Method for producing carbon-coated lithium iron phosphate material

Abstract

To provide a method for producing a carbon-coated lithium iron phosphate material in which a slurry temperature is controlled in order to ensure a carbon content of the carbon-coated lithium iron phosphate material and to improve the stability of product quality at the same time.SOLUTION: A method for producing a carbon-coated lithium iron phosphate material includes the following steps. Step (a): a first slurry, a carbon source and a lithium source are provided, and the first slurry is formed of an iron source and a phosphorus source. Step (b): the first slurry, the carbon source, and the lithium source are mixed to form a second slurry, and the second slurry is ground in a barrel at a first temperature to form a third slurry, and the first temperature is 25°C to 40°C. Step (c): the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material, the carbon-coated lithium iron phosphate material comprising a core layer and a coating layer, the coating layer coating the core layer, the core layer comprising the lithium source, the iron source, and the phosphorus source, and the coating layer comprising the carbon source.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a cathode material, and more particularly to a method for manufacturing a carbon-coated lithium iron phosphate material.

Background Art

[0002] Lithium-ion batteries are widely used in the field of energy storage due to their good cycle charge and discharge characteristics and high energy density. Among them, lithium-ion batteries using lithium iron phosphate (LiFePO 4 ) as the cathode material are attracting attention as batteries with potential for development, characterized by low material cost and high safety. However, due to the olivine structure of lithium iron phosphate, the diffusivity of lithium ions and the electron conductivity are low, restricting the application of lithium iron phosphate.

[0003] Considering the above drawbacks, most of the current industry carbon-coats (coats) lithium iron phosphate to improve performance. In the conventional carbon coating process, since the lithium-containing slurry is alkaline and the temperature rises during the grinding process, the carbon source is easily oxidized and decomposed in this alkaline and high-temperature environment, and finally the carbon content of the formed carbon-coated lithium iron phosphate material decreases. Also, the solubility of the lithium salt in the slurry changes due to the temperature difference during grinding, thereby reducing the quality stability of the manufactured carbon-coated lithium iron phosphate material. Therefore, the carbon-coated lithium iron phosphate materials manufactured by the conventional carbon coating process often have insufficient carbon content and unstable quality.

[0004] In view of such circumstances, the present invention provides a method for manufacturing a carbon-coated lithium iron phosphate material that controls the slurry temperature in order to ensure the carbon content of the carbon-coated lithium iron phosphate material and at the same time improve the stability of product quality.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present invention is to provide a method for manufacturing a carbon-coated lithium iron phosphate material that controls the slurry temperature in order to ensure the carbon content of the carbon-coated lithium iron phosphate material and at the same time improve the stability of product quality. First, a first slurry formed of a carbon source (material), a lithium source (material), an iron source (material), and a phosphorus source (material) is provided. Next, the first slurry, the carbon source (material), and the lithium source (material) are mixed to form a second slurry, and the second slurry is pulverized in a barrel at 25°C to 40°C to form a third slurry. Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. By controlling the slurry temperature within a specific temperature range, it is possible to ensure the uniformity (consistency) of the solubility of the lithium source in the slurry, and at the same time prevent the carbon source in the slurry from being oxidized and decomposed in a high-temperature environment, ensure the carbon content of the carbon-coated lithium iron phosphate material, and improve the stability of the product quality. Furthermore, the slurry temperature is controlled, for example, by liquid cooling through a cooling water jacket. The cooling water jacket is arranged so as to surround the internal space of the barrel that houses the slurry, and can smoothly and uniformly control the rise and fall of the temperature, thereby further improving the stability of the product quality.

[0006] In order to achieve the above object, the present invention provides a method for manufacturing a carbon-coated lithium iron phosphate material. The method for manufacturing a carbon-coated lithium iron phosphate material includes step (a) of providing a first slurry, a carbon source, and a lithium source, where the first slurry is formed of an iron source and a phosphorus source; step (b) of mixing the first slurry, the carbon source, and the lithium source to form a second slurry, and pulverizing the second slurry in a barrel at a first temperature to form a third slurry, where the first temperature is 25°C to 40°C; and step (c) of drying and sintering the third slurry to form a carbon-coated lithium iron phosphate material, where the carbon-coated lithium iron phosphate material includes a core layer and a coating layer, the coating layer coats the core layer, the core layer is formed of a lithium source, an iron source, and a phosphorus source, and the coating layer is formed of a carbon source.

