Sintering method of phosphate positive electrode material

Abstract

The invention provides a sintering method of a phosphate positive electrode material, and belongs to the technical field of lithium batteries. The sintering method of the phosphate positive electrode material comprises the following steps: performing primary sintering on a raw material containing a precursor of the phosphate positive electrode material to obtain a pre-sintered material, and then performing secondary sintering on the pre-sintered material to obtain the positive electrode material. The first sintering comprises sintering for 6-11 hours in a rotary kiln, and the second sintering comprises sintering for 15-20 hours in a roller kiln. According to the method, a precursor and a first carbon source are pre-sintered through a rotary kiln, so that the material is primarily crystallized to form crystal nucleuses or crystal grains, then the prepared pre-sintered material is sintered through a roller kiln, crystals further grow in the roller kiln, and the positive electrode material is obtained. According to the method, the raw materials are sintered in the rotary kiln for 6-11 h and sintered in the roller kiln for 15-20 h in sequence, the sintering time of the positive electrode material can be shortened, the productivity of the rotary kiln can be matched with the productivity of the roller kiln, and therefore the overall productivity of a production line is improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and more specifically, to a sintering method for a phosphate-based cathode material. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Lithium phosphates with an olivine structure outperform traditional lithium-ion battery cathode materials in terms of cycle performance and safety. Furthermore, due to the abundance of resources required for their synthesis, they also have a significant cost advantage and have been widely adopted.

[0003] In the preparation of phosphate-based cathode materials, roller kilns are commonly used as sintering furnaces. However, sintering phosphate-based cathode materials in roller kilns results in long sintering times and low production capacity. Therefore, the production capacity of existing phosphate-based cathode materials still needs to be improved. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a sintering method for phosphate-based cathode materials, which can improve production capacity without affecting the electrical properties of the obtained cathode materials.

[0005] To achieve the above objectives, the first aspect of this application provides a sintering method for a phosphate-based cathode material, comprising: sintering a raw material containing a precursor of the phosphate-based cathode material in a first sintering process to obtain a pre-sintered material, and then sintering the pre-sintered material in a second sintering process to obtain the cathode material. The first sintering includes sintering in a rotary kiln for 6 to 11 hours, and the second sintering includes sintering in a roller kiln for 15 to 20 hours. Both the first and second sintering processes are carried out under an inert atmosphere with an oxygen content ≤200 ppm.

[0006] Therefore, by sequentially sintering the raw materials containing the precursor of phosphate-based cathode materials in a rotary kiln for 6-11 hours and in a roller kiln for 15-20 hours, this application can shorten the sintering time of the cathode material, and the capacity of the rotary kiln can be matched with that of the roller kiln, thereby improving the overall capacity of the production line.

[0007] In any embodiment, the first sintering includes a first holding stage, which involves holding at a temperature of 400°C to 750°C for 3 to 9 hours. By keeping the holding temperature and holding time of the first holding stage within the above range, the raw material can be initially crystallized in the rotary kiln.

[0008] In any embodiment, the first sintering also includes a first heating stage and a first cooling stage, wherein the duration of the first heating stage is 0.5 h to 2 h, and the duration of the first cooling stage is 0.5 h to 2 h. By ensuring that the heating time of the first heating stage and the cooling time of the first cooling stage are within the above-mentioned ranges, it is beneficial to control the sintering time of the entire cathode material sintering process, thereby shortening the sintering time of the cathode material and increasing production capacity.

[0009] In any embodiment, the second sintering includes a second holding stage, which involves holding at a temperature of 600°C to 750°C for 6 to 10 hours. By keeping the holding temperature and holding time of the first holding stage within the above range, crystals can be grown in the roller kiln to obtain the cathode material.

[0010] In any embodiment, the cathode material includes lithium manganese iron phosphate and / or lithium iron phosphate.

[0011] In any embodiment, the precursor of the phosphate-based cathode material includes carbonate and / or oxalate. When the precursor of the phosphate-based cathode material includes carbonate and / or oxalate, the precursor will release gas during sintering. The sintering method of this application utilizes the high exhaust efficiency of rotary kilns. The raw material is first pre-calcined in a rotary kiln, where it reacts and decomposes rapidly, releasing gases such as carbon dioxide and water vapor. Preliminary crystallization forms crystal nuclei or grains, yielding pre-calcined material. The pre-calcined material is then transferred to a roller kiln for sintering, where the crystals further grow, thereby reducing the burn-off rate of the roller kiln.

[0012] In any embodiment, after the first sintering, the pre-fired material at a temperature of 150℃~250℃ is stored in a transfer silo, and then transferred from the transfer silo to the roller kiln for a second sintering. The transfer silo between the rotary kiln and the roller kiln allows the pre-fired material obtained from rotary kiln sintering to be stored in the transfer silo without cooling or after cooling to 150℃~250℃, reducing the rotary kiln cooling water flow rate and the energy consumption of the cooling water pump, thereby reducing production costs.

[0013] In any embodiment, the temperature of the pre-fired material entering the roller kiln is 100℃~200℃. The pre-fired material entering the transfer silo is naturally cooled to 100℃~200℃ before entering the roller kiln for the first sintering. This effectively utilizes the waste heat of the pre-fired material, eliminating the need to raise the temperature of the pre-fired material from room temperature, reducing the energy consumption for raising the pre-fired material to the target temperature, and shortening the overall sintering time, thereby increasing production capacity.

[0014] In any embodiment, the raw material includes a first carbon source. Adding the first carbon source to the raw material enables the first carbon source to be fully carbonized during sintering and to form a uniform and dense carbon coating layer on the surface of the active material.

