Preparation method of iron phosphate precursor for battery

Abstract

The invention discloses a preparation method of an iron phosphate precursor for a battery, which comprises the following steps: (a) phosphoric acid and iron powder are provided, the apparent density of the iron powder ranges from 2.3 g / cm < 3 > to 2.6 g / cm < 3 >, the particle size of the iron powder consists of a first particle size range and a second particle size range, the first particle size range is larger than the second particle size range, and the second particle size range is larger than the first particle size range; the weight of the iron powder in the second particle size range accounts for 10-30% of the total weight of the iron powder; (b) reacting phosphoric acid with iron powder to generate a first product; and (c) calcining the first product in an air or oxygen atmosphere to generate an iron phosphate precursor.

Description

Technical Field

[0001] The present invention relates to a preparation method, particularly to a preparation method of a ferric phosphate precursor for batteries. Background Art

[0002] Due to the continuous shortage of global energy, the high price of oil, and the increasing awareness of environmental protection in recent years, the most concerned issue in the current related industries is how to provide environmentally friendly, clean and efficient energy. Among various alternative energies, chemical batteries are the technologies actively researched and developed by the industry. With the continuous investment in research and development by the related industries, not only the battery technology has been continuously improved and enhanced, but also it has been widely applied in daily life, such as consumer electronics, medical devices, electric bicycles, electric motorcycles, electric vehicles, and electric buses.

[0003] Among them, lithium iron phosphate (LiFePO 4 , abbreviated as LFP) composite batteries are widely accepted by the market to replace traditional low-power and highly polluting batteries such as lead-acid, nickel-metal hydride, and nickel-cadmium because they do not have the risk of explosion and have advantages such as high current and long cycle life. After years of research and development, the nano metal oxide co-crystallized lithium iron phosphate compound (LFP-NCO) battery has been developed. It is a single indivisible compound formed by a precursor containing lithium, iron, phosphorus, and a metal or metal compound, and is a non-doped and non-coated material, which can greatly improve the problems of low conductivity and many impurities of traditional lithium iron phosphate materials, and is cheaper than traditional lithium iron phosphate materials, with better market competitiveness, and thus has become the mainstream in the current market.

[0004] However, currently, the preparation methods applied to the nano metal oxide co-crystallized lithium iron phosphate compound mostly involve reacting ferric phosphate (FePO 4) , lithium hydroxide (LiOH), and lithium carbonate (Li 2 CO 3 ). Among them, the morphology of the ferric phosphate precursor before reacting with lithium hydroxide (LiOH) and lithium carbonate (Li 2 CO 3 ) more affects the production efficiency of the final lithium iron phosphate compound. Since the ferric phosphate precursor is mainly prepared by reacting iron with phosphoric acid, the reaction process needs to consider the reaction rate, heat release effect, and process operation difficulty, and the conversion rate of the obtained ferric phosphate precursor seriously affects the product quality.

[0005] In view of this, how to provide a preparation method of a ferric phosphate precursor for batteries to improve product quality, reduce raw material, time costs, and process operation difficulty, and improve the deficiencies of the prior art is an urgent problem to be solved currently. Summary of the Invention

[0006] The main object of this case is to provide a method for preparing iron phosphate precursor for batteries, so as to improve product quality and reduce raw material, time costs, and the difficulty of process operation.

[0007] Another object of this case is to provide a method for preparing iron phosphate precursor for batteries. By optimizing the preparation reaction of iron phosphate precursor through controlling the specifications of raw material iron powder, the difficulty of process operation caused by too fast reaction rate can be avoided. On the other hand, in the secondary reaction of phosphoric acid, deionized water and iron powder, when the iron powder reactant has not completely reacted, the amorphous iron phosphate coating attached to the surface of the iron powder reactant is removed by cooperating with the grinding process, so that the iron powder reactant can contact phosphoric acid again and react fully, achieving the effect of effectively reducing the waste of raw materials and comprehensively improving the conversion rate of iron phosphate precursor.

[0008] Another object of this case is to provide a method for preparing iron phosphate precursor for batteries. Through the secondary reaction of phosphoric acid, deionized water and iron powder, phosphoric acid and iron powder can react fully, achieving the effect of effectively reducing the waste of raw materials and comprehensively improving product quality. Combining with the preparation method of iron phosphate precursor to further form a battery composite material can significantly shorten the grinding time required, thereby reducing the unit time and money costs. At the same time, it can also achieve reducing the pH value sensitivity of the process, avoiding raw material viscosity and pipeline blockage, and stably controlling the process temperature, thereby reducing the operation difficulty of the process and production line.