[0007] In an embodiment, the first temperature is maintained by a liquid cooling method.

[0008] In one embodiment, the barrel includes a first space and a cooling water jacket. The first space is configured to accommodate a second slurry and a third slurry. The cooling water jacket is provided to surround the first space, and the liquid cooling method is performed through the cooling water jacket.

[0009] In one embodiment, the cooling water jacket includes at least two flow paths and a second space. The second space is communicated between the at least two flow paths and surrounds the first space. The at least two flow paths are provided such that a liquid flows into and out of the second space.

[0010] In one embodiment, the carbon source, the lithium source, and the first slurry are pulverized by a ball milling method.

[0011] In one embodiment, the second slurry and the third slurry are alkaline.

[0012] In one embodiment, the iron source is iron powder, the phosphorus source is an aqueous phosphoric acid solution, and the first slurry is formed by reacting iron powder with the aqueous phosphoric acid solution.

[0013] In one embodiment, the third slurry is dried by a spray drying method.

[0014] In one embodiment, the third slurry is sintered at a sintering temperature, and the sintering temperature is 550°C to 750°C.

[0015] In one embodiment, the third slurry is sintered in a non-oxidizing atmosphere.

[0016] In one embodiment, the carbon content ratio of the carbon-coated lithium iron phosphate material is 1.0% to 1.6%.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2A

Figure 2B

Embodiments for Carrying Out the Invention

[0018] Some exemplary embodiments showing the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can be modified in various ways without departing from the scope of the present invention, and the description and drawings are essentially for illustrative purposes and are not intended to limit the present invention. Although the broad numerical ranges and parameters of the present invention are all approximate values, specific values are described as accurately as possible in specific cases. Terms such as "first", "second", "third", etc. can be used to describe different components in the claims, but these components should not be limited by these terms, and it should be understood that these components described in the embodiments are indicated by different component symbols. These terms are for distinguishing different components. For example, the first component can be referred to as the second component, and similarly, the second component can also be referred to as the first component without departing from the scope of the embodiments. Also, the term "and / or" in the specification means any one or a combination of one or more related features. Also, the term "about" refers to an average value within the standard error range generally accepted by those skilled in the art. Unless clearly defined in the embodiments regarding operations / acts, all numerical ranges, amounts, numerical values, percentages, etc. (such as angles, durations, temperatures, operating conditions, ratios, and corresponding percentages, etc.) described in this specification should be understood as the term "about" or "substantially" in all embodiments. Unless otherwise stated in the content, the numerical values of the present invention and the claims can be taken as approximate values that can change as needed. For example, each parameter can be interpreted by applying the normal rounding principle in light of at least the significant digits described. Also, the numerical ranges in this specification can be expressed as from one endpoint to the other endpoint or as the range between two endpoints. It should be noted that all ranges described in this specification include the endpoints unless otherwise specifically defined.

[0019] Please refer to FIGS. 1 to 2B. FIG. 1 is a flowchart of a method for manufacturing a carbon-coated lithium iron phosphate material according to an embodiment of the present invention. FIG. 2A is a conceptual diagram of the three-dimensional structure of a barrel according to an embodiment of the present invention. FIG. 2B is a cross-sectional view taken along line A-A' of FIG. 2A. In this embodiment, the method for manufacturing a carbon-coated lithium iron phosphate material includes the following steps. First, as shown in step S1, a first slurry, a carbon source, and a lithium source are provided (prepared). The first slurry is formed of an iron source and a phosphorus source. In this embodiment, the iron source is, for example, iron powder, and the phosphorus source is, for example, phosphoric acid (H 3 PO 4 ), and the first slurry is formed, for example, by reacting iron powder with an aqueous phosphoric acid solution. To form a more stable first slurry, the reaction time is, for example, 17 hours to 24 hours. The carbon source includes, for example, water-soluble saccharides such as glucose, fructose, galactose, sucrose, maltose, or lactose, but the present invention is not limited thereto. The lithium source includes, for example, lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ), lithium nitrate (LiNO 3 ) or lithium salts such as lithium chloride (LiCl), but the present invention is not limited thereto. Note that the lithium source may be, for example, a combination of a plurality of different lithium salts, and the present invention is not limited thereto.

