyclone separator of the subsequent collection system and the dust removal device of the subsequent stage. The gas after gas-solid separation is discharged through a vacuum pump or reused for continued powder discharge after compression. The artificial graphite powder is retained in the cyclone separator and the dust collector, and continues to be cooled to below 200°C, and then discharged. In the normal pressure atmosphere, it is screened and washed by a subsequent vibrating screen or air flow classification, and magnetic foreign matter is removed, and it can be packaged and stored as a finished artificial graphite negative electrode material. .

[0018] The method for manufacturing artificial graphite negative electrode material by inoculating high and low temperature molten iron using the device of the present invention mainly comprises the following steps:

[0019] Step 1: Prepare a product with a true density greater than 2.10 g / cm 3 The raw materials of the graphite precursor powder include purified needle coke, natural graphite, mesophase carbon microbeads, metallurgical coke, anthracite, hard carbon, and a combination of one or more of the above carbon materials, and the true density of the graphite precursor powder is controlled to be greater than 2.10 g / cm 3, carbon content is greater than 99%; raw material powders with low true density are prone to micropores or microcracks, and the finished powders formed after high and low temperature molten iron inoculation may contain iron impurities; the volatile matter in the raw material powder is controlled to be less than 0.50%, and the ash content is less than 0.50%; the particle size of the raw material powder is controlled to have an average particle size D50 between 5-30 microns and D95 ​​less than 40 microns;

[0020] Step 2, high-temperature incubation of graphite precursor fine powder in high-temperature molten iron, after vacuuming, the molten iron in the graphite crucible inside the lower vacuum chamber is induction heated to between 1600° C. and 1950° C., the raw material of graphite precursor fine powder is preheated to 1200-1700° C. in the upper vacuum chamber by induction heating, the preheated raw material of graphite precursor fine powder is directly conveyed to the high-temperature molten iron by a variable compression ratio spiral quantitative conveyor, and then the liquid-solid two-phase mixture of molten iron and graphite precursor fine powder is heated together to a high temperature range (HT) of 1600-1950° C., and the total time of high-temperature incubation in this (HT) high temperature range is between 10-120 minutes;

[0021] Step 3, low-temperature incubation and floating discharge of graphite precursor fine powder in low-temperature molten iron, the mixture of graphite precursor fine powder and molten iron after high-temperature incubation is cooled to a low-temperature range (LT) of 1250-1500°C, and low-temperature incubation is carried out in this low-temperature range for a total time of 30-120 minutes, and then the carbon powder after low-temperature incubation is naturally floated to the discharge blind area on the upper part of the graphite crucible above the liquid surface of the molten iron; the inert gas for discharge is introduced from the water-cooled air inlet pipe installed in the lower vacuum chamber, and introduced into the air inlet of the discharge blind area on the upper part of the graphite crucible through the graphite air inlet pipe connected to the water-cooled air inlet pipe inside the lower vacuum chamber, so that the "near-finished powder aggregate in a slightly compressed state" after floating from the molten iron can flow The graphite powder is then transported to the graphite discharge pipe and the connected powder water-cooling screw conveyor by pneumatic conveying in a negative pressure suction mode, and then transported to the outside. The powder water-cooling screw conveyor is simultaneously started to rotate actively to realize the mechanical transportation of the artificial graphite powder. The high-temperature gas-solid mixture of the nearly finished powder and the conveying gas is forcibly cooled in the powder water-cooling screw conveyor and then enters the subsequent cyclone separator and dust collector. After the nearly finished powder floating in the graphite crucible is controllably discharged from the vacuum furnace body, the cyclone separator and the dust collector are filled with inert gas or maintained in vacuum, and the artificial graphite powder mainly distributed inside the cyclone separator is further cooled to below 200°C and discharged. After subsequent air flow mill particle sorting and demagnetization, the artificial graphite negative electrode material is obtained.

[0022] Step 4, continue to add the next batch of graphite precursor powder raw materials into the molten iron, and repeat the above-mentioned high and low temperature molten iron incubation process of artificial graphite negative electrode material manufacturing.

[0023] The advantages of the present invention are further explained below.