[0009] To achieve the above object, a broader implementation aspect of this case is to provide a method for preparing iron phosphate precursor for batteries, including the steps of: (a) providing phosphoric acid and iron powder, wherein the apparent density of the iron powder ranges from 2.3 g / cm 3 to 2.6 g / cm 3 , the particle size of the iron powder consists of a first particle size range and a second particle size range, wherein the first particle size range is larger than the second particle size range, and the weight of the iron powder in the second particle size range accounts for 10% to 30% of the total weight of the iron powder; (b) reacting phosphoric acid with the iron powder to generate a first product; and (c) calcining the first product in an air or oxygen atmosphere to generate an iron phosphate precursor.

[0010] In one embodiment, the iron powder has a BET surface area in the range of 700 cm 2 / g to 1300 cm 2 / g, the first particle size range is less than 212 μm and greater than 45 μm, and the second particle size range is less than or equal to 45 μm.

[0011] In one embodiment, step (c) is to maintain the calcination time for at least one hour within the temperature range of 610 °C to 670 °C.

[0012] In one embodiment, the first particle size range is less than 212 μm and greater than 45 μm, the second particle size range is less than or equal to 45 μm, and the weight of the iron powder in the second particle size range accounts for 10% to 25% of the total weight of the iron powder.

[0013] In one embodiment, the first product is amorphous phosphates, having the chemical formula a-FePO 4 ·xH 2 O, where x > 0.

[0014] In one embodiment, step (b) further includes the steps of: (b11) in a first temperature environment, dissolving a first quantity of the phosphoric acid in deionized water to form a first phosphoric acid solution; (b12) in a second temperature environment, reacting the first phosphoric acid solution with the iron powder, and after reaching the second temperature, cooling to a third temperature and maintaining for a first period of time; and (b13) cooling to a fourth temperature, and adding a second phosphoric acid solution having a second quantity of phosphoric acid, and continuously reacting the first phosphoric acid solution, the second phosphoric acid solution with the iron powder for a second period of time to generate the first product.

[0015] In one embodiment, the weight ratio of the first quantity to the second quantity is 3 to 1.

[0016] In one embodiment, the first temperature is 35°C to 45°C, the second temperature is below 60°C, the third temperature is below 50°C, and the fourth temperature is below 30°C.

[0017] In one embodiment, the first period of time is at least 3 hours, and the second period of time is between 5 hours and 9 hours.

[0018] In one embodiment, step (b) further includes the steps of: (b21) performing a first grinding so that the D99 particle size of the particles of the first product is less than a first length; and (b22) continuously reacting for a third period of time.

[0019] In one embodiment, the first length is less than 100 μm, and the range of the third period of time is between 6 hours and 12 hours.

[0020] In one embodiment, step (b) further includes the steps of: (b31) adding a carbon source and a metal compound to generate a precursor solution with the first product, and performing a second grinding; and (b32) when the D70 particle size of the particles in the precursor solution is less than a second length during the second grinding, performing a spray drying operation on the precursor solution.

[0021] In one embodiment, the spray drying operation is achieved through a rotary disk spray dryer. The inlet temperature of the rotary disk spray dryer is 210°C, the outlet temperature is 95°C, and the rotational speed of the disk is between 300 Hz and 400 Hz.

[0022] In one embodiment, the second length range is between 1 μm and 10 μm.

[0023] In one embodiment, the rotational speed ranges of the first grinding and the second grinding are from 450 revolutions per minute to 650 revolutions per minute.

[0024] In one embodiment, a metal compound and the iron phosphate precursor form an iron phosphate precursor composite material in step (c), and then are calcined to generate a battery composite material, wherein the chemical formula of the battery composite material is LiFePO 4 , and the metal compound is a lithium-containing compound.

[0025] In one embodiment, the lithium-containing compound is selected from lithium hydroxide, lithium carbonate or a mixture thereof, and the battery composite material is a nano metal oxide co-crystallized lithium iron phosphate compound (LFP-NCO).

[0026] In one embodiment, step (c) includes maintaining the temperature at 325°C for 0.5 hours, maintaining the temperature at 550°C for 0.5 hours, and maintaining the temperature at 650°C for 1 hour. Description of the Drawings

[0027] Figure 1 It is a flowchart of the preparation method of the iron phosphate precursor for batteries of the preferred embodiment of this case.

[0028] Figure 2 It is a detailed flowchart of the preparation method of the iron phosphate precursor for batteries of this case.

[0029] Figure 3 It is another detailed flowchart of the preparation method of the iron phosphate precursor for batteries of this case.

[0030] Figure 4 It is a detailed flowchart of the preparation method of the combination of the iron phosphate precursor for batteries and the battery composite material of this case.

