A hard carbon preparation system and method

Abstract

The application discloses a hard carbon preparation system and a hard carbon preparation method for polymer-based hard carbon. The hard carbon preparation system comprises a solution preparation kettle, a spray granulation tower, a dryer, a first carbonization furnace, a second carbonization furnace and a cooling furnace which are sequentially connected. The hard carbon preparation system can realize full recycling of heat and gas, and can save energy consumption and reduce the production cost of polymer-based hard carbon material when applied to the preparation of the polymer-based hard carbon material. The hard carbon preparation method breaks through the limitation of raw materials, and can produce organic hard carbon at low cost under the condition that the biomass raw material production capacity is difficult to guarantee. The prepared hard carbon product has good performance, and solves the problems of difficult guarantee of the biomass raw material production capacity and unstable supply of the hard carbon product.

Description

TECHNICAL FIELD

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

[0002] Sodium ion batteries are attracting more and more attention in the field of large-scale energy storage due to the abundant and widely distributed sodium resources. However, for the practical application of sodium ion batteries, the development of feasible negative electrode materials is still a great challenge. At present, the negative electrode materials for sodium batteries mainly include metal sulfide / phosphide materials, metal oxide materials, carbon-based materials, alloy materials and titanate materials. Among the carbon-based materials, hard carbon materials have more interlayer spaces, more sodium storage sites, excellent electrical conductivity and good structural stability, and are expected to become the next generation of negative electrode energy storage materials for sodium ion batteries.

[0003] Hard carbon refers to amorphous carbon that is difficult to be completely graphitized at a temperature of 2000 DEG C or above. The carbon-containing material is obtained by carbonizing carbon-containing raw materials in an oxygen-free atmosphere by using a certain pyrolysis temperature. However, due to the different types of carbon-containing precursors, the hard carbon preparation process systems are obviously different. Among them, biomass, coal-based and polymer are currently the three main carbon sources. Biomass raw materials are abundant and low in price, but the collection and pretreatment are complicated, and the current production capacity of biomass carbon source cannot meet the market demand in the future. Coal-based hard carbon has many impurities, is difficult to handle and has poor stability. While the organic carbon source has stable performance and sufficient supply, but the preparation cost is relatively high. SUMMARY

[0004] The present application aims to overcome the problem of high cost of organic carbon source in the prior art for preparing hard carbon, and provides a hard carbon preparation system for polymer-based hard carbon materials. Meanwhile, the present application also provides a preparation method for preparing polymer-based hard carbon materials by using the hard carbon preparation system. The polymer-based hard carbon material prepared by the method has excellent and stable performance, and at the same time has low energy consumption and production cost, greatly improving the market competitiveness of polymer-based hard carbon products.

[0005] To achieve the above-mentioned purpose, on the one hand, the present application provides a hard carbon preparation system, which comprises a solution preparation kettle, a spray granulation tower, a dryer, a first carbonization furnace, a second carbonization furnace and a cooling furnace which are sequentially connected. The spray granulation tower, the dryer and the first carbonization furnace are all connected with a hot gas pipeline. The dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace are all connected with an inert gas pipeline.

[0006] The hard carbon preparation system comprises a solution preparation kettle, a spray granulation tower, a dryer, a first carbonization furnace, a second carbonization furnace and a cooling furnace connected in sequence, the solution preparation kettle is used for preparation of an organic precursor solution, an organic carbon source is prepared into the organic precursor solution in the solution preparation kettle and is fed into the spray granulation tower through a material conveying system, the spray granulation tower is used for forming and preliminary drying of the material, the organic precursor solution prepared through the solution preparation kettle is dried into a microsphere precursor after spray granulation, the dryer is used for drying the microsphere precursor sprayed and granulated by the spray granulation tower, the first carbonization furnace is used for preliminary carbonization of the microsphere precursor, and a pre-carbonized material is obtained, and the second carbonization furnace is used for further high-temperature carbonization of the pre-carbonized material, and the product after high-temperature carbonization is cooled in the cooling furnace to obtain the hard carbon.

[0007] In use, the organic carbon source is prepared into the organic precursor solution in the solution preparation kettle, the organic precursor solution is fed into the spray granulation tower by a conveying pump to obtain solid material, the solid material is fully dried in the dryer, and then is fed into the first carbonization furnace for preliminary carbonization to obtain the pre-carbonized material, the pre-carbonized material is further treated by high-temperature carbonization in the second carbonization furnace, and then is cooled in the cooling furnace to obtain the hard carbon.