[0024] The novel device for inoculating artificial graphite negative electrode materials with high and low temperature molten iron of the present invention can controllably and efficiently deliver preheated high temperature graphite precursor powder into molten iron, and the nearly finished powder entering the discharge blind area on the upper part of the graphite crucible after inoculation with high and low temperature molten iron is controllably formed into "slightly compressed nearly finished powder aggregates", and the high temperature gas-solid two-phase mixture can be controllably and smoothly discharged and fully cooled. The novel device can realize smooth production of the entire process, and no carbon powder leaks into the external space of the graphite crucible in the vacuum furnace. The obtained artificial graphite powder product has good quality consistency and high production efficiency. The gram capacity of the batch-produced product is higher than 355 mAh / g, and the first efficiency is greater than 93.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The system schematic diagram of a typical device for incubating artificial graphite negative electrode materials with high and low temperature molten iron of the present invention, wherein 1 is an air charging valve; 2 is a bearing and a water-cooled dynamic seal; 3 is a driving motor; 4 is a water-cooled driving rod; 5 is a rotary joint; 6 is an air inlet valve; 7 is a vacuum valve; 8 is a storage bin; 9 is a stirring paddle; 10 is a flap valve; 11 is an upper vacuum chamber cover plate; 12 is an upper vacuum chamber furnace cavity; 13 is a heat-insulating material; 14 is a stirring rod; 15 is a stirring blade (graphite rod); 16 is a spiral quantitative conveyor, which is made of graphite material and is used to convey raw material powder into molten iron; 17 is an induction coil A, which is cooled by water inside and is used for preheating raw material powder; 18 is a driving motor; 19 is a powder outlet water-cooled screw conveyor; 20 is an upper cover of a graphite crucible; 21 is a floating The artificial graphite powder is in the form of "slightly compressed near-finished powder aggregate"; 22 is a graphite crucible; 23 is a heat-insulating material; 24 is an induction coil B with water cooling inside, which is used for induction heating of the graphite crucible and the molten iron and carbon powder inside it; 25 is an iron / carbon liquid-solid two-phase region; 26 is a dispersion paddle; 27 is a refractory brick foundation, which adopts a zirconia-based sintered high-strength material; 28 is a diffusion barrier, which adopts a porous ceramic material mainly composed of ZrC to prevent the graphite crucible and the zirconia-based refractory brick foundation from melting at high temperatures; 29 is high-temperature molten iron; 30 is a lower vacuum chamber furnace cavity; 31 is a water-cooled air inlet pipe; 32 is a temperature measuring thermocouple; 33 is a vacuum valve; 34 is a lower vacuum furnace cover; 35 is a silo support; 36 is a graphite silo, which is used for caching and preheating carbon powder raw materials.

[0027] Figure 2 for Figure 1The enlarged partial view of the circled I in the middle, where 1 is the graphite air inlet pipe; 2 is the thermal insulation material; 3 is the graphite packing static seal I; 4 is the upper cover of the graphite crucible; 5 is the temperature measuring thermocouple; 6 is the graphite packing static seal II; 7 is the graphite pressure plate; 8 is the variable compression ratio screw conveyor; 9 is the graphite sleeve of the screw conveyor; 10 is the floating carbon powder; 11 is the air inlet, which is the air inlet processed on the cylinder wall of the graphite crucible.

[0028] Figure 3 for Figure 1 Schematic diagram of the bottom of a graphite crucible, where 1 is a refractory brick foundation; 2 is a diffusion barrier; 3 is a thermal insulation material; 4 is a graphite crucible; 5 is a dispersion paddle, which is fixed to the lower part of a spiral quantitative conveyor for conveying raw material powders and is made of isostatically pressed graphite high-strength material; and 6 is molten iron. DETAILED DESCRIPTION

[0029] The embodiments described below are implemented based on the technical solutions and spirit of the present invention, and provide detailed implementation methods and specific processes, but do not limit the protection scope of the patent of the present invention. Any technical solutions obtained in the form of replacement or equivalent transformation should be understood to fall within the protection scope of the present invention.

[0030] Example 1. A device for incubating artificial graphite negative electrode materials with high and low temperature molten iron, using the attached figure of the specification Figure 1 The main structure comprises a graphite crucible with an inner diameter of 550 mm, an outer diameter of 720 mm and a total height of 2600 mm. A set of inclined discharge graphite tubes for powder discharge and a connected powder discharge spiral water-cooled conveyor are arranged on the side wall of the graphite crucible at a discharge blind area on the top of the graphite crucible. The liquid level of the liquid-solid two-phase mixture of high-temperature molten iron is about 2033 mm. Before a batch of about 388 kg of graphite precursor fine powder raw materials is put into processing, the liquid level of the pure molten iron is about 1453 mm. During high and low temperature incubation, the height of the "slightly compressed near-finished powder aggregate" in the discharge blind area on the top of the graphite crucible is about 408 mm.