[0031] Figure 5 It is another detailed flowchart of the preparation method of the combination of the iron phosphate precursor for batteries and the battery composite material of this case.

[0032] Figure 6 It is an X-ray diffraction analysis diagram of the iron phosphate precursor product prepared by the preparation method of the iron phosphate precursor for batteries of this case.

[0033] Figure 7Disclose a relationship diagram of the proportion of fine powder of raw material iron powder ≤ 45μm corresponding to the relative conversion rate of the obtained first product.

[0034] Figure 8 Disclose a relationship diagram of the proportion of fine powder of raw material iron powder ≤ 45μm corresponding to the final particle size D99 of the obtained first product. Detailed implementation manners

[0035] Some typical embodiments reflecting the features and advantages of this case will be described in detail in the following description. It should be understood that this case can have various changes in different aspects, all of which do not deviate from the scope of this case, and the descriptions and drawings therein are essentially for illustrative purposes rather than for limiting this case. For example, if the following content of this disclosure describes a first feature being disposed on or above a second feature, it means that it includes embodiments where the above-mentioned first feature and the above-mentioned second feature are in direct contact, and also includes embodiments where additional features can be disposed between the above-mentioned first feature and the above-mentioned second feature, so that the above-mentioned first feature and the above-mentioned second feature may not be in direct contact. Additionally, repeated reference signs and / or labels may be used in different embodiments of this disclosure. These repetitions are for the purpose of simplification and clarity, and are not used to limit the relationship between each embodiment and / or the described appearance structure. Although the numerical ranges and parameters in the broad scope of this disclosure are approximate values, the numerical values are stated as precisely as possible in specific examples. Additionally, it can be understood that although terms such as "first", "second", "third", etc. may be used in the claims to describe different components, these components should not be limited by these terms. In the embodiments, these components described correspondingly are represented by different component symbols. These terms are used to distinguish 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. The term "and / or" used in this way includes any and all combinations of one or more of the related listed items. Except in operating / work examples, or unless explicitly specified, all numerical ranges, amounts, values, and percentages (such as those percentages of angles, time durations, temperatures, operating conditions, quantity ratios, and the like) disclosed in this article should be understood to be modified by the term "about" or "substantially" in all embodiments. Accordingly, unless otherwise indicated, the numerical parameters stated in this disclosure and the appended claims are approximate values that can vary as needed. For example, each numerical parameter should be interpreted at least according to the number of significant digits and by applying the ordinary rounding principle. Ranges can be expressed in this article as from one endpoint to the other endpoint or between two endpoints. All ranges disclosed in this article include endpoints, unless otherwise specified.

[0036] Please refer to Figure 1 , which is a flow chart of the preparation method of the iron phosphate precursor for batteries of a preferred embodiment of this case. AsFigure 1 As shown, the preparation method of the battery composite material in this case includes the following steps: First, as shown in step S100, phosphoric acid and iron powder are provided. Among them, the chemical formula of phosphoric acid is H 3 PO 4 , and the chemical formula of iron powder is Fe. In addition, the iron powder has a specific specification to optimize the preparation reaction of the iron phosphate precursor and avoid the increase in the process operation difficulty or the occurrence of safety problems due to too fast reaction rate. In this embodiment, the apparent density of the iron powder ranges from 2.3 g / cm 3 to 2.6 g / cm 3 . The particle size of the iron powder consists of a first particle size range and a second particle size range, and is divided into two ranges by sieving, for example. In this embodiment, the first particle size range is coarse powder less than 212 μm and greater than 45 μm, and the second particle size range is fine powder less than or equal to 45 μm, that is, the first particle size range is greater than the second particle size range. The weight of the iron powder in the first particle size range accounts for 90% to 70% of the total weight of the iron powder; and the weight of the iron powder in the second particle size range accounts for 10% to 30% of the total weight of the iron powder. In other words, by sieving, iron powder with a maximum particle size less than 212 μm can be obtained, and the weight of the fine powder of iron powder ≤ 45 μm accounts for 10% to 30% of the total weight of the iron powder to meet the requirements. Preferably, the weight of the iron powder in the first particle size range accounts for 90% to 75% of the total weight of the iron powder; the weight of the iron powder in the second particle size range further accounts for 10% to 25% of the total weight of the iron powder, that is, the weight of the fine powder of iron powder ≤ 45 μm accounts for 10% to 25% of the total weight of the iron powder. In this embodiment, the iron powder further has a BET surface area in the range of 700 cm 2 / g to 1300 cm 2 / g. Of course, the first particle size range and the second particle size range can be adjusted according to actual application requirements and divided into two ranges of coarse powder and fine powder by screening, for example. The following first particle size range and second particle size range are respectively described with the coarse powder less than 212 μm and greater than 45 μm and the fine powder ≤ 45 μm obtained by sieving, but this case is not limited thereto.

