Method for producing carbon-coated lithium iron phosphate material

Abstract

To provide a method for producing a carbon-coated lithium iron phosphate material, capable of immediately detecting a slurry carbon content.SOLUTION: A method for producing a carbon-coated lithium iron phosphate material includes the following steps of: (a) providing a first slurry, and a first carbon source and lithium source having a first weight, the first slurry being formed with an iron source and a phosphorus source and the first weight being equal to the input value; (b) mixing and grinding the first carbon source, the lithium source, and the first slurry to form a second slurry; (c) analyzing a carbon content of the second slurry to determine the amount of loss; (d) adding a second carbon source having a second weight to the second slurry to form a third slurry, the second weight being equal to the amount of loss; and (e) drying and sintering the third slurry to form a carbon-coated lithium iron phosphate positive electrode material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a carbon-coated lithium iron phosphate material, and particularly to a method for manufacturing a carbon-coated lithium iron phosphate material for immediately detecting the carbon content of a slurry.

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 (LiFePO4) as the cathode material are attracting attention as batteries with development potential because of their 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, which limits the application of lithium iron phosphate.

[0003] Considering the above disadvantages, most of the current industries carbon coat (coat) lithium iron phosphate to improve performance. In the carbon coating process, since the lithium-containing slurry is alkaline and the temperature rises due to the grinding process, the carbon source is easily oxidized and decomposed in this alkaline and high-temperature environment, and the carbon content of the finally formed carbon-coated lithium iron phosphate material decreases. Therefore, in the conventional carbon coating process, in order to confirm whether the carbon content meets the requirements, the carbon content of the carbon-coated lithium iron phosphate material is analyzed by a combustion method. However, if the carbon content detected in this way does not meet the requirements, the carbon-coated lithium iron phosphate material formed by sintering can no longer be adjusted, and it can only be discarded and reproduced with new raw materials. Therefore, in the conventional carbon coating process, the product quality is not stable, and the cost is likely to increase and time is wasted.

[0004] It has been made in view of such circumstances, and in the present invention, in order to reduce waste of cost and time while ensuring the stability of product quality, it is necessary to provide a method for manufacturing a carbon-coated lithium iron phosphate material capable of immediately detecting the carbon content of a slurry.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a method for manufacturing a carbon-coated lithium iron phosphate material capable of immediately detecting the carbon content of a slurry, and to achieve cost reduction and shortening of manufacturing time while ensuring the stability of product quality. First, a first slurry, a first carbon source (material) such as a water-soluble saccharide, and a lithium source (material) are mixed to form a second slurry. The first slurry is formed of an iron source (material) and a phosphorus source (material), and the first carbon source (material) has a first weight equal to the input value. Next, the second slurry is sampled (specimen extraction), and the carbon content of the sample is analyzed with a saccharimeter or the like to obtain the loss amount. Next, a second carbon source (material) such as a water-soluble saccharide is added to the second slurry to form a third slurry. Here, the second carbon source (material) has a second weight equal to the loss amount. Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. By analyzing the carbon content of the slurry before drying and sintering the slurry, if the measured carbon content does not meet the requirements, the second carbon source (material) can be added according to the loss amount, ensuring the stability of product quality and reducing the extra cost and time wasted due to the need for reproduction because the product does not meet the requirements. Compared with a conventional elemental analyzer that analyzes the carbon amount by combustion, the saccharimeter is not only suitable for the carbon content of the liquid slurry, but also can quickly obtain the detection value, so the time from sampling analysis to obtaining the detection value can be shortened, the analysis cost can be reduced, and the decrease in carbon content caused by oxidation and decomposition of the carbon source (material) can be prevented.