[0008] As a preferred embodiment of the hard carbon preparation system, the first carbonization furnace is further connected with a waste heat boiler, and the waste heat boiler is in communication with the hot gas pipelines of the spray granulation tower and the dryer. The waste heat boiler is used for collecting combustible gas discharged from the first carbonization furnace, the combustible gas is combusted in the waste heat boiler, and the generated hot gas can be used by the spray granulation tower and the dryer, so that heat recycling can be realized.

[0009] As a preferred embodiment of the hard carbon preparation system, the cooling furnace is further connected with a product processing device, and the product processing device comprises at least one of a product grading device, a product crushing device and a product packaging device. The hard carbon obtained after cooling in the cooling furnace usually needs to be further processed by the product processing device to obtain a hard carbon product, and the product processing device comprises but is not limited to a product grading device, a product crushing device and a product packaging device.

[0010] As a preferred embodiment of the hard carbon preparation system, the spray granulation tower is further connected with a dust removal device. When the spray granulation tower is further connected with the dust removal device, the tail gas of the spray granulation tower for spray drying to form the microsphere precursor can be treated by the dust removal device and then recycled, which is beneficial to saving energy consumption.

[0011] As a preferred embodiment of the hard carbon preparation system of the present application, the spray granulation tower is a large centrifugal spray granulation tower or an air flow spray granulation tower. The spray granulation tower in the present application can only realize the spray granulation of the organic precursor solution to obtain the microsphere precursor, and the selection includes but is not limited to a large centrifugal spray granulation tower, an air flow spray granulation tower, etc.

[0012] In the spray granulation tower, the sprayed solution is an organic precursor solution prepared from an organic carbon source, and the organic precursor solution contains small organic molecules. After the treatment of the spray granulation tower, the spray granulation tower can prepare the organic precursor solution into the microsphere precursor.

[0013] As a preferred embodiment of the hard carbon preparation system of the present application, the dryer is a rotary dryer. The dryer is used for sufficient drying of the microsphere precursor sprayed by the spray granulation tower, and includes but is not limited to a rotary dryer.

[0014] As a preferred embodiment of the hard carbon preparation system of the present application, the primary carbonization furnace is a rotary sintering kiln. The primary carbonization furnace can use a natural gas / air conveying system for heating.

[0015] As a preferred embodiment of the hard carbon preparation system of the present application, the secondary carbonization furnace is a vacuum furnace or an atmosphere furnace. As a more preferred embodiment of the hard carbon preparation system of the present application, the vacuum furnace is an intermittent closed calcination furnace, and the atmosphere furnace is a push plate type continuous calcination furnace. The secondary carbonization furnace can use an electric heating method for heating.

[0016] As a preferred embodiment of the hard carbon preparation system of the present application, the cooling furnace is a rotary cooling furnace. The cooling furnace is connected with the secondary carbonization furnace. The hard carbon formed by high-temperature carbonization in the secondary carbonization furnace is introduced into the cooling furnace through a conveying system. The hard carbon after the cooling treatment can be further introduced into a product processing device, for example, after being classified by a product classification device, it is introduced into a product crushing device for crushing and screening, and finally the hard carbon product is obtained.

[0017] As a preferred embodiment of the hard carbon preparation system of the present application, the cooling furnace uses the method of room temperature nitrogen blowing to cool, so that the hard carbon obtained by high-temperature carbonization in the secondary carbonization furnace is rapidly cooled, and the product preparation time is shortened.

[0018] As a preferred embodiment of the hard carbon preparation system, the hard carbon preparation system further comprises a gas circulation system, which comprises an inert gas delivery system, a natural gas / air delivery system and a waste gas delivery system. In the hard carbon preparation system, the spray granulation tower, the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace are all in communication with the inert gas delivery system. The natural gas / air delivery system is a low-temperature carbonization auxiliary heating system, which sequentially passes through the first carbonization furnace, the dryer and the spray granulation tower, and is introduced into the waste heat boiler to produce heat and treat the combustible gas discharged from the first carbonization furnace at the same time. The second carbonization furnace is protected by inert gas (such as nitrogen or argon) and the inert gas is recycled after being purified. The inert gas can be used in the spray granulation tower, the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace at the same time, and the gas outlet is introduced into the waste heat boiler and the tail gas is discharged after being treated by combustion.