[0031] The method for manufacturing artificial graphite negative electrode material inoculated by high and low temperature molten iron mainly comprises the following steps:

[0032] Step 1, preparing graphite precursor powder, the graphite precursor raw material adopts needle coke, the volatilization weight loss after treatment at 900°C / 30 minutes under inert gas protection is less than 0.20%, the particle size after crushing and classification is controlled to have an average particle size D50 between 12-15 microns, D95 less than 30 microns, ash content less than 0.20%, and the true density of the raw material powder is between 2.13-2.16 g / cm3;

[0033] Step 2, high-temperature molten iron incubation, after vacuuming, the molten iron is induction heated to 1700°C, the graphite precursor fine powder raw material is preheated to 1500-1600°C in the upper vacuum chamber by induction heating, the preheated graphite precursor fine powder raw material is directly transported to the high-temperature molten iron by a spiral quantitative conveyor, and then the liquid-solid two-phase mixture of the molten iron and the graphite precursor fine powder is heated together to a high temperature range (HT) of 1750-1800°C, and the total time for high-temperature incubation in the high temperature range of 1750-1800°C is 60 minutes;

[0034] Step 3, low temperature incubation and floating discharge, the mixture of carbon powder and molten iron after high temperature incubation is cooled to the temperature range of 1300-1350℃, and the molten iron is used for low temperature incubation in this low temperature range for a total of 60 minutes, and then negative pressure suction combined with spiral conveying is used for discharge, and the "slightly compressed near-finished powder aggregates" in the discharge blind area above the graphite crucible are discharged.

[0035] After forced cooling by the powder outlet water-cooled screw conveyor, the gas-solid two-phase mixture is transferred to the cyclone separator outside the vacuum furnace in stages. The nearly finished powder undergoes subsequent particle sorting after cooling, and the artificial graphite negative electrode material is obtained after demagnetization; the true density of the artificial graphite powder is tested to be 2.247 g / cubic centimeter, and button batteries are made. The tested gram capacity is between 360-367mAh / g, and the first efficiency is 94.5%.

Claims

1. A device for incubating artificial graphite negative electrode materials with high and low temperature molten iron, characterized in that: The device mainly comprises: using a part of carbon powder in a nearly finished product state that floats up from the molten iron to be confined in a discharge blind area on the upper part of the graphite crucible; the upper part of the graphite crucible adopts a fixed upper cover plate and corresponding graphite packing to form a static sealing dustproof measure; a discharge blind area functional area on the upper part of the graphite crucible is artificially set and constructed between the upper part of the molten iron liquid surface and the upper cover plate of the graphite crucible; the upward buoyancy formed by the remaining carbon powder that is still immersed in the molten iron at the lower part and has not yet floated up is used to apply upward pressure to the part of the carbon powder in a nearly finished product state that exists in the discharge blind area on the upper part of the graphite crucible; the part of the nearly finished product state that exists in the discharge blind area on the upper part of the graphite crucible is The carbon powder in the state forms a "slightly compressed near-finished powder aggregate", which realizes the function of dynamically pressing the remaining carbon powder immersed in the molten iron and not yet floating up in the molten iron; inside the graphite crucible, the carbon powder immersed in the molten iron and not yet floating up to the surface of the molten iron forms an iron / carbon liquid-solid two-phase region with the molten iron; when discharging, a combination of negative pressure suction / pneumatic conveying and screw conveying is adopted, and the "slightly compressed near-finished powder aggregate" in the discharge blind area at the top of the graphite crucible is dynamically sucked under negative pressure into the graphite discharge pipe and the connected powder discharge water-cooled screw conveyor, and the graphite crucible The carbon powder in the iron / carbon liquid-solid two-phase area below the discharge blind area naturally floats up to the discharge blind area in stages; molten iron with a liquid level greater than or equal to 1400 mm or a liquid-solid two-phase mixture of molten iron and carbon powder is used to achieve liquid sealing for the inert gas introduced into the vacuum furnace for the discharge process, so as to prevent the inert gas with a pressure close to one atmosphere used during discharge from carrying the powder to the external space of the graphite crucible in the furnace chamber; in the link of conveying the carbon powder raw materials for feeding, a spiral quantitative conveyor with a variable compression ratio of 1.0 to a maximum of 1.6 is used to directly feed the preheated carbon powder raw materials into the molten iron, and a screw quantitative conveyor with a compression ratio of 1.0 to a maximum of 1.6 is arranged at the lower discharge port of the spiral quantitative conveyor. The graphite blade with stirring and dispersing function centrifuges and disperses the carbon powder aggregate in a controllable compacted state at the lower outlet after being conveyed by the spiral quantitative conveyor and distributes it in the molten iron, and then performs subsequent high and low temperature inoculation treatment in the molten iron; when the high temperature inoculation treatment is performed at a high temperature above 1650°C, a melting reaction is easily generated between the graphite crucible and the refractory brick support base. The present invention adopts a diffusion barrier material at the interface between the graphite crucible and the refractory brick support base, and the refractory brick support base adopts a high-strength and low-thermal conductivity refractory material sintered at high temperature by a zirconium oxide-based material, wherein the content of zirconium oxide-hafnium oxide is greater than 91wt.%, and the volume density is between 4.5-5.6g / cm 3 The diffusion barrier material adopts porous ceramic material mainly composed of ZrC.