[0015] In any embodiment, the first carbon source includes an organic carbon source and / or an inorganic carbon source. When the first carbon source includes an organic carbon source and / or an inorganic carbon source, the first carbon source can be fully carbonized during the sintering process and form a uniform and dense carbon coating layer on the surface of the active material.

[0016] In any embodiment, the organic carbon source includes any one or more of glucose, starch, sucrose, fructose, cellulose, citric acid, ascorbic acid, and polyethylene glycol; and / or, the inorganic carbon source includes any one or more of conductive carbon, graphene, conductive carbon fiber, and carbon nanotubes. All of the above carbon sources are capable of being fully carbonized during sintering and forming a uniform, dense carbon coating layer on the surface of the active material.

[0017] In any embodiment, after the first sintering is completed, the pre-sintered material and the second carbon source are mixed for carbon coating, and then the carbon-coated pre-sintered material is placed in a roller kiln for a second sintering. A first carbon source is added to the raw material, which can carbonize during the first sintering process and form a thin carbon coating layer on the surface of the active material. After the first sintering process is completed, a second carbon source is added to the sintered material for carbon coating, which can fully carbonize during the second sintering process and form a uniform and dense carbon coating layer on the surface of the active material.

[0018] In any embodiment, the mass ratio of the first carbon source to the second carbon source is 1:9 to 3:7. By keeping the mass ratio of the first carbon source to the second carbon source within the above range, the first carbon source can be carbonized during the first sintering process and form a thin carbon coating layer on the surface of the active material, while the second carbon source is fully carbonized during the second sintering process and forms a uniform and dense carbon coating layer on the surface of the active material.

[0019] This application provides a sintering method for phosphate-based cathode materials. In this method, a mixture containing a precursor of the phosphate-based cathode material and a first carbon source is first pre-calcined in a rotary kiln, thereby allowing the material to initially crystallize and form crystal nuclei or grains. Then, the obtained pre-calcined material is sintered in a roller kiln, where the crystals further grow to obtain the cathode material. By sequentially sintering the raw material containing the precursor of the phosphate-based cathode material in a rotary kiln for 6-11 hours and in a roller kiln for 15-20 hours, this application can shorten the sintering time of the cathode material, and the capacity of the rotary kiln can be matched with that of the roller kiln, thereby improving the overall capacity of the production line. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the first sintering method according to an embodiment of this application;

[0021] Figure 2 This is a schematic diagram of the second sintering method according to an embodiment of this application;

[0022] Figure 3 This is a scanning electron microscope image of the positive electrode material prepared in Example 1 of this application;

[0023] Figure 4 This is a scanning electron microscope image of the positive electrode material prepared in Example 6 of this application. Detailed Implementation

[0024] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the sintering method for the phosphate-based cathode material of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0025] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0027] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0028] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0029] In the preparation of phosphate-based cathode materials, roller kilns are often used as sintering furnaces. In order to improve the low production capacity of phosphate-based cathode materials, it is necessary to shorten the sintering time of phosphate-based cathode materials. However, if the sintering time of roller kilns is shortened directly, the raw materials containing precursors will not react sufficiently, resulting in low discharge capacity of the batteries made from cathode materials.

[0030] Based on this, this application proposes a sintering method for phosphate-based cathode materials. The following provides a more detailed description of this application and its optional embodiments.

[0031] This application provides a sintering method for phosphate-based cathode materials, comprising: sintering a raw material containing a precursor of the phosphate-based cathode material in a first sintering process to obtain a pre-sintered material, and then sintering the pre-sintered material in a second sintering process to obtain the cathode material. The first sintering includes sintering in a rotary kiln for 6 to 11 hours, and the second sintering includes sintering in a roller kiln for 15 to 20 hours. Both the first and second sintering processes are carried out under an inert atmosphere with an oxygen content ≤200 ppm.

[0032] A rotary kiln is an industrial processing device primarily used for heat treatment of various materials at high temperatures. A rotary kiln can be a long cylindrical container, typically placed horizontally with a certain angle of inclination. The kiln walls are usually lined with refractory material, and the interior is hollow, stably supported by three rollers to ensure smooth operation. Material enters from one end, gradually moves along the axial direction as the kiln rotates, and finally exits from the other end. During this process, the material is uniformly heated and calcined. Rotary kilns are widely used in the production of cement, lime, kaolin, titanium dioxide, iron ore, and other products. Its main characteristics include the combination of continuous operation, gas flow, fuel combustion, heat transfer, and material movement, allowing the heat generated by complete fuel combustion to be effectively transferred to the material, causing a series of physicochemical changes, ultimately forming the finished product.

[0033] In addition, the material in the rotary kiln can be distributed on the inner wall of the kiln with a relatively thin thickness, the material heats up rapidly, and the exhaust can be achieved quickly, thus achieving preliminary crystal formation.

[0034] A roller kiln is a high-temperature processing equipment belonging to the heat treatment industry, mainly used for producing ceramics, building materials, and refractory materials. A roller kiln is a continuous firing furnace, a tunnel kiln that uses rotating rollers as the carrier for the ceramic blanks. In a roller kiln, blanks and finished products are placed on many closely spaced horizontal refractory rollers, and the rotation of the rollers transports the ceramic from the kiln head to the kiln tail. The principle of the roller kiln is based on physicochemical reactions at high temperatures. By controlling parameters such as temperature, atmosphere composition, and flow rate, the performance of the product can be adjusted and controlled. Roller kilns are characterized by high production efficiency, high energy utilization, and stable product quality. Furthermore, roller kilns have a simpler structure than tunnel kilns, lower equipment costs, are easier to operate and maintain, have lower energy consumption, and higher productivity.

[0035] As an example, the first sintering time can be 6h, 7h, 8h, 9h, 10h or 11h.