[0019] In the hard carbon preparation system, the inert gas can be recycled to the maximum extent, and the pure inert gas in the cooling furnace and the second carbonization furnace can be reused; therefore, the recycled outlet gas of the two devices can be directly supplied to the first carbonization furnace, the dryer or the spray granulation tower to realize the reuse of resources and energy.

[0020] As a preferred embodiment of the hard carbon preparation system, the spray granulation tower, the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace are sequentially communicated from top to bottom. When the spray granulation tower, the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace are sequentially communicated from top to bottom, the material transportation can be assisted by gravity, which is more energy-saving.

[0021] The lower end of the dryer and the spray granulation tower is connected, and the microsphere powder obtained by spraying is directly introduced into the dryer to completely dry the material. The first carbonization furnace and the dryer are connected by a conveying pipeline, the microsphere precursor is preliminarily carbonized in the first carbonization furnace, and the obtained pre-carbonized material is introduced into the second carbonization furnace. The second carbonization furnace is connected with the first carbonization furnace by a conveying pipeline, the pre-carbonized material is introduced into the second carbonization furnace for high-temperature carbonization to obtain hard carbon.

[0022] On the other hand, the present application also provides a high polymer-based hard carbon preparation method with lower energy consumption and lower production cost. To achieve this object, the technical scheme adopted by the present application is as follows: a method for preparing hard carbon by using the above-mentioned hard carbon preparation system, which comprises the following steps:

[0023] (1) dissolving the organic matter pre-polymer and the auxiliary agent in a solution preparation kettle to obtain an organic matter precursor solution;

[0024] (2) spray granulating the organic matter precursor solution in a spray granulation tower to obtain a microsphere precursor;

[0025] (3) The microsphere precursor is dried in a dryer under inert gas protection, and then pyrolyzed in a first carbonization furnace to obtain a pre-carbonized material;

[0026] (4) The pre-carbonized material is pyrolyzed in a second carbonization furnace under inert gas protection, and then cooled in a cooling furnace to obtain the hard carbon.

[0027] In the hard carbon preparation method, the organic matter pre-polymer is prepared into an organic matter precursor solution in a solution preparation kettle as a carbon source and an additive, the organic matter precursor solution contains small organic molecules, and then the organic matter precursor solution is sprayed and granulated in a spray granulation tower to prepare a microsphere precursor; the microsphere precursor is fully dried in a dryer under inert gas protection, and then directly carbonized in a first carbonization furnace to obtain a pre-carbonized material with rich pores; and finally, the pre-carbonized material is deeply carbonized in a second carbonization furnace under inert gas protection to obtain hard carbon with closed pores.

[0028] As a preferred embodiment of the hard carbon preparation method, the organic matter pre-polymer in step (1) is phenolic resin. In the hard carbon preparation method, the organic matter pre-polymer is used as a carbon source, and the organic matter pre-polymer is preferably but not limited to phenolic resin. When the organic pre-polymer is phenolic resin, the particle size D50 of the phenolic resin is preferably 10-20 μm.

[0029] As a preferred embodiment of the hard carbon preparation method, the inert gas includes but is not limited to nitrogen or argon. The fuel gas used for heating in the first carbonization furnace is liquefied petroleum gas and air.

[0030] As a preferred embodiment of the hard carbon preparation method, the additive in step (1) includes a solvent, and the solvent is a strong alkali solution. More preferably, the solvent is at least one of NaOH and KOH solution.

[0031] As a preferred embodiment of the hard carbon preparation method, the additive amount of the solvent in the additive is 3-20% of the mass of the organic matter pre-polymer. More preferably, the additive amount of the solvent is 5-10% of the mass of the organic matter pre-polymer.

[0032] As a preferred embodiment of the hard carbon preparation method, the additive in step (1) includes a pore former, and the additive amount of the pore former is 2-5% of the mass of the organic matter pre-polymer. More preferably, the pore former includes but is not limited to glucose.

[0033] In a preferred embodiment of the hard carbon preparation method of the present invention, the spray granulation temperature in step (2) is 150–240°C. More preferably, the spray granulation temperature in step (2) is 180–220°C. Through experimental research, the inventors of this application have discovered that in the spray granulation process, a spray granulation temperature of 150–240°C allows the organic precursor liquid to rapidly and efficiently form microsphere precursors with a particle size distribution controlled within the D50 range of 10–20 μm after spraying. These microsphere precursors with a particle size distribution range are more conducive to subsequent thorough drying and primary and secondary carbonization.