2. The device for inoculating artificial graphite negative electrode materials with high and low temperature molten iron according to claim 1, and the method for manufacturing artificial graphite negative electrode materials by inoculating with high and low temperature molten iron using the device, characterized in that: The main steps include: Step 1: Prepare a product with a true density greater than 2.10 g / cm 3 The raw materials of the graphite precursor powder include purified needle coke, natural graphite, mesophase carbon microspheres, metallurgical coke, anthracite, hard carbon, and a combination of one or more of the above carbon materials, and the true density of the graphite precursor powder is controlled to be greater than 2.10g / cm 3 , carbon content greater than 99%; control the volatile matter in the raw material powder to be less than 0.50%, and the ash content to be less than 0.50%; the particle size of the raw material powder is controlled to have an average particle size D50 between 5-30 microns and D95 ​​less than 40 microns; Step 2, high-temperature incubation of graphite precursor fine powder in high-temperature molten iron, after vacuuming, the molten iron in the graphite crucible inside the lower vacuum chamber is induction heated to between 1600° C. and 1950° C., the raw material of graphite precursor fine powder is preheated to 1200-1700° C. in the upper vacuum chamber by induction heating, the preheated raw material of graphite precursor fine powder is directly conveyed to the high-temperature molten iron by a variable compression ratio spiral quantitative conveyor, and then the liquid-solid two-phase mixture of molten iron and graphite precursor fine powder is heated together to a high temperature range (HT) of 1600-1950° C., and the total time of high-temperature incubation in this (HT) high temperature range is between 10-120 minutes; Step 3, low-temperature incubation and floating discharge of graphite precursor fine powder in low-temperature molten iron, the mixture of graphite precursor fine powder and molten iron after high-temperature incubation is cooled to a low-temperature range (LT) of 1250-1500°C, and low-temperature incubation is carried out in this low-temperature range for a total time of 30-120 minutes, and then the carbon powder after low-temperature incubation is naturally floated to the discharge blind area on the upper part of the graphite crucible above the liquid surface of the molten iron; the inert gas for discharge is introduced from the water-cooled air inlet pipe installed in the lower vacuum chamber, and introduced into the air inlet of the discharge blind area on the upper part of the graphite crucible through the graphite air inlet pipe connected to the water-cooled air inlet pipe inside the lower vacuum chamber, so that the carbon powder from the molten iron can be discharged from the molten iron. After floating, the "slightly compressed near-finished powder aggregate" is fluidized, and at the same time, it is pneumatically conveyed by negative pressure suction to enter the graphite discharge pipe and the connected powder discharge water-cooled screw conveyor, and then continues to be transported to the outside. The powder discharge water-cooled screw conveyor starts active rotation at the same time to realize the mechanical conveying of artificial graphite powder; the high-temperature gas-solid mixture of the near-finished powder and the conveying gas is forced to cool in the powder discharge water-cooled screw conveyor and then enters the subsequent cyclone separator and dust collector; the artificial graphite powder mainly distributed in the cyclone separator is further cooled to below 200°C and discharged, and after subsequent air flow mill particle sorting and demagnetization, the artificial graphite negative electrode material is obtained; Step 4, continue to add the next batch of graphite precursor powder raw materials into the molten iron, and repeat the above-mentioned high and low temperature molten iron incubation process of artificial graphite negative electrode material manufacturing.

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