[0036] Optionally, the first sintering time is 6h to 10.5h.

[0037] As an example, the second sintering time can be 15h, 16h, 17h, 18h, 19h or 20h.

[0038] Optionally, the second sintering time is 15.5h to 18h.

[0039] Optionally, the inert atmosphere includes one or more of nitrogen, helium, argon, and xenon.

[0040] As an example, the inert atmosphere can be nitrogen, helium, argon or xenon, or a mixture of nitrogen and helium, or a mixture of helium and argon, or a mixture of nitrogen and argon, or a mixture of nitrogen, helium and argon.

[0041] In the sintering method of the phosphate-based cathode material of this application, a mixture containing a precursor of the phosphate-based cathode material and a first carbon source is first pre-calcined in a rotary kiln, thereby allowing the material to initially crystallize and form crystal nuclei or grains. The pre-calcined material is then sintered in a roller kiln, where the crystals further grow to obtain the cathode material. This application shortens the sintering time of the cathode material by sequentially sintering the raw material containing the precursor of the phosphate-based cathode material in a rotary kiln for 6-11 hours and in a roller kiln for 15-20 hours. Furthermore, the capacity of the rotary kiln can be matched with that of the roller kiln, thereby increasing the overall production line capacity.

[0042] In some embodiments, the first sintering includes a first holding stage, which includes holding at a temperature of 400°C to 750°C for 3 to 9 hours.

[0043] The first heat preservation stage refers to the stage in which the rotary kiln maintains the target temperature after the temperature inside the kiln reaches the target temperature during the first sintering process.

[0044] As an example, the temperature of the first heat preservation stage can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃ or 750℃; the duration of the first heat preservation stage can be 3h, 4h, 5h, 6h, 7h, 8h or 9h.

[0045] By keeping the holding temperature and holding time of the first holding stage within the above range, the raw material can be initially crystallized in the rotary kiln.

[0046] When the pre-burned material does not require carbon coating, the temperature of the first heat preservation stage is 400℃~700℃, and the time of the first heat preservation stage is 4h~9h.

[0047] When pre-burned material needs to be coated with carbon, the temperature of the first heat preservation stage is 620℃~750℃, and the time of the first heat preservation stage is 3h~8h.

[0048] In some embodiments, the first sintering also includes a first heating stage and a first cooling stage, wherein the first heating stage lasts for 0.5 h to 2 h and the first cooling stage lasts for 0.5 h to 2 h.

[0049] The first heating stage refers to the stage in which the temperature inside the rotary kiln rises from room temperature or another temperature lower than the target temperature to the target temperature during the first sintering process.

[0050] As an example, the duration of the first heating stage can be 0.5h, 1h, 1.5h, or 2h.

[0051] The first cooling stage refers to the stage in which the temperature inside the rotary kiln drops from the target temperature to room temperature or another temperature lower than the target temperature during the first sintering process.

[0052] As an example, the duration of the first cooling phase can be 0.5h, 1h, 1.5h, or 2h.

[0053] By ensuring that the heating time of the first heating stage and the cooling time of the first cooling stage are within the aforementioned range, it is beneficial to control the sintering time of the entire cathode material sintering process, thereby shortening the sintering time of the cathode material and increasing production capacity.

[0054] In some embodiments, the second sintering includes a second holding stage, which involves holding at a temperature of 600°C to 750°C for 6 to 10 hours.

[0055] The second heat preservation stage refers to the stage in which the roller kiln maintains the target temperature after the temperature inside the roller kiln reaches the target temperature during the first sintering process.

[0056] As an example, the temperature of the second heat preservation stage can be 600℃, 620℃, 650℃, 680℃, 700℃, 720℃, or 750℃. The duration of the second heat preservation stage can be 6h, 7h, 8h, 9h, or 10h.

[0057] By keeping the holding temperature and holding time of the first holding stage within the above range, crystals can be grown in the roller kiln to obtain cathode materials.

[0058] The second sintering process also includes a second heating stage and a second cooling stage. The second heating stage lasts for 2 to 6 hours, and the second cooling stage lasts for 4 to 6 hours.

[0059] In some embodiments, the cathode material includes lithium manganese iron phosphate and / or lithium iron phosphate.

[0060] As an example, the cathode material is lithium manganese iron phosphate or lithium iron phosphate, or a combination of lithium manganese iron phosphate and lithium iron phosphate.

[0061] In some embodiments, the precursor of the phosphate-based cathode material includes carbonate and / or oxalate.

[0062] Both carbonates and oxalates decompose during high-temperature sintering, releasing large amounts of gas and causing a decrease in the loss on ignition. The sintering method of this application utilizes the high exhaust efficiency of rotary kilns. The raw materials are first pre-calcined in the rotary kiln, where they react and decompose rapidly, releasing gases such as carbon dioxide and water vapor. Preliminary crystallization forms nuclei or grains, yielding pre-calcined material. This pre-calcined material is then transferred to a roller kiln for sintering, where the crystals further grow, thereby reducing the loss on ignition rate.

[0063] When the cathode material is lithium manganese iron phosphate, the precursor of the phosphate-based cathode material includes a manganese source, an iron source and a lithium source. The manganese source includes manganese oxalate dihydrate and / or manganese carbonate dihydrate, the iron source includes iron oxalate dihydrate and / or iron carbonate dihydrate, and the lithium source includes lithium dihydrogen phosphate.

[0064] When the cathode material is lithium iron phosphate, the precursor of the phosphate-based cathode material includes an iron source and a lithium source. The iron source includes iron oxalate dihydrate and / or iron carbonate dihydrate, and the lithium source includes lithium dihydrogen phosphate.