[0037] Secondly, as shown in step S200, phosphoric acid and iron powder are reacted to generate a first product. In this embodiment, the first product is an amorphous form of iron phosphate with the chemical formula a-FePO 4 ·xH 2 O, where x > 0.

[0038] Then, as shown in step S300, the first product is calcined in an air or oxygen atmosphere to generate an iron phosphate precursor. In this embodiment, the iron phosphate precursor can be obtained by continuously calcining the first product at a temperature in the range of 610 °C to 670 °C for at least one hour. Of course, this case is not limited thereto.

[0039] Please refer to Figure 2 and cooperate with Figure 1 , in which Figure 2 is a detailed flowchart of one of the preparation methods of the iron phosphate precursor for the battery in this case. As Figure 1 and Figure 2 shown, the detailed process of step S200 in the preparation method of the iron phosphate precursor for the battery in this case includes the steps: As shown in step S201, in an environment of a first temperature, for example, in an environment preheated to 35°C to 45°C, dissolve a first quantitative amount of phosphoric acid with deionized water to form a first phosphoric acid solution, and it is preferably an environment preheated to 42°C, but not limited thereto. Then, as shown in step S202, in an environment of a second temperature, react the first phosphoric acid solution with iron powder, and after reaching the second temperature, cool down to a third temperature and maintain for a first period of time. According to the concept of this case, other compounds that release phosphate ions in an aqueous solution after mixing can also be used to react with iron powder, and this case is not limited thereto. The second temperature can be 60°C or less and is preferably 60°C, and the third temperature can be 50°C or less and is preferably 50°C. As for the first period of time, it is at least 3 hours and is preferably 3 hours.

[0040] In one embodiment, a preferred step S202 is: React the first phosphoric acid solution with iron powder in an environment of 60°C, and after reaching 60°C, cool down to 50°C and maintain the temperature for 3 hours, but not limited thereto. Then, as shown in step S203, cool down to a fourth temperature, and add a second phosphoric acid solution having a second quantitative amount of phosphoric acid, and continuously react the first phosphoric acid solution, the second phosphoric acid solution with iron powder for a second period of time to generate a first product.

[0041] In this embodiment, the first product is an amorphous form of iron phosphate, with the chemical formula a-FePO 4 ·xH 2 O (x>0), the fourth temperature is 30°C or less, preferably 30°C, the second period of time is 5 to 9 hours, and the weight ratio of the first quantitative amount to the second quantitative amount is 3:1, that is, the first quantitative amount is 75% and the second quantitative amount is 25%

[0042] Please refer to Figure 3 and cooperate with Figure 1 , in which Figure 3 is another detailed flowchart of the preparation method of the iron phosphate precursor for the battery in this case. As Figure 1 and Figure 3As shown, the detailed process of step S200 of the preparation method of the iron phosphate precursor for the battery in this case further includes the following steps: as shown in step S211, after the above-mentioned reaction is completed for 5 to 9 hours, a first grinding is performed to make the particle D99 diameter of the first product smaller than a first length. Then, as shown in step S212, the reaction is continued for a third time to promote the reaction so that the reaction between phosphoric acid and iron powder is more complete. In this embodiment, the iron powder has specific specifications. Although powdered metal has the characteristic of fast reaction speed, it is also easy to form a barrier on the surface of the powder due to excessive reaction rate. In this embodiment, when the iron powder has not yet completely reacted with phosphoric acid, the amorphous iron phosphate film attached to the surface of the iron powder is removed by moderate grinding, so that the iron powder reactant can be re-contacted with phosphoric acid, making the overall reaction more complete.

[0043] In this embodiment, the first length is less than 100 μm, and the third time ranges from 6 hours to 12 hours. In this embodiment, the first grinding is performed at a first rotation speed, for example, and the first rotation speed is 450 to 650 revolutions per minute (450rpm~650rpm), and 550 revolutions per minute (550rpm) is preferred. Through the secondary reaction of phosphoric acid, deionized water and iron powder, the phosphoric acid solution and iron powder can fully react, so as to effectively reduce the waste of raw materials and comprehensively improve the product quality.

[0044] It should be noted that the preparation of the iron phosphate precursor for the battery in this case can also be used to prepare the battery composite material. Figure 4 This is a detailed flow chart of the preparation method of the iron phosphate precursor combined with the battery composite material for this case.