[0034] In a preferred embodiment of the hard carbon preparation method of the present invention, the microsphere precursor in step (3) is dried in a dryer for no less than 2 hours, and the drying time at a temperature range of 100–300°C is no less than 1 hour. More preferably, the drying time at a temperature range of 240–280°C in step (3) is no less than 1 hour. Only by drying for a specific time within the specified temperature range can the microsphere precursor be ensured to be sufficiently dried in the dryer, so as to better carbonize and pyrolyze it in the primary carbonization furnace.

[0035] In a preferred embodiment of the hard carbon preparation method of the present invention, the pyrolysis temperature in the primary carbonization furnace in step (3) is 700-1000°C, and the pyrolysis time is not less than 1 hour. Preferably, the rotation speed in the primary carbonization furnace is not less than 10 rpm. More preferably, the pyrolysis temperature in the primary carbonization furnace in step (3) is 900-950°C. If the pyrolysis temperature of the primary carbonization furnace is too low, the microsphere precursor cannot be effectively carbonized and cannot form a good pre-carbonized material; if the pyrolysis temperature of the primary carbonization furnace is too high, it will also lead to a porous structure formed when the microsphere precursor is prepared into a pre-carbonized material. After repeated experiments and explorations, the inventors of this application finally found that the pyrolysis temperature and time in the primary carbonization furnace need to be within the specific range to ensure that a pre-carbonized material with rich pores is obtained after primary carbonization.

[0036] In a preferred embodiment of the hard carbon preparation method of the present invention, the pyrolysis temperature in the secondary carbonization furnace in step (4) is 1200–1800°C, and the pyrolysis time is not less than 1 hour. More preferably, the pyrolysis temperature in the secondary carbonization furnace in step (4) is 1300–1600°C. The selection of the pyrolysis temperature in the secondary carbonization furnace directly affects the closed pore condition of the hard carbon obtained after secondary carbonization, thereby affecting the performance of the hard carbon. The inventors of this application have found through experiments that when the pyrolysis temperature in the secondary carbonization furnace is 1200–1800°C, especially 1300–1600°C, the obtained hard carbon has abundant closed pores and exhibits better sodium storage performance and first-time efficiency.

[0037] As a preferred embodiment of the preparation method of the hard carbon, the preparation method comprises further grading, crushing and screening treatment of the hard carbon obtained in step (4), and the average particle size of the hard carbon after the crushing treatment is 5-10 μm.

[0038] Finally, the application also provides a hard carbon prepared by the preparation method.

[0039] The hard carbon preparation system can realize full recycling of heat and gas, and can save energy consumption and reduce the production cost of the polymer-based hard carbon material when used for preparing the polymer-based hard carbon material. The preparation method of the application adopts the hard carbon preparation system, selects an organic carbon source, breaks through the limitation of raw materials, and can produce the organic hard carbon at low cost under the condition that the biomass raw material production capacity is difficult to guarantee, realizes stable product supply, and not only has good performance and product batch stability, but also has low energy consumption and production cost, and the whole preparation process is economic and environmentally friendly. The hard carbon has good performance, solves the problems of difficult guarantee of biomass raw material production capacity and unstable supply of hard carbon products. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a structure schematic diagram of an embodiment of the hard carbon preparation system.

[0041] Figure 2 It is a process flow chart of an embodiment of the hard carbon preparation method.

[0042] Figure 3 It is a first-time sodium deintercalation curve of embodiment 2 in the hard carbon preparation method.

[0043] Figure 4 It is a first-time sodium deintercalation curve of embodiment 3 in the hard carbon preparation method.

[0044] Wherein Figure 1 1 is a solution preparation kettle, 2 is a spray granulation tower, 3 is a dryer, 4 is a first-stage carbonization furnace, 5 is a second-stage carbonization furnace, 6 is a cooling furnace, 7 is a waste heat boiler, and 8 is a dust removal device DETAILED DESCRIPTION

[0045] In order to better illustrate the purpose, technical scheme and advantages of the application, the application will be further described below in combination with the drawings and specific embodiments.