[0065] In some implementations, please refer to Figure 1 After the first sintering is completed, the pre-fired material at a temperature of 150℃~250℃ is stored in a transfer silo, and then the pre-fired material is transferred from the transfer silo to the roller kiln for the second sintering.

[0066] A transfer silo is a container located between the discharge port of a rotary kiln and the feed port of a roller kiln, used to store pre-fired materials. The transfer silo can be connected to both the discharge port of the rotary kiln and the feed port of the roller kiln via pipelines. This allows the pre-fired material, after sintering, to be directly stored in the transfer silo. When a second sintering is required, the pre-fired material in the transfer silo can be directly fed into the roller kiln for further sintering.

[0067] As an example, the temperature of the pre-burned material stored in the transfer silo can be 200℃, 205℃, 210℃, 225℃, 220℃, 235℃, 23℃, 245℃ or 250℃.

[0068] It should be noted that before storing the pre-burned material in the transfer silo, inert gas should be introduced into the transfer silo. Since the temperature of the pre-burned material stored in the transfer silo is relatively high, introducing inert gas into the transfer silo in advance can effectively prevent the pre-burned material from oxidizing.

[0069] By setting up a transfer silo between the rotary kiln and the roller kiln, the pre-fired material obtained from sintering in the rotary kiln can be stored in the transfer silo without cooling or after cooling to 150℃~250℃. This reduces the cooling water flow rate of the rotary kiln and the energy consumption of the cooling water pump, thereby reducing production costs.

[0070] Furthermore, due to the presence of the transfer hopper, the discharge temperature of the first sintering is higher than that of the first sintering without the transfer hopper, and the time of the first cooling stage is shortened by 0.5 hours, with the first cooling stage lasting from 0.5 hours to 1.5 hours.

[0071] In some implementations, the temperature of the pre-burned material entering the roller kiln is 100°C to 200°C.

[0072] As an example, the temperature of the pre-burned material entering the roller kiln can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or 250℃.

[0073] The pre-fired material entering the transfer silo is naturally cooled to 100℃~200℃ before entering the roller kiln for the first sintering. This effectively utilizes the waste heat of the pre-fired material, eliminating the need to raise the temperature of the pre-fired material from room temperature. This reduces the energy consumption of raising the temperature of the pre-fired material to the target temperature and shortens the overall sintering time, thereby increasing production capacity.

[0074] It should be noted that due to the different production cycles of rotary kilns and roller kilns, pre-fired material from a rotary kiln cannot directly enter the roller kiln for secondary sintering. However, under normal circumstances, pre-fired material only needs to be stored in a transfer silo for ≤6 hours before it can enter the roller kiln for sintering. The transfer silo exchanges heat with the external environment, causing the pre-fired material in the transfer silo to slowly cool down to 100℃~200℃ during storage.

[0075] Optionally, the pre-burned material is stored in a transfer silo for 1 to 2 hours.

[0076] Furthermore, due to the presence of the transfer hopper, the feed temperature for the second sintering is higher than that for the second sintering without the transfer hopper, and the time for the second heating stage is shortened by 1 hour, with the second heating stage lasting from 2 to 5 hours.

[0077] In some implementations, the raw materials include a first carbon source.

[0078] The first carbon source refers to a substance that contains carbon and can be carbonized during sintering to form carbon materials.

[0079] Adding a first carbon source to the raw materials enables the first carbon source to be fully carbonized during the sintering process and form a uniform dense carbon coating layer on the surface of the active material.

[0080] In some implementations, the first carbon source includes an organic carbon source and / or an inorganic carbon source.

[0081] Organic carbon sources refer to organic substances that contain carbon elements and can be carbonized during sintering to form carbon materials.

[0082] Inorganic carbon sources refer to inorganic substances that contain carbon elements and can be carbonized during sintering to form carbon materials.

[0083] When the first carbon source includes organic carbon source and / or inorganic carbon source, the first carbon source can be fully carbonized during sintering and form a uniform dense carbon coating layer on the surface of the active material.

[0084] In some embodiments, the organic carbon source includes any one or more of glucose, starch, sucrose, fructose, cellulose, citric acid, ascorbic acid, and polyethylene glycol; and / or, the inorganic carbon source includes any one or more of conductive carbon, graphene, conductive carbon fiber, and carbon nanotubes.

[0085] As an example, the organic carbon source may be glucose, starch, sucrose, fructose, cellulose, citric acid, ascorbic acid, or polyethylene glycol, or may be a mixture of glucose and sucrose, or a mixture of glucose and fructose, or a mixture of sucrose and fructose, or a mixture of citric acid and ascorbic acid.

[0086] The organic carbon source can be conductive carbon, graphene, conductive carbon fiber or carbon nanotube, or a mixture of conductive carbon and graphene, or a mixture of conductive carbon fiber and carbon nanotube, or a mixture of conductive carbon, graphene and carbon nanotube.

[0087] All of the above carbon sources can be fully carbonized during the sintering process and form a uniform and dense carbon coating layer on the surface of the active material.

[0088] In some implementations, please refer to Figure 2 After the first sintering is completed, the pre-fired material is mixed with the second carbon source for carbon coating, and then the carbon-coated pre-fired material is placed in a roller kiln for the second sintering.

[0089] Carbon coating methods include dry carbon coating and wet carbon coating. This application provides a specific method for dry carbon coating and wet carbon coating, as follows:

[0090] Dry carbon coating: The pre-burned material is added to a high-speed mixer, and a second carbon source is added. The mixture is stirred to obtain the pre-burned material coated with carbon.

[0091] Wet carbon coating: The pre-burned material, the second carbon source and pure water are mixed and stirred to form a suspension. The suspension is then added to a sand mill and ground to form a suspension. The suspension is then dried by a sprayer to obtain the pre-burned material coated with carbon.