[0045] Figure 5 This is another detailed flow chart of the preparation method of the iron phosphate precursor for the battery combined with the battery composite material in this case. In this embodiment, as shown in step S221, the carbon source and metal compound required for the battery composite material can be added to the first product formed by the sufficient reaction of the aforementioned phosphoric acid solution and the iron powder, so that the carbon source, the metal compound and the first product form a precursor solution, and a second grinding is performed. In this embodiment, the carbon source is, for example, a carbohydrate, an organic compound, a polymer or a high molecular material. In some embodiments, carbohydrates can be, for example, but not limited to fructose, sucrose, lactose, galactose, etc., and the high molecular material can be, for example, but not limited to polyvinyl pyrrolidone (PVP, chemical formula (C 6 H 9 NO) n ). In this embodiment, the metal compound may be lithium carbonate (chemical formula is Li 2 CO 3 ), lithium hydroxide (chemical formula LiOH), or other compounds containing lithium atoms, or a mixture of several lithium-containing compounds, but not limited to this.

[0046] Thereafter, as shown in step S222, when the second grinding makes the particle size D70 in the precursor solution smaller than a second length, a spray drying action is performed on the precursor solution. In this embodiment, the rotation speed range of the second grinding can be the same as the rotation speed range of the aforementioned first grinding, which is between 450 and 650 revolutions per minute. The second length range is between 1μm and 10μm. In this embodiment, the spray drying action is achieved through a rotary disk spray dryer, the inlet temperature of the rotary disk spray dryer is 210°C, the outlet temperature is 95°C, and the rotary disk speed is between 300 Hz and 400 Hz, but not limited to this. In this embodiment, the addition of the carbon source is mainly used to prevent grain growth and avoid excessive melting. The dispersant used in the conventional spray drying moving parts is a dispersant containing metal ions, and the present case uses a carbon source to replace the conventional dispersant. Since the carbon source is an organic compound, it can not only serve as an auxiliary dispersant, but also can be removed by subsequent calcination under air or oxygen, leaving no other metal cations, which can further improve the purity of the product. Of course, this case is not limited to this.

[0047] As shown in step S301, the spray-dried metal compound and the iron phosphate precursor are calcined at high temperature. In this embodiment, the spray-dried metal compound and the iron phosphate precursor are placed in an air or oxygen atmosphere, first at 325°C for 0.5 hours, then at 550°C for 0.5 hours, and then at 650°C for 1 hour. Finally, as shown in step S302, the iron phosphate precursor composite material formed by the metal compound and the iron phosphate precursor can be calcined to generate a battery composite material, such as LiFePO 4 . In other embodiments, metal oxides such as V may also be added in step S221. 2 O 5 , MgO, etc., then LiFePO containing metal oxides can be obtained 4 Material, the LiFePO containing metal oxide 4 The material can be called "Nanometallic Oxide Eutectic Lithium Iron Phosphate Compound (LFP-NCO)".

[0048] It can be seen that in this case, phosphoric acid and iron powder can be fully reacted through the secondary reaction of phosphoric acid, deionized water and iron powder, so as to effectively reduce the waste of raw materials and comprehensively improve the quality of products. Combining the preparation method of iron phosphate precursor to further form battery composite materials can greatly shorten the time required for grinding, thereby reducing unit time and money costs. At the same time, it is also possible to combine the above-mentioned many parameter changes to reduce the pH sensitivity of the process, avoid raw material viscosity and pipeline blockage, and stably control the process temperature, thereby reducing the difficulty of operating the process and production line.

[0049] ​The preparation method of the iron phosphate precursor for batteries in this case will be assisted by exemplary embodiments hereinafter.

[0050] Demonstration Example 1

[0051] First, 12.385 grams of phosphoric acid (purity above 85%), 50 cc of deionized water, and 6 grams of iron powder (purity above 99%) are provided. The apparent density of the iron powder ranges from 2.3 g / cm 3 to 2.6 g / cm 3 . The maximum particle size of the iron powder is less than 212 μm, and the weight of the fine powder with iron powder ≤ 45 μm accounts for 21.6% of the total weight of the iron powder. The phosphoric acid and the iron powder are placed in a water jacket reaction tank according to the aforementioned steps S201 and S202 for secondary reaction and stirring. After the second phosphoric acid solution of the second quantitative phosphoric acid is added and the reaction continues for 5 hours, as shown in the aforementioned steps S211 and S212, a horizontal sand mill is used for grinding (rotation speed 550 rpm) for the first grinding to make the particle D99 size of the first product less than 100 μm, and the reaction continues for a third time of 6 hours. The first product after spray drying is continuously calcined at a temperature range of 610 °C to 670 °C for at least one hour to obtain the iron phosphate precursor. The X-ray Diffraction (XRD) analysis results are as Figure 6 shown. After comparing with the standard diffraction pattern (JCPDS Card), it is confirmed that its structure is FePO 4 .