[0020] Next, as shown in step S2, the first slurry, the carbon source, and the lithium source are mixed to form a second slurry, and the second slurry in the barrel 1 is pulverized at the first temperature to form a third slurry. Here, the first temperature is 25°C to 40°C, preferably 27°C to 35°C. In the present embodiment, the carbon source, the lithium source, and the first slurry are mixed and reacted at, for example, the second temperature to form the second slurry. The second temperature is, for example, 50°C or lower, preferably 30°C to 50°C. The second slurry is pulverized for 9 to 12 hours using, for example, the ball mill method to form the third slurry. The median particle size (D50) of the third slurry is, for example, 1.0 μm. The second slurry and the third slurry are alkaline. Note that the pulverization conditions of the present invention and the median particle size (D50) of the third slurry are not limited to this and can be adjusted according to actual requirements.

[0021] In this embodiment, the barrel 1 includes a first space 10 and a cooling water jacket 20. The first space 10 is provided for accommodating a second slurry and a third slurry. The cooling water jacket 20 is provided so as to surround the first space 10. The first temperature can be maintained by a liquid cooling method using the cooling water jacket 20. The cooling water jacket 20 includes a second space 21, a first flow path 22, and a second flow path 23. The second space 21 is connected between the first flow path 22 and the second flow path 23 and surrounds the first space 10. In this embodiment, the second space 21 is, for example, a spiral flow path that is concentric with the first space 10 and surrounds the first space 10 in an annular shape. The first flow path 22 and the second flow path 23 are configured such that a liquid can flow into and out of the second space 21. In this embodiment, the liquid flows into the second space 21 along the first flow path 22, the heat of the second slurry is transferred from the first space 10 to the second space 21, and is absorbed by the liquid in the second space 21. The liquid that has absorbed the heat flows out along the second flow path 23. The temperature of the second slurry in the barrel 1 is maintained through the liquid flow in the cooling water jacket 20 of the barrel 1. Further, the second space 21 through which the liquid flows is installed so as to surround the first space 10 that accommodates the slurry, and can control the rise and fall of the temperature smoothly and uniformly, ensure the uniformity (consistency) of the solubility of the lithium source in the slurry, and at the same time, prevent the oxidative decomposition of the carbon source in the slurry in a high-temperature environment. In this embodiment, the first flow path 22 and the second flow path 23 are arranged, for example, at the upper and lower parts of the barrel 1 along the vertical direction (Z-axis direction). In another embodiment, the first flow path 22 is configured such that a liquid flows into the second space 21, the second flow path 23 is configured such that a liquid flows out of the second space 21, and the first flow path 22 and the second flow path 23 are arranged, for example, both at the upper part of the barrel 1. In another embodiment, the first flow path 22 is configured such that a liquid flows into the second space 21, the second flow path 23 is configured such that a liquid flows out of the second space 21, and the first flow path 22 and the second flow path 23 are arranged, for example, both at the lower part of the barrel 1.In another embodiment, the first flow path 22 is configured such that liquid flows into the second space 21, and the second flow path 23 is configured such that liquid flows out of the second space 21. The two first flow paths 22 are respectively arranged in the upper and lower parts of the barrel (the upper and lower spaces of the barrel) along the vertical direction (Z-axis direction), and the two second flow paths 23 are also arranged in the upper and lower parts of the barrel (the upper and lower spaces of the barrel) along the vertical direction (Z-axis direction), but the details thereof are omitted. In the present invention, the number and configuration of the flow paths for the inflow and outflow of liquid into and out of the second space 21 are not limited, and the details thereof are omitted. In this embodiment, the barrel 1 includes, for example, a supply port 30, a discharge port 40, and a lid member 50, and the supply port 30 and the discharge port 40 communicate with the first space 10 respectively. The pulverization assembly (not shown) is connected to, for example, the supply port 30 and the discharge port 40 in order to communicate with the first space 10. During the mixing and pulverization process, the second slurry is discharged from the first space 10 through, for example, the discharge port 40, supplied to the pulverization assembly, pulverized in the pulverization step, and then discharged from the pulverization assembly through the supply port 30 and supplied to the first space 10 for mixing and cooling. Thereby, the slurry can be continuously cooled during the mixing and pulverization process, the temperature is smoothly and uniformly controlled, and the stability of the product quality is improved. The lid member 50 is arranged, for example, above the first space 10, and can prevent the mixing of impurities and foreign matters into the slurry during the process by shielding the first space 10 from the vertical direction (Z-axis direction). In this embodiment, the lid member 50 further includes, for example, a through hole 51, and the through hole 51 is used for introducing a solid lithium salt into the first space 10. The through hole 51 may be provided in plurality, such as for introducing lithium salt into the first space 10 or inserting a thermometer into the first space 10 to measure the temperature of the internal slurry, and the diameter may also vary. The present invention is not limited thereto. Note that, for example, the carbon source, the lithium source, and the first slurry may be mixed and reacted in the barrel 1 to form the second slurry so that the second temperature is controlled to be 50°C or less.