[0092] A first carbon source is added to the raw materials. The first carbon source can carbonize during the first sintering process and form a thin carbon coating layer on the surface of the active material. After the first sintering process is completed, a second carbon source is added to the sintered material for carbon coating. The second carbon source can fully carbonize during the second sintering process and form a uniform and dense carbon coating layer on the surface of the active material.

[0093] When the cathode material is lithium manganese iron phosphate, adding a first carbon source for pre-coating during the first sintering process can prevent manganese precipitation.

[0094] In some embodiments, the mass ratio of the first carbon source to the second carbon source is 1:9 to 3:7.

[0095] As an example, the mass ratio of the first carbon source to the second carbon source can be 1:9, 1.5:8.5, 2:8, 2.5:7.5, or 3:7.

[0096] By ensuring that the mass ratio of the first carbon source and the second carbon source is within the above range, the first carbon source can be carbonized during the first sintering process and form a thin carbon coating layer on the surface of the active material, while the second carbon source is fully carbonized during the second sintering process and forms a uniform and dense carbon coating layer on the surface of the active material.

[0097] Optionally, the mass ratio of the first carbon source to the second carbon source is 1.5–2.5:7.5–8.5.

[0098] Optionally, the mass ratio of the first carbon source to the second carbon source is 2:8.

[0099] Example

[0100] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0101] Example 1

[0102] This application includes a sintering method for a phosphate-based cathode material, comprising the following steps:

[0103] S1. Preparation of raw materials

[0104] Manganese oxalate dihydrate, iron oxalate dihydrate, lithium dihydrogen phosphate, and polyvinyl alcohol were added to pure water in a molar ratio of 0.61:0.39:1.05:0.10 and stirred to form a suspension with a solid content of 35%. The suspension was added to a sand mill and ground to form a suspension with a D50 of 0.45 μm. The suspension was dried by a sprayer at a speed of 30,000 rpm to obtain lithium manganese iron phosphate raw material A.

[0105] S2, Preparation of pre-burned material

[0106] Take 15 kg of lithium manganese iron phosphate raw material A and place it in a rotary kiln. Under helium protection, first heat it to 650℃ for 1 hour, then keep it at 650℃ for 4.5 hours, and finally cool it down to below 80℃ for 1 hour to obtain 9.148 kg of pre-burned material.

[0107] S3. Preparation of cathode materials

[0108] 8.5 kg of pre-burned material at 25°C was placed in a roller kiln. Under helium protection, the temperature was first raised to 680°C in 4 hours, then held at 680°C for 8 hours, and finally cooled to below 80°C in 4.8 hours to obtain 8.096 kg of lithium manganese iron phosphate.

[0109] Comparative Example 1

[0110] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0111] S1. Preparation of raw materials

[0112] Lithium manganese iron phosphate raw material A was prepared according to the method in Example 1.

[0113] S2, Preparation of cathode materials

[0114] Take 8.5 kg of lithium manganese iron phosphate raw material A and place it in a roller kiln. Under helium protection, first heat it to 680℃ for 12 hours, then keep it at 680℃ for 12 hours, and finally cool it down to below 80℃ for 9.6 hours to obtain 4.693 kg of lithium manganese iron phosphate.

[0115] Comparative Example 2

[0116] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0117] S1. Preparation of raw materials

[0118] Lithium manganese iron phosphate raw material A was prepared according to the method in Example 1.

[0119] S2, Preparation of cathode materials

[0120] Take 8.5 kg of lithium manganese iron phosphate raw material A and place it in a roller kiln. Under helium protection, first heat it to 680℃ for 5 hours, then keep it at 680℃ for 12.5 hours, and finally cool it down to below 80℃ for 5.8 hours to obtain 4.722 kg of lithium manganese iron phosphate.

[0121] The relevant parameters of the sintering method for the phosphate-based cathode materials in Examples 2-4 are shown in Tables 1-2 below.

[0122] Example 5

[0123] This application includes a sintering method for a phosphate-based cathode material, comprising the following steps:

[0124] S1. Preparation of raw materials

[0125] Manganese carbonate, iron carbonate, lithium dihydrogen phosphate, and polyvinyl alcohol were added to pure water in a molar ratio of 0.61:0.39:1.05:0.10 and stirred to form a suspension with a solid content of 35%. The suspension was then added to a sand mill and ground to form a suspension with a D50 of 0.45 μm. The suspension was dried by a sprayer at a speed of 30,000 rpm to obtain lithium manganese iron phosphate raw material B.

[0126] S2, Preparation of pre-burned material

[0127] 10.575 kg of pre-burned material was prepared according to the method in Example 1.

[0128] S3. Preparation of cathode materials

[0129] 8.132 kg of lithium manganese iron phosphate was prepared according to the method in Example 1.

[0130] Comparative Example 3

[0131] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0132] S1. Preparation of raw materials

[0133] Lithium manganese iron phosphate raw material B was prepared according to the method in Example 5.

[0134] S2, Preparation of cathode materials

[0135] 5.722 kg of lithium manganese iron phosphate was prepared according to the method of Comparative Example 1.

[0136] Comparative Example 4

[0137] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0138] S1. Preparation of raw materials

[0139] Lithium manganese iron phosphate raw material B was prepared according to the method in Example 5.

[0140] S2, Preparation of cathode materials

[0141] 5.733 kg of lithium manganese iron phosphate was prepared according to the method of Comparative Example 2.