[0052] Demonstration Example 2

[0053] In Demonstration Example 2, 12.385 grams of phosphoric acid (purity above 85%), 50 cc of deionized water, and 6 grams of iron powder (purity above 99%) are provided. The apparent density of the iron powder used for preparing the iron phosphate precursor for batteries ranges from 2.3 g / cm 3 to 2.6 g / cm 3 . The maximum particle size of the iron powder is less than 212 μm, and the weight of the fine powder with iron powder ≤ 45 μm accounts for 13.3% of the total weight of the iron powder. The phosphoric acid and the iron powder are placed in a water jacket reaction tank according to the aforementioned steps S201 and S202 for secondary reaction and stirring. The initial reaction rate of the phosphoric acid and the iron powder is moderate (the initial heating rate is 1.54 °C / min), the operability during the reaction is good, and phosphoric acid is used for peptization. The relative conversion rate of the obtained first product is about 90.3%, the final particle size D99 is 110.2 μm, and the final pH value is 2.41.

[0054] Demonstration Example 3

[0055] In Example 3, 12.385 grams of phosphoric acid (purity above 85%), 50 cc of deionized water, and 6 grams of iron powder (purity above 99%) are provided. The apparent density of the iron powder used for preparing the iron phosphate precursor for the battery ranges from 2.3 g / cm 3 to 2.6 g / cm 3 . The maximum particle size of the iron powder is less than 212 μm, and the weight of the fine powder with iron powder ≤ 45 μm accounts for 25.0% of the total weight of the iron powder. Phosphoric acid and the iron powder are placed in a water jacket reaction tank according to the aforementioned steps S201 and S202 for secondary reaction and stirring. The initial reaction rate of phosphoric acid and the iron powder is moderate (the initial heating rate is 1.54 °C / min), and the process of peptization needs to be assisted manually during the reaction. The relative conversion rate of the obtained first product is about 98.1%, the final particle size D99 is 133.4 μm, and the final pH value is 2.35.

[0056] Example 4

[0057] In Example 4, 12.385 grams of phosphoric acid (purity above 85%), 50 cc of deionized water, and 6 grams of iron powder (purity above 99%) are provided. The apparent density of the iron powder used for preparing the iron phosphate precursor for the battery ranges from 2.3 g / cm 3 to 2.6 g / cm 3 . The maximum particle size of the iron powder is less than 212 μm, and the weight of the fine powder with iron powder ≤ 45 μm accounts for 16.4% of the total weight of the iron powder. Phosphoric acid and the iron powder are placed in a water jacket reaction tank according to the aforementioned steps S201 and S202 for secondary reaction and stirring. The initial reaction rate of phosphoric acid and the iron powder is gentle (the initial heating rate is 1.40 °C / min), and the process of peptization needs to be assisted manually during the reaction. The relative conversion rate of the obtained first product is about 95.9%, the final particle size D99 is 119.4 μm, and the final pH value is 2.23.

[0058] Comparative Example 1

[0059] In Comparative Example 1, 12.385 grams of phosphoric acid (purity above 85%), 50 cc of deionized water, and 6 grams of iron powder (purity above 99%) are provided, and the apparent density of the iron powder ranges from 2.3 g / cm 3 to 2.6 g / cm 3The maximum particle size of the iron powder is less than 212 μm, and the weight of the fine powder of the iron powder with a particle size of ≤ 45 μm accounts for 5.0% of the total weight of the iron powder. Phosphoric acid and the iron powder are placed in a water jacket reaction tank according to the aforementioned steps S201 and S202 for secondary reaction and stirring. The initial reaction rate of phosphoric acid and the iron powder is too fast (the initial heating rate is 1.71 °C / min), the operation during the reaction process is good, and there is no need to use phosphoric acid for peptization. The relative conversion rate of the obtained first product is about 85.1%, the final particle size D99 is 100.0 μm, and the final pH value is 2.51.