[0022] Finally, as shown in step S3, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material includes a core layer and a coating layer. The coating layer coats the core layer. The core layer is composed of a lithium source, an iron source, and a phosphorus source, and the coating layer is composed of a carbon source. In this embodiment, the product of the previous step is dried, for example, by a spray drying method, and sintered, for example, in a non-oxidizing atmosphere at a temperature of 550°C to 750°C for 7 hours to 15 hours. The carbon content ratio of the carbon-coated lithium iron phosphate material is, for example, 1.0% to 1.6%. Note that the drying method, sintering conditions, and carbon content ratio of the carbon-coated lithium iron phosphate material of the present invention are not limited to this and can be adjusted according to actual needs.

[0023] Hereinafter, the manufacturing process and effects of the carbon-coated lithium iron phosphate material of the present invention will be described in detail using examples.

[0024] First Example: Provide a first slurry, a carbon source, and a lithium source. The first slurry is formed by reacting 5585 g of iron powder, 11529 g of 85% phosphoric acid aqueous solution, and 40 L of deionized water in a barrel for 20 hours. In this embodiment, the target weight of the carbon-coated lithium iron phosphate material is 1578 g, the target carbon content ratio (target carbon weight content ratio) is 1.30%, and the carbon weight in the carbon-coated lithium iron phosphate material is 50% of the carbon weight in the third slurry (that is, 50% of the carbon weight is lost in the sintering process). Therefore, it is necessary to add 41.0 g of carbon. Since the carbon source in this embodiment is glucose and the mass ratio of carbon atoms in the molecule is 40%, it is necessary to provide 102.5 g of glucose to satisfy the carbon weight of 41.0 g. The lithium source is 1197 g of lithium hydroxide (LiOH) and 1847 g of lithium carbonate (Li 2 CO 3 )). 5585 g of iron powder contains 100 moles of iron, 11529 g of 85% phosphoric acid aqueous solution contains 100 moles of phosphorus, and 1197 g of lithium hydroxide and 1847 g of lithium carbonate contain a total of 100 moles of lithium. Thus, 100 moles of lithium iron phosphate (LiFePO 4) can be generated.

[0025] Next, 102.5 g of glucose, 1197 g of lithium hydroxide, and 1847 g of lithium carbonate are added to the stirring first slurry and reacted to form a second slurry. The second slurry is pulverized by a ball mill method to form a third slurry. During pulverization, the temperature of the second slurry is maintained at 25 °C by a liquid cooling method using the cooling water jacket of the barrel. The median particle size of the third slurry is 1.0 μm.

[0026] Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. It is dried by a spray drying method, and sintered at a temperature of 550 °C to 750 °C for 10 hours in a nitrogen atmosphere to form a carbon-coated lithium iron phosphate material. When the carbon-coated lithium iron phosphate of the first example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 9.60 cm 2 / g. When the carbon-coated lithium iron phosphate of the first example was analyzed by an elemental analyzer, it was found that the carbon content ratio was 1.15%.