[0142] Example 6

[0143] This application includes a sintering method for a phosphate-based cathode material, comprising the following steps:

[0144] S1. Preparation of raw materials

[0145] Manganese oxalate dihydrate, iron oxalate dihydrate, lithium dihydrogen phosphate, and polyvinyl alcohol were added to pure water in a molar ratio of 0.61:0.39:1.05:0.03 and stirred to form a suspension with a solid content of 35%. The suspension was then added to a sand mill and ground to form a suspension with a D50 of 0.45 μm. The suspension was dried by a sprayer at a speed of 30,000 rpm to obtain lithium manganese iron phosphate raw material C.

[0146] S2, Preparation of pre-burned material

[0147] Take 15 kg of lithium manganese iron phosphate raw material C and place it in a rotary kiln. Under helium protection, first heat it to 650℃ for 1 hour, then keep it at 650℃ for 6 hours, and finally cool it down to below 80℃ for 1 hour to obtain 8.736 kg of pre-burned material.

[0148] S3, Carbon Packaging

[0149] Take 8.7 kg of pre-burned material and crush it. Then add 0.783 kg of polyvinyl alcohol to the pre-burned material. The mass of polyvinyl alcohol is 9% of the mass of the pre-burned material. Mix in a high-speed mixer for 40 minutes to complete the carbon coating of the pre-burned material.

[0150] S4. Preparation of cathode materials

[0151] 8.5 kg of carbon-coated pre-calcined material at 25°C was placed in a roller kiln. Under helium protection, the temperature was first raised to 680°C over 4 hours, then held at 680°C for 8 hours, and finally cooled to below 80°C over 4.8 hours to obtain 7.894 kg of lithium manganese iron phosphate.

[0152] Comparative Example 5

[0153] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0154] S1. Preparation of raw materials

[0155] Lithium manganese iron phosphate raw material C was prepared according to the method in Example 6.

[0156] S2, Preparation of pre-burned material

[0157] Take 15 kg of raw manganese iron lithium phosphate C and place it in a roller kiln. Under helium protection, first heat it to 650℃ for 6 hours, then keep it at 650℃ for 10 hours, and finally cool it down to below 80℃ for 6 hours to obtain 8.722 kg of pre-burned material.

[0158] S3, Carbon Packaging

[0159] Take 8.7 kg of pre-burned material and crush it. Then add 0.783 kg of polyvinyl alcohol to the pre-burned material. The mass of polyvinyl alcohol is 9% of the mass of the pre-burned material. Mix in a high-speed mixer for 40 minutes to complete the carbon coating of the pre-burned material.

[0160] S4. Preparation of cathode materials

[0161] 8.5 kg of carbon-coated pre-calcined material at 25°C was placed in a roller kiln. Under helium protection, the temperature was first raised to 680°C over 4 hours, then held at 680°C for 8 hours, and finally cooled to below 80°C over 4.8 hours to obtain 7.908 kg of lithium manganese iron phosphate.

[0162] Comparative Example 6

[0163] This application includes a comparative example of a sintering method for a phosphate-based cathode material, which includes the following steps:

[0164] S1. Preparation of raw materials

[0165] Lithium manganese iron phosphate raw material C was prepared according to the method in Example 6.

[0166] S2, Preparation of pre-burned material

[0167] Take 15 kg of raw manganese iron lithium phosphate C and place it in a roller kiln. Under helium protection, first heat it to 650℃ for 1 hour, then keep it at 650℃ for 6 hours, and finally cool it down to below 80℃ for 1 hour to obtain 8.718 kg of pre-burned material.

[0168] S3, Carbon Packaging

[0169] Take 8.7 kg of pre-burned material and crush it. Then add 0.783 kg of polyvinyl alcohol to the pre-burned material. The mass of polyvinyl alcohol is 9% of the mass of the pre-burned material. Mix in a high-speed mixer for 40 minutes to complete the carbon coating of the pre-burned material.

[0170] S4. Preparation of cathode materials

[0171] 8.5 kg of carbon-coated pre-calcined material at 25°C was placed in a roller kiln. Under helium protection, the temperature was first raised to 680°C over 4 hours, then held at 680°C for 8 hours, and finally cooled to below 80°C over 4.8 hours to obtain 7.911 kg of lithium manganese iron phosphate.

[0172] The relevant parameters of the sintering method of the phosphate-based cathode materials in Examples 7 and 8 are shown in Tables 1 and 2 below.

[0173] Example 9

[0174] This application includes a sintering method for a phosphate-based cathode material, comprising the following steps:

[0175] S1. Preparation of raw materials

[0176] Ferric oxalate dihydrate, lithium dihydrogen phosphate, and polyvinyl alcohol were added to pure water at a molar ratio of 1:1.05:0.10 and stirred to form a suspension with a solid content of 35%. The suspension was added to a sand mill and ground to form a suspension with a D50 of 0.45 μm. The suspension was dried by a sprayer at a speed of 30,000 rpm to obtain lithium iron phosphate raw material D.

[0177] S2, Preparation of pre-burned material

[0178] 15 kg of lithium iron phosphate raw material D was placed in a rotary kiln. Under helium protection, the temperature was first raised to 740°C in 1 hour, then held at 740°C for 4 hours, and finally cooled to below 80°C in 1 hour to obtain 9.156 kg of pre-burned material.

[0179] S3. Preparation of cathode materials

[0180] 8.5 kg of pre-burned material at 25°C was placed in a roller kiln. Under helium protection, the temperature was first raised to 740°C in 4 hours, then held at 740°C for 8 hours, and finally cooled to below 80°C in 4.8 hours to obtain 7.902 kg of lithium iron phosphate.

[0181] The relevant parameters of the sintering methods for the phosphate-based cathode materials of Examples 1-9 and Comparative Examples 1-6 are shown in Tables 1-2 below.

[0182] Table 1. Parameter results of the first sintering of Examples 1-9 and Comparative Examples 1-6.