Means for Solving the Problems

[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 lithium source, and a first carbon source having a first weight, wherein the first slurry is formed of an iron source and a phosphorus source, and the lithium source, the iron source, and the phosphorus source constitute a core layer of the carbon-coated lithium iron phosphate material, and the first weight is equal to an input value; step (b) of mixing and pulverizing the first carbon source, the lithium source, and the first slurry to form a second slurry; step (c) of analyzing the carbon content of the second slurry to obtain a loss amount, wherein the loss amount is smaller than the input value and larger than 0; step (d) of adding a second carbon source having a second weight to the second slurry to form a third slurry, wherein the second weight is equal to the loss amount; and step (e) of drying and sintering the third slurry to form a carbon-coated lithium iron phosphate material, wherein the carbon-coated lithium iron phosphate material includes a carbon coating layer covering the core layer, and the carbon coating layer is composed of the first carbon source and the second carbon source.

[0007] In one embodiment, the first carbon source is a water-soluble saccharide.

[0008] In one embodiment, the carbon content is analyzed using a saccharimeter.

[0009] In one embodiment, the analysis of the carbon content is performed on a sample, and the sample is taken from the second slurry.

[0010] In one embodiment, the sample contains a flocculant.

[0011] In one embodiment, the carbon source, the lithium source, and the first slurry are pulverized by a ball milling method.

[0012] In one embodiment, the third slurry is dried by a spray drying method.

[0013] In one embodiment, the third slurry is sintered in a non-oxidizing atmosphere.

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

[0015] In one embodiment, the carbon-coated lithium iron phosphate material has a third weight and a carbon weight content, and the carbon weight content is the target value divided by the value of the third weight, and the target value is 40% to 70% of the input value.

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

[0017] In one embodiment, the loss amount is 30% or less of the input value.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0019] Several exemplary embodiments demonstrating the features and advantages of the present invention will be described in detail in the following explanation. 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 used for explanatory purposes and are not intended to limit the present invention. Although the numerical ranges and parameters of the broad scope 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. 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 embodiment. 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 the 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 terms "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.

[0020] Please refer to FIGS. 1 and 2. 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. 2 is a diagram showing the sugar content - carbon weight content (weight percentage of carbon content) of the slurry according to an embodiment of the present invention. In this embodiment, the method for manufacturing the carbon-coated lithium iron phosphate material includes the following steps. First, as shown in step S1, a first slurry, a first carbon source having a first weight (mass), and a lithium source are provided (prepared). The first slurry is formed from an iron source and a phosphorus source, and the lithium source, the iron source, and the phosphorus source are configured to be blended to form the core layer of the carbon-coated lithium iron phosphate material, and the first weight is equal to the input value. In this embodiment, the iron source is, for example, iron powder, the phosphorus source is, for example, phosphoric acid (H3PO4), 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. In this embodiment, the first 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 salts such as lithium hydroxide (LiOH), lithium carbonate (Li2CO3), lithium nitrate (LiNO3), or 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. In this embodiment, the target value is the carbon weight included in the carbon-coated lithium iron phosphate material of the present invention and can be converted from the target weight and the target carbon weight content of the carbon-coated lithium iron phosphate material. The target value is, for example, 40% to 70% of the input value, and the ratio of the target value to the input value is determined by different sintering processes. In this embodiment, the target value is preferably 50% of the input value. In an embodiment, the weight of the carbon-coated lithium iron phosphate material is, for example, 1000 g, the target carbon weight content is, for example, 1.0%, and the target value is 50% of the input value. By calculation, it can be found that the target value is 10 g, and the input value and the first weight are 20 g.

[0021] As shown in step S2, the first carbon source, the lithium source, and the first slurry are mixed and pulverized to form a second slurry. In this embodiment, the first carbon source, the lithium source, and the first slurry are pulverized for 9 to 12 hours by, for example, the ball milling method to form a second slurry. The median particle diameter (D50) of the second slurry is, for example, 1.0 μm. Note that the pulverization conditions of the present invention and the median particle diameter (D50) of the second slurry are not limited thereto and can be changed according to actual needs. Further, by adding the first carbon source having the first weight in step S1 and mixing and pulverizing the first carbon source, the lithium source, and the first slurry in step S2, the first carbon source can be uniformly dispersed between the precursors of the lithium iron phosphate carbon-containing material.