[0027] First Comparative Example: The first comparative example is generally the same as the manufacturing process of the first example, but during mixing and pulverization, the temperature of the second slurry of the first comparative example is maintained at 45 °C. When the carbon-coated lithium iron phosphate of the first comparative example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 8.58 cm 2 / g. When the carbon-coated lithium iron phosphate of the first comparative example was analyzed by an elemental analyzer, it was found that the carbon content ratio was 1.02%.

[0028] Please refer to Table 1. Table 1 shows the slurry temperatures (°C) of the first example and the first comparative example and the specific surface areas (cm 2 / g) and the carbon content (carbon weight percentage, %). When compared with the target carbon content ratio of 1.30%, the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the first example is 11.5%, and it was found that the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the first comparative example is 21.5%. Thus, the degree of carbon loss in the first example where the slurry temperature is 25°C is smaller than that in the first comparative example where the slurry temperature is 45°C, and it can be seen that the specific surface area of the carbon-coated lithium iron phosphate in the first example is larger than that in the first comparative example. In other words, by controlling the slurry temperature to 25°C to 40°C in a liquid cooling manner using a cooling water jacket, the uniformity (consistency) of the solubility of the lithium source in the slurry can be ensured. At the same time, the oxidative decomposition of the carbon source in the slurry in a high-temperature environment can be prevented, the carbon content of the carbon-coated lithium iron phosphate material can be ensured, and the stability of the product quality can be improved. JPEG0007690556000001.jpg34164

[0029] Second Example: Provide a first slurry, a carbon source, and a lithium source. The first slurry was formed by reacting 5585 g of iron powder, 11529 g of 85% phosphoric acid aqueous solution, and 40 L of deionized water in a barrel for 20 hours. In this example, the target weight of the carbon-coated lithium iron phosphate material is 1578 g, the target carbon content ratio (target carbon weight percentage) is 1.40%, and since the carbon weight in the carbon-coated lithium iron phosphate material is 50% of the carbon weight in the third slurry (i.e., 50% of the carbon weight is lost during the sintering process), it is necessary to add 44.2 g of carbon. Also, the carbon source in this example is glucose, and the mass ratio of carbon atoms in the molecule is 40%. To satisfy 44.2 g of carbon weight, it is necessary to provide 110.5 g of glucose. The lithium source is 1197 g of lithium hydroxide (LiOH) and 1847 g of lithium carbonate (Li 2 CO 3) That is. 5585 g of iron powder contains 100 moles of iron, 11529 g of 85% phosphoric acid aqueous solution contains 100 moles of phosphorus, and 1197 g of lithium hydroxide and 1847 g of lithium carbonate contain a total of 100 moles of lithium. As a result, 100 moles of lithium iron phosphate (LiFePO 4 ) can be produced.

[0030] Next, 110.5 g of glucose, 1197 g of lithium hydroxide and 1847 g of lithium carbonate are added to the stirring first slurry and reacted to form a second slurry. The second slurry is pulverized by a ball mill method to form a third slurry. During the pulverization, the temperature of the second slurry was maintained at 27 °C by a liquid cooling method using the cooling water jacket of the barrel. The median particle size of the third slurry is 1.0 μm.

[0031] Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. It was dried by a spray drying method and sintered at a temperature of 550 °C to 750 °C for 10 hours under a nitrogen atmosphere to form a carbon-coated lithium iron phosphate material. When the carbon-coated lithium iron phosphate of the second example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 9.40 cm 2 / g. When the carbon-coated lithium iron phosphate of the second example was analyzed by an elemental analyzer, it was found that the carbon content ratio (carbon weight content ratio) was 1.25%.

[0032] Second Comparative Example: The second comparative example is generally the same as the manufacturing process of the second example. However, during mixing and pulverization, the temperature of the second slurry of the second comparative example was maintained at 45 °C. When the carbon-coated lithium iron phosphate of the second comparative example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 9.04 cm 2 / g. When the carbon-coated lithium iron phosphate of the second comparative example was analyzed by an elemental analyzer, it was found that the carbon content ratio (carbon weight content ratio) was 1.11%.