[0183]

[0184] Table 2 shows the parameter results for the second sintering of Examples 1-9 and Comparative Examples 1-6.

[0185]

[0186]

[0187] In addition, the sintering time and production capacity of the phosphate-based cathode materials in Examples 1-12 and Comparative Examples 1-7 were calculated, and the cathode materials obtained in Examples 1-12 and Comparative Examples 1-7 were prepared into coin cells as shown below for performance testing. The test results are shown in Table 3 below. Figures 3-4 As shown.

[0188] (1) Calculate the total sintering time

[0189] Total sintering time (h) = Total sintering time of rotary kiln (h) + Total sintering time of roller kiln (h).

[0190] (2) Calculate the yield of the roller kiln

[0191] Roller kiln yield (%) = mass of cathode material / mass of pre-burned material or mass of raw material.

[0192] (3) Testing procedures for scanning electron microscopy images of cathode materials

[0193] The microstructure of the materials in Examples 1 and 6 was observed using a scanning electron microscope (SEM, instrument brand: ZEISS Sigma 300).

[0194] (4) Procedure for testing the discharge capacity at 0.1C under constant temperature conditions of 25±2℃.

[0195] 10g of the positive electrode material prepared in each example and comparative example was weighed out to fabricate CR2430 coin cells. The cells were tested using a Lamborghini BT2018AS tester. The testing method is as follows:

[0196] S1. Let stand for 180 minutes;

[0197] S2, 0.1C constant current charging to 4.30V;

[0198] S3, 4.30V constant voltage charging until the current is less than 0.05C;

[0199] S4. Let stand for 5 minutes;

[0200] S5, 0.1C constant current discharge to 2.00V;

[0201] S6. Let stand for 5 minutes.

[0202] CR2430 button cell is produced by the following method:

[0203] Positive electrode sheet:

[0204] The positive electrode material, conductive carbon black and PVDF are mixed in a mass ratio of 90:5:5 and then N-methylpyrrolidone solvent is added. The mixture is coated on one side of aluminum foil, and after cold pressing and cutting, a positive electrode sheet is obtained. The positive electrode is then punched into a positive electrode film of a specified diameter.

[0205] Negative electrode plate:

[0206] The negative electrode is a lithium sheet of a specified diameter;

[0207] Separating membrane:

[0208] A polyethylene film with a thickness of 13 μm was used as the separator.

[0209] Electrolyte:

[0210] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0211] Assembly:

[0212] Assembly is carried out in a glove box filled with dry nitrogen, where the moisture and oxygen content is less than 0.1 ppm. Qualified small round plates are placed on the positive electrode side of the coin cell casing, which has a gasket placed in place beforehand, with the coated side facing away from the positive electrode. Then, 1-2 drops of electrolyte are added to the positive electrode plate, followed by the separator and 1-2 drops of electrolyte. Next, the pure lithium sheet, gasket, and spring are placed, and finally, the negative electrode side of the coin cell casing is placed on top. After assembly, the casing is sealed using a sealing machine.

[0213] Table 3 Performance test results of Examples 1-9 and Comparative Examples 1-6

[0214]

[0215]

[0216] As can be seen from Examples 1 to 8, lithium manganese iron phosphate was prepared by a combination of rotary kiln and roller kiln sintering in Examples 1 to 8, with a total sintering time of 21.8h to 27.5h; the roller kiln yield of Examples 1 to 8 was 92.84% to 95.67%; and the 0.1C discharge capacity of the batteries prepared from lithium manganese iron phosphate in Examples 1 to 8 was 143.7mAh / g to 146.4mAh / g.

[0217] Comparing Examples 1 and 6, it can be seen that Example 1 has no intermediate material hopper, the discharge temperature after the first sintering needs to be ≤80℃, and the feed temperature for the second sintering is 25℃. In contrast, Example 6 has an intermediate material hopper, the discharge temperature after the first sintering is 200℃, and the feed temperature for the second sintering is 150℃. The cooling time for the first sintering in Example 6 is 0.5h shorter than that in Example 1, the heating time for the second sintering in Example 6 is 1h shorter than that in Example 1, and the total sintering time in Example 6 is 1.5h shorter than that in Example 1, thus increasing production capacity.

[0218] Comparing Example 1 and Comparative Example 1, it can be seen that Example 1 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 1 uses a one-step sintering method with a roller kiln and a longer sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 1 is 23.3 h, which is shorter than the sintering time of Comparative Example 1 (33.6 h), thus improving the production capacity. The roller kiln yield of Example 1 is 95.25%, which is higher than the roller kiln yield of Comparative Example 1 (55.21%). The 0.1C discharge capacity of the battery made from lithium manganese iron phosphate in Example 1 is 144.6 mAh / g, which is similar to the 0.1C discharge capacity of the battery made from lithium manganese iron phosphate in Comparative Example 1. This indicates that the phosphate-based cathode material prepared according to the sintering method of this application will not affect the electrical performance of the battery product.

[0219] Comparing Example 1 and Comparative Example 2, it can be seen that Example 1 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 2 uses a one-step sintering method with a roller kiln and a shorter sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 1 and Comparative Example 2 is the same, but the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Comparative Example 2 is only 135.8 mAh / g, which is lower than the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Example 1. This indicates that the specific capacity of lithium manganese iron phosphate produced by the one-step sintering method with a roller kiln and a shorter sintering time is low and does not meet production requirements.