[0022] As shown in step S3, the carbon content of the second slurry is analyzed to obtain the loss amount, and the loss amount is smaller than the input value and larger than zero. The loss amount is preferably 30% or less of the input value. In this embodiment, for the carbon content analysis, the second slurry is sampled to obtain a sample (a sample is taken from the second slurry), and the sugar content value of the sample is measured with a saccharimeter. In an embodiment, the sample can be first clarified, for example, using a flocculant. The correspondence between the sugar content of the slurry and the carbon weight content ratio of the carbon-coated lithium iron phosphate material is shown in FIG. 2. When regression analysis is performed on the data of the sugar content and the carbon weight content ratio, the following regression linear equation (1) is obtained. y = 0.4523x - 1.1487 (1)

[0023] In the regression linear equation (1), x is the sugar content (°Bx), y is the carbon weight content ratio (%), and the coefficient of determination (R 2) is 0.8311. In other words, the correlation coefficient (R) between the sugar content of the slurry and the carbon weight content of the carbon-coated lithium iron phosphate material is 0.9117, indicating a high positive correlation between the two. In this embodiment, the loss amount is the weight loss of the first carbon source due to oxidative decomposition in the previous step, that is, the value obtained by subtracting the carbon weight contained in the second slurry from the input value. The carbon weight contained in the second slurry can be calculated using the weight of the carbon-coated lithium iron phosphate material, the sugar content value measured from the sample of the second slurry, and the ratio of the target value to the input value. In this embodiment, the weight of the carbon-coated lithium iron phosphate material is, for example, 1000 g, the target carbon weight content is 1.0%, the target value is 10 g, the input value is 20 g, and the sugar content value measured from the sample of the second slurry is, for example, 4.53 °Bx. Using the above-mentioned regression linear equation (1) for conversion, it can be found that the carbon weight content of the carbon-coated lithium iron phosphate material formed from the second slurry is 0.9%. Using the ratio (50%) of the weight of the carbon-coated lithium iron phosphate material and the target value to the input value for conversion, it can be found that the carbon weight in the current second slurry is 18 g. Finally, subtracting the carbon weight in the 18 g second slurry from the 20 g input value, it can be found that the loss amount is 2 g. It should be noted that the method for converting the sugar content and carbon weight content used in the present invention is not limited to the above-mentioned regression linear equation (1), and can be optimized and adjusted based on more data or different statistical analysis methods. In this embodiment, the resolution of the sugar meter is 0.04 °Bx. Therefore, the resolution of the carbon content loss amount of the carbon-coated lithium iron phosphate material that can be detected using the above-mentioned regression linear equation (1) is less than 0.02%, and the weight of the first carbon source lost due to oxidative decomposition in the previous step can be efficiently and accurately detected. It should be noted that the present invention is not limited to this.

[0024] As shown in step S4, a second carbon source having a second weight (a second carbon source having a second weight) is added to the second slurry to form a third slurry, and the second weight is equal to the loss amount. In the present embodiment, the loss amount is preferably 30% or less of the input value. The larger the loss amount, the more the second carbon source having the second weight of the second slurry added in step S4 is added. In this case, in order for the second carbon source to be uniformly dispersed to form the third slurry, it is necessary to lengthen the additional mixing and dispersion time, but there is a problem that the second carbon source is oxidatively decomposed during the mixing process. In the present embodiment, since the loss amount is 30% or less of the input value, it is not necessary to lengthen the additional mixing and separation time so much, and the second carbon source and the second slurry can be uniformly mixed to form the third slurry. Of course, the present invention is not limited to this. In the present embodiment, since the loss amount is, for example, 0.5 g, a second carbon source having a second weight of 0.5 g is added to the second slurry and mixed. Before drying and sintering the second slurry, the carbon content is analyzed. If the measured carbon content does not meet the requirements, the second carbon source is added according to the loss amount to ensure the stability of the product quality and reduce the need for reproduction, additional costs, and waste of time due to the product not meeting the standards. In addition, the saccharimeter is not only suitable for analyzing the carbon content in the liquid-phase slurry, but also the detection value can be obtained quickly, so the time from sampling analysis to obtaining the detection value is shortened, and the decrease in the carbon content of the carbon source due to oxidative decomposition is also reduced. In addition, by adding a flocculant to the sample for clarification treatment, the detection accuracy of the saccharimeter is also improved.