[0033] Please refer to Table 2. Table 2 shows the slurry temperatures (°C) of the second example and the second comparative example, as well as the specific surface areas (cm 2 / g) and carbon contents (carbon weight content, %) of the formed carbon-coated lithium iron phosphate. When compared with the target carbon content ratio (target carbon weight content) of 1.40%, the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the second example is 10.7%, and the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the second comparative example is 20.7%. Thus, the degree of carbon loss in the second example with a slurry temperature of 27°C is smaller than that in the second comparative example with a slurry temperature of 45°C, and the specific surface area of the carbon-coated lithium iron phosphate in the second example is larger than that in the second comparative example. Also, the degree of carbon loss in the second example with a slurry temperature of 27°C is smaller than that in the first example with a slurry temperature of 25°C. In other words, by controlling the slurry temperature to 27°C - 40°C in a liquid cooling manner using a cooling water jacket, the uniformity (consistency) of the solubility of the lithium source in the slurry can be ensured. At the same time, the oxidative decomposition of the carbon source in the slurry in a high-temperature environment can be prevented, the carbon content of the carbon-coated lithium iron phosphate material can be ensured, and the stability of the product quality can be improved. JPEG0007690556000002.jpg35164

[0034] Third Example: Provide a first slurry, a carbon source, and a lithium source. The first slurry was formed by reacting 5585 g of iron powder, 11529 g of 85% phosphoric acid aqueous solution, and 40 L of deionized water in a barrel for 20 hours. In this example, the target weight of the carbon-coated lithium iron phosphate material is 1578 g, the target carbon content ratio (target carbon weight content) is 1.40%, and since the carbon weight in the carbon-coated lithium iron phosphate material is 50% of the carbon weight in the third slurry (i.e., 50% of the carbon weight is lost during the sintering process), it is necessary to add 44.2 g of carbon. Also, the carbon source in this example is glucose, and the mass ratio of carbon atoms in the molecule is 40%. To satisfy a carbon weight of 44.2 g, it is necessary to provide 110.5 g of glucose. The lithium source is 1197 g of lithium hydroxide (LiOH) and 1847 g of lithium carbonate (Li2 CO 3 ) is as follows. 5585 g of iron powder contains 100 moles of iron, 11529 g of 85% phosphoric acid aqueous solution contains 100 moles of phosphorus, and 1197 g of lithium hydroxide and 1847 g of lithium carbonate contain a total of 100 moles of lithium. As a result, 100 moles of lithium iron phosphate (LiFePO 4 ) can be produced.

[0035] Next, 110.5 g of glucose, 1197 g of lithium hydroxide, and 1847 g of lithium carbonate were added to the stirring first slurry and reacted to form a second slurry. The second slurry was pulverized by a ball mill method to form a third slurry. During the pulverization, the temperature of the second slurry was maintained at 25 °C by a liquid cooling method using the cooling water jacket of the barrel. The median particle size of the third slurry is 1.0 μm.

[0036] Finally, the third slurry was dried and sintered to form a carbon-coated lithium iron phosphate material. It was dried by a spray drying method and sintered at a temperature of 550 °C to 750 °C for 10 hours in a nitrogen atmosphere to form a carbon-coated lithium iron phosphate material. When the carbon-coated lithium iron phosphate of the third example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 9.82 cm 2 / g. When the carbon-coated lithium iron phosphate of the third example was analyzed by an elemental analyzer, it was found that the carbon content ratio was 1.24%.

[0037] Example 4: Example 4 is generally the same as the manufacturing process of Example 3, but during mixing and pulverization, the temperature of the second slurry of Example 4 was maintained at 35 °C. When the carbon-coated lithium iron phosphate of Example 4 was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 10.08 cm 2 / g. When the carbon-coated lithium iron phosphate of Example 4 was analyzed by an elemental analyzer, it was found that the carbon content ratio (carbon weight content ratio) was 1.28%.