[0220] Comparing Example 5 and Comparative Example 3, it can be seen that Example 5 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 3 uses a one-step sintering method with a roller kiln and a longer sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 5 is 23.3 h, which is shorter than the sintering time of Comparative Example 3 (33.6 h), thus improving the production capacity. The roller kiln yield of Example 5 is 95.67%, which is higher than the roller kiln yield of Comparative Example 3 (67.32%). The 0.1C discharge capacity of the battery made from lithium manganese iron phosphate in Example 5 is 145.2 mAh / g, which is similar to the 0.1C discharge capacity of the battery made from lithium manganese iron phosphate in Comparative Example 3. This indicates that the phosphate-based cathode material prepared according to the sintering method of this application will not affect the electrical performance of the battery product.

[0221] Comparing Example 5 and Comparative Example 4, it can be seen that Example 5 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 4 uses a one-step sintering method with a roller kiln and a shorter sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 5 is the same as that of Comparative Example 4, but the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Comparative Example 4 is only 136.2 mAh / g, which is lower than the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Example 5. This indicates that the specific capacity of lithium manganese iron phosphate produced by the one-step sintering method with a roller kiln and a shorter sintering time is low and does not meet production requirements.

[0222] A comparison of Example 6 and Comparative Example 6 shows that Example 6 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 6 uses a one-step sintering method with a roller kiln and a longer sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 6 is 24.8 h, which is shorter than the sintering time of Comparative Example 6 (38.8 h), thus improving the production capacity. The roller kiln yield of Example 6 is 92.87%, which is higher than the roller kiln yield of Comparative Example 6 (52.72%). The 0.1C discharge capacity of the battery made from lithium manganese iron phosphate in Example 6 is 146.1 mAh / g, which is similar to that of the battery made from lithium manganese iron phosphate in Comparative Example 6. This indicates that the phosphate-based cathode material prepared according to the sintering method of this application does not affect the electrical performance of the battery product.

[0223] A comparison of Example 6 and Comparative Example 7 shows that Example 6 uses a combination of rotary kiln and roller kiln to produce lithium manganese iron phosphate, while Comparative Example 7 uses a one-step sintering method with a roller kiln and a shorter sintering time to produce lithium manganese iron phosphate. The total sintering time of Example 6 is the same as that of Comparative Example 7, but the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Comparative Example 7 is only 135.6 mAh / g, which is lower than the 0.1C discharge capacity of the battery produced by the lithium manganese iron phosphate in Example 7. This indicates that the specific capacity of lithium manganese iron phosphate produced by the one-step sintering method with a roller kiln and a shorter sintering time is low and does not meet production requirements.

[0224] As can be seen from Example 9, lithium iron phosphate was prepared by a combination of rotary kiln and roller kiln sintering, with a total sintering time of 22.8h; the roller kiln yield of Example 9 was 92.96%; and the 0.1C discharge capacity of the battery prepared from the lithium iron phosphate of Example 9 was 157.9mAh / g.

[0225] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sintering method for a phosphate-based cathode material, characterized in that, The sintering method of the phosphate-based cathode material includes: sintering a raw material containing a precursor of the phosphate-based cathode material in a first sintering to obtain a pre-sintered material, and then sintering the pre-sintered material in a second sintering to obtain the cathode material; The first sintering includes sintering in a rotary kiln for 6 to 11 hours, and the second sintering includes sintering in a roller kiln for 15 to 20 hours. Both the first and second sintering are performed under an inert atmosphere, wherein the oxygen content in the inert atmosphere is ≤200ppm.

2. The sintering method for the phosphate-based cathode material according to claim 1, characterized in that, The first sintering includes a first heat preservation stage, which includes heat preservation at a temperature of 400℃ to 750℃ for 3h to 9h.

3. The sintering method for the phosphate-based cathode material according to claim 2, characterized in that, The first sintering also includes a first heating stage and a first cooling stage, the first heating stage lasting 0.5h to 2h and the first cooling stage lasting 0.5h to 2h.

4. The sintering method for the phosphate-based cathode material according to any one of claims 1 to 3, characterized in that, The second sintering includes a second heat preservation stage, which involves holding at a temperature of 600℃ to 750℃ for 6 hours to 10 hours.

5. The sintering method for the phosphate-based cathode material according to any one of claims 1 to 4, characterized in that, The cathode material includes lithium manganese iron phosphate and / or lithium iron phosphate.

6. The sintering method for the phosphate-based cathode material according to any one of claims 1 to 5, characterized in that, The precursors of the phosphate-based cathode material include carbonates and / or oxalates.

7. The sintering method for the phosphate-based cathode material according to any one of claims 1 to 6, characterized in that, After the first sintering is completed, the pre-fired material at a temperature of 150℃~250℃ is first stored in a transfer silo, and then the pre-fired material is transferred from the transfer silo to the roller kiln for the second sintering.

8. The sintering method for the phosphate-based cathode material according to claim 7, characterized in that, The temperature of the pre-fired material entering the roller kiln is 100℃~200℃.

9. The sintering method for the phosphate-based cathode material according to any one of claims 1 to 8, characterized in that, The raw materials include a first carbon source.

10. The sintering method for the phosphate-based cathode material according to claim 9, characterized in that, The first carbon source includes organic carbon sources and / or inorganic carbon sources.

11. The sintering method for the phosphate-based cathode material according to claim 10, characterized in that, The organic carbon source includes any one or more of glucose, starch, sucrose, fructose, cellulose, citric acid, ascorbic acid, and polyethylene glycol; and / or, The inorganic carbon source includes any one or more of conductive carbon, graphene, conductive carbon fiber, and carbon nanotubes.

12. The sintering method for the phosphate-based cathode material according to claim 9 or 10, characterized in that, After the first sintering is completed, the pre-fired material and the second carbon source are mixed and coated with carbon, and then the pre-fired material with carbon coating is placed in the roller kiln for the second sintering.

13. The sintering method for the phosphate-based cathode material according to claim 12, characterized in that, The mass ratio of the first carbon source to the second carbon source is 1:9 to 3:7.

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