[0025] As shown in step S5, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material further includes a carbon coating layer that coats the core layer, and the carbon coating layer is composed of a first carbon source and a second carbon source. In this embodiment, the product of the previous step is dried, for example, by a spray drying method and sintered at a temperature of 550°C to 750°C for 7 to 15 hours in a non-oxidizing atmosphere. The carbon weight content of the carbon-coated lithium iron phosphate material is, for example, 1.0% to 1.6%. It should be noted that the drying method, sintering conditions of the present invention, and the carbon weight content of the carbon-coated lithium iron phosphate material are not limited thereto and can be adjusted according to actual needs.

[0026] Hereinafter, with reference to examples, a method for manufacturing a carbon-coated lithium iron phosphate material of the present invention will be described.

[0027] Examples:

[0028] Provide a first slurry, a first carbon source, and a lithium source. The first slurry is formed by reacting 5585 g of iron powder, 11526 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 carbonate material is 1578 g, the target carbon weight content is 1.4%, and the target value is 50% of the input value. Calculated therefrom, it can be seen that the target value is 22.1 g, and the input value and the first weight are 44.2 g. The first carbon source in this example is glucose, and since the mass ratio of carbon atoms in the molecule is 40%, 110.5 g of glucose is provided to satisfy the first weight of 44.2 g. The lithium source is 1197 g of lithium hydroxide monohydrate (LiOH) and 1847 g of lithium carbonate (Li2CO3). 5585 g of iron powder contains 100 moles of iron, 11526 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 100 moles of lithium, whereby 100 moles of lithium iron phosphate (LiFePO4) can be produced.

[0029] 110.5 g of glucose, 1197 g of lithium hydroxide, and 1847 g of lithium carbonate were each added to the stirring first slurry for reaction, and pulverized by the ball mill method to form a second slurry. The median particle size of the second slurry is 1.0 μm.

[0030] The second slurry was sampled to obtain a sample. A flocculant was added to the sample for clarification, and the clarified sample was measured with a saccharimeter, and a sugar content value of 5.10 °Bx was detected. When converted using the regression linear equation (1) described above, the carbon weight content of the iron lithium phosphate material coated with carbon formed in the second slurry is 1.16%. When converted using the target weight of 1578 g of the iron lithium phosphate material coated with carbon and the ratio of the target value to the input value (50%), it can be seen that the carbon weight in the current second slurry is 36.6 g. Since the input value in this example is 44.2 g, the loss amount is 7.6 g.

[0031] Next, a second carbon source having a second weight was added to the second slurry to form a third slurry, and the second weight is equal to the loss amount of 7.6 g. The second carbon source in this example is glucose, and since the mass ratio of carbon atoms in the molecule is 40%, in order to satisfy the second weight of 7.6 g, it is necessary to provide 19 g of glucose. 19 g of glucose is added to the second slurry by a method of adding deionized water to form an aqueous glucose solution in order to mix more rapidly with the second slurry.

[0032] Finally, the product of the previous step was dried and sintered to form an iron lithium phosphate material coated with carbon. The product of the previous step 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 an iron lithium phosphate material coated with carbon. For the iron lithium phosphate material coated with carbon of the example, elemental analysis was performed using an elemental analyzer, and the carbon weight content was 1.4%.