[0060] Table 1 shows the comparison of the reaction processes and final results of Comparative Example 1, Demonstration Example 2, Demonstration Example 3, and Demonstration Example 4:

[0061]

[0062] Figure 7 It reveals a relationship diagram of the proportion of the fine powder of the raw material iron powder with a particle size of ≤ 45 μm corresponding to the relative conversion rate of the obtained first product. Figure 8 It reveals a relationship diagram of the proportion of the fine powder of the raw material iron powder with a particle size of ≤ 45 μm corresponding to the final particle size D99 of the obtained first product. From Table 1 and Figures 7 to Figure 8 As can be seen from the results of, when the proportion of the fine powder of the iron powder with a particle size of ≤ 45 μm increases, the relative conversion rate of the first product also increases, and the final particle size D99 is also larger. When the proportion of the fine powder of the iron powder with a particle size of ≤ 45 μm approaches 30%, the increase in the relative conversion rate tends to level off. The proportion of the fine powder of the iron powder with a particle size of ≤ 45 μm is not related to the final pH value. By increasing the proportion of the fine powder of the iron powder with a particle size of ≤ 45 μm, although the relative conversion rate and the final particle size of the first product can be significantly improved, the situation of gelation and swelling during the reaction process is serious, the amount of phosphoric acid for peptization needs to be increased, and manual assistance for peptization is required, resulting in poor operability. Therefore, in this case, by controlling the specifications of the raw material iron powder, an apparent density in the range of 2.3 g / cm 3 to 2.6 g / cm 3 , a BET surface area in the range of 700 cm 2 / g to 1300 cm 2 / g, a maximum particle size less than 212 μm, and the weight of the fine powder of the iron powder with a particle size of ≤ 45 μm accounting for 10% to 30% of the total weight of the iron powder are helpful for optimizing the preparation reaction of the iron phosphate precursor, avoiding too fast reaction rate and increasing the process operation difficulty, and at the same time improving the product quality.

[0063] In this embodiment, the gelling reaction in the aforementioned reaction process can be regarded as the initial reaction degree (exothermic degree). The gelling reaction can be slowed down by increasing the holding temperature of the water jacket reaction tank or increasing the proportion of large-particle-size iron powder. When the holding temperature of the water jacket reaction tank is controlled between 45°C and 60°C, it will not affect the conversion rate of the subsequent first product. However, when the holding temperature of the water jacket reaction tank is increased to 65°C, the conversion rate of the first product will decrease.

[0064] In other embodiments, if there is still unreacted iron powder reactant in the secondary reaction of phosphoric acid, deionized water and iron powder, the amorphous iron phosphate coating attached to the surface of the iron powder reactant can be further removed by cooperating with the aforementioned grinding process, so that the iron powder reactant can come into contact with phosphoric acid again and react fully, achieving the effect of effectively reducing the waste of raw materials and comprehensively improving the conversion rate of the iron phosphate precursor. The preparation method of the iron phosphate precursor can also be further combined with the preparation of battery composite materials, greatly shortening the grinding time required, and thus reducing the unit time and cost. At the same time, it is also possible to combine the aforementioned various parameter changes to reduce the pH value sensitivity of the process, avoid raw material sticking and pipeline blockage, and stably control the process temperature, thereby reducing the operation difficulty of the process and the production line. Of course, the application of the iron phosphate precursor in this case is not limited to this, and will not be elaborated further.

[0065] In summary, this case provides a preparation method of an iron phosphate precursor for batteries to improve product quality and reduce raw material, time costs, and process operation difficulty. By controlling the specifications of the raw material iron powder, the preparation reaction of the iron phosphate precursor is optimized to avoid the reaction rate being too fast and increasing the process operation difficulty. On the other hand, in the secondary reaction of phosphoric acid, deionized water and iron powder, when there is still unreacted iron powder reactant, the amorphous iron phosphate coating attached to the surface of the iron powder reactant is removed by cooperating with the grinding process, so that the iron powder reactant can come into contact with phosphoric acid again and react fully, achieving the effect of effectively reducing the waste of raw materials and comprehensively improving the conversion rate of the iron phosphate precursor. Furthermore, through the secondary reaction of phosphoric acid, deionized water and iron powder, phosphoric acid and iron powder can react fully, achieving the effect of effectively reducing the waste of raw materials and comprehensively improving product quality. Combining the preparation method of the iron phosphate precursor to further form a battery composite material can greatly shorten the grinding time required, and thus reduce the unit time and cost. At the same time, it is also possible to reduce the pH value sensitivity of the process, avoid raw material sticking and pipeline blockage, and stably control the process temperature, thereby reducing the operation difficulty of the process and the production line.

[0066] Even though the present invention has been described in detail by the above embodiments and can be variously modified by those skilled in the art, they all fall within the scope as claimed in the appended patent application.