[0046] Embodiment 1

[0047] An embodiment of the hard carbon preparation system, the structure schematic diagram of the hard carbon preparation system in the embodiment is as shown in the accompanying Figure 1As shown, the hard carbon preparation system described in the embodiment includes a solution preparation kettle 1, a spray granulation tower 2, a dryer 3, a first carbonization furnace 4, a second carbonization furnace 5, a cooling furnace 6 and a product processing device (not shown in the figure) connected in sequence. The product processing device is a device for grading, crushing and packaging the product. The hard carbon preparation system is arranged from top to bottom as follows: the spray granulation tower 2 (on the fifth floor), the dryer 3 (on the fourth floor), the first carbonization furnace 4 (on the third floor), the second carbonization furnace 5 (on the second floor), the cooling furnace 6 (on the first floor), and the product processing device is also arranged on the first floor. The solution preparation kettle can be placed flexibly, and the organic precursor in the solution preparation kettle can be transported to the spray granulation tower by a power transmission system. The material in the spray granulation tower, the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace can be assisted by gravity for transmission.

[0048] In the hard carbon preparation system, the spray granulation tower, the dryer and the first carbonization furnace are connected with hot gas pipelines, and the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace are connected with inert gas pipelines. The materials in the dryer, the first carbonization furnace, the second carbonization furnace and the cooling furnace all need an inert gas environment. The inert gas is selected to be nitrogen or argon. The inert gas in the cooling furnace can be supplied to the dryer, the second carbonization furnace and the first carbonization furnace. The inert gas in the dryer can be supplied to the second carbonization furnace and the first carbonization furnace. The inert gas in the second carbonization furnace can be supplied to the dryer and the first carbonization furnace after cooling treatment.

[0049] The first carbonization furnace is also connected with a waste heat boiler, and the waste heat boiler is connected with the spray granulation tower and the dryer. The tail gas of the first carbonization furnace and the spray granulation tower enters the waste heat boiler after spray treatment for recycling. A large amount of waste gas is discharged after the preliminary carbonization of the first carbonization furnace, and enters the waste heat boiler for combustion after spray absorption to produce heat. The heat generated can be used for the solution preparation kettle, the spray granulation tower, the dryer and the first carbonization furnace, realizing the degradation use of heat.

[0050] The spray granulation tower is connected with a dust removal device, which can treat the tail gas formed by the spray granulation tower and be used for subsequent recycling.

[0051] In the embodiment, the spray granulation tower is a large centrifugal spray granulation tower, the dryer is a rotary dryer, the first carbonization furnace is a vacuum furnace, and the cooling furnace is a rotary cooling furnace.

[0052] The hard carbon preparation system described in the embodiment includes a gas circulation system, which includes an inert gas delivery system, a natural gas / air delivery system and a waste gas delivery system. The first carbonization furnace can use the natural gas / air delivery system for heating, and the second carbonization furnace can use an electric heating method for heating.

[0053] The hard carbon preparation system described in the embodiment, when in use, dissolves the organic matter pre-polymer and the auxiliary agent in the solution preparation kettle to obtain an organic matter precursor solution, then transports the organic matter precursor solution to the spray granulation tower to perform spray granulation, removes most of the solvent in the organic matter precursor solution to obtain microsphere precursors; the microsphere precursors enter the dryer through the material conveying pipeline to be fully dried, and the dried material enters the primary carbonization furnace to be preliminarily carbonized to obtain pre-carbonized material, which is transported into the secondary carbonization furnace to be further pyrolyzed and carbonized to obtain a hard carbon crude product, which enters the cooling furnace to be cooled, and after the cooling is completed, enters the product processing device to be sequentially graded, crushed and packed to finally obtain the hard carbon product.

[0054] The hard carbon prepared by using the organic carbon source is often high in cost, and in the hard carbon preparation system described in the embodiment, the inert gas in the cooling furnace can be directly introduced into the secondary carbonization furnace for use after being heat-exchanged with the material, or can be directly supplied to the primary carbonization furnace or the dryer. The inert gas stream of the secondary carbonization furnace can be supplied to the primary carbonization furnace or the dryer for use after being moderately cooled. Therefore, the cost of the hard carbon based on the polymer is reduced from the aspects of process and yield, and the hard carbon preparation system described in the embodiment is more suitable for the production of hard carbon based on low-cost organic carbon sources.