[0033] As described above, the present invention provides a method for manufacturing a carbon-coated lithium iron phosphate material capable of immediately detecting the carbon content of a slurry, and can achieve cost reduction and manufacturing time shortening while ensuring the stability of product quality. First, a first slurry, a first carbon source such as water-soluble saccharides, and a lithium source are mixed to form a second slurry. The first slurry is formed of an iron source and a phosphorus source, and the first carbon source has a first weight equal to the input value. Next, the second slurry is sampled, and the carbon content of the sample is analyzed with a saccharimeter or the like to obtain the loss amount. Next, a second carbon source such as water-soluble saccharides is added to the second slurry to form a third slurry. Here, the second carbon source has a second weight equal to the loss amount. Finally, the third slurry is dried and sintered to form a carbon-coated lithium iron phosphate material. By analyzing the carbon content of the slurry before drying and sintering the slurry, if the measured carbon content does not meet the requirements, the second carbon source can be added according to the loss amount, ensuring the stability of product quality and reducing the extra costs and time wasted due to the need for reproduction because the product does not meet the requirements. Compared with the conventional elemental analyzer that analyzes the carbon amount by combustion, the saccharimeter is not only suitable for the carbon content of the liquid slurry, but also can quickly obtain the detection value, shortening the time from sampling analysis to obtaining the detection value and reducing the analysis cost. Therefore, it is possible to prevent the decrease in carbon content caused by the oxidation and decomposition of the carbon source.

[0034] Those skilled in the art can make various modifications to the present invention, but will not depart from the scope defined by the claims.

Explanation of symbols

[0035] S1, S2, S3, S4, S5: Steps

Claims

1. A method for manufacturing a carbon-coated lithium iron phosphate material, comprising: Step (a) of providing a first slurry, a lithium source, and a first carbon source having a first carbon weight, wherein the first slurry is formed from an iron source and a phosphorus source, and the lithium source, the iron source, and the phosphorus source constitute the core of the carbon-coated lithium iron phosphate material, and the first carbon weight is equal to the input value; Step (b) of mixing and pulverizing the first carbon source, the lithium source, and the first slurry to form a second slurry; Step (c) of analyzing the carbon content of the second slurry to determine the loss amount, wherein the loss amount is less than the input value and greater than 0; Step (d) of adding a second carbon source having a second carbon weight to the second slurry to form a third slurry, wherein the second carbon weight is equal to the loss amount; Step (e) of drying and sintering the third slurry to form the carbon-coated lithium iron phosphate material, wherein the carbon-coated lithium iron phosphate material includes a carbon coating layer covering the core, and the carbon coating layer is composed of the first carbon source and the second carbon source. A method for manufacturing a carbon-coated lithium iron phosphate material, characterized by comprising the above steps.

2. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 1, wherein the first carbon source is a water-soluble saccharide.

3. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 2, wherein the carbon content is analyzed using a saccharimeter.

4. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 3, wherein the analysis of the carbon content is performed on a sample, and the sample is taken from the second slurry.

5. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 4, wherein the sample contains a flocculant.

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

7. The method for manufacturing a carbon-coated lithium iron phosphate material according to claim 1, wherein the third slurry is dried by a spray drying method.

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

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

10. The carbon-coated lithium iron phosphate material has a third weight and a carbon weight content, and the carbon weight content is obtained by dividing a target value by the numerical value of the third weight. The target value is 40% to 70% of the input value. The method for producing the carbon-coated lithium iron phosphate material according to claim 1, characterized in that.

11. The method for producing the carbon-coated lithium iron phosphate material according to claim 10, wherein the carbon weight content of the carbon-coated lithium iron phosphate material is 1.0% to 1.6%.

12. The method for producing the carbon-coated lithium iron phosphate material according to claim 1, wherein the loss amount is 30% or less of the input value.

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