[0038] Please refer to Table III. Table III shows the slurry temperatures (°C) of the third and fourth embodiments, as well as the specific surface area (cm 2 / g) and carbon content (carbon weight content, %) of the formed carbon-coated lithium iron phosphate. Compared with the target carbon content ratio (target carbon weight content) of 1.40%, the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the third embodiment is 11.4%, and the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the fourth embodiment is 8.6%. Thus, the degree of carbon loss in the fourth embodiment with a slurry temperature of 35°C is smaller than that in the third embodiment with a slurry temperature of 25°C, and the specific surface area of the carbon-coated lithium iron phosphate in the fourth embodiment is larger than that in the third embodiment. In other words, by controlling the slurry temperature to 27°C - 35°C in a liquid cooling manner with a cooling water jacket, the uniformity (consistency) of the solubility of the lithium source in the slurry is ensured. At the same time, the oxidative decomposition of the carbon source in the slurry in a high-temperature environment is prevented, the carbon content of the carbon-coated lithium iron phosphate material is ensured, and the stability of the product quality can be improved. JPEG0007690556000003.jpg35164

[0039] Fifth Embodiment: Provide a first slurry, a carbon source, and a lithium source. The first slurry is formed by reacting 5585 g of iron powder, 11529 g of 85% phosphoric acid aqueous solution, and 40 L of deionized water in a barrel for 20 hours. In this embodiment, the target weight of the carbon-coated lithium iron phosphate material is 1578 g, the target carbon content ratio (target carbon weight content) is 1.20%, and since the carbon weight in the carbon-coated lithium iron phosphate material is 50% of the carbon weight in the third slurry (i.e., 50% of the carbon weight is lost during the sintering process), it is necessary to add 37.9 g of carbon. Also, the carbon source in this embodiment is glucose, and the mass ratio of carbon atoms in the molecule is 40%. To meet the carbon weight of 37.9 g, it is necessary to provide 94.7 g of glucose. The lithium source is 1197 g of lithium hydroxide (LiOH) and 1847 g of lithium carbonate (Li 2 CO 3) That is. 5585 g of iron powder contains 100 moles of iron, 11529 g of 85% phosphoric acid aqueous solution contains 100 moles of phosphorus, 1197 g of lithium hydroxide and 1847 g of lithium carbonate contain 100 moles of lithium in total. As a result, 100 moles of lithium iron phosphate (LiFePO 4 ) can be produced.

[0040] Next, 94.7 g of glucose, 1197 g of lithium hydroxide and 1847 g of lithium carbonate are added to the stirring first slurry and reacted to form a second slurry. The second slurry is pulverized by a ball mill method to form a third slurry. During the pulverization, the temperature of the second slurry is maintained at 25 °C by a liquid cooling method using the cooling water jacket of the barrel. The median particle size of the third slurry is 1.0 μm.

[0041] Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. It is dried by a spray drying method and sintered at a temperature of 550 °C to 750 °C for 10 hours in a nitrogen atmosphere to form a carbon-coated lithium iron phosphate material. When the carbon-coated lithium iron phosphate of the fifth example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 8.97 cm 2 / g. When the carbon-coated lithium iron phosphate of the fifth example was analyzed by an elemental analyzer, it was found that the carbon content ratio was 1.10%.

[0042] Example 6: The sixth example is generally the same as the manufacturing process of the fifth example, but during mixing and pulverization, the temperature of the second slurry of the sixth example was maintained at 35 °C. When the carbon-coated lithium iron phosphate of the sixth example was analyzed by the BET specific surface area measurement method, it was found that the specific surface area was 9.34 cm 2 / g. When the carbon-coated lithium iron phosphate of the sixth example was analyzed by an elemental analyzer, it was found that the carbon content ratio was 1.11%.