[0055] Embodiment 2

[0056] In an embodiment of the hard carbon preparation method described in the embodiment, the hard carbon preparation method described in the embodiment uses the hard carbon preparation system described in embodiment 1, wherein each device is used at an average frequency of 6 times per day, and the process flow chart of the hard carbon preparation method described in the embodiment is shown in FIG. 1, and specifically includes the following steps: Figure 2

[0057] (1) Dissolve the phenolic resin, glucose and NaOH solution in the solution preparation kettle to obtain an organic matter precursor solution, wherein the particle size D50 of the phenolic resin is 10-20 μm, the addition amount of the glucose is 2% of the mass of the phenolic resin, and the addition amount of the NaOH solution is 10% of the mass of the phenolic resin;

[0058] (2) Perform spray granulation on the organic matter precursor solution in the spray granulation tower, wherein the particle size distribution of the spray granulation tower is controlled to be D50 = 10-20 μm to obtain microsphere precursors;

[0059] (3) Under the protection of inert gas, the microsphere precursors are introduced into the dryer to be dried, wherein the residence time of the microsphere precursors in the dryer is 3 h, and the residence time at 150°C, 250°C and 300°C is 1 h respectively; then pyrolysis is performed in the primary carbonization furnace, wherein the temperature of the primary carbonization furnace is 900°C, and the pyrolysis time is 2 h to obtain pre-carbonized material;

[0060] ​(4) under inert gas protection, the pre-carbonized material is passed into a secondary carbonization furnace for pyrolysis, the temperature of the secondary carbonization furnace is 1400℃, the pyrolysis time in the secondary carbonization furnace is 2h, then it is passed into a cooling furnace for cooling, when the temperature is lowered to 150℃ or below, air atmosphere can be used for further cooling, hard carbon with a particle size D50 = 8-15μm is obtained, then a small amount of caked impurities is filtered, after magnetic removal and grading, the hard carbon product is directly packaged.

[0061] In this embodiment, the raw material phenolic microspheres with a particle size D50 = 10-20μm are reduced in size to D50 = 8-15μm after high temperature treatment, a small amount of caked impurities is filtered, after magnetic removal and grading, the hard carbon product is directly packaged.

[0062] In this embodiment, the NaOH solution in step (1) can also be replaced by an equal amount of KOH solution.

[0063] Example 3

[0064] In one embodiment of the hard carbon preparation method described in the present application, the hard carbon preparation system described in Example 1 is used, wherein each device is used at an average frequency of 6 times per day, the process flow chart of the hard carbon preparation method described in this embodiment is shown in FIG. 2, and specifically includes the following steps: Figure 2

[0065] (1) Dissolve phenolic resin and NaOH solution in a solution preparation kettle to obtain an organic precursor solution, the particle size D50 of the phenolic resin is 10-20μm, and the addition amount of the NaOH solution is 20% of the mass of the phenolic resin;

[0066] (2) Spray granulation of the organic precursor solution in a spray granulation tower, the particle size distribution of the spray granulation tower is controlled at D50 = 10-20μm, and a microsphere precursor is obtained;

[0067] (3) Under inert gas protection, the microsphere precursor is passed into a dryer for drying, the residence time of the microsphere precursor in the dryer is 2h, wherein the residence time at 200℃ and 300℃ is 1h respectively; then pyrolysis is carried out in a primary carbonization furnace, the temperature of the primary carbonization furnace is 900℃, and the pyrolysis time is 1h, to obtain a pre-carbonized material;

[0068] (4) Under inert gas protection, the pre-carbonized material is passed into a secondary carbonization furnace for pyrolysis, the temperature of the secondary carbonization furnace is 1500℃, the pyrolysis time in the secondary carbonization furnace is 1h, then it is passed into a cooling furnace for cooling, when the temperature is lowered to 150℃ or below, air atmosphere can be used for further cooling, hard carbon with a particle size D50 = 8-15μm is obtained, then a small amount of caked impurities is filtered, after magnetic removal and grading, the hard carbon product is directly packaged.

[0069] ​In this embodiment, phenolic microspheres with a raw material particle size of D50 = 10-20 μm are treated at high temperature to reduce their size to D50 = 8-15 μm. After filtering out trace amounts of agglomerated impurities, and after demagnetization and grading, they are directly packaged to obtain the hard carbon product.

[0070] In this embodiment, the NaOH solution in step (1) can also be replaced by an equal amount of KOH solution.

[0071] Example 4

[0072] This invention provides an embodiment of the hard carbon preparation method. The hard carbon preparation method in this embodiment is identical to that in Example 2, except that the pyrolysis temperature and time in the primary carbonization furnace in step (3) differ from those in Example 2. In this embodiment, the pyrolysis temperature in the primary carbonization furnace in step (3) is 950°C, and the pyrolysis time is 2 hours.