[0067] Symbol Explanation

[0068] S100, S200, S201, S202, S203, S211, S212, S221, S222, S300, S301, S302: Steps

Claims

1. A method for preparing an iron phosphate precursor for a battery, comprising the steps of: (a) providing phosphoric acid and iron powder, wherein the apparent density of the iron powder is in the range of 2.3 g / cm 3 Up to 2.6g / cm 3 , the particle size of the iron powder consists of a first particle size range and a second particle size range, wherein the first particle size range is larger than the second particle size range, and the weight of the iron powder in the second particle size range accounts for between 10% and 30% of the total weight of the iron powder; (b) reacting the phosphoric acid with the iron powder to generate a first product; and (c) calcining the first product in an air or oxygen atmosphere to generate an iron monophosphate precursor.

2. The method for preparing an iron phosphate precursor for a battery as claimed in claim 1, wherein the iron powder has a diameter of 700 cm 2 / g to 1300cm 2 / g range, the first particle size range is less than 212 μm and greater than 45 μm, and the second particle size range is less than or equal to 45 μm.

3. The method for preparing an iron phosphate precursor for a battery as claimed in claim 1, wherein the step (c) is to maintain the calcination time at a temperature range of 610°C to 670°C for at least one hour.

4. The method for preparing an iron phosphate precursor for a battery as described in claim 1, wherein the first particle size range is less than 212 μm and greater than 45 μm, the second particle size range is less than or equal to 45 μm, and the weight of the iron powder in the second particle size range accounts for between 10% and 25% of the total weight of the iron powder.

5. The method for preparing an iron phosphate precursor for a battery as claimed in claim 1, wherein the first product is an amorphous iron phosphate having a chemical formula of a-FePO4·xH2O, where x>0.

6. The method for preparing an iron phosphate precursor for a battery as claimed in claim 1, wherein the step (b) further comprises the steps of: (b11) dissolving a first amount of phosphoric acid in deionized water in a first temperature environment to form a first phosphoric acid solution; (b12) reacting the first phosphoric acid solution with the iron powder in a second temperature environment, and after reaching the second temperature, cooling the temperature to a third temperature and maintaining the temperature for a first time; and (b13) cooling to a fourth temperature, adding a second phosphoric acid solution having a second quantitative amount of phosphoric acid, and allowing the first phosphoric acid solution, the second phosphoric acid solution and the iron powder to react for a second time to generate the first product. 7 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 6 , wherein a weight ratio of the first quantitative amount to the second quantitative amount is 3 to 1. 8 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 6 , wherein the first temperature is 35° C. to 45° C., the second temperature is below 60° C., the third temperature is below 50° C., and the fourth temperature is below 30° C. 9 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 6 , wherein the first time is at least 3 hours, and the second time is between 5 hours and 9 hours.

10. The method for preparing an iron phosphate precursor for a battery as claimed in claim 9, wherein the step (b) further comprises the steps of: (b21) performing a first grinding to make the particle D99 diameter of the first product particles smaller than a first length; and (b22) continuing the reaction for a third time period. 11 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 10 , wherein the first length is less than 100 μm, and the third time ranges from 6 hours to 12 hours.

12. The method for preparing an iron phosphate precursor for a battery as claimed in claim 10, wherein the step (b) further comprises the steps of: (b31) adding a carbon source and a metal compound to generate a precursor solution with the first product, and performing a second grinding; and (b32) When the second grinding causes the particle size D70 in the precursor solution to be smaller than a second length, spray drying the precursor solution.

13. The method for preparing an iron phosphate precursor for a battery as claimed in claim 12, wherein the spray drying action is achieved through a rotary disk spray dryer, the inlet temperature of the rotary disk spray dryer is 210°C, the outlet temperature is 95°C, and the rotary disk rotation speed is between 300 Hz and 400 Hz. 14 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 12 , wherein the second length range is between 1 μm and 10 μm. 15 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 12 , wherein the rotation speed of the first grinding and the second grinding ranges from 450 to 650 revolutions per minute.

16. The method for preparing an iron phosphate precursor for a battery as claimed in claim 12, wherein the metal compound and the iron phosphate precursor form an iron phosphate precursor composite material in the step (c), which is then calcined to form a battery composite material, wherein the chemical formula of the battery composite material is LiFePO4, and the metal compound is a lithium-containing compound.

17. The method for preparing a battery iron phosphate precursor as claimed in claim 16, wherein the lithium-containing compound is selected from lithium hydroxide, lithium carbonate or a mixture thereof, and the battery composite material is a nano-metal oxide eutectic lithium iron phosphate compound (LFP-NCO).

18. The method for preparing an iron phosphate precursor for a battery as claimed in claim 16, wherein the step (c) comprises maintaining the temperature at 325°C for 0.5 hour, maintaining the temperature at 550°C for 0.5 hour and maintaining the temperature at 650°C for 1 hour.

Images