[0043] Refer to Table 4. Table 4 shows the slurry temperatures (°C) of the fifth and sixth embodiments, as well as the specific surface areas (cm 2 / g) and carbon contents (carbon weight content, %) of the formed carbon-coated lithium iron phosphate. Compared with the target carbon content ratio of 1.20%, the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the fifth embodiment is 8.3%, and the loss rate of the carbon content of the carbon-coated lithium iron phosphate formed in the sixth embodiment is 7.5%. Thus, the degree of carbon loss in the sixth embodiment with a slurry temperature of 35°C is smaller than that in the fifth embodiment with a slurry temperature of 25°C, and the specific surface area of the carbon-coated lithium iron phosphate in the sixth embodiment is larger than that in the fifth embodiment. In other words, by controlling the slurry temperature to 27°C to 35°C in a liquid cooling manner using a cooling water jacket, the uniformity (consistency) of the solubility of the lithium source in the slurry can be ensured. At the same time, the oxidative decomposition of the carbon source in the slurry in a high-temperature environment can be prevented, the carbon content of the carbon-coated lithium iron phosphate material can be ensured, and the stability of the product quality can be improved. JPEG0007690556000004.jpg35164

[0044] As described above, the present invention provides a method for manufacturing a carbon-coated lithium iron phosphate material that controls the slurry temperature in order to ensure the carbon content of the carbon-coated lithium iron phosphate material and at the same time improve the stability of product quality. First, a carbon source, a lithium source, and a first slurry formed from an iron source and a phosphorus source are provided. Next, the first slurry, the carbon source, and the lithium source are mixed to form a second slurry, and the second slurry is pulverized in a barrel at 25°C to 40°C to form a third slurry. Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. By controlling the slurry temperature within a specific temperature range, it is possible to ensure the uniformity (consistency) of the solubility of the lithium source in the slurry, and at the same time prevent the carbon source in the slurry from being oxidized and decomposed in a high-temperature environment, ensure the carbon content of the carbon-coated lithium iron phosphate material, and improve the stability of the product quality. Furthermore, the slurry temperature is controlled, for example, by liquid cooling through a cooling water jacket. The cooling water jacket is arranged so as to surround the internal space of the barrel that houses the slurry, and can control the rise and fall of the temperature smoothly and uniformly, so that the stability of the product quality can be further improved.

[0045] Those skilled in the art can make various modifications to the present invention, but will not deviate from the scope defined by the claims.

Explanation of Reference Numerals

[0046] 1: Barrel 10: First Space 20: Cooling Water Jacket 21: Second Space 22: First Flow Path 23: Second Flow Path 30: Supply Port 40: Discharge Port 50: Lid Member A-A': Line S1, S2, S3: Steps X, Y, Z: Axes

Claims

1. A method for manufacturing a carbon-coated lithium iron phosphate material, comprising: Step (a) of providing a first slurry, a carbon source, and a lithium source, wherein the first slurry is formed of an iron source and a phosphorus source; Step (b) of mixing the first slurry, the carbon source, and the lithium source to form a second slurry, and mixing and grinding the second slurry at a first temperature in a barrel to form a third slurry, wherein the first temperature is 25°C to 40°C; Step (c) of drying and sintering the third slurry to form the carbon-coated lithium iron phosphate material, wherein the carbon-coated lithium iron phosphate material comprises a core layer and a coating layer, the coating layer coats the core layer, the core layer is composed of the lithium source, the iron source, and the phosphorus source, and the coating layer is composed of the carbon source.

2. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 1, wherein the first temperature is maintained by a liquid cooling method.

3. The barrel comprises a first space and a cooling water jacket. The first space is provided to accommodate the second slurry and the third slurry. The cooling water jacket is provided to surround the first space. The liquid cooling method is to cool through the cooling water jacket. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 2.

4. The cooling water jacket comprises at least two flow paths and a second space. The second space is communicated between the at least two flow paths and surrounds the first space. The at least two flow paths are provided such that liquid flows into or out of the second space. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 3.

5. The carbon source, the lithium source, and the first slurry are ground by a ball milling method. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 1.

6. The second slurry and the third slurry are alkaline. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 1.

7. The iron source is iron powder, the phosphorus source is an aqueous phosphoric acid solution, and the first slurry is formed by reacting the iron powder with the aqueous phosphoric acid solution. The method for producing a carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

8. The third slurry is dried by a spray drying method. The method for producing a carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

9. The third slurry is sintered at a sintering temperature of 550°C to 750°C. The method for producing a carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

10. The third slurry is sintered in a non-oxidizing atmosphere. The method for producing a carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

11. The carbon weight content of the carbon-coated lithium iron phosphate material is 1.0% to 1.6%. The method for producing a carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

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