[0073] Example 5

[0074] This invention provides an embodiment of the hard carbon preparation method. The hard carbon preparation method in this embodiment is identical to that in Example 3, except that the pyrolysis temperature and time in the primary carbonization furnace in step (3) differ from those in Example 3. In this embodiment, the pyrolysis temperature in the primary carbonization furnace in step (3) is 1000℃, and the pyrolysis time is 1 hour.

[0075] Example 6

[0076] This invention provides an embodiment of the hard carbon preparation method. The hard carbon preparation method in this embodiment is identical to that in Example 2, except that the pyrolysis temperature and time in the primary carbonization furnace in step (3) differ from those in Example 2. In this embodiment, the pyrolysis temperature in the primary carbonization furnace in step (3) is 700°C, and the pyrolysis time is 3 hours.

[0077] Example 7

[0078] This invention provides an embodiment of the hard carbon preparation method. The hard carbon preparation method in this embodiment is identical to that in Example 2, except that the pyrolysis temperature and time in the secondary carbonization furnace in step (4) differ from those in Example 2. In this embodiment, the pyrolysis temperature in the secondary carbonization furnace in step (4) is 1600℃, and the pyrolysis time is 1 hour.

[0079] Example 8

[0080] This invention provides an embodiment of the hard carbon preparation method. The hard carbon preparation method in this embodiment is identical to that in Example 3, except that the pyrolysis temperature and time in the secondary carbonization furnace in step (3) differ from those in Example 3. In this embodiment, the pyrolysis temperature in the secondary carbonization furnace in step (3) is 1300℃, and the pyrolysis time is 2 hours.

[0081] Example 9

[0082] In one embodiment of the method for preparing the hard carbon, the method for preparing the hard carbon is the same as that of Example 3, except that the pyrolysis temperature and time in the secondary carbonization furnace in step (3) are different from those of Example 3. In this embodiment, the pyrolysis temperature in the secondary carbonization furnace in step (3) is 1200°C, and the pyrolysis time is 2h.

[0083] Example 10

[0084] In one embodiment of the method for preparing the hard carbon, the method for preparing the hard carbon is the same as that of Example 2, except that the pyrolysis temperature and time in the secondary carbonization furnace in step (4) are different from those of Example 2. In this embodiment, the pyrolysis temperature in the secondary carbonization furnace in step (4) is 1800°C, and the pyrolysis time is 1h.

[0085] Example 1

[0086] Test of the sodium storage performance of the hard carbon product

[0087] The sodium storage performance of the hard carbon products prepared in Examples 2-10 was tested, and the test method was as follows:

[0088] 1) Preparation of the negative electrode sheet: the prepared hard carbon product powder, SP and CMC were mixed uniformly at a mass ratio of 90:3:7, water was added and stirred to prepare a slurry, which was coated on an aluminum foil, dried and cut into a diameter of 12mm electrode sheet.

[0089] 2) The test method for the sodium storage performance was as follows: the prepared electrode sheet was placed in a vacuum oven and vacuum dried at 90°C for 12 hours, and then weighed after cooling. Sodium sheet was used as the counter electrode, 1mol / L NaPF6 solution in Diglyme solution was used as the electrolyte, CR2016 button cell was prepared in an argon glove box with a water oxygen content of less than 0.5ppm, and the test was carried out using a Shenzhen Xinneng battery test system, the half-cell test voltage range was 0-2V, and the charge and discharge current was 0.1C (1C=300mAh / g).

[0090] The test results are shown in Table 1 below:

[0091] Table 1 Test results of the sodium storage performance of the hard carbon products prepared in Examples 2-10

[0092] Example Primary carbonization temperature (°C) Secondary carbonization temperature (°C) Reversible capacity (mAh / g) Initial efficiency (%) 2 900 1400 320-330 mAh / g 89～91 3 900 1500 300-320 mAh / g 90～92 4 950 1400 310-320 mAh / g 89～91 5 1000 1500 300-320 mAh / g 90～92 6 700 1400 320-330 mAh / g 89～91 7 900 1600 280-300 mAh / g 91～93 8 900 1300 310-340 mAh / g 87～90 9 900 1200 300-310 mAh / g 87～90 10 900 1800 270-300 mAh / g 92～94

[0093] From the above table, it can be seen that the primary carbonization temperature has no obvious effect on the performance of the product, and the higher the maximum treatment temperature, the lower the product capacity and the higher the initial efficiency; the lower the maximum treatment temperature, the higher the product capacity and the lower the initial efficiency. In addition, it should be pointed out that the pre-carbonization temperature of the conventional process can be 600-800℃ to meet the purpose of removing volatile matter, and the carbon source used in the present application also contains a certain amount of alkali metal elements (sodium, potassium, etc.), which needs to be removed at a temperature above 900℃. Therefore, in order to save energy, the optimal treatment temperature is generally controlled between 900-950℃; and the maximum carbonization temperature between 1300-1500℃ can not only keep the product capacity above 300mAh / g, but also make the initial efficiency average above 90%, reaching the commercial hard carbon index.

[0094] In addition, the first charge-discharge curves of the hard carbon products prepared in Examples 2 and 3 above were tested on metal sodium, and the test method was as follows:

[0095] 1) Negative electrode tab preparation: the hard carbon material powder, SP and CMC prepared in Examples 2 and 3 were mixed uniformly according to a mass ratio of 93:5:5, water was added and stirred to form a slurry, which was coated on an aluminum foil, dried and cut into a diameter of 12mm tab.

[0096] 2) The sodium storage performance test method was as follows: the prepared tab was placed in a vacuum oven, dried at 90℃ for 12 hours, and weighed after cooling. Sodium sheet was used as the counter electrode, 1mol / L NaPF6 solution in Diglyme solution was used as the electrolyte, and CR2016 button cell was prepared in an argon glove box with water oxygen content below 0.5ppm, and tested by Shenzhen Xinwei battery test system, with the half-cell test voltage range of 0-2V and the charge-discharge current of 0.1C (1C=300mAh / g).

[0097] The test results are shown in the attached Figure 3 and 4 It can be seen from the attached Figure 3 and 4 that the sodium storage reversible capacity of the hard carbon materials prepared in Examples 2 and 3 is about 310-330mAh / g, and the initial efficiency is higher than 90%, meeting the demand of commercial use.

[0098] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application, but not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method of producing hard carbon, characterized by, The method comprises the following steps: (1) dissolving organic prepolymer and an additive in a solution preparation kettle to obtain an organic precursor solution; the additive comprises a pore-forming agent, and the pore-forming agent is added in an amount of 2-5% of the mass of the organic prepolymer; (2) performing spray granulation of the organic precursor solution in a spray granulation tower to obtain a microsphere precursor; the spray granulation is performed at a temperature of 150-240°C; (3) under the protection of an inert gas, the microsphere precursor is introduced into a dryer for drying, the microsphere precursor is kept in the dryer for not less than 2h, and the drying time at a temperature in the range of 100-300°C is not less than 1h; then pyrolysis is performed on the microsphere precursor in a first carbonization furnace at 900-950°C for not less than 1h to obtain a pre-carbonized material; (4) under the protection of an inert gas, the pre-carbonized material is introduced into a second carbonization furnace for pyrolysis at 1300-1500°C for not less than 1h, and then is introduced into a cooling furnace for cooling to obtain the hard carbon; the additive in step (1) comprises a solvent, the solvent is a strong alkali solution, and the solvent is added in an amount of 3-20% of the mass of the organic prepolymer.

2. The method of claim 1, wherein the hard carbon is prepared by the process of: the organic prepolymer in step (1) is a phenolic resin.

3. The method for preparing hard carbon as described in claim 2, characterized in that, in the additive in step (1), the solvent is at least one of NaOH and KOH solutions; and / or, in the additive in step (1), the solvent is added in an amount of 5-10% of the mass of the organic prepolymer; and / or, in the additive in step (1), the pore-forming agent is glucose.

4. The method of claim 1, wherein the hard carbon is prepared by the process of: in step (3), the rotation speed is not less than 10rmp; and / or, the method for preparing the hard carbon further comprises grading, crushing and screening treatment of the hard carbon obtained in step (4), and the average particle size of the hard carbon after the crushing treatment is 5-10μm.

5. The method of claim 4, wherein the hard carbon is prepared by the process of: 5 in step (2), the temperature for the spray granulation is 180-220°C; and / or, in step (3), the drying time at a temperature in the range of 240-280°C is not less than 1h.

6. A hard carbon prepared by the method according to any one of claims 1